PATENT DOCUMENT

Publication Number: US-8780986-B2
Application Number: US-41547809-A
Country: US
Kind Code: B2

Title: Refresh pixel group selection and coding adjustment

Abstract:
Apparatuses and methods for improving coding processes and coding parameters for coding video data are provided for. A coder may select coding parameters for video data according to a default coding policy. The default coding policy may include selection of prediction modes (e.g., intra-coding or inter-coding) for each pixel group in each frame. A video coder may select some pixel groups in a frame to be coded as refresh pixel groups as an exception to the default assignment policies. The selection of refresh pixel groups may be based on prediction relationships among multiple frames of source video data. The default coding of the refresh pixel groups is then modified to enhanced the coding of the refresh pixel groups. The refresh pixel groups may permit fewer intra (I) frames be sent and/or may improve the quality of the recovered video.

Claims:
We claim: 
     
       1. A method of coding video data, comprising:
 selecting pixel groups from the video to be coded as refresh pixel groups, wherein over a predetermined span of frames at least one refresh pixel group covers each pixel group location of the video, the selection of each refresh pixel group being based on a calculated number of pixel groups that depend on the refresh pixel group; 
 adjusting the coding of the refresh pixel groups to code the refresh pixel groups to a predetermined quality of coding according to a refresh coding policy to produce refreshed coded video, wherein coding parameters and a rate of refreshing are adjusted based on the calculated number of pixel groups; 
 adjusting the coding of non-refresh pixel groups to code the non-refresh pixel groups to a predetermined quality of coding according to a non-refresh coding policy to produce non-refreshed coded video; and 
 outputting to a channel the refreshed coded video. 
 
     
     
       2. The method of  claim 1 , wherein the selecting further comprises:
 computing the predictability of a plurality of pixel groups from the video, 
 selecting pixel groups to be the refresh pixel groups based on their computed predictability. 
 
     
     
       3. The method of  claim 1 , wherein adjusting the coding of the refresh pixel groups further comprises:
 calculating the predictability pixel groups that depend on the refresh pixel group, 
 selecting coding parameters of the refresh pixel group based on the predictability of the pixel groups that are dependent on the refresh pixel group. 
 
     
     
       4. The method of  claim 1 , wherein adjusting the coding of the refresh pixel groups further comprises:
 calculating the predictability of the refresh pixel groups and pixel groups surrounding the refresh pixel group, 
 selecting coding parameters of the refresh pixel group to achieve consistent coding quality across the refresh pixel groups and the surrounding pixel groups. 
 
     
     
       5. The method of  claim 4 , whereby the surrounding pixel groups are temporally adjacent to the refresh pixel group. 
     
     
       6. The method of  claim 4 , whereby the surrounding pixel groups are spatially adjacent to the refresh pixel group. 
     
     
       7. The method of  claim 4 , whereby the surrounding pixel groups are related to the refresh pixel group through a dependency chain. 
     
     
       8. The method of  claim 1 , wherein adjusting the coding of the non-refresh pixel groups further comprises:
 determining a dependency chain distance between a non-refresh pixel group and a refresh pixel group on which the non-refresh pixel group depends, 
 selecting coding parameters of the non-refresh pixel group based on the dependency chain distance. 
 
     
     
       9. The method of  claim 1 , wherein adjusting comprises coding the refresh pixel groups as intra-coded data. 
     
     
       10. The method of  claim 1 , wherein adjusting the coding of the non-refresh pixel groups further comprises:
 calculating the predictability of the non-refresh pixel groups and pixel groups surrounding the non-refresh pixel group, 
 selecting coding parameters of the non-refresh pixel group based on the calculated predictability. 
 
     
     
       11. The method of  claim 1 , wherein adjusting the coding of the non-refresh pixel groups further comprises:
 calculating perceptual metrics of pixel groups surrounding the non-refresh pixel group, 
 selecting coding parameters of the non-refresh pixel group based on the calculated perceptual metrics. 
 
     
     
       12. The method of  claim 1 , further comprises:
 calculating whether the refreshed coded video is acceptable, and if the refreshed coded video is not acceptable then iterating by coding the refreshed coded video according to a default coding policy, the iteration of the default coding policy eliminating an I frame. 
 
     
     
       13. The method of  claim 1 , wherein selecting refresh pixel groups further comprises:
 selecting refresh pixel groups based on the number of pixel groups that reference the refresh pixel groups. 
 
     
     
       14. The method of  claim 1 , wherein selecting refresh pixel groups further comprises:
 selecting refresh pixel groups based on the predictability of a temporal sequence of pixel groups that includes the refresh pixel groups. 
 
     
     
       15. The method of  claim 1 , where selecting refresh pixel groups further comprises:
 selecting refresh pixel groups based on at least one of: perceptual models, texture information, and motion. 
 
     
     
       16. The method of  claim 1 , where selecting refresh pixel groups further comprises:
 selecting refresh pixel groups based on a distance from previously selected refresh pixel groups. 
 
     
     
       17. The method of  claim 1 , where selecting refresh pixel groups further comprises:
 selecting refresh pixel groups based on portions of the video data with more importance. 
 
     
     
       18. The method of  claim 1 , where selecting refresh pixel groups further comprises:
 dividing the video data into macroblocks, the macroblocks being a number of pixel groups; 
 assigning an importance to the macroblocks; 
 selecting refresh pixel groups based on the importance of the macroblocks; 
 modifying the coding to improve an encoding quality for a refreshed macroblock. 
 
     
     
       19. The method of  claim 1 , where selecting refresh pixel groups further comprises:
 selecting refresh pixel groups based on portions of the video data that are coincident with two or more video data streams. 
 
     
     
       20. The method of  claim 1 , wherein outputting further comprises:
 selecting between a refresh coding and a non-refresh coding of pixel groups; 
 if the non-refresh coding is selected then outputting to the channel the non-refresh coding, 
 otherwise outputting to the channel the refresh coding. 
 
     
     
       21. The method of  claim 1 , wherein adjusting the coding of the refresh pixel groups further comprises:
 adjusting the coding of the refresh pixel groups to intra-code the refresh pixel groups to a predetermined quality of coding according to a refresh coding policy to produce refreshed coded video. 
 
     
     
       22. A system for encoding video data, comprising:
 a processor operable to: 
 select pixel groups from the video to be coded as refresh pixel groups, wherein over a predetermined span of frames at least one refresh pixel group covers each pixel group location of the video, the selection of each refresh pixel group being based on a calculated number of pixel groups that depend on the refresh pixel group; 
 adjust coding of the refresh pixel groups to code the refresh pixel groups to a predetermined quality of coding according to a refresh coding policy to produce refreshed coded video, wherein coding parameters and a rate of refreshing are adjusted based on the calculated number of pixel groups; 
 adjust the coding of non-refresh pixel groups to code the non-refresh pixel groups to a predetermined quality of coding according to a non-refresh coding policy to produce non-refreshed coded video; and 
 output the refreshed coded video and the non-refreshed coded video to a channel. 
 
     
     
       23. The system of  claim 22 , wherein the selection further comprises:
 computing the predictability of a plurality of pixel groups from the video, 
 selecting pixel groups to be the refresh pixel groups based on their computed predictability. 
 
     
     
       24. The system of  claim 22 , wherein the adjustment of coding of the refresh pixel groups further comprises:
 calculating the predictability pixel groups that depend on the refresh pixel group, 
 selecting coding parameters of the refresh pixel group based on the predictability of the pixel groups that are dependent on the refresh pixel group. 
 
     
     
       25. The system of  claim 22 , wherein the adjustment of coding of the refresh pixel groups further comprises:
 calculating the predictability of the refresh pixel groups and pixel groups surrounding the refresh pixel group, 
 selecting coding parameters of the refresh pixel group to achieve consistent coding quality across the refresh pixel groups and the surrounding pixel groups. 
 
     
     
       26. The system of  claim 25 , whereby the surrounding pixel groups are temporally adjacent to the refresh pixel group. 
     
     
       27. The system of  claim 25 , whereby the surrounding pixel groups are spatially adjacent to the refresh pixel group. 
     
     
       28. The system of  claim 25 , whereby the surrounding pixel groups are related to the refresh pixel group through a dependency chain. 
     
     
       29. The system of  claim 22 , wherein the adjustment of coding of the non-refresh pixel groups further comprises:
 determining a dependency chain distance between a non-refresh pixel group and a refresh pixel group on which the non-refresh pixel group depends, 
 selecting coding parameters of the non-refresh pixel group based on the dependency chain distance. 
 
     
     
       30. The system of  claim 22 , wherein the adjustment comprises coding the refresh pixel groups as intra-coded data. 
     
     
       31. The system of  claim 22 , wherein the adjustment of coding of the non-refresh pixel groups further comprises:
 calculating the predictability of the non-refresh pixel groups and pixel groups surrounding the non-refresh pixel group, 
 selecting coding parameters of the non-refresh pixel group based on the calculated predictability. 
 
     
     
       32. The system of  claim 22 , wherein the adjustment of coding of the non-refresh pixel groups further comprises:
 calculating perceptual metrics of pixel groups surrounding the non-refresh pixel group, 
 selecting coding parameters of the non-refresh pixel group based on the calculated perceptual metrics. 
 
     
     
       33. The system of  claim 22 , wherein the processor is further operable to:
 calculate whether the refreshed coded video is acceptable, and if the refreshed coded video is not acceptable then iterating by coding the refreshed coded video according to a default coding policy, the iteration of the default coding policy eliminating an I frame. 
 
     
     
       34. The system of  claim 22 , wherein the processor is further operable to select pixel groups based on the number of pixel groups that reference the refresh pixel groups. 
     
     
       35. The system of  claim 22 , wherein the processor is further operable to select refresh pixel groups based on the predictability of a temporal sequence of pixel groups that includes the refresh pixel groups. 
     
     
       36. The system of  claim 22 , wherein the processor is further operable to select refresh pixel groups based on at least one of: perceptual models, texture information, and motion. 
     
     
       37. The system of  claim 22 , wherein the processor is further operable to select refresh pixel groups based on a distance from previously selected refresh pixel groups. 
     
     
       38. The system of  claim 22 , wherein the processor is further operable to select refresh pixel groups based on portions of the video data with more importance. 
     
     
       39. The system of  claim 22 , wherein the processor is further operable to:
 divide the video data into macroblocks, the macroblocks being a number of pixel groups; 
 assign an importance to the macroblocks; 
 select refresh pixel groups based on the importance of the macroblocks; 
 modify the coding to improve an encoding quality for a macroblock. 
 
     
     
       40. The system of  claim 22 , wherein the processor is further operable to select refresh pixel groups based on portions of the video data that are coincident with two or more video data streams. 
     
     
       41. The system of  claim 22 , wherein the processor is further operable to
 select between a refresh coding and a non-refresh coding for the pixel groups; 
 if the non-refresh coding is selected then output to the channel the non-refresh coded pixel groups, 
 otherwise output to the channel the refresh coded pixel groups. 
 
     
     
       42. The system of  claim 22 , wherein the processor&#39;s adjustment further comprises:
 adjusting the coding of the refresh pixel groups to intra-code the refresh pixel groups to a predetermined quality of coding according to a refresh coding policy to produce refreshed coded video. 
 
     
     
       43. A non-transitory computer-readable medium encoded with a computer-executable program to perform a method comprising:
 coding video data according to a default coding policy to produce coded video, the coded video assigning refresh pixel groups, the refresh pixel groups being sources of prediction for other pixel groups, wherein over a predetermined span of frames at least one refresh pixel group covers each pixel group location of the video data; 
 selecting refresh pixel groups from the coded video to be refresh pixel groups, the selection of each refresh pixel group being based on a calculated number of pixel groups that depend on the refresh pixel group; 
 modifying the coding of the refresh pixel groups to code the refresh pixel groups to a predetermined quality of coding according to a refresh coding policy to produce refreshed coded video, wherein coding parameters and a rate of refreshing are adjusted based on the calculated number of pixel groups; and 
 outputting to a channel the refreshed coded video. 
 
     
     
       44. A method of coding video data, comprising:
 coding video data according to a default coding policy to produce coded video, the coded video assigning refresh pixel groups, the refresh pixel groups being sources of prediction for other pixel groups, wherein over a predetermined span of frames at least one refresh pixel group covers each pixel group location of the video data; 
 selecting refresh pixel groups from the coded video to be refresh pixel groups, the selection of each refresh pixel group being based on a calculated number of pixel groups that depend on the refresh pixel group; 
 modifying the coding of the refresh pixel groups to intra-code the refresh pixel groups to a predetermined quality of coding according to a refresh coding policy to produce refreshed coded video, wherein coding parameters and a rate of refreshing are adjusted based on the calculated number of pixel groups; 
 outputting to a channel the refreshed coded video.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application 61/059,721, with a filing data of Jun. 6, 2008, and entitled “Reference Refresh Method”, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the present invention relate to a video coder and, more specifically, to apparatuses and methods for improving default coding parameters. 
     BACKGROUND 
     Video coders are well known devices. They code a sequence of image data (“source video data”) according to predetermined coding processes for presentation of coded video data to a channel. The coded video data often occupies less bandwidth in a channel than the source video data and, therefore, many video coders achieve a high degree of data compression. Many video coding processes are lossy processes; when coded video data is retrieved from a channel decoded, it generates recovered video data that is similar but not identical to the source video data. When source video data is coded, a video coder selects various coding parameters that can affect the quality of the recovered video data at the decoder and the bandwidth occupied by the coded video data in the channel. Additionally, the selection of coding parameters can affect the complexity of coding processes that are to be performed at the video coder and the video decoder. 
       FIG. 1  illustrates a functional block diagram of a basic video coder  100 . A video coder  100  takes data from source video data  110  and codes the source video data  110  to produce coded video data  170  for presentation to a channel  120  to be decoded by a decoder connected to the channel  120 .The video coder  100  partially codes the source video data  110  and generates partially coded data  160  and coder parameters  165  for video coder engine  150  to code the partially coded data  160  according to commonly used procedures using the coder parameters  165 , e.g. quantizer parameter settings, spatial transforms, run-length coding, and entropy coding. 
     Typically, the coder  100  generates the partially coded data  160  and selects the coder parameters  165  to balance a set of constraints including: 1) the quality of recovered video, 2) the bit rates available from the channel  120 , 3) the complexity available at the video coder  100 , and 4) the complexity available at the decoder. The complexity of the decoder needs to be considered because the decoding process is performed on the decoder, and the resources available on the decoder are often limited. 
     The video coder  100  performs coding processes according to a coding policy to generate the partially coded data  160  and the coding parameters  165 . Commonly, the coding processes operate on the source video data  110  on a frame-by-frame basis in which the video coder  100  parses a frame into a plurality of pixel groups (e.g., 8×8 or 16×16 blocks of pixels) and codes the frame on a pixel group by pixel group basis. For each pixel group being coded, the video coder  100  may attempt to predict the pixel group from other pixel groups of the current frame (I or intra coding) or from pixel groups of other frames (B, P or inter coding). The pixel groups used to predict other pixel groups may be called reference pixel groups. For example, the video coder  100  may code a pixel group by referring to a source pixel group with instructions for applying a difference (residual) to the source pixel group to get an approximation of the pixel group. (e.g., if an object such as a ball were in a scene for several seconds then pixel groups of the ball from earlier in the scene may be used to predict pixel groups later in the scene). Applying a difference may be necessary to compensate for such things as lighting changes, camera angle changes, etc. By using prediction, the video coder  100  may exploit spatial or temporal redundancy in the source video data  110  to code pixel groups with fewer pixels. However, using prediction is a lossy process, and when chains of predictions are used the quality of the recovered video on the decoder may suffer due to propagation errors, and transmission errors may corrupt not only a current frame but also all the frames that are predicted from the current frame. One way to reset these types of errors is to send an I frame, or a frame with pixel groups that only refers to other pixel groups in the current frame. The decoder is reset, because the decoder may only refer to frames after the I frame. 
     Thus, video coders  100  according to a coding policy assign certain frames from the source video data  110  to be reference frames for prediction purposes whereas others may not be so assigned. The video coder  100  according to a coding policy may also select coder parameters  160  for video coder engine  150  to code the partially coded data  160  according to commonly used procedures, e.g. quantizer parameter settings, spatial transforms, run-length coding, and entropy coding. Quantization parameter selections can strongly influence bandwidth consumption and image quality in recovered video data. Generally speaking, higher quantization parameters can achieve higher compression ratios but can also lower quality of recovered image data. Therefore, the selection of quantization parameters (and other coder parameters) can be influenced by performance constraints such as channel bit rate limits and image quality requirements. 
     The coded video data  170  is transmitted across the channel  120  to a decoder. The coded video data  170  may be merged into a channel bitstream with data of other pixel groups and frames and with coded data representing other artifacts of the image sequence (such as audio). During transmission the coded video data  170  may be corrupted due to transmission errors relating to the channel  120  and/or the decoder. 
     When an (intra-coded)I frame is used in video coding, it may reset the state of a video decoder. However, the I frames typically are large compared to inter-coded frames and, therefore, they consume much more bandwidth. The inventors of the present application believe that modern coding processes do not require transmission of intra-coded frames that completely reset a video sequence. Instead, it may be useful to perform such reset operations on a pixel group by pixel group basis. In doing so, it may be useful to base such reset operations on a determination of how often pixel groups of frames are referenced by the encoding of other pixel groups in determining the quality of coding to use for pixel groups. Accordingly, there is a need in the art for apparatuses and methods to reduce the need to send I frames to reset the state of a video decoder by identifying pixel groups for enhanced coding and then enhancing the coding of the identified pixel groups. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a basic video coder. 
         FIG. 2  is a functional block diagram of a coder to code source video data according to an embodiment of the present invention. 
         FIG. 3  illustrates an embodiment of a method for encoding video data using a refresh method. 
         FIG. 4  illustrates reference pixel groups selected as refresh pixel groups based on the number of times the default encoding parameters refer to the reference pixel groups. 
         FIG. 5  illustrates the selection of pixels to receive enhanced encoding based on being used to encode a pixel group selected as a refresh pixel group. 
         FIG. 6  illustrates that the encoder may select pixel groups at the beginning of a scene to be refresh pixel groups. 
         FIG. 7  illustrates that the coder may select pixel groups based on their location in a frame to be refresh pixel groups. 
         FIG. 8  is a simplified functional block diagram of a computer system. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention provide apparatuses and methods for improving the coding of video data. A coder may code video data according to a default coding policy to produce coded video. The coded video may include reference pixel groups which are pixel groups used as sources of prediction for other pixel groups. The coder then may select reference pixel groups from the coded video to be refresh pixel groups. The coder then may modify the coding of the refresh pixel groups to code the refresh pixel groups to a predetermined quality of coding according to a refresh coding policy to produce refreshed coded video. The coder then may output to a channel the refreshed coded video. The refresh coded video can provide advantages similar to intra-coded frames but at reduced bandwidth consumption because the refresh coding is applied to a smaller portion of a frame, i.e. at a pixel group level. 
       FIG. 2  is a functional block diagram of a coder  200  to code source video data  210  according to an embodiment of the present invention. The coder  200  may include a coder controller  220 . The source video data  210  may be examined by the coder controller  220 . The coder controller  220  then may calculate coding constraints  230  including bit rate budget  230 . 1 , image quality requirements  230 . 2  and coder complexity estimate  230 . 3 . The coder controller  220  then may generate a refresh coding policy  240  and a default coding policy  250  based on the coding constraints  230 . The coder controller  220  then may perform coding processes on the source video data  210  and generate partially-coded data  292  coder parameters  294  according to the refresh coding policy  240  and partially coded data  296  and coder parameters  298  according to the default coding policy  250 . The coder controller  220  may then select between the partially coded data  292  and coder parameters  294 , and the partially coded data  296  and coder parameters  298 . The video coder engine  295 then may code the selected partially coded data  280  according to the coder parameters  285 . Then the coded data  270  may be transmitted over a channel  260  to a decoder (not illustrated.) 
     In an embodiment, the encoder controller  220  may iterate one or more times by reapplying the default coding policy  250  and/or the refresh coding policy  240  to the partially coded data  292   296  and/or the coder parameters  294 ,  298 . 
       FIG. 3  illustrates an embodiment of a method for encoding video data using a refresh method. The method begins at step  310  with retrieving source video data. The method optionally continues at step  320  with coding video data according to a default coding policy to produce coded video data for a group I of video data. The coder, according to the default coding policy, may generate partially coded video data and coder parameters. This may involve many processes including splitting the source video data into groups for coding(e.g., a number of frames of the video data may be grouped together, and then each frame may be coded pixel group by pixel group.) In an embodiment, the coder may predict pixel groups using other pixel groups and thus generate reference pixel groups, which are pixel groups that are used to predict other pixel groups. Some pixel groups may be used to predict multiple pixel groups. Frames may have multiple pixel groups. Pixel groups in a frame may be predicted from pixel groups in the same frame or pixel groups in different frames. If all the pixel groups are predicted from pixel groups in the same frame, then the frame is an I (intra-frame.) If some of the pixel groups are predicted from other frames, then the frame is an inter-coded frame (e.g. B or P frame.)In an embodiment, the coder according to the default coding policy calculates a predictability of a temporal sequence of pixel groups (e.g. co-located or connected through motion detection.)For example, the coder may calculate whether the predictability of a temporal sequence of video data is high, medium, or low. In an embodiment, the coder divides the video data into segments based on the predictability of the source video data. In an embodiment, the coder calculates perceptual models, texture information, and/or motion. 
     The coder may generate the partially coded video data and coder parameters iteratively after modifications have been made to encode refresh pixel groups at a higher quality of coding. In an embodiment, the coder may calculate known errors in the encoder and/or the decoder. In an embodiment, the coder calculates the distance of previous refresh pixel groups and/or I frames. In an embodiment, the coder identifies portions of the frame that should be given more importance. For example, in video data including a talking person the mouth of the person may be identified to be more important. In an embodiment, the coder selects macroblocks. The coder may calculate an importance of the macro blocks. In an embodiment, the coder may share the video data between two devices with some of the data being independent to a first device and some of the data being independent to a second device, and some of the data being shared between the two devices. The coder may identify the video data that is shared between the two devices. Method and apparatuses for sharing video data are disclosed in a related application, U.S. Provisional Application 61/079,373, with a filing data of Jul. 9, 2008, and entitled “Video Streaming Using Multiple Channels”, which is incorporated herein by reference. 
     In an embodiment, the coder, according to refresh coding policy, may generate partially coded video data and coder parameters. The refresh coding policy may include the default coding policy. 
     The method continues at step  330  with selecting pixel groups from the coded video to be refresh pixel groups. The coder, according to the refresh coding policy, may select refresh pixel groups in a number of different ways. In an embodiment, the refresh pixel groups are selected based on the number of pixel groups that reference the refresh pixel groups. The selection may be based on inter and/or intra references to the refresh pixel groups, i.e. the number of other pixel groups predicted from the pixel group. In an embodiment, after refresh pixel groups have been selected to be refresh pixel groups, if the refresh pixel groups are encoded with motion vectors, both the pixel groups that refer to the selected refresh pixel groups and the pixel groups that are referred to by the refresh pixel group may be selected as refresh pixel groups to receive enhanced coding. In an embodiment, after refresh pixel groups have been selected, if the refresh pixel groups are intra-coded, then pixels that are related to the refresh pixel groups by the intra-coding may be selected as refresh pixel groups to receive enhanced encoding. In an embodiment, after refresh pixel groups have been selected, and a selected mode has been selected, pixel groups that are related to the refresh pixel groups by the selected mode may be selected as refresh pixel groups to receive enhanced encoding. In an embodiment, the refresh pixel groups are selected based on the predictability of a temporal sequence of pixel groups. For example, refresh pixel groups are less likely to be selected for low-motion highly predictable video segments and high motion unpredictable video segments compared with medium motion medium predictable segments. In an embodiment, refresh pixel groups may be selected whose predictability is very different from those of the surrounding pixel groups. For example, if a neighborhood of pixel groups are well predicted except one pixel group, the one poorly predicted pixel group can be selected to be refreshed. 
     In an embodiment, the source video data may be partitioned into segments based on the motion predictability, and refresh pixel groups are selected at the beginning of prediction chains to improve the quality of the image at the head of the prediction chains. In an embodiment, the refresh pixel groups are selected based on perceptual models, texture information, and/or motion. For example, a background that is calculated to be not important for the video data may be less likely to be selected as refresh pixel groups. In an embodiment, the refresh pixel groups may be selected to compensate for known errors of the encoder and/or decoder. In an embodiment, the refresh pixel groups may be selected based on the distance of previous refresh pixel groups and/or I frames. In an embodiment, the refresh pixel groups may be selected based on a calculated propagation error for the pixel group. For example, if a pixel group is predicted from another pixel group from a chain of pixel groups, the coder may calculate that the propagation error is high, and select the pixel group to be a refresh pixel group to lower the propagation error. In an embodiment, the refresh pixel groups may be selected based on portions of the frame that are given more importance. For example, in video data including a talking person the mouth of the person may be more likely to be selected as refresh pixels. In an embodiment, the refresh pixel groups may be selected based on an importance assigned to macroblocks. Macroblocks may be selected to have their coding quality lowered and other macroblocks may be selected to be refresh pixel groups. In an embodiment, refresh pixel groups are selected based on the coincidence of pixel groups. The pixel groups that are coincident with two or more video data streams are more likely to be selected as refresh pixel groups. 
     In an embodiment, refresh pixel groups may be selected based on their location within the frame and based on the location of other pixel groups selected as refresh pixel groups. For example, the coder may select a pixel groups based on its location in the frame so that all the locations within the frame are refreshed during some unit of time or number of frames. 
     Adjusting the degree to which a pixel group of one or more members is refreshed (i.e. how well it is coded, or how many resources—bits, power, memory—are used to code it) may depend on a number of criteria. In an embodiment, the degree of refreshing for a first pixel group may be controlled to vary based on the number of other pixel groups that have prediction dependencies that rely on the first pixel group. In an embodiment, the degree of refreshing depends on the degree to which the dependent pixel groups are well predicted (temporally or spatially), measured often by the quantity of residual data to be coded following prediction. In another embodiment, the degree of refreshing depends on the degree to which a pixel group is unpredictable relative to the surrounding pixel group. For example, a pixel group that is poorly predicted temporally or spatially and that is surrounded by other pixels groups that are better predicted temporally or spatially can be refreshed so that visual quality is consistent across the pixels groups. 
     The method continues to step  340 , with adjusting the coding of non-refresh pixel groups. Non-refresh pixel groups that depend on a refresh pixel group can be coded with different parameters than those used to code the refresh pixel group. Quantization parameters (often higher), decode or encode complexity of the tools (often lower), and other such coding parameters can be adjusted non-refresh pixel groups to be different from that of refresh pixel groups. The degree to which these parameters can be adjusted for a non-refresh pixel group can depend on it&#39;s predictability, how far away it is from the last refresh picture group, perceptual metrics, and so on. 
     The method continues at step  350  with modifying the coding of the refresh pixel groups to code the refresh pixel groups to a predetermined quality of coding. The coder may according to the refresh coding policy modify the coding of the selected refresh pixel groups to a predetermined quality of coding in a number of ways. In an embodiment, the quantization to be applied to the refresh pixel groups is modified to a finer quantization. In an embodiment, the motion vectors used to code the refresh pixel groups are modified to use alternative motion vectors under different motion estimation strategies. In an embodiment, the mode selection used to code the refresh pixel groups is modified to use alternative prediction mode selection strategies. In an embodiment, the macroblock coding modes used to code the refresh pixel groups are modified to use alternative macroblock coding modes. In an embodiment, the macroblock decision strategies used to code the refresh pixel group is modified to use different macroblock mode decision strategies. In an embodiment, the bit stream elements used to encode the refresh pixel groups are modified to use bit stream elements that incur higher decoder complexity. In an embodiment, the coding time used to code the refresh pixel groups is modified to incur longer coding time to make higher quality pixel groups. In an embodiment, the coding used to code pixel groups not selected as refresh pixel groups is lowered to enable the modification of the coding of the refresh pixel groups. In an embodiment, the modifications to the coding of the refresh pixel groups is achieved under the encoding constraints. The modification to the coding of the refresh pixel groups may be called enhancements to the coding of the refresh pixel groups. 
     The method continues at step  360  with calculating whether the modified coding is acceptable. The coder may examine the modified coding, which may include modifications to the partially coded video data and/or the coder engine parameters, with the coding constraints to calculate whether or not the constraints have been exceeded and/or whether or not the coding constraints would permit additional modifications to the coding. Additionally, the coder may examine the modified coding to calculate whether or not another iteration of the coder according to the refresh coding policy and/or the default coding policy may improve the coding of the video data. The motion estimation stage, the intra prediction stage, and/or the mode decision stage may be changed as a result of the iteration. Both the refresh coding policy and/or the default coding policy may recognize the refresh pixel groups and maintain modified coding for the refresh pixel groups. The iteration of coding may use fewer I frames due to the modified coding of the refresh pixel groups. Thus, the refresh pixel groups may be selected and modified by using a multi-pass coding strategy. 
     The method continues at step  370  with coding the group i of the source image data. The coder may use the modified coder engine parameters to code group i of the source video data. In an embodiment, the coder may select either the modified coder engine parameters or the coder engine parameters. In an embodiment, the coder may use coder engine parameters according to the default coding policy and/or according to the refresh coding policy. The coded video may be output from the encoder. In an embodiment, the coded group i of source video data may be transmitted on a channel to a decoder. 
     The method continues at step  380  with calculating whether there is another group of source video data to encode. If there is more source video data to encode, then the method increments i at  390  and then returns to step  320  to begin encoding the next group i of the source image data. If there is no more source image data to encode then the method terminates. In an embodiment, the method may transmit the encoded source image data to a decoder using a channel after encoding all the source image data. The flow ends if there is no more source image data to encode. 
       FIG. 4  illustrates an exemplary sequence  410  of image data and a pixel group selected as a refresh pixel group based on the number of times other pixel groups were predicted from the selected refresh pixel group. The coder first partially codes the source video data to generate the frames  410  (shown as I 1 , B 2 , B 3 , B 4 , P 5 , B 6 ). Some of the pixel groups  420  were predicted from other pixel groups in the coding. So, for example, pixel group  420 . 1  of frame B 2  is shown as predicted from pixel group  420 . 3 of frame P 5 . Pixel groups that were used to predict other pixel groups may be called reference pixel groups. Pixel group  420 . 3  was used to predict 4 (four) other pixel groups and thus is a reference pixel group. Additionally, the coder according to the refresh coding policy selected pixel group  420 . 3  to be a refresh pixel group based on the number of other pixel groups predicted from pixel group  420 . 3 . The coding of pixel group  420 . 3  may be then modified using one of the methods described herein to improve the coding of pixel group  420 . 3 . 
       FIG. 5  illustrates the selection of pixels to receive modified or enhanced coding based on being used to code a pixel group selected as a refresh pixel group. Frame  510  of the video data includes 12 (twelve)pixel groups with pixel group  520  whose coding depends on surrounding pixels  530 . Based on being used in or affecting the coding of a pixel group  520 , the neighboring pixels  530  and the blocks which include them can be selected as refresh pixel groups to have their coding modified or enhanced. In an embodiment, if pixel group  520  was predicted from a source pixel group, then the source pixel group may be selected as a refresh pixel group. 
       FIG. 6  illustrates that the coder may select pixel groups at the head of a dependency chain within a scene to be refresh pixel groups. The video data may be divided into a number of frames  610 . The coder according to the refresh coding policy or the default coding policy identifies a scene  620  in the frames  610 . Assuming that the P frames depend on temporally previous frames and that the B frames depend on temporally adjacent frames, the coder according to the refresh coding policy may then be more likely to select pixel groups at the beginning of the scene  630  to refresh pixel groups. 
       FIG. 7  illustrates that the coder may select pixel groups based on their location in a frame to be refresh pixel groups. In  FIG. 7 , the coder has split the source video data into a number of frames  710  (shown as I 1 , B 2 , B 3 , B 4 , P 5 , B 6 , B 7 , I 8 , B 9 , B 10 , B 11 , P 12 , B 13 , B 14 , and I 15 .) In  FIG. 7 ,  720 , illustrates the operation of the coder according to the refresh method. The coder has split each of the frames into 9 (nine) pixel groups. The coder has selected the dark pixel groups as refresh pixel group,  730 . 1 ,  730 . 2 ,  730 . 3 ,  730 . 4 ,  730 . 5 ,  730 . 6 ,  730 . 7 ,  730 . 8 , and  730 . 9 . In selecting pixel group  730 . 8  and/or  730 . 9 , the coder may consider the position of the pixel groups in relation to other pixel groups that have been selected as refresh pixel groups according to a predetermined metric.(For example, the predetermined metric may have been since the last I frame was sent.)Element  740  illustrates the relative positions of the selected refresh pixel groups since the last I frame. As illustrated, the selection of  730 . 8  and  730 . 9  may enable the coder to not send an I frame I 8  since each of the pixel groups areas has been refreshed since the last I frame, I 1 , was sent. Thus, pixel groups may be selected as refresh pixel groups based on the position of the pixel group relative to other pixel groups selected as refresh pixel groups. 
       FIG. 8  is a simplified functional block diagram of a computer system  800 . An encoder and decoder of the present invention can be implemented in hardware, software or some combination thereof. For example, an encoder and/or decoder of the present invention can be implemented using a computer system. 
     As shown in  FIG. 8 , the computer system  800  includes a processor  802 , a memory system  804  and one or more input/output (I/O) devices  806  in communication by a communication fabric. The communication fabric can be implemented in a variety of ways and may include one or more computer buses  808 ,  810  and/or bridge devices  812  as shown in  FIG. 8 . The I/O devices  806  can include network adapters and/or mass storage devices from which the computer system  800  can receive compressed video data for decoding by the processor  802  when the computer system  800  operates as a decoder. Alternatively, the computer system  800  can receive source video data for encoding by the processor  802  when the computer system  800  operates as an encoder. 
     By using the apparatuses and methods described herein larger I, P, and B frames than standard encoding parameters encode may be generated. By using the methods described herein apparatuses higher quality encoding can be achieved without breaking prediction dependencies. 
     It should be understood that there exist implementations of other variations and modifications of the invention and its various aspects, as may be readily apparent to those of ordinary skill in the art, and that the invention is not limited by specific embodiments described herein. Features and embodiments described above may be combined. It is therefore contemplated to cover any and all modifications, variations, combinations or equivalents that fall within the scope of the basic underlying principals disclosed and claimed herein.

Metadata:
Filing Date: 20090331
Publication Date: 20140715
Grant Date: 20140715
Priority Date: 20080606
Inventors: WU HSI-JUNG
ZHOU XIAOSONG
SHI XIAOJIN
LIU YUXIN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04N19/176", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N19/176", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N19/61", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N19/137", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N19/137", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N19/61", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N19/107", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04N19/107", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04N7/26031", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N7/5086", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N19/0003", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 41400295