CIELAB color space

While the LAB space is not truly perceptually uniform, it nevertheless is useful in industry for detecting small differences in color.

The CIELAB space is three-dimensional and covers the entire gamut (range) of human color perception.

The a* and b* axes are unbounded and depending on the reference white they can easily exceed ±150 to cover the human gamut.

[4] The lightness value, L* in CIELAB is calculated using the cube root of the relative luminance with an offset near black.

This results in an effective power curve with an exponent of approximately 0.43 which represents the human eye's response to light under daylight (photopic) conditions.

The asterisks (*) after L*, a*, and b* are pronounced star and are part of the full name to distinguish L*a*b* from Hunter's Lab, described below.

In color managed systems, ICC profiles contains these needed data, which are then used to perform the conversions.

Unlike the RGB and CMYK color models, CIELAB is designed to approximate human vision.

The L* component closely matches human perception of lightness, though it does not take the Helmholtz–Kohlrausch effect into account.

In an integer implementation such as TIFF, ICC or Photoshop, the large coordinate space results in substantial data inefficiency due to unused code values.

[7] Using CIELAB in an 8-bit per channel integer format typically results in significant quantization errors.

Even 16-bit per channel can result in clipping, as the full gamut extends past the bounding coordinate space.

for the CIE 1931 (2°) standard colorimetric observer and assuming normalization where the reference white has Y = 100, the values are: For Standard Illuminant D65: For illuminant D50, which is used in the printing industry: The division of the domain of the f function into two parts was done to prevent an infinite slope at t = 0.

The HSL values are a polar coordinate transformation of what is technically defined RGB cube color space.

This name is commonly used by information visualization practitioners who want to present data without the bias implicit in using varying saturation.

CIELAB and CIELUV can also be expressed in cylindrical form (CIELChab[13] and CIELChuv, respectively), with the chromaticity components replaced by correlates of chroma and hue.

Oklab is built on the same spatial structure and achieves greater perceptual uniformity.

It was designed to be computed via simple formulas from the CIEXYZ space, but to be more perceptually uniform.