Make specific color in a texture transparent I am working with very old model files that have BMP textures. The designers did not use a transparency in the textures or a separate alpha b/w texture. They used a specific color value that was then removed by the engine to create a transparency, similar to a chroma key. In this case, all textures used a bright purple/pink color. 

I cannot modifying the original texture images by converting them to PNG and add an alpha. I would like to figure out how to do it all in nodes.

The goal is to have this value keyed out and transparent. I have been messing around in the shader editor and cannot figure this out.  I've also been looking around online and in this forum, but the only search terms I can think of are chroma-keying which only results in Compositing results, which I don't believe is what I'm looking for.

Here is an example of the texture (its very small) and it's context:





Any help or direction would be much appreciated!
You can use a &quot;Mix RGB&quot; node set to &quot;Subtract&quot; and invert the resulting mask to get your alpha value.

Note : &quot;Compare&quot; node is a &quot;Math&quot; node with the operation set to &quot;Compare&quot;
Note : &quot;Length&quot; node is a &quot;Vector Math&quot; node with the operation set to &quot;Length&quot;. Why it is important.
Result :

You can tweak the third input of the compare node if your magenta isnt pure, to add a threshold. This will also progressively get rid of colors that are closer to the input color. Example :

Also real-life example (Green screen) :