`(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: **CIE:DE***` color1 color2 white-point`

— Function:**CIE:DE***` color1 color2`

— Function:

Returns the Euclidean distance in L*a*b* space between

color1andcolor2.

— 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`

— Function:

— Function:

— Function:

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.lab1is the “reference” color andlab2is 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-factorsargument is a list of 3 quantities kL, kC and kH.parametric-factorsindependently 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`

— Function:

— Function:

— Function:

— Function:

— Function:

`CMC:DE`

is a L*C*h metric. Theparametric-factorsargument is a list of 2 numberslandc.landcparameterize this metric. 1 and 1 are recommended for perceptibility; the default, 2 and 1, for acceptability.