Here is a function that compares two HEX colors for similarity. This can be useful if you want to detect colors that are not different enough to see for the naked eye. It returns a bool: TRUE if the colors are similar to each other (within tolerance) or FALSE if they are different enough.
I tested a few colors and came up with a tolerance of 35 (rgb value - should be between 0 and 255) but you can change that tolerance by passing a third parameter to the function.
<?php
function compareColors ($col1, $col2, $tolerance=35) {
$col1Rgb = array(
"r" => hexdec(substr($col1, 0, 2)),
"g" => hexdec(substr($col1, 2, 2)),
"b" => hexdec(substr($col1, 4, 2))
);
$col2Rgb = array(
"r" => hexdec(substr($col2, 0, 2)),
"g" => hexdec(substr($col2, 2, 2)),
"b" => hexdec(substr($col2, 4, 2))
);
return ($col1Rgb['r'] >= $col2Rgb['r'] - $tolerance && $col1Rgb['r'] <= $col2Rgb['r'] + $tolerance) && ($col1Rgb['g'] >= $col2Rgb['g'] - $tolerance && $col1Rgb['g'] <= $col2Rgb['g'] + $tolerance) && ($col1Rgb['b'] >= $col2Rgb['b'] - $tolerance && $col1Rgb['b'] <= $col2Rgb['b'] + $tolerance);
}
?>
imagecolorclosest
(PHP 4, PHP 5, PHP 7, PHP 8)
imagecolorclosest — 取得与指定的颜色最接近的颜色索引值
说明
返回图像调色板中与指定的 RGB 值最“接近”的颜色索引。
计算所需颜色与调色板中每种颜色之间的“距离”，就好像 RGB 值表示三维空间中的点一样。
如果图象由文件创建，只有该图象使用到的颜色会被解析。仅存在于调色板中的颜色不会被解析。
参数
-
image -
由图象创建函数(例如imagecreatetruecolor())返回的 GdImage 对象。
-
red -
红色成分的值。
-
green -
绿色成分的值。
-
blue -
蓝色成分的值。
返回值
返回图像调色板中最接近指定颜色的索引
示例
示例 #1 在图像中搜索一组颜色
<?php
// Start with an image and convert it to a palette-based image
$im = imagecreatefrompng('figures/imagecolorclosest.png');
imagetruecolortopalette($im, false, 255);
// Search colors (RGB)
$colors = array(
array(254, 145, 154),
array(153, 145, 188),
array(153, 90, 145),
array(255, 137, 92)
);
// Loop through each search and find the closest color in the palette.
// Return the search number, the search RGB and the converted RGB match
foreach($colors as $id => $rgb)
{
$result = imagecolorclosest($im, $rgb[0], $rgb[1], $rgb[2]);
$result = imagecolorsforindex($im, $result);
$result = "({$result['red']}, {$result['green']}, {$result['blue']})";
echo "#$id: Search ($rgb[0], $rgb[1], $rgb[2]); Closest match: $result.\n";
}
imagedestroy($im);
?>以上示例的输出类似于：
#0: Search (254, 145, 154); Closest match: (252, 150, 148). #1: Search (153, 145, 188); Closest match: (148, 150, 196). #2: Search (153, 90, 145); Closest match: (148, 90, 156). #3: Search (255, 137, 92); Closest match: (252, 150, 92).
参见
- imagecolorexact() - 取得指定颜色的索引值
- imagecolorclosestalpha() - 获取最接近指定颜色 + alpha 的颜色索引
- imagecolorclosesthwb() - 取得与给定颜色最接近的色度的黑白色的索引
add a note
User Contributed Notes 4 notes
info at codeworx dot ch ¶
13 years ago
Hayley Watson ¶
7 years ago
RGB space isn't the best choice for measuring the distance between two colours, since it ignores, for example, the fact that we count both dark green and light green as "green" (the RGB distance between #000000 and #7f7f7f is the same as the distance between #000000 and #5443c0 - a slightly darkened SlateBlue).
A better choice of colour space that conforms better to how colours are perceived is the so-called Lab space, which measures colours according to how light/dark, red/green, and yellow/blue they are. (There are still better models, but they come at the expense of increased computation.)
<?php
function warp1($c)
{
if($c > 10.3148)
{
return pow((561 + 40*$c)/10761, 2.4);
}
else
{
return $c / 3294.6;
}
}
function warp2($c)
{
if($c > 0.008856)
{
return pow($c, 1/3);
}
else
{
return 7.787 * $c + 4/29;
}
}
function rgb2lab($rgb)
{
[$red, $green, $blue] = array_map('warp1', $rgb);
$x = warp2($red * 0.4339 + $green * 0.3762 + $blue * 0.1899);
$y = warp2($red * 0.2126 + $green * 0.7152 + $blue * 0.0722);
$z = warp2($red * 0.0178 + $green * 0.1098 + $blue * 0.8730);
$l = 116*$y - 16;
$a = 500 * ($x - $y);
$b = 200 * ($y - $z);
return array_map('intval', [$l, $a, $b]);
}
function generate_palette_from_image($image)
{
$pal = [];
$width = imagesx($image);
$height = imagesy($image);
for($x = 0; $x < $width; ++$x)
{
for($y = 0; $y < $height; ++$y)
{
$pal[] = imagecolorat($image, $x, $y);
}
}
return array_map(function($col)use($image)
{
$rgba = imagecolorsforindex($image, $col);
return [$rgba['red'], $rgba['green'], $rgba['blue']];
}, array_unique($pal));
}
function closest_rgb_in_palette($rgb, $palette)
{
// Quick return when the exact
// colour is in the palette.
if(($idx = array_search($rgb, $palette)) !== false)
{
return $idx;
}
[$tl, $ta, $tb] = rgb2lab($rgb);
$dists = array_map(function($plab)use($tl, $ta, $tb)
{
[$pl, $pa, $pb] = $plab;
$dl = $pl - $tl;
$da = $pa - $ta;
$db = $pa - $tb;
return $dl * $dl + $da * $da + $db * $db;
}, array_map('rgb2lab', $palette));
return array_search(min($dists), $dists);
}
function closest_rgb_in_image($rgb, $image)
{
$palette = generate_palette_from_image($image);
return $palette[closest_rgb_in_palette($rgb, $palette)];
}
$lena = imagecreatefrompng('lena.png');
$red = closest_rgb_in_image([255,0,0],$lena);
echo join(' ', $red); // 228 71 82
?>
If you're going to be matching a lot of colours to a palette, you may want to precompute and reuse the Lab palette, instead of generating it fresh each time as done here.
MagicalTux at FF dot st ¶
19 years ago
A way to get each time an answer :
<?php
function imagegetcolor($im, $r, $g, $b) {
$c=imagecolorexact($im, $r, $g, $b);
if ($c!=-1) return $c;
$c=imagecolorallocate($im, $r, $g, $b);
if ($c!=-1) return $c;
return imagecolorclosest($im, $r, $g, $b);
}
?>
If the *exact* color is found in the image, it will be returned. If we don't have the exact color, we try to allocate it. If we can't allocate it, we return the closest color in the image.
Vikrant Korde <vakorde at hotmail dot com> ¶
21 years ago
This functuion is useful when you are dealing with previously present images like .png, .jpg, etc. You can use this function for writing a text on the image.
For me the function imagecolorallocate() was returning the -1 value. after lot of RnD and site search i found a function use of imagecolorclosest(). This solved my problem of writing the text on the image with customised color.
Actually previously it was writing on the image but the color was not distinct. It was using the same color as of that background image.
The following code segment was fine with me.
header ("Content-type: image/jpeg");
$im = imagecreatefromjpeg("BlankButton.jpg");
$white = imageColorClosest($im, 255,255,255);
// this is for TTF fonts
imagettftext ($im, 20, 0, 16, 30, $white, "/usr/X11R6/lib/X11/fonts/TTF/luximb.ttf", "Vikrant");
//this is for notmal font
imagestring($im, 4, 0,0,"Korde", $white);
imagejpeg($im,"",150);
imagedestroy ($im);
