Visually equal color gradient steps require geometrically increasing physical differences, not arithmetically equal ones

The Weber-Fechner Law states: visual perception of an arithmetical progression depends upon a physical geometric progression. Applied to color gradations: adding equal physical increments (e.g., equal numbers of paint layers) produces diminishing perceived steps — each physical increment looks smaller than the last, approaching saturation. To produce visually even steps (where each step looks as large as the next), the physical quantities must grow geometrically (1, 2, 4, 8, 16…). This law applies across senses (sound, weight, temperature) and explains why linear ramps in RGB or ink layers do not look linear. Consequence for digital design: perceptually uniform color spaces (CIELAB L*, OKLAB) encode lightness along a Weber-Fechner-corrected axis.

Examples

A grey scale built with equal increments of India ink layers looks bottom-heavy. Geometric progression of layers looks visually even. In GLSL: linearizing sRGB before blending (gamma correction) corrects the Weber-Fechner nonlinearity.

Assessment

Explain why a linear gradient from 0 to 1 in RGB looks different from a linear gradient in CIELAB L*. Name the law governing this difference and describe what physical quantity sequence would produce visually even steps.