I must have misunderstood the question. I took it as will this "single image as a diffuse work as a diffuse and spec map in my 3D package"? That's why I mentioned shaders. The engine the art test is for must have a shader that uses the diffuse alpha as a specular map.
This is good advice. For some materials I will delete the diffuse texture altogether and just have spec+normal - especially if you have a very dark diffuse map.
i have seen this being used where the alpha channel of the diffuse is being used for the specular map. Is this really as simple as making your diffuse black and white, doing a color range select then copying that into the alpha channel?? or is there another way to do this?
You would never want to use a greyscale version of your diffuse map as a specular map. You should always make a proper texture rather than just copying the diffuse map, regardless of whether it's going to be greyscale in the alpha channel or full colour on its own.
This is very poor general advice, and varies wildly on the material type and content of the textures(some textures can be resized easier without noticing a quality loss). After doing a texture optimization pass on basically every texture in a game, i can tell you that sometimes you will want to resize the diffuse,…
One thing to note, at least in my experince when dealing with compression is that Diffuse + alpha = the same amount of texture memory compressed as diffuse, and full color spec compressed. The reason for this is that a standard 24 bit image will take 1/4th the amount of memory compressed, but a 32 bit image with alpha will…
As mentioned already, it depends on the Tech. For instance, in the Source engine, it's possible to use the alpha channel of the diffuse map for transparency, and the alpha channel of the normal map for specular.
No, you can't have a coloured spec if you need to store it in the alpha. Paint the grayscale spec map, get it looking right, then just create an alpha channel for the diffuse and paste the spec map in.
In 3dsmax you can have any map use the alpha channel. In this case you would copy your diffuse to the spec slot, and Under Mono Channel Output, switch it from "RGB Intensity" to "Alpha".