Color model (Lab / IPT)

A color model is just a coordinate system for describing color. RGB (the 3D cube) is device-referred — perfect for driving a display, poor for reasoning about appearance, because equal RGB steps don’t look equal. So the science uses others. CIE XYZ is the device-independent master space everything converts through. CIELAB and IPT are perceptual, opponent models: they split color into a lightness axis and two color axes (roughly red–green and yellow–blue), matching how the eye encodes color after the cones. IPT (and its relative ICtCp) has more stable hue lines, which is why HDR standards lean on it. The practical takeaway: “a perceptual space” means one where a straight push holds its hue instead of drifting.

First used in: 3.1 · Color science foundations