Patent Publication Number: US-9838669-B2

Title: Apparatus and method for depth-based image scaling of 3D visual content

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application is related to U.S. patent application Ser. No. 13/556,969, filed Jul. 24, 2012, entitled “APPARATUS AND METHOD FOR ADJUSTING THE PERCEIVED DEPTH OF 3D VISUAL CONTENT”, which claims priority to U.S. Provisional Application Ser. No. 61/511,380, filed Jul. 25, 2011. Both applications are hereby incorporated by reference into the present application as if fully set forth herein. 
     TECHNICAL FIELD OF THE INVENTION 
     The present application is related to systems and methods that enable the viewer of 3D content to adjust the perceived depth of the 3D content using depth-based image scaling (DBIS). 
     BACKGROUND OF THE INVENTION 
     Three-dimensional (3D) movies and videos are becoming increasing prevalent in the marketplace. When a stereoscopic 3D movie or video is created, two different views of a scene are either captured by physical stereoscopic cameras or artificially generated by means of computer graphics. Typically, the distance (baseline) between the cameras is kept fixed during production according to the 3D visual effects desired by the filmmaker. At the time of viewing the 3D movie or video (e.g., on a 3D television by wearing active or passive 3D glasses), a viewer will experience a “default” depth perception effect as planned by the film or video maker. 
     Stereoscopic 3D content can be processed in order to perform artificial adjustments to the cameras baseline (manipulation of the stereo visual cue) by means of synthesis of novel left and right views. This enables the 3D movie of video viewer to adjust (increase or decrease) the perceived depth to a point that makes the viewer feel more comfortable when viewing the 3D content. However, sometimes the perceived changes in depth are small. This problem often occurs because a single visual cue (stereo) is being manipulated. For example, the perceived depth in a scene may be increased by increasing the baseline. However, the spatial dimensions of the objects in the image remain fixed. Thus, although one can observe the depth range being expanded, one does not feel that close objects become closer. Therefore, there is a need in the art for an improved apparatuses and methods for adjusting the perceived depth of 3D video content. 
     SUMMARY OF THE INVENTION 
     A system is provided for performing depth-based scaling of 3D content. In an advantageous embodiment, the system comprises: 1) a content source configured to provide an input image comprising a plurality of input image objects; and 2) a processor configured to receive the input image and to receive a depth map comprising depth data associated with each of the plurality of input image objects. The processor generates an output image comprising a plurality of output image objects, wherein each of the plurality of output image objects corresponding to one of the plurality of input image objects. The processor scales a size of a first output image object relative to the size of a second output image object based on depth data associated with the first output image object and the second output image object. 
     A method is provided for performing depth-based scaling of 3D content in response to a viewer input control signal. The method comprises: 1) receiving an input image comprising a plurality of input image objects; 2) receiving a depth map comprising depth data associated with each of the plurality of input image objects; and 3) generating an output image comprising a plurality of output image objects, each of the plurality of output image objects corresponding to one of the plurality of input image objects, and wherein a size of a first output image object is scaled relative to the size of a second output image object based on depth data associated with the first output image object and the second output image object. 
     Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  illustrates a high-level diagram of a video depth control (VDC) system in accordance with the described embodiments. 
         FIG. 2  illustrates a high-level diagram of a depth-based image scaling (DBIS) system in accordance with the described embodiments. 
         FIG. 3  is an exemplary monotonically increasing function that defines a set of scaling factors used in a depth-based image scaling (DBIS) system in accordance with the described embodiments. 
         FIG. 4  illustrates a high level exemplary diagram of a combined video depth control (VDC) system and depth-based image scaling (DBIS) system in accordance with the described embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 through 4 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged 3D content processing system. 
     The present disclosure describes systems, apparatuses and methods that address the problems mentioned above by enabling a 3D movie (or video) viewer to adjust (i.e., increase or decrease) the perceived depth to a point that makes the viewer feel more comfortable when viewing the 3D content. In particular, the present disclosure describes systems, apparatuses and methods that: i) reuse or share a low-cost disparity estimator from a motion-compensated temporal interpolation frame rate conversion engine, ii) decrease or increase the perceived depth via a scaling parameter, as well as applying a depth offset, iii) avoid the use of a dedicated occlusion handling system on the stereoscopic images, and iv) use a low-cost model-based warping (MBW) engine that produces high quality stereoscopic image synthesis. In an exemplary embodiment, a system according to the principles of the present disclosure may be fully implemented in hardware on an application-specific integrated circuit (ASIC). 
       FIG. 1  illustrates a high-level diagram of system  100 , which comprises video depth control (VDC) system  120  in accordance with the described embodiments. System  120  was previously described in U.S. patent application Ser. No. 13/556,969, filed Jul. 24, 2012, and was previously incorporated by reference above. System  100  may comprise any of a number of different devices that are capable of performing three-dimensional (3D) image processing. By way of example and not limitation, system  100  may comprise a 3D television set, a digital video recorder (DVR), a digital versatile disc (DVD) player, a computer system capable of executing 3D video applications, a video projector, or any similar device. System  100  comprises 3D content source  110  and VDC system  120 . VDC system  120  comprises disparity estimation circuitry  130 , disparity processing circuitry  140  and warping engine circuitry  150 . 3D content source  110  provides 3D image data to VDC system  120 . In an exemplary embodiment, the 3D image data may comprises a pair of input left and right stereoscopic images, respectively L 1  and R 1 . VDC system  120  generates a pair of output left and right stereoscopic images, respectively Lo 1  and Ro 1 . 
     The nature of 3D content source  110  will vary depending on system  100 . By way of example and not of limitation, if system  100  is a DVD player, 3D content source  110  may be a digital versatile disc. If system  100  is a DVR machine, 3D content source  110  may be a large magnetic storage disc. If system  100  is a computer, 3D content source  110  may be an internal or external hard drive. If system  100  is a 3D television set, 3D content source  110  may be a cable connection that provides the input left (L 1 ) and input right (R 1 ) stereoscopic images. 
     There are two basic methods for producing a perceived depth change on stereoscopic content (i.e., L 1  and R 1 ). The first method is based on shifting the whole depth range “inwards” or “outwards” with respect to the screen surface. This method is known as Horizontal Image Translation. The second method is based on artificial changes of the baseline (separation) of the stereo cameras, where intermediate left and right images are synthesized. The present disclosure describes a system that supports both the baseline method and the Horizontal Image Translation method. 
     Accordingly, in  FIG. 1 , L 1  and R 1  represent a pair of input left and right stereoscopic images, respectively, and Lo 1  and Ro 1  represent a new pair of synthesized stereoscopic left and right images, which produce an increased or decreased perceived depth effect, with respect to the default depth effect produced by L 1  and R 1 , when viewed by the user. Disparity estimation circuitry  130  computes stereo correspondences between L 1  and R 1 , disparity processing circuitry  140  performs conditioning of the computed disparities, and warping engine circuitry  150  warps the input images and performs interpolation in order to synthesize the output images Lo 1  and Ro 1 . VDC system  120  receives user input control signals that control the amount of change in the perceived depth. In an exemplary embodiment, the user input control signals may be provided by a remote control (not shown) operated by the viewer. 
     Disparity Estimation Circuitry  130 — 
     VDC system  120  may receive motion estimation information from an MCTI engine (not shown) that is coupled to VDC system  130  in order to compute disparities in stereoscopic images. The disparities are effectively the horizontal component of the vectors computed from a stereoscopic image pair L 1  and R 1 . Disparity estimation circuitry  130  computes two disparity fields: L-R (from left-to-right) and R-L (from right-to-left). It is assumed that the input images L 1  and R 1  are already rectified by means of some epipolar rectification mechanism (in order to emulate aligned stereo cameras to simplify the matching process). 
     Disparity Processing Circuitry  140 — 
     After the disparities are computed, an adaptive 2D filtering mechanism is applied. In an exemplary embodiment, a bank of two-dimensional filters with different shapes may be used in order to filter the decimated disparity arrays adaptively depending upon the local structure of the disparities. A structure analysis stage may be used in order to select the proper filter according to the local characteristics of the disparities region. Such an adaptive filtering mechanism is designed to fill in the existing occlusion areas in the disparity array while minimizing distortions on the synthesized output images. After filtering, the disparity fields are up-scaled to the original image dimensions. Next, the actual values of the disparities are adjusted in two ways: 1) the disparities are multiplied by a scale factor that has a range comprising both negative and positive values (including zero), and 2) an offset (negative or positive) is added to the disparities. These two adjustments enable the user to adjust the perceived depth when viewing the final 3D outputs. 
     Model-Based Warping (MBW) Engine Circuitry  150 — 
     After the values of the disparities have been scaled by the user control scaling factor, a new pair of stereoscopic images, Lo 1  and Ro 1 , may be synthesized. Warping engine circuitry  150  is based on the use of transformation models that model how a first region of an input image is mapped onto an equivalent region in the warped image. A warped image may have a greater vertical dimension than an input image and also may have a greater horizontal dimension than an input image  310 . 
     Let “p” be a point in an input image. A transformed point, “q”, is obtained in a warped image by applying a transformation function: q=T[p]. The transformation function, T[ ], is a model with its respective parameters. Exemplary models may include, but are not limited to, the following: i) 2nd-degree polynomials (conics) in x and y; and ii) Affine models. These models may be used for the cases where the disparities have both vertical and horizontal components (i.e., when the input images are not aligned or pre-rectified). For the specific case when the vertical component of the disparities is zero (i.e., when using aligned or pre-rectified stereo images, a simplified version of the affine transformation may be used: 
     
       
         
           
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     The present disclosure provides additional depth-based image scaling (DBIS) techniques that may be combined with the video depth control (VDC) techniques described above and in related U.S. patent application Ser. No. 13/556,969, which was incorporated by reference above. 
     The present disclosure provides apparatuses and methods for adjusting the spatial scales (sizes) of at least some selected objects in an image based on the depths of those selected objects. For example, an object that is close to the viewer is scaled spatially so that it occupies a larger area in the image and is therefore perceived to be even closer to the viewer. Thus, in this case, a perspective or scaling cue is manipulated. This, however, can be combined with the baseline adjustment method or with the manipulation of other depth cues, such as texture, shading, and the like, in order to improve the perceived depth changes experienced by the viewer. The advantages provided by the present disclosure are: 1) enhancement of the adjustment of perceived depth by allowing the sizes of objects to change according to their depths; and 2) the system can be combined with other forms of depth adjustment, such as baseline-based view synthesis. 
     There are two well-known methods for producing a perceived depth change on stereoscopic content. The first one is based on shifting the whole depth range inwards or outwards with respect to the screen surface. This method is known as “Horizontal Image Translation”. The second method is based on artificial changes of the baseline (separation) of the stereo cameras where novel, intermediate left and right images are synthesized. 
     The present disclosure does not use either of these two techniques. Instead, the present disclosure describes systems and methods for performing spatial scaling of the objects in the image according to their assigned depth (disparity). 
       FIG. 2  illustrates a high-level diagram of a depth-based image scaling (DBIS) system  200  in system  100  in accordance with the described embodiments. DBIS system  200  comprises depth-based image scaling (DBIS) processor  230  that receives input image  210  and depth map  220  and generates therefrom output image  240 . In  FIG. 2 , it is assumed that the disparity map of input image  210  is available. 
     DBIS system  200  enables the viewer of the 3D content to use a viewer input device (e.g., a TV remote control) to make adjustments (increase or decrease) to the spatial scales (i.e., sizes) of the objects in the image based on their depth in order to make them look a bit farther or a bit closer to the viewer. Thus, in this case, a perspective (or scaling) cue is manipulated. This, however, can be combined with a baseline adjustment method or with the manipulation of other depth cues, such as depth from texture, shading, and the like in order to improve the perceived depth changes experienced by the viewer. 
     The inputs to the proposed depth-based image scaling (DBIS) system  200  disclosed herein are: 1) input image  210 ; and 2) the corresponding depth map  220  of input image  210 ; and 3) user input control parameters. In  FIG. 2 , input image  210  may be either a left input image or a right input image from a stereoscopic image pair. 
     In input image  210 , four (4) objects are indicated: OBJ 1 , OBJ 2 , OBJ 3  and OBJ 4 . For ease of explanation, these four objects are presented as rectangles arranged at various depths. Object OBJ 1  is closest to the viewer and is disposed in front of Object OBJ 2 . Object OBJ 2  is disposed in front of Object OBJ 3  so that Object OBJ 2  is closer to the viewer than Object OBJ 3 . Object OBJ 3  is disposed in front of Object OBJ 4  so that Object OBJ 3  is closer to the viewer than Object OBJ 4 . Thus Object OBJ 1  is closest to the viewer and Object OBJ 4  is farthest from the viewer. Each one of Objects OBJ 1 , OBJ 2 , OBJ 3  and OBJ 4  has corresponding depth information D 1 , D 2 , D 3  and D 4 , respectively, as shown in depth map  220 . 
     Depth-based image scaling (DBIS) processor  230  receives input image  210  and depth map  220 . The output of DBIS processor  230  is a synthesized image, namely output image  240 , where the Objects OBJ 1 , OBJ 2 , OBJ 3  and OBJ 4  have been scaled according to their corresponding depths. Although  FIG. 2  is not to scale, it is intended to convey that the closest object (OBJ 1 ) in input image  210  has been increased the most (as OBJ 1 ′), while the farthest object (OBJ 4 ) has been increased the least or not at all (as OBJ 4 ′). DBIS system  200  may be implemented in an Application-Specific Integrated Circuit (ASIC). 
     In  FIG. 2 , it is assumed that depth map  220  is available. DBIS processor  230  quantizes depth map  230  into K levels or layers where iε{1, 2, . . . , K}. Each layer l i  covers a region R i  (i.e., a set of image locations) from input image  210 , or “I”. Therefore, I={I R1 ∪I R2 ∪ . . . ∪I RK }, which means that the image I is composed of all the sub-images I Ri . For example, in  FIG. 2 , depth map  220  has originally five layers, including the four layers of Objects OBJ 1 , OBJ 2 , OBJ 3  and OBJ 4 , plus the background layer. If no quantization is done, then each layer in depth map  230  will correspond to a sub-image I Ri  in image I. 
       FIG. 3  is an exemplary monotonically increasing function that defines a set of scaling factors used in depth-based image scaling (DBIS) system  200  in accordance with the described embodiments. After the quantizing step above, DBIS processor  230  next performs individual spatial two-dimensional (2D) scaling of each of the sub-images I Ri . Each sub-image is scaled (horizontally and vertically) by its corresponding scaling factor α i . The set of scaling factors S={α i , α 2 , α 3 , . . . , α K } may be defined by means of a 1-D function as shown in  FIG. 3 . The function in  FIG. 3  is a monotonically increasing function. DBIS processor  230  performs the individual scaling of each sub-image I Ri  in order to produce its scaled version I′ Ri . DBIS processor  230  starts the scaling process from the layer corresponding to the image surface (i.e., zero depth), for example, depth D 1  in depth map  220 . By processing and scaling the farthest objects first, the scaling factor at layer i will be greater than that of layer i−1. Thus, the outer areas of the scaled sub-image I′ Ri  will overlap (overwrite) some area from the previous sub-image I′ Ri-1 , which is desirable to avoid holes. 
     The focus of expansion (FOE) {right arrow over (x)} is programmable. It may be defined based on the centroid of the closest object or it may be set to the image center. During the scaling of each sub-image, {right arrow over (x)} is subtracted from the image coordinates, and the result is centered back at {right arrow over (x)}. 
     Post Processing— 
     The overlapping due to scaling mentioned above effectively helps to avoid the appearance of holes in the output synthesized images. However, the final image may still contain a number of holes. DBIS processor  230  may mitigate this problem by applying median filtering to the output image. 
     In an advantageous embodiment of the disclosure, DBIS system  200  may combined with a stereo baseline-based depth adjustment method, the manipulated cues will support each other producing an enhanced depth adjustment experience as desired. 
       FIG. 4  illustrates a high level exemplary diagram of a combined video depth control (VDC) system and depth-based image scaling (DBIS) system in accordance with the described embodiments. An exemplary VDC system was previously described in U.S. patent application Ser. No. 13/556,969 and is discussed further in  FIG. 1  above. In  FIG. 4 , a left input image and a right input image are processed together. 
     Model-based warping (MBW) engine  150   a  receives the left input image LI on a first input and receives left adjusted disparities (DLadj) data from disparity processing block  140  on a second input to produce a warped left input image LI′. Similarly, MBW engine  150   b  receives left depth map DL corresponding to the left input image LI on a first input and receives left adjusted disparities (DLadj) data from disparity processing block  140  on a second input to produce a warped left depth map DL′ corresponding to the warped left input image LI′. 
     Model-based warping (MBW) engine  150   c  receives the right input image RI on a first input and receives right adjusted disparities (DRadj) data from disparity processing block  140  on a second input to produce a warped right input image RI′ Similarly, MBW engine  150   d  receives right depth map DR corresponding to the right input image RI on a first input and receives right adjusted disparities (DRadj) data from disparity processing block  140  on a second input to produce a warped right depth map DR′ corresponding to the warped right input image RI′. 
     DBIS processor  230   a  receives the warped left input image LI′ on a first input and receives the warped left depth map DL′ corresponding to the warped left input image LI′ on a second input. DBIS processor  230   a  then performs the quantizing step, the scaling step, and the post-processing as described above in  FIGS. 2 and 3  to produce the scaled and warped left output image LO′. Similarly, DBIS processor  230   b  receives the warped right input image RI′ on a first input and receives the warped right depth map DR′ corresponding to the warped right input image RI′ on a second input. DBIS processor  230   b  then performs the quantizing step, the scaling step, and the post-processing as described above in  FIGS. 2 and 3  to produce the scaled and warped right output image RO′. The scaled and warped left and right output images, LO′ and RO′, form a stereoscopic pair that may be viewed as 3D content on a 3D TV by the viewer. 
     Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.