Calculation of Metamerism and Color Constancy Index

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CalculationofMetamerismindexandColorConstancyIndex.docx

Calculation of Metamerism index and Color Constancy Index.

Lab 8:  Calculation of Metamerism and Color Constancy Index.

Purpose: Students learn the basic skills to calculate and then evaluate the metamerism of a colored pair and color constancy for a colored object.

Tasks 1: Metamerism-Index - Calculate the color difference between A vs. B under D65 and A illuminate

Metamerism exists when two materials match under some lighting conditions but not under other lighting conditions. This can be a serious problem for manufacturers who combine various parts of different materials or materials from different sources into one product. A customer expects all the parts of a car that are the same color to match whether it is a sunny or cloudy day. Someone why buys a coordinated outfit expects the jacket and slacks to match in daylights as well as under the fluorescent light of the department store. Metamerism index is a single-number index that indicates how well two materials that match under one illuminant will match under another illuminant. Typically, CIE illuminant D65 is the reference illuminant and the test illuminant is one chosen depending on the end-use of the materials. An example of a metameric pair of colors is shown in the figure below.

 Step1: Use the data in the table to calculate DE and MI. 

 

1964 10 Degree

L*

a*

b*

D65 illuminant

Fabric A (Standard)

64.80

31.99

33.07

Fabric B (Sample)

64.31

37.16

34.26

A illuminant

Fabric A (Standard)

69.63

38.06

40.91

Fabric B (Sample)

69.64

36.20

43.66

  

Step 2: Calculate  Metamerism Index using formulas:

 

For Metamerism Index(MI): 

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Example: MI 64.80 - 64.31 + (31.99 - 37.31 + (33.07 – 34.26

Complete the table in below: 

 

1964 10 Degree

Metamerism Index (D65 vs A)

D65 illuminant

Fabric A

 

Fabric B

A illuminant

Fabric A

Fabric B

 

 

Task 2: Color Constancy.

Color Constancy is the ability to perceive colors of objects, invariant to the color of the light source. This ability is generally accredited to the Human Visual System, although the exact details remain uncertain. An example of the ability in different lighting conditions is shown in the figure below.

Step 1: Two fabrics, A and B. Please see the CIE color coordinates as below:

 

1964 10 Degree

L*

a*

b*

Fabric A

D65 illuminant (Ref)

64.80

31.99

33.07

A illuminant (Test)

69.647

36.204

43.663

Fabric B

D65 illuminant

64.314

37.166

34.262

A illuminant

69.633

38.060

40.910

Step 2: Calculate parameters for Color Constancy Index:

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1964 10 Degree Observer

L*

a*

b*

C*ab

Cusd

hab

Fabric A

D65 illuminant (Ref)

64.80

31.99

33.07

 

 

 

A illuminant (Test)

69.647

36.204

43.663

 

 

 

Fabric B

D65 illuminant (Ref)

64.314

37.166

34.262

 

 

 

A illuminant (Test)

69.633

38.060

40.910

 

 

 

 

Step 3: Calculation of Color Constancy Index:

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Color Inconstancy Index (CII)

D65 vs A

Fabric A

 

Fabric B