Multi-metric filtering

Abstract

A filter unit of a video encoder or video decoder can determine a first metric for a group of pixels within a block of pixels, determine a second metric for the group of pixels, determine a filter based on the first metric and the second metric, and generate a filtered image by applying the filter to the group of pixels. The first metric and second metric can be an activity metric and a direction metric, respectively, or can be other metrics such as an edge metric, horizontal activity metric, vertical activity metric, or diagonal activity metric.

The invention claimed is: 
     
       1. A method of video coding, the method comprising:
 determining a first metric for a group of pixels within a block of pixels, wherein the first metric comprises a non-direction specific activity metric; 
 determining a second metric for the group of pixels, wherein the second metric comprises a direction metric, wherein determining the first metric comprises determining the first metric with reference to the second metric; 
 based on the first metric and the second metric, determining a filter; and 
 generating a filtered image by applying the filter to the group of pixels. 
 
     
     
       2. The method of  claim 1 , wherein the direction metric is determined based on comparing a measure of horizontal activity to a measure of vertical activity. 
     
     
       3. The method of  claim 2 , wherein the measure of horizontal activity is determined based on comparing a pixel value of a current pixel to a pixel value of a left neighboring pixel and a pixel value of a right neighboring pixel. 
     
     
       4. The method of  claim 2 , wherein the measure of vertical activity is determined based on comparing a pixel value of a current pixel to a pixel value of an upper neighboring pixel and a pixel value of lower neighboring pixel. 
     
     
       5. The method of  claim 2 , wherein the non-direction specific activity metric is determined based on a sum of the measure of horizontal activity and the measure of vertical activity. 
     
     
       6. The method of  claim 1 , wherein the group of pixels comprises a 4x4 block of pixels. 
     
     
       7. The method of  claim 1 , wherein the group of pixels comprises one pixel. 
     
     
       8. The method of  claim 1 , wherein the method of video coding implements a Quadtree-based Adaptive Loop Filter (QALF) scheme with multiple filters. 
     
     
       9. The method of  claim 1 , wherein the method is performed by a video coding device comprising a video encoder. 
     
     
       10. The method of  claim 1 , wherein the method is performed by a video coding device comprising a video decoder. 
     
     
       11. A video coding device comprising:
 a memory configured to store video data; and 
 one or more processors configured to:
 determine a first metric for a group of pixels within a block of pixels of the video data, wherein the first metric comprises a non-direction specific activity metric; 
 determine a second metric for the group of pixels, wherein the second metric comprises a direction metric, wherein to determine the first metric, the one or more processors are further configured to determine the first metric with reference to the second metric; 
 determine a filter based on the first metric and the second metric; and 
 generate a filtered image by applying the filter to the group of pixels. 
 
 
     
     
       12. The video coding device of  claim 11 , wherein the one or more processors are configured to determine the direction metric based on comparing a measure of horizontal activity to a measure of vertical activity. 
     
     
       13. The video coding device of  claim 12 , wherein the one or more processors are configured to determine the measure of horizontal activity based on comparing a pixel value of a current pixel to a pixel value of a left neighboring pixel and a pixel value of a right neighboring pixel. 
     
     
       14. The video coding device of  claim 11 , wherein the one or more processors are configured to determine the measure of vertical activity based on comparing a pixel value of a current pixel to a pixel value of an upper neighboring pixel and a pixel value of lower neighboring pixel. 
     
     
       15. The video coding device of  claim 11 , wherein the non-direction specific activity metric is determined based on a sum of the measure of horizontal activity and the measure of vertical activity. 
     
     
       16. The video coding device of  claim 11 , wherein the group of pixels comprises a 4×4 block of pixels. 
     
     
       17. The video coding device of  claim 11 , wherein the group of pixels comprises one pixel. 
     
     
       18. The video coding device of  claim 11 , wherein the video coding device implements a Quadtree-based Adaptive Loop Filter (QALF) scheme with multiple filters. 
     
     
       19. An apparatus comprising:
 means for determining a first metric for a group of pixels within a block of pixels, wherein the first metric comprises a non-direction specific activity metric; 
 means for determining a second metric for the group of pixels, wherein the second metric comprises a direction metric, wherein the means for determining the first metric comprises means for determining the first metric with reference to the second metric; 
 means for determining a filter based on the first metric and the second metric; and 
 means for generating a filtered image by applying the filter to the group of pixels. 
 
     
     
       20. The apparatus of  claim 19 , wherein the direction metric is determined based on comparing a measure of horizontal activity to a measure of vertical activity. 
     
     
       21. A non-transitory computer-readable storage medium having stored thereon instructions that when executed cause one or more processors to:
 determine a first metric for a group of pixels within a block of pixels, wherein the first metric comprises a non-direction specific activity metric; 
 determine a second metric for the group of pixels, wherein the second metric comprises a direction metric, wherein to determine the first metric, the instructions cause the one or more processors to determine the first metric with reference to the second metric; 
 determine a filter based on the first metric and the second metric; and 
 generate a filtered image by applying the filter to the group of pixels. 
 
     
     
       22. The non-transitory computer-readable storage medium of  claim 21 , wherein the direction metric is determined based on comparing a measure of horizontal activity to a measure of vertical activity. 
     
     
       23. The method of  claim 1 , wherein the non-direction specific activity metric comprises a sum-modified Laplacian value. 
     
     
       24. The video coding device of  claim 11 , wherein the non-direction specific activity metric comprises a sum-modified Laplacian value. 
     
     
       25. The method of  claim 2 , further comprising:
 based on comparing the measure of horizontal activity to the measure of vertical activity, determining that the second metric corresponds to one of a horizontal direction, a vertical direction, or no direction. 
 
     
     
       26. The method of  claim 25 , further comprising:
 in response to the measure of horizontal activity being greater than the measure of vertical activity, determining that the second metric corresponds to the horizontal direction; and 
 in response to the measure of vertical activity being greater than the measure of horizontal activity, determining that the second metric corresponds to the vertical direction. 
 
     
     
       27. The video coding device of  claim 12 , wherein the one or more processors are further configured to:
 based on comparing the measure of horizontal activity to the measure of vertical activity, determine that the second metric corresponds to one of a horizontal direction, a vertical direction, or no direction. 
 
     
     
       28. The video coding device  claim 27 , wherein the one or more processors are further configured to:
 in response to the measure of horizontal activity being greater than the measure of vertical activity, determine that the second metric corresponds to the horizontal direction; and 
 in response to the measure of vertical activity being greater than the measure of horizontal activity, determine that the second metric corresponds to the vertical direction. 
 
     
     
       29. The video coding device of  claim 11 , wherein the video coding device comprises a wireless communication device, further comprising a receiver configured to receive encoded video data. 
     
     
       30. The video coding device of  claim 29 , wherein the wireless communication device comprises a telephone handset and wherein the receiver is configured to demodulate, according to a wireless communication standard, a signal comprising the encoded video data.