Wednesday, 10 October 2018

Define Hue, value and chroma, explain uniform (L* a* b*) 3 dimensional color space according to CIE Lab system.


Experiment No: 03

Experiment Name: Define Hue, value and chroma, explain uniform (L* a* b*) 3 dimensional color space according to CIE Lab system.

Fig: Uniform (L* a* b*) 3 dimensional color space.

Figure:

CIE Lab system:

CIE stands for commission of internation’ale E’clarge.

In 1976 CIE recommended the CIE L* a* b* (Three dimensional color system) system. The system is intended to be a uniform color space with the following properties:

(1) A rectangular three dimensional color space (L* a* b*) in which all surface color can be represented.
(2) The distance between the points representing the colors of two sample is proportional to the visual color difference between them.
(3) L* a* b* values can be easily interpreted in terms of hue, lightness (value) and depth of color (chroma).
(4) L* is the vertical axis and represents lightness 0 being a perfect black and 100 a perfect white.
(5) a* in the axis in the plane normal to L* which represent redness (a*+) and greenness (a*-).
(6) b* in the axis normal to both L* and a* which indicate yellowness and balances  

h0 = 00 Perfect red.
h0 = 3600 Perfect red.
h0 = 450 Orange.
h0 = 1350 Lime green (light green).
h0 = 2250 Cyan.
h0 = 2700 Blue.
h0 = 3150 Magenta.
Figure:

In CIE L* a* b* space the color difference between a standard and a trial sample is expressed by numerically DE.

\ DE =  √(("" L^(*2)+ "" a^(*2)+ "" b^(*2)))

Where  = LT – LS (S = Std, T = Trial)
a^* = aT - aS
 b^*= bT - bS








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