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Chapter Two · Filter (Processors)

Normal Map

Turns a picture into a normal map: the blue-lilac image used in 3D work to describe which way a surface is facing at every point, so flat geometry can be lit as though it had bumps.

It reads brightness as height. Bright means high, dark means low. Then it measures the slope at each pixel in both directions and writes those two numbers into the red and green channels, with blue carrying what is left.

Two details are worth knowing. Height is measured using a perceptual brightness rather than a simple channel average, so the surface follows how bright things look rather than what their numbers say, which matters on saturated colours. And the edges wrap, so a tiling source produces a tiling normal map, which is what you want if the texture is going to repeat.

Further reading Normal mapping Bump mapping