imagecolorallocate

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

imagecolorallocate — Alloziert eine Farbe für eine Grafik

Beschreibung

imagecolorallocate(
    GdImage $image,
    int $red,
    int $green,
    int $blue
): int|false

Gibt einen Farb-Kennzeichner zurück, der die aus den gegebenen RGB-Komponenten bestehende Farbe darstellt.

imagecolorallocate() muss aufgerufen werden, um jede Farbe zu erzeugen, die in dem durch image angegebenen Bild verwendet werden soll.

Hinweis:
Der erste Aufruf von imagecolorallocate() bestimmt die Hintergrundfarbe von palettenbasierten Bilder – also Bildern, die durch imagecreate() erzeugt wurden.

Parameter-Liste

image: Ein GdImage-Objekt, das von einer der Funktionen zur Bilderzeugung, z. B. imagecreatetruecolor(), zurückgegeben wurde.
red: Wert der Rotkomponente.
green: Wert der Grünkomponente.
blue: Wert der Blaukomponente.

Diese Parameter sind Ganzzahlen zwischen 0 und 255 oder Hexadezimalzahlen zwischen 0x00 und 0xFF.

Rückgabewerte

Ein Farb-Kennzeichner oder false, falls die Farbe nicht alloziert werden konnte.

Warnung

Diese Funktion kann sowohl das boolsche false zurückliefern, als auch einen nicht-boolschen Wert, welcher zu false ausgewertet wird. Weitere Informationen entnehmen Sie bitte dem Abschnitt über die boolschen Typen. Benutzen Sie deshalb den === Operator, um den Rückgabewert dieser Funktion zu überprüfen.

Changelog

Version	Beschreibung
8.0.0	`image` erwartet nun eine GdImage-Instanz; vorher wurde eine gültige `gd`-Ressource erwartet.

Beispiele

Beispiel #1 imagecolorallocate()-Beispiel

<?php

$im = imagecreate(100, 100);

// färbt den Hintergrund rot
$background = imagecolorallocate($im, 255, 0, 0);

// alloziert weitere Farben
$white = imagecolorallocate($im, 255, 255, 255);
$black = imagecolorallocate($im, 0, 0, 0);

// hexadezimale Schreibweise
$white = imagecolorallocate($im, 0xFF, 0xFF, 0xFF);
$black = imagecolorallocate($im, 0x00, 0x00, 0x00);

?>

Siehe auch

imagecolorallocatealpha() - Allocate a color for an image
imagecolordeallocate() - Löscht eine Farbdefinition

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User Contributed Notes 21 notes

down

jahservant 13 at gmail dot com ¶

14 years ago

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...
     }
?>

down

Ludo ¶

17 years ago

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);
?>

down

William Barath ¶

17 years ago

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);
?>

down

jernberg at fairytale dot se ¶

20 years ago

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 );

?>

down

andreoli dot carlo at libero dot it ¶

19 years ago

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);

}

?>

down

smoli at paranoya dot ch ¶

20 years ago

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;

  }

?>

down

SW ¶

18 years ago

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");
?>

down

picklecj at rose-hulman dot edu ¶

17 years ago

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.

down

tyberis ¶

19 years ago

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".

down

chris at drunkenpirates dot co dot uk ¶

21 years ago

<?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);
?>

down

bisqwit at iki dot fi ¶

22 years ago

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.

down

behun at webconsult dot sk ¶

18 years ago

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

down

aaron at parecki dot com ¶

19 years ago

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);

?>

down

phillip dot gooch at gmail dot com ¶

13 years ago

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.

down

mlse ¶

18 years ago

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.

down

mail at kailashnadh dot name ¶

19 years ago

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);
}

?>

down

mv at brazil dot com ¶

19 years ago

<?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);



?>

down

Zigbigidorlu at hotmail dot com ¶

19 years ago

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);

}

?>

down

Anonymous ¶

19 years ago

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!

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-1

leif at harmsen dot net ¶

21 years ago

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 ....

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-3

divinity76 at gmail dot com ¶

8 years ago

you have VERY limited space for color indexes (255 indexes on my system, with over 10 GB ram available, cli, no memory limit), when there is no more indexes available, imagecolorallocate will return false. when you create 2x indexes with the same r/g/b, you waste this very limited space. the function below should never fail, AND never waste any color index space. if there's already an index with the rgb, it will return the existing index, else it will try allocate 1, in the event that allocation fail (presumably because all index space is used up already), it will return the closest match to what you requested, and warn you via $couldFindExact.

function myimagecolorallocate($gd,int $red,int $green,int $blue,bool &$couldFindExact=null):int{
    $ret=imagecolorexact($gd, $red, $green, $blue);
    if($ret===-1){
        $ret=imagecolorallocate($gd, $red, $green, $blue);
        if($ret===false){
            $couldFindExact=false;//out of color indexes (255 index by default..wish i knew why)
            $ret=imagecolorclosest($gd, $red, $green, $blue);
        } else {
            $couldFindExact=true;
        }
    } else {
        $couldFindExact=true;
    }
    return $ret;
}

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