// 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;