shithub: hugo

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resource: Use Floyd-Steinberg dithering for PNGs

Fixes #4453

--- a/resource/image.go

+++ b/resource/image.go

@@ -80,7 +80,7 @@

 	// Add or increment if changes to an image format's processing requires

 	// re-generation.

 	imageFormatsVersions = map[imaging.Format]int{

-		imaging.PNG: 1, // 1: Add proper palette handling

+		imaging.PNG: 2, // Floyd Steinberg dithering

 	}

 	// Increment to mark all processed images as stale. Only use when absolutely needed.

@@ -266,7 +266,7 @@

 			// Apply the colour palette from the source

 			if paletted, ok := src.(*image.Paletted); ok {

 				tmp := image.NewPaletted(converted.Bounds(), paletted.Palette)

-				draw.Src.Draw(tmp, tmp.Bounds(), converted, converted.Bounds().Min)

+				draw.FloydSteinberg.Draw(tmp, tmp.Bounds(), converted, converted.Bounds().Min)

 				converted = tmp

 			}

 		}

--- a/resource/image_test.go

+++ b/resource/image_test.go

@@ -273,7 +273,7 @@

 	resized, err := image.Resize("800x")

 	assert.NoError(err)

 	assert.Equal(imaging.PNG, resized.format)

-	assert.Equal("/a/gohugoio_hu0e1b9e4a4be4d6f86c7b37b9ccce3fbc_73886_800x0_resize_linear_1.png", resized.RelPermalink())

+	assert.Equal("/a/gohugoio_hu0e1b9e4a4be4d6f86c7b37b9ccce3fbc_73886_800x0_resize_linear_2.png", resized.RelPermalink())

 	assert.Equal(800, resized.Width())

 }