Enhancing Bumps Through Rake Lighting
By Neil Blevins
Created On: June 13th 2006
Updated On: June 1st 2009

Go here to read this tutorial in Russian.

Just a few notes on a lighting phenomena that you should keep in mind when setting up your lights. In CG, if we want texture to be more or less apparent (like a strong bumpy texture), we can just increase or decrease the amount of bump. However, in the real world, we don't have that kind of option, and so the best way to remove texture is to move your lights.

Lets say you have a bumpy wall. The following 3 images were produced in 3dsmax with a light directly from camera (position 1), at 22.5 degrees to the camera (position 2), and 45 degrees to the wall (position 3). Here's the file (max 5 format).

Notice how the closer the light gets to Position 3, the more evident the texture is. That's because as the light comes to a stronger glazing angle (also known sometimes as a raking light), there's more of the bump that's shadowed visible to the camera.

Here's a photo of a real wall with a real light. Notice as the texture on the wall gets further from the light (ie, at a greater angle from the light source), the bump gets stronger looking.

Lets consider this sphere is a really small bump on a wall. Now notice as we move the light, more and more of the sphere is appearing darker. This is the same reason why bumps become more pronounced as the light moves to the side.

People who do photograph portraits know that if you place a light from the side on a person's face, and have tight, harsh shadows, they tend to look older. This is because the principal above accentuates the wrinkles and pores on the person's skin. So to reduce that phenomena, the person lighting the scene places lights a little more at position 2 (position 1 tends to flatten out the face and is also undesirable), and use a more diffused light. You can also use this principal to make a rocky surface look even more rocky, or a flat wall feel richer with surface detail by placing the light closer to the glancing angle.

So even though we have the power to artificially increase the bumpyness of a surface in cg, to get something that looks more convincing, you may want to consider the way lighting is done in the real world and move your lights rather than changing your bump maps to an unreasonable level. Just another trick in the bag.

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