A similar problem occurred whilst attempting to render the whole thing… I tried to avoid rendering lots of separate layers of geometry (i.e. characters, foreground, background) and any kind of global illumination solutions that could fight with animation by flickering and getting out of hand. I had no experience with it then and I'm still avoiding it as much as I can now by faking it… I'm waiting for a real-time GI!!
After a few weird experiments with mental-ray GI, I decided to go with simple scanline and the power of Max's shadow maps. I used lots of lights: 2 main spot lights doing the sunlight through the windows and casting the sharpest shadows in the scene (I wish I had the present viewport shadow preview then!); other lights were meant to create an impression of GI by casting very soft shadows around the scene – I placed a few to reflect the sunlit floor around the room; others were mostly omni lights and spot lights directed at parts of geometry that would just look nice if lit by an angle that I decided would look nice. I also lit parts of the scene that were too dark and boring, although no light could get there in real life (the purple light on the ceiling above the fridge for example).
So, a cartoonish, unrealistic approach to lighting, I guess? Especially by creating colour contrasts with warm and cold, light colours! My first and only goal was just making it feel nice and cosy without trying to think about what's possible and what would not happen in real life... Max's translucent material helped a lot; it's bad if used with shadow maps due to unwanted artefacts which make it practically useless, but I guess the artefacts disappear and cancel each other out when lots of shadow-mapped lights are hitting it. Plants, character's skin, ears, teeth and the yellow plastic ducky are good examples of it! I think that material deserves a little more attention: it's a really good fake, especially with the occlusion layer overlaid on top!
I played with reflection maps a lot, too. Every model I did had smooth fillet edges and reflections made the highlights look cuter. In the end I used just one map, I think: a small .jpg that had good light/dark parts and some greenish shades. Every material had it, mostly mixed with fresnel and blurred a lot. This helps defining your volume, even if it's very weak. I guess I could have made a spherical map of the room and used it instead…? (Fig04)
Later I combined the scanline pass with an ambient occlusion pass and that really made a lot of difference. Occ. is a really cool invention in rendering and it saves my neck often! I rendered a few animation shots and the render time was OK, keeping in mind that I used several layers for each shot; scanline (regular mighty max scanline with speculars, reflections and shadow maps), mray occlusion, volumetric (for sun spotlights). Plus a fake DOF channel, which is a simple greyscale falloff shader applied to the whole scene and linked to a helper object's distance. That way I can control what is in focus by animating the helper's position in the scene, and doing extra tweaks in After Effects by applying curves to it. Although it can be used to accentuate the geometry in focus in many ways, it's best as a mask for Compound Blur to fake DOF. Finally, the image went thru a lot of colour corrections and some painted highlights in Photoshop to get the more cartoonish feel (Fig05).
The character's hair grew later, so I created another layer for that, and for the saliva hanging from his teeth. The animation was rendered in smaller resolution (1280x720) than the image I'm presenting now, but the render process and post work was basically the same.
You can download the HD quality WIP at: http://sittingducky.deviantart.com/art/theRapture-part1-wip-57192771
and the longer, unrendered version at: http://www.sharecg.com/v/17954/animation/theRapture-Wip2
I hope this helps a little! Thank you for reading, and to 3DTotal for Excellence Award.:)