There’s a War in Wunderland has an unmistakable style. This is down to a few things - the texture work, the simple characters, the animation, the rendering and post-processing and the presentation. I was responsible for a lot of the look and feel of the finished frame, and here’s a quick explanation of how it goes together.
There’s a strong dichotomy between the realism of the rendering and the cartoonish subject and art style. This is intentional, and found in another popular animation technique - stop motion. It’s important that the audience realises that they’re watching paper models, but that can’t get in the way of the stylised world that the texture artists and modellers spent so much effort on making. This conflict was responsible for a lot of the decisions that had to be made in the compositing process.
Colour and Ambient
The first example of this is in the bottom two passes (refer to the diagram) - the colour and the ambient. The colour is a strongly-lit scene, with stark contrast between the shadows and the highlights - the sort of setup you might use to demonstrate a model. The ambient pass has just one neutral ambient light illuminating everything. This has the important effect of making every rendered pixel identical to its corresponding texel - everything is the same colour as it is on the texture map. By balancing the two (varying the opacity of the upper one) you can choose how much effect the lighting has.
Of course, the same effect could be achieved by altering the lighting setup before you render, but having both passes allows much more immediate control over the setup. Small changes can be made with no additional render time or loss of quality. While it’s good to reduce your render time as much as possible, when rendering out another pass gives allows you to be intuitive, impulsive and artistic it’s usually worth it.
I could not imagine doing a film like this without ambient occlusion. The flat colours in the textures would make the film look dull if it were lit with hard lights. Raytraced and area lights would overcome this, but with a big hit on render time. They are also harder to balance and to maintain uniformity across all the shots.
Ambient occlusion allows us to generate those tones, and adds a lot to the realism of the scene. For the exterior shots I used two AO passes, which surprised some people. It’s certainly hard on render time, but I think it was justified. The narrow pass contains everything in the scene, and results in the effect you’re used to. The broad AO pass contains only the environment. Because the exterior shots are set in a city, complex lighting is needed to darken alleyways, lighten parks and burn out rooftops. An ambient occlusion setup to register occlusion at a high distance is an excellent way to fake this, and is much faster than an equivalent raytraced light.
It would have been nice to bake the broad AO into the textures, but for speed reasons I advised against this. The UV maps had a lot of shared space, which can be overcome but not too easily.
Ambient occlusion presents a special problem when dealing with decals - planes with an alpha channel defining the shape. The AO shader would ignore the alpha channel, leaving an unsightly border around it. So we omitted decals from the AO pass, and if necessary rendered them into their own layer.
The character had his own pass so that he could be made to stand out from his surroundings. While it’s usually better to achieve this with texturing, lighting, shot composition and so on, this additional technique can be effective when used subtly.
The character pass was also used to mask out the broad ambient occlusion - when compositing an AO pass it’s important to be careful that everything visible in the AO is also visible in the other passes, otherwise ghostlike effects occur.
Finally, a depth pass was rendered to make it easy to add a depth of field effect. After Effects and Photoshop have a Lens Blur filter which can read a depth map and accurately simulate depth of field. By sampling form the depth channel you can accurately set the focal distance to the character, and even animate this for focus pulls.
Depth of field is important for adding to the realism of a scene, and can also be used to convey a sense of scale - by carefully mimicking the camera used in miniature work, you can subtly suggest that these are models.
One effect we particularly wanted to avoid was motion blur. Though it’s often an important tool used to make a scene realistic, in this case it would be entirely inappropriate. Stop motion is only ever sampling still scenes, and so there is no motion blur. There are exceptions when it can be added manually for fast moving objects, but most professional stop motion studios would prefer to use traditional animation techniques such as squash and stretch to convey this.
A shadow pass was also rendered in some exterior scenes. It’s useful to ground distant characters, present a time of day and, in one shot, add dramatic effect.
Skies and clouds were imported separately, which made it easier to control but introduced extra difficulties in camera moves.
So that’s how it was done.