U.S. patent application number 09/778486 was filed with the patent office on 2005-06-02 for color image display accuracy using green-limited gamma estimate.
This patent application is currently assigned to Imation Corp. Invention is credited to Edge, Christopher J., Fischer, Timothy A..
Application Number | 20050116961 09/778486 |
Document ID | / |
Family ID | 33437047 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050116961 |
Kind Code |
A9 |
Edge, Christopher J. ; et
al. |
June 2, 2005 |
Color image display accuracy using green-limited gamma estimate
Abstract
Improved color image display accuracy can be achieved across a
computer network by obtaining information characterizing the color
response of display devices associated with a client residing on
the computer network, and using the information to modify color
images delivered to the client. The information may include a gamma
estimate. In one embodiment, the gamma estimate is limited to only
the green color channel, without reference to the gammas for the
red and blue channels. In this manner, the gamma estimate
concentrates on the most dominant color channel and avoids errors
that can arise due to the red-blue imbalances that are highly
prevalent in many display devices. The information can be obtained,
for example, by guiding the client through a color profiling
process that profiles the color response of the display device. For
example, such guidance may take the form of a series of
instructional web pages that are delivered to the client. The web
pages can be made interactive to enable collection of color
characterization data from the client.
Inventors: |
Edge, Christopher J.; (Saint
Paul, MN) ; Fischer, Timothy A.; (Mendota Heights,
MN) |
Correspondence
Address: |
Steven J. Shumaker
Shumaker & Sieffert, P.A.
8425 Seasons Parkway
Suite 105
St. Paul
MN
55125
US
|
Assignee: |
Imation Corp
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 0058253 A1 |
March 27, 2003 |
|
|
Family ID: |
33437047 |
Appl. No.: |
09/778486 |
Filed: |
February 7, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09778486 |
Feb 7, 2001 |
|
|
|
09631312 |
Aug 3, 2000 |
|
|
|
60193725 |
Mar 31, 2000 |
|
|
|
60246890 |
Nov 8, 2000 |
|
|
|
Current U.S.
Class: |
345/600 ;
348/E9.051; 348/E9.054 |
Current CPC
Class: |
G09G 2320/0673 20130101;
G09G 2320/0606 20130101; G06T 11/001 20130101; G09G 2320/0626
20130101; H04N 9/73 20130101; G09G 2320/066 20130101; H04N 9/69
20130101; G09G 2320/0666 20130101; G09G 5/02 20130101 |
Class at
Publication: |
345/600 |
International
Class: |
G09G 005/02 |
Claims
1. A method comprising: estimating an initial gamma for a display
device based on selection of a displayed green element that appears
to most closely blend with a dithered green background;
characterizing overall gamma for red, blue, and green channels of
the display device based on the estimated gamma; and modifying the
overall gamma based on a gray balance evaluation for the red and
blue color channels.
2. The method of claim 1, the method further comprising: modifying
a color image based at least in part on the estimated gamma; and
delivering the modified color image to the display device.
3. The method of claim 1, wherein the display device is associated
with a client residing on a computer network, the method further
comprising: transmitting information representing the estimated
gamma to a remote server on the network; modifying the color image
at the remote server based on the information; and delivering the
modified color image to the client via the computer network for
display on the display device.
4. The method of claim 1, wherein estimating the gamma includes:
selecting one of a first plurality of green elements displayed by
the display device that appears to most closely blend with the
dithered green background; estimating a coarse gamma for the
display device based on the selected one of the first plurality of
green elements; selecting one of a second plurality of green
elements displayed by the display device that appears to most
closely blend with the dithered green background, wherein the
second plurality of green elements includes the selected one of the
first plurality of green elements; and estimating a fine gamma for
the display device based on the selected one of the second
plurality of green elements, wherein the estimated fine gamma is
the estimated gamma.
5. The method of claim 4, wherein the first plurality of green
elements represent greater gradations in green intensity that the
second plurality of green elements.
6. The method of claim 1, further comprising: selecting one of the
selected green element and a plurality of red-blue shifted elements
displayed by the display device that appears to most closely blend
with the dithered green background displayed by the display device;
and estimating the gray balance of the display device based on the
selected one of the selected green element or selected red-blue
shifted element.
7. The method of claim 6, wherein the red-blue shifted elements
represent shifts in red, blue, or a combination of red and blue
away from the color value of the selected green element.
8. The method of claim 6, wherein the red-blue shifted elements do
not represent any substantial shift in green away from the color
value of the selected green element.
9. The method of claim 1, wherein the estimated gamma is limited to
the green channel.
10. The method of claim 1, further comprising: estimating both the
blackpoint and the gray balance of the display device; and
characterizing the colorimetric response of the display device
based on the estimated gamma, blackpoint, and gray balance.
11. The method of claim 10, wherein the display device is
associated with a client residing on a computer network, the method
further comprising: transmitting information representing the
estimated blackpoint, gamma, and gray balance to a remote server on
the network; modifying the color image at the remote server based
on the information; and delivering the modified color image to the
client via the computer network for display on the display
device.
12. The method of claim 10, further comprising: modifying a color
image based on the estimated blackpoint, gamma, and gray balance;
and delivering the modified color image to the display device.
13. The method of claim 1, wherein the dithered green background is
a dithered approximately 33% green background.
14. The method of claim 1, wherein the display device is associated
with a client on a computer network, the method further comprising
guiding the client through the process of obtaining the estimated
gamma by delivering one or more instructional web pages to the
client.
15. A system comprising: a web server to transmit web pages to
clients residing on a computer network; a color image server to
transmit color images referenced by the web pages to the clients
for display on display devices associated with the clients; a color
profile server to guide the clients through a color profiling
process and obtain information characterizing the color responses
of the display devices associated with the clients, wherein the
information includes an initial gamma for the display device, the
initial gamma being determined based on selection of a displayed
green element that appears to most closely blend with a dithered
green background, and an overall gamma for red, blue, and green
channels of the display device determined from on modification of
the initial gamma based on a gray balance evaluation for the red
and blue color channels; and one or more color correction modules
to modify the color images transmitted by the color image server
based on the information to improve the accuracy of the color
images when displayed on the respective display device.
16. The system of claim 15, wherein the color image server stores
the information to the client in a web cookie, the client transmits
the web cookie from the client to the server, and the color image
server modifies the color image via the server based on the
contents of the web cookie.
17. The system of claim 15, wherein the color profiling process
includes: estimating the gray balance of the display device by
selecting one of the selected green elements and a plurality of
red-blue shifted elements displayed by the display device that most
closely blends with the dithered gray background displayed by the
display device; generating a color profile for the display device
based on the estimated gamma, and the estimated gray balance; and
modifying the color image for the display device using the color
profile.
18. The system of claim 17, wherein the color profiling process
includes: selecting one of the selected green element and a
plurality of red-blue shifted elements displayed by the display
device that appears to most closely blend with the dithered green
background displayed by the display device; and estimating the gray
balance of the display device based on the selected one of the
selected green element or selected red-blue shifted element.
19. The system of claim 18, wherein the red-blue shifted elements
represent shifts in red, blue, or a combination of red and blue
away from the color value of the selected green element.
20. The method of claim 18, wherein the red-blue shifted elements
do not represent any substantial shift in green away from the color
value of the selected green element.
21. The system of claim 15, wherein estimating the gamma includes:
selecting one of a first plurality of green elements displayed by
the display device that appears to most closely blend with the
dithered green background; estimating a coarse gamma for the
display device based on the selected one of the first plurality of
green elements; selecting one of a second plurality of green
elements displayed by the display device that appears to most
closely blend with the dithered green background, wherein the
second plurality of green elements includes the selected one of the
first plurality of green elements; and estimating a fine gamma for
the display device based on the selected one of the second
plurality of green elements, wherein the estimated fine gamma is
the estimated gamma.
22. The system of claim 21, wherein the first plurality of green
elements represent greater gradations in green intensity that the
second plurality of green elements.
23. The system of claim 15, wherein the estimated gamma is limited
to the green channel.
24. The system of claim 15, wherein the color profiling process
includes: estimating both the blackpoint and the gray balance of
the display device; and characterizing the colorimetric response of
the display device based on the estimated gamma, blackpoint, and
gray balance.
25. The system of claim 15, wherein the dithered green background
is a dithered approximately 33% green background.
26. A computer-readable medium containing instructions to cause a
programmable processor to: estimate a gamma for the display device
based on selection of a displayed green element that appears to
most closely blend with a dithered green background; and
characterize overall gamma for red, blue, and green channels of the
display device based on the estimated gamma; and modify the overall
gamma based on a gray balance evaluation for the red and blue color
channels.
27. The computer-readable medium of claim 26, wherein the
instructions cause the processor to: modify a color image based at
least in part on the estimated gamma; and deliver the modified
color image to the display device.
28. The computer-readable medium of claim 26, wherein the display
device is associated with a client residing on a computer network,
and the instructions cause the processor to: transmit information
representing the estimated gamma to a remote server on the network;
modify the color image at the remote server based on the
information; and deliver the modified color image to the client via
the computer network for display on the display device.
29. The computer-readable medium of claim 26, wherein estimating
the gamma includes: selecting one of a first plurality of green
elements displayed by the display device that appears to most
closely blend with the dithered green background; estimating a
coarse gamma for the display device based on the selected one of
the first plurality of green elements; selecting one of a second
plurality of green elements displayed by the display device that
appears to most closely blend with the dithered green background,
wherein the second plurality of green elements includes the
selected one of the first plurality of green elements; and
estimating a fine gamma for the display device based on the
selected one of the second plurality of green elements, wherein the
estimated fine gamma is the estimated gamma.
30. The computer-readable medium of claim 29, wherein the first
plurality of green elements represent greater gradations in green
intensity that the second plurality of green elements.
31. The computer-readable medium of claim 26, wherein the
instructions cause the processor to: select one of the selected
green element and a plurality of red-blue shifted elements
displayed by the display device that appears to most closely blend
with the dithered green background displayed by the display device;
and estimate the gray balance of the display device based on the
selected one of the selected green element or selected red-blue
shifted element.
32. The computer-readable medium of claim 31, wherein the red-blue
shifted elements represent shifts in red, blue, or a combination of
red and blue away from the color value of the selected green
element.
33. The computer-readable medium of claim 31, wherein the red-blue
shifted elements do not represent any substantial shift in green
away from the color value of the selected green element.
34. The computer-readable medium of claim 26, wherein the estimated
gamma is limited to the green channel.
35. The computer-readable medium of claim 26, wherein the
instructions cause the processor to: estimate both the blackpoint
and the gray balance of the display device; and characterize the
colorimetric response of the display device based on the estimated
gamma, blackpoint, and gray balance.
36. The computer-readable medium of claim 35, wherein the display
device is associated with a client residing on a computer network,
and the instructions cause the processor to: transmit information
representing the estimated blackpoint, gamma, and gray balance to a
remote server on the network; modify the color image at the remote
server based on the information; and deliver the modified color
image to the client via the computer network for display on the
display device.
37. The computer-readable medium of claim 26, wherein the
instructions cause the processor to: modify a color image based on
the estimated blackpoint, gamma, and gray balance; and deliver the
modified color image to the display device.
38. The computer-readable medium of claim 26, wherein the dithered
green background is a dithered approximately 33% green
background.
39. The computer-readable medium of claim 26, wherein the display
device is associated with a client on a computer network, and the
instructions cause the processor to guide the client through the
process of obtaining the estimated gamma by delivering one or more
instructional web pages to the client.
40. The computer-readable medium of claim 26, wherein the
instructions are contained both in physical data storage media and
signals transmitted between the client and other resources on the
computer network.
Description
[0001] This application claims priority from U.S. provisional
application serial No. 60/193,725, filed Mar. 31, 2000, U.S.
utility application Ser. No. 09/631,312, filed Aug. 3, 2000, and
U.S. provisional application serial No. 60/246,890, filed Nov. 1,
2000, the entire content of each being incorporated herein by
reference.
TECHNICAL FIELD
[0002] The invention relates to color imaging and, more
particularly, to presentation of color images on display
devices.
BACKGROUND
[0003] The growth of the Internet has created sizable opportunities
for online retailers. Most major retailers of consumer products
have established commercial sites on the World Wide Web. At the
same time, the availability of website presence has eliminated many
of the marketing barriers previously experienced by smaller
retailers. Virtually any retailer can now post product information
for easy access by potential customers, and take orders for
products in an automated fashion.
[0004] The product information may include a large number of
images. The images enable web customers situated at client devices
to view products before submitting an online purchase order. For
some items, the user is permitted to click on a "thumbnail" image
to view the item in a higher resolution format. For many retailers,
however, the quality of the images can be a significant concern.
Color accuracy, in particular, can be very important for retailers
of products for which color matters.
[0005] In the case of clothing retailers, for example, an image of
a sweater should match its actual color as closely as possible.
Unfortunately, the color output characteristics of different
display devices can differ significantly. A cathode ray tube (CRT)
or flat panel display, video card, driver software, and operating
system together determine how RGB pixel values will be rendered and
displayed, and vary significantly from system to system.
[0006] Consequently, an online customer may order what appears to
be a burgundy sweater but instead receive a bright red sweater.
Indeed, color inaccuracy has become a significant cause for return
of merchandise purchased by online customers. In some cases, this
problem can erase the advantages obtained by the retailer's
commitment to online merchandising, and undermine continued
investment.
SUMMARY
[0007] The invention relates to improvement of color image display
accuracy among display devices with different color output
characteristics.
[0008] The invention, in one embodiment, makes use of a
green-limited gamma estimate. Gamma is an estimate of the overall
display device gamma, which aids in colorimetric characterization
of the display device. The gamma determination is initially
determined based on the green color channel of the display device
only, without reference to the red and blue channels.
[0009] Green is the most dominant and intense phosphor among red,
green, and blue, and is highest in contrast. Green also has the
highest L* (in the L*a*b* color space), and most closely matches
the photopic V(.lambda.) response of the eye. This approach to
obtaining an initial RGB average gamma determination considers only
the green color channel, and essentially ignores red and blue. In
this sense, the initial gamma determination is "green-limited,"
i.e., limited to the green channel.
[0010] The green-limited gamma measurement concentrates on the most
dominant color channel and avoids errors that can arise due to the
red-blue imbalances that are highly prevalent in many display
devices. Thus, the elements displayed for the gamma determination
may be green patches with different darkness or lightness values.
The elements may be displayed against a green dithered background.
Limiting the gamma determination to the green channel simplifies
the user's selection process, and can reduce the likelihood of user
error.
[0011] The gamma determination may involve a coarse gamma estimate,
followed by a fine gamma estimate. The coarse gamma estimate may
serve as a first estimate for a subsequent step of gamma
determination. The subsequent step fine-tunes the initial gamma
estimate to form a more accurate colorimetric characterization of
the gamma of the display device.
[0012] The green-limited gamma estimate may be determined in
conjunction with a blackpoint estimate and a gray balance estimate
for the display device. Together, the blackpoint, gamma, and gray
balance characterize the colorimetric response of the display
device.
[0013] In some embodiments, the green patch selected for the coarse
gamma measurement is used as a central green patch among a range of
green patches used to measure the fine gamma. The gamma associated
with the green patch selected for the fine gamma estimate then can
be used to form a central gray patch among a range of gray patches
for a gray balance determination. The term "gray," as used herein,
generally refers to a color formed by combinations of two or more
color channels of various gray levels, in contrast to colors formed
by single color channels.
[0014] In particular, a central gray patch can be displayed against
a gray dithered background among a range of gray patches. The range
of gray patches represent shifts away from the gamma indicated by
the green patch along the red and blue axes. The central gray patch
has equal amounts of red, green, and blue that correspond to the
value of the initial fine gamma estimate. Every gray patch has the
same green value but different red and blue values. This step
eliminates one axis of variation, green, but facilitates
identification of imbalance between red and blue. This limits the
range of choices to a more finely-tuned area, and aids the user in
making a more accurate selection.
[0015] Thus, in many circumstances, a more accurate colorimetric
characterization can be obtained using a green-limited gamma
estimate. This enables greater accuracy in a process for
modification of color images that are delivered to, and displayed
on, a particular display device. In this manner, the invention can
provide improved color image display accuracy.
[0016] Improved color image display accuracy can be achieved, for
example, by obtaining the green-limited gamma estimate and the
other information characterizing the color response of a display
device associated with a client device residing on a computer
network such as the World Wide Web. The information can be used
advantageously to modify color images delivered to the client from
a server.
[0017] In particular, the invention, in various embodiments, may be
applied to provide color image modifications that compensate for
the color response of the individual display device associated with
the client. The display device may take the form of a cathode ray
tube monitor, flat panel display, or similar color image display
device.
[0018] The green-limited gamma estimate and additional information
can be obtained, for example, by guiding the client through a color
profiling process that profiles the color response of the display
device. Guidance may take the form of a series of instructional web
pages that are delivered to the client via the computer
network.
[0019] The web pages can be made interactive to enable collection
of color characterization data from the client. The color
characterization data can be used to estimate a variety of
information concerning display device characteristics such as the
blackpoint estimate, gamma, gray balance, and the like.
[0020] Once the information has been collected, a color profile can
be created for the client's display device, and thereafter used for
modification of color images delivered to the client. The color
profile can be incorporated in information that is transmitted by
the client to an image server for modification of color images to
be delivered to the client. The information transmitted by the
client can be embodied in a web cookie or other information
container.
[0021] A cookie, or alternative container, can provide a persistent
representation of the color response characteristics of the
client's display device. Each time the client accesses a web server
and color images are identified in web page content, the cookie can
be sent to the appropriate image server to improve the accuracy of
the color image displayed on the client's display device. The
cookie may contain a computed color profile for a display device or
parameters useful in computing such a color profile and thereby
rendering color modifications, or "corrections," to images provided
to a client.
[0022] With improved color image accuracy, the images viewed by the
client appear as intended. The invention is capable of providing
accurate characterization of a display device, while affording
reliability and ease of use for the user. In a retail context, for
example, the color of an item of interest more closely matches the
actual color. As a result, items ordered by online customers are
less likely to be returned based on color mismatch. Online
retailers suffer from less returns, and online customers can shop
with greater confidence that the items they order will arrive in
the expected color.
[0023] In general, users viewing online images are able to see the
colors intended by the original source without the need for
significant adjustments to the display device. Improved color image
accuracy can thereby enhance the online experience for the client.
At the same time, in many embodiments, the user need not be
burdened with downloadable plug-ins, client side scripts, and the
like, which can consume time and precious attention span. Instead,
in more preferred embodiments, the color profiling process can be
carried out by a series of web pages.
[0024] In one embodiment, the invention provides a method
comprising estimating a gamma for a display device based on
selection of a displayed green element that appears to most closely
blend with a dithered green background, characterizing overall
gamma for red, blue, and green channels of the display device based
on the estimated gamma, and modifying the overall gamma based on a
gray balance evaluation for the red and blue color channels.
[0025] In an additional embodiment, the invention provides a
computer-readable medium containing instructions to cause a
programmable processor to estimate a gamma for the display device
based on selection of a displayed green element that appears to
most closely blend with a dithered green background, characterize
overall gamma for red, blue, and green channels of the display
device based on the estimated gamma, and modify the overall gamma
based on a gray balance evaluation for the red and blue color
channels.
[0026] In another embodiment, the invention provides a system
comprising a web server to transmit web pages to clients residing
on a computer network. A color image server transmits color images
referenced by the web pages to the clients for display on display
devices associated with the clients. A color profile server guides
the clients through a color profiling process and obtains
information characterizing the color responses of the display
devices associated with the clients. The information includes an
initial gamma for the display device. The initial gamma is
determined based on selection of a displayed green element that
appears to most closely blend with a dithered green background. The
information also includes an overall gamma for red, blue, and green
channels of the display device that is determined from on
modification of the initial gamma based on a gray balance
evaluation for the red and blue color channels. One or more color
correction modules modify the color images transmitted by the color
image server based on the information to improve the accuracy of
the color images when displayed on the respective display
device.
[0027] The details of one or more embodiments of the present
invention are set forth in the accompanying drawings and the
description below. Other features, objects, and advantages of the
present invention will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a block diagram of a system for improving color
image display accuracy in a computer network;
[0029] FIG. 2 is a block diagram of a web-based environment
incorporating a system as shown in FIG. 1;
[0030] FIG. 3 is a flow diagram illustrating a method for improving
color image display accuracy in a computer network;
[0031] FIG. 4 is a flow diagram illustrating a color profiling
process for a display device;
[0032] FIG. 5 is a flow diagram illustrating a multi-channel
blackpoint determination in a color profiling process as shown in
FIG. 4;
[0033] FIG. 6 is a diagram of a web page for analog adjustment of a
color display prior to blackpoint determination;
[0034] FIG. 7 is a diagram of a web page for determination of
blackpoint for a particular color channel;
[0035] FIG. 8 is a flow diagram illustrating gamma and gray balance
determination in a color profiling process as shown in FIG. 4;
[0036] FIG. 9 illustrates a range of green elements for use in
determining a coarse gamma in a color profiling process as shown in
FIG. 4;
[0037] FIG. 10 illustrates a range of green elements for use in
determining a fine gamma in a color profiling process as shown in
FIG. 4;
[0038] FIG. 11 illustrates a range of gray elements for use in
determining gray balance in a color profiling process as shown in
FIG. 4;
[0039] FIG. 12 illustrates an example of a color image transmitted
to a client in a system as shown in FIGS. 1 and 2;
[0040] FIG. 13 is block diagram illustrating transmission of color
correction information in a system as shown in FIGS. 1 and 2;
and
[0041] FIG. 14 is a block diagram illustrating an alternative
architecture for a system for improving color image display
accuracy in a computer network.
DETAILED DESCRIPTION
[0042] FIG. 1 is a block diagram of a system 10 for improving color
image display accuracy across a computer network. The computer
network may take the form of a local area network, wide area
network, or global computer network such as the World Wide Web. In
accordance with one embodiment, system 10 may be configured to
obtain an initial green-limited gamma estimate that assists in
characterizing the colorimetric response of a display device
associated with a client on the network. In particular, the initial
gamma estimate is limited in the sense that it is based on only the
green color channel, without reference to the gammas for the red
and blue channels.
[0043] As shown in FIG. 1, system 10 may include a web server 12, a
client 14, a color image server 16, and a color profile server 18.
Web server 12 provides client 14 with access to one or more web
pages incorporating graphic content such as color images. Some of
the color images can be incorporated in the web pages stored at web
server 12 while other color images can be stored at color image
server 16. Web server 12 may store lower resolution color images,
for example, as well as images that are less color-intensive.
Higher resolution color images and more color-intensive images can
be stored at color image server 16.
[0044] Web server 12, client 14, color image server 16, and color
profile server 18 each execute instructions in the form of program
code that is stored on computer-readable media residing locally
with the respective device or executed remotely. For client 14, for
example, the program code may reside in random access memory (RAM)
that is accessed and executed by the client computer. The program
code can be loaded into the memory from another memory device, such
as a fixed hard drive or removable media device associated with
client 14.
[0045] In particular, the program code can be initially carried on
computer-readable media such as magnetic, optical, magneto-optic or
other disk or tape media, or electronic media such as EEPROM.
Alternatively, the program code can be loaded into the medium by
transmission from a remote data archive, e.g., via a local area
network, wide area network, or global network such as the Internet.
A substantial portion of the code may be web page code that is
transmitted to the respective device and executed by a server or
browser application.
[0046] The web pages generated by web server 12 may comprise a
variety of code, e.g., Hypertext Markup Language (HTML), Extensible
Markup Language (XML), or the like, and may include image tags that
point to specific color images stored at color image server 16 or
elsewhere. When client 14 accesses a particular web page delivered
by web server 12 and assembles the page content according to the
HTML, client 14 may access color image server 16 to obtain any
images tagged within the web page.
[0047] Thus, the content of a web page assembled for client 14 may
include objects obtained from different resources within the
network occupied by system 10, such as web server 12 and color
image server 16. In some embodiments, web server 12 and color image
server 16 may be integrated with one another. In the example of
FIG. 1, however, color image server 16 and web server 12 are
separate entities. Web server 12 and color image server 16 each may
interact with a database server and file server to obtain access to
selected color images for delivery to client 14.
[0048] Client 14 may take the form of a variety of devices that
permit a user to access resources on system 10 and display color
images obtained from such resources. Examples of client 14 include
desktop or portable computers operating in a Windows, Macintosh,
Unix, or Linux environment, personal digital assistants (PDA's),
based on the Palm, Windows CE, or similar operating system
environments for small portable devices, Internet-equipped wireless
telephones, interactive televisions with set-top boxes for Internet
access, Internet kiosks available to the general public, and future
Internet appliances that may emerge.
[0049] Each client 14 preferably executes a graphical viewing
application such as a web browser to access resources residing on
other resources, such as web server 12 and color image server 16,
attached to system 10. A web browser application permits the user
associated with client 14 to readily view web pages generated by
web server 12, and images served by color image server 16. Other
user interface applications may be useful in accessing web server
12 provided the information is presented in a user-interactive
format.
[0050] In some embodiments, color image server 16 may be configured
to deliver color corrected video imagery, in addition to static
images. Video, such as MPEG clips, streaming video, and the like
may suffer from similar color accuracy issues if they are not
compensated for the effects of the display device associated with
an individual client 14. Thus, some embodiments of the invention
may be particularly useful for broadcast-like video content.
[0051] In each case, client 14 includes a display device, such as a
cathode ray tube or flat panel display, for display of color images
obtained from web server 12 and color image server 16. Other types
of displays, as well as dynamic viewing media such as electronic
paper, are contemplated. Communication between web server 12,
client 14, and color image server 16 may take place using
conventional network protocols such as TCP/IP. Although some of the
client devices described above, such as PDA's and wireless
telephones, presently incorporate relatively low quality color
displays, it is anticipated that such devices will benefit from
higher quality color displays in the near future. Accordingly,
system 10 will be readily applicable in enhancing the quality of
color images displayed by PDA's, wireless telephones, and similar
devices in the future.
[0052] As an illustration, web server 12 may deliver web pages
associated with an online retailer such as a clothing merchandiser.
In this example, the web pages delivered by web server 12 may
contain information concerning an array of items offered for sale
by the retailer, as well as color images of the items for viewing
by online customers. Some of the color images may constitute low
resolution "thumbnail" images placed coincident with hypertext
links to higher resolution images stored at color image server 16.
Client 14 executes the code delivered by web server 12 within a
browser application to assemble a web page for display on a display
device associated with the client.
[0053] When a user associated with client 14 clicks on one of the
thumbnail images with a pointing device, such as mouse, trackball,
pen, or the like, client 14 accesses color image server 16 to
obtain the higher resolution color image designated by an image tag
embedded in the web page code. To permit display of the higher
resolution color image with greater color accuracy, color image
server 16 modifies the color image based on information obtained
for client 14. In particular, color image server 16 obtains
information characterizing the color response of a display device
associated with client 14.
[0054] The information can be uploaded to color image server 16,
e.g., in the form of a web cookie or other content container.
Alternatively, the information can be transmitted, i.e.,
broadcasted, to a number of subscriber color image servers in
system 10, which are recognized by color profile server 18. The
information can be generated by guiding a user associated with
client 14 through a color profiling process that profiles the color
response of the display device.
[0055] When client 14 accesses a color image from color image
server 16, the user may be given a choice between viewing a version
of the image with default color settings, or initiating the color
profiling process to produce custom color settings for the user's
display device and thereby improve the quality of the color image.
In particular, the color image delivered by color image server 16
may be embedded in a web page with one or more hypertext links for
initiation of the color profiling process through interaction with
color profile server 18. When the user clicks on the hypertext
link, client 14 accesses color profile server 18 for delivery of a
series of instructional web pages to the user.
[0056] The instructional web pages provided by color profile server
18 guide the user through a number of steps designed to estimate
the color response characteristics of the particular display device
associated with client 14. When the process is complete, color
profile server 18 delivers a web page with content that, when
executed, generates a cookie containing the color profile
information. The cookie then can be uploaded to color image server
16 for use in modifying the color image, and subsequently accessed
color images, to produce higher quality color output on the display
device associated with client 14. Exemplary color profiling
processes will be described in greater detail later in this
detailed description.
[0057] Other techniques for obtaining the color profiling
information may not require direct interaction by the user with a
color image server 16a-16n. Instead, the user may voluntarily visit
a web site to perform color profiling. The web site may be provided
by color profile server 18 or be within the same domain as the
color profile server. Alternatively, users may profile the display
devices associated with their individual clients 14a-14n by
executing software downloaded or physically delivered to them.
Moreover, display devices could be configured to produce a color
profile when put in use, and transmit the color profile to
subscriber color image servers, e.g., in a cookie. In each case,
color profile server 18 receives essentially the same information
for transfer to a number of individual color image servers for
delivery of color corrected images to client 14.
[0058] FIG. 2 is a block diagram of a web-based environment 20
incorporating a system as shown in FIG. 1. Web-based environment 20
includes a number of subscribers 22a, 22b, and 22c-22n, each of
which may represent a commercial retailer with an online
merchandising web site Of course, subscribers 22a-22n may include
non-commercial entities as well, such as art museums and the like.
For each subscriber 22a, 22b, and 22c-,22n, a subscriber web
server, or "subscriber server" (SS.sub.1-SS.sub.N) 12a, 12b, and
12c-12n, delivers web pages with content describing the
subscriber's merchandise, and a color image server
(CIS.sub.1-CIS.sub.N) 16a, 16b, and 16c-16n delivers high quality
color images that may be modified based on color profiles generated
for individual clients 14a, 14b, and 14c-14n. Thus, each of
subscribers 22a-22n posts its high quality color images to a
respective color image server 16a-16n, and maintains web pages that
invoke the high quality images at a respective subscriber server
12a-12n. Note that there may be many more clients 14a-14n than
subscribers 22a-22n.
[0059] One of the subscriber servers 12a-12n and one of the color
image servers 16a-16n are typically under the control of the
respective subscriber. In other words, subscriber 22a may be
responsible for maintenance, administration, and content of
subscriber server 12a and color image server 16a, while subscriber
22b is responsible for subscriber server 12b and color image server
16b. In this manner, subscribers 22a-22n can readily update the
contents of subscriber servers 12a-12n and color image servers
16a-16n themselves. Consequently, subscribers 22a-22n do not need
to relinquish control of their image content to some third party in
order to take advantage of the color image quality improvements
contemplated in accordance with this embodiment of the
invention.
[0060] Instead, subscribers 22a-22n make use of their own color
image servers 16a-16b and interaction with a color profile server
18 that guides the color profiling process for clients 14a-14n.
Nevertheless, in some embodiments, use of a central image server
for all subscribers may be desirable. The commercial entities
associated with subscriber servers 12a-12b and color image servers
16a-16n are "subscribers" in the sense that they all make use of
color profiles generated by interaction with one or more common
color profile servers 18. Thus, a subscriber may be a retailer or
collection of retailers with a web site that employs color
correction as described herein, and makes use of color profile
server 18.
[0061] Subscriber server 12a-12n may be the subscriber's main web
server. Color image server 16a-16n can be a server that is
co-located with or remotely located from a corresponding subscriber
server 12a-12n and contains the subscriber's high resolution or
color-intensive color images and a color correction module for
modifying the images and serving corrected images to clients
14a-14n. Each color image server 16a-16n may be within the domain
of the respective subscriber server 12a-12n, but this is not a
requirement. Thus, in the environment of FIG. 2, clients 14a-14n
are potential customers of subscribers 22a-22n who view the
subscriber's web pages with their own browsers.
[0062] Clients 14a-14n access subscriber servers 12a-12n, color
image servers 16a-16n, and color profile server 18 via a computer
network such as World Wide Web 24. Although the number of clients
14a-14n and subscribers 22a-22n shown in FIG. 1 is limited for ease
of illustration, the actual number can be virtually unlimited
subject to the bandwidth limitations of subscriber servers 12a-12n,
color image servers 16a-16n, color profile servers 18 and web
24.
[0063] With a large number of clients 14a-14n accessing subscribers
22a-22n, the color responses of individual display devices can be
quite varied. The color profiling process and color image
modifications administered by color profile server 18 and color
image servers 16a-16n, however, compensate for differences between
the various client display devices and thereby increase the
consistency of color output viewed by users situated across web 24.
If subscribers 22a-22n are clothing retailers, for example, the
color images viewed by clients 14a-14n on disparate display devices
can be made to more closely match the color of actual clothing
items.
[0064] FIG. 3 is a flow diagram illustrating a method for improving
color image display accuracy in a computer network as shown in
FIGS. 1 and 2. When a client 14 seeks to download a web page from a
subscriber server 12, the client receives HTML code (or some other
form of web page code) with embedded image tags identifying the
locations of color images to be incorporated in the web page when
it is presented on a display device (40). For lower resolution
images, such as so-called "thumbnails," the image tags may point to
locations resident at subscriber server 12. When a user clicks on a
thumbnail to access a higher resolution image, or when a higher
resolution is embedded in the web page in the first instance,
client 14 accesses and downloads a corresponding color image from a
designated color image server 16 (42).
[0065] In the example of FIG. 3, client 14 queries whether a color
profile cookie visible to the color image server has been generated
for the particular client (44). A cookie is visible, for example,
if it corresponds to the domain of color image server 16.
Management of cookies will be described later in this description.
The color profile cookie contains information characterizing the
color response of the display device associated with client 14, and
typically resides locally with the client. If a color profile
cookie has been generated, client 14 uploads the cookie to color
image server 16 (46).
[0066] Color image server 18 retrieves the image requested by
client 14 and modifies the image based on the contents of the
cookie by applying a color correction (48). The color correction
modifies the image to compensate for variations in the color
response characteristics of the display device associated with
client 14. Color image server 16 then downloads the color corrected
image to client 14 (50) and the process ends (52) In the above
manner, client 14 receives a color corrected image that is
customized for the client's display device to provide more accurate
color output.
[0067] If a color profile cookie has not been generated previously,
client 14 downloads a default color image from color image server
16 (54) for presentation on the display device associated with the
client. The image is a "default" image in the sense that it has not
been color corrected or otherwise customized for the individual
display devices associated with client 14. As a result, when
displayed by client 14, the default image may exhibit significant
color inaccuracy relative to the original color image. With the
default image, however, client 14 may present a color profiling
option (56).
[0068] In particular, client 14 may download with the image an
indication of whether color profiling and correction has been
applied to the image. With the image, client 14 may display that
indication along with a hypertext icon that may invite the user to
carry out color profiling. The user may click on the profiling icon
with a pointing device to access the color profiling process. In
some embodiments, the profiling icon may indicate that profiling
has already been performed and that the image has been color
corrected, e.g., by displaying the icon in color. If profiling has
not been performed previously, the icon may be displayed in
black-and-white or some other indication can be provided. By
clicking on the icon, the user can commence profiling, either in
the first instance or as a profiling update
[0069] If the option is not selected (58), the user simply views
the default image and the process ends (52). If the option is
selected, however, client 14 accesses color profile server 18,
e.g., via the hypertext link associated with the icon. Color
profile server 18 guides the user associated with client 14 through
a color profiling process (60). The color profiling process
produces information characterizing the color response exhibited by
the display device associated with the particular client 14.
[0070] Following completion of the color profiling process, client
14 generates a color profile cookie (62). The color profile cookie
contains the color characterization information. Client 14 then
uploads the color profile cookie to color image server 16 (46) to
obtain a color corrected image for improved color image accuracy.
As will be explained, the cookie may need to be rewritten for the
domain of color image server 16.
[0071] Notably, as will be described, the color profiling process
optionally requires no plug-ins, Java scripts, or other significant
client-side processes. Instead, interaction between subscriber
server 12, client 14, color image server 16, and color profile
server 18 is driven by a series of web pages delivered to client
14. This approach yields significant convenience for the end user
associated with client 14. At the same time, subscribers 22 are not
required to retain color information for individual users.
[0072] Rather, the information can be uploaded to color image
server 16, e.g., in the form of a cookie, whenever color images are
requested by a client 14. Moreover, subscribers 22 can maintain
their own color images at color image servers 16, and provide color
correction by incorporating a color correction module capable of
handling the color profile cookies uploaded by individual clients
14. Accordingly, there is no need for subscribers 22 to post their
web pages or images to a central web repository.
[0073] To carry out a color profiling process as described with
reference to FIG. 3, client 14 interacts with color profile server
18. Color profile server 18 delivers a series of web pages to
client 14. Each of the web pages is designed to guide the user
through a given step in the color profiling process. One web page,
for example, may include instructions and image content designed to
extract from the user an estimate of the blackpoint of the display
device. In one embodiment, the blackpoint estimate may be an
estimate of multiple, channel-specific blackpoints. Other web pages
may include instructions and content designed to extract coarse
gamma, fine gamma, and gray balance information. In particular,
each web page may include interactive media such as hypertext icons
and the like that can be clicked upon by the user to transfer
information from client 14 to color profile server 18.
[0074] Upon collecting the necessary information, color profile
server 18 creates the cookie and delivers it to client 14 for local
storage and future use. In some embodiments, two cookies can be
provided to client 14. A first cookie may correspond to a domain
name associated with color profile server 18, and be used for
future interaction between the particular client 14 and the color
profile server. The first cookie can be referred to as the
"profiler cookie."
[0075] A second cookie may correspond to a domain name associated
with the particular color image server 16 (corresponding to a
particular subscriber such as a retailer) from which the color
image is to be downloaded. In other words, the second cookie may
correspond to the color image server 16 at which the color
profiling process was initiated. In this manner, future images
delivered by that color image server 16 will be modified based on
the contents of the cookie associated with the pertinent domain.
The second cookie can be referred to as the "subscriber
cookie."
[0076] The profiler cookie can be used to produce additional
subscriber cookies for use with color image servers 16 associated
with other domains. Specifically, when a user situated at a client
14 accesses a color image server 16 from which the user has not
previously downloaded color corrected images, the user can click on
the color profiling option and be directed to color profile server
18. Upon interaction with color profile server 18, client 14 simply
uploads the profiler cookie instead of repeating the color
profiling process. Information concerning the domain associated
with the new color image server 16 can be incorporated in the
profiler cookie.
[0077] In response to receipt of the profiler cookie, color profile
server 18 delivers a web page advising the user associated with
client 14 of the intent to send the cookie contents to the domain
indicated in the cookie, and may request user approval for, among
other reasons, privacy concerns. Upon approval by the users, color
profile server 18 transmits the cookie contents to the color image
server 16 designated by the domain in the profiler cookie. In
response, the color image server 16 creates a subscriber cookie for
its own domain, and writes the cookie to client 14 for future use.
Thereafter, client 14 uploads the appropriate subscriber cookie to
the pertinent color image server 16 when requesting color corrected
images for the pertinent subscriber 22, and can bypass interaction
with color profile server 18.
[0078] The reliance on first and second cookies, one for color
profile server 18 and the other for a particular subscriber server
12a-12n or color image server 16, is driven in part by existing web
design considerations. In particular, cookies stored on a client's
browser typically are marked by the domain of the server that
generates them, and are not generally visible to other domains.
Thus, cookies created by color profile server 18 are not generally
visible to color image servers 16, and vice versa.
[0079] Cookie visibility can be further restricted by marking the
cookie with a path within a server's domain. This sort of cookie
will then not be visible on requests to pages outside the path,
even if to the same domain Further, a browser routinely sends all
visible cookies on each request to a server. This includes not only
the initial request for an HTML page, but also the requests for
images to be embedded in the page. Because an image can come from a
different server than the HTML page, however, the cookies sent for
the HTML page can differ from those sent for the image.
[0080] In light of the above considerations, color profile server
18 acts as an intermediary not only for administration of the color
profiling process, but for generation of subscriber cookies. This
intermediary function enables color correction of all subscriber
images to be performed at color image servers 16 rather than at a
centralized site. Also, with this intermediary function, once a
client has gone through the color profiling process, he generally
will not have to repeat it to obtain color correction of images for
additional subscribers. As an exception, the user may voluntarily
repeat the color profiling process when local driver software or
hardware such as the display device or video card associated with a
client 14 has changed. Indeed, to encourage updates from time to
time in order to accommodate hardware changes, expiration dates can
be applied to the profiler cookie and subscriber cookies.
[0081] The three different servers, i.e., subscriber server 12,
color image server 16, and color profile server 18, divide the
labor involved in color correction transactions. In particular,
assuming the existence of a profiler cookie and a subscriber
cookie, a subscriber server 12 serves the HTML for the subscriber's
own web pages and handles most other requests for those pages,
including serving of images that are not subject to color
correction. Color image server 16 serves the images that are
subject to color correction.
[0082] If color image server 16 receives the appropriate subscriber
cookie, it performs color correction based on the cookie contents
and serves the color corrected image to the appropriate client
device 14. Color image server 16 also may serve an icon near the
correctable color images that indicates whether the color images
have indeed been corrected. If color image server 16 finds no
subscriber cookie, for example, it displays an icon suggesting that
the user click the icon to initiate the color profiling process.
Otherwise, the icon merely indicates that color correction is
turned "on," i.e., that color correction has been applied to the
image.
[0083] Color profile server 18, as mentioned above, serves the
pages for the color profiling process. If the color profiling
process is invoked by clicking the icon displayed with a color
image delivered by color image server 16, the respective client 14
probably does not have a subscriber cookie for the pertinent
subscriber 22. In some cases, however, client 14 may be voluntarily
repeating the color correction process to update the profile for
new hardware or software. If a profiler cookie exists, then the
process can be abbreviated by simply shipping the contents of the
cookie to the appropriate subscriber domain for creation of the
subscriber cookie.
[0084] If the profiler cookie does not exist, then the full color
profiling process is served by color profile server 18. Upon
completion of the color profiling process, color profile server 18
generates the profiler cookie for client 14, and passes the
contents of the profiler cookie to the pertinent color image server
16. Color image server 16 then generates the subscriber cookie
based on the profiler cookie contents and invokes the original
subscriber URL from which the color profiling process was
invoked.
[0085] The mechanisms for exchanging color correction information
between the profiler cookie generated by color profile server 18
and the subscription cookie generated by color image server 16 may
vary. In particular, rather than delivering cookies to clients 14,
color profile server 18 may be arranged to transmit the color
correction information to all of the color image servers 16
associated with a recognized group of subscribers 22.
[0086] In this manner, the color profile information obtained by
color profile server 18 as a result of the color profiling process
can be "broadcasted" for storage by subscribers 22. The advantage
of this approach is that information transfer is seamless. There is
no need for the user associated with a client 14 to interact with
color profile server 18 following the initial color profiling
process, other than to update the color profile. Rather, each
subscriber 22 stores the color correction information associated
with the individual client 14, e.g., with a client ID code.
[0087] When the client 14 accesses one of the color image servers
16, the client ID code is used to retrieve the appropriate color
correction information and thereby serve a color corrected image.
The downside is that each subscriber 22 needs to maintain a
database of color correction information for clients 14 requesting
color corrected images from the participating subscribers,
including clients who may never access a respective subscriber
server 12. Thus, an approach that makes use of cookies for transfer
of color correction information may be more desirable for some
subscribers 22. Nevertheless, broadcasting of color correction
information remains a viable option that may be acceptable to some
subscribers 22, and highly convenient for end users.
[0088] The following is a description of some of the details that
may be associated with passing information between subscriber
servers 12, clients 14, color image servers 16, and color profile
server 18 according to an indirect cookie transfer approach. This
approach is indirect in the sense that the user intervenes and
enters approval before the profiler cookie contents are transferred
from color profile server 18 to a respective color image server 16.
In delivering web pages to clients 14, subscriber servers 12 pass
the URL's for correctable images stored on associated color image
servers 16. In addition, subscriber servers 12 preferably
incorporate color profiling icons near the images. The URL's for
the color profiling icons point to the pertinent color image server
16, while the hypertext link associated with the icon points to
color profile server 18.
[0089] To accomplish passing of color correction information back
to color image server 16, the URL of the page viewed by the user is
passed to color profile server 18 when the hypertext link
associated with the icon is followed by a client 14. This step of
passing the URL can be accomplished either by including the URL as
a parameter on the target URL, or by POSTing the information from a
form that wraps the icon, i.e., with the URL stored in a hidden
entry field. In the latter case, the icon serves as a button, which
may require some minimal client-side scripting. In addition, as
will be described, the name of the subscriber 22 and the URL of a
completion page to be served by the color image server 16 after the
color profiling process is complete may be included in the request
to color profile server 18. Subscribers 22 can be provided with a
server-side scripting function that inserts the icon code with the
appropriate URLs.
[0090] For the color profiling process, color profile server 18
serves a number of web pages that can be invoked by execution of a
web page provided by subscriber server 12. In this case, the
"return URL" is passed forward to each page in the sequence. The
return URL can be passed as a parameter in the target URL, or by
using hidden fields in forms. In some cases, the return URL can be
stored as a server variable. As mentioned above, color profile
server 18 handles two scenarios: (1) full color profiling when no
profiler cookie exists, and (2) creation of a subscriber cookie
when a profiler cookie already exists. In both scenarios, color
profile server 18 transfers the contents of the existing or newly
created profiling cookie to the pertinent subscriber 22. In
particular, color profile server 18 may present a button that
requests permission of the user associated with client 14 to
transfer the information.
[0091] The URL for the button points to a page served by color
image server 16. The request sent to color image server 16 includes
both the return URL and the color information written in the
profiler cookie The request preferably is a POST request from a
form, rather than a GET request with all the information set forth
in the URL due to length considerations. Color profile server 18
determines the URL of the destination page at subscriber 22 by
reference to the return URL. Prior to transfer of the cookie
contents, the user will want to know the destination. Accordingly,
color profile server 18 displays the name of the particular
subscriber 22 along with the button. If the name of the subscriber
is not easy to determine from the URL, it can be generated by
cross-referencing the URL to a name in a database accessible by
color profile server 18, or by passing the name with the return URL
in the original request from the page generated by subscriber
server 12.
[0092] Upon receipt of the information from color profile server
18, the pertinent color image server 16 serves a page indicating
that the color profiling process is complete. The page may be
invoked by the POST request containing the color correction
information and the URL of the "return" page, as received from
color profile server 18. Color image server 16 writes the color
correction information to the pertinent client 14 as a client
cookie. From that point forward, the subscriber cookie is stored by
the respective client 14, and is sent to the color image server 16
associated with the pertinent subscriber 22 with any request for a
color correctable image. In response, color image server 16
extracts the contents of the subscriber cookie, applies a color
correction to the requested image based on the contents, and
delivers the color-corrected image to the client 14.
[0093] As an alternative approach, color correction can be passed
from color profile server 18 to the color image server 16
associated with the respective subscriber 22 via a direct request,
rather than being embedded in a request generated when client 14
clicks on a button, anchor, or other input medium. This approach is
direct in the sense that the user need not intervene by submitting
approval for the transfer to color profile server 18. Instead, the
transfer of the content of the profile cookie to the appropriate
color image server 16 can be made seamless.
[0094] Indeed, in some embodiments, the user associated with client
14 does not even view pages sent by color profile server 18 for
transfer of information following the initial profiling. In this
manner, the transfer of color correction information from color
profile server 18 to a color image server 16 happens automatically,
without requiring the user associated with a client 14 to click on
a link to effect the transfer. This approach makes the transfer
appear more seamless to the user. The end result is the same, i.e.,
the transfer of color correction information contained in a
profiler cookie to create a subscriber cookie without the need for
reexecution of the color profiling process by the user.
[0095] To facilitate transfer by direct request, the client 14 is
assigned a client ID. Ordinarily, the client ID can be stored in
and received from a subscriber cookie on the browser associated
with a client 14. A client 14 that is new to the particular
subscriber 22, i.e., a client that does not send a subscriber
cookie to the particular color image server 16, will be assigned a
new client ID, which is sent as a cookie with the HTML in the
response from the color image server.
[0096] All URLs pointing to color profile server 18 then bear both
the client ID and a subscriber ID as parameters, so that the color
profile server can correlate requests for color correction
information for the respective client 14. The URL for the color
profiling icon points to color profile server 18 if there is no
subscriber cookie. For this approach, it is preferred that the
respective subscriber server 12 and corresponding color image
server 16 occupy the same domain so that they can view the same
cookies.
[0097] As in the indirect approach, a color profiling icon, which
appears adjacent a color correctable image, may be served from
either color image server 16 or color profile server 18 in the
direct transfer approach, depending on whether the color image
server receives a subscriber cookie. If a subscriber cookie is
present, the profiling icon is served by color image server 16, and
is formulated in appearance to indicate that color correction is
active, e.g., with a text message to that effect. This will be the
case for most images served by color image server 16 because only
new clients 14 will not have the subscriber cookie.
[0098] If the subscriber cookie is not presented, the icon is
served by color profile server 18. In other words, the web page
served by color image server 16 has embedded in it an icon served
by color profile server 18. If a profiler cookie is present, color
profile server 18 serves an icon that indicates the client 14 has
already been through the color profiling process. If not, the icon
indicates that the color profiling process has not previously been
completed by the respective client 14. This may be represented by a
colored icon to indicate that color profiling has been completed,
and a black-and-white icon to indicate that it has not.
[0099] In some embodiments, the icon may indicate that the client
14 has been through the color profiling process, but that the color
correction information has not yet been forwarded to the particular
subscriber 22, and that the image has not been color corrected. In
either case, color profile server 18 also receives the ID for the
client 14 and the subscriber 22, which are included in the URL
forwarded to color profile server 18. If the profiler cookie is
present, color profile server 18 immediately forwards the client ID
and the contents of the profiler cookie to the pertinent color
image server 16 in a special-purpose request.
[0100] If the subscriber cookie is present, color image server 16
performs the color correction based on the information contained in
the cookie. If the subscriber cookie is not present, color image
server 16 waits a short time to receive color information for this
client from color profile server 18. If the information is
forthcoming, color image server 16 applies the color correction and
writes a subscriber cookie to the browser associated with the
client 14. Otherwise, color image server 16 serves an uncorrected
image.
[0101] With this direct approach, it may be necessary for color
image server 16 to keep track of color correction information
forwarded by the color profile server 18 because such information
may not be received synchronously with image requests from clients
14. Accordingly, it may be necessary to incorporate a database
application that can be shared by color image server 16 for
temporary tracking of color correction information associated with
individual clients 14, and subscriber server 12 for tracking and
generation of client ID information. Once the information has been
written to a subscriber cookie, the ID and color correction
information for the respective client 14 can be purged from the
database.
[0102] Management of ID's according to the direct transfer approach
may take place as follows. The original color correction
information generated by color profile server 18 can be stamped
with a unique ID. The unique ID can be maintained in copies of the
color correction information forwarded to subscribers 22. This ID
changes if the client 14 repeats the color profiling process, and
can be referred to as the profiler ID. The profiler ID will remain
unchanged until the next pass through the color profiling process,
which may occur months later. In effect, the profiler ID
corresponds to a particular color profiling sequence. The profiler
ID is supplemented by the client ID and the subscriber ID. The
client ID identifies a client for whom a subscriber 22 is
requesting color information, and the subscriber ID identifies the
particular subscriber.
[0103] The client and subscriber IDs are passed via URL parameters
to color profile server 18 whenever a color image server 16 has no
color correction information for a particular client 14. The
subscriber ID is passed back with the color correction information
from color profile server 18 to the color image server 16 when the
color profile server determines the appropriate information for the
client, based on the contents of a profiler cookie or the results
of running the color profiling process. Once color image server 16
receives this information and writes it as a subscriber cookie to
the client's browser, the subscriber ID is no longer needed.
[0104] FIG. 4 is a flow diagram illustrating an example color
profiling process for a display device. A process as shown in FIG.
4 can be used to generate the contents of a profiler cookie as
discussed above with reference to FIG. 3. Notably, the entire color
profiling process can be completed by the user with as few as three
"clicks" of a pointing device. If the user is required to click a
continue button to proceed after selecting a patch, the process may
take additional clicks.
[0105] If the user is permitted to proceed automatically following
selection of a patch, however, the entire process can be completed
in three clicks. With optional analog adjustment, separate R, G,
and B blackpoints, and fine gamma steps, to be described, the
process may require up to six or seven clicks. Also, in many
embodiments, the color profiling process requires no plug-ins or
client side scripting when utilizing the method of selecting
discrete elements, although such mechanisms can be provided in some
embodiments such as in the use of slider adjustments.
[0106] The color profiling process enables visual profiling of a
display device by determining accurate values of blackpoint and
gamma for the R, G, and B phosphors or photodiode elements. Gamma
refers to a parameter y that indicates the rate of change in light
intensity with change in digital device value. The term
"blackpoint" refers to the lowest RGB values capable of
representation on the display device. For color values below the
blackpoint, there is no further decrease in light emitted by the
display device. Blackpoint is sometimes alternatively referred to
as black onset. In accordance with the invention, three separate
blackpoints are optionally determined, one for each of the R, G,
and B color channels of the monitor. For use with more accurate
monitors, a single dark gray RGB selection can be used to estimate
a single average blackpoint value for R, G, and B.
[0107] In some display devices, such as older CRT monitors,
different color channels can produce very different blackpoints.
Accordingly, reliance on a single RGB blackpoint measurement in
generating a color profile can introduce inaccuracies.
Determination of channel-specific blackpoints, however, can reduce
the degree of inaccuracy. In other words, by estimating the
blackpoint for each color channel individually, a more accurate
characterization of the colorimetric response of the display device
can be obtained. A more accurate colorimetric characterization
enables greater accuracy in conversion of color images for delivery
and display on the particular monitor. For purposes of example,
alternative color profiling processes are disclosed in U.S. patent
application Ser. No. 09/631,312, to Kruse et al., filed Aug. 3,
2000, and entitled "COLOR IMAGE DISPLAY ACCURACY ACROSS A GLOBAL
COMPUTER NETWORK," the entire content of which is incorporated
herein by reference.
[0108] Color profile server 18 may administer a color profiling
process as shown in FIG. 4 by serving a series of instructional web
pages to client 14. In general, the color profiling process may
involve determination of (1) blackpoint for each of the red, green,
and blue (R, G, and B) color channels of the display device, (2)
average gamma for R, G, and B, and (3) differences in gamma for R,
G, and B. Due to the wide range of differences in display device
properties, determination (2) above can be subdivided into
determination of (2a) a coarse gamma estimate, and (2b) a fine
gamma estimate. This process is described in greater detail below
with reference to FIGS. 4-11.
[0109] With reference to FIG. 4, the color profiling process first
involves determination of an estimated blackpoint for each of the
color channels of the color display device (64), e.g., R, G, B.
After determining the blackpoints, which may be merely an estimate,
the color profiling process involves determination of the gamma
exhibited by the display device. In particular, the process may
involve determination of a coarse gamma (66), followed by
determination of a fine gamma (68). Determination of the fine gamma
may rely in part on the coarse gamma. In other words, the coarse
gamma can be used as an initial estimate and starting point for
convergence toward a more finely tuned gamma.
[0110] After determining the fine gamma, the process may involve
determination of the gray balance exhibited by the display device
(70). Gray balance provides an indication of the amount of color
shift of a neutral gray toward one or more of the color channels
used by the display device, e.g., red, green, and blue. The gray
balance determination may rely in part on the gamma determined
previously in the color profiling process and, in a particular
embodiment, the fine gamma.
[0111] Next, the color profiling process involves generation of a
color profile (72). The color profile contains information that
characterizes the color response of the display device based on the
determinations (64, 66, 68, 70), i.e., blackpoints, gamma, and gray
balance. The color profile then can be loaded into a cookie, or
other content container, and stored locally with client 14 for
uploading to any of color image servers 16 when needed (74).
[0112] The estimated blackpoint parameters define the lower bound
of the dynamic range of the display device. Because the maximum RGB
value always defines white, the blackpoint defines the black end
point, and therefore defines the domain of values for each of the
R, G, and B color channels that results in a continuous change from
black to white. Again, blackpoint refers to the R, G, or B value
below which there is no further decrease in light emitted by the
display device.
[0113] For an individual color channel, such as R, the blackpoint
is the point at which further decreases in the R value produce no
further decreases in R channel light emitted by the display device.
If the blackpoint for a given color channel of a display device is
high, values for that channel in darker regions will be mapped to
the darkest shade and shadow detail will be lost if no image
correction is performed. Accordingly, obtaining an accurate
blackpoint estimate is important for the accuracy of images
represented by the display device.
[0114] In addition to a multi-channel blackpoint estimate, the
color profile includes a gamma parameter. The color profile also
may include a gray balance parameter. The parameters together
define the colorimetric response of an individual display device to
enable modification of color images for more accurate
representation on the device. The gamma parameter most affects the
overall appearance of the image. Gamma determines whether an image
appears overall too light or dark, or with too much contrast or too
little. The third parameter, R, G, B gamma difference or "gray
balance," is important because the human eye is very sensitive to
gray balance. The gray balance parameter indicates the relative
balance, or imbalance, between the different color channels of a
display device when producing RGB color combinations.
[0115] FIG. 5 is a flow diagram illustrating a color profiling
process as shown in FIG. 4 in greater detail. As shown in FIG. 5,
for blackpoint determination, color profile server 18 may serve one
or more web pages for display device adjustment. Initially, the web
page instructs the user to adjust the brightness and contrast of
the display device This step of display device adjustment is
optional, but generally desirable in preparing the display device
for blackpoint determination. Color profile server 18 may serve a
web page containing several rows of dark elements such as bars,
patches, characters, letters, numerals and the like (76).
[0116] Instead of patches or bars, color profile server 18 may
serve a web page having display elements with alternative shapes
such as numerals. Whereas the patches or bars may be generally
rectangular, more complex shapes can be used to aid the human eye
in resolving visual differences. For example, numerals, letters,
and other complex shapes can better engage the pattern recognition
capabilities of the human eye and result in heightened sensitivity
to gray scale differences.
[0117] When the human eye is called upon to perform pattern
recognition, its sensitivity to color gradations between a given
pattern and a surrounding area increase. The complex shape presents
a longer boundary relative to simple shapes and promotes an
increased perimeter for contrast. Elements with complex shapes may
be used in the blackpoint, coarse gamma, and fine gamma
determinations to characterize the monitor.
[0118] As an alternative to rows, the elements can be arranged in
columns placed side-by-side across the web page. As a further
alternative, each row or column may contain, instead of several
elements, only one or a small number of elements. A larger number
of elements in each given row may aid the user in resolving
differences between elements in adjacent rows.
[0119] The web page may instruct the user to set the brightness and
contrast of the display device to maximum (78). The rows (or
columns) of elements may be arranged in a series. The elements in
each row preferably exhibit the same darkness or lightness.
However, the elements in each row in the series differ in relative
darkness or lightness relative to the elements in other adjacent
rows. For example, the darkest row of elements could be situated at
the bottom, with rows containing elements with progressively
lighter shades being situated above in ascending order. The web
page instructs the user to reduce the brightness until the darkest
row of elements is barely visible (80). At this point, the user may
select "next" or some similar hypertext icon and proceed to the
next step in the color profiling process, e.g., blackpoint
determination for each of the red, blue, and green channels on an
individual basis.
[0120] FIG. 6 illustrates an example web page 122 for use in
display device adjustment in a color profiling process as shown in
FIG. 5. Client 14 displays rows 124 of dark elements with the
elements of each row having the same gray level value, but elements
in adjacent rows having different gray levels. As an example, rows
124 of dark elements (shown as numerals in the example of FIG. 7)
may be presented to the user with the following gray level values:
8, 16, 24, and 32. In other words, the rows of "zeros," "ones,"
"twos," and "threes" may have gray levels of 8, 16, 24, and 32,
respectively.
[0121] As the rows of dark elements are displayed, the user is
instructed to set brightness and contrast of the display device to
maximum, using the analog or digital controls provided with the
display device The user is then further instructed to reduce the
brightness of the display device until the row with the darkest
(lowest gray level value) elements is barely visible, and then
click "next" upon completion. This optional step of display device
adjustment serves to prepare the monitor for the blackpoint
determination carried out with respect to each color channel, as
described below.
[0122] To carry out the blackpoint determination process for each
color channel, several rows (or columns) of dark elements for each
color channel may be displayed on successive web pages.
Specifically, red channel, blue channel, and green channel web
pages for channel-specific blackpoint determination can be served
to the client in any order. In each case, the dark elements for a
given color channel may be arranged in rows in ascending or
descending order of relative lightness or darkness, as in web page
122 of FIG. 6, which is served for display device adjustment. The
rows provide a sequence of gray level gradations.
[0123] The bottom row for the red channel blackpoint determination
web page, for example, may be a row of "zeros" having elements
bearing the darkest shade (lowest gray value) of red among the
elements shown on the web page. As with web page 122, arrangement
of the elements in rows or columns is for purposes of illustration.
In some embodiments, display of a series of individual elements
(rather than rows of elements) may suffice.
[0124] The row of darkest elements that is barely visible to the
user will depend on the blackpoint for the respective channel of
the display device. The rows of elements are displayed against a
black, i.e., RGB=0, background. With some display devices, the user
may be unable to see elements with intensity levels of 8, 16, or
higher. The user is instructed to select the row of elements that
is barely visible on the display device This step determines the
blackpoint, i.e., the visible "cut-off" point at which further
decreases at which further decreases in the color channel value
produce no further decreases in light emitted by the display device
for that color channel. As an alternative, the user could be
prompted to make the least visible row of elements vanish for a
given color channel and then click on the remaining barely visible
bar. In either case, the blackpoint can be estimated.
[0125] FIG. 7 illustrates an example web page 128 for use in
blackpoint determination in a color profiling process as shown in
FIG. 5. Web page 128 may be substantially similar to web page 122
of FIG. 6. For example, web page 128 may include rows 130 of shaded
elements. Again, display of columns of elements or a series of
elements may be sufficient for some applications. As shown in FIG.
7, web page 128 directs the user to select the row of elements 130
that is barely visible on the display device. As in web page 122,
the rows 130 in web page 128 may be arranged as rows of "zeros,"
"ones," "twos," and "threes" having, for example, intensity levels
of 8, 16, 24, and 32, respectively. Web page 128 in FIG. 7
represents the web page for red channel blackpoint determination,
and includes rows of red elements set against a black
background.
[0126] Upon selection of the row that is barely visible for the red
channel, e.g., upon clicking on any element in the row, color
profile server 18 automatically serves the user a substantially
identical web page containing rows of green elements set against a
black background for purposes of determining the green channel
blackpoint. In this manner, the user selects a visible row or
element that most closely appears to match, or blend with, the
black background. Following selection of a row of green elements
that is barely visible, color profile server 18 serves the user a
substantially identical web page for blue channel blackpoint
determination and the user makes a similar selection. Thus, color
profile server 18 automatically servers successive web pages
governing blackpoint determination for each color channel following
selection of a row for a preceding channel. Alternatively, the web
pages may prompt the user to click on a "next" icon or similar
device. Serving successive web pages automatically following
selection of an element may be desirable, of course, to reduce the
overall number of clicks involved in the process.
[0127] In the above manner, the user selects the row of elements
that is barely visible for each color channel, and thereby provides
an indication of the blackpoint for each color channel. FIG. 5
further illustrates the process. In particular, FIG. 5 shows the
display of rows of dark red elements or characters (82), and
selection of the row that is barely visible (84), and further
illustrates the computation of the estimated blackpoint for the red
channel based on the selected row (86). Similarly, for the green
channel, a row of dark green characters is displayed (88), followed
by selection of the row that is barely visible (90), and
computation of an estimated blackpoint for the green channel based
on the selected row (92). Finally, for the blue channel, a row of
dark blue characters is displayed (94), followed by selection of
the row that is barely visible (96), and computation of an
estimated blackpoint for the blue channel based on the selected row
(98).
[0128] Following selection of the barely visible row of elements
displayed on each successive web page, client device 14 transmits
the result to color profile server 18. Alternatively, the results
for all color channels can be transmitted at the same time
following completion of the blackpoint determination for the last
color channel. Color profile server 18 then may compute the
estimated blackpoint for each channel (86, 92, 98), or simply store
the parameters for later computation, e.g., by color imager server
16.
[0129] The complete description of the display device behavior can
be represented by the following equation which relates RGB to XYZ:
1 [ X Y Z ] = [ X r , max X g , max X b , max Y r , max Y g , max Y
b , max Z r , max Z g , max Z b , max ] [ R G B ]
[0130] where 2 R = { [ ( d r - k o . r ) / ( 1.0 - k o . r ) ] r 0
, [ ( d r - k o . r ) / ( 1.0 - k o . r ) ] 0 [ ( d r - k o . r ) /
( 1.0 - k o . r ) ] < 0 } G = { [ ( d g - k o . g ) / ( 1.0 - k
o . g ) ] g 0 , [ ( d g - k o . g ) / ( 1.0 - k o . g ) ] 0 [ ( d g
- k o . g ) / ( 1.0 - k o . g ) ] < 0 } 3 B = { [ ( d b - k o .
b ) / ( 1.0 - k o . b ) ] b 0 , [ ( d b - k o . b ) / ( 1.0 - k o .
b ) ] 0 [ ( d b - k o . b ) / ( 1.0 - k o . b ) ] < 0 }
[0131] The variables d.sub.r, d.sub.g, and d.sub.b are the digital
input values normalized to 1.0. The parameters k.sub.o,r,
k.sub.o,g, and k.sub.o,b, are the blackpoints and the parameters
.gamma..sub.r, .gamma..sub.g, and .gamma..sub.b are the gammas for
the red, green, blue channels.
[0132] The values of parameters k.sub.o,r, k.sub.o,g, and
k.sub.o,b, are determined as follows: Assume that (regardless of
the properties of a particular monitor) for the red channel there
exists a minimal visible set of values for XYZ that can be detected
by the human eye, designated as the vector (X.sub.t,r,Y.sub.t,r,
Z.sub.t,r). This vector will have a unique corresponding value for
R in the expression above, designated as R.sub.t. For a particular
monitor with specific values of .gamma..sub.r and k.sub.o,r there
will be a unique device value associated with R.sub.t which is
designated by d.sub.t,r: 4 R t = { [ ( d t , r - k o . r ) / ( 1.0
- k o . r ) ] r 0 , [ ( d t , r - k o . r ) / ( 1.0 - k o . r ) ] 0
[ ( d t , r - k o . r ) / ( 1.0 - k o . r ) ] < 0 }
[0133] This device value d.sub.t,r is determined by the user during
the color profiling procedure as described, i.e., by selecting the
darkest barely visible row of elements in the blackpoint
determination web page for red. The value of R.sub.t is empirically
determined. For example, for a calibrated display system in a dark
room with k.sub.o,r=0.0 and .gamma..sub.r=2.2, a red patch may be
visible for d.sub.t,r=8/255 gray levels which implies
R.sub.t=(8/255).sup.2.2.
[0134] The exact value of k.sub.o,r can be calculated by solving
two simultaneous equations, namely the equation above for R.sub.t
and the equation for R.sub.0.33 which will be described below.
Alternatively, a reasonable estimate can be made for k.sub.o,r by
assuming a gamma of 2.2. If this assumption is made, the value of
k.sub.o,r can be estimated as: 5 R t = ( 8.0 255.0 ) 2.2 = [ ( d t
, r - k o . r ) / ( 1.0 - k o . r ) ] 2.2 ( 8.0 255.0 ) = [ ( d t ,
r - k o . r ) / ( 1.0 - k o . r ) ] d t , r - k o . r k o . r = d t
, r - ( 8.0 255.0 )
[0135] In a similar fashion, the values for k.sub.o,g and
k.sub.o,b, can be determined.
[0136] FIG. 8 is a flow diagram illustrating gamma and gray balance
determination in a color profiling process as shown in FIG. 5. For
determination of coarse gamma, one of the web pages served by color
profile server 18 displays a range of green elements, e.g.,
patches, against a dithered green background (100). The coarse
gamma determination web page can be served immediately and
automatically following selection of a row of elements in the last
blackpoint determination web page, or in response to selection of a
"next" icon or similar device.
[0137] In one embodiment, the coarse gamma determination is limited
to only the green color channel. Specifically, the coarse gamma
determination is made using a series of green elements against a
green dithered background. Green is the most dominant and intense
phosphor among red, green, and blue, and is highest in contrast.
Green also has the highest L*. Note also that green most closely
matches the photopic V(.lambda.) response of the eye. This approach
to coarse gamma determination considers only the green color
channel, and essentially ignores red and blue.
[0138] In this manner, the coarse gamma measurement concentrates on
the most dominant color channel and avoids errors that can arise to
the red-blue imbalances that are highly prevalent in many display
devices. Thus, the elements displayed for the coarse gamma
determination may be green patches with different darkness or
lightness values. Alternatively, a combined coarse gamma for all of
the color channels may be determined as described in the
above-referenced U.S. patent application Ser. No. 09/631,312.
[0139] Upon display of the green patches, the user is instructed to
select a patch that appears to most closely blend with the dithered
green background (102), as indicated in FIG. 8. The green patch
"blends" with the dithered background in the sense that it appears
to closely match the level of the background. An example of a range
of green patches displayed against a green dithered background is
shown in FIG. 9 and indicated by reference numeral 132. This range
of green patches and the green dithered background can be displayed
in a web page served by color profile server 18.
[0140] Based on the selected green patch, which again may be
selected by clicking on it with a pointing device, color profile
server 18 computes a coarse gamma (104), as indicated in FIG. 8.
Alternatively, the computation may take place later at color image
server 16. The coarse gamma determined in this step can be used as
an estimate for the average gamma of R, G, and B via selection of a
green patch from the set of green patches against the dithered
green background The dithered green background may be set at
approximately 25% to 50%. Dithered backgrounds approaching
approximately 33% may more closely match the actual midpoint of
black to green transition for the display device, and may be
preferred for typical display devices.
[0141] By alternating black and green at an appropriate frequency,
a 25%, 33%, or 50% green background can be produced. For a CRT,
turning on or off all of the pixels in a given horizontal line
should produce more predictable output from display device to
display device than modulating individual pixels to form vertical
lines, due to the video bandwidth of the device. For flat panel
devices, this is less of an issue. To accommodate clients using
both CRT's and flat panel devices, however, generation of the
dithered background by use of alternating horizontal lines is
preferred.
[0142] The center patch in the range 132 of patches can be based on
an average gamma of 2.0, since most monitors range from 1.6 to 2.5.
The other green patches that surround the center patch may proceed
in a sequence with relatively large steps, e.g., 8 gray levels
apart from one another. Coarse gamma can be estimated using the
equation:
G.sub.0.33=0.333=[(d.sub.0.33,g-k.sub.o,g)/(1.0-k.sub.o,g)].sup..gamma..su-
p..sub.g
[0143] where d.sub.0.33,g is the gray level value (normalized to
1.0) of the selected patch that appears to most closely blend in
with the background, k.sub.o,g is the previously determined
blackpoint, G.sub.0.33 is the relative intensity of the green
channel (equal to 1/3), and .gamma..sub.g is the green gamma. As an
alternative to actually computing the coarse gamma, the green level
value of the selected patch simply is carried forward for use in
the fine gamma process. In this case, the value can eventually be
discarded.
[0144] After the coarse gamma estimate is obtained, fine gamma is
estimated. Fine gamma is a refined or "fine-tuned" estimate for the
average gamma of R, G, and B. Fine gamma can be determined by
selection of another green patch from a set of green patches
presented against a dithered green background. In this case, the
center patch may be identical to the green patch selected by the
user for determination of coarse gamma. Thus, the coarse gamma step
"informs" the fine gamma step. In effect, the selected coarse gamma
patch may serve as a starting point for the fine gamma
determination. Specifically, the green patch selected in the coarse
gamma determination can be used to form the central patch for the
fine gamma determination.
[0145] A range of patches for determining fine gamma is illustrated
in FIG. 10 and designated by reference numeral 134. The patches in
this range are in a sequence with smaller steps centered about the
center green patch selected in the coarse gamma process. For
example, the patches may be set at 4 green levels apart, in
contrast to the 8 green levels used as the difference for the
coarse gamma determination. In this manner, a narrower range is
used to "fine-tune" the coarse gamma estimate, with the center of
the range having been "learned" from the coarse gamma estimate.
[0146] A web page served by color profile server 18 displays the
selected green patch from the coarse gamma estimate among a
narrower range of green patches (106). The user then is instructed
to select the green patch that most closely blends with the same
dithered green background as used for coarse gamma (108). Based on
the selected patch, color profile server 18 computes a single fine
RGB gamma (110). Thus, the fine gamma is the overall gamma
estimated for each of the RGB channels.
[0147] Alternatively, as mentioned above, the RGB value of the
selected patch can simply be stored for use by color image server
16 in computing fine gamma and rendering color corrections. In any
event, a refined estimate for gamma can be computed according to
the equation:
G.sub.0.33=0.333=[(d.sub.33,g-k.sub.o,g)/(1.0-k.sub.o,g)].sup..gamma..sup.-
.sub.g
[0148] where d.sub.0.33,g is the green level value (normalized to
1.0) of the selected patch that blends in with the background,
k.sub.o,g is the previously determined blackpoint, G.sub.0.33 is
the relative intensity of the green channel (equal to 1/3), and
.gamma..sub.g is the green gamma.
[0149] To determine gray balance, color profile server 18 serves a
web page that displays a plurality of RGB patches. The RGB patches
can be generated with the same value of green selected in the
previous fine gamma step in conjunction with values of red and blue
that are substantially equal to or systematically shifted from the
previously selected value of green. The RGB patches can be
displayed against a gray background which is dithered in the same
manner as the green dithered background of the previous step (fine
gamma) (112).
[0150] Again, this step "learns" from the previous one, and forms
part of a cascading series of color profiling steps (coarse gamma,
fine gamma, and gray balance) that help narrow the search for the
correct gamma The user is then instructed to select the gray patch
that appears to most closely blend with the dithered gray
background (114). Based on the selected gray patch, individual RGB
gammas are computed (116). Notably, the overall gray balance
determination can be made with a single click of the user's
pointing device.
[0151] Thus, in this gray balance process, the green intensity
value for the patch selected in the fine gamma process is used to
generate the gray patches that exhibit +/-(plus/minus) differences
or "shifts" in red and blue about the value of the central gray
patch derived from the gamma estimate. For example, the value of
green selected in the fine gamma process can be displayed om a
patch in the center of the range in conjunction with substantially
identical values of red and blue.
[0152] The gammas for red and blue are then fine tuned by the gray
balance determination, which helps identify red-blue imbalance in
the display device. Thus, the green gamma is "locked in" in the
gray balance step, while the red and blue imbalance is determined.
In other words, every patch in the gray balance array carries the
same green value, but is modulated by different gradations of red
and blue. This step eliminates one axis of variation, green, but
permits identification of any imbalance between red and green or
between blue and green. This limits the range of choices to a more
finely-tuned area, and aids the user in making a more accurate
selection.
[0153] The range of patches for the gray balance determination may
be a two-dimensional array of patches with red-blue-shifted patches
arranged around the central gray patch formed according to the
gamma estimate from the fine gamma process. In particular, the
central gray element can be based on the estimated RGB gamma
derived from the green channel in the gamma determination. In other
embodiments, the red channel could be used to determine the initial
RGB gamma estimate, followed by a gray balance determination that
resolves imbalance between green and red or blue and red.
[0154] FIG. 11 illustrates an example of a two-dimensional range
136 of gray patches arranged in a five-by-five matrix for use in
the gray balance determination. Each patch represents a shift away
from the central gray patch along either the blue axis, the red
axis, or a combination of both, but preferably does not represent
any further green shift. The user selects the patch that appears to
most closely blend with the dithered gray background, which may be
a 33% dithered background. The central patch can optionally be
highlighted to indicate it is the preferred default choice.
[0155] The number of patches and the exact values of RGB for each
patch can be quite flexible. For example, in the case of the image
in FIG. 11, all patches can be selected to have identical values of
L* as indicated by the estimated profile for the display based on
phosphors, average gamma, and blackpoint. Patches adjacent to the
center may differ by all permutations of +/-3 .DELTA.E for a* and
for b* as estimated from a Matrix TRC (tone reproduction curve)
profile constructed from the above parameters.
[0156] Patches around the outer perimeter of the grid array may
differ from the center by +/-6 .DELTA.E in R and B. Alternatively,
for simplicity, one can elect to vary R and B only by +/- a fixed
amount such as +/-5 gray levels and +/-10 gray levels. Preferably,
all patches are relatively small deviations from the central patch
in all directions of color space of approximately constant L*. This
test will help determine in a sensitive manner whether there exists
a significant difference in the gammas of R, G, and B, and thereby
expose significant gray imbalance between R and B.
[0157] The two-dimensional format of the patches shown in FIG. 11
may aid the user's selection of the correct patch. A gray patch
with red, green, and blue values that correspond to the initial
gamma from the previous step in the color profiling process, i.e.,
fine gamma, is placed at the center in this embodiment. Adjacent
patches differ in gray level as the array extends outward such that
the outer periphery of the array contains patches that are two
gradations removed from the central patch. The array produces a
visual "funnel" effect that, from experience, tends to direct the
user toward the central patch as the starting point for matching
with the background. The differences between patches in the
two-dimensional array are more clear and dramatic than in a
one-dimensional strip of patches. As the array extends outward, the
shift becomes greater. Thus, the gradations are well pronounced and
aid the user in picking the appropriate patch which, in many cases,
will be the central patch selected in the previous step of the
color profiling process.
[0158] If the user selects the central patch, the same gamma value
is used for the R, G, and B channels. If one of the other patches
are selected, three separate gammas are calculated based on the
equations:
R.sub.0.33=0.333=[(d.sub.0.33,r-k.sub.o,r)/(1.0-k.sub.o,r)].sup..gamma..su-
p..sub.r
B.sub.0.33=0.333=[(d.sub.0.33,b-k.sub.o,b)/(1.0-k.sub.o,b)].sup..gamma..su-
p..sub.b
[0159] where the subscripts for .gamma. and d.sub.0.33 indicate
unique values for the R and B channels. The values for d.sub.0.33
for each channel are given by the values of RGB of the particular
patch selected in this gray balance step. These equations are
combined with a set of phosphor values to generate accurate
profiles for the client's display device, using equations well
known in the art, and referred to as Matrix TRC formalism in the
International Color Consortium (ICC) specification. Again,
calculations can be performed by color profile server 18 or by a
color correction module associated with color image servers 16.
[0160] The process of selecting patches in the coarse gamma, fine
gamma, and gray balance determination steps is advantageous
because, in preferred embodiments, it requires no applications,
applets, or other client-side scripts to be loaded at the client
side. Rather, the user may simply select one of the patches
displayed in a web page. In other embodiments, however, if
applications, applets, or client-side scripts are used, it is
conceivable that smooth slider bars, +/- arrows, and the like could
be used to adjust the color of a single patch in real-time for
comparison to the dithered background. In this manner, the user has
the ability to precisely match a single patch to the background,
rather than select from a finite set of patches the one that most
closely matches. This technique of real-time adjustment also may be
useful for non-networked approaches to color calibration and
characterization. In this case, for blackpoints, gamma, and/or gray
balance, the patch or element selected by the user may be a single
adjustable patch in a condition in which the slider or other
adjustment medium has adjusted its color to a level that is
visually acceptable to the user, i.e., to a point at which the
patch appears to match the dithered background.
[0161] Based on the blackpoint, coarse gamma, fine gamma, and gray
balance processes, a color profile for the display device is
generated (118). Upon generation of the color profile, a color
profiler cookie is created (120). Information representative of the
color profile is added to the color profiler cookie for future use.
In particular, the information can be used to create a subscriber
cookie for future interaction between the particular client 14 and
the particular subscriber 22 and color image server 16. Although
the color profile is especially useful for characterizing display
devices in a network, it also may be useful in a non-networked
application. In particular, the color profiling process described
herein may find ready use in the calibration and characterization
of an individual display device for correction of content generated
or obtained locally with the device, rather than across a
network.
[0162] Advantageously, there is no need for the client 14 to
provide information regarding the configuration of its display
device. Very satisfactory results can occur using an average set of
phosphor values based on published standards such as sRGB, Apple
Macintosh RGB, and the like. If desired, further steps can be
added, particularly in order to address the issue of phosphor
values and white point The color profiling process simply results
in generation of a cookie that serves as a container and vehicle
for passing information characterizing the color response of the
display device associated with client 14 to color image server 16.
Alternatively, the chromaticity information and white point can in
some cases be obtained from the display utilizing communication
protocols such as VESA and/or from the operating system of the
computer. The usefulness of this invention will continue because,
with current technology, the RGB blackpoints and gammas are
difficult to maintain perfectly at the hardware level even with
expensive electronic circuitry.
[0163] Ordinarily, all cookies visible to a particular domain are
attached to each request from a browser application executed by a
client 14. For this reason, a typical browser limits each domain to
a maximum of twenty cookies. To avoid consuming the allotment of
cookies for a particular subscriber 22, all of the color correction
information for a particular client 14 preferably is packed into a
single profiler cookie and a single subscriber cookie. For example,
a number of items can be packed into the value string of the
subscriber cookie or the profiler cookie, as the case may be. In
particular, each cookie should include the gamma values for R, G,
and B. Each gamma value may be a value between 1.0 and about 3.0.
In addition, the cookie may include the chromaticity values for
black and white, e.g., expressed as a value between 0 and
+1000.0.
[0164] An exemplary cookie may have the following items packed into
its value string, each demarcated by a separator:
[0165] (1) Cookie format version code--a numeric code, e.g., 1 to 3
bytes, plus separator.
[0166] (2) Cookie installation date--the usual cookie-style
timestamp (milliseconds after midnight of Jan. 1, 1970, GMT), e.g.,
12 to 13 bytes, plus separator.
[0167] (3) Unique profiler ID assigned to this color information
when it is generated by the color correction sequence; a long
integer, e.g., 4 bytes, plus separator (but possibly longer).
[0168] (4) Gamma and blackpoint values for R, G, B--each a text
representation of a floating-point value between 1.0 and about 3.0,
retaining 4 decimal digits. The decimal point could be implied.
Thus, the gamma values may take up 5 or 6 bytes plus a separator
each, or three times that overall. Alternatively, the selected tint
values chosen for R, G, and B can be indicated, enabling the gamma
and blackpoint values to be calculated at a later time by a server
upon upload of the cookie.
[0169] (5) Chromaticity for Black and White--each a text
representation of a floating-point value between 0 and +1000.0,
retaining 4 significant digits. Thus, this may take up 6 or 7 bytes
plus a separator each, or two times that overall.
[0170] (6) Number of bits per color--two decimal digits: two bytes
plus separator.
[0171] (7) Display Device ID code--an alphanumeric code, which may
be roughly 10 bytes plus separator.
[0172] (8) Cookie Data Checksum--a long integer: 4 bytes. The
example cookie described above has about 68 bytes plus 10
separators. The separator character should be chosen so that the
string does not have to be "escaped"; the caret ({circumflex over (
)}) is frequently used this way. Thus, the typical size for the
value string may be about 80 bytes.
[0173] FIG. 12 is an example of a color image 184 transmitted to a
client 14 in a system as shown in FIGS. 1 and 2. As shown in FIG.
12, the image 184 may be presented on a screen 182 on a display
device associated with a client 14. A color image server 16
associated with a particular subscriber 22, such as "ABC Company,"
delivers image 184 to the client 14 upon request. For purposes of
illustration, image 184 may be accompanied by a legend 186 that
identifies the subscriber 22 and a particular item being displayed.
Also, an icon, button, or the like may accompany image 184 and
indicate whether color correction has been applied by color image
server 16, as indicated by reference numeral 188. In the example of
FIG. 12, color correction has not been applied, e.g., because a
subscriber cookie has not yet been generated for the particular
subscriber 22. Another icon, button, or the like may be displayed
to invite the user to profile its display device, as indicated by
reference numeral 190.
[0174] Elements 188 and 190 could be integrated with one another,
as discussed previously, and take on an appearance such as a
particular color scheme that indicates whether color correction has
been applied. In either case, element 190 provides a hypertext link
to the URL associated with color profile server 18. Thus, when the
user clicks on element 190, pages are requested from color profile
server 18 for initiation of the color profiling process. If a
profiler cookie already exists, however, it is sent by client 14 to
color profile server 18. In that case, there is no need to repeat
the color profiling process. Instead, color profile server 18
creates a subscriber cookie for the pertinent subscriber 22, and
forwards it to the associated color image server 16, either
directly without user intervention or indirectly with user approval
as previously described.
[0175] FIG. 13 is block diagram illustrating transmission of color
correction information in a system as shown in FIGS. 1 and 2. In
particular, FIG. 13 illustrates a situation in which subscriber
cookies have already been created for color image servers 194, 198
associated with particular subscribers 22 accessed by an individual
client 196. In this case, upon accessing a web page from a
subscriber server 12, client 196 requests images from color image
server 194. When requesting images from another subscriber 22,
client 196 requests images from color image server 198. Color image
server 194 incorporates both a color correction module 200 and an
archive 202 of color images. Similarly, color image server 198
includes a color correction module 204 and an archive of color
images 206.
[0176] When client 196 sends an image request to color image server
194, it sends along a color profile cookie, i.e., a subscriber
cookie, as indicated by line 208. Likewise, as indicated by line
210, client 196 sends a subscriber cookie to color image server 198
when requesting an image. In each case, the subscriber cookie
contains a color profile that provides color correction information
for use by the respective color correction module 200, 204 in
modifying, i.e., color correcting, the color images served from
image archives 202, 206, respectively. Thus, when a request is
received, color images server 194 or 198 processes the accompanying
subscriber cookie to extract the contents, and controls the color
correction module 200, 204 based on the extracted contents. In this
manner, client 196 receives color corrected images, as indicated by
reference numerals 212 and 214.
[0177] The manner in which color correction modules make use of the
color profiles contained in the subscriber cookies will now be
described. The foregoing discussion associated with FIGS. 4-11
above has utilized simplified one dimensional formulas to explain
the relevance of blackpoint, average gamma, and adjusted gammas for
RGB to account for gray balance. In the embodiment described with
reference to FIGS. 4-11, blackpoints for each color channel are
estimated based on red, green, and blue elements selected by a user
associated with a respective client 14. Thus, the output of the
color profiling process is a blackpoint RGB value and a gamma, or
individual RGB gammas. Now we assume that these values have been
determined in the manner described above. The complete description
of the display device behavior can be given by the following
equation which relates RGB->XYZ: 6 [ X Y Z ] = [ X r , max X g ,
max X b , max Y r , max Y g , max Y b , max Z r , max Z g , max Z b
, max ] [ R G B ]
[0178] where 7 R = { [ ( d r - k o . r ) / ( 1.0 - k o . r ) ] r 0
, [ ( d r - k o . r ) / ( 1.0 - k o . r ) ] 0 [ ( d r - k o . r ) /
( 1.0 - k o . r ) ] < 0 } G = { [ ( d g - k o . g ) / ( 1.0 - k
o . g ) ] g 0 , [ ( d g - k o . g ) / ( 1.0 - k o . g ) ] 0 [ ( d g
- k o . g ) / ( 1.0 - k o . g ) ] < 0 } B = { [ ( d b - k o . b
) / ( 1.0 - k o . b ) ] b 0 , [ ( d b - k o . b ) / ( 1.0 - k o . b
) ] 0 [ ( d b - k o . b ) / ( 1.0 - k o . b ) ] < 0 }
[0179] The variables d.sub.r, d.sub.g, and d.sub.b are the digital
input values for the red, green, and blue channels normalized to
1.0. The parameters k.sub.o,r, k.sub.o,g, and k.sub.o,b, are the
blackpoints for the red, green, and blue channels, and the
parameters .gamma..sub.r, .gamma..sub.g, and .gamma..sub.b are the
gammas for the red, green, blue channels. Thus, the gamma and
blackpoint information contained in the subscriber cookie for a
respective display device can be used in the above equations to
produce, in effect, a destination device profile. The destination
device profile, with a source profile previously computed for the
requested image, can be used to perform a transformation of the
image data sufficient to produce calibrated output on the display
device.
[0180] The above approach is different than other attempts to
characterize display devices such as equation 21 in Berns, "CRT
Colorimetry. Part I: Theory and Practice."In most
characterizations, the "k" parameters are used to describe black
offset rather than blackpoint. Black offset refers to the non-zero
intensity measured or perceived from a display for RGB=0. In our
experience, the contrast/brightness adjustment procedure used in a
color profiling process in accordance with embodiments of this
invention minimizes the effect of this phenomenon. However,
non-zero blackpoints are very possible even after the
contrast/brightness adjustment, and therefore should be taken into
account.
[0181] This profile description can either be used in this format
or converted to formats such as those specified by the ICC. This
format is also known as the Matrix TRC format, and utilizes a
generic lookup table for the expressions above for R, G, and B
rather than an equation combined with a matrix similar to above.
The above information, e.g., gammas, blackpoints, and the like, can
be stored in a cookie on a computer associated with a client 14.
Alternatively, the individual data which are the RGB values of the
patches selected by the user can be stored in the cookie, which can
permit improved profile technology to be employed at a later date
utilizing the same input information.
[0182] To implement a system as described herein with an existing
archive of images and HTML codebase for a particular subscriber 22,
the existing subscriber server 12 is modified to replace existing
image file references indicated in HTML pages with similar
references to a pertinent color image server 16 equipped with a
color correction module. For example, an existing subscriber image
file reference called:
[0183] http://HSubscriberName.com/images/ImageName.jpg could be
replaced with:
[0184]
http://correction.SubscriberName.com/images/ImageName.jpg.
[0185] These modified references in the HTML page then issue a
command to the color image server 16 to serve the requested image.
When the color image server 16 receives the command, it also
receives the subscriber cookie, if one exists, and applies the
information contained in the cookie to perform color correction.
The color image server 16 then reads the pertinent image file,
creates a unique display profile utilizing the display parameters
stored in the subscriber cookie, and converts the image from source
to destination before sending it to the client's browser.
[0186] All images stored on the subscriber server 12 may have a
corresponding copy file of the same name residing on the subscriber
color image server 16. The color image server 16 may access this
database of image files to read, convert, and send images
referenced by the HTML page sent to the client 14. According to one
embodiment, color image server 16 may use a very simple and quick
technique for color management. In particular, all images on the
color image server 16 preferably have a predetermined RGB color
space. This typically means that original images are converted from
the color space of corresponding source devices, e.g., such as
scanners, digital cameras, and the like, to the standard color
space determined by the subscriber 22. Good examples of standard
RGB color spaces are ColorMatch RGB, which has a color temperature
for the "virtual display" of D50. Other color spaces such as Adobe
RGB have an excellent gamut, but have a color temperature of D65.
When an image on an HTML page sent to the client 14 is referenced
via the color image server 16 associated with a subscriber server
12 such as:
[0187] correction.SubscriberName.com/images/ImageName jpg
[0188] color image server 16 accesses the corresponding image and
converts the RGB data in real time before sending the image to the
client destination. The conversion can be performed according to
the following calculation: 8 R s = { [ ( d r , s - k o , r , s ) /
( 1.0 - k o , r , s ) ] r , s 0 , [ ( d r , s - k o , r , s ) / (
1.0 - k o , r , s ) ] 0 [ ( d r , s - k o , r , s ) / ( 1.0 - k o ,
r , s ) ] < 0 } G s = { [ ( d g , s - k o , g , s ) / ( 1.0 - k
o , g , s ) ] g , s 0 , [ ( d g , s - k o , g , s ) / ( 1.0 - k o ,
g , s ) ] 0 [ ( d g , s - k o , g , s ) / ( 1.0 - k o , g , s ) ]
< 0 } B s = { [ ( d b , s - k o , b , s ) / ( 1.0 - k o , b , s
) ] b , s 0 , [ ( d b , s - k o , b , s ) / ( 1.0 - k o , b , s ) ]
0 [ ( d b , s - k o , b , s ) / ( 1.0 - k o , b , s ) ] < 0
}
d.sub.r,c=k.sub.o,r,c+(1.0-k.sub.o,r,c)min(1.0,R.sub.c).sup.1/.gamma..sup.-
.sub.rf
d.sub.g,c=k.sub.o,g,c+(1.0-k.sub.o,g,c)min(1.0,G.sub.c).sup.1/.gamma..sup.-
.sub.g,c
d.sub.b,c=k.sub.o,b,c+(1.0-k.sub.o,b,c)min(1.0,B.sub.c).sup.1/.gamma..sup.-
.sub.b,c
[0189] Note that the matrices above can be concatenated into a
single matrix for increased processing speed.
[0190] FIG. 14 is a block diagram illustrating an alternative
architecture for a system 214 for improving color image display
accuracy in a computer network. System 214 conforms substantially
to the system shown in FIG. 2, except that all images for the
subscribers are stored at a central color image server 16. Color
profiling server 18 may reside or be integrated with color image
server 16 in the embodiment of FIG. 14. In this case, color
profiling server 18 provides web pages for guidance of a color
profiling process as described herein.
[0191] Color image server 16 or color profile server 18 may include
a database server for storage of individual color profiles
associated with clients 14. When a client 14 requests an image
tagged in the code sent by one of subscriber servers 12, it is
directed to the central color image server 16. The color image
server 16 may use a client ID sent from the client to retrieve the
appropriate color profile and apply it to modify the requested
color image using techniques as described herein for color
correction. In this manner, color image server 16 provides color
corrected images without the need for transfer of cookies and the
like between clients 14 and the color image server.
[0192] A number of embodiments of the present invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, these and other embodiments
are within the scope of the following claims.
* * * * *
References