Prefer integer (un)premultiply for faster RGBA resize

lovell · Jan 24, 2023 · 9e2207f · 9e2207f
1 parent 802f560
commit 9e2207f
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Showing 14 changed files with 3 additions and 8 deletions.
diff --git a/src/pipeline.cc b/src/pipeline.cc
@@ -367,11 +367,12 @@ class PipelineWorker : public Napi::AsyncWorker {
         image = sharp::EnsureAlpha(image, 1);
       }
 
+      VipsBandFormat premultiplyFormat = image.format();
       bool const shouldPremultiplyAlpha = sharp::HasAlpha(image) &&
         (shouldResize || shouldBlur || shouldConv || shouldSharpen);
 
       if (shouldPremultiplyAlpha) {
-        image = image.premultiply();
+        image = image.premultiply().cast(premultiplyFormat);
       }
 
       // Resize
@@ -583,13 +584,7 @@ class PipelineWorker : public Napi::AsyncWorker {
 
       // Reverse premultiplication after all transformations
       if (shouldPremultiplyAlpha) {
-        image = image.unpremultiply();
-        // Cast pixel values to integer
-        if (sharp::Is16Bit(image.interpretation())) {
-          image = image.cast(VIPS_FORMAT_USHORT);
-        } else {
-          image = image.cast(VIPS_FORMAT_UCHAR);
-        }
+        image = image.unpremultiply().cast(premultiplyFormat);
       }
       baton->premultiplied = shouldPremultiplyAlpha;
 

diff --git a/test/fixtures/expected/extract-alpha-16bit.png b/test/fixtures/expected/extract-alpha-16bit.png
diff --git a/test/fixtures/expected/modulate-hue-angle-120.png b/test/fixtures/expected/modulate-hue-angle-120.png
diff --git a/test/fixtures/expected/modulate-hue-angle-150.png b/test/fixtures/expected/modulate-hue-angle-150.png
diff --git a/test/fixtures/expected/modulate-hue-angle-180.png b/test/fixtures/expected/modulate-hue-angle-180.png
diff --git a/test/fixtures/expected/modulate-hue-angle-210.png b/test/fixtures/expected/modulate-hue-angle-210.png
diff --git a/test/fixtures/expected/modulate-hue-angle-240.png b/test/fixtures/expected/modulate-hue-angle-240.png
diff --git a/test/fixtures/expected/modulate-hue-angle-270.png b/test/fixtures/expected/modulate-hue-angle-270.png
diff --git a/test/fixtures/expected/modulate-hue-angle-30.png b/test/fixtures/expected/modulate-hue-angle-30.png
diff --git a/test/fixtures/expected/modulate-hue-angle-300.png b/test/fixtures/expected/modulate-hue-angle-300.png
diff --git a/test/fixtures/expected/modulate-hue-angle-330.png b/test/fixtures/expected/modulate-hue-angle-330.png
diff --git a/test/fixtures/expected/modulate-hue-angle-360.png b/test/fixtures/expected/modulate-hue-angle-360.png
diff --git a/test/fixtures/expected/modulate-hue-angle-60.png b/test/fixtures/expected/modulate-hue-angle-60.png
diff --git a/test/fixtures/expected/modulate-hue-angle-90.png b/test/fixtures/expected/modulate-hue-angle-90.png