Lab Color Space
Overview
The Lab color space is a color-opponent space with dimensions L for lightness and a and b for the color-opponent dimensions, based on nonlinearly compressed CIE XYZ color space coordinates. The Lab color space is designed to approximate human vision and so it aspires to perceptual uniformity. The L component closely matches human perception of lightness.
History
The Lab color space was designed by Richard S. Hunter in 1948 as Hunter Lab. It was then refined by the International Commission on Illumination (CIE) in 1976, becoming the CIE 1976 (L*, a*, b*) or simply CIE Lab color space. The asterisks (*) after L, a and b are pronounced star and are part of the full name, to distinguish them from Hunter's Lab. This color space is now one of the most widely used color spaces because of its ability to describe all the colors visible to the human eye.
Characteristics
The Lab color space includes all perceivable colors, which means that its gamut exceeds those of the RGB and CMYK color models. One of the most important attributes of the Lab model is device independence. This means that the colors are defined independent of their nature of creation or the device they are displayed on.
The three parameters in the model represent the lightness of the color (L* = 0 yields black and L* = 100 indicates diffuse white; specular white may be higher), its position between red/magenta and green (a*, negative values indicate green while positive values indicate magenta) and its position between yellow and blue (b*, negative values indicate blue and positive values indicate yellow). The asterisk (*) after L, a and b are part of the full name, to distinguish them from Hunter's Lab.
Usage
The Lab color space is used in various industries. In digital imaging, it is useful for retouching images, as its lightness component is separate from color. This makes it easy to adjust the lightness and color of an image separately, without one affecting the other. In the printing industry, it is used to ensure accurate color reproduction, as it is device-independent. In the textile industry, it is used for color matching and quality control.
Conversion to/from RGB
Conversion from an RGB color space to Lab can be accomplished in three steps. The RGB values are first converted to linear RGB, then to the XYZ color space, and finally to Lab. The conversion from Lab to RGB is the reverse process.
Advantages and Disadvantages
The main advantage of the Lab color space is its device independence, which allows it to describe all the colors visible to the human eye. It is also more perceptually uniform than other color spaces, with a change of the same amount in a color value perceived as about the same change in color.
However, the Lab color space is more computationally intensive than other color spaces, as it requires more processing power to calculate. It also does not have a direct correlation with the RGB or CMYK color models, making it less intuitive to use for those familiar with these models.