imagecolorclosest

(PHP 4, PHP 5, PHP 7, PHP 8)

imagecolorclosest — 取得与指定的颜色最接近的颜色的索引值

说明

imagecolorclosest(
    resource $image,
    int $red,
    int $green,
    int $blue
): int

返回图像调色板中与指定的 RGB 值最“接近”的颜色。

指定的颜色与调色板中的每个颜色的“距离”的计算方法是把 RGB 值当成三维空间中点的坐标。

如果从文件创建了图像，只有图像中使用了的颜色会被辨析。仅出现在调色板中的颜色不会被辨析。

参见 imagecolorexact()。

add a note

User Contributed Notes 4 notes

down

info at codeworx dot ch ¶

10 years ago


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);
}
?>

down

Hayley Watson ¶

4 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.

down

-1

MagicalTux at FF dot st ¶

16 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.

down

-1

Vikrant Korde <vakorde at hotmail dot com> ¶

18 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);

add a note

官方地址：https://www.php.net/manual/en/function.imagecolorclosest.php

有任何技术问题请点击这里网站运营推广招聘

IT PHP 编程语言 Linux 开发编程科技 Elasticsearch HTML/CSS/XML 网络 JAVA NoSQL 数据库面试 C/C++ Golang Git 算法操作系统正则表达式 Redis 互联网 MySql JavaScript 运维软件国际架构设计 Mac OS TCP/IP Excel Vim Windows Socket Oracle VR MongoDB Python 运营 MemCache 商业硬件电子娱乐设计 nginx 摄影游戏 WordPress HTTP 团建数码电器

php7 安装fileinfo扩展 preg_split — 通过一个正则表达式分隔字符串 php位值,解决 PHP 中 usort 在值相同时改变原始位置的问题 [PHP] inet_pton/inet_ntop IP地址转换函数 array_multisort() 多字段排序 PHPMailer设置utf8 PHPMailer字符集CharSet ADORecordSet对象 adodb手册 PHP 8.1 [鸟哥]PHP_INT_MIN 和 -9223372036854775808 opcache预加载 Composer的Packagist资源 mysql面试题 [鸟哥]PHP FFI详解 - 一种全新的PHP扩展方式 PHP7添加redis扩展 PHP mkdir()写出来的权限与mode值不符合 Packagist / Composer 中国全量镜像利用php soap实现web service PHP获取指定函数定义在哪个文件中及行号支持php7的性能采集扩展

略微加速

PHP官方手册 - 互联网笔记

imagecolorclosest

说明

User Contributed Notes 4 notes