Color Difference

A library for calculating the perceptual difference between colors (∆E).

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).

Quick Start

This library is available on packagist, like so:

composer require itwmw/color-difference

Usage

The color difference metrics are implemented via the following functions:

• Euclidean RGB getDifferenceEuclideanRGB(Color $color): float
• Euclidean Lab getDifferenceEuclideanLab(Color $color): float
• Weighted Euclidean RGB getDifferenceWeightedEuclideanRGB(Color $color): float
• Din99 getDifferenceDin99(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

use Itwmw\ColorDifference\Color;
use Itwmw\ColorDifference\Lib\RGB;
use Itwmw\ColorDifference\Support\CIE94;
use Itwmw\ColorDifference\Support\CMC;

$color  = new Color(new RGB(255, 183, 255));
$color2 = new Color(new RGB(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.

Reference White

Use referenceWhite to specify Reference White for the Color class Support:

• 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

new Color(new RGB(255, 183, 255), referenceWhite: ReferenceWhite::D65);

RGB Working Space

Use RGBSpace to specify RGB Working Space for the Color class Support:

• 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

new Color(new RGB(255, 183, 255), RGBSpace: RGBSpace::sRGB_D65);

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

The default is:

new Color(new RGB(255, 183, 255), referenceWhite: ReferenceWhite::D65, RGBSpace: RGBSpace::sRGB_D65);