L*a*b* Color is the most complete color mode used to describe the colors visible to the human eye. The three parameters of color are L for luminance of the color, a represents the color’s position between red and green, and b represents its position between yellow and blue.
The Lab Color mode was created to serve as a device-independent, absolute model to be used for a reference. Lab attempts to simulate the full gamut of color; however, it is a three-dimensional model and can’t be represented properly within Photoshop. Therefore, the * after the L, a, and b is used to signify that it is a derivative model. Lab images can only be printed on PostScript Level 2 and Level 3 printers; for all other professional printers, Lab images must first be converted to CMYK mode.
The Lab Color mode is generally only used by imaging professionals seeking the truest color fidelity because it supports all the colors in both the RGB and CMYK Color modes.
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