Reshaping filter average calculation for video coding

A device for decoding video data, the device comprising:

• a memory configured to store video data;
• and
• one or more processors implemented in circuitry and configured to:
• calculate an average value of a subset of pixels of a luminance block of the video data, without using pixels of the luminance block that are not included in the subset;
• decode chrominance transform coefficients for a chrominance residual block of a chrominance block of the video data, the chrominance block corresponding to the luminance block;
• inverse transform the chrominance transform coefficients to produce chrominance residual values of the chrominance residual block;
• determine a scaling value using the average value;
• scale the chrominance residual values using the scaling value;
• and
• decode the chrominance block using the scaled chrominance residual values of the chrominance residual block.

A device for decoding video data, the device comprising:

• means for calculating an average value of a subset of pixels of a luminance block of video data, without using pixels of the luminance block that are not included in the subset;
• means for decoding chrominance transform coefficients for a chrominance residual block of a chrominance block of the video data, the chrominance block corresponding to the luminance block;
• means for inverse transforming the chrominance transform coefficients to produce chrominance residual values of the chrominance residual block;
• means for determining a scaling value using the average value;
• means for scaling the chrominance residual values using the scaling value;
• and
• means for decoding the chrominance block using the scaled chrominance residual values of the chrominance residual block.

A computer-readable storage medium having stored thereon instructions that, when executed, cause a processor of a device for decoding video data to:

• calculate an average value of a subset of pixels of a luminance block of video data, without using pixels of the luminance block that are not included in the subset;
• decode chrominance transform coefficients for a chrominance residual block of a chrominance block of the video data, the chrominance block corresponding to the luminance block;
• inverse transform the chrominance transform coefficients to produce chrominance residual values of the chrominance residual block;
• determine a scaling value using the average value;
• scale the chrominance residual values using the scaling value;
• and
• decode the chrominance block using the scaled chrominance residual values of the chrominance residual block.