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### Transcript of 6. colour difference measurement

• COLOUR DIFFERENCE MEASUREMENTGranch Berhe

By Granch BerheTheory of Colouration Teaching Material

• C*=ChromaH*= Hue

• *Color difference(E) measurementsDelta CIELAB and CIELCH Assessment of color is more than a numeric expression. Usually its an assessment of the TOTAL color difference (delta) from a known standard to a given sample. Commonly CIELAB and CIELCH are used to compare the colors of two objects

One measure of the difference in colour between two stimuli or Objects is the Euclidean distance E between the two points in the three-dimensional space.E = { (X)2+ (Y)2+ (Z)2}1/2The term Eis derived from the German word for sensation Empfindung. E therefore literally means difference in sensation.

• Color difference Equation indexCIE 1976 L*, a*, b* (CIELAB) (rectangular coordinate)

E*ab=[(L*)2+ (a*)2+(b*)]1/2L=L* sample-L* standard a*=a* sample-a*standard b*=b* sample-b*standardCIE 1976 L*,C*,H*(CIELAB)(Polar coordinate)E*ab=[(L*)2+ (H*)2+(C*)]1/2 where H* is difference in hue, and C* is difference in Chroma of sample and standard.NB H* =Lab h* (/180) is metric hue difference and h* is metric hue angle diffrences.

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• By Granch BerheTheory of Colouration Teaching Material