Overview

How are water painting effects implemented in software?

High level techniques

Consider the how brushes work in real life. A brush deposits water and pigment analogly (continuously). To reflect this digitally, we takes a snapshot of the brush’s texture that is the bristles on the brush’s tip and store it as a stamp or texture. Then the brush stroke is nothing but a series of stamp/textures.

• low alpha per stamp/dab (0.05 - 0.2)
• normal/multiply blending modes

Low-alpha pigment accumluation

When pigments overlap, color builds and the opacity increases. Digitally, we replicate this effect but having every stamp is very very light but pressure/overlap induces darker colors.

• radial gradients
• two-pass stamps (inner wash + ege ring)

Soft edges + edge pooling (bloom)

Water spreads on contact; digitally, we slur the pixels slightly.

• small blur

Irregularity

Human strokes are irregular and not often modelled by liner equations. We want to add jitter to the position, size, and alpha.

• position jitter
• size jitter
• alpha jitter

Stroke design

To produce this, we want the following:

• a stamp function