Observation. In an additive system (a sensor, a display) increasing saturation raises at least one channel and increases luminance. In a subtractive system (dye layers on film) increasing colour concentration absorbs more light and decreases luminance. This difference explains much of the "heavier" colour of film.

Implementation. Subtractive Density converts to scene linear, measures saturation (C / max) and hue per pixel, and applies an exposure reduction:

stops = Density × w(hue) × saturation^Response × (1 − Protect × brightness)

Applied as a pure gain, this preserves hue and chromaticity. An optional, small Richness term restores perceived saturation in proportion to the density applied.

Parameters

• Density (0–2 stops, default 0.6)
• Per-vector weights: Red 1.0, Yellow 0.6, Green 1.0, Cyan 0.8, Blue 1.2, Magenta 1.0 (yellow is kept low to protect skin)
• Saturation Response (0.5–3.0)
• Richness (0–1)
• Highlight Protect (0–1), which eases off above roughly 1 stop over grey
• Show Density Map

Working encodings: DaVinci Intermediate, ACEScct, linear. Requires Resolve Studio (DCTL).