Motion estimation and compensation of video object planes for interlaced digital video

Abstract

A motion estimation and compensation technique is provided for interlaced digital video such as video object planes (VOPs). Predictor motion vectors for use in differentially encoding a current field coded macroblock are obtained using the median of motion vectors of surrounding blocks or macroblocks. When a surrounding macroblock is itself interlaced coded, an average motion vector for that macroblock is used, with fractional pixel values being mapped to the half-pixel. When the current block is not interlaced coded but a surrounding block is, the field motion vectors may be used individually or averaged. In a repetitive padding technique for an interlaced coded VOP, the even and odd lines of the VOP and surrounding block are grouped. Within each field, exterior pixels are padded by setting them to the value of the nearest boundary pixel, or to an average of two boundary pixels. The lines are then reordered to provide a single padded reference VOP image.

What is claimed is:  
     
       1. A method for padding a digital video image which includes a field coded video object plane (VOP) comprising top and bottom field pixel lines carried in an interleaved order to provide a reference padded VOP, said VOP being carried, at least in part, in a region which includes pixels which are exterior to boundary pixels of said VOP, said method comprising the steps of: 
       reordering said top and bottom field pixel lines from said interleaved order to provide a top field block comprising said top field pixel lines, and a bottom field block comprising said bottom field pixel lines; and  
       padding said exterior pixels separately within said respective top and bottom field blocks.  
     
     
       2. The method of  claim 1 , comprising the further step of: 
       reordering said top and bottom field pixel lines comprising said padded exterior pixels back to said interleaved order to provide said reference padded VOP.  
     
     
       3. The method of  claim 1 , wherein: 
       when a particular one of said exterior pixels is located between two of said boundary pixels of said VOP in the corresponding field block, said padding step comprises the further step of:  
       assigning said particular one of said exterior pixels a value according to an average of said two boundary pixels.  
     
     
       4. The method of  claim 1 , wherein: 
       when a particular one of said exterior pixels is located between one of said boundary pixels of said VOP and an edge of said region in the corresponding field block, but not between two of said boundary pixels of said VOP in the corresponding field block, said padding step comprises the further step of:  
       assigning said particular one of said exterior pixels a value according to said one of said boundary pixels.  
     
     
       5. The method of  claim 1 , wherein: 
       when a particular one of said exterior pixels is located between two edges of said region in the corresponding field block, but not between one of said boundary pixels of said VOP and an edge of said region in the corresponding field block, and not between two of said boundary pixels of said VOP in the corresponding field block, said padding step comprises the further step of:  
       assigning said particular one of said exterior pixels a value according to at least one of:  
       (a) a padded exterior pixel which is closest to said particular one of said exterior pixels moving horizontally in said region in the corresponding field block; and  
       (b) a padded exterior pixel which is closest to said particular one of said exterior pixels moving vertically in said region in the corresponding field block.  
     
     
       6. An apparatus for padding a digital video image which includes a field coded video object plane (VOP) comprising top and bottom field pixel lines carried in an interleaved order to provide a reference padded VOP, said VOP being carried, at least in part, in a region which includes pixels which are exterior to boundary pixels of said VOP, said apparatus comprising: 
       means for reordering said top and bottom field pixel lines from said interleaved order to provide a top field block comprising said top field pixel lines, and a bottom field block comprising said bottom field pixel lines; and  
       means for padding said exterior pixels separately within said respective top and bottom field blocks.  
     
     
       7. The apparatus of  claim 6 , further comprising: 
       means for reordering said top and bottom field pixel lines comprising said padded exterior pixels back to said interleaved order to provide said reference padded VOP.  
     
     
       8. The apparatus of  claim 6 , wherein: 
       said means for padding comprises means for assigning; and  
       when a particular one of said exterior pixels is located between two of said boundary pixels of said VOP in the corresponding field block, said means for assigning assigns said particular one of said exterior pixels a value according to an average of said two boundary pixels.  
     
     
       9. The apparatus of  claim 6 , wherein: 
       said means for padding comprises means for assigning; and  
       when a particular one of said exterior pixels is located between one of said boundary pixels of said VOP and an edge of said region in the corresponding field block, but not between two of said boundary pixels of said VOP in the corresponding field block, said means for assigning assigns said particular one of said exterior pixels a value according to said one of said boundary pixels.  
     
     
       10. The apparatus of  claim 6 , wherein: 
       said means for padding comprises means for assigning; and  
       when a particular one of said exterior pixels is located between two edges of said region in the corresponding field block, but not between one of said boundary pixels of said VOP and an edge of said region in the corresponding field block, and not between two of said boundary pixels of said VOP in the corresponding field block, said means for assigning assigns said particular one of said exterior pixels a value according to at least one of:  
       (a) a padded exterior pixel which is closest to said particular one of said exterior pixels moving horizontally in said region in the corresponding field block; and  
       (b) a padded exterior pixel which is closest to said particular one of said exterior pixels moving vertically in said region in the corresponding field block.  
     
     
       11. The apparatus of  claim 6 , further comprising: 
       means for using said reference padded VOP for motion prediction of another VOP.  
     
     
       12. The method of  claim 1 , comprising the further step of: 
       using said reference padded VOP for motion prediction of another VOP.  
     
     
       13. A decoder for recovering a padded digital video image which includes a field coded video object plane ( VOP )  comprising top and bottom field pixel lines carried in an interleaved order to provide a reference padded VOP, said VOP being carried, at least in part, in a region which includes pixels which are exterior to boundary pixels of said VOP, said decoder comprising:    
       
         a detector for detecting padding in the exterior pixels separately within respective top and bottom field blocks;  
       
       
         said top and bottom field blocks being representative of said top and bottom field pixel lines reordered from said interleaved order,  
       
       
         said top field block comprising reordered data from said top field pixel lines, and  
       
       
         said bottom field block comprising reordered data from said bottom field pixel lines. 
       
     
     
       14. A decoder in accordance with  claim 13 , wherein means are provided for using said reference padded VOP for motion prediction of another VOP. 
     
     
       15. A signal carrying a padded digital video image which includes a field coded video object plane ( VOP )  having top and bottom field pixel lines carried in an interleaved order to provide a reference padded VOP, said VOP being carried, at least in part, in a region which includes pixels which are exterior to boundary pixels of said VOP, said signal including:    
       
         a top field block comprising top field pixel lines reordered from said interleaved order;  
       
       
         a bottom field block comprising bottom field pixel lines reordered from said interleaved order; and  
       
       
         separately padded exterior pixels within said respective top and bottom field blocks. 
       
     
     
       16. A communications signal for use in a system in which horizontal and vertical motion vector components are used to differentially encode respective horizontal and vertical motion vector components of a current block of a digital video image, wherein: 
       
         candidate first, second and third blocks have associated horizontal and vertical motion vector components;  
       
       
         said first block being at least a portion of a first macroblock which immediately precedes said current block in a current row;  
       
       
         said second block being at least a portion of a second macroblock which is immediately above said current block in a preceding row;  
       
       
         said third block being at least a portion of a third macroblock which immediately follows said second macroblock in said preceding row; and  
       
         at least one of said first, second and third candidate blocks and said current block is field - coded;    
       
         said communications signal including at least one of:  
       
       
         a selected horizontal motion vector component used to differentially encode the horizontal motion vector component of said current block according to a value derived from the horizontal motion vector components of said first, second and third candidate blocks,  
       
       
         a selected vertical motion vector component used to differentially encode the vertical motion vector component of said current block according to a value derived from the vertical motion vector components of said first, second and third candidate blocks. 
       
     
     
       17. A signal in accordance with  claim 16  further including data indicating whether said current block is field coded. 
     
     
       18. A signal in accordance with  claim 17 , wherein said data is provided in at least one of the selected horizontal motion vector component and selected vertical motion vector component. 
     
     
       19. A signal in accordance with  claim 16 , including both a selected horizontal motion vector component and a selected vertical motion vector component. 
     
     
       20. A communications channel carrying a padded digital video image signal which includes a field coded video object plane ( VOP )  having top and bottom field pixel lines carried in an interleaved order to provide a reference padded VOP, said VOP being carried, at least in part, in a region which includes pixels which are exterior to boundary pixels of said VOP, said signal including:    
       
         a top field block comprising top field pixel lines reordered from said interleaved order;  
       
       
         a bottom field block comprising bottom field pixel lines reordered from said interleaved order; and  
       
       
         separately padded exterior pixels within said respective top and bottom field blocks. 
       
     
     
       21. A communications channel carrying a signal for use in a system in which horizontal and vertical motion vector components are used to differentially encode respective horizontal and vertical motion vector components of a current block of a digital video image, wherein: 
       
         candidate first, second and third blocks have associated horizontal and vertical motion vector components;  
       
       
         said first block being at least a portion of a first macroblock which immediately precedes said current block in a current row;  
       
       
         said second block being at least a portion of a second macroblock which is immediately above said current block in a preceding row;  
       
       
         said third block being at least a portion of a third macroblock which immediately follows said second macroblock in said preceding row; and  
       
         at least one of said first, second and third candidate blocks and said current block is field - coded;    
       
         said communications signal including at least one of:  
       
       
         a selected horizontal motion vector component used to differentially encode the horizontal motion vector component of said current block according to a value derived from the horizontal motion vector components of said first, second and third candidate blocks,  
       
       
         a selected vertical motion vector component used to differentially encode the vertical motion vector component of said current block according to a value derived from the vertical motion vector components of said first, second and third candidate blocks.