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The difference or distance between two colors is a metric of interest in color science. It allows quantified examination of a notion that formerly could only be described with adjectives. Quantification of these properties is of great importance to those whose work is color-critical. Common definitions make use of the Euclidean distance in a device independent color space.

The following measurements are supported:

• Euclidean
• Weighted Euclidean
• DIN99 (2007)
• CIE76 (1976)
• CIE94 (1994)
• CIEDE2000 (2000)
• CMC l:c (1984)

All calculations are performed in either L*a*b* or L*C*H* space (as the metrics prescribe).

This library is available on packagist, like so:

composer require itwmw/color-difference

The color difference metrics are implemented via the following functions:

• Euclidean RGBgetDifferenceEuclideanRGB(Color $color): float
• Euclidean LabgetDifferenceEuclideanLab(Color $color): float
• Weighted Euclidean RGBgetDifferenceWeightedEuclideanRGB(Color $color): float
• Din99getDifferenceDin99(Color $color): float
• CIE76:getDifferenceCIE76(Color $color): float
• CIE94:getDifferenceCIE94(Color $color, CIE94 $type = CIE94::GraphicArts): float
• CIEDE2000:getDifferenceCIEDE2000(Color $color): float
• CMC l:c:getDifferenceCMC(Color $color, CMC $type = CMC::Imperceptibility): float

useItwmw\ColorDifference\Color;useItwmw\ColorDifference\Lib\RGB;useItwmw\ColorDifference\Support\CIE94;useItwmw\ColorDifference\Support\CMC;$color  =newColor(newRGB(255,183,255));$color2 =newColor(newRGB(55,65,53));echo('Din99:' .$color->getDifferenceDin99($color2) ."\n");echo('CIE76:' .$color->getDifferenceCIE76($color2) ."\n");echo('CIE94-GraphicArts:' .$color->getDifferenceCIE94($color2,CIE94::GraphicArts) ."\n");echo('CIE94-Textiles:' .$color->getDifferenceCIE94($color2,CIE94::Textiles) ."\n");echo('CMC-Acceptability:' .$color->getDifferenceCMC($color2,CMC::Acceptability) ."\n");echo('CMC-Imperceptibility:' .$color->getDifferenceCMC($color2,CMC::Imperceptibility) ."\n");echo('CIEDE2000:' .$color->getDifferenceCIEDE2000($color2) ."\n");echo('Euclidean RGB:' .$color->getDifferenceEuclideanRGB($color2) ."\n");echo('Euclidean Lab:' .$color->getDifferenceEuclideanLab($color2) ."\n");echo('Weighted Euclidean RGB:' .$color->getDifferenceWeightedEuclideanRGB($color2) ."\n");

CIE94 and CMC l:c accept an optional parameter adjusting the metric for the kind of quasimetric being evaluated. CIE94 offers an application type choice of either 'graphicArts' or 'textiles' for their eponymous use. CMC l:c offers a threshold choice of either 'acceptability' or 'imperceptibility' that nuances the just-noticeable difference between the colors.

UsereferenceWhite to specify Reference White for the Color classSupport:

• A; //Incandescent/tungsten
• B; //Old direct sunlight at noon
• C; //Old daylight
• D50; //ICC profile PCS
• D55; //Mid-morning daylight
• D65; //Daylight, sRGB, Adobe-RGB
• D75; //North sky daylight
• E; //Equal energy
• F1; //Daylight Fluorescent
• F2; //Cool fluorescent
• F3; //White Fluorescent
• F4; //Warm White Fluorescent
• F5; //Daylight Fluorescent
• F6; //Lite White Fluorescent
• F7; //Daylight fluorescent, D65 simulator
• F8; //Sylvania F40, D50 simulator
• F9; //Cool White Fluorescent
• F10; //Ultralume 50, Philips TL85
• F11; //Ultralume 40, Philips TL84
• F12; //Ultralume 30, Philips TL83

newColor(newRGB(255,183,255), referenceWhite: ReferenceWhite::D65);

UseRGBSpace to specify RGB Working Space for the Color classSupport:

• Adobe RGB (1998)
• AppleRGB
• Best RGB
• Beta RGB
• Bruce RGB
• CIE RGB
• ColorMatch RGB
• Don RGB 4
• ECI RGB
• Ekta Space PS5
• NTSC RGB
• PAL/SECAM RGB
• ProPhoto RGB
• SMPTE-C RGB
• sRGB
• Wide Gamut RGB

newColor(newRGB(255,183,255), RGBSpace: RGBSpace::sRGB_D65);

In general,RGB Working Space needs to correspond toReference White.

The default is:

newColor(newRGB(255,183,255), referenceWhite: ReferenceWhite::D65, RGBSpace: RGBSpace::sRGB_D65);