GD and Image 函数
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imagecolorallocate

(PHP 4, PHP 5)

imagecolorallocate — 为一幅图像分配颜色

说明

int imagecolorallocate ( resource $image , int $red , int $green , int $blue )

imagecolorallocate() 返回一个标识符，代表了由给定的 RGB 成分组成的颜色。red，green 和 blue 分别是所需要的颜色的红，绿，蓝成分。这些参数是 0 到 255 的整数或者十六进制的 0x00 到 0xFF。imagecolorallocate() 必须被调用以创建每一种用在 image 所代表的图像中的颜色。

Note:

第一次对 imagecolorallocate() 的调用会给基于调色板的图像填充背景色，即用 imagecreate() 建立的图像。

Example #1 imagecolorallocate() 例子

<?php
$im = imagecreate('example.jpg', 100, 100);
// 背景设为红色
$background = imagecolorallocate($im, 255, 0, 0);
// 设定一些颜色
$white = imagecolorallocate($im, 255, 255, 255);
$black = imagecolorallocate($im, 0, 0, 0);
// 十六进制方式
$white = imagecolorallocate($im, 0xFF, 0xFF, 0xFF);
$black = imagecolorallocate($im, 0x00, 0x00, 0x00);
?>

如果分配失败则返回 -1。

参见 imagecolorallocatealpha() 和 imagecolordeallocate()。

GD and Image 函数
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PHP手册 - N: 为一幅图像分配颜色

用户评论:

phillip dot gooch at gmail dot com (09-Dec-2010 03:52)

If you even in a situation where it's not allocating the color you want it could be because of your images color allocation table. GIF and 8-bit PNG images are very susceptible to this.

If your using an GIF and PNG try dropping a color from the table, should let you allocate another.

oni-kun[at]oni-kun[dot]com (08-Aug-2010 07:57)

If you're uncomfortable with using RGB codes you can bypass this function completely by assigning the hex values directly, two example replacements are:

<?php
//Equivalents
$white = imagecolorallocate($im, 255, 255, 255);
$white = 0x00FFFFFF; //First two are alpha, then triplet

$grey = imagecolorallocate($im, 62, 62, 62);
$grey = 0x003E3E3E;
?>

This should work in all applications, as it seems that is all the function returns.

yettycz at gmail dot com (16-Mar-2010 06:27)

Two useful functions for convert integer from imageCollorAllocate to RGB hex (FFFFFF eg.) and to array of integers 0..255:

<?php
/**
 * Convert color from imageColorAllocate() to hex in XXXXXX (eg. FFFFFF, 000000, FF0000)
 *
 * name: color2rgb
 * author: Yetty
 * @param $color value from imageColorAllocate()
 * @return string; color in style XXXXXX (eg. FFFFFF, 000000, FF0000)
 */
function color2rgb($color) {
    return str_pad(base_convert($color, 10, 16), 6, 0, STR_PAD_LEFT);
}

/**
 * Convert color from hex in XXXXXX (eg. FFFFFF, 000000, FF0000) to array(R, G, B)
 * of integers (0-255).
 *
 * name: rgb2array
 * author: Yetty
 * @param $color hex in XXXXXX (eg. FFFFFF, 000000, FF0000)
 * @return string; array(R, G, B) of integers (0-255)
 */
function rgb2array($rgb) {
    return array(
        base_convert(substr($rgb, 0, 2), 16, 10),
        base_convert(substr($rgb, 2, 2), 16, 10),
        base_convert(substr($rgb, 4, 2), 16, 10),
    );
}
?>

jahservant 13 at gmail dot com (25-Nov-2009 12:55)

Note that you can only assign 255 colors to any image palette.  If you try assigning more, imagecolorallocate() will fail.

If, for example, you are randomly allocating colors, it will be wise to check if you have used up all of the colors possible.  You can use imagecolorclosest() to get the closest assigned color:
<?php
     //assign random rgb values
     $c1 = mt_rand(50,200); //r(ed)
     $c2 = mt_rand(50,200); //g(reen)
     $c3 = mt_rand(50,200); //b(lue)
     //test if we have used up palette
     if(imagecolorstotal($pic)>=255) {
          //palette used up; pick closest assigned color
          $color = imagecolorclosest($pic, $c1, $c2, $c3);
     } else {
          //palette NOT used up; assign new color
          $color = imagecolorallocate($pic, $c1, $c2, $c3);
     }
?>

Also, imagecolorallocate() will assign a new color EVERY time the function is called, even if the color already exists in the palette:
<?php
     // [...]
     imagecolorallocate($pic,125,125,125); //returns 5
     imagecolorallocate($pic,125,125,125); //returns 6
     imagecolorallocate($pic,125,125,125); //returns 7
     // [...]
     imagecolorallocate($pic,125,125,125); //returns 23
     imagecolorallocate($pic,125,125,125); //returns 25
     // [...]
     // etc...
?>

So here, imagecolorexact() is useful:
<?php
     //see if color already exists
     $color = imagecolorexact($pic, $c1, $c2, $c3);
     if($color==-1) {
          //color does not exist; allocate a new one
          $color = imagecolorallocate($pic, $c1, $c2, $c3);
     }
?>

And, for nerdy-ness sake, we can put the two ideas together:
<?php
     //assign random rgb values
     $c1 = mt_rand(50,200); //r(ed)
     $c2 = mt_rand(50,200); //g(reen)
     $c3 = mt_rand(50,200); //b(lue)
     //get color from palette
     $color = imagecolorexact($pic, $c1, $c2, $c3);
     if($color==-1) {
          //color does not exist...
          //test if we have used up palette
          if(imagecolorstotal($pic)>=255) {
               //palette used up; pick closest assigned color
               $color = imagecolorclosest($pic, $c1, $c2, $c3);
          } else {
               //palette NOT used up; assign new color
               $color = imagecolorallocate($pic, $c1, $c2, $c3);
          }
     }
?>

Or as a function:
<?php
     function createcolor($pic,$c1,$c2,$c3) {
          //get color from palette
          $color = imagecolorexact($pic, $c1, $c2, $c3);
          if($color==-1) {
               //color does not exist...
               //test if we have used up palette
               if(imagecolorstotal($pic)>=255) {
                    //palette used up; pick closest assigned color
                    $color = imagecolorclosest($pic, $c1, $c2, $c3);
               } else {
                    //palette NOT used up; assign new color
                    $color = imagecolorallocate($pic, $c1, $c2, $c3);
               }
          }
          return $color;
     }

     for($i=0; $i<1000; $i++) { //1000 because it is significantly greater than 255
          //assign random rgb values
          $c1 = mt_rand(50,200); //r(ed)
          $c2 = mt_rand(50,200); //g(reen)
          $c3 = mt_rand(50,200); //b(lue)
          //generate the color
          $color = createcolor($pic,$c1,$c2,$c3);
          //do something with color...
     }
?>

shinesoldier at gmail dot com (07-May-2009 12:16)

Here's a very simple function that basically does the same as imagecolorallocate(), only without needing an image resource to work.

<?php
function createcolor($r, $g, $b) {
  return hexdec(str_pad(dechex($r), 2, 0, STR_PAD_LEFT).str_pad(dechex($g), 2, 0, STR_PAD_LEFT).str_pad(dechex($b), 2, 0, STR_PAD_LEFT));
}

/* As said earlier, this function does the exact same thing as imagecolorallocate(), without needing an image resource. This means that the following two blocks of code result in the exact same thing: */

//Block 1
$color = colorcreate(105, 199, 204);

//Block 2
$img = imagecreatetruecolor(100, 100); //the arguments here don't really matter
$color = imagecolorallocate($img, 105, 199, 204);
imagedestroy($img);
?>

federicot at gmail dot com (21-May-2008 03:08)

Little correction to marc-gutt's regural expression to validate hex color values. You can use this little function:

<?php
// Validate an hex color string. Return true if valid, false otherwise
function validateHexColor($color) {
    $color = substr($color, 0, 7);
    return preg_match('/#[0-9a-fA-F]{6}/', $color);
}
?>

djcassis at gmail dot com (21-Nov-2007 08:06)

I also find the following useful when dealing with HTML hexadecimal colors :
<?php
$color = '#FFffFF';
print_r(sscanf($color, '#%2x%2x%2x'));
?>
outputs :
Array
(
    [0] => 255
    [1] => 255
    [2] => 255
)

Ludo (24-Oct-2007 10:35)

When working on an existant GIF images, if the number of different colours has reached the limits of the GIF format, imagecolorallocate will not use to the colour you ask her within the parameters, she will apply black !

That's a problem when generating images "on-the-fly" with many manipulations, from a GIF image.
To go round the problem, you have to convert the GIF image into a PNG one, and then you can work on the PNG and everything will be ok.

For example :
<?php
// first, convert into a PNG image
$handle = imagecreatefromgif('my_image.gif');
imagepng($handle, 'my_image.png');
imagedestroy($handle);

// then, you can work on it
$handle = imagecreatefrompng('my_image.png');
/*
* work on the image
*/
imagegif($handle);
?>

William Barath (29-Sep-2007 12:15)

Lots of hsv2rgb commentary but no working example, so here's mine:

<?php // hsv2rgb example translated from ImageMagick C code
function hsv2rgb($h, $s, $v)
{
    $s /= 256.0;
    if ($s == 0.0) return array($v,$v,$v);
    $h /= (256.0 / 6.0);
    $i = floor($h);
    $f = $h - $i;
    $p = (integer)($v * (1.0 - $s));
    $q = (integer)($v * (1.0 - $s * $f));
    $t = (integer)($v * (1.0 - $s * (1.0 - $f)));
    switch($i) {
    case 0: return array($v,$t,$p);
    case 1: return array($q,$v,$p);
    case 2: return array($p,$v,$t);
    case 3: return array($p,$q,$v);
    case 4: return array($t,$p,$v);
    default: return array($v,$p,$q);
    }
}

$image = ImageCreateTrueColor(256,128);
for ($y=0; $y<64; $y++) for($x=0; $x<256; $x++){
    list($r,$g,$b) = hsv2rgb($x | 7,255,($y*4) |7);
    $color = ($r << 16 ) | ($g << 8) | $b;
    imagesetpixel($image, $x, $y-4, $color);
}
for ($y=64; $y<128; $y++) for($x=0; $x<256; $x++){
    list($r,$g,$b) = hsv2rgb($x|7,((127-$y)*4)|7,255);
    $color = ($r << 16) | ($g << 8) | $b;
    imagesetpixel($image, $x, $y-4, $color);
}
for ($y=120; $y<128; $y++) for($x=0; $x<256; $x++){
    $color = (($x |7) << 16) | (($x |7) << 8) | ($x |7);
    imagesetpixel($image, $x, $y, $color);
}
header("Content-Type: image/png");
imagepng($image);
?>

info at marc-gutt dot de Marc Gutt (04-Aug-2007 01:50)

rgb from hex without creating a new function or using split features:

<?php

$color = 'FF9900';
$color = imagecolorallocate($im, hexdec('0x' . $color{0} . $color{1}), hexdec('0x' . $color{2} . $color{3}), hexdec('0x' . $color{4} . $color{5}));

?>

You can validate $color with preg_match('#[a-z0-9]{6}#i', $color) if necessary.

picklecj at rose-hulman dot edu (13-Jun-2007 04:15)

Another solution to color limitation issues when creating gradients. This file takes width (px) and left and right colors (hex) and makes a gradient while only allocating 250 colors.

<?php
$leftR = hexdec(substr($_GET["left"],0,2));
$leftG = hexdec(substr($_GET["left"],2,2));
$leftB = hexdec(substr($_GET["left"],4,2));
$rightR = hexdec(substr($_GET["right"],0,2));
$rightG = hexdec(substr($_GET["right"],2,2));
$rightB = hexdec(substr($_GET["right"],4,2));
$image=imagecreate($_GET["width"],1);
for($i=0;$i<250;$i++) {
    $colorset[$i] = imagecolorallocate($image, $leftR + ($i*(($rightR-$leftR)/250)), $leftG + ($i*(($rightG-$leftG)/250)), $leftB + ($i*(($rightB-$leftB)/250)));
}
for($i=0;$i<($_GET["width"]);$i++) {
  imagesetpixel ($image, $i, 0, $colorset[(int)($i/($_GET["width"]/250))] );
}
header("Content-type: image/png");
imagepng($image);
imagedestroy($image);
?>

example: gradient.php?width=640&left=000000&right=FF0000

Makes a 640px-wide image that fades from black to red.

LPEspecial at home dot nl (19-Sep-2006 04:04)

This might help someone who want to  use 'ImageColorAllocate ' with a hex value

<?php
function ImageColorAllocateFromHex ($img, $hexstr)
{
  $int = hexdec($hexstr);

  return ImageColorAllocate ($img,
         0xFF & ($int >> 0x10),
         0xFF & ($int >> 0x8),
         0xFF & $int);
}
?>

behun at webconsult dot sk (27-Aug-2006 09:56)

Also, when you need more then 256 colors, use imagecreatetruecolor function. With this function you can use unlimited number of colors.

SW (13-Jan-2006 10:00)

This works! A Black-Image with vertical centered white Aliased Arial-Text and same left and right margin - used for Menu-Buttons.

<?php

  function createImgText ($string="", $fontsize=0, $marginX=0, $imgH=0 , $fontfile="", $imgColorHex="", $txtColorHex=""){
    if($string!=""){
        Header("Content-type: image/png");    
        //
        $spacing = 0;
          $line = array("linespacing" => $spacing);
        $box = @imageftbbox($fontsize,0,$fontfile,$string,$line)
        or die("ERROR");
        $tw=$box[4]-$box[0]; //image width
        $marginY = $imgH - (($imgH - $fontsize) / 2);
        $imgWidth = $tw + (2*$marginX);
        $im = ImageCreate($imgWidth, $imgH);
        $int = hexdec($imgColorHex);
        $arr = array("red" => 0xFF & ($int >> 0x10),
               "green" => 0xFF & ($int >> 0x8),
               "blue" => 0xFF & $int);
        $black = ImageColorAllocate($im, $arr["red"], $arr["green"], $arr["blue"]);
        $int = hexdec($txtColorHex);
        $arr = array("red" => 0xFF & ($int >> 0x10),
               "green" => 0xFF & ($int >> 0x8),
               "blue" => 0xFF & $int);
        $white = ImageColorAllocate($im, $arr["red"], $arr["green"], $arr["blue"]);
        ImageFtText($im, $fontsize, 0, $marginX, $marginY, $white, $fontfile, $string, array());
        ImagePng($im);
        ImageDestroy($im);
    }else{
        echo "ERROR!";
    }
}
createImgText ("Hello World", 9, 10, 18, "arial.ttf", "000000", "FFFFFF");
?>

mlse (15-Nov-2005 09:49)

Another more general variation on the theme using the same naming conventions as the hexdec and dechex built-in functions ...

Prototype:

array hexrgb ( string hex_string )

Returns:

An associative array of the RGB components specified in hex_string.

hexrgb() example:

<?php
$rgb = hexrgb("0xAABBCC");
print_r($rgb);
?>

Output is:

Array
(
  [red] => 170
  [green] => 187
  [blue] => 204
)

Implementation:

<?php
function hexrgb ($hexstr)
{
  $int = hexdec($hexstr);

  return array("red" => 0xFF & ($int >> 0x10),
               "green" => 0xFF & ($int >> 0x8),
               "blue" => 0xFF & $int);
}
?>

The output of hexdec can then be passed to imagecolorallocate and manipulated as required.

Zigbigidorlu at hotmail dot com (06-Oct-2005 08:05)

Here's a very simple and very effective code to change a HEX color to RGB.

<?php
function HEX2RGB($color){
 $color_array = array();
 $hex_color = strtoupper($color);
 for($i = 0; $i < 6; $i++){
  $hex = substr($hex_color,$i,1);
  switch($hex){
   case "A": $num = 10; break;
   case "B": $num = 11; break;
   case "C": $num = 12; break;
   case "D": $num = 13; break;
   case "E": $num = 14; break;
   case "F": $num = 15; break;
   default: $num = $hex; break;
  }
  array_push($color_array,$num);
 }
 $R = (($color_array[0] * 16) + $color_array[1]);
 $G = (($color_array[2] * 16) + $color_array[3]);
 $B = (($color_array[4] * 16) + $color_array[5]);
 return array($R,$G,$B);
 unset($color_array,$hex,$R,$G,$B);
}
?>

mail at kailashnadh dot name (28-Jun-2005 03:47)

This nifty function will produce the negative of a given image!

<?php

/********************************

     Code by Kailash Nadh
     http://kailashnadh.name

     usage:
     img2neg("my_pic.jpg");

*********************************/

function img2neg($pic) {

    header("Content-type: image/jpeg");

    $source=imagecreatefromjpeg($pic);    // Source
    $width=imagesx($source);    $height=imagesy($source);

    $im = imagecreatetruecolor($width, $height);    // Our negative img in the making

    for($y=0; $y < $height; $y++) {
        for($x=0; $x < $width; $x++) {

        $colors=imagecolorsforindex($source, imagecolorat($source, $x,$y));

            // this is what makes the colors negative
            $r=255-$colors['red'];
            $g=255-$colors['green'];
            $b=255-$colors['blue'];
            $test=imagecolorallocate($im, $r,$g,$b);
            imagesetpixel($im,$x, $y, $test);
        }
    }

    imagejpeg($im);
    imagedestroy($im);
}

?>

andreoli dot carlo at libero dot it (08-Jun-2005 02:38)

hsl to RGB
(not yet optimized but it function)

<?php
function hslToRgb ($h, $s, $l) {
    if ($h>240 || $h<0) return array(0,0,0);
    if ($s>240 || $s<0) return array(0,0,0);
    if ($l>240 || $l<0) return array(0,0,0);    
    if ($h<=40) {
        $R=255;
        $G=(int)($h/40*256);
        $B=0;
    }
    elseif ($h>40 && $h<=80) {
        $R=(1-($h-40)/40)*256;
        $G=255;
        $B=0;
    }
    elseif ($h>80 && $h<=120) {
        $R=0;
        $G=255;
        $B=($h-80)/40*256;
    }
    elseif ($h>120 && $h<=160) {
        $R=0;
        $G=(1-($h-120)/40)*256;
        $B=255;
    }
    elseif ($h>160 && $h<=200) {
        $R=($h-160)/40*256;
        $G=0;
        $B=255;
    }
    elseif ($h>200) {
        $R=255;
        $G=0;
        $B=(1-($h-200)/40)*256;
    }
    $R=$R+(240-$s)/240*(128-$R);
    $G=$G+(240-$s)/240*(128-$G);
    $B=$B+(240-$s)/240*(128-$B);
    if ($l<120) {
        $R=($R/120)*$l;
        $G=($G/120)*$l;
        $B=($B/120)*$l;
    }
    else {
        $R=$l*((256-$R)/120)+2*$R-256;
        $G=$l*((256-$G)/120)+2*$G-256;
        $B=$l*((256-$B)/120)+2*$B-256;
    }
    if ($R<0) $R=0;
    if ($R>255) $R=255;
    if ($G<0) $G=0;
    if ($G>255) $G=255;
    if ($B<0) $B=0;
    if ($B>255) $B=255;
   
    return array((int)$R,(int)$G,(int)$B);
}
?>

mv at brazil dot com (15-Mar-2005 07:34)

<?php

/**
 * Create a image bar using lib GD
 * Ege. <img src="color_sample.php?color=FF0000" width="10 height="30">
 */

// Split the HTML color representation
$hexcolor = str_split($_GET["color"], 2);

// Convert HEX values to DECIMAL
$bincolor[0] = hexdec("0x{$hexcolor[0]}");
$bincolor[1] = hexdec("0x{$hexcolor[1]}");
$bincolor[2] = hexdec("0x{$hexcolor[2]}");

$im = ImageCreate(100, 100);
$colorallocate = ImageColorAllocate($im, $bincolor[0], $bincolor[1], $bincolor[2]);
ImageFilledRectangle($im, 0, 0, 100, 100, $colorallocate);
header('Content-Type: image/png');
ImagePNG($im);

?>

(18-Jan-2005 10:23)

When you are using truecolor images, you can also use bitwise operations to generate the color:
<?php
$color = ($r << 16) | ($g << 8) | $b; // 2261213
?>
This is identical to the imagecolorallocate() function, in truecolor images!

aaron at parecki dot com (22-Dec-2004 10:10)

This will let you tint an image to any specific color. The blacks of the source image become your specified color, and the whites remain white. Works best for colorizing greyscale images.

<?php

$r = 224;
$g = 192;
$b = 0;
$source_file = "picture.jpg";

$im_src = ImageCreateFromJpeg($source_file);
$im_tint = ImageCreate(imagesx($im_src),imagesy($im_src));
for ($c = 0; $c < 255; $c++) {
     ImageColorAllocate($im_tint, max($r,$c), max($g,$c), max($b,$c));
}
ImageCopyMerge($im_tint,$im_src,0,0,0,0, imagesx($im_src), imagesy($im_src), 100);
ImageDestroy($im_src);

header("Content-type: image/jpeg");
imagejpeg($im_tint);

?>

tyberis (28-Nov-2004 12:58)

2 functions to convert from HSV colorspace (hue/saturation/brightness) to RGB (red/green/blue) colorspace and back.
<?php
// $c = array($red, $green, $blue)
// $red=[0..1], $green=[0..1], $blue=[0..1];
function rgb2hsv($c) {
 list($r,$g,$b)=$c;
 $v=max($r,$g,$b);
 $t=min($r,$g,$b);
 $s=($v==0)?0:($v-$t)/$v;
 if ($s==0)
  $h=-1;
 else {
  $a=$v-$t;
  $cr=($v-$r)/$a;
  $cg=($v-$g)/$a;
  $cb=($v-$b)/$a;
  $h=($r==$v)?$cb-$cg:(($g==$v)?2+$cr-$cb:(($b==$v)?$h=4+$cg-$cr:0));
  $h=60*$h;
  $h=($h<0)?$h+360:$h;
 }
 return array($h,$s,$v);
}

// $c = array($hue, $saturation, $brightness)
// $hue=[0..360], $saturation=[0..1], $brightness=[0..1]
function hsv2rgb($c) {
 list($h,$s,$v)=$c;
 if ($s==0)
  return array($v,$v,$v);
 else {
  $h=($h%=360)/60;
  $i=floor($h);
  $f=$h-$i;
  $q[0]=$q[1]=$v*(1-$s);
  $q[2]=$v*(1-$s*(1-$f));
  $q[3]=$q[4]=$v;
  $q[5]=$v*(1-$s*$f);
  //return(array($q[($i+4)%5],$q[($i+2)%5],$q[$i%5]));
  return(array($q[($i+4)%6],$q[($i+2)%6],$q[$i%6])); //[1]
 }
}
?>

[1] - EDITOR NOTE: THIS IS A FIX FROM "hc at hob(removethis)soft dot net".

smoli at paranoya dot ch (19-Jul-2004 07:10)

Some of you maybe want to use HSV color model for drawing color selectors and circles:

<?php
  function &colormap_hsv_to_rgb($h, $s, $v)
  {
    $ret = new stdClass();

    if($s == 0)
    {
      $ret->r = $v;
      $ret->g = $v;
      $ret->b = $v;

      return $ret;
    }
    else
    {
      $h = floatval($h) / 255.0;
      $s = floatval($s) / 255.0;
      $v = floatval($v) / 255.0;

      $hue = $h;

      if($hue == 1.0)
        $hue = 0.0;

      $hue *= 6.0;

      $i = intval($hue);
      $f = $hue - floatval($i);
      $w = $v * (1.0 - $s);
      $q = $v * (1.0 - ($s * $f));
      $t = $v * (1.0 - ($s * (1.0 - $f)));

      switch($i)
      {
         case 0: $ret->r = $v; $ret->g = $t; $ret->b = $w; break;
         case 1: $ret->r = $q; $ret->g = $v; $ret->b = $w; break;
         case 2: $ret->r = $w; $ret->g = $v; $ret->b = $t; break;
         case 3: $ret->r = $w; $ret->g = $q; $ret->b = $v; break;
         case 4: $ret->r = $t; $ret->g = $w; $ret->b = $v; break;
         case 5: $ret->r = $v; $ret->g = $w; $ret->b = $q; break;
      }
    }
   
    $ret->r = intval($ret->r * 255.0);
    $ret->g = intval($ret->g * 255.0);
    $ret->b = intval($ret->b * 255.0);

    return $ret;
  }
?>

jernberg at fairytale dot se (05-Mar-2004 06:43)

this might help someone, how to allocate an color from an html color-definition:

<?php
$fg = "#ff0080";

$red = 100;
$green = 100;
$blue = 100;
if( eregi( "[#]?([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})", $fg, $ret ) )
{
    $red = hexdec( $ret[1] );
    $green = hexdec( $ret[2] );
    $blue = hexdec( $ret[3] );
}

$text_color = ImageColorAllocate( $img1, $red, $green, $blue );
?>

chris at drunkenpirates dot co dot uk (14-Sep-2003 01:44)

<?php

/*
An example combining the use of ImageColorAllocate, Imagesetpixel, Imagecopyresized and some basic Trig
*/

Header("Content-type: image/png");

$height = 128;
$width = 128;

$imA = ImageCreate($width, $height);
$imB = ImageCreate($width*4, $height*4);
$bckA = ImageColorAllocate($imA, 0,0,0);
$bckB = ImageColorAllocate($imB, 0,0,0);

//GENERATE GRAY SCALE PALLETE

for($c=0;$c<256;$c++){
                ImageColorAllocate($imA, $c, $c, $c);
                }

//PRODUCE DATA

$m=rand(0,10);
for($c=0;$c<128;$c++){
                $s=  (sin( deg2rad($c*360*$m/128) )+1)*127;
                $col_arr[$c]=$s;
                }
for($y=0;$y<$height;$y++){
        for($x=0;$x<$width;$x++){
                $imgA[$x][$y]=$col_arr[$x];
                }
        }
for($y=0;$y<$height;$y++){
        for($x=0;$x<$width;$x++){
                $imgB[$x][$y]=$col_arr[$y];
                }
        }

//SET PIXELS

for($y=0;$y<$height;$y++){
        for($x=0;$x<$width;$x++){
                $imgC[$x][$y]=$imgA[$x][$y]+$imgB[$x][$y];
                $s=$imgC[$x][$y]/2;
                Imagesetpixel($imA,$x,$y,$s);
                }
        }

//RESIZE IMAGE FOR DISPLAY

Imagecopyresized ($imB, $imA, 0, 0, 0, 0, $width*4, $height*4, $width, $width);
ImagePNG($imB);
?>

leif at harmsen dot net (16-Apr-2003 03:31)

I was unable to get any of the posted methods for converting colour to grayscale to work.  The problem appears to be the way gd creates images from jpeg inconsistently over various versions.  Eventually I wrote my own that works for me - this approach allocates the 256 color pallete first.  You can also play with separate $r, $g, $b variables before using imagecolorallocate in order to tone or tint the image.

<?php
$resource = 'whatever.jpg';
$im_size = GetImageSize($resource);
$imageWidth = $im_size[0];
$imageHeight = $im_size[1];
$im = imageCreate($imageWidth,$imageHeight);
for ($c = 0; $c < 256; $c++) {    
     ImageColorAllocate($im, $c,$c,$c);
}
$im2 = ImageCreateFromJpeg($resource);
ImageCopyMerge($im,$im2,0,0,0,0, $imageWidth, $imageHeight, 100);
ImageDestroy($im2);
?>

go on using $im as your image, it is now grayscale ....

jasper at pointless dot net (21-Jan-2003 01:20)

a patch to php 4.3.0 to add imagecolorallocatealpha is here:

http://pointless.net/~jasper/php-4.3.0-imagecolorallocatealpha.patch

cd php-4.3.0/ext/gd
patch < path/to/patch

and recompile and reinstall.

bisqwit at iki dot fi (17-Feb-2002 04:30)

Actually, you can't allocate more than 256 colours for an paletted image (ImageCreate).
Use ImageCreateTrueColor instead. For it to work, you need libgd version 2 support in php though.