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`(require 'color-space)`

The low-level metric functions operate on lists of 3 numbers, lab1, lab2, lch1, or lch2.

`(require 'color)`

The wrapped functions operate on objects of type color, color1 and color2 in the function entries.

- Function:
**L*a*b*:DE****lab1 lab2* Returns the Euclidean distance between

`lab1`and`lab2`.

- Function:
**CIE:DE****color1 color2 white-point* - Function:
**CIE:DE****color1 color2* Returns the Euclidean distance in L*a*b* space between

`color1`and`color2`.

- Function:
**L*a*b*:DE*94***lab1 lab2 parametric-factors* - Function:
**L*a*b*:DE*94***lab1 lab2* - Function:
**CIE:DE*94***color1 color2 parametric-factors* - Function:
**CIE:DE*94***color1 color2* -
Measures distance in the L*a*b* color-space. The three axes are individually scaled in their contributions to the total distance.

`DE*94`

is not symmetrical in its arguments.`lab1`is the “reference” color and`lab2`is the “sample” color.The CIE has defined reference conditions under which the metric with default parameters can be expected to perform well. These are:

- The specimens are homogeneous in colour.
- The colour difference (CIELAB) is <= 5 units.
- They are placed in direct edge contact.
- Each specimen subtends an angle of >4 degrees to the assessor, whose colour vision is normal.
- They are illuminated at 1000 lux, and viewed against a background of uniform grey, with L* of 50, under illumination simulating D65.

The

`parametric-factors`argument is a list of 3 quantities kL, kC and kH.`parametric-factors`independently adjust each colour-difference term to account for any deviations from the reference viewing conditions. Under the reference conditions explained above, the default is kL = kC = kH = 1.

The Color Measurement Committee of The Society of Dyers and Colorists in Great Britain created a more sophisticated color-distance function for use in judging the consistency of dye lots. With CMC:DE* it is possible to use a single value pass/fail tolerance for all shades.

- Function:
**CMC-DE***lch1 lch2 parametric-factors* - Function:
**CMC-DE***lch1 lch2 l c* - Function:
**CMC-DE***lch1 lch2 l* - Function:
**CMC-DE***lch1 lch2* - Function:
**CMC:DE****color1 color2 l c* - Function:
**CMC:DE****color1 color2* -
`CMC:DE`

is a L*C*h metric. The`parametric-factors`argument is a list of 2 numbers`l`and`c`.`l`and`c`parameterize this metric. 1 and 1 are recommended for perceptibility; the default, 2 and 1, for acceptability.

Next: Color Conversions, Previous: Spectra, Up: Color [Contents][Index]