Overcast Lighting - Compositing

I only waited about 8 minutes for this render, which was 1920x1080:












The results were pretty satisfying, but I knew that they were just a jumping point for the final image. The parts that were working for me were the very even lighting and wide specularity of the objects, including those that had originally exhibited sharp spec highlights in the moonlight scene. Also, the light had a beautifully smooth falloff from the window to the foreground. This falloff worked very well with the variant specularity of the walls and floor especially, with blurry "blobs" that created the illusion of slightly dirty surfaces.

I rendered out a quick ambient occlusion pass to help carve out crevices and add some depth to the scene (even though the diffuse lighting was meant to flatten out the lighting quite a bit):
In Nuke, I adjusted its histogram to reduce the contrast and also redistribute the occlusion to be less spread out:

I color-corrected the beauty pass and comped it in Nuke with its ambient occlusion pass and depth pass, as well as with an image for the background behind the window:







One of my favorite things about the image was that it was lit by a single light and did not carry the CG quality of looking too consistent and clean. However, I felt that it looked too flat because of its lack of specularity, and I wanted to bring back the shininess of specific surfaces, such as the sink and pipes, bathtub, shower rod, mirror and radiator.

I knew that if I were to be rendering out an image sequence, I would prefer to create a specular pass instead of adding lights to the scene and facing a possibly drastically higher render time. From my experience with rendering, I've found that doing so would probably have more of an exponential rather than additive increase in render time. I created a very simple Blinn with the following settings, including a Solid Fractal mapped to its Specular Color node:





















I was satisfied with the lighting of my moonlight scene and knew that I had lit the scene to accent the spec highlights of the scene. So, I ended up re-using the exact same light rig, knowing that I could adjust the render's color and exposure in the compositing stage. I used Mental Ray to render the scene with this light setup and the Blinn mapped to the necessary objects. All of the objects whose specularity I wanted to remain untouched in the final composite were assigned a black surface shader. (In this screenshot, I've made the surface shader green to help distinguish the specular-shaded objects from what did not have spec attached):
The rendered spec pass (of course with the surface shader turned to black again):
This pass took about 5 minutes to render, versus what I predicted to be at least 15 minute render if I had rendered out the photon-mapped scene with this light rig - not to mention some tedious adjustment of the light rig in order to get it to play well with the photon mapping.

I also adjusted the hue of the spec pass to make it less blue and a bit more yellow, and screened it on top of the beauty pass.





















My final composited image:
I was very happy with the outcome of the final image. Using a combination of photon mapping, direct lighting and basic compositing, I felt that I was able to effectively immitate the overcast light of my reference photos. Lighting was nicely gradated but not flat to the point of looking perfectly CG, the green wall color radiated off of the bathtub, and the specular pass really helped to sell the believability of the scene. I'll definitely be using this approach in my thesis project, and I know that with better shaders, I'll be able to get even better results.