How can I perform colour and alpha replacements based on colour channel?

Question

I have extracted texture files from a game that I intend to use in Unity. In doing so, I have one texture map labeled "Multi" that is intended to be overlaid on top of the Diffuse texture. Problem is, I have found few details about "Multi" texture maps online, so I decided I would manually overlay it onto the Diffuse texture itself.

That brings me to my current issue: the Multi texture map has a red background. The foreground transitions from red to yellow, and has certain white spots. As I understand it, everywhere it is red should be transparent. Places where it is yellow should be a colour (we'll denote it A). White areas should be another colour (denoted B). This corresponds pretty neatly with the image's colour channels:

• Red -> Colour A
• Green -> Opacity
• Blue -> Colour B

There is a slight complication in that the Blue channel shouldn't simply represent Colour B directly. Since Red is maxed everywhere Blue is, it should somehow represent the "spectrum" from A to B.

How can I take the image of this texture and convert it as described? I have access to photoshop.

Here is the texture in question.

Answer 1

The red channel is almost white, but has a slightly grey tone and some details here and there. I'll ignore that here. Some of it might just come from image compression.

• Select the layer with the original image.
• Enter the Channels panel.
• Click the Blue channel.
• Press Ctrl /Cmd + A to Select All.
• Press Ctrl /Cmd + C to Copy.
• Click RGB to select all channels.
• Enter the Layers panel.
• Create a new Solid Color layer and select the color you want for the white areas.
• Alt + click the Layer Mask of the Solid Color layer to enter it.
• Press Ctrl /Cmd + V to Paste.
• Click the Solid Color layer's icon to exit the mask.
• Turn off the Solid Color layer.
• Select the layer with the original image.
• Enter the Channels panel.
• Click the Green channel.
• Press Ctrl /Cmd + A to Select All.
• Press Ctrl /Cmd + C to Copy.
• Click RGB to select all channels.
• Enter the Layers panel.
• Create a new Solid Color layer and select the color you want for the yellow areas.
• Alt + click the Layer Mask of the Solid Color layer to enter it.
• Press Ctrl /Cmd + V to Paste.
• Click the Solid Color layer's icon to exit the mask.
• Turn off the layer with the original image.
• Turn on the first Solid Color layer.
• Press Ctrl /Cmd + D to Deselect.

(The chosen colors can be changed later by double-clicking the icons of the Solid Color layers.)