commit f9297fa7611a410d326c066a3fe3b5f443ff0d8f
author Vignesh Venkatasubramanian <vigneshv@google.com> Wed Aug 17 11:51:59 2022 -0700
committer Vignesh Venkatasubramanian <vigneshvg@users.noreply.github.com> Wed Aug 17 12:52:50 2022 -0700
tree a1d1fc46eb5d553144521ae9e2e6bba7ef3c1265
parent 7a084710fae7ebe78c6c437df746b39ab90ef977

avifenc: Set YUV format to 400 for grayscale PNGs

If the input is a grayscale PNG file, then AVIF output format can
be set to monochrome (YUV400) if the user does not set the --yuv
option explicitly.

apps/shared/avifpng.c

diff --git a/apps/shared/avifpng.c b/apps/shared/avifpng.c
index 5bc1b3e..effaa6b 100644
--- a/apps/shared/avifpng.c
+++ b/apps/shared/avifpng.c
@@ -127,9 +127,14 @@
     avif->height = rawHeight;
     avif->yuvFormat = requestedFormat;
     if (avif->yuvFormat == AVIF_PIXEL_FORMAT_NONE) {
-        // Identity is only valid with YUV444.
-        avif->yuvFormat = (avif->matrixCoefficients == AVIF_MATRIX_COEFFICIENTS_IDENTITY) ? AVIF_PIXEL_FORMAT_YUV444
-                                                                                          : AVIF_APP_DEFAULT_PIXEL_FORMAT;
+        if (avif->matrixCoefficients == AVIF_MATRIX_COEFFICIENTS_IDENTITY) {
+            // Identity is only valid with YUV444.
+            avif->yuvFormat = AVIF_PIXEL_FORMAT_YUV444;
+        } else if ((rawColorType == PNG_COLOR_TYPE_GRAY) || (rawColorType == PNG_COLOR_TYPE_GRAY_ALPHA)) {
+            avif->yuvFormat = AVIF_PIXEL_FORMAT_YUV400;
+        } else {
+            avif->yuvFormat = AVIF_APP_DEFAULT_PIXEL_FORMAT;
+        }
     }
     avif->depth = requestedDepth;
     if (avif->depth == 0) {