Replace all colours to specific colour

[defunky]

I have a regular image with multiple colours, what is the most efficient way to replace all these colours to a single colour, e.g. all pixels non-alpha pixels become red.

I found Opaque() method but that targets a single colour only.

[dlemstra]

One option could be to use the Fx method:

using var image = new MagickImage("input.png");
image.Fx("a == 0 ? a : red");
image.Write("output.png");

Some documentation about that can be found here: https://imagemagick.org/script/fx.php.