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Allow libyuv to use identity matrix with YUV 4:0:0 #1488

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Aug 2, 2023
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Allow libyuv to use identity matrix with YUV 4:0:0 #1488

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9 changes: 7 additions & 2 deletions src/reformat_libyuv.c
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Original file line number Diff line number Diff line change
Expand Up @@ -737,8 +737,13 @@ static avifBool getLibYUVConversionFunction(avifPixelFormat yuvFormat,

static void getLibYUVConstants(const avifImage * image, const struct YuvConstants ** matrixYUV, const struct YuvConstants ** matrixYVU)
{
// Allow the identity matrix to be used with YUV 4:0:0. Replace the identity matrix with
// MatrixCoefficients 6 (BT.601).
const avifBool yuv400WithIdentityMatrix = (image->yuvFormat == AVIF_PIXEL_FORMAT_YUV400) &&
(image->matrixCoefficients == AVIF_MATRIX_COEFFICIENTS_IDENTITY);
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In the Chromium CL, the condition I used is just image->yuvFormat == AVIF_PIXEL_FORMAT_YUV400. I am planning to change Chromium to match this condition.

const avifMatrixCoefficients matrixCoefficients = yuv400WithIdentityMatrix ? AVIF_MATRIX_COEFFICIENTS_BT601 : image->matrixCoefficients;
if (image->yuvRange == AVIF_RANGE_FULL) {
switch (image->matrixCoefficients) {
switch (matrixCoefficients) {
// BT.709 full range YuvConstants were added in libyuv version 1772.
// See https://chromium-review.googlesource.com/c/libyuv/libyuv/+/2646472.
case AVIF_MATRIX_COEFFICIENTS_BT709:
Expand Down Expand Up @@ -805,7 +810,7 @@ static void getLibYUVConstants(const avifImage * image, const struct YuvConstant
break;
}
} else { // image->yuvRange == AVIF_RANGE_LIMITED
switch (image->matrixCoefficients) {
switch (matrixCoefficients) {
case AVIF_MATRIX_COEFFICIENTS_BT709:
*matrixYUV = &kYuvH709Constants;
*matrixYVU = &kYvuH709Constants;
Expand Down