Channel Select Map for R-G-B-A

[OccultMonk]

Is it possible to select the Red, Green, Blue or Alpha channel individually from a RGB(A) image? This is a widely used technique in game engines like Unreal, where a RGB(A) image is used for example to add scratches, wear, colors, material variations. In 3dsmax it is normally possible to do this with the color correction map by selecting 'custom' and settings all the channels to one specific channel. It would be handy for rendering game assets that already have RGB(A) maps without having to create individual grayscale images for each.

[profbetis]

You could try using Multiply node with the color of the channel you want. Multiplying by Red will get you only Red information. The image you have will now be red but I think it will still give you the values you need