Change AVIF matrix coefficients default to BT.601

Change the AVIF matrix coefficients default to 6 (BT.601). This is
specified in the draft MIAF Amendment 2.

Bug: 1119465
Change-Id: I2aa6a07e709327fd1f776effc5767c887928c660
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2364026
Commit-Queue: Wan-Teh Chang <wtc@google.com>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799908}

third_party/blink/renderer/platform/image-decoders/avif/avif_image_decoder.cc

@@ -47,14 +47,20 @@ namespace {
 // YUV-to-RGB conversion. If the image does not have an ICC profile, this color
 // space is also used to create the embedded color profile.
 gfx::ColorSpace GetColorSpace(const avifImage* image) {
-  // MIAF Section 7.3.6.4 says:
+  // (As of ISO/IEC 23000-22:2019 Amendment 2) MIAF Section 7.3.6.4 says:
   //   If a coded image has no associated colour property, the default property
   //   is defined as having colour_type equal to 'nclx' with properties as
   //   follows:
-  //   – For YCbCr encoding, sYCC should be assumed as indicated by
-  //   colour_primaries equal to 1, transfer_characteristics equal to 13,
-  //   matrix_coefficients equal to 1, and full_range_flag equal to 1.
+  //   – colour_primaries equal to 1,
+  //   - transfer_characteristics equal to 13,
+  //   - matrix_coefficients equal to 5 or 6 (which are functionally identical),
+  //     and
+  //   - full_range_flag equal to 1.
   //   ...
+  // These values correspond to AVIF_COLOR_PRIMARIES_BT709,
+  // AVIF_TRANSFER_CHARACTERISTICS_SRGB, and AVIF_MATRIX_COEFFICIENTS_BT601,
+  // respectively.
+  //
   // Note that this only specifies the default color property when the color
   // property is absent. It does not really specify the default values for
   // colour_primaries, transfer_characteristics, and matrix_coefficients when
@@ -73,7 +79,7 @@ gfx::ColorSpace GetColorSpace(const avifImage* image) {
                             : image->transferCharacteristics;
   const auto matrix =
       image->matrixCoefficients == AVIF_MATRIX_COEFFICIENTS_UNSPECIFIED
-          ? AVIF_MATRIX_COEFFICIENTS_BT709
+          ? AVIF_MATRIX_COEFFICIENTS_BT601
           : image->matrixCoefficients;
   const auto range = image->yuvRange == AVIF_RANGE_FULL
                          ? gfx::ColorSpace::RangeID::FULL

third_party/blink/renderer/platform/image-decoders/avif/avif_image_decoder_test.cc

@@ -157,6 +157,18 @@ StaticColorCheckParam kTestParams[] = {
          {gfx::Point(1, 1), SkColorSetARGB(255, 255, 0, 0)},
          {gfx::Point(2, 2), SkColorSetARGB(255, 255, 0, 0)},
      }},
+    {"/images/resources/avif/red-full-range-unspecified-420-8bpc.avif",
+     8,
+     ColorType::kRgb,
+     ImageDecoder::kLosslessFormat,
+     ImageDecoder::kAlphaNotPremultiplied,
+     ColorBehavior::Tag(),
+     3,
+     {
+         {gfx::Point(0, 0), SkColorSetARGB(255, 255, 0, 0)},
+         {gfx::Point(1, 1), SkColorSetARGB(255, 255, 0, 0)},
+         {gfx::Point(2, 2), SkColorSetARGB(255, 255, 0, 0)},
+     }},
     {"/images/resources/avif/silver-full-range-srgb-420-8bpc.avif",
      8,
      ColorType::kRgb,

third_party/blink/web_tests/images/resources/avif/README.md

@@ -60,6 +60,11 @@ avifenc -r f -d 10 -y 444 -s 0 --nclx 9/18/9 red.png red-full-range-bt2020-hlg-4
 avifenc -r f -d 10 -y 444 -s 0 --nclx 9/18/9 red.png red-full-range-bt2020-hlg-444-12bpc.avif
 ```
 
+Unspecified color primaries, transfer characteristics, and matrix coefficients:
+```
+avifenc -r f -d  8 -y 420 -s 0 --nclx 2/2/2 red.png red-full-range-unspecified-420-8bpc.avif
+```
+
 ### silver-full-range-srgb-420-8bpc.avif
 This is generated from silver.png (3x3 rgb(192, 192, 192)) with the appropriate
 avifenc command line: