U.S. patent application number 13/830678 was filed with the patent office on 2014-09-18 for methods and systems for measuring and correcting electronic visual displays.
The applicant listed for this patent is Ronald F. Rykowski. Invention is credited to Ronald F. Rykowski.
Application Number | 20140267784 13/830678 |
Document ID | / |
Family ID | 51493402 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140267784 |
Kind Code |
A1 |
Rykowski; Ronald F. |
September 18, 2014 |
METHODS AND SYSTEMS FOR MEASURING AND CORRECTING ELECTRONIC VISUAL
DISPLAYS
Abstract
The present disclosure relates to methods and systems for
measuring and correcting electronic visual displays. A method in
accordance with one embodiment of the present technology includes
generating a series of patterns for illuminating proper subsets of
the light emitting elements of the display, such as regular grids
of nonadjacent activated light emitting elements with the elements
in between deactivated. For each generated pattern, an imaging
device captures information about the activated light emitting
elements. A computing device analyzes the captured information,
comparing the output of the activated light emitting elements to
target output values, and determines correction factors to
calibrate the display to better achieve the target output values.
In some embodiments, the correction factors may be uploaded to
firmware controlling the display or used to process images to be
shown on the display.
Inventors: |
Rykowski; Ronald F.;
(Bellevue, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rykowski; Ronald F. |
Bellevue |
WA |
US |
|
|
Family ID: |
51493402 |
Appl. No.: |
13/830678 |
Filed: |
March 14, 2013 |
Current U.S.
Class: |
348/189 ;
29/593 |
Current CPC
Class: |
G09G 2320/0693 20130101;
G09G 2320/0233 20130101; H04N 17/04 20130101; G09G 2360/145
20130101; G09G 3/20 20130101; H04N 17/004 20130101; Y10T 29/49004
20150115; G09G 3/30 20130101; G09G 3/006 20130101 |
Class at
Publication: |
348/189 ;
29/593 |
International
Class: |
H04N 17/00 20060101
H04N017/00 |
Claims
1. A method in a computing system having a pattern generator and an
image capture device for calibrating a visual display comprising an
array of a number of pixels and corresponding subpixels, the method
comprising: identifying a fraction of the number of pixels and
corresponding subpixels of the display; generating, by the pattern
generator, patterns for illuminating proper subsets of the pixels
and corresponding subpixels of the display, such that-- each
pattern illuminates the identified fraction of the number of pixels
and corresponding subpixels of the display, and each of the pixels
and corresponding subpixels of the display is illuminated in at
least one pattern; and for each generated pattern-- illuminating
subpixels of the display according to the generated pattern;
capturing, by the image capture device, information about the
illuminated subpixels; analyzing, by the computing system, the
captured information about the illuminated subpixels; calculating
correction factors for illuminated pixels and corresponding
subpixels.
2. The method of claim 1, further comprising using the correction
factors to calibrate the visual display.
3. The method of claim 2 wherein using the correction factors to
calibrate the visual display comprises uploading the correction
factors to firmware or software controlling the display.
4. The method of claim 2 wherein using the correction factors to
calibrate the visual display comprises applying the correction
factors to process an image to be shown on the display.
5. The method of claim 4, further comprising applying the
correction factors to process substantially every image to be shown
on the display.
6. The method of claim 1 wherein the subpixels are light-emitting
diodes.
7. The method of claim 1 wherein the subpixels are organic
light-emitting diodes.
8. The method of claim 1 wherein identifying a fraction of the
number of pixels and corresponding subpixels of the display
comprises receiving input specifying the fraction.
9. The method of claim 1 wherein identifying a fraction of the
number of pixels and corresponding subpixels of the display
comprises: determining characteristics of the display and of
measurement equipment for capturing information about the
illuminated subpixels; and calculating the fraction based on the
determined characteristics.
10. The method of claim 1 wherein the fraction is 1/4 or
smaller.
11. The method of claim 1 wherein a pattern comprises a regular
grid of nonadjacent illuminated pixels.
12. The method of claim 1 wherein each pattern comprises a distinct
set of nonadjacent illuminated pixels.
13. The method of claim 1 wherein a pattern comprises illuminated
subpixels that are substantially evenly distributed across the
display.
14. The method of claim 1, further comprising, for each generated
pattern, illuminating subpixels of the display according to the
generated pattern at more than one brightness level.
15. The method of claim 14 wherein the brightness levels comprise
full brightness, one-half brightness, one-quarter brightness, and
one-eighth brightness.
16. The method of claim 1 wherein capturing information about the
illuminated subpixels comprises measuring the illuminated subpixels
using an imaging colorimeter.
17. The method of claim 1 wherein analyzing the captured
information about the illuminated subpixels comprises: locating and
registering illuminated subpixels of the display; and determining a
chromaticity value and a luminance value for each registered
subpixel.
18. The method of claim 17 wherein calculating correction factors
for illuminated pixels and corresponding subpixels comprises:
converting the chromaticity and luminance value for each registered
subpixel value to measured tristimulus values; converting a target
chromaticity value and a target luminance value for a given color
to target tristimulus values; and calculating correction factors
for each registered subpixel based on a difference between the
measured tristimulus values and the target tristimulus values.
19. The method of claim 18 wherein correction factors for each
registered subpixel comprise a three by three matrix of values that
indicate fractional amounts of power to turn on each registered
subpixel for a given color and brightness level.
20. The method of claim 1 wherein the illuminating and capturing
are performed in a testing station configured to block out or
inhibit ambient light.
21. An apparatus for measuring and calibrating a visual display
having pixels and corresponding subpixels, the apparatus
comprising: a pattern generator operably coupled to the display,
wherein the pattern generator is configured to illuminate a proper
subset of the pixels and corresponding subpixels of the display; an
imaging device configured to capture information about pixels and
corresponding subpixels of the display illuminated by the pattern
generator; and a computing device operably coupled to the pattern
generator and to the imaging device, wherein the computing device
comprises a processor and a computer-readable medium having
instructions stored thereon that, when executed by the processor--
cause the pattern generator to illuminate a proper subset of the
pixels and corresponding subpixels of the display; cause the
imaging device to capture information about the illuminated proper
subset of the pixels and corresponding subpixels of the display;
analyze the captured information about the illuminated subpixels;
and calculate correction factors for the illuminated subpixels.
22. The apparatus of claim 21 wherein the pattern generator
comprises standalone test equipment.
23. The apparatus of claim 21 wherein the pattern generator
comprises software in the computing device, such that the computing
device is operably coupled to the display and configured to
transmit patterns to the display.
24. The apparatus of claim 21, further comprising a testing station
configured to receive at least a portion of the display being
measured and calibrated and block ambient light to the display
during processing.
25-31. (canceled)
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to electronic
visual displays, and more particularly, to methods and systems for
measuring and calibrating the output from such displays.
BACKGROUND
[0002] Electronic visual displays ("displays") have become
commonplace. Displays of increasingly high resolution are used in a
wide variety of contexts, from personal electronics with screens a
few inches or smaller in size to computer screens and televisions
several feet across to scoreboards and billboards covering hundreds
of square feet. Some displays are assembled from a series of
smaller panels, each of which may further consist of a series of
internally connected modules. Virtually all displays are made up of
arrays of individual light-emitting elements called "pixels." In
turn, each pixel is made up of a plurality of light-emitting points
(e.g., one red, one green, and one blue). The light-emitting points
are termed "subpixels."
[0003] It is often desirable for a display to be calibrated. For
example, calibration may improve the uniformity of the display and
improve consistency between displays. During calibration of a
display (or, e.g., of each module of a display), the color and
brightness of each pixel or subpixel is measured. Adjustments are
determined so the pixels can display particular colors at desired
brightness levels. The adjustments are then stored (e.g., in
software or firmware that controls the display or module), so that
those adjustments or correction factors can be applied.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a schematic view of an electronic visual display
calibration system configured in accordance with an embodiment of
the disclosure.
[0005] FIG. 2 is an isometric front view of an electronic visual
display calibration system configured in accordance with an
embodiment of the disclosure.
[0006] FIG. 3 is a schematic block diagram of the electronic visual
display calibration system of FIG. 1.
[0007] FIGS. 4A and 4B are enlarged partial front views of a
portion of an electronic visual display configured to be used with
embodiments of the disclosure.
[0008] FIG. 5 is a diagram of a color gamut triangle.
[0009] FIG. 6 is a flow diagram of a method or process configured
in accordance with an embodiment of the disclosure.
DETAILED DESCRIPTION
A. Overview
[0010] The following disclosure describes electronic visual display
calibration systems and associated methods for measuring and
calibrating electronic visual displays. As described in greater
detail below, a display measurement method and/or system configured
in accordance with one aspect of the disclosure is configured to
measure the luminance and the color of the individual pixels or
subpixels of an electronic visual display, such as a
high-resolution liquid crystal display ("LCD") or an organic
light-emitting diode ("OLED") display.
[0011] The inventors have recognized that when pixels are very
closely spaced, such as is typical in many LCDs, OLED displays, and
high resolution light-emitting diode ("LED") displays, measuring
individual pixel or subpixel attributes becomes more difficult.
Accordingly, embodiments of the present technology use a pattern
generator (e.g., standalone hardware test equipment, a logic
analyzer add-on module, a computer peripheral, software in a
computing device or controller connected to the display, output
from a serial digital interface ("SDI"), digital video interface
("DVI") or high-definition multimedia interface ("HDMI") port,
etc.) to display only a desired subset of pixels or subpixels to be
measured. In some embodiments, for example, the pattern generator
illuminates only every third or every fourth pixel of the display,
such that the pixels between them remain off. The technology uses
an imaging device (which typically has a considerably higher
resolution than the display itself) to measure only the illuminated
pixels (and/or subpixels). Because only a subset of the pixels are
illuminated and measured at once, the display under test
effectively has a much lower pixel resolution. After measuring the
illuminated pixels, the pattern can then be shifted (e.g., by one
pixel) and then measurements can be repeated until all of the pixel
of the display have been measured.
[0012] In one particular embodiment, for example, if every fifth
pixel of a 1,920.times.1,080 pixel high definition television
("HDTV") display is illuminated at a time, then the effective
resolution is 384.times.216 pixels. To measure the illuminated
pixels with an imaging device having a resolution about six times
greater than the display's pixel resolution, a camera with a
resolution of approximately 2,300.times.1,300--i.e., a camera
readily available for a reasonable price--could potentially be
used. In contrast with the present technology, however, many
conventional approaches for analyzing the 1,920.times.1,080 pixel
HDTV display would require a camera having a resolution of
approximately 12,000.times.6,000, or 72,000,000 pixels. Such a
camera (with resolution high enough for the display to be measured)
is expected to be prohibitively expensive and/or unavailable. As a
result, measuring and calibrating such displays using conventional
techniques is often impractical and/or too expensive.
[0013] Another conventional approach for measuring such large or
high-resolution displays is to divide the display (or its
constituent panels or modules) into sections small enough that the
imaging system has sufficient resolving power to enable an accurate
measurement of the pixels or subpixels of each section. Using this
approach, the imaging device (or the display being measured) is
generally mounted on an x-y stage for horizontal and vertical
positioning, or rotated to align to each section being measured.
Moving or rotating either the camera or the display, however,
requires additional, potentially expensive additional equipment, as
well as time to perform the movement or rotation and to align the
imaging device to the display. Furthermore, this technique can lead
to slight mismatches or discontinuities of measurement between the
individual sections. If the measurements are used for uniformity
correction, such mismatches must be addressed, typically with
further measurements and/or post-processing the display measurement
data.
[0014] In contrast with conventional techniques, embodiments of the
present technology are expected to enable precise measurement of
individual pixel or subpixel output for any display (e.g., an OLED
display) without requiring expensive, high resolution imaging
devices, and without additional equipment for moving the
relationship between the imaging device and the display, time for
moving and aligning them, or mismatches between sections of the
display.
[0015] Certain details are set forth in the following description
and in FIGS. 1-6 to provide a thorough understanding of various
embodiments of the disclosure. However, other details describing
well-known structures and systems often associated with visual
displays and related optical equipment and/or other aspects of
visual display calibration systems are not set forth below to avoid
unnecessarily obscuring the description of various embodiments of
the disclosure.
[0016] Many of the details, dimensions, angles, and other features
shown in the Figures are merely illustrative of particular
embodiments of the disclosure. Accordingly, other embodiments can
have other details, dimensions, angles, and features without
departing from the spirit or scope of the present disclosure. In
addition, those of ordinary skill in the art will appreciate that
further embodiments of the disclosure can be practiced without
several of the details described below.
B. Embodiments of Electronic Visual Display Calibration Systems and
Associated Methods for Calibrating Electronic Visual Displays
[0017] FIG. 1 is a schematic view of an electronic visual display
calibration system ("the system") 100 configured in accordance with
an embodiment of the disclosure. The system 100 is configured to
collect, manage, and/or analyze display data for the purpose of
processing image patterns (e.g., static image patterns, video
streams comprised of a series of image patterns, etc.) that are
shown on an electronic visual display 150. The pattern 160 shown on
the display 150 is generated by a pattern generator 110. The
display 150 can be, for example, a large electronic display or sign
composed of smaller panels or modules. The pattern 160 generated by
the pattern generator 110 and displayed on the display 150
illustrated in FIG. 1 is described in further detail below in
connection with FIGS. 4A-4B.
[0018] In the embodiment illustrated in FIG. 1, the system 100
includes a computing device 130 operably coupled to an imaging
device 120 (e.g., an imaging colorimeter or other photometer). In
the illustrated embodiment, the imaging device 120 is spaced apart
from the display 150 (e.g., so that the entire display 150 is
within the field of view of the imaging device 120, and, in the
case of a large elevated sign, for improving the convenience of
measurement) and configured to sense or capture display information
(e.g., color data, luminance data, etc.) from selectively
illuminated pixels or subpixels 160 of the display 150. For
example, the pattern generator 110 can illuminate every nth pixel
of the display 150. The captured display information is transferred
from the imaging device 120 to the computing device 130. After
capturing or otherwise sensing the display information for one
pattern 160, the pattern generator 110 can generate additional
patterns 160 on the display 150. For example, the pattern generator
110 can illuminate every next nth pixel of the display 150. This
process can be repeated (e.g., n times) until the computing device
130 obtains display information for all the pixels or subpixels of
the entire display 150. The computing device 130 is configured to
store, manage, and/or analyze the display information from each
pattern 160 to determine one or more correction factors for the
display 150 or for its pixels or subpixels.
[0019] In some embodiments, the correction factors for the display
150 are applied to the firmware and/or software controlling the
display 150 to calibrate the display 150. In alternate embodiments,
the corrections are applied in real time to a video stream to be
shown on the display 150. In such embodiments, the technology
includes comparing the actual display value with a desired display
value for the one or more portions of the display 150, and
determining a correction factor for the pixels or subpixels of the
display 150 as determined from the measurements of the patterns 160
described above. The technology processes or adjusts the image with
the correction factors for the corresponding pixels of the display
150. After processing the image to account for variations in the
display 150, the technology can further include transmitting the
image to the display 150 and showing the image on the display 150.
Accordingly, in some embodiments, the image on the display 150 can
be presented according to the desired display values without
modifying or calibrating the actual display 150.
[0020] One of ordinary skill in the art will understand that
although the system 100 illustrated in FIG. 1 includes separate
components (e.g., the pattern generator 110, the imaging device
120, and the computing device 130), in other embodiments the system
100 can incorporate more or less than three components. Moreover,
the various components can be further divided into subcomponents,
or the various components and functions may be combined and
integrated. In addition, these components can communicate via wired
or wireless communication, as well as by information contained in
storage media. The various components and features of the
electronic visual display calibration system 100 are described in
greater detail below in connection with FIG. 3.
[0021] FIG. 2 is an isometric front view of an electronic visual
display calibration system 200 configured in accordance with an
embodiment of the disclosure. The system 200 is configured to
perform correction of the brightness and color of light-emitting
elements that are used in electronic visual displays. In one
embodiment, the calibration system 200 can include a test pattern
generator 210, a test station 240, an interface 230, and an
electronic visual display 250. In the embodiment illustrated in
FIG. 2, the calibration system 200 is designed to calibrate a
display 250 that is placed within the test station 240. In
alternate embodiments, it is possible to calibrate multiple
displays or multiple panels of a larger display within the test
station 240.
[0022] The test pattern generator 210 is configured to generate a
series of test patterns 260, each of which illuminates a proper
subset of the pixels or subpixels of the display 250. The test
station 240 is configured to capture a series of images from an
imaging area covering all of the display 250. The captured image
data is transferred from the test station 240 to the interface 230.
The interface 230 compiles and manages the image data, performs a
series of calculations to determine the appropriate correction
factors that should be made to the image data, and then stores the
data. This process is repeated until images of each of the pixels
or subpixels of display 250 have been obtained. After collection of
all the necessary data, the processed correction data is then
uploaded from the interface 230 to the firmware and/or software
controlling the display 250 and used to recalibrate the display
250.
[0023] In the embodiment illustrated in FIG. 2, the test station
240 can include a lightproof chamber for calibrating a display 250
in a fully-illuminated room or factory. The test station 240 can
include a digital camera 220 mounted on the top portion 244 of the
test station 240. The test station 240 can further include light
baffles to eliminate any stray light that might be reflected off
the walls of the test station chamber 242 back into the camera 220.
In the illustrated embodiment, the display 250 is positioned
beneath the test station 240. The test station 240 includes
mechanical and electrical fixtures for receiving the display 250
and placing it in position within the test station 240 for
calibration. In other embodiments, the test station 240 may be in
other orientations, e.g., facing upward at a display positioned
above the test station or facing horizontally. Further, in some
embodiments the test station 240 may have a different arrangement
and/or include different features.
[0024] In the illustrated embodiment, the test station 240 also
incorporates a ground glass diffuser 246 positioned just above the
display 250. The diffuser 246 scatters the light emitted from each
subpixel in the display 250, which effectively partially integrates
the emitted light angularly. Accordingly, the camera 220 is
actually measuring the average light emitted into a cone rather
than only the light traveling directly from each subpixel on the
display 250 toward the camera 220. One advantage of this
arrangement is that the display 250 will be corrected to optimize
viewing over a wider angular range. The diffuser 246 is an optional
component that may not be included in some embodiments.
[0025] The interface 230 that is operably coupled to the test
station 240 is configured to manage the data that is collected,
stored, and used for calculation of new correction factors that
will be used to recalibrate the display 250. The interface 230
automates the operation of the pattern generator 210 and the test
station 240 and writes all the data into a database. In one
embodiment, the interface 230 can be a personal computer with
software for pattern selection, camera control, image data
acquisition, and image data analysis. Optionally, in other
embodiments various devices capable of operating the software can
be used, such as handheld computers.
[0026] FIG. 3 is a schematic block diagram of the electronic visual
display calibration system 100 of FIG. 1. In the illustrated
embodiment, the imaging device 120 can include a camera 320, such
as a digital camera suitable for high-resolution imaging. For
example, the camera 320 can include optics capable of measuring
subpixels of the display 150 (which can be a few millimeters in
size) from a distance of 25 meters or more. If the displayed
pattern 160 does not illuminate adjacent subpixels or pixels,
imaging resolution requirements for the camera 320 may be less
stringent, allowing the use of a less expensive imaging device 120.
In some embodiments, the camera 320 can be a CCD camera. Suitable
CCD digital color cameras include ProMetric.RTM. imaging
colorimeters and photometers, which are commercially available from
the assignee of the present disclosure, Radiant Zemax, LLC, of
Redmond, Wash. In other embodiments, the camera 320 can be a
complementary metal oxide semiconductor ("CMOS") camera, or another
type of suitable camera for imaging with sufficient resolution at a
certain distance from the display.
[0027] According to another aspect of the illustrated embodiment,
the imaging device 120 can also include a lens 322. In one
embodiment, for example, the lens 322 can be a reflecting telescope
that is operably coupled to the camera 320 to provide sufficiently
high resolution for long distance imaging of the display 150. In
other embodiments, however, the lens 322 can include other suitable
configurations for viewing and/or capturing display information
from the display 150. Suitable imaging devices 320 and lenses 322
are disclosed in U.S. Pat. Nos. 7,907,154 and 7,911,485, both of
which are incorporated herein by reference in their entireties.
[0028] The imaging device 120 can accordingly be positioned at a
distance L from the display 150. The distance L can vary depending
on the size of the display 150, and can include relatively large
distances. In one embodiment, for example, the imaging device 120
can be positioned at a distance L that is generally similar to a
typical viewing distance of the display 150. In a sports stadium,
for example, the imaging device 120 can be positioned in a seating
area facing toward the display 150. In other embodiments, however,
the distance L can be less that a typical viewing distance and
direction, and the imaging system 120 can be configured to account
for any viewing distance and/or direction differences. In some
embodiments, the imaging device 120 has a wide field of view and
the distance L can be less than the width of the display 150 (e.g.,
approximately one meter for a typical HDTV display). In other
embodiments, the imaging device 120 has a long-focus lens 322
(e.g., a telephoto lens) and the distance L can be significantly
greater than the width of the display 150 (e.g., between
approximately 100 and 300 meters for an outdoor billboard or video
screen). In yet other embodiments, the distance L can have other
values.
[0029] The computing device 130 is configured to cause the pattern
generator 110 to send images 160 (e.g., pixel or subpixel patterns)
to the display 150. In various embodiments, the pattern generator
110 is standalone hardware test equipment, a logic analyzer add-on
module, a computer peripheral operably coupled to the computing
device 130, or software in the computing device 130 or in a
controller connected to the display 150. In other embodiments, the
pattern generator 110 operates independently of the computing
device 130. In alternative embodiments, the patterns 160 are
provided to the display 150 via standard video signal input, e.g.,
using a DVI, HDMI, or SDI input to the display. The patterns 160
generated by the pattern generator 110 for displaying on the
electronic visual display 150 are discussed in greater detail in
connection with FIGS. 4A and 4B below.
[0030] Continuing with respect to FIG. 3, the computing device 130
is configured to receive, manage, store, and/or process the display
data collected by the imaging device 120 (e.g., for the purpose of
adjusting the appearance of images 160 that will be displayed on
the display 150). In other embodiments, display data associated
with the display 150, including correction factors and related
data, can be processed by a computer that is separate from the
imaging device 120. A typical display 150, such as a quad extended
graphics array ("QXGA")-resolution (2048.times.1536) visual display
for example, can have over nine million subpixels that provide
display data for the computing device 130 to manage and process.
The pattern generator 110 may illuminate only a fraction of those
subpixels at any one time, but by sending a series of patterns 160
to the display 150, information about all the subpixels will be
delivered to the computing device 130. As such, the computing
device 130 includes the necessary hardware and corresponding
software components for managing and processing the display data.
More specifically, the computing device 130 configured in
accordance with an embodiment of the disclosure can include a
processor 330, a memory 332, input/output devices 334, one or more
sensors 336 in addition to sensors of the imaging device 120,
and/or any other suitable subsystems and/or components 338
(displays, speakers, communication modules, etc.). The memory 332
can be configured to store the display data from the patterns 160
shown on the display 150. The computing device 130 includes
computer readable media (e.g., memory 332, disk drives, or other
storage media, excluding only a transitory, propagating signal per
se) including instructions or software stored thereon that, when
executed by the processor 330 or computing device 130, cause the
processor 330 or computing device 130 to process an image as
described herein. Moreover, the processor 330 can be configured for
performing or otherwise controlling calculations, analysis, and any
other functions associated with the methods described herein.
[0031] In some embodiments, the memory 332 includes software to
control the imaging device 120 as well as measurement software to
identify portions of the display 150 (e.g., subpixels of the
display 150) and to image or otherwise extract the display data
(e.g., subpixel brightness data, pixel color data, etc.). One
example of suitable software for controlling the imaging device 120
and/or acquiring the display data is VisionCAL.TM. screen
correction software, which is commercially available from the
assignee of the present disclosure, Radiant Zemax, LLC, of Redmond,
Wash. In other embodiments, other suitable software can be
implemented with the system 100. Moreover, the memory 332 can also
store one or more databases used to store the display data from the
patterns 160 shown on display 150, as well as calculated correction
factors for the display data. In one embodiment, for example, the
database is a Microsoft Access.RTM. database designed by the
assignee of the present disclosure. In other embodiments, however,
the display data is stored in other types of databases or data
files.
[0032] FIG. 4A is an enlarged partial front view of a portion of an
electronic visual display 450 configured to be used with
embodiments of the disclosure. The illustrated view is
representative of a portion of a display 450 (e.g., display 150
(FIG. 1) or display 250 (FIG. 2)) displaying a pattern 460a. The
display 450 is made up of a large number (e.g., millions) of
individual light sources or light-emitting elements or pixels 430.
Each pixel 430 comprises multiple light-emitting points or
subpixels 432 (identified as first, second, and third subpixels
432a-432c, respectively). In certain embodiments, the subpixels 432
are LEDs or OLEDs. For example, the subpixels 432a-432c can
correspond to red, green, and blue LEDs, respectively. In other
embodiments, each pixel 430 can include more or less than three
subpixels 432. For example, some pixels 430 may have four subpixels
432 (e.g., two green subpixels, one blue subpixel, and one red
subpixel, or other combinations). Pixels and subpixels may be laid
out in various geometric arrangements (e.g., triangular or
hexagonal arrays in various color orders, vertical or oblique
stripes, etc.). Furthermore, in certain embodiments, the red,
green, and blue ("RGB") color space may not be used. Rather, a
different color space can serve as the basis for processing and
display of color images on the display 450. For example, the
subpixels 432 may be cyan, magenta, and yellow, respectively.
[0033] In addition to the color level of each subpixel 432, the
luminance level of each subpixel 432 can vary. Accordingly, the
additive primary colors represented by a red subpixel, a green
subpixel, and a blue subpixel can be selectively combined to
produce the colors within the color gamut defined by a color gamut
triangle, as shown in FIG. 5. For example, when only "pure" red is
displayed, the green and blue subpixels may be turned on only
slightly to achieve a specific chromaticity for the red color.
[0034] In addition, the measurement process described herein may be
performed at various brightness levels. For example, in some
embodiments, each pixel 430 or subpixel 432 is measured at input
levels (using values from 0 to 255) of 255 (full brightness), 128
(one half brightness), 64 (one quarter brightness), and 32 (one
eighth brightness). Data from such measurements can be used in
calibration to achieve the same chromaticity for a particular color
at various input brightness levels, or, e.g., to improve the
uniformity of color and luminance response curves for each pixel or
subpixel.
[0035] Returning to FIG. 4A, an illustrative pattern 460a
illuminates a proper subset of the pixels of the display 450. In
the illustrated embodiment, every fourth pixel 430 vertically and
every fourth pixel 430 horizontally is illuminated, and the pixels
between are switched off. Thus, for the illustrated pattern 460a,
only one of every sixteen pixels 430 is illuminated, and the spaces
between illuminated pixels are four times larger in each direction
than there would be if every pixel 430 were illuminated. As a
result, the effective pixel density of the display 450 is one
sixteenth of the actual pixel density. For example, if pattern 460a
is displayed on a "4K Ultra HD" television display 450 having a
screen resolution of 3,840.times.2,160 pixels (a total of
approximately 8.3 million pixels ("megapixels")), only
(3,840/4).times.(2,160/4) pixels, i.e., 960.times.540 pixels (a
total of approximately five hundred thousand pixels (half a
megapixel)) are lit at once. Such a reduction in the effective
pixel resolution of the display 450 can permit use of imaging
equipment (e.g., a camera sensor and lens) that is less
sophisticated and expensive than would otherwise be required to
measure the display 450.
[0036] The technology displays a series of patterns to illuminate
and measure each pixel or subpixel of the display at least once
(and potentially multiple times, e.g., at different brightness
input levels). FIG. 4B illustrates another pattern 460b on the same
enlarged partial front view of a portion of the electronic visual
display 450. In the pattern 460b of FIG. 4B, each pixel 430 that
was illuminated in the pattern 460a of FIG. 4A is switched off, and
the next pixel to the right is illuminated. In the illustrated
embodiment, measuring the output of each pixel 430 of the display
450 requires displaying and measuring a total of sixteen patterns
(multiplied by the number of different brightness levels for each
pattern). Different patterns 460 of pixels 430 and/or subpixels 432
could require a smaller or larger number of patterns 460 to ensure
full coverage of the display 450. For example, a pattern that
illuminates every third pixel 430 horizontally and vertically
requires nine patterns to cover every pixel 430 in the display
450.
[0037] In alternative embodiments, the patterns 460 illuminate
individual subpixels 432 (e.g., one or more at a time of subpixels
432a-432c) rather than whole pixels 430. In various embodiments,
the patterns 460 are displayed and measured at more than one
brightness level. Separately illuminating each subpixel 432 and
measuring individual pixels or subpixels at different brightness
levels correspondingly multiplies the number of required
measurements. In some embodiments, patterns are tailored to a
particular display or a particular measurement. The patterns are
not necessarily as regular or evenly distributed as the examples
illustrated in FIGS. 4A-4B, and different patterns may illuminate
different numbers of pixels or subpixels.
[0038] In addition to color and/or luminance, the subpixels 432 may
have other visual properties that can be measured and analyzed in
accordance with embodiments of the present disclosure. Moreover,
although the displayed patterns 460 are described above with
reference to pixels 430 and subpixels 432, other embodiments of the
disclosure can be used with displays having different types of
light emitting elements or components.
[0039] FIG. 6 is a flow diagram of a method or process 600
configured in accordance with an embodiment of the disclosure. At
block 610, the method includes identifying a fraction 1/n of the
pixels or subpixels of the display to be illuminated for
measurement. In some embodiments, the technology receives the
number, e.g., from user input or from a configuration file. In some
embodiments, the technology determines a number based on a
heuristic and the characteristics of the display to be measured and
the measuring equipment. Such characteristics may include, e.g.,
the size of the display, the pixel resolution of the display, the
pixel density or dot pitch (i.e., distance between pixels) of the
display, the distance from the display to the imaging device, the
optical resolving power or angular resolution of the imaging
device, and the pixel resolution of the imaging device. An example
heuristic is that the pixel resolution of the imaging device is
such that 50 pixels on the imaging device correspond to one
illuminated subpixel on the display.
[0040] By way of example, in one embodiment the imaging device has
a pixel resolution of 3,072.times.2,048=6,291,456 pixels. According
to the heuristic that fifty pixels of resolution from the imaging
device correspond to one subpixel on the display, the imaging
device can capture data from 125,829 subpixels on the display
(6,291,456 camera pixels/50 camera pixels per display subpixel) in
a single captured image. In other embodiments, the correlation
between the resolution of the imaging device and the display can
vary between, e.g., 6 to 200 pixels on the imaging device
corresponding to one subpixel on the display. Assuming, for
example, that no other characteristic of the imaging device or its
relationship to the display restricts its ability to measure the
display, then the technology can determine the appropriate fraction
1/n in this case by dividing 125,829 (the number of subpixels to be
illuminated in each captured image) by the total number of
subpixels in the display. For example, to measure a display having
a pixel resolution of 1,280.times.720=921,600 pixels, the fraction
1/n would be 125,829/921,600=1/7.324 or (rounding the denominator
up) 1/8. In other words, if 1/8 of the display's subpixels are
illuminated, the total number of illuminated subpixels will be
below the threshold of 125,829 subpixels that can be captured in a
single image by the selected imaging device in accordance with the
applicable heuristic.
[0041] At block 620, the technology displays a pattern selectively
illuminating 1/n of the pixels or subpixels of the display (e.g.,
in the example above, 1 of every 8 subpixels of the display). For
example, every nth pixel (or subpixel of a particular color) may be
illuminated. An example of such a pattern is described above in
connection with FIG. 4A. As described above, the technology may
illuminate each pixel or subpixel at various brightness levels. At
block 630, the imaging device captures at least one image of the
pattern of pixels or subpixels illuminated on the display. Each
subpixel captured by the imaging device can be characterized, e.g.,
by its color value, typically expressed as chromaticity (Cx, Cy),
and its brightness, typically expressed as luminance Lv. At block
640, the captured image data is analyzed by a computing device,
e.g., the computing device described above in connection with FIGS.
1 and 3.
[0042] In some embodiments, the computing device compares the color
and brightness of each captured pixel with target color and
brightness values, e.g., points within the color gamut defined by a
color gamut triangle, such as shown in FIG. 5. The actual pixel or
subpixel color or brightness values may differ from desired or
target display values for the display. For example, there is
typically significant variation in color or luminance of each
subpixel of the display, especially if the subpixels are LEDs or
OLEDs. Moreover, over time the visual properties of the display may
degrade or otherwise vary from desired or target display values.
Accordingly, at block 650, the technology compares actual captured
and analyzed values with target or desired display values for the
pixels or subpixels illuminated according to the displayed pattern,
and determines a correction value applicable to each analyzed pixel
or subpixel.
[0043] Determining the correction values can include creating a
correction data set or map. In some embodiments, the computing
device calculates a three-by-three matrix of values for each pixel
that indicate some fractional amount of power to turn on each
subpixel to obtain each of the three primary colors (red, green,
and blue) at target color and brightness levels. A sample matrix is
displayed below:
TABLE-US-00001 Fractional values for each subpixel of a pixel
Primary color Red Green Blue Red 0.60 0.10 0.05 Green 0.15 0.70
0.08 Blue 0.03 0.08 0.75
For example, according to the above matrix for a particular
brightness level, when a pixel of the display should be red, the
technology has calculated that the display should turn on its red
subpixel at 60% power, its green subpixel at 10% power, and its
blue subpixel at 5% power.
[0044] The determination of the correction values is based, at
least in part, on the comparison between the captured and analyzed
values and the target values for the display. More specifically,
each correction factor can compensate for the difference between
the captured and analyzed values and the corresponding target
display value. For example, if the captured and analyzed value is
less bright than the corresponding target display value, the
correction factor can include the amount of brightness that would
be required for the captured and analyzed value of the pixel or
subpixel to be generally equal to the target display value.
Moreover, the correction factor can correlate to the corresponding
type of display value. For example, the correction value can be
expressed in terms of color or brightness correction values, or in
terms of other visual display property correction values. Suitable
methods and systems for determining correction values or correction
factors are disclosed in U.S. Pat. Nos. 7,907,154 and 7,911,485
referenced above.
[0045] At block 660, the process branches depending on whether or
not all the pixels or subpixels of the display have been
illuminated, captured, analyzed, and corrected as described above
in blocks 620-650. If the technology illuminates a fraction 1/n of
the pixels or subpixels of the display in each pattern, then at
least n iterations are required to measure and calibrate the entire
display. For example, after displaying a first pattern such as the
pattern described above in connection with FIG. 4A, in which every
nth pixel (or subpixel of a particular color) is illuminated, the
technology returns to block 620. At block 620, the technology
illuminates a different pattern of pixels or subpixels, e.g., a
distinct subset of the pixels or subpixels of the display. For
example, the technology might next display the pattern described
above in connection with FIG. 4B, in which the next neighbor of
every nth pixel (or subpixel of a particular color) is illuminated.
The process then continues as described above.
[0046] After n iterations have been completed, at block 670, the
method 600 can further include sending the calibration correction
values to the display. In some embodiments, the correction factors
are stored in firmware within the display or a controller of the
display. In some embodiments, the correction factor data set or map
can be saved and, e.g., provided to a third party such as the owner
of the display, or used to process video images outside the display
such that the display can show the processed image according to
desired or target display properties without calibrating or
adjusting the display itself. Suitable methods and systems for
correcting images to calibrate their appearance on a particular
display are disclosed in U.S. patent application Ser. No.
12/772,916, filed May 3, 2010, entitled "Methods and systems for
correcting the appearance of images displayed on an electronic
visual display," which is incorporated herein in its entirety by
reference. In some embodiments, the technology verifies or improves
the calibration by measuring the calibrated output of each pixel or
subpixel as described in blocks 610-660 above, and optionally
modifying the correction factors applied to the display.
[0047] From the foregoing, it will be appreciated that specific
embodiments of the disclosure have been described herein for
purposes of illustration, but that various modifications may be
made without deviating from the spirit and scope of the various
embodiments of the disclosure. Further, while various advantages
associated with certain embodiments of the disclosure have been
described above in the context of those embodiments, other
embodiments may also exhibit such advantages, and not all
embodiments need necessarily exhibit such advantages to fall within
the scope of the disclosure. Accordingly, the disclosure is not
limited, except as by the appended claims.
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