A distance of '1' is the maximum distance in the color space e.g. from 0, 0, 0 to 255, 255, 255 in RGB color space.

The only difference between ImagickPixel::isSimilar and ImagickPixel::isPixelSimilar is that isSimilar needs to be scaled by the quantum value.


Color 1 Color 2 Test distance * 255 Is within distance
rgb(245, 0, 0) rgb(255, 0, 0) 5.196152423 no
rgb(245, 0, 0) rgb(255, 0, 0) 5.773502692 yes
rgb(0, 0, 0) rgb(7, 7, 0) 5.196152423 no
rgb(0, 0, 0) rgb(7, 7, 0) 5.773502692 yes
rgba(0, 0, 0, 1) rgba(7, 7, 0, 1) 5.196152423 no
rgba(0, 0, 0, 1) rgba(7, 7, 0, 1) 5.773502692 yes
rgb(128, 128, 128) rgb(128, 128, 120) 4.041451884 no
rgb(128, 128, 128) rgb(128, 128, 120) 4.618802154 yes
rgb(0, 0, 0) rgb(255, 255, 255) 254.9 no
rgb(0, 0, 0) rgb(255, 255, 255) 255 yes
rgb(255, 0, 0) rgb(0, 255, 255) 254.9 no
rgb(255, 0, 0) rgb(0, 255, 255) 255 yes
black rgba(0, 0, 0) 0 yes
black rgba(10, 0, 0, 1.0) 5.773502692 yes

A distance of '1' is the maximum distance in the color space e.g. from 0, 0, 0 to 255, 255, 255 in RGB color space.

The only difference between ImagickPixel::isSimilar and ImagickPixel::isPixelSimilar is that isSimilar needs to be scaled by the quantum value.

        // The tests below are written with the maximum distance expressed as 255
        // so we need to scale them by the square root of 3 - the diagonal length
        // of a unit cube.
        $root3 = 1.732050807568877;

        $tests = array(
            ['rgb(245, 0, 0)', 'rgb(255, 0, 0)', 9 / $root3, false,],
            ['rgb(245, 0, 0)', 'rgb(255, 0, 0)', 10 / $root3, true,],
            ['rgb(0, 0, 0)', 'rgb(7, 7, 0)', 9 / $root3, false,],
            ['rgb(0, 0, 0)', 'rgb(7, 7, 0)', 10 / $root3, true,],
            ['rgba(0, 0, 0, 1)', 'rgba(7, 7, 0, 1)', 9 / $root3, false,],
            ['rgba(0, 0, 0, 1)', 'rgba(7, 7, 0, 1)', 10 / $root3, true,],
            ['rgb(128, 128, 128)', 'rgb(128, 128, 120)', 7 / $root3, false,],
            ['rgb(128, 128, 128)', 'rgb(128, 128, 120)', 8 / $root3, true,],
            ['rgb(0, 0, 0)', 'rgb(255, 255, 255)', 254.9, false,],
            ['rgb(0, 0, 0)', 'rgb(255, 255, 255)', 255, true,],
            ['rgb(255, 0, 0)', 'rgb(0, 255, 255)', 254.9, false,],
            ['rgb(255, 0, 0)', 'rgb(0, 255, 255)', 255, true,],
            ['black', 'rgba(0, 0, 0)', 0.0, true],
            ['black', 'rgba(10, 0, 0, 1.0)', 10.0 / $root3, true],);

        $output = "";

        $output .= "";

        foreach ($tests as $testInfo) {
            $color1 = $testInfo[0];
            $color2 = $testInfo[1];
            $distance = $testInfo[2];
            $expectation = $testInfo[3];
            $testDistance = ($distance / 255.0);

            $color1Pixel = new \ImagickPixel($color1);
            $color2Pixel = new \ImagickPixel($color2);

            $isSimilar = $color1Pixel->isPixelSimilar($color2Pixel, $testDistance);

            if ($isSimilar !== $expectation) {
                echo "Test distance failed. Color [$color1] compared to color [$color2] is not within distance $testDistance FAILED." . NL;
            }

            $layout = "";

            $output .= sprintf(
                $layout,
                $color1,
                $color2,
                $distance,
                $isSimilar ? 'yes' : 'no'
            );
        }

        $output .= "
Color 1 Color 2 Test distance * 255 Is within distance
%s %s %s %s
"; return $output;