# Patent

## Title
Combining stereo image layers for display

## Abstract

A system and method for stereoscopic pair layers includes aligning a left eye image and a right eye image of a first stereo image pair layer according to a first calibrated offset to produce an aligned first stereo image pair layer that appears at a first depth in a display environment. A left eye image and a right eye image of a second stereo image pair layer are aligned according to a second calibrated offset to produce an aligned second stereo image pair layer that appears at a second depth in the display environment that is different than the first depth. The aligned first stereo image pair layer and the aligned second stereo image pair layer combined to produce a calibrated stereoscopic image that is suitable for display.

## Background
BACKGROUND
1. Field of the Invention
The present invention relates generally to the display of stereo images and more specifically to a system and method for combining stereo image layers during playback.
2. Description of the Related Art
Historically, stereo images were displayed using two projectors, one projecting images viewed only by the left eye, and the other projecting images viewed only by the right eye. The left and right eye images were then manually aligned to control the convergence point of the stereo image produced by each left-eye/right-eye image pair projected onto a screen. More recently, the use of single lens stereo projection systems, has made adjusting the convergence point of a stereo image impossible when the stereo image is displayed.
When stereo image content is created, a displayed image size is assumed, and the perceived distance from the viewer where objects appear in a scene (e.g., in front of the screen, coincident with the screen, or behind the screen) is controlled by the author of the stereo image content assuming a predetermined alignment between the left and right eye image pairs. The predetermined alignment corresponds to the assumed displayed image size. One problem with such as approach is that, when the image content is displayed on a smaller or larger screen, the perceived distance of the objects in the scene is affected as a result of an increased or decreased image pair alignment. In some cases, the increased or decreased alignment causes a viewer to experience discomfort due to eye strain or eye fatigue. This problem is further illustrated below in FIGS. 1A-1F.
FIG. 1A is an illustration of a prior art stereoscopic geometry with a convergence depth 111 that equals the display surface depth. A left eye 101 and right eye 102 are separated by an interoccular separation 105. An object that has no separation for the left eye image relative to the right eye image is perceived to appear coincident with display surface 104. In other words, objects that are not separated in the left and right eye images appear in the plane of the display surface. The intersection of the view vectors from left eye 101 and right eye 105 is convergence point 110, which is shown as coincident with display surface 104. During construction of a stereoscopic image, the alignment of left and right eye views for objects in the scene is determined by the author and controls the perceived depth at which the objects appear to a viewer.
FIG. 1B is an illustration of a prior art stereoscopic geometry with a convergence depth 122 that is less than the depth of display surface 104. An object that is offset to the left by stereo image offset 125 in the right eye image compared with the left eye image appears to the viewer at convergence point 120 (i.e., in front of display surface 104). When the right eye image and left eye image are scaled up, the convergence point shifts closer to the viewer. FIG. 1C is an illustration of a prior art stereoscopic geometry for a larger display surface 114 with a convergence depth 123 that is less than the intended convergence depth 122. As shown, as stereo images are scaled to fit the larger display surface 114 (relative to the display surface 104), stereo image offset 125 is scaled to equal larger stereo image offset 124. The viewer may experience discomfort due to increased cross-eyedness as a result of larger stereo image offset 124 since objects in the scene appear at convergence point 121 instead of at convergence point 120.
FIG. 1D is an illustration of a prior art stereoscopic geometry with a convergence depth 127 that is greater than the depth of display surface 104. An object that is offset to the right by stereo image offset 126 in the right eye image compared with the left eye image appears to the viewer at convergence point 123 (i.e., behind display surface 104). When the right eye image and left eye image are scaled up, the convergence point shifts further from the viewer. Objects that are separated by interoccular separation 105 in the left eye and right eye images appear at infinity. FIG. 1E is an illustration of a prior art stereoscopic geometry for larger display surface 114 with a convergence depth 128 that is greater than the intended convergence depth 127 since the separation between the left eye and right eye images is greater than interoccular separation 105. As shown, as stereo images are scaled to fit the larger display surface 114 (relative to the display surface 104) stereo image offset 126 is scaled to equal larger stereo image offset 129 as the stereo images are scaled to fit larger display surface 114. The viewer more than likely may see double images or experience discomfort due to increased divergence as a result of larger stereo image offset 129 since objects in the scene appear beyond infinity instead of at convergence point 123.
Similarly, when the right eye image and left eye image are scaled down, the convergence point shifts closer to the viewer and objects that were intended to appear behind the screen may appear coincident with the screen. FIG. 1F is an illustration of prior art stereoscopic geometry for a smaller display surface 134 with convergence depth 137 that is less than the intended convergence depth 127. As shown, as stereo images are scaled to fit the smaller display surface 134 (relative to the display surface 104) stereo image offset 126 is scaled to equal smaller stereo image offset 136. Again, objects in the scene do not appear at the depths that were intended when the stereoscopic content was created since the stereo image offset used to produce the content does not match smaller stereo image offset 136.
As the foregoing illustrates, what is needed in the art is the ability to modify the alignment between stereoscopic images based on the size of the display surface when a single lens stereo projection system is used.
SUMMARY
A system and method for combining stereoscopic image layers for display allows for calibration of the stereo image content for each display environment. An offset between displayed stereo image pairs may be characterized and adjusted for each stereo image pair layer to control the perceived depth at which each layer appears to a viewer. The stereo image pair layers are combined to produce a combined stereo image pair for display. The stereo image content is typically authored assuming a particular display image size. When the stereo image content is displayed in a display environment that does not conform to the particular display image size the offset between displayed stereo image pair layers is increased or decreased, resulting in a viewing experience that is different than intended. In some cases, the viewer may experience discomfort due to eye strain or eye fatigue. Adjusting the offset during the playback of the stereo image content may improve the viewer experience.
A system and method for combining stereoscopic pair layers includes aligning a left eye image and a right eye image of a first stereo image pair layer according to a first calibrated offset to produce an aligned first stereo image pair layer that appears at a first depth in a display environment, aligning a left eye image and a right eye image of a second stereo image pair layer according to a second calibrated offset to produce an aligned second stereo image pair layer that appears at a second depth in the display environment that is different than the first depth, and combining the aligned first stereo image pair layer and the aligned second stereo image pair layer to produce a calibrated stereoscopic image that is suitable for display.
Various embodiments of the invention include a stereoscopic image system for combining stereoscopic pair layers. The system includes a display processor configured to align a left eye image and a right eye image of a first stereo image pair layer according to a first calibrated offset to produce an aligned first stereo image pair layer that appears at a first depth and align a left eye image and a right eye image of a second stereo image pair layer according to a second calibrated offset to produce an aligned second stereo image pair layer that appears at a second depth that is different than the first depth. The display processor is configured to combine the aligned first stereo image pair layer and the aligned second stereo image pair layer to produce a calibrated stereoscopic image that is suitable for display.



BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1A is an illustration of a prior art stereoscopic geometry with a convergence depth that equals the display surface depth;
FIG. 1B is an illustration of a prior art stereoscopic geometry with a convergence depth that is less than the display surface depth;
FIG. 1C is an illustration of a prior art stereoscopic geometry for a larger display surface with a convergence depth that is less than the display surface depth;
FIG. 1D is an illustration of a prior art stereoscopic geometry with a convergence depth that is greater than the display surface depth;
FIG. 1E is an illustration of a prior art stereoscopic geometry for a larger display surface with convergence depth that is greater than the display surface depth;
FIG. 1F is an illustration of a prior art stereoscopic geometry for a smaller display surface with convergence depth that is less than the display surface depth;
FIG. 2A is an illustration of stereoscopic geometry for a larger display surface using an adjusted stereo image offset, according to one embodiment of the present invention;
FIG. 2B is an illustration of stereoscopic geometry for a smaller display surface using an adjusted stereo image offset, according to one embodiment of the present invention;
FIG. 2C is an illustration of a display system with associated stereoscopic geometry, according to one embodiment of the present invention;
FIG. 3A is a flow diagram of method steps for characterizing and adjusting a convergence point for playback of a stereo content, according to one embodiment of the present invention;
FIG. 3B is a flow diagram of method steps for characterizing and adjusting a convergence point for playback of a stereo content using a dynamic adjustment factor, according to another embodiment of the present invention;
FIG. 4A is an illustration of stereoscopic geometry for a display system configured to combine multiple stereoscopic pair layers, according to one embodiment of the present invention;
FIG. 4B is a flow diagram of method steps for combining multiple stereoscopic pair layers for playback of a stereo content, according to one embodiment of the present invention;
FIG. 4C is a flow diagram of method steps for characterizing, aligning, and combining multiple stereoscopic pair layers for playback of a stereo content, according to one embodiment of the present invention; and
FIG. 5 is a block diagram of a system configured to implement one or more aspects of the present invention.



DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Embodiments of the invention provide a method and system for adjusting the convergence point of a stereoscopic image displayed on a display environment by determining a characterized offset between a left eye image and a right eye image of a stereo image pair in a display environment. When the characterized offset does not equal a predetermined offset value an adjustment factor is determined. The adjustment factor is applied to the characterized offset to adjust the convergence point for the display environment by producing a calibrated offset between the left eye image and the right eye image of the stereo image pair.
Additionally, embodiments of the invention provide a method and system for combining stereoscopic pair layers, as described in conjunction with FIGS. 4A, 4B, and 4C. A left eye image and a right eye image of a first stereo image pair layer is aligned according to a first calibrated offset to produce an aligned first stereo image pair layer that appears at a first depth in a display environment. A left eye image and a right eye image of a second stereo image pair layer are aligned according to a second calibrated offset to produce an aligned second stereo image pair layer that appears at a second depth in the display environment that is different than the first depth. The aligned first stereo image pair layer and the aligned second stereo image pair layer combined to produce a calibrated stereoscopic image that is suitable for display.
FIG. 2A is an illustration of stereoscopic geometry for a larger display surface 214 using an adjusted stereo image offset 226, according to one embodiment of the present invention. A left eye 201 and a right eye 202 are separated by an interoccular separation 205. Rather than simply scaling the left eye image and the right eye image for display on larger display surface 214, thereby increasing the stereo image offset, the alignment of the left eye image and right eye image is modified to reduce the actual stereo image offset to equal calibrated stereo image offset 226. Calibrated stereo image offset 226 equals a predetermined offset that corresponds to the convergence point 223 and convergence depth 227 originally intended by the content author. With this technique, objects in the stereoscopic image intended to appear at a particular depth, based on an assumed screen size used to create the image content, will appear at that depth when the image is scaled to fit larger display surface 214. Consequently, the likelihood that a viewer will experience eyestrain resulting from scaling up stereo images is reduced.
Advantageously, since calibrated stereo image offset 226 is used to align stereo image pairs as they are scaled up or down at the time of display, stereo image pairs authored for particular screen sizes may be adjusted using different image offsets and displayed on a variety of different screen sizes. Thus, different sets of image pairs do not need to be created for each target screen size.
FIG. 2B is an illustration of stereoscopic geometry for a smaller display surface 234 using a calibrated stereo image offset 236, according to one embodiment of the present invention. Rather than simply scaling the left eye image and the right eye image for display on smaller display surface 234, thereby decreasing the stereo image offset, the alignment of the left eye image and right eye image is modified to increase the actual stereo image offset to equal calibrated stereo image offset 226. Again, calibrated stereo image offset 226 equals a predetermined offset that corresponds to the convergence point 233 and convergence depth 237 originally intended by the content author. Similar to that described above, with this technique objects in the stereoscopic image intended by the content author to appear at a particular depth, based on an assumed screen size used to create the image content, will appear at that particular depth when the content is scaled to fill smaller display surface 234. In this fashion, the likelihood that a viewer will experience eyestrain resulting from scaling down stereo images is reduced.
FIG. 2C is an illustration of a display system 250 with associated stereoscopic geometry, according to one embodiment of the present invention. Display system 250 may include a media center and projector that is configured to project stereo images onto a display surface 200. In an alternative embodiment, display surface 200 may be a flat panel display, and display system 250 may provide data to produce an image on display surface 200. In the configuration shown, a viewer may be positioned either in front of or behind display surface 200. Characterized offset 252 is the actual image offset produced by any scaling of the stereo images being displayed on display surface 200. The value of characterized offset 252 is first determined, and then the left eye image and the right eye image are aligned by modifying the (actual image) offset to equal a calibrated offset 254. Calibrated offset 254 should equal the predetermined offset that was used to create the stereo image content. As persons skilled in the art will appreciate, when the offset requires no adjustment to equal calibrated offset 254, display surface 200 is the display size used to create the stereo image content.
As also shown in FIG. 2C, characterized offset 252 is larger than calibrated offset 254, indicating that the stereo image pair was scaled up by display system 250 for display on display surface 200. Display system 250 is configured to adjust the alignment between the left and right eye images by modifying the offset that initially equals characterized offset 252, to match calibrated offset 254 before projecting the stereo image pair onto display surface 200. Typically, the alignment is adjusted in the horizontal direction.
FIG. 3A is a flow diagram of method steps for characterizing and adjusting a convergence point for playback of a stereo content, according to one embodiment of the present invention. Although the method steps are described with respect to FIGS. 2A-2C, persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention.
The method begins in step 300, where characterization data for a display environment is determined. Several techniques may be used to determine the characterization data. For example, the stereo image offset between a left and a right eye image of a stereo pair, such as characterized offset 252, may be measured to produce the characterization data. The characterization data may be determined by projecting a stereoscopic test pattern onto display surface 200 and physically measuring a characteristic of the displayed stereoscopic text pattern to determine characterized offset 252. The measured characteristic can be a distance between elements of the stereoscopic test pattern, such as crosshairs, circles or other shapes, a diameter or radius of a shape, and the like. Alternatively, characterized offset 252 is encoded as part of the stereoscopic test pattern, such that the displayed stereoscopic test pattern visually indicates the value of characterized offset 252. Various different values of characterized offset 252 are encoded in the stereoscopic test pattern, and the value that corresponds to the particular display environment is visible in the displayed stereoscopic test pattern.
Alternatively, in step 300, the characterization data may be computed based on the screen size, the predetermined offset used to create the stereoscopic image content, and the size of display surface 200. The predetermined offset may be a standard human interoccular distance, such as interoccular distance 205. In other embodiments of the present invention, the characterization data may be determined using a physical device to calibrate display system 250. The physical device may indicate the length of calibrated offset 254 and the offset between the left and right eye images may be dynamically adjusted by display system 250 while a stereoscopic test pattern is displayed. When the offset matches calibrated offset 254, the characterization data can be determined by display system 250 based on the adjustment that was applied.
If, in step 305, a determination is made that the characterized offset 252 matches the calibrated offset 254, i.e., that the actual offset is correct, then no adjustment of the alignment between the left and right eye images is needed to produce the convergence point intended by the content author. The method then proceeds directly to step 330, where the stereoscopic images are displayed using characterized offset 252. Otherwise, if characterized offset 252 is determined to not match calibrated offset 254, then in step 310, display system 250 determines if calibration is enabled for displaying the stereoscopic content. If calibration is not enabled, then the method proceeds directly to step 330, where the stereoscopic images are displayed using characterized offset 252. In some use scenarios, displaying the stereoscopic content without adjusting the offset between stereo pairs may be desirable. For example, characterized offset 252 may be considered to be correct when it is within a threshold of calibrated offset 254. The threshold may be a percentage of calibrated offset 254 or a value that is fixed or specified by a viewer, content author, or display system 254.
If, in step 310, display system 250 determines that calibration is enabled, then in step 320, an adjustment factor is determined. The adjustment factor may be computed using the characterization data. For example, the adjustment factor may be a ratio of the size of display surface 200 to the screen size assumed by the content author when creating the image content or a ratio of characterized offset 252 to calibrated offset 254. The adjustment factor may also be determined when the physical device is used to calibrate display system 250.
In step 325, the adjustment factor is applied by display system 250 to produce an adjusted offset between the left and right eye images of each stereo pair in the stereoscopic content. Specifically, using the adjustment factor, display system 250 adjusts the offset, as needed, to equal calibrated offset 254. In step 330, the images are output by display system 250 for display on display surface 200 using calibrated offset 254. Just as a threshold may be used to determine whether or not the offset is correct, a threshold may be used to adjust the offset to be within a certain range of calibrated offset 254. In other words, characterized offset 252 may be adjusted to equal calibrated offset 254 plus or minus the threshold. The threshold may be a percentage of calibrated offset 254 or a value that is fixed or specified by a viewer, content author, or display system 250.
In some cases, all of the stereo image pairs of the stereo content may be displayed using a single adjustment factor. In other cases, it may be desirable to dynamically change the adjustment factor. For such a purpose, additional characterization data may be encoded within the stereo content. For example, an author of the stereo content may want to change a viewer's focus from an actor's face, having an associated convergence point on display surface 200, to distant vista, having no convergence point, with separation equal to the interoccular separation. The author may change the convergence point for each frame (i.e., each stereo image pair), each shot, or at any other desired frequency. The additional characterization data that is encoded within the stereo content represents changes in the convergence point, i.e., animates the convergence point.
FIG. 3B is a flow diagram of method steps for characterizing and adjusting a convergence point for playback of a stereo content using a dynamic adjustment factor, according to another embodiment of the present invention. Although the method steps are described in reference to FIGS. 2A-2C, persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention.
In one embodiment, steps 300, 305, 310, and 320 are first performed as described above in FIG. 3A. Therefore, no additional description is provided herein. The method then process to step 340, where display system 250 determines if the stereo content includes additional characterization data indicating that the adjustment factor used to control the convergence point should be determined dynamically. If not, the method proceeds directly to step 350. Otherwise, in step 345, the adjustment factor is updated to reflect the convergence point specified by the additional characterization data. In step 350, the adjustment factor is applied by display system 250 to produce calibrated offset 254 between the left and right eye images of each stereo pair in the stereo content. When the adjustment factor is dynamic, reflecting updates from step 345, calibrated offset 254 varies as the adjustment factor varies, thereby producing a dynamic convergence point. In step 355, the stereo image pair is output by display system 250 for display on display surface 200 using calibrated offset 254. Steps 340, 345, 350, and 355 are repeated for each stereo pair in the stereo content.
Adjusting the offset between the stereo images enables display system 250 to replicate the viewer experience that was intended by the author of the stereo content. Additionally, viewer discomfort due to eye strain or eye fatigue may be reduced or avoided when the stereo content is scaled up or down from the intended display size. Finally, performing the offset adjustment in display system 250 allows for stereo content to be retargeted to different display sizes without regenerating the stereo content.
Combining Stereoscopic Image Pair Layers
During the generation of stereo image content an object in the left eye and right eye images are offset based on how close or far from a viewer the object should appear when the stereo image content is displayed. Once the objects are composited to generate each left eye and right eye image pair the relative depths of different objects is fixed. In other words an object in the background will appear behind an object in the foreground of a scene. After the objects are composited, the object in the background cannot be made to appear in front of an object in the foreground.
In order to provide greater control over the relative depths of objects in the stereo image content, two or more stereoscopic image layers may be generated that are combined at the time of display. For example, a first layer may include a stereo image pair with text for the title and credits and a second layer may include a stereo image pair with a background. An offset between the left eye image and right eye image of each stereo pair layer can be adjusted to control the depth at which each layer appears to a viewer. A first offset for the first layer may be adjusted so that the first layer appears in front of, coincident with, or behind the second layer. After the offsets for each layer are adjusted, the layers are combined to produce a stereo image pair for display.
In addition to providing the ability to control the relative depth of the different layers, the offsets can be adjusted to reduce viewer discomfort due to eye strain or eye fatigue when the stereo image content is displayed in a display environment that does not conform to the display image size used to author the content. Adjusting the offset during the playback of the stereo image content to compensate for scaling the stereo content for a particular display environment and allow control of the convergence point position to match the position intended by the content author.
FIG. 4A is an illustration of stereoscopic geometry for a display system configured to combine multiple stereoscopic pair layers, according to one embodiment of the present invention. Three stereo pair layers are shown in FIG. 4A, a screen stereo pair layer 402 that is coincident with a display surface 414, a behind stereo pair layer 401 and a front stereo pair layer 403. Screen stereo pair layer 402, behind stereo pair layer 401, and front stereo pair layer 403 each include a left eye image and a right eye image. When each layer is viewed using a calibrated offset that matches an intended offset for that layer, the layers are perceived by a viewer to appear at display surface 414, behind convergence depth 421, and front convergence depth 423, respectively.
Front stereo pair layer 403, screen stereo pair layer 402, and behind stereo pair layer 401 are combined to produce a combined left eye stereo image and a combined right eye stereo image. The stereo pair layers may be combined in a front-to-back order or a back-to-front order to produce the combined stereo image pair. In some embodiments, only two stereo pair layers are combined to produce the stereo image pair for display. In other embodiments, more than two or three stereo image pair layers are combined to produce the stereo image pair for display.
FIG. 4B is a flow diagram of method steps for combining multiple stereoscopic pair layers for playback of a stereo content, according to one embodiment of the present invention. The steps shown in FIG. 4B are performed to produce a combined stereo image pair that is suitable for display in a stereoscopic display environment, such as display system 250. Although the method steps are described in reference to FIG. 4A, persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention.
In step 400 a left eye image and a right eye image of a first stereo pair layer, e.g., front stereo pair layer 403, screen stereo pair layer 402, behind stereo pair layer 401, and the like, is aligned according to a calibrated offset that corresponds to front convergence depth 423. In step 405 a left eye image and a right eye image of a first stereo pair layer, e.g., front stereo pair layer 403, screen stereo pair layer 402, or behind stereo pair layer 401, is aligned according to a calibrated offset that corresponds to an respective convergence depth, e.g., front convergence depth 423, screen convergence depth 422, or behind convergence depth 421. In step 410 the aligned first stereo image pair layer is combined with the aligned other stereo image pair layer to produce a calibrated stereoscopic layer that is suitable for display.
In step 415 the method determines if another layer is provided to produce the calibrated stereoscopic image, and, if so, steps 405, 410, and 415 are repeated for each additional stereo pair layer to produce the combined stereo pair image. When all of the stereo pair layers have been combined, in step 420 the combined stereo image pair is displayed in the display environment. Note, that in some embodiments, all of the stereo pairs may be aligned and then all combined to produce the combined stereo pair image pair.
As previously described, when the stereo pair images are scaled for display on a display surface that is larger or smaller than the intended display size, the actual offset between the left eye image and the right eye image within a stereo pair may not equal the calibrated offset of the display environment. Similarly, when stereo pair layers are scaled for display, the actual offset for one or more of the stereo pair layers may not equal the respective calibrated offset for the display environment. Consequently, the convergence depths for each layer or the combined stereo image may cause viewer eye strain or eye fatigue when used to display the stereo image rather than the calibrated offsets.
FIG. 4C is a flow diagram of method steps for characterizing, aligning, and combining multiple stereoscopic pair layers for playback of a stereo content, according to one embodiment of the present invention. The steps shown in FIG. 4C are performed to produce a combined stereo image pair that is suitable for display in a stereoscopic display environment, such as display system 250. Although the method steps are described in reference to FIG. 4A, persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention.
The method begins in step 425, where characterization data for a display environment is determined. As previously described with reference to step 300 of FIG. 3A, several techniques may be used to determine the characterization data. In step 430, an adjustment factor is determined. The adjustment factor may be computed using the characterization data. For example, the adjustment factor may be a ratio of the size of display surface 414 to the screen size assumed by the content author when creating the image content or a ratio of the characterized offset to the calibrated offset for the stereo pair layer. The adjustment factor may also be determined by increasing or decreasing the offset that initially equals the characterized offset to equal the calibrated offset and measuring the amount that the offset was increased or decreased.
In step 435 the method determines if another layer is provided to produce the calibrated stereoscopic image, and, if so, steps 425, 430, and 435 are repeated for each additional stereo pair layer to determine the characterization data and adjustment factor for each stereo pair layer. When the characterization data and adjustment factor for each stereo pair layer has been determined, in step 440, the adjustment factor for the first stereo pair layer is applied by display system 250 to produce an aligned first stereo image pair layer. Specifically, using the adjustment factor, display system 250 adjusts the offset for the first stereo pair layer, as needed, to equal the calibrated offset for the first stereo pair layer. In step 445, the adjustment factor for another stereo pair layer is applied by display system 250 to produce an aligned other stereo image pair layer. Specifically, using the adjustment factor, display system 250 adjusts the offset for the other stereo pair layer, as needed, to equal the calibrated offset for the other stereo pair layer.
A threshold may be used to adjust the offset for each stereo pair layer to be within a certain range of the calibrated offset for that stereo pair layer. In other words, the offset may be adjusted to equal the calibrated offset plus or minus the threshold. The threshold may be a percentage of the calibrated offset or a value that is fixed or specified by a viewer, content author, or display system 250.
In step 450 the aligned first stereo image pair layer is combined with the aligned other stereo image pair layer to produce a calibrated stereoscopic layer that is suitable for display. If, in step 455 the method determines that another layer is provided to produce the calibrated stereoscopic image then, steps 445, 450, and 455 are repeated for each additional stereo pair layer to produce the combined stereo pair image. When all of the stereo pair layers have been combined, in step 460 the combined stereo image pair is displayed in the display environment. Note, that in some embodiments, all of the stereo pairs may be aligned and then all combined to produce the combined stereo pair image pair.
Multiple stereo pair layers may be combined at the time of display to control the depth at which objects in the scene are perceived to appear to a viewer. The offset between a left eye image and a right eye image may be adjusted for each layer to control the convergence point for each layer. The offset for each stereo pair layer may be characterized in the display environment and adjusted to improve the viewer experience. When the stereo pair layers are scaled for display on a surface that is larger or smaller than the size of the display that was assumed during generation of the stereo pair layers, the offset for each layer may be calibrated to reduce viewer discomfort due to eye strain or eye fatigue.
FIG. 5 is a block diagram of a system 500 configured to implement one or more aspects of the present invention. System 500 may be a personal computer, video game console, personal digital assistant, or any other device suitable for practicing one or more embodiments of the present invention. Any number of the elements shown in system 500 may be included in display system 250.
As shown, system 500 includes a central processing unit (CPU) 502 and a system memory 504 communicating via a bus path that may include a memory bridge 505. CPU 502 includes one or more processing cores, and, in operation, CPU 502 is the master processor of system 500, controlling and coordinating operations of other system components. System memory 504 stores software applications and data for use by CPU 502. CPU 502 runs software applications and optionally an operating system. Memory bridge 505, which may be, e.g., a Northbridge chip, is connected via a bus or other communication path (e.g., a HyperTransport link) to an I/O (input/output) bridge 507. I/O bridge 507, which may be, e.g., a Southbridge chip, receives user input from one or more user input devices 508 (e.g., keyboard, mouse, joystick, digitizer tablets, touch pads, touch screens, still or video cameras, motion sensors, and/or microphones) and forwards the input to CPU 502 via memory bridge 505.
A display processor 512 is coupled to memory bridge 505 via a bus or other communication path (e.g., a PCI Express, Accelerated Graphics Port, or HyperTransport link); in one embodiment display processor 512 is a graphics subsystem that includes at least one graphics processing unit (GPU) and graphics memory. Graphics memory includes a display memory (e.g., a frame buffer) used for storing pixel data for each pixel of an output image. Graphics memory can be integrated in the same device as the GPU, connected as a separate device with the GPU, and/or implemented within system memory 504.
Display processor 512 periodically delivers pixels to a display device 510 (e.g., a screen or conventional CRT, plasma, OLED, SED or LCD based monitor). Additionally, display processor 512 may output pixels to film recorders adapted to reproduce computer generated images on photographic film. Display processor 512 can provide display device 510 with an analog or digital signal.
A system disk 514 is also connected to I/O bridge 507 and may be configured to store stereo content and applications and data for use by CPU 502 and display processor 512. System disk 514 provides non-volatile storage for applications and data and may include fixed or removable hard disk drives, flash memory devices, and CD-ROM, DVD-ROM, Blu-ray, HD-DVD, or other magnetic, optical, or solid state storage devices.
A switch 516 provides connections between I/O bridge 507 and other components such as a network adapter 518 and various add-in cards 520 and 521. Network adapter 518 allows system 500 to communicate with other systems via an electronic communications network, and may include wired or wireless communication over local area networks and wide area networks such as the Internet.
Other components (not explicitly shown), including USB or other port connections, film recording devices, and the like, may also be connected to I/O bridge 507. For example, an audio processor may be used to generate analog or digital audio output from instructions and/or data provided by CPU 502, system memory 504, or system disk 514. Communication paths interconnecting the various components in FIG. 5 may be implemented using any suitable protocols, such as PCI (Peripheral Component Interconnect), PCI Express (PCI-E), AGP (Accelerated Graphics Port), HyperTransport, or any other bus or point-to-point communication protocol(s), and connections between different devices may use different protocols as is known in the art.
In one embodiment, display processor 512 incorporates circuitry optimized for graphics and video processing, including, for example, video output circuitry, and constitutes a graphics processing unit (GPU). In another embodiment, display processor 512 incorporates circuitry optimized for general purpose processing. In yet another embodiment, display processor 512 may be integrated with one or more other system elements, such as the memory bridge 505, CPU 502, and I/O bridge 507 to form a system on chip (SoC). In still further embodiments, display processor 512 is omitted and software executed by CPU 502 performs the functions of display processor 512.
Pixel data can be provided to display processor 512 directly from CPU 502. In some embodiments of the present invention, instructions and/or data representing a scene are provided to a renderfarm or a set of server computers, each similar to system 500, via network adapter 518 or system disk 514. The renderfarm generates one or more rendered images of the scene using the provided instructions and/or data. These rendered images may be stored on computer-readable media in a digital format and optionally returned to system 500 for display. Similarly, stereo image pairs processed by display processor 512 may be output to other systems for display, stored in system disk 514, or stored on computer-readable media in a digital format.
Alternatively, CPU 502 provides display processor 512 with data and/or instructions defining the desired output images, from which display processor 512 generates the pixel data of one or more output images, including characterizing and/or adjusting the offset between stereo image pairs. The data and/or instructions defining the desired output images can be stored in system memory 504 or graphics memory within display processor 512. In an embodiment, display processor 512 includes 3D rendering capabilities for generating pixel data for output images from instructions and data defining the geometry, lighting shading, texturing, motion, and/or camera parameters for a scene. Display processor 512 can further include one or more programmable execution units capable of executing shader programs, tone mapping programs, and the like.
CPU 502, renderfarm, and/or display processor 512 can employ any surface or volume rendering technique known in the art to create one or more rendered images from the provided data and instructions, including rasterization, scanline rendering REYES or micropolygon rendering, ray casting, ray tracing, image-based rendering techniques, and/or combinations of these and any other rendering or image processing techniques known in the art.
It will be appreciated that the system shown herein is illustrative and that variations and modifications are possible. The connection topology, including the number and arrangement of bridges, may be modified as desired. For instance, in some embodiments, system memory 504 is connected to CPU 502 directly rather than through a bridge, and other devices communicate with system memory 504 via memory bridge 505 and CPU 502. In other alternative topologies display processor 512 is connected to I/O bridge 507 or directly to CPU 502, rather than to memory bridge 505. In still other embodiments, I/O bridge 507 and memory bridge 505 might be integrated into a single chip. The particular components shown herein are optional; for instance, any number of add-in cards or peripheral devices might be supported. In some embodiments, switch 516 is eliminated, and network adapter 518 and add-in cards 520, 521 connect directly to I/O bridge 507.
Various embodiments of the present invention may be implemented as a program product for use with a computer system. The program(s) of the program product define functions of the embodiments (including the methods described herein) and can be contained on a variety of computer-readable storage media. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored.
The invention has been described above with reference to specific embodiments and numerous specific details are set forth to provide a more thorough understanding of the present invention. Persons skilled in the art, however, will understand that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The foregoing description and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

## Claims

1. A method for combining stereoscopic pair layers, the method comprising:
receiving a first left eye image and a first right eye image of a first stereo image pair layer, wherein the first left eye image is aligned with the first right eye image according to a first predetermined offset value used when the first stereo image pair layer was created to produce the first stereo image pair layer that appears at a first convergence depth in a display environment;
receiving a second left eye image and a second right eye image of a second stereo image pair layer, wherein the second left eye image is aligned with the second right eye image according to a second predetermined offset value to produce the second stereo image pair layer that appears at a second convergence depth in the display environment that is different than the first convergence depth;
combining the first left eye image and the second left eye image to produce a combined left eye image of a stereoscopic image that is suitable for display; and
combining the first right eye image and the second right eye image to produce a combined right eye image of the stereoscopic image.

2. The method of claim 1, wherein the first convergence depth is coincident with a display surface in the display environment.

3. The method of claim 2, wherein the second convergence depth is behind the display surface in the display environment.

4. The method of claim 2, wherein the second convergence depth is in front of the display surface in the display environment.

5. The method of claim 1, further comprising the steps of:
receiving a third left eye image and a third right eye image of a third stereo image pair layer, wherein the third left eye image is aligned with the third right eye image according to a third predetermined offset value used when the first stereo image pair layer was created to produce the third stereo image pair layer that appears at a third convergence depth in the display environment that is different than the first convergence depth and the second convergence depth;
combining the third left eye image with the first left eye image and the second left eye image to produce the combined left eye image; and
combining the third right eye image with the first right eye image and the second right eye image to produce the combined right eye image.

6. The method of claim 1, further compromising the step of determining a characterized offset that is an offset between the first left eye image and the first right eye image of the first stereo image pair layer in the display environment.

7. The method of claim 6, further comprising the step of determining that the characterized offset does not equal the first predetermined offset value.

8. The method of claim 7, wherein the first predetermined offset value is greater than the characterized offset.

9. The method of claim 7, wherein the first predetermined offset value is less than the characterized offset.

10. The method of claim 7, wherein the characterized offset is determined to not equal the first predetermined offset value when the characterized offset is not within a threshold of the first predetermined offset value.

11. The method of claim 6, wherein a ratio of the first predetermined offset value to the characterized offset equals a ratio of a dimension of an intended display surface used when the first stereo image pair layer was created to the dimension of a display surface in the display environment.

12. The method of claim 11, wherein the dimension is a horizontal width.

13. The method of claim 6, wherein the step of determining a characterized offset comprises displaying a stereoscopic test pattern in the display environment.

14. The method of claim 13, wherein the step of determining a characterized offset comprises measuring a characteristic of the stereoscopic test pattern in the display environment.

15. The method of claim 13, wherein the characterized offset is encoded as part of the stereoscopic test pattern and a value of the characterized offset is indicated when the stereoscopic test pattern is displayed in the display environment.

16. The method of claim 6, wherein step of determining a characterized offset comprises increasing or decreasing the offset until the offset equals the first predetermined offset value to determine an adjustment factor that can be applied to the offset to produce the first predetermined offset value during the display of the first stereo image pair layer in the display environment.

17. The method of claim 1, further comprising the steps of:
determining that the first predetermined offset value has changed from a first value to a second value between a first frame and a second frame; and
aligning a left eye image and a right eye image of a first stereo image pair layer for the second frame according to the changed first predetermined offset value to produce an aligned first stereo image pair layer for the second frame that appears at a third convergence depth, the third convergence depth being different than the first convergence depth.

18. The method of claim 1, wherein the first predetermined offset value is encoded with the first stereo image pair layer and the second predetermined offset value is encoded with the second stereo image pair layer.

19. The method of claim 1, wherein a width of an intended display surface used when the first stereo image pair was created is different than a width of a display surface in the display environment.

20. A non-transitory computer readable medium storing instructions for causing a processor to combine stereoscopic pair layers by performing the steps of:
receiving a first left eye image and a first right eye image of a first stereo image pair layer, wherein the first left eye image is aligned with the first right eye image according to a first predetermined offset value used when the first stereo image pair was created to produce the first stereo image pair layer that appears at a first convergence depth in a display environment;
receiving a second left eye image and a second right eye image of a second stereo image pair layer, wherein the second left eye image is aligned with the second right eye image according to a second predetermined offset value to produce the second stereo image pair layer that appears at a second convergence depth in the display environment that is different than the first convergence depth;
combining the first left eye image and the second left eye image to produce a combined left eye image of a stereoscopic image that is suitable for display; and
combining the first right eye image and the second right eye image to produce a combined right eye image of the stereoscopic image.

21. The non-transitory computer readable medium of claim 20, wherein a width of an intended display surface used when the first stereo image pair was created is different than a width of a display surface in the display environment.

22. A stereoscopic image system, comprising:
a memory configured to store instructions for combining a first stereo image pair layer and a second stereo image pair layer; and
a display processor configured to:
receive a first left eye image and a first right eye image of a first stereo image pair layer, wherein the first left eye image is aligned with the first right eye image according to a first predetermined offset value used when the first stereo image pair was created to produce the first stereo image pair layer that appears at a first convergence depth in a display environment;
receive a second left eye image and a second right eye image of a second stereo image pair layer, wherein the second left eye image is aligned with the second right eye image according to a second predetermined offset value to produce the second stereo image pair layer that appears at a second convergence depth in the display environment that is different than the first convergence depth;
combine the first left eye image and the second left eye image to produce a combined left eye image of a stereoscopic image that is suitable for display; and
combine the first right eye image and the second right eye image to produce a combined right eye image of the stereoscopic image.

23. The system of claim 22, wherein the first convergence depth is coincident with a display surface in the display environment.

24. The system of claim 23, wherein the second convergence depth is behind the display surface in the display environment.

25. The system of claim 23, wherein the second convergence depth is in front of the display surface in the display environment.

26. The system of claim 22, wherein the display processor is further configured to:
receive a third left eye image and a third right eye image of a third stereo image pair layer, wherein the third left eye image is aligned with the third right eye image according to a third predetermined offset value used when the first stereo image pair layer was created to produce the third stereo image pair layer that appears at a third convergence depth in the display environment that is different than the first convergence depth and the second convergence depth;
combine the third left eye image with the first left eye image and the second left eye image to produce the combined left eye image; and
combine the third right eye image with the first right eye image and the second right eye image to produce the combined right eye image.

27. The system of claim 22, wherein the display processor is further configured to determine a characterized offset that is an offset between the first left eye image and the first right eye image of the first stereo image pair layer in the display environment.

28. The system of claim 27, wherein a ratio of the first predetermined offset value to the characterized offset equals a ratio of a dimension of an intended display surface used when the first stereo image pair layer was created to the dimension of a display surface in the display environment.

29. The system of claim 22, wherein the system further comprises a projector that is coupled to the display processor and configured to project the stereoscopic image onto a display surface within the display environment.

30. The system of claim 29, wherein the projector is further configured to display a stereoscopic test pattern in the display environment.

31. The system of claim 22, wherein the display processor is further configured to:
determine that the first predetermined offset value has changed from a first value to a second value between a first frame and a second frame; and
align a left eye image and a right eye image of a first stereo image pair layer for the second frame according to the changed first predetermined offset value to produce an aligned first stereo image pair layer for the second frame that appears at a third convergence depth, the third convergence depth being different than the first convergence depth.

32. The system of claim 22, wherein the first predetermined offset value is encoded with the first stereo image pair layer and the second predetermined offset value is encoded with the second stereo image pair layer.

33. The system of claim 22, wherein a width of an intended display surface used when the first stereo image pair was created is different than a width of a display surface in the display environment.