U.S. patent application number 11/287681 was filed with the patent office on 2006-04-13 for optical scanning system with variable focus lens.
This patent application is currently assigned to University of Washington. Invention is credited to Richard S. Johnston, Joel S. Kollin, Charles D. Melville, Michael Tidwell.
Application Number | 20060077121 11/287681 |
Document ID | / |
Family ID | 22695443 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060077121 |
Kind Code |
A1 |
Melville; Charles D. ; et
al. |
April 13, 2006 |
Optical scanning system with variable focus lens
Abstract
Apparent distance of a pixel within an optical field of view is
determined. Incoming light is scanned along a raster pattern to
direct light for a select pixel onto a light distance detector. The
distance is sampled for each pixel or for a group of pixels. The
light distance detector includes a concentric set of rings sensors.
The larger the spot of light corresponding to the pixel, the more
rings are impinged. The diameter of the spot is proportional to the
distance at which the light originated (e.g., light source or
object from which light was reflected). Alternatively, a variable
focus lens (VFL) adjusts focal length for a given pixel to achieve
a standard spot size. The distance at which the light originated
correlates to the focal length of the VFL.
Inventors: |
Melville; Charles D.;
(Issaquah, WA) ; Tidwell; Michael; (Seattle,
WA) ; Johnston; Richard S.; (Issaquah, WA) ;
Kollin; Joel S.; (Long Island City, NY) |
Correspondence
Address: |
KODA LAW OFFICE
No. 307
9689-7th Avenue NE
Poulsbo
WA
98370
US
|
Assignee: |
University of Washington
Seattle
WA
|
Family ID: |
22695443 |
Appl. No.: |
11/287681 |
Filed: |
November 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10246020 |
Sep 17, 2002 |
6977631 |
|
|
11287681 |
Nov 28, 2005 |
|
|
|
09740272 |
Dec 18, 2000 |
6492962 |
|
|
10246020 |
Sep 17, 2002 |
|
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09188991 |
Nov 9, 1998 |
6191761 |
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09740272 |
Dec 18, 2000 |
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Current U.S.
Class: |
345/7 |
Current CPC
Class: |
H04N 13/236 20180501;
G02B 7/28 20130101; G01S 11/12 20130101; G01C 3/08 20130101 |
Class at
Publication: |
345/007 |
International
Class: |
G09G 5/00 20060101
G09G005/00 |
Claims
1. A system for capturing and displaying three-dimensional images
comprising: a scanning image capture apparatus operable to capture
a three-dimensional image of a field-of-view and generate a signal
corresponding to the three-dimensional image; and a controller
coupled to the scanning image capture apparatus and operable to
receive the signal corresponding to the three-dimensional image
from the scanning image capture apparatus and operable to output a
display signal corresponding to the three-dimensional image.
2. The system for capturing and displaying three-dimensional images
of claim 1 further comprising: a display apparatus coupled to the
controller and operable to receive the display signal corresponding
to the three-dimensional image from the controller and display the
three-dimensional image.
3. The system for capturing and displaying three-dimensional images
of claim 2 wherein the display apparatus includes a scanning
display.
4. The system for capturing and displaying three-dimensional images
of claim 2 wherein the display apparatus is operable to display a
three-dimensional representation of the captured three-dimensional
image.
5. The system for capturing and displaying three-dimensional images
of claim 1 wherein the controller is further operable to store the
captured three-dimensional image in memory storage.
6. The system for capturing and displaying three-dimensional images
of claim 5 wherein the controller is further operable to output the
stored three-dimensional image as a display signal.
7. The system for capturing and displaying three-dimensional images
of claim 1 wherein the three-dimensional image includes a video
image comprising a plurality of frames.
8. The system for capturing and displaying three-dimensional images
of claim 1 wherein the three-dimensional image includes at least
one still image comprising a single frame.
9. The system for capturing and displaying three-dimensional images
of claim 1 wherein the scanning image capture apparatus further
includes a variable focus lens operable to variably converge
light.
10. The system for capturing and displaying three-dimensional
images of claim 9 wherein the variable focus lens is operable to
variably converge light from the field-of-view.
11. A method for capturing and displaying three-dimensional images
comprising the steps of: operating a scanning image capture
apparatus to capture a three-dimensional image of a field-of-view
and generate a signal corresponding to the three-dimensional image;
and operating a controller coupled to the scanning image capture
apparatus to receive the signal corresponding to the
three-dimensional image from the scanning image capture apparatus
and output a display signal corresponding to the three-dimensional
image.
12. The method for capturing and displaying three-dimensional
images of claim 11 further comprising the steps of: operating a
display apparatus coupled to the controller to receive the display
signal corresponding to the three-dimensional image from the
controller and display the three-dimensional image.
13. The method for capturing and displaying three-dimensional
images of claim 12 wherein the display apparatus includes a
scanning display.
14. The method for capturing and displaying three-dimensional
images of claim 12 wherein the display apparatus is operable to
display a three-dimensional representation of the captured
three-dimensional image.
15. The method for capturing and displaying three-dimensional
images of claim 11 further comprising the steps of: operating the
controller to store the captured three-dimensional image in memory
storage.
16. The method for capturing and displaying three-dimensional
images of claim 15 further comprising the steps of: operating the
controller to output the stored three-dimensional image as a
display signal.
17. The method for capturing and displaying three-dimensional
images of claim 11 wherein the three-dimensional image includes a
video image comprising a plurality of frames.
18. The method for capturing and displaying three-dimensional
images of claim 11 wherein the three-dimensional image includes at
least one still image comprising a single frame.
19. The method for capturing and displaying three-dimensional
images of claim 11 wherein the step of operating the scanning image
capture apparatus further includes operating a variable focus lens
to variably converge light.
20. The method for capturing and displaying three-dimensional
images of claim 19 wherein the step of operating the variable focus
lens includes operating the variable focus lens to variably
converge light from the field-of-view.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
10/246,020 filed Sep. 17, 2002 for "Optical Scanning System with
Variable Focus Lens" of Melville et al., which is a continuation of
U.S. Pat. No. 6,492,962 issued Dec. 10, 2002 on application Ser.
No. 09/740,272 filed Dec. 18, 2000 for "Optical Scanning System
with Variable Focus Lens" of Melville et al., which is a
continuation of U.S. Pat. No. 6,191,761 issued Feb. 20, 2001 on
U.S. patent application Ser. No. 09/188,991 filed Nov. 9, 1998 for
"Method and Apparatus for Determining Optical Distance," of
Melville et al. The contents of such patents and applications are
incorporated herein by reference and made a part hereof.
BACKGROUND OF THE INVENTION
[0002] This invention relates to methods and apparatus for
determining an optical distance, such as a distance of an object
within a field of view, and more particularly to a method and
apparatus for scanning distances within a field of view.
[0003] A conventional camera includes an objective lens and a light
detector, such as a photographic film, CCD array or other
photosensitive device or structure. Light from a viewing
environment enters the camera through the objective lens and
impinges on the light detector. The portion of the viewing
environment for which light enters is the camera's field of view.
Some cameras pass the light to a viewfinder or eyepiece allowing an
operator to select a desired field of view from the background
environment. To take a picture or record, the light detector
captures frames of the background light from the field of view.
[0004] Often the field of view is divided into discrete picture
elements or pixels. In conventional digital video cameras the light
detector records data for each pixel within the field of view for a
given video frame. The data includes color, intensity and the pixel
coordinates (i.e., x,y coordinates).
[0005] Conventional still cameras and video cameras include optics
for focusing within the field of view. Thus, an operator can select
to focus on a near field object or a far field object. Some cameras
even include autofocus devices which automatically adjust the focal
length of the objective lens to focus within the field of view.
SUMMARY OF THE INVENTION
[0006] According to the invention, an apparent distance of one or
more points within an optical field of view is determined. For
example, an apparent distance is determined for each pixel, or for
one or more group of pixels, within a field of view. Such distance
is also referred to as a depth of view. One advantage of the
invention is that pixel data for an object viewed may be recorded,
input to a computer and mapped enabling display of a 3-dimensional
model of the object. Another advantage is that an augmented display
device or camera device can have variable accommodation.
[0007] Incoming light is scanned along a raster pattern to direct
light for a select pixel onto a light distance detector. The
distance is sampled for each pixel or for a group of pixels. In one
embodiment a light distance detector is used. In an alternative
embodiment a variable focus lens is used.
[0008] The light distance detector includes a concentric set of
ring sensors. The larger the spot of light corresponding to the
pixel, the more rings are impinged. For light entering from a far
distance, such as from infinity to about 20 feet, the spot will be
small. For light coming from closer distances the spot is larger.
The diameter of the spot is proportional to the distance at which
the light originated (e.g., light source or object from which light
was reflected). Each ring corresponds to a distance. The number of
rings impinged determines the distance for the pixel being
sampled.
[0009] The variable focus lens (VFL) is included in the light path.
For a given pixel to be sampled, the focal length of the VFL is
varied to achieve a small spot size. The distance at which the
light originated correlates to the resulting focal length of the
VFL.
[0010] Although, distance is sampled for each pixel or for a group
of pixels, light intensity and color also may be sampled to record
a digital image of a field of view, such as for a camera
implementation.
[0011] The invention will be better understood by reference to the
following detailed description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagram of a conventional image detection
apparatus;
[0013] FIG. 2 is a diagram of an apparatus for scanning optical
distance within a field of view according to an embodiment of this
invention;
[0014] FIG. 3 is a diagram of the light detector of FIG. 2;
[0015] FIG. 4 is a diagram of the light detector of FIG. 3 with an
impinging spot of light;
[0016] FIG. 5 is a diagram of an electro-mechanically variable
focus lens for a lensing system of FIG. 2 according to an
embodiment of this invention;
[0017] FIG. 6 is a diagram of an alternative variable focus lens
embodiment for the lensing system of FIG. 2;
[0018] FIG. 7 is a diagram of another alternative variable focus
lens embodiment for the lensing system of FIG. 2;
[0019] FIG. 8 is a diagram of a plurality of cascaded lens for the
lensing system of FIG. 2 according to an embodiment of this
invention;
[0020] FIG. 9 is a block diagram of a feedback control scheme for
detecting light distance according to an embodiment of this
invention; and
[0021] FIG. 10 is a diagram of an image recording apparatus
according to an embodiment of this invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Overview
[0022] Referring to FIG. 1, in a conventional image detection
apparatus 10, background light from a field of view F impinges on
an objective lens 14 which converges the light toward a light
detector 16. In a digital camera the light detector 16 may be a
charge-coupled device (CCD), which also serves as a viewfinder.
Light from objects within the field of view F, such as a first
object 18 (e.g., a tree) and a second object 20 (e.g., a bird) is
captured to record an image of the field of view or a part
thereof.
[0023] Referring to FIG. 2, an apparatus 30 detects optical
distance (i.e., depth of view) for objects 18, 20 in the field of
view F according to an embodiment of this invention. The apparatus
30 includes an objective lens 14, a scanning system 32, a lensing
system 34 and a light distance detector 36. Background light 12,
from the field of view F, including light reflected from the
objects 18, 20 enters the apparatus 30 at the objective lens 14.
The light is directed to the scanning system which scans the
background light along two axes to select at any given time a pixel
area of the field of view to be analyzed. Light originating within
the select pixel area is directed into the lensing system 34 which
converges the light onto the light distance detector 36. Preferably
only light originating from a single, select pixel area is focused
onto the light distance detector 36. In alternative embodiment the
size of the area being measured for distance may vary to include
multiple pixels. The size of the field portion measured for
distance is determined by the size of a mirror surface on scanners
38, 40 within the scanner system 32, the relative location of the
mirror surface relative to the objective lens 14 and the lensing
system 34, and the relative location of the lensing system 34
relative to the light distance detector 36.
[0024] During operation, the scanning system 32 periodically scans
along a prescribed scanning pattern, such as a raster pattern. For
scanning a two dimensional raster pattern, a horizontal scanner 38
scans along a horizontal axis and a vertical scanner 40 scans along
a vertical axis. A sample is taken at the light distance detector
for multiple points along each given horizontal scanning line. Such
sample, for example, corresponds to a pixel. The light distance
detector signal 35 corresponds to the depth of view of the light
sample. In some embodiments a table of correlation data is stored
in memory 37. A controller 43 compares the light distance detector
signal 35 to entries in the table to derive the depth of view for
the light sample. The determined depth of view is read from the
memory 37 and stored as the depth of view for the pixel that was
sampled. Thus, a distance (i.e., depth of view) is determined for
each pixel within the field of view.
[0025] In some embodiments the distance is stored in memory
together with the pixel coordinates (i.e., field of view
coordinates) for later retrieval. Light intensity and color also
may be detected and stored, as for a camera or other recording
implementation.
Light Distance Detector
[0026] Referring to FIG. 3, a light distance detector 36 according
to one embodiment of this invention includes concentrically
positioned light detection sensors 42-50 that form a set of
concentric rings. The number of rings and radial increment may vary
depending on the distance resolution desired. Light 52 from select
pixel region is converged by the lensing system 34 onto the light
distance detector 36. Referring to FIG. 4, such light 52 forms a
spot 54, preferably centered at the center of the detector 36. The
smaller the spot 54, the farther the focal source of the light 52
for the select pixel. For light, at approximately 20 feet or
further from the system 30, the light waves are flat and focus down
to a common point size. Accordingly, light at such distance is not
differentiated (i.e., resolved). Light from zero feet to
approximately 20 feet from the system 30, however is differentiated
by identifying which ring sensors detect light. In the example
illustrated in FIG. 4, the light spot 54 encompasses sensors 42-48.
A specific distance corresponds to activation of such sensors
42-48.
[0027] An alternative method for detecting the optical distance for
pixel light is achieved, by modifying the focal length of the
lensing system 34 until a spot of a desired standard size is
achieved. For example, the focal length may be varied until the
spot size encompasses only sensors 42 and 44. Alternatively, only
sensor 42 may define the standard spot size or only sensors 42-46,
or some other prescribed subset of sensors 42-50 may define the
prescribed spot size. Following is a description of a lensing
system which can vary its focal distance.
Lensing System with Variable Focal Length
[0028] To vary the focal length, the lensing system 14 includes a
variable focus lens (VFL). In some embodiments the VFL has its
focus varied by controlling the shape or thickness of the lens. In
other embodiment the VFL has its focus varied by varying the index
of refraction of the lens. FIG. 5 shows an electromechanically
variable focus lens (VFL) 60 which changes its shape. A central
portion 62 of the VFL 60 is constructed of a piezoelectric resonant
crystalline quartz. In operation, a pair of transparent conductive
electrodes 64 provide an electrical field that deforms the
piezoelectric material in a known manner. Such deformation changes
the thickness of the central portion 62 along its optical axis to
effectively change the focus of the VFL 60. Because the VFL 60 is a
resonant device, its focal length varies periodically in a very
predictable pattern. By controlling the time when a light pulse
enters the resonant lens, the effective focal position of the VFL
60 can be controlled.
[0029] In some applications, it may be undesirable to selectively
delay pulses of light according to the resonant frequency of the
VFL 60. In such cases, the VFL 60 is designed to be nonresonant at
the frequencies of interest, yet fast enough to focus for each
image pixel.
[0030] In an alternative embodiment, the variable focus lens is
formed from a material that changes its index of refraction in
response to an electric field or other input. For example, the lens
material may be an electrooptic or acoustooptic material. In the
preferred embodiment, the central portion 62 (see FIG. 11) is
formed from lithium niobate, which is both electrooptic and
acoustooptic. The central portion 62 thus exhibits an index of
refraction that depends upon an applied electric field or acoustic
energy. In operation, the electrodes 64 apply an electric field to
control the index of refraction of the lithium niobate central
portion 62. In another embodiment a quartz lens includes a
transparent indium tin oxide coating that forms the electrode
64.
[0031] In another embodiment shown in FIG. 6, a lens 70 includes a
compressible cylindrical center 72 having a gradient index of
refraction as a function of its radius. A cylindrical piezoelectric
transducer 74 forms an outer shell that surrounds the cylindrical
center 72. When an electric field is applied to the transducer 74,
the transducer 74 compresses the center 72. This compression
deforms the center 72, thereby changing the gradient of the index
of refraction. The changed gradient index changes the focal length
of the center 72.
[0032] In another embodiment shown in FIG. 7 the variable focus
element is a semiconductor device 80 that has an index of
refraction that depends upon the free carrier concentration in a
transmissive region 82. Applying either a forward or reverse
voltage to the device 80 through a pair of electrodes 84 produces
either a current that increases the free-carrier concentration or a
reverse bias that depletes the free carrier concentration. Since
the index of refraction depends upon the free carrier
concentration, the applied voltage can control the index of
refraction. Memory 86 and control electronics 88 may be used to
control the index of refraction.
[0033] In still another embodiment shown in FIG. 8 a plurality of
lenses 90-92 are cascaded in series. One or more piezoelectric
positioners 94-96 move one or more of the respective lenses 90-92
along the light path changing the focal distance of the light beam.
By changing the relative position of the lenses to each other the
curvature of the light varies.
[0034] According to one control approach, the lensing system 34
continuously varies its focal length as needed to maintain a
constant spot size. Referring to FIG. 9 the light distance detector
36 and lensing system 14 are coupled in a feedback loop. The output
of the light distance detector 36 is fed to focal control
electronics 100. The focal control electronics 100 vary the focal
length of a VFL 102 to maintain a constant spot size (e.g., the
prescribed standard spot size previously described). The focal
length at any given sample time correlates to the light distance
(i.e., depth of view) for such sample.
[0035] According to another control approach, the lensing system
performs a sweep of the focal length range of the VFL during each
light sample to be measured. During the sweep the spot 54 (see FIG.
4) will achieve its smallest size. The focal length at such time is
used to define the light distance.
[0036] According to these control techniques, the precise light
distance for any given sample is determined from the focal length
of the lensing system 14 at the time such sample is taken. One of
ordinary skill in the art will appreciate that a specific distance
can be derived from the focal length using the various optical
parameters (e.g., magnification factors, relative positions of
components) of a system 30 embodiment.
Scanning System
[0037] In one embodiment, the scanning system 32 includes a
resonant scanner for performing horizontal scanning and a
galvanometer for performing vertical scanning. The scanner serving
as the horizontal scanner receives a drive signal having a
horizontal scanning frequency. Similarly, the galvanometer serving
as the vertical scanner receives a drive signal having a vertical
scanning frequency. Preferably, the horizontal scanner has a
resonant frequency corresponding to the horizontal scanning
frequency. In other embodiments the vertical scanner also is a
resonant scanner.
[0038] One embodiment of a resonant scanner is described in related
U.S. patent application Ser. No. 09/188,993 (Attorney Docket No.
OT2.P17 filed on the same day and having the same inventive entity)
filed Nov. 9, 1998 of Michael Tidwell et al. for Scanned Beam
Display With Adjustable Accommodation. The content of that
application is incorporated herein by reference and made a part
hereof. The resonant scanner includes a mirror driven by a drive
circuit (e.g., electromagnetic drive circuit or piezoelectric
actuator) to oscillate at a high frequency about an axis of
rotation. The drive circuit moves the mirror responsive to a drive
signal which defines the frequency of motion.
[0039] Referring to FIG. 2, background light 12 impinges on the
mirror 39 of one scanner 38, then is reflected to another scanner
40, where its mirror 41 deflects the light toward the lensing
system 34. As the scanner mirrors 39, 41 move, different portions
(e.g., pixel areas) of the background field of view are directed
toward the lensing system 34 and light distance detector 36.
[0040] In alternative embodiments, the scanning system 32 instead
includes acousto-optical deflectors, electro-optical deflectors, or
rotating polygons to perform the horizontal and vertical light
deflection. In some embodiments, two of the same type of scanning
device are used. In other embodiments different types of scanning
devices are used for the horizontal scanner and the vertical
scanner.
Image Capturing System
[0041] Referring to FIG. 10, an image capturing system 150 is shown
in which image data is obtained and stored for each pixel within
the field of view F for a single still frame or for multiple video
image frames. The system 150 operates in the same manner as
described for the system 30 of FIG. 2 and like parts performing
like functions are given the same part numbers. In addition to
detecting light distance however, light intensity and light color
also is detected for each pixel within the field of view.
Accordingly, a light intensity sensor 152 is included along with
color sensor 154. One of ordinary skill in the art will appreciate
that the sensors 152, 154 and 36 may be combined into a common
device, or that the color sensing and intensity sensing can be
achieved with a common device. Further, rather than color detection
gray scales may be detected for black and white monochromatic
viewing.
[0042] For each pixel in the field of view, image data is obtained
and stored in memory storage 156. The image data includes the pixel
coordinates, the determined light distance, the light intensity and
the light color. Such image data may be recalled and displayed at
display device 158 to replay the captured image frame(s). A
controller 160 coordinates the field of view scanning and the image
replay.
[0043] Although preferred embodiments of the invention have been
illustrated and described, various alternatives, modifications and
equivalents may be used. Therefore, the foregoing description
should not be taken as limiting the scope of the inventions which
are defined by the appended claims.
* * * * *