Lab Color Space
A perceptually uniform color space where numerical distance between colors matches human visual perception. Used as the device-independent connection space in ICC color management for accurate color conversion between RGB, CMYK, and display profiles.
Lab color space (formally CIELAB or CIE L*a*b*) is a perceptually uniform color space standardized by the CIE in 1976. Its defining property is that Euclidean distance between two points approximates perceived color difference. This makes Lab indispensable for quantitative color evaluation and device-independent color description.
- L* (Lightness): Ranges from 0 (black) to 100 (white) on a nonlinear scale matching human lightness perception. L*=50 corresponds to perceptual mid-gray
- a* (green-red axis): Negative values indicate green, positive values indicate red. Typical range spans approximately -128 to +127
- b* (blue-yellow axis): Negative values indicate blue, positive values indicate yellow, mirroring the a* range
Lab's greatest strength is device independence. While RGB and CMYK are tied to specific device gamuts, Lab encompasses all human-visible colors. In ICC color management, conversions route through Lab as the Profile Connection Space: source profile maps to Lab, then Lab maps to the destination profile.
Color difference is quantified using ΔE metrics. The original ΔE*ab has been superseded by CIEDE2000 (ΔE00), which corrects for perceptual non-uniformities. A ΔE00 below 1.0 is generally imperceptible. In image processing, operating on L* alone allows contrast and sharpness adjustments without shifting hue or saturation.