Color Space Converter

A hex code is nothing more than three sRGB channel values written in base 16, so the conversions on this page fall into two groups. HSL, HSV and the naive CMYK figures are pure algebra on those encoded numbers: HSL and HSV are cylindrical re-projections of the RGB cube, and CMYK here is derived by taking the key value as one minus the largest channel and expressing the rest as ink percentages. The XYZ and CIELAB outputs require a real physical step first, namely linearizing sRGB by dividing by 12.92 below 0.04045 and otherwise raising ((c + 0.055) / 1.055) to the power 2.4. The linear values are then multiplied by the sRGB D65 matrix whose second row, 0.2126, 0.7152 and 0.0722, is the relative luminance formula that WCAG contrast ratios depend on. CIELAB is computed against the D65 reference white of X 95.047, Y 100.0 and Z 108.883, giving L from 0 to 100 and a and b typically spanning about minus 128 to plus 127. Knowing which numbers are device-referred matters more than the arithmetic. The CMYK values shown are a profile-free approximation with no ink limit, no dot gain compensation, and no gray component replacement strategy, so they will not match what a press produces. CIELAB is the space to use when you need to quantify a difference rather than describe a color: a Delta-E of roughly 1.0 sits near the just-noticeable difference for a trained observer, and 2.0 is a common commercial tolerance in printing and manufacturing.

The reference point for every space on this page was fixed at the 1931 meeting of the International Commission on Illumination in Cambridge, England, which adopted a standard observer built from color matching experiments run independently by William David Wright at Imperial College and by John Guild at the National Physical Laboratory. Their combined data produced the CIE XYZ space, deliberately constructed so that all real colors have positive coordinates. David MacAdam demonstrated in 1942 that the resulting xy chromaticity diagram is badly non-uniform, with the size of a just-noticeable difference varying by more than an order of magnitude across the plane, and the CIE responded in 1976 by publishing the more nearly uniform CIELUV and CIELAB spaces that are still the working standard for color difference. Albert Munsell had already ordered colors perceptually by hue, value and chroma in 1905, and Alvy Ray Smith formalized the HSV cylinder in a 1978 SIGGRAPH paper specifically so that computer artists would have controls that behaved like mixing rather than like voltages. The sRGB specification was proposed by Hewlett-Packard and Microsoft in 1996 to give the emerging web a single assumed display space and was ratified as IEC 61966-2-1 in 1999. The International Color Consortium, founded in 1993 by eight vendors, standardized the ICC profile format and chose XYZ and Lab as its profile connection spaces, which is why device-to-device conversion always routes through the 1931 data.