Lighting
The light rig used for the planet’s surface
Above you can see my lighting setup for the terrain, the vehicles were lit separately.
In most shots the terrain was lit by some 15 individual light sources, adding to the 10 or so that were needed to light each of the “characters”. If you look closely, you can make out the sky dome surrounding the landscape, which is used to create the colours of the sky.
A single directional light was used to simulate the sun, which was also the only one casting shadows. The novice would think that one directional light could simulate the sun well enough, but that’s far from the truth: To effectively simulate outdoor light in a 3D program you’ll need to use either a technique called “Global illumination” (GI), or you can always fake it using an array of well placed lights.
I opted for the second approach, because even though GI can give you more realistic and fancy results , the render times will shoot through the roof making it infeasible for use in animation.
Also, and this was even more important to me, the traditional way of placing lights gives you much more creative freedom in developing the look of your images!
Lighting is a time consuming task where the most subtle of changes can make a big difference in the final image. While adding lights you must always keep track of the number of lights you already have in your scene, because every light source adds to the final render time.
Compositing
Perhaps the worst part about rendering 3D imagery is the time required to actually see your output. Since every single frame of the film must be processed separately by the render program, you never know where a mistake or artifact may popup until it’s too late.
Through thorough optimisation and tweaking I was able to cut down the render time to an average of about 1 minute per frame, which is quite acceptable for a high quality DVD format image.
Still, I simply didn’t have the computing power to render all those frames (around 4500) in my little “render farm” consisting of my workstation and the awesome combined power of my family’s two personal computers. What I needed was a way to render my frames quicker, without reducing the overall quality!
Having lived in Japan, I was introduced to the way anime is created. I remembered that anime is produced in “layers”: You generally have a background layer consisting of the scenery or location, and a foreground layer with the characters and any other moving objects.
The foreground was rendered separately
For Bagel 2 I found it was possible to employ this exact method to tremendously shorten my render times: Fortunately for me, on Mars there needn’t be any movement in the background, so in shots without camera movement the terrain is simply rendered a single time. Later the character’s animation is rendered alone in a separate pass, eliminating the need to render the computationally intensive background again for each frame. This technique reduced the render time by around two thirds per shot .
Compositing Shadows
There is a problem with this approach, though: Shadows cast on objects can only appear if the object itself is visible in the scene, obviously. But as I already mentioned, the background which would include the shadows is only rendered once� meaning that the shadow wouldn’t move according to the movement of the character. The practical solution is to use a special shader that receives shadows and simply makes everything else transparent, just like it isn’t there.
After rendering, the file sequence containing the character and shadow can then be stacked as layers in a compositing program to create the illusion of a single intact image or, in this case, film.
