I have been working on using Blender Cycles to bake textures for a game environment but the open source code that Sony provided is not optimized at all and because of this Cycles currently renders very slowly so we pretty much have to render at low resolutions. This is fine for the indirect diffuse lighting of Cycles but really makes a mess of high resolution/high frequency textures.
To deal with this, I would like to just bake the diffuse shader result to a texture and then scale it up to match the high-res base texture and combine them using GIMP.
Unfortunately, none of the simple default layer combining methods work very well for this. Darken, and Multiply work well enough for the brightness but ruin the color.
I assume that I will have to use several layers in combination with different settings to achieve this but I'm not sure where to start.
Here are some textures to help illustrate this point.
(i) a basic colored procedural texture baked with no lighting(Blender Internal).
(ii) a texture baked with Cycles_OSL diffuse lighting only
(iii) a texture baked with both of the above(this is what I'm hoping to avoid), I would like to use GIMP to get this result using textures (i) and (ii).
(iv) The final scene with textures applied and no lighting.