commit 7ace982ac3f1a1dbda8aa5753a06fe5c937060fa
author Yuan Tong <tongyuan200097@gmail.com> Fri Mar 26 01:45:20 2021 +0800
committer GitHub <noreply@github.com> Thu Mar 25 10:45:20 2021 -0700
tree ae3a98143d27b0ab68660c4628cd7813f0779fd8
parent dfa2f0a31959f6e66ba0825d9e1418f4d805968e

Check if alpha plane is present when deciding toRGBAlphaMode (#558)

src/reformat.c

diff --git a/src/reformat.c b/src/reformat.c
index bd1acfc..3287ba0 100644
--- a/src/reformat.c
+++ b/src/reformat.c
@@ -134,17 +134,19 @@
     }
 
     state->toRGBAlphaMode = AVIF_ALPHA_MULTIPLY_MODE_NO_OP;
-    if (!avifRGBFormatHasAlpha(rgb->format) || rgb->ignoreAlpha) {
-        // if we are converting some image with alpha into a format without alpha, we should do 'premultiply alpha' before
-        // discarding alpha plane. This has the same effect of rendering this image on a black background, which makes sense.
-        if (!image->alphaPremultiplied) {
-            state->toRGBAlphaMode = AVIF_ALPHA_MULTIPLY_MODE_MULTIPLY;
-        }
-    } else {
-        if (!image->alphaPremultiplied && rgb->alphaPremultiplied) {
-            state->toRGBAlphaMode = AVIF_ALPHA_MULTIPLY_MODE_MULTIPLY;
-        } else if (image->alphaPremultiplied && !rgb->alphaPremultiplied) {
-            state->toRGBAlphaMode = AVIF_ALPHA_MULTIPLY_MODE_UNMULTIPLY;
+    if (image->alphaPlane != NULL) {
+        if (!avifRGBFormatHasAlpha(rgb->format) || rgb->ignoreAlpha) {
+            // if we are converting some image with alpha into a format without alpha, we should do 'premultiply alpha' before
+            // discarding alpha plane. This has the same effect of rendering this image on a black background, which makes sense.
+            if (!image->alphaPremultiplied) {
+                state->toRGBAlphaMode = AVIF_ALPHA_MULTIPLY_MODE_MULTIPLY;
+            }
+        } else {
+            if (!image->alphaPremultiplied && rgb->alphaPremultiplied) {
+                state->toRGBAlphaMode = AVIF_ALPHA_MULTIPLY_MODE_MULTIPLY;
+            } else if (image->alphaPremultiplied && !rgb->alphaPremultiplied) {
+                state->toRGBAlphaMode = AVIF_ALPHA_MULTIPLY_MODE_UNMULTIPLY;
+            }
         }
     }