How to Put an 'x-map' in a 'y-channel'

[Slamm]

As in, putting a specular map in a diffuse texture's alpha channel.

I have no idea how to do this. I am using Gimp and am really happy with it especially considering the price.

There has got to be a way to do this in gimp right?

The idea of storing a whole map in a single channel is foreign to me. (Heck, channels are barely less foreign) Any time I do a search on it, it comes up with a lot of unrelated hits, or sites that assume a higher degree of intelligence than I currently possess. Can someone link a tutorial or tell me a keyword that will get me headed in the right direction?

Part 2: At what point does it become 'cheaper' to stack more information into a single image file, as opposed to separate simpler image files, which I would guess draws more strain on the processer?
I.E. Putting something in an alpha channel and then in the material passing that image through several opperators before it gets plugged in to, say the specular.
Vs.
Having a separate specular image that plugs directly into the specular field of the material. Which would likely cost more memory.

[darthviper107]

If it's like Photoshop you go to the channels tab and then add an Alpha channel, there's a little button on the bottom, then you make the RGB Alpha channel visible and paste.

It's cheaper to use nodes than to add more texture maps, I'm sure at some point it becomes worse to add nodes than to just make the map, but I don't know at what point that would be.

One trick you can do is to put several maps into one image using the different color channels. Like if you have 3 maps you need that are a single color or black and white you can put each into separate channels rather than separate texture maps. So you could put an Alpha, Specular, and Emissive all into one single RGB image.

[JessieG]

Putting 3 separate textures into the 3 RGB slots only works for greyscale images, not color. Though you can multiply say, a greyscale emissive map by a vector value in the material editor to give it color.

I'm sure it's just a simple copy paste function in gimp. Just look up alpha channel creation and you should be able to figure it out. Just make sure to save the texture in a format that saves the alpha channel (I use 32 bit targas) and do not turn on the "compression no alpha" option when importing the texture to UDK.

[darthviper107]

Yeah, that's why I said single color--if you wanted a yellow specular you could change a black and white image to make it yellow. But if it needed to be multiple colors you wouldn't be able to do it like that.