Silent data corruption of output images resulting in incorrect colors

[park-jemin]

Magick.NET version

Magick.NET-Q8-AnyCPU v14.10.4

Environment (Operating system, version and so on)

Linux

Description

Starting with Magick.NET 14.10.4 (which bundles ImageMagick 7.1.2-16), images with alpha channels appear visibly dimmer after being processed with a CopyAlpha composite operation.

Steps to Reproduce

// Upload any PNG with transparency as an image
var magickImage = new MagickImage(inputStream);  // PNG with alpha

// Resize with alpha preservation
using var sourceImageAlpha = new MagickImage(magickImage);
sourceImageAlpha.Resize(150, 150);
magickImage.Alpha(AlphaOption.Off);
magickImage.Resize(150, 150);
magickImage.Composite(sourceImageAlpha, CompositeOperator.CopyAlpha);

// Convert and write
magickImage.Format = MagickFormat.Png;
await magickImage.WriteAsync(outputStream);

// Result: output image appears dimmer than input, dark areas become transparent

Images

Original:

Output:

[dlemstra]

I found what caused this on the ImageMagick side and I pushed a patch to restore the old behavior. This should be resolved in the next release.