How can I combine two colored textures so that the final image is blended to match a specific lighting setup I have been working on using Cycles to bake textures for a game environment.  This works well for base lighting which can be rendered at low resolutions, then scaled-up and blurred but for high resolution/high frequency textures Cycles takes way to long to render.  Basically this takes about an hour per texture at 1024x1024 since I have to render at higher samples since the final texture cannot be blurred.  However this only takes a few minutes for the base diffuse texture rendered at 512x512 then blurred and scaled up.

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 both using the compositor but I really have no idea where to begin.  What nodes would I use and with what settings?  

Here are some textures to help illustrate this point.

(i) a basic colored procedural texture baked with no lighting(Blender Internal), the original is 2048x2048.

(ii) a texture baked with Cycles_OSL diffuse lighting only.(512x512)

(iii) a texture baked with both of the above(this is what I'm hoping to avoid)

(iv) The final scene with textures applied and no lighting.









UPDATE: Well, the multiply node seems to be what I needed for this, thanks, here is a test that that uses more diverse colors.  The strip on the left is the Cycles bake output done the way things are normally done and the strip to the right uses the compositor node to combine the original colors with the diffuse shader node output.  Both look identical so this all works.(except for the weird margin problem but that's off-topic)

To the right is the scene, the center cube was baked.
Basic node trees would be like this:



Sample file

Note:


The Composite node will only output based on Scene size set in Render tab. If you want to output full-size composite result, you have to use File Output node.
Mask node is sort of a trick to apply the transform result without being limited by the original image size.