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  = L_T – L_S (S = Std, T = Trial)

a^* = a_T - a_S

 b^*= b_T - b_S