Restoration in video coding using domain transform recursive filters

An apparatus for restoring a degraded tile of a degraded frame resulting from reconstruction of a source tile, comprising:

• a processor configured to:
• transform the degraded tile from a pixel domain to a gradient domain comprising gradients of pixel values;
• after transforming the degraded tile, determine a first error with respect to the source tile, the first error corresponding to applying a domain transform recursive filter using a first scaling factor to the degraded tile;
• after transforming the degraded tile, determine a second error with respect to the source tile, the second error corresponding to applying the domain transform recursive filter using a second scaling factor to the degraded tile;
• and
• encode, in an encoded bitstream, a scaling parameter that identifies one of the first scaling factor or the second scaling factor corresponding to whichever of the first error or the second error is smaller, wherein the first and second scaling factors are each a function of a filter variance over a spatial domain of the degraded tile and a filter variance over a range of the pixel values of the degraded tile, the filter variance over the range of the pixel values determines how strongly edges affect filtering operations, and the filter variance over the spatial domain controls a filter kernel size.

An apparatus for restoring a degraded tile of a degraded frame resulting from a decoder reconstruction, the apparatus comprising:

• a processor configured to:
• determine, from an encoded bitstream, a scaling factor by one of:
• decoding a range filter variance from the encoded bitstream, and calculating the scaling factor using the range filter variance and a spatial domain filter variance, wherein the range filter variance determines how edges in the degraded tile affect filtering operations and the spatial domain filter variance controls a filter kernel size;
• decoding the spatial domain filter variance from the encoded bitstream, and calculating the scaling factor using the range filter variance and the spatial domain filter variance;
• or
• decoding the scaling factor from the encoded bitstream;
• and
• domain transform recursively filter, resulting in a restored tile, the degraded tile using the scaling factor, wherein to domain transform recursive filter the degraded tile comprises to transform, before filtering, the degraded tile from a pixel domain to a gradient domain comprising gradients of pixel values.