A blend mode is a per-pixel formula that determines how two image layers combine into a composite result

Blend modes (also blending modes or mixing modes) are mathematical operations applied per pixel when two layers are composited. The default mode is Normal: the top layer fully obscures the bottom. Because each pixel has numeric channel values (0.0 = black, 1.0 = white in normalised notation), dozens of other operations are possible — multiplying, adding, inverting, comparing, etc. Each produces a different visual result. In graphics software like Photoshop, Resolume, or Hydra, blend modes are the core vocabulary of layer compositing. Understanding the underlying math turns ‘which mode?’ from guesswork into intentional control.

Examples

Normal blend: top layer alone. Multiply: f(a,b) = ab — always darker or equal. Screen: f(a,b) = 1-(1-a)(1-b) — always lighter or equal. Difference: |a-b| — black where layers match, brightens where they differ.

Assessment

Without looking them up: predict visually what Multiply does when the top layer is solid white, solid black, and 50% grey. Then check against the formula f(a,b)=ab.