The Lab color model (L*a*b*) is a device-independent color model known as CIELab. It was developed in the 1930s by the Commission Internationale d`Eclairage( CIE) and is based on human perception and not on colorimetric color values.
The Lab color model can be used as a reference color space. It contains device-independent color spectra such as the RGB and CMYK color models and supports the lossless conversion of color information from one color model to another. Therefore, the Lab color model is also used as an exchange format between devices with different color models.
The Lab color model is a three-axis color model. In the Lab name, the "L" stands for luminance, daa "a" represents the horizontal red- green axis, and the "b" represents the vertical yellow- blue axis. The horizontal a-axis has the value range between -128 for green and +127 for red, the vertical b-axis has the value range between -128 for blue and +127 for yellow and the luminance axis has the value range between 0 for black and 100 for white. If the horizontal value is positive, then it is red, if it is negative, then it is green. In the vertical axis, a positive value corresponds to yellow, a negative one to blue. The achromatic point is at the coordinate center. The color saturation corresponds to the length of the color vector, the hue to its angularity. The color space of the Lab color model includes more colors than the color spaces of the RGB color model or the CMYK color model.
For color matching, separate color spaces are specified for each input device and output device, which characterize the color gamut. The color spaces are device-dependent and vary in size. For the color matching CIELab offers description models with which one can develop exact conversion methods between the different device profiles.