Erasing solid color background from behind a transparent object

Question

I would like to erase solid color background from a picture like this:

Representation of result as it would appear in graphics editing software:

Is there a straight forward way to do this in Magick.NET, ImageMagick or maybe even System.Drawing.Common?

I am fine with the object being single color instead of grayscale, as I can just repeat the process for black and white pixels separately.

I already learned how to apply composite operators, filters like grayscale and such.

Something like ImageMagick's level-colors looks like it might do the job but I am failing at trying to work with the operators.

I also know that as a last resort I can do some pixel math manually like this

foreach (var pixel in magickImageClone.GetPixels())
{

}

but I am trying to avoid to do so.

Honestly I can't do much more than trial and error here because Magick.NET function names like OutDst don't really tell me me much.

fmw42 · Accepted Answer · 2024-09-17 15:40:51Z

0

In Imagemagick 6 command line (sorry I do not know C#), try

convert img.png -colorspace gray -alpha copy result.png

Is that what you want?

If on Imagemagick 7, change convert to magick.

answered Sep 17, 2024 at 5:05

fmw42

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