Composite w/ CopyAlpha

[forensicmike]

Hi all, thanks for taking the time to look. I am striking out on masking an image using the Composite / CopyAlpha operator.

I essentially have the same problem as this ancient issue: #20

I've confirmed that the mask looks like it should - e.g. a black background with white pixels where I want pixels to be copied. I also confirmed that the mask's HasAlpha is set to false, as per the resolution for issue 20.

The output, however, is the entire input image. Doesn't matter what I do it's the entire input image!

I've tried using separate input images, including different formats (png and jpeg), and it simply does nothing.

Here's the code - I am using imagemagick.net q16-anyCPU v13.1.3. Note my use case is polygons but I've just gone with the circle here as it's what was asked in the referenced issue above, and is simpler code.

using var mg = new MagickImage(CurrentFilePath);
//mg.VirtualPixelMethod = VirtualPixelMethod.Transparent;
using var mask = new MagickImage(MagickColors.Black, mg.Width, mg.Height);
mask.HasAlpha = false;

var diameter = mask.Width < mask.Height ? mask.Width : mask.Height;
int originY = (mask.Height - diameter) / 2 + diameter / 2;
int originX = (mask.Width - diameter) / 2 + diameter / 2;

var drawables = new Drawables();
drawables.FillColor(MagickColors.White);
drawables.StrokeColor(MagickColors.White);
drawables.Circle(originX, originY, 0, originY);

mask.Draw(drawables);

mg.Composite(mask, CompositeOperator.CopyAlpha);
using var ms = new MemoryStream();
mg.Write(ms, MagickFormat.Png);

ms.Position = 0;
BitmapImage bitmapImage = new();
bitmapImage.BeginInit();
bitmapImage.StreamSource = ms;
bitmapImage.CacheOption = BitmapCacheOption.OnLoad;
bitmapImage.EndInit();

Clipboard.SetImage(bitmapImage);

So to reiterate when I set mg.Write(ms, MagickFormat.Png); to mask.Write(ms, MagickFormat.Png); the result looks good:

But when I change it back to mg.Write, the pasted image looks identical to the input image - no masking at all.

Does anyone have any idea what I'm doing wrong?

I've also tried mg.Write with MagickFormat.Jpg just in case. Also, the mg.VirtualPixelMethod is commented out but I have tried it with and without and there is no difference in output. I've also tried pasting into multiple apps (Paint, Photoshop) with same result.

[forensicmike]

It looks like it's the Clipboards fault? I threw in a File.WriteAllBytes(@"c:\temp\test.png", mg.ToByteArray()); and the resultant image is perfect. Closing this.

[dlemstra]

What happens when you use ToBitmapSource extension method from the Magick.NET.SystemWindowsMedia NuGet package?