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It has been suggested that this article be split into multiple articles.This article lacks historical information.CIE XYZ color space coordinates.However, Lab is now more often used as an informal abbreviation for the CIE 1976 (L*, a*, b*) color space (also called CIELAB, whose coordinates are actually L*, a*, and b*).Thus the initials Lab by themselves are somewhat ambiguous.The color spaces are related in purpose, but differ in implementation.Both spaces are derived from the "master" space CIE 1931 XYZ color space, which can predict which spectral power distributions will be perceived as the same color (see metamerism), but which is not particularly perceptually uniform.XYZ space, but is more perceptually uniform than XYZ.Perceptually uniform means that a change of the same amount in a color value should produce a change of about the same visual importance.When storing colors in limited precision values, this can improve the reproduction of tones.Both Lab spaces are relative to the white point of the XYZ data they were converted from.Lab values do not define absolute colors unless the white point is also specified.Often, in practice, the white point is assumed to follow a standard and is not explicitly stated (e.ICC L*a*b* values are relative to CIE standard illuminant D50, while they are relative to the unprinted substrate for other rendering intents).The lightness correlate in CIELAB is calculated using the cube root of the relative luminance, and using the square root in Hunter Lab (an older approximation).Except where data must be compared with existing Hunter L,a,b values, it is recommended that CIELAB be used for new applications.Advantages of Lab
2 Which "Lab"?CIE 1976 (L*, a*, b*) color space (CIELAB)
3.CIE XYZ to CIE L*a*b* (CIELAB) and CIELAB to CIE XYZ conversions
3.Hunter Lab Color Space
4.Approximate formulas for Ka and Kb
4.Advantages of Lab
Unlike the RGB and CMYK color models, Lab color is designed to approximate human vision.It aspires to perceptual uniformity, and its L component closely matches human perception of lightness.It can thus be used to make accurate color balance corrections by modifying output curves in the a and b components, or to adjust the lightness contrast using the L component.In RGB or CMYK spaces, which model the output of physical devices rather than human visual perception, these transformations can only be done with the help of appropriate blend modes in the editing application.Because Lab space is much larger than the gamut of computer displays, printers, or even human vision, a bitmap image represented as Lab requires more data per pixel to obtain the same precision as an RGB or CMYK bitmap.RGB image to Lab and back was a lossy operation.Dan Margulis claims that this access to imaginary colors is useful going between several steps in the manipulation of a picture.In Adobe Photoshop, image editing using "Lab mode" is CIELAB D50.In ICC Profiles, the "Lab color space" used as a profile connection space is CIELAB D50.In TIFF files, the CIELAB color space may be used.In PDF documents, the "Lab color space" is CIELAB.CIE 1976 (L*, a*, b*) color space (CIELAB)
CIE L*a*b* (CIELAB) is the most complete color space specified by the International Commission on Illumination (Commission Internationale d'Eclairage, hence its CIE initialism).It describes all the colors visible to the human eye and was created to serve as a device independent model to be used as a reference.The asterisk (*) after L, a and b are part of the full name, since they represent L*, a* and b*, to distinguish them from Hunter's L, a and b, described below.CIELAB is a chromatic value color space.CIE 1976 (L*, u*, v*) color space, which preserves the same L* as L*a*b* but has a different representation of the chromaticity components.Since CIELAB and CIELUV, the CIE has been incorporating an increasing number of color appearance phenomena into their models, to better model color vision.The nonlinear relations for L*, a*, and b* are intended to mimic the nonlinear response of the eye.Furthermore, uniform changes of components in the L*a*b* color space aim to correspond to uniform changes in perceived color, so the relative perceptual differences between any two colors in L*a*b* can be approximated by treating each color as a point in a three dimensional space (with three components: L*, a*, b*) and taking the Euclidean distance between them.The RGB or CMYK values first need to be transformed to a specific absolute color space, such as sRGB or Adobe RGB.This adjustment will be device dependent, but the resulting data from the transform will be device independent, allowing data to be transformed to the CIE 1931 color space and then transformed into L*a*b*.Yn is the Y tristimulus value of a specified white object.Ka is a coefficient which depends upon the illuminant (for D65, Ka is 172.The other opponent color axis, b, is positive for yellow colors and negative for blue colors.Both a and b will be zero for objects which have the same chromaticity coordinates as the specified white objects (i.Approximate formulas for Ka and Kb
In the previous version of the Hunter Lab color space, Ka was 175 and Kb was 70.Apparently, Hunter Associates Lab discovered that better agreement could be obtained with other color difference metrics, such as CIELAB (see below) by allowing these coefficients to depend upon the illuminants.Illuminant C, the original illuminant with which the Lab color space was used.The Hunter Lab Color Space as an Adams chromatic valence space
Adams chromatic valence color spaces are based on two elements: a (relatively) uniform lightness scale, and a (relatively) uniform chromaticity scale.Therefore, the Hunter Lab color space is an Adams chromatic valence color space.Hunter, Richard Sewall (July 1948).International Color Consortium, Specification ICC.Architecture, profile format, and data structure, (2006).Photoshop Lab Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace."Color and Image Appearance Models", Color Appearance Models.John Wiley and Sons, 340.Reston, VA, USA: Hunter Associates Laboratories.This page was last modified on 25 April 2008, at 16:04.All text is available under the terms of the GNU Free Documentation License.Design and the Elastic Mind was an exhibit at New York City's MoMA with works by MIT Media Lab researchers.Rocky's pictures in the photo album.We couldn't be any happier with Rocky.This was Rosie, a slender yellow female...Copper is a wonderful boy!We are with the pups every day...They stand alone in being the perfect child friendly dog.Fear of dogs does not have time to develop."The Email field is required.""The City field is required.""The State field is required."Sign up for the Labpups newsletter.Since 1956 LAB has specialized in the manufacturing of lock pins.LAB has the reputation
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Industries.Like a wild pony emerging from a wall of flames, the second issue of LAB is here!With a whinny and a snort, it impatiently awaits to be mounted by your dauntless intellect.As in the previous issue, 0.Fancy words, snazzy pictures, and jazzy colors.Learn how LabRecyclers helps companies
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