What are CIE XYZ tristimulus values?

CIE XYZ is a device-independent color space defined by the CIE in 1931 that models human color perception. X, Y, and Z are tristimulus values, with Y representing luminance. Almost every other perceptual space, including Lab, Luv, and Oklab, is derived from XYZ.

Why is the sRGB linearized first?

sRGB values are gamma-encoded so that bits are allocated efficiently for human vision. The XYZ matrix expects linear-light values, so each channel must first be inverse-gamma-corrected before the matrix multiplication. Skipping this step gives wrong results.

What does the D65 illuminant mean?

D65 is a standard daylight white point with a correlated color temperature near 6500K. sRGB is defined relative to D65, so this converter uses the D65 RGB-to-XYZ matrix. Using a different white point would shift every output value.

What scale are X, Y, and Z on?

Here they are scaled so the reference white has Y equal to 100, the most common convention for Lab conversions. Some tools instead use a 0 to 1 range; just divide each value by 100 to switch between the two.

What are the x and y chromaticity coordinates?

Lowercase x and y are normalized values computed as X over (X+Y+Z) and Y over (X+Y+Z). They pin down the color's chromaticity on the CIE 1931 diagram independent of how bright it is, which is useful for comparing displays and light sources.

RGB to CIE XYZ Color Converter

Convert sRGB to CIE XYZ

CIE XYZ is the master color space from which nearly all perceptual color math descends. Converting an sRGB or hex value into XYZ tristimulus values is the first step toward Lab, Luv, color-difference (Delta-E) calculations, and device-independent color management. This converter handles the gamma linearization and the standard D65 matrix for you, and also reports chromaticity coordinates.

How it works

Each sRGB channel is first scaled to 0–1 and linearized: values at or below 0.04045 are divided by 12.92, and higher values follow ((c + 0.055) / 1.055) ^ 2.4. The linear R, G, B vector is then multiplied by the standard sRGB-to-XYZ matrix for the D65 white point:

X = 0.4124564*R + 0.3575761*G + 0.1804375*B
Y = 0.2126729*R + 0.7151522*G + 0.0721750*B
Z = 0.0193339*R + 0.1191920*G + 0.9503041*B

The result is multiplied by 100 so the reference white sits at Y = 100.

Example and notes

White #ffffff converts to approximately X = 95.05, Y = 100.00, Z = 108.88 — exactly the D65 reference white. Note that Y is luminance, so two colors with the same Y have equal brightness. The chromaticity pair x = X/(X+Y+Z) and y = Y/(X+Y+Z) strips out brightness entirely, which is why it is plotted on the familiar horseshoe-shaped CIE 1931 diagram. To feed these values into a Lab conversion, keep them on the Y = 100 scale.