Broadcast video decoder with reduced memory and processing requirements suitable for handheld and mobile applications
The present application relates to an apparatus for programmable video size reduction with dynamic image filtering for use in block-based video decoding system. The invention improves the image quality within low video memory requirements and allows for efficient decoding of higher resolution video to be displayed on a lower resolution display device.
1. An apparatus for downsampling video data comprising block data and motion vectors comprising:
a) a motion vector scaler for downscaling the motion vectors;
b) a block data decoder for producing transformed block data;
c) a block downsampler for only downsampling the transformed block data produced by the block data decoder to produce downsampled block data;
d) a frame memory for storing at least one downsampled frame of the video;
e) a frame module employing the downscaled motion vectors, the down sampled block data, and at least one downsampled frame of video from the frame memory to produce a subsequent downsampled frame of video; and
e) a filter for filtering the subsequent downsampled frame of video and storing the filtered downsampled frame in the frame memory.
2. An apparatus according to claim 1 , wherein the downscaling of the motion vector is programmable.
3. An apparatus according to claim 1 , wherein the downsampling of the block downsampler is programmable.
4. An apparatus according to claim 1 , wherein the data blocks comprise a matrix of 16 by 16 data values and the downsampled data block comprises a matrix of 16/N by 16/M data values, where N and M are non-zero integer numbers.
5. An apparatus according to claim 1 , wherein the downsampler employs an adder and divider to produce an average value for subblocks in the transformed block being downsampled.
6. An apparatus according to claim 1 , wherein the filter is a dynamic filter and wherein the filter is configured to distinguish between blocking artifacts or inherent gradients present in the image and adjusts the degree of filtering to reduce blocking artifacts in the downsampled frame.
7. An apparatus according to claim 6 , wherein the filter is configured to distinguish between blocking artifacts and inherent gradients using at least one border strength value, wherein the at least one border strength value for a block is determined with respect to one or more neighbouring blocks, and wherein increased filtering is applied for higher border strengths.
8. An apparatus according to claim 7 , wherein a vertical and a horizontal border strength are calculated.
9. An apparatus according to claim 8 , wherein the vertical border strength for a block is calculated with respect to one vertically adjacent block.
10. An apparatus according to claim 9 , wherein the horizontal border strength is calculated with respect to one horizontally adjacent block.
11. An apparatus according to claim 8 , wherein a first filter is performed based on the vertical strength.
12. An apparatus according to claim 11 , wherein a second filter is performed based upon the horizontal strength.
13. An apparatus according to claim 1 , wherein for a chroma data block, the border strength is calculated from previously calculated LUMA border strengths.
14. An apparatus according to claim 1 , wherein the downsampler applies a downsampling ratio when downsampling and where the downsampling ratio is adjustable.
15. An apparatus according to claim 14 , wherein the downsampling ratio is adjustable between a factor of 2 or 4 in the horizontal or the vertical direction.
16. An apparatus according to claim 1 , wherein the apparatus further comprises a screen for displaying the frames.
17. An apparatus according to claim 1 , wherein the apparatus is a handheld device.
18. An apparatus according to claim 1 , wherein the apparatus is a mobile phone or similar battery-powered or portable device.
19. An apparatus according to claim 1 , wherein the apparatus is a TV and the downsampled image is employed to generate a ‘picture in picture’ feature of the TV.
20. An apparatus according to claim 1 , wherein the video is coded in accordance the MPEG format.
21. An apparatus according to claim 6 , wherein the filter employs macroblock quantization values to generate an index value, wherein a first threshold value is retrieved from a first look-up table using said index value, and wherein the filter is not applied where the difference between adjoining pixels on either side of a border is less than said first threshold value.
22. An apparatus according to claim 21 , wherein the values of the first look-up table are as set forth in column a of table 600 in FIG. 6 .
23. An apparatus according to claim 21 , wherein a second threshold value is retrieved from a second look-up table using said index value and wherein the filter is not applied where the difference between corresponding pixels adjacent to adjoining pixels on either side of a border is less than said second threshold value.
24. An apparatus according to claim 23 , wherein the values of the second look-up table are as set forth in column 13 of table 600 in FIG. 6 .
25. An apparatus according to claim 23 , wherein a third threshold value is retrieved from a third look-up table using at least said index value and wherein said third value is employed in at least one clipping function within said filter.
26. An apparatus according to claim 25 , wherein a border strength value is also employed in the retrieval of the third threshold value from the third look-up table.
27. An apparatus according to claim 26 , wherein the values of the third lookup table are as set forth in table 601 in FIG. 6 .