U.S. patent application number 15/295944 was filed with the patent office on 2019-01-31 for depth-map generation for an input image using an example approximate depth-map associated with an example similar image.
The applicant listed for this patent is Google Inc.. Invention is credited to Debargha Mukherjee, Meng Wang, Chen Wu.
Application Number | 20190037197 15/295944 |
Document ID | / |
Family ID | 48171927 |
Filed Date | 2019-01-31 |
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United States Patent
Application |
20190037197 |
Kind Code |
A1 |
Mukherjee; Debargha ; et
al. |
January 31, 2019 |
DEPTH-MAP GENERATION FOR AN INPUT IMAGE USING AN EXAMPLE
APPROXIMATE DEPTH-MAP ASSOCIATED WITH AN EXAMPLE SIMILAR IMAGE
Abstract
A two-dimensional image to be converted to a first
three-dimensional image may be received. A second three-dimensional
image that is visually similar to the two-dimensional image that is
to be converted may be identified. A feature-to-depth mapping
function may be computed for the first three-dimensional image by
using an approximate depth map of the second three-dimensional
image that is visually similar to the two-dimensional image that is
to be converted. The feature-to-depth mapping function may be
applied to a plurality of pixels of the two-dimensional image to
determine a depth value for the plurality of pixels of the
two-dimensional image. The first three-dimensional image may be
generated based on the depth values for the plurality of pixels of
the two-dimensional image.
Inventors: |
Mukherjee; Debargha;
(Cupertino, CA) ; Wu; Chen; (Cupertino, CA)
; Wang; Meng; (Brookline, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Google Inc. |
Mountain View |
CA |
US |
|
|
Family ID: |
48171927 |
Appl. No.: |
15/295944 |
Filed: |
October 17, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13478449 |
May 23, 2012 |
9471988 |
|
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15295944 |
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61554670 |
Nov 2, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06T 7/55 20170101; G06T
2207/10024 20130101; H04N 13/122 20180501; G06T 15/00 20130101;
H04N 2013/0081 20130101; G06T 7/50 20170101; H04N 13/128 20180501;
H04N 13/239 20180501; G06T 7/90 20170101; G06T 2200/04 20130101;
G06T 15/40 20130101; H04N 13/261 20180501 |
International
Class: |
H04N 13/02 20060101
H04N013/02; G06T 7/40 20060101 G06T007/40; G06T 7/00 20060101
G06T007/00; H04N 13/00 20060101 H04N013/00 |
Claims
1. A method comprising: receiving a two-dimensional image to be
converted to a first three-dimensional image; identifying a second
three-dimensional image that is visually similar to the
two-dimensional image that is to be converted, the second
three-dimensional image sharing a threshold number of color
features with the two-dimensional image; identifying an approximate
depth map of the second three-dimensional image that shares the
threshold number of color features with the two-dimensional image;
identifying a distribution of spatial variation of the second
three-dimensional image; computing, by a processing device, a
plurality of feature-to-depth mapping functions for the first
three-dimensional image by using the approximate depth map of the
second three-dimensional image that shares the threshold number of
color features with the two-dimensional image, wherein a number of
the plurality of feature-to-depth mapping functions that are
computed is based on the distribution of the spatial variation of
the second three-dimensional image; applying the plurality of
feature-to-depth mapping functions to a plurality of pixels of the
two-dimensional image to determine depth values for the plurality
of pixels of the two-dimensional image, wherein the plurality of
feature-to-depth mapping functions determine the depth values for
the plurality of pixels of the two-dimensional image based on a
color value of each of the plurality of pixels; and generating the
first three-dimensional image based on the depth values for the
plurality of pixels of the two-dimensional image.
2. (canceled)
3. The method of claim 1, further comprising: dividing the second
three-dimensional image into a plurality of regions; wherein each
of the plurality of feature-to-depth mapping functions is
associated with a different region of the plurality of regions of
the second three-dimensional image.
4. The method of claim 3, wherein the determination of the depth
values is based on an interpolation of depth values associated with
the plurality of feature-to-depth mapping functions for each of the
different regions of the plurality of regions of the second
three-dimensional image.
5. The method of claim 1, wherein applying the plurality of
feature-to-depth mappings function comprises: identifying a feature
of each of the plurality of pixels of the two-dimensional image;
and calculating a corresponding depth value for each of the
plurality of pixels of the two-dimensional image, wherein
calculating the depth value for each of the plurality of pixels
comprises computing a linear interpolation based on the calculated
depth values for each of the plurality of pixels of the
two-dimensional image.
6. The method of claim 1, wherein the plurality of feature-to-depth
mapping functions are based on a color space.
7. The method of claim 6, wherein the color space is Y-Cb-Cr.
8. A system comprising: a memory; and a processing device,
operatively coupled with the memory, to: receive a two-dimensional
image to be converted to a first three-dimensional image; identify
a second three-dimensional image that is visually similar to the
two-dimensional image that is to be converted, the second
three-dimensional image sharing a threshold number of color
features with the two-dimensional image; identify an approximate
depth map of the second three-dimensional image that shares the
threshold number of color features with the two-dimensional image;
identify a distribution of spatial variation of the second
three-dimensional image; compute a plurality of feature-to-depth
mapping functions for the first three-dimensional image by using
the approximate depth map of the second three-dimensional image
that shares the threshold number of color features with the
two-dimensional image wherein a number of the plurality of
feature-to-depth mapping functions that are computed is based on
the distribution of the spatial variation of the second
three-dimensional image; apply plurality of feature-to-depth
mapping functions to a plurality of pixels of the two-dimensional
image to determine depth values for the plurality of pixels of the
two-dimensional image, wherein plurality of feature-to-depth
mapping functions determine the depth values for the plurality of
pixels of the two-dimensional image based on a color value of each
of the plurality of pixels; and generate the first
three-dimensional image based on the depth values for the plurality
of pixels of the two-dimensional image.
9. (canceled)
10. The system of claim 8, wherein the processing device is further
to: divide the second three-dimensional image into a plurality of
regions; wherein each of the plurality of feature-to-depth mapping
functions is associated with a different region of the plurality of
regions of the second three-dimensional image.
11. The system of claim 10, wherein the determination of the depth
values is based on an interpolation of depth values associated with
the plurality of feature-to-depth mapping functions for each of the
different regions of the plurality of regions of the second
three-dimensional image.
12. The system of claim 8, wherein to apply the plurality of
feature-to-depth mappings, the processing device is further to:
identify a feature of each of the plurality of pixels of the
two-dimensional image; and calculate a corresponding depth value
for each of the plurality of pixels of the two-dimensional image,
wherein calculating the depth value for each of the plurality of
pixels comprises computing a linear interpolation based on the
calculated depth values for each of the plurality of pixels of the
two-dimensional image.
13. The system of claim 8, wherein the plurality of
feature-to-depth mappings are based on a color space.
14. The system of claim 13, wherein the color space is Y-Cb-Cr.
15. A non-transitory machine-readable storage medium storing
instructions which, when executed by a processing device, cause the
processing device to perform operations comprising: receiving a
two-dimensional image to be converted to a first three-dimensional
image; identifying a second three-dimensional image that is
visually similar to the two-dimensional image that is to be
converted, the second three-dimensional image sharing a threshold
number of color features with the two-dimensional image;
identifying an approximate depth map of the second
three-dimensional image that shares the threshold number of color
features with the two-dimensional image; identifying a distribution
of spatial variation of the second three-dimensional image;
computing a plurality of feature-to-depth mapping functions for the
first three-dimensional image by using the approximate depth map of
the second three-dimensional image that shares the threshold number
of color features with the two-dimensional image, wherein a number
of the plurality of feature-to-depth mapping functions that are
computed is based on the distribution of the spatial variation of
the second three-dimensional image; applying the plurality of
feature-to-depth mapping functions to a plurality of pixels of the
two-dimensional image to determine depth values for the plurality
of pixels of the two-dimensional image, wherein the plurality of
feature-to-depth mapping functions determine the depth values to
for the plurality of pixels of the two-dimensional image based on a
color value of each of the plurality of pixels; and generating the
first three-dimensional image based on the depth values for the
plurality of pixels of the two-dimensional image.
16. (canceled)
17. The non-transitory machine-readable storage medium of claim 15,
the operations further comprising: dividing the second
three-dimensional image into a plurality of regions; and wherein
each of the plurality of feature-to-depth mapping functions is
associated with a different region of the plurality of regions of
the second three-dimensional image.
18. The non-transitory machine-readable storage medium of claim 17,
wherein the determination of the depth values is based on an
interpolation of depth values associated with the plurality of
feature-to-depth mapping functions for each of the different
regions of the plurality of regions of the second three-dimensional
image.
19. The non-transitory machine-readable storage medium of claim 15,
wherein to apply the plurality of feature-to-depth mappings, the
operations further comprise: identifying a feature of each of the
plurality of pixels of the two-dimensional image; and calculating a
corresponding depth value for each of the plurality of pixels of
the two-dimensional image, wherein calculating the depth value for
each of the plurality of pixels comprises computing a linear
interpolation based on the calculated depth values for each of the
plurality of pixels of the two-dimensional image.
20. The non-transitory machine-readable storage medium of claim 15,
wherein the plurality of feature-to-depth mappings are based on a
color space.
21. The method of claim 1, wherein each of the plurality of
feature-to-depth mapping functions is associated with a different
region of the first three-dimensional image.
Description
RELATED APPLICATIONS
[0001] This continuation application claims priority to U.S. patent
application Ser. No. 13/478,449 filed on May 23, 2012 which is
related to and claims the benefit of U.S. Provisional Patent
Application No. 61/554,670, filed Nov. 2, 2011, all of which are
hereby incorporated by reference herein.
TECHNICAL FIELD
[0002] This disclosure relates to the field of image processing
and, in particular, to conversion of monoscopic visual content to
stereoscopic 3D.
BACKGROUND
[0003] Advances in display technology have caused display devices
capable of conveying a stereoscopic perception of three-dimensional
(3D) depth to a view to become increasingly common. These 3D
displays may be found in high-definition (HD) television sets,
gaming devices, and other computing devices. The growing number of
3D displays has led to a need for additional 3D visual content
(e.g., images, video). Conventionally, creating 3D content has been
a difficult and time consuming process. A content creator, for
example, would capture a subject using two cameras, combine the
video or images from each camera, and use special software to make
the 3D effect look accurate. This typically includes a lengthy,
highly technical and expensive manual process. Further,
conventional techniques for converting two-dimensional (2D) images
and video to 3D may not be scalable given the time and resources it
would require to convert a large number of images or video. In
addition, conventional techniques are limited to converting
specific types of images and video and may not be used for general
2D to 3D conversion tasks.
SUMMARY
[0004] The following is a simplified summary of the disclosure in
order to provide a basic understanding of some aspects of the
disclosure. This summary is not an extensive overview of the
disclosure. It is intended to neither identify key or critical
elements of the disclosure, nor delineate any scope of the
particular implementations of the disclosure or any scope of the
claims. Its sole purpose is to present some concepts of the
disclosure in a simplified form as a prelude to the more detailed
description that is presented later.
[0005] In one implementation, an image converter receives a
two-dimensional image to be converted to a first three-dimensional
image. The image converter computes a feature-to-depth mapping
function based on an approximate depth map associated with a second
three-dimensional image. The image converter applies the
feature-to-depth mapping function to a plurality of pixels of the
two-dimensional image to determine a depth value for each of the
plurality of pixels and generates the first three-dimensional image
based on the depth values for the plurality of pixels of the
two-dimensional image.
[0006] In one implementation, a method includes receiving a
two-dimensional image to be converted to a first three-dimensional
image; computing, a feature-to-depth mapping function based on an
approximate depth map associated with a second three-dimensional
image; applying the feature-to-depth mapping function to a
plurality of pixels of the two-dimensional image to determine a
depth value for each of the plurality of pixels; and generating the
first three-dimensional image based on the depth values for the
plurality of pixels of the two-dimensional image.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The present disclosure is illustrated by way of example, and
not by way of limitation, in the figures of the accompanying
drawings.
[0008] FIG. 1 is a block diagram illustrating an exemplary network
architecture in which aspects of the present disclosure may be
implemented.
[0009] FIG. 2A is a block diagram illustrating an image converter
for depth map generation using an approximate depth map associated
with an example similar image, according to an implementation.
[0010] FIG. 2B is a diagram illustrating an image divided into
regions for feature-to-depth mapping, according to an
implementation.
[0011] FIG. 3 is a block diagram illustrating an image conversion
processing flow, according to an implementation.
[0012] FIG. 4 is a diagram illustrating a feature-to-depth mapping
function, according to an implementation.
[0013] FIG. 5 is a diagram illustrating a depth map computed
according to an implementation.
[0014] FIG. 6 is a flow diagram illustrating a method for image
conversion, according to an implementation.
[0015] FIG. 7 is a flow diagram illustrating a method for computing
a feature-to-depth mapping function, according to an
implementation.
[0016] FIG. 8A is a flow diagram illustrating a method for applying
a feature-to-depth mapping function to an input image, according to
an implementation.
[0017] FIG. 8B is a diagram illustrating a one-dimensional linear
interpolation between color-depth bins, according to an
implementation.
[0018] FIG. 9 is a block diagram illustrating one implementation of
a computer system, in accordance with an aspect of this
disclosure.
DETAILED DESCRIPTION
[0019] Implementations are described for generating a depth map for
a two-dimensional (2D) input image. The depth map may be used to
convert the 2D input image into a three-dimensional (3D) output
image. The 2D input image may be provided by a user or selected
from a database of available images. The image converter described
herein may have access to another database storing 3D images. These
3D images may have been captured initially in 3D or may have been
previously converted from 2D to 3D. The image converter can
identify a 3D example image from the database that is visually
similar to the 2D input image. The visually similar image may share
a number of features with the 2D input image, such as similar
colors, similar subject matter, may be taken in a similar location,
etc. While details are provided herein specifically relating to
images as an example for clarity of explanation, it shall be
appreciated that such details may be equally applicable to other
types of media, e.g., video, documents, text (e.g., tweets),
flash-content, etc., as applicable.
[0020] Since the visually similar example image is a 3D image,
depth information may be known for the image. If the depth
information is not known or readily available, it may be computed
using depth interpolation techniques. The depth information may be
stored in the form of a depth map. The depth map can include a
depth value for each pixel in the 3D example image that is used to
render the 3D effects for the image. Since the depth map is
associated with the 3D example image, it will not be directly
related to the 2D input image. Thus, the depth map may be referred
to as an approximate depth map in relation to the 2D input image.
However, since the 3D example image is visually similar to the 2D
input image, the approximate depth map can be a good starting point
for generating a final depth map for the 2D input image.
[0021] Using the 3D example image and the approximate depth map, in
one implementation, the image converter can generate a
feature-to-depth mapping function that relates a feature value,
such as color, of each pixel or group of pixels in the 3D example
image to a depth value. The image converter can apply this function
to the known feature values of the 2D input image to generate a
depth value for each pixel of the 2D input image. These depth
values can form the final depth map for the 2D input image. Using
the final depth map, the image converter can render a 3D output
image based on the 2D input image. Thus, the 2D input image can be
efficiently converted to a 3D output image.
[0022] Implementations of the conversion techniques described
herein provide for fully automatic conversion of 2D visual content
to 3D. This can allow an individual to avoid the costly and
time-intensive processes of capturing a 3D image or manually
converting an existing 2D image to 3D. The use of a
feature-to-depth mapping function, which corresponds to images that
are visually similar to the input image, allows for a more accurate
prediction of the depth values for the image. In turn, this can
lead to a more accurate and realistic rendering of the 3D output
image. In addition, utilizing a large database of images for the
comparison increases the possibility that a visually similar image
or images can be found, facilitating the conversion of many types
of visual content. In one implementation, millions of images are
available for comparison.
[0023] FIG. 1 is a block diagram illustrating an exemplary network
architecture in which aspects of the present disclosure may be
implemented. The network architecture 100 can include one or more
servers 102 communicating with one or more user devices 130, 132,
134 over one or more networks 140, according to one implementation.
Network 140 can be a local area network (LAN), a wireless network,
a telephone network, a mobile communications network, a wide area
network (WAN), such as the Internet, or similar communication
system. User devices 130, 132, 134 may be any type of computing
device including server computers, gateway computers, desktop
computers, laptop computers, mobile communications devices, cell
phones, smart phones, hand-held computers, tablets, or similar
computing devices. The user devices 130, 132, 134 can be variously
configured with different features to enable viewing of visual
content, such as images, videos, etc.
[0024] Server 102 can include a network-accessible server-based
functionality, various data stores, and/or other data processing
equipment. The server 102 can be implemented by a single machine or
a cluster of machines. Server 102 can include, for example,
computer system 900 of FIG. 9. In one implementation, server 102
includes image converter 110 and storage device 120. In another
implementation, storage device 120 may be external to server 102
and may be connected to server 102 over a network or other
connection. In other implementations, server 102 can include
different and/or additional components which are not shown here so
as not to obscure the present disclosure. Storage device 120 can
include one or more mass storage devices which can include, for
example, flash memory, magnetic or optical disks, or tape drives,
read-only memory (ROM); random-access memory (RAM); erasable
programmable memory (e.g., EPROM and EEPROM); flash memory; or any
other type of storage medium.
[0025] In one implementation, storage device 120 includes an image
data store including a number of 3D images as well as a number of
2D images or videos. For at least some of the 2D or 3D images, an
associated depth map may also be stored in storage device 120. In
one implementation, the depth map includes a depth value for each
pixel (or each group of pixels) in the image. In another
implementation, for each of the 3D images, a feature-to-depth
mapping database, which includes a predetermined feature-to-depth
mapping function, can be provided and stored in storage device
120.
[0026] Image converter 110 can receive a user request to convert a
2D input image to a 3D output image. The 2D input image to be
converted can be an image previously provided by a user or a
computer application program and stored in storage device 120 or an
image provided by the user along with the request. Image converter
110 can identify a 3D example image (or images) that is visually
similar to the 2D image being converted, and an approximate depth
map associated with the example image. The example similar image
and the associated approximate depth map can be stored in storage
device 120. The visually similar 3D example image may be identified
by the features that it shares with the 2D input image, such as
similar colors, subject matter, location, context, etc. The
approximate depth map can include a depth value for each pixel (or
group of pixels) in the 3D example image that is used to render the
3D effects for the image. In another implementation, the
approximate depth map may not be associated with the 3D example
image, but rather may be otherwise selected by the user or by image
converter 110 from a selection of available depth maps for use in
converting the 2D input image to 3D. As will be described below,
image converter 110 can use the approximate depth map to
automatically convert the 2D input image into a 3D output
image.
[0027] FIG. 2A is a block diagram illustrating an image converter
for depth map generation using an approximate depth map associated
with an example similar image, according to an implementation of
the present disclosure. In one implementation, image converter 110
can include feature handling module 212, feature-to-depth mapping
module 214, depth map generation module 216 and image rendering
module 218. This arrangement of modules may be a logical
separation, and in other implementations, these modules or other
components can be combined together or separated into further
components, according to a particular implementation. In one
implementation, storage device 120 can include image data store 222
and feature-to-depth mapping database 224 that are used by image
converter 110 for more accurate 2D to 3D conversion.
[0028] Image converter 110 can receive a 2D input image (e.g., from
a user or a computer application program) that is to be converted
to a 3D output image and can find an example similar image in data
store 222 and an associated approximate depth map. In one
implementation, a threshold is defined, such as a number of
features or characteristics that must be shared between the input
image and an image from data store 222, to consider the image from
data store 222 to be similar to the input image being converted.
Once the similar image is identified, a feature-to-depth mapping
function for the 3D similar image is determined using the
approximate depth map associated with the similar image. In another
implementation, the feature-to-depth mapping function may be
determined for the 3D similar image ahead of time and stored in
feature-to-depth mapping database 224.
[0029] In one implementation, the feature-to-depth mapping function
is determined by feature handling module 212 and feature-to-depth
mapping module 214. In particular, in one implementation, each 3D
image (or frame of a 3D video) in image data store 222 includes or
is associated with a stereo image pair which, when viewed, creates
an illusion of depth. Generally, the image pair includes two images
(e.g., left image and right image) of the same subject, taken from
slightly different viewpoints (roughly equal to the distance
between a person's eyes). Thus, each point in the two images will
have a slight offset (measured in pixels) that is proportional to
the distance the point is from the viewpoint. This offset may be
referred to as disparity. In one implementation, the depth value
for each pixel in the approximate depth map associated with the 3D
example image may be equal to or proportional to the calculated
disparity.
[0030] In order to generate the feature-to-depth mapping function
for the 3D example image, features of the 3D example image may be
related to the depth values in the approximate depth map. In one
implementation, feature handling module 212 can identify one or
more features of the 3D example image from image data store 222. In
one implementation, the feature may include a color value of each
pixel in the example image. In other implementations, some other
feature may be used such as motion (or associated motion vector),
location, texture, edge, or gradient histogram based on image
features such as scale-invariant feature transform (SIFT). The
feature-to-depth mapping described herein may be used with any of
these or other features.
[0031] In one implementation, feature handling module 212 can
determine a number of bins in a color space (e.g., YUV, RGB,
YCbCr). Binning may be used to reduce the number of colors taken
into account. YUV, for example may have a 24 bit color value, which
may be too large for a typical feature-to-depth mapping function.
Thus, feature handling module 212 can combine different color
values to have a manageable number of bins. For the example image
from image data store 222, feature handling module 212 can
associate each pixel with an appropriate bin based on the color
value of the pixel. Using the approximate depth map, feature
handling module 212 can also combine (e.g., average) the depth
values for each pixel in a certain bin to generate an aggregate
depth value for the bin. A similar combination may be performed for
the colors in each of the remaining bins, until a series of data
points are obtained.
[0032] Feature-to-depth mapping module 214 can generate a
feature-to-depth mapping function for the example image based on
one or more features of the image and the depth values determined
by feature handling module 212. In one implementation, the feature
used to generate the function may be color. Each pixel of the
example image has a known color value (e.g., determined from the
image metadata) and may have a depth value determined for each
color bin by feature handling module 212. The feature-to-depth
mapping function can aggregate the depth values for pixels of the
same or similar colors, based on the assumption that objects in the
image having the same or similar color will also have a same or
similar depth value. In other implementations, other features may
be used to generate the feature-to-depth mapping function, either
in place of or in addition to color, such as texture, location,
shape, etc. The resulting function can ultimately receive a color
value (or other feature value) for a certain pixel or other point
as an input, and output a depth value for that pixel. Additional
details of the feature-to-depth mapping function are described
below with respect to FIG. 4.
[0033] In one implementation, rather than generating just one
feature-to-depth mapping function for the 3D example image,
feature-to-depth mapping module 214 can generate multiple
feature-to-depth mapping functions for a single example image in
image data store 222. Different functions may be generated, for
example, for different regions of the image. In one implementation,
an image from image data store 222 may be logically divided into a
number of regions (e.g., two, four). The image can be tiled in
different ways, depending on distribution of the major spatial
variation in the image. For example, for an outdoor mountain-sky
image, it may be sufficient to divide the image horizontally into
two parts, the top and the bottom half image. For an indoor image,
it may be better to have more spatial components, where the left
vs. right half images may have different depth mapping as well.
FIG. 2B is a diagram illustrating an example image 250, logically
divided into four equal regions 252-258. Feature-to-depth mapping
module 214 can treat each region 252-258 as its own individual
image and determine a feature-to-depth mapping function specific to
that region in the manner described above. In one implementation,
feature-to-depth mapping module 214 can store the multiple
functions corresponding to the regions of the image in database
224. In another implementation, the multiple functions may be
combined (e.g., using a linear combination based on the distance
from a pixel P to the center of each region C1-C4) into a single
function that is stored in database 224 for example. The linear
combination may eliminate potential "boundary effects" generated by
switching feature-to-depth mapping functions across the different
regions. When applying the feature-to-depth mappings to the 2D
input image, the final depth value may be an interpolation between
the different regions. When computing the depth value for a pixel
P, its distance to the centers C1-C4 of the regions are first
computed, and may be denoted as d1, d2, d3 and d4. With
feature-to-depth mapping of region 252, it gives a depth value v1
for pixel P. Similarly, we get v2, v3 and v4 with feature-to-depth
mapping from other regions 254-258. The final depth value of P may
be calculated by combining v1 thru v4 which is
inversely-proportional to d1 thru d4; e.g., depth of
P=(v1/d1+v2/d2+v3/d3+v4/d4)/(1/d1+1/d2+1/d3+1/d4).
[0034] Upon completion of generating the feature-to-depth mapping
function, the feature-to-depth mapping function for the image from
image data store 222 can be stored in a corresponding entry in
feature-to-depth mapping database 224. In one implementation,
feature-to-depth mapping database 224 can have some other structure
besides a database (e.g., a list of key-value pairs). In one
implementation, feature-to-depth mapping database 224 can be a
separate data structure (as shown), however in other
implementations, the mapping information may be stored in the
metadata of image data store 222. Image converter 110 can use the
feature-to-depth mapping database 224 to automatically generate a
3D output image from a 2D input image.
[0035] In one implementation, depth map generation module 216 can
compute a depth map for the 2D input image based on the
feature-to-depth mapping function determined by feature-to-depth
mapping module 214. Image data and/or metadata received with the
input image may include, for example, a color value associated with
each pixel in the input image. A depth value can then be calculated
for each pixel by applying the color values (or other appropriate
feature values) as inputs to the feature-to-depth mapping function
which was generated based on the 3D example image and the
approximate depth map. Depth-map generation module 216 can perform
the calculations to make this determination and can store the
resulting depth values (e.g., a final depth map) in storage device
120. An example of one resulting depth map 510 is shown in FIG.
5.
[0036] Image rendering module 218 can render a 3D output image
(i.e., a stereo image pair) based on the input image and the depth
values calculated by depth map generation module 216. In one
implementation, rendering module 218 uses depth image based
rendering (DIBR) techniques to generate the 3D image. DIBR
techniques can render a 2D image based on another 2D image and a
per pixel depth map. The original 2D image becomes one of two views
that make up a 3D image, while the DIBR-rendered 2D image becomes
the second view. In one implementation, the original 2D image is
the left view, while the rendered 2D image is the right view. In
other implementations, this may be reversed.
[0037] As an example, given the per-pixel depth map, a displacement
map may be generated indicating how much each pixel should move
from the left view to the right view. The relationship between
depth and displacement may be approximately linear; however, some
parameters may be adjusted in order to control how much an object
"pops out" of a screen or how much it appears to extend behind the
screen. Once the displacement map is generated, the pixels may be
shifted from the left view to the right view to render the right
view, while making sure that pixels which are in front occlude
pixels in the back, if multiple pixels from the left view map to
the same pixel in the right rendered image space. Once all the
pixels have been shifted, there may still be some holes left in the
rendered right view. An in-painting (image interpolation) technique
may be employed to fill up the holes from the neighboring pixels in
the rendered image. This yields the final rendered right view. In
order to create high quality rendering, the rendering may be
conducted in an intermediate higher resolution pixel grid by
interpolating based on the left view and the per-pixel depth map.
Once the rendered image is obtained at the higher intermediate
resolution, it can be scaled back to the desired resolution. In one
implementation, the rendered image may be filtered using, for
example, cross bilateral filtering. Cross bilateral filtering is a
way to filter an image with respect to the geometry of objects in
the image. For example, when an image is filtered, a pixel value
may be combined with values from the neighborhood of the pixel to
remove aliasing, noise, and other undesirable features. This may
result in averaging values that possibly do not belong to the same
object in the image, and thus can lead to incoherent values. Cross
bilateral filtering tries to solve this by using multiple source
images (instead of just one) to help identify objects. As a result,
when filtering, the neighborhood pixel values may be weighted by
their screen space distance, and also using an expression that
takes into account a depth difference to determine if both pixels
belong to the same object. This may help to prevent blurring in the
resulting filtered image.
[0038] FIG. 3 is a block diagram illustrating an image conversion
processing flow, according to an implementation of the present
disclosure. The various modules and components may be described in
regards to their roles in generating a depth map for an input image
using an approximate depth map associated with an example similar
image.
[0039] In one implementation, the processing flow 300 begins with
receiving a 2D input image at block 310. At block 320, an example
similar image is identified. At block 322 an approximate depth map
is identified. The approximate depth map may be associated with the
example similar image or may be associated with some other visually
similar image. At block 330, a feature-to-depth mapping function is
determined for the example image. Feature-to-depth mapping module
214 can determine a feature-to-depth mapping function for the
example similar image based on features of the example similar
image 320 and the approximate depth map 322. At block 340, a depth
map is generated for the input image based on the feature-to-depth
mapping function. Depth map generation module 216 can generate the
depth map by applying a feature value (e.g., color) for each pixel
in the input image to the feature-to-depth mapping function to
determine the depth values. At block 350, the depth map may be used
with rendering techniques (e.g., DIBR) to generate the 3D output
image 360.
[0040] For simplicity of explanation, the flows and methods of this
disclosure are depicted and described as a series of acts. However,
acts in accordance with this disclosure can occur in various orders
and/or concurrently, and with other acts not presented and
described herein. For example, identifying the approximate depth
map at block 322 and feature-to-depth mapping at block 330
associated with the example similar image can occur before the
input image is received at block 310 and stored, e.g., in storage
device 120. Once the example similar image is identified at block
320, the pre-processed approximate depth map and feature-to-depth
mapping function can be retrieved and used to generate the depth
map at block 340.
[0041] FIG. 4 is a diagram illustrating a feature-to-depth mapping
function, according to an implementation of the present disclosure.
In this implementation, the feature-to-depth mapping function 400
is based on the color of each pixel in an image. The function 400
can receive a color value for a certain pixel or other point as an
input and output a depth value for that pixel. FIG. 4 illustrates
depth as a function of color in one dimension for ease of
understanding. One of skill in the art would recognize that in
practice, the function could illustrate similar properties in a
multi-dimensional color space (e.g., YUV, RGB). In one
implementation, binning is used to reduce the number of colors
taken into account by the function. YUV, for example may have a 24
bit color value, which may be larger than desired for a typical
feature-to-depth mapping function. In some cases the over 16
million different colors represented in a 24-bit color scheme may
make computing a color-to-depth mapping function too
computationally expensive and time consuming. In FIG. 4, the color
values have been reduced to eight bins (A-H), although in other
implementations, some other number may be used. For one of the
images in image data store 222, for which the color values and
depth values are known, the depth values corresponding to each
pixel having one of the colors in a certain bin (e.g., bin A) are
combined (e.g., averaged) to generate an aggregate depth value.
This value may be stored as part of function 400. A similar
combination may be performed for the colors in each of the
remaining bins, until a series of data points are obtained.
Feature-to-depth mapping module 214 can perform a form of
polynomial fit (e.g., curve fitting) to generate the
feature-to-depth mapping function 400. The resulting function may
be expressed as f(color)=depth, or in the case of YUV color,
f(YUV)=depth. Thus, the depth value for a given pixel can be
computed as a function of the YUV color values for that pixel. The
function 400 may be stored in feature-to-depth mapping database
224.
[0042] FIG. 5 is a diagram illustrating a depth map computed
according to implementations of the present disclosure. Depth map
generation module 216 can compute a depth map for the input image
based on a feature-to-depth mapping function, such as
feature-to-depth mapping function 400 determined by
feature-to-depth mapping module 214. In the depth map 510 of FIG.
5, the shading is proportional to the distance of the surfaces of
scene objects from the viewpoint in the source image 500. In this
implementation, darker colors indicate a depth that is closer to
the viewpoint, while lighter colors indicate a depth that is
further away. In other implementations, the shading may be
reversed.
[0043] FIG. 6 is a flow diagram illustrating a method for image
conversion according to an implementation of the present
disclosure. The method 600 may be performed by processing logic
that includes hardware (e.g., circuitry, dedicated logic,
programmable logic, microcode, etc.), software (e.g., instructions
run on a processing device to perform hardware simulation), or a
combination thereof. The method 600 can generate a depth map for an
input image using an approximate depth map associated with one or
more example similar images. In one implementation, method 600 may
be performed by image converter 110 as shown in FIG. 1.
[0044] Referring to FIG. 6, at block 610, method 600 receives a 2D
input image for conversion to 3D. The input image may be received
from a user (e.g., through a user interface provided by image
converter 110), from another computer application program (e.g.,
through an application interface, such as an API), or from some
other source.
[0045] At block 620, method 600 identifies (e.g., by computing or
retrieving from storage) a feature-to-depth mapping function for
the input image based on an approximate depth map associated with a
similar 3D image. In one implementation, feature-to-depth mapping
module 214 can aggregate the depth values for pixels of the same or
similar feature (e.g., colors) in the example similar image, e.g.,
based on the assumption that objects in the image having the same
or similar color will also have the same or similar depth value.
The resulting function, such as function 400, can ultimately
receive a color value (or other feature value) for a certain pixel
or other point in the input image as an input and output a depth
value for that pixel. The feature-to-depth mapping function may be
stored, for example, in database 224.
[0046] At block 630, method 600 applies the feature-to-depth
mapping function identified at block 620 to the pixels in the input
image to determine a depth value for each of the pixels. Depth map
generation module 216 can generate a resulting depth map for the
input image. In one implementation, depth map generation module 216
can apply color values (or other appropriate feature values) as
inputs to the feature-to-depth mapping function generated at block
620. This results in a depth value being calculated for each pixel
of the input image. The depth values may be combined, based on the
location of their associated pixels, to form a depth map 510 as
shown in FIG. 5.
[0047] At block 640, method 600 generates a stereo pair for a 3D
output image. In one implementation, image rendering module 218 can
render a 3D output image based on the input image and the depth
values calculated by depth map generation module 216 at block 630.
In one implementation, rendering module 218 can use depth image
based rendering (DIBR) techniques to generate the 3D image. In one
implementation, the 3D output image includes a second image to be
used in conjunction with the input image to form a stereo pair. The
second image may be either the left image or the right image,
depending on the implementation, and may be generated by image
rendering module 218. The first and second images together may form
the 3D output image. The 3D output image may be stored or displayed
for viewing by a user.
[0048] FIG. 7 is a flow diagram illustrating a method for computing
a feature-to-depth mapping function according to an implementation
of the present disclosure. The method 700 may be performed by
processing logic that includes hardware (e.g., circuitry, dedicated
logic, programmable logic, microcode, etc.), software (e.g.,
instructions run on a processing device to perform hardware
simulation), or a combination thereof. The method 700 can create a
feature-to-depth mapping function used to convert monoscopic visual
content to stereoscopic 3D. In one implementation, method 700 may
be performed by image converter 110 as shown in FIG. 1.
[0049] Referring to FIG. 7, at block 710, method 700 identifies one
or more visually similar images from image data store 222. In one
implementation, data store 222 may include a corpus of 3D images
and/or videos for which feature information (e.g., color) and depth
values are known. In one implementation, the corpus includes
millions of images and/or videos. Any number of techniques may be
used to identify the visually similar images, such as
fingerprinting, K-nearest neighbor, etc. At block 720, method 700
identifies a number of bins to be used for the given color space.
Binning may be used to reduce the number of colors taken into
account. In one implementation where the color space is YCbCr, the
space may be divided into bins on Y, Cb and Cr independently. In
one implementation, the Y component is divided into 32 bins, and
the Cb and Cr components are each divided into 16 bins, so that
there are 8192 bins in total. In other implementations, some other
number of bins and/or some other color space may be used.
[0050] At block 730, method 700 associates the pixels in the
example similar image identified at block 710 with the bins
identified at block 720. For the example image from image data
store 222, feature handling module 212 can associate each pixel
with an appropriate bin based on the color value of the pixel. Each
bin may include pixels of the same or similar colors (or other
relevant feature).
[0051] At block 740, method 700 determines a depth value for each
color bin. For example, for each (Y, Cb, Cr) bin, there may be
multiple depth values. In order to generate the feature-to-depth
mapping function, only one depth value for each (Y, Cb, Cr) bin may
be used. All the depth values in one bin may thus be combined into
a single depth value. In one implementation, the combined depth
value for the bin is simply the average of all the example depths
that map to it. In another implementation, the combined depth is
the median of all the example depths that map to it. In yet another
implementation, a RANSAC (Random Sample Consensus) method is used
to detect outliers in the depth values and the mean of the inliers
is output. Assuming the total number of depth values is N, for each
iteration of RANSAC, a random subset (N1) of the depth values is
chosen and its mean is computed. The difference between this mean
depth and all the N depth values is computed. Those with a
difference smaller than a threshold may be included in an inlier
set. The iteration may stop when the inlier set does not change or
a max iteration number is reached. If the inlier set size is bigger
than M (which may be specified as a percentage of N), this inlier
set is claimed as valid, and its mean may be used as a
summarization of all the depth values.
[0052] At block 750, method 700 computes a weight value for each
bin. Feature handing module 212 can compute a weight for each bin
that is a function of the ratio of the occupancy within the bin and
the average occupancy for any bin. So if there are N pixels in the
example image, and a total of B bins, then the occupancy ratio of a
bin with n hits is n/(BN). The weight for each bin may be a
function of this occupancy ratio, i.e., w(n/(BN)). In one
implementation, the function is w(x)=1-exp(-kx), where k is chosen
such that w(x) is small for small occupancy ratios, but quickly
gets close to one for non-trivial occupancies. In another
implementation, the weighting function w(x) equals 0 for x <a
small value, and equals one otherwise, in order to reject bins with
very small occupancy which may be due to noise.
[0053] At block 760, method 700 generates the feature-to-depth
mapping function. Feature-to-depth mapping module 214 can perform a
form of polynomial fit (e.g., curve fitting) to generate the
feature-to-depth mapping function 400. The resulting function may
be expressed as f(color)=depth, or in the case of YUV color,
f(YUV)=depth. Thus, the depth value for a given pixel is computed
as a function of the YUV color values for that pixel.
Feature-to-depth mapping module 214 can also smooth the mapping
function. Since the mapping function may be noisy, module 214 can
smooth the mapping function by convolving it with a predefined
smoothing kernel. For example, a bin, j, may be reassigned with a
weighted average of its neighboring bins where the weight is the
product of the smoothing kernel with the occupancy based weight
computed above at block 750. In one implementation, the final depth
(D) for this bin, j, may be computed as:
D ' j = i .di-elect cons. N ( j ) Diwi i .di-elect cons. N ( j ) wi
##EQU00001##
In this equation, N(j) denotes the neighborhood of the bin. The
feature-to-depth mapping function may be stored, for example, in a
data store such as database 224.
[0054] FIG. 8A is a flow diagram illustrating a method for applying
a feature-to-depth mapping function to an input image, according to
an implementation of the present disclosure. The method 800 may be
performed by processing logic that includes hardware (e.g.,
circuitry, dedicated logic, programmable logic, microcode, etc.),
software (e.g., instructions run on a processing device to perform
hardware simulation), or a combination thereof. The method 800 can
apply a feature-to-depth mapping function to an input image to
convert the input image to stereoscopic 3D. In one implementation,
method 800 may be performed by image converter 110 as shown in FIG.
1.
[0055] Referring to FIG. 8A, at block 810, method 800 receives a 2D
input image to be converted to 3D. At block 820, method 800
identifies the feature (e.g., color value) of each pixel in the
input image. In one implementation the feature data may be stored
in metadata associated with the image, and feature handling module
212 can determine the feature value, e.g., color value, from this
metadata.
[0056] At block 830, method 800 calculates the depth of each pixel
in the input image based on the feature-to-depth mapping function
determined from the approximate depth map (e.g., as discussed above
in conjunction with FIG. 7). In one implementation, depth map
generation module 216 can perform an n-linear interpolation in the
feature space to get a depth of the query pixel. For example, in a
one-dimensional case, the two bin centers surrounding the actual
value of the query pixel may be denoted as C1 and C2. The weighted
depth values of those bins may be D1 and D2, respectively. Depth
map generation module 216 can compute the distances between the
query pixel and C1 and C2, and denote them by d1 and d2
respectively. Depth map generation module 216 can use the distances
as weights to interpolate a depth value between these two bins
using a formula such as:
D = d 2 D 1 + d 1 D 2 d 1 + d 2 ##EQU00002##
[0057] FIG. 8B is a diagram illustrating a one-dimensional linear
interpolation between color-depth bins, according to an
implementation. An interpolated value 852 may be returned as the
depth value for the query pixel. Using a histogram representation
of the feature-to-depth mapping 850, the approximated mapping is
not smooth. Depth value may change abruptly near bin boundaries. In
one implementation, interpolation may be used on the approximated
mapping. In one implementation, a trilinear interpolation of the
mapping may be used, since we have a 3D mapping function f(y, u,
v)=d. Since features tend to follow object contours in the image,
with this method a good segmentation in the depth-map that follows
object boundaries may be achieved.
[0058] Referring again to FIG. 8A, at block 840, method 800
generates a stereo pair for a 3D output image. In one
implementation, image rendering module 218 can render a 3D output
image based on the input image and the depth values calculated by
depth map generation module 216 at block 830. In one
implementation, rendering module 218 can use depth image based
rendering (DIBR) techniques to generate the 3D image. The output
image may be stored or displayed for viewing by a user.
[0059] FIG. 9 illustrates a diagrammatic representation of a
machine in the exemplary form of a computer system 900 within which
a set of instructions, for causing the machine to perform any one
or more of the methodologies discussed herein, may be executed. In
alternative implementations, the machine may be connected (e.g.,
networked) to other machines in a local area network (LAN), an
intranet, an extranet, or the Internet. The machine may operate in
the capacity of a server or a client machine in a client-server
network environment, or as a peer machine in a peer-to-peer (or
distributed) network environment. The machine may be a personal
computer (PC), a tablet PC, a set-top box (STB), a Personal Digital
Assistant (PDA), a mobile telephone, a web appliance, a server, a
network router, switch or bridge, or any machine capable of
executing a set of instructions (sequential or otherwise) that
specify actions to be taken by that machine. Further, while only a
single machine is illustrated, the term "machine" shall also be
taken to include any collection of machines that individually or
jointly execute a set (or multiple sets) of instructions to perform
any one or more of the methodologies discussed herein. In one
implementation, computer system 900 may be representative of a
server, such as server 102, running image converter 110.
[0060] The exemplary computer system 900 includes a processing
device 902, a main memory 904 (e.g., read-only memory (ROM), flash
memory, dynamic random access memory (DRAM) (such as synchronous
DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 906
(e.g., flash memory, static random access memory (SRAM), etc.), and
a data storage device 918, which communicate with each other via a
bus 930. Any of the signals provided over various buses described
herein may be time multiplexed with other signals and provided over
one or more common buses. Additionally, the interconnection between
circuit components or blocks may be shown as buses or as single
signal lines. Each of the buses may alternatively be one or more
single signal lines and each of the single signal lines may
alternatively be buses.
[0061] Processing device 902 represents one or more general-purpose
processing devices such as a microprocessor, central processing
unit, or the like. More particularly, the processing device may be
complex instruction set computing (CISC) microprocessor, reduced
instruction set computer (RISC) microprocessor, very long
instruction word (VLIW) microprocessor, or processor implementing
other instruction sets, or processors implementing a combination of
instruction sets. Processing device 902 may also be one or more
special-purpose processing devices such as an application specific
integrated circuit (ASIC), a field programmable gate array (FPGA),
a digital signal processor (DSP), network processor, or the like.
The processing device 902 is configured to execute processing logic
926 for performing the operations and steps discussed herein.
[0062] The computer system 900 may further include a network
interface device 908. The computer system 900 also may include a
video display unit 910 (e.g., a liquid crystal display (LCD) or a
cathode ray tube (CRT)), an alphanumeric input device 912 (e.g., a
keyboard), a cursor control device 914 (e.g., a mouse), and a
signal generation device 916 (e.g., a speaker).
[0063] The data storage device 918 may include a machine-readable
storage medium 928, on which is stored one or more set of
instructions 922 (e.g., software) embodying any one or more of the
methodologies of functions described herein. The instructions 922
may also reside, completely or at least partially, within the main
memory 904 and/or within the processing device 902 during execution
thereof by the computer system 900; the main memory 904 and the
processing device 902 also constituting machine-readable storage
media. The instructions 922 may further be transmitted or received
over a network 920 via the network interface device 908.
[0064] The machine-readable storage medium 928 may also be used to
store instructions to perform a method for generating a depth map
for an input image using an example approximate depth-map
associated with an example similar image, as described herein.
While the machine-readable storage medium 928 is shown in an
exemplary implementation to be a single medium, the term
"machine-readable storage medium" should be taken to include a
single medium or multiple media (e.g., a centralized or distributed
database, and/or associated caches and servers) that store the one
or more sets of instructions. A machine-readable medium includes
any mechanism for storing information in a form (e.g., software,
processing application) readable by a machine (e.g., a computer).
The machine-readable medium may include, but is not limited to,
magnetic storage medium (e.g., floppy diskette); optical storage
medium (e.g., CD-ROM); magneto-optical storage medium; read-only
memory (ROM); random-access memory (RAM); erasable programmable
memory (e.g., EPROM and EEPROM); flash memory; or another type of
medium suitable for storing electronic instructions.
[0065] The preceding description sets forth numerous specific
details such as examples of specific systems, components, methods,
and so forth, in order to provide a good understanding of several
aspects of the present disclosure. It will be apparent to one
skilled in the art, however, that at least some implementations of
the present disclosure may be practiced without these specific
details. In other instances, well-known components or methods are
not described in detail or are presented in simple block diagram
format in order to avoid unnecessarily obscuring the present
disclosure. Thus, the specific details set forth are merely
exemplary. Particular implementations may vary from these exemplary
details and still be contemplated to be within the scope of the
present disclosure.
[0066] Reference throughout this specification to "one
implementation" or "an implementation" means that a particular
feature, structure, or characteristic described in connection with
the implementation is included in at least one implementation.
Thus, the appearances of the phrase "in one implementation" or "in
an implementation" in various places throughout this specification
are not necessarily all referring to the same implementation. In
addition, the term "or" is intended to mean an inclusive "or"
rather than an exclusive "or." Moreover, the words "example" or
"exemplary" are used herein to mean serving as an example,
instance, or illustration. Any aspect or design described herein as
"exemplary" is not necessarily to be construed as preferred or
advantageous over other aspects or designs. Rather, use of the
words "example" or "exemplary" is intended to present concepts in a
concrete fashion.
[0067] Although the operations of the methods herein are shown and
described in a particular order, the order of the operations of
each method may be altered so that certain operations may be
performed in an inverse order or so that certain operation may be
performed, at least in part, concurrently with other operations. In
another implementation, instructions or sub-operations of distinct
operations may be in an intermittent and/or alternating manner.
Furthermore, not all illustrated acts may be required to implement
aspects of the disclosed subject matter. In addition, those skilled
in the art will understand and appreciate that the methods could
alternatively be represented as a series of interrelated states via
a state diagram or events. Additionally, it should be appreciated
that the methods disclosed in this specification are capable of
being stored on an article of manufacture to facilitate
transporting and transferring such methods to computing devices.
The term "article of manufacture," as used herein, is intended to
encompass a computer program accessible from any computer-readable
device or storage media.
* * * * *