Flatness

No, I’m not talking about my stomach, as then I would have put “Roundness” or “Flabbiness” as the title. I’m cheating a bit as I’ve already put some of this elsewhere in blogdom. A nice thing about technology is when it lets you separate out bits of the world so that you can appreciate them.

We were discussing why shadows aren’t completely black and I didn’t come up with a good explanation beyond the fact that light usually gets to a particular point e.g. the floor via many routes, bouncing off other things or going direct from the sun or lightbulb, and usually the thing casting the shadow only blocks off one of the routes. I then found a video showing the effects of radiosity, which is the term (in computer graphics, at least) for light bouncing off things and going on other things. Most of the video is showing how whizzy some product is because it works out the radiosity instantly, but towards the end it shows what happens if you do computer graphics to show a room without worrying about radiosity.

The result is unrealistic and flat – obviously computer-generated. It turns out that to capture reality is really hard! The spotlight (in this case) shines on loads of different surfaces in the room – each surface is more or less shiny, has a colour, and is at a certain angle relative to each other surface in the room. The spotlight shines on a given surface and then some fraction of it (depending on how shiny it is) bounces off. What the reflection hits depends on the angles things are at and how far away things are from other things, and what colour the light is depends on the colour of the first surface – white light shining on a green wall will give only a green reflection.

The trouble is, this process repeats and repeats, with light bouncing all over the place. It’s limited mostly by the fact that the surfaces don’t reflect 100% of the light as they’re not perfect mirrors, so eventually it all peters out. Doing all this in a computer involves lots of maths (beyond me), and the video is saying “Look, we can do this maths really quickly”. I showed the video to the boys, who were impressed more by the music than the pictures *sigh*. To be expected, I suppose.

I really liked The Incredibles DVD – the story was fab (the children loved it too) and there were some nice extras. One of the extras was for geeks like me, about the computer graphics. They deliberately aimed for a cartoon kind of look, but there were some things that they worried about, such as the hair and skin. It turns out that the surface of skin traps the light falling on it a bit, so that it bounces around inside and makes it glow slightly. If you don’t model this in your computer graphics it looks like plastic rather than skin.

Radiosity reminded me of being in a sound-treated room in a linguistics lab, where nearly all of the echo was absorbed by the walls. (In a way radiosity is like the light equivalent of echoes.) We take echo so much for granted, but without it the world seemed flat in a very off-putting way. It’s hard to describe for people who haven’t experienced it – the closest is 2D sound rather than 3D – but not mono vs. stereo. I guess we subconsciously use echo to keep track of how far away things are, and without echoes our brain flails about as it doesn’t know where things are so well.