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imagecolorsforindex

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

imagecolorsforindex — Retourne la couleur associée à un index

Description

imagecolorsforindex(GdImage $image, int $color): array

Retourne la couleur associée à un index spécifié.

Liste de paramètres

image: Un objet GdImage, retournée par une des fonctions de création d'images, comme imagecreatetruecolor().
color: L'index de la couleur.

Valeurs de retour

Retourne un tableau associatif avec les clés "red", "green", "blue" et "alpha" qui contiennent les valeurs pour l'index de la couleur spécifiée.

Historique

Version	Description
8.0.0	`image` attend une instance de GdImage désormais; auparavant, une resource `gd` était attendue.
8.0.0	La fonction imagecolorsforindex() lance désormais une exception ValueError si `color` est hors de portée; auparavant, `false` était retourné à la place.

Exemples

Exemple #1 Exemple avec imagecolorsforindex()

<?php

// on ouvre une image
$im = imagecreatefrompng('nexen.png');

// on obtient une couleur
$start_x = 40;
$start_y = 50;
$color_index = imagecolorat($im, $start_x, $start_y);

// on la rend lisible
$color_tran = imagecolorsforindex($im, $color_index);

// quelle est-elle ?
print_r($color_tran);

?>

Résultat de l'exemple ci-dessus est similaire à :

Array
(
   [red] => 226
   [green] => 222
   [blue] => 252
   [alpha] => 0
)

Voir aussi

imagecolorat() - Retourne l'index de la couleur d'un pixel donné
imagecolorexact() - Retourne l'index de la couleur donnée

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User Contributed Notes 10 notes

down

matrebatre ¶

16 years ago


Be aware that

<?php
$rgba     = imagecolorat($image, $x, $y);
$r = ($rgba >> 16) & 0xFF;
$g = ($rgba >> 8) & 0xFF;
$b = $rgba & 0xFF;
$a     = ($rgba & 0x7F000000) >> 24;
?> 

will only work for truecolor images. With eg GIF images, this will have strange results. For GIF images, you should always use imagecolorsforindex().

down

slepichev at yahoo dot com ¶

17 years ago


If you would like to change the intensity or lightness level of a specific color, you will need to convert the color format from RGB to HSL. 
following function convert RGB array(red,green,blue) to HSL array(hue, saturation, lightness)
<?php
/**
 * Convert RGB colors array into HSL array
 * 
 * @param array $ RGB colors set
 * @return array HSL set
 */
 function rgb2hsl($rgb){
    
     $clrR = ($rgb[0] / 255);
     $clrG = ($rgb[1] / 255);
     $clrB = ($rgb[2] / 255);
    
     $clrMin = min($clrR, $clrG, $clrB);
     $clrMax = max($clrR, $clrG, $clrB);
     $deltaMax = $clrMax - $clrMin;
    
     $L = ($clrMax + $clrMin) / 2;
    
     if (0 == $deltaMax){
         $H = 0;
         $S = 0;
         }
    else{
         if (0.5 > $L){
             $S = $deltaMax / ($clrMax + $clrMin);
             }
        else{
             $S = $deltaMax / (2 - $clrMax - $clrMin);
             }
         $deltaR = ((($clrMax - $clrR) / 6) + ($deltaMax / 2)) / $deltaMax;
         $deltaG = ((($clrMax - $clrG) / 6) + ($deltaMax / 2)) / $deltaMax;
         $deltaB = ((($clrMax - $clrB) / 6) + ($deltaMax / 2)) / $deltaMax;
         if ($clrR == $clrMax){
             $H = $deltaB - $deltaG;
             }
        else if ($clrG == $clrMax){
             $H = (1 / 3) + $deltaR - $deltaB;
             }
        else if ($clrB == $clrMax){
             $H = (2 / 3) + $deltaG - $deltaR;
             }
         if (0 > $H) $H += 1;
         if (1 < $H) $H -= 1;
         }
     return array($H, $S, $L);
     }
?>

down

joe dot scylla at gmail dot com ¶

17 years ago


While it's quite easy and intuitive to get the alpha transparency of a pixel with:

<?php
$rgba     = imagecolorsforindex($image, imagecolorat($image, $x, $y));
$alpha     = $rgba["alpha"];
?>

you should use the return value of the command imagecolorat to get the alpha transparency with the code below because it's much faster and will have a major impact if you process every pixel of an image:

<?php
$rgba     = imagecolorat($image, $x, $y);
$alpha     = ($rgba & 0x7F000000) >> 24;
?>

down

hofstadler dot andi at gmx dot at ¶

16 years ago


I have optimized the rgb2hsl function from slepichev a bit, so that it is a bit shorter and hopefully a bit faster:

<?php
/**
 * Convert RGB colors array into HSL array
 * 
 * @param array $ RGB colors set, each color component with range 0 to 255
 * @return array HSL set, each color component with range 0 to 1
 */
function rgb2hsl($rgb){
    $clrR = ($rgb[0]);
    $clrG = ($rgb[1]);
    $clrB = ($rgb[2]);
     
    $clrMin = min($clrR, $clrG, $clrB);
    $clrMax = max($clrR, $clrG, $clrB);
    $deltaMax = $clrMax - $clrMin;
     
    $L = ($clrMax + $clrMin) / 510;
     
    if (0 == $deltaMax){
        $H = 0;
        $S = 0;
    }
    else{
        if (0.5 > $L){
            $S = $deltaMax / ($clrMax + $clrMin);
        }
        else{
            $S = $deltaMax / (510 - $clrMax - $clrMin);
        }

        if ($clrMax == $clrR) {
            $H = ($clrG - $clrB) / (6.0 * $deltaMax);
        }
        else if ($clrMax == $clrG) {
            $H = 1/3 + ($clrB - $clrR) / (6.0 * $deltaMax);
        }
        else {
            $H = 2 / 3 + ($clrR - $clrG) / (6.0 * $deltaMax);
        }

        if (0 > $H) $H += 1;
        if (1 < $H) $H -= 1;
    }
    return array($H, $S,$L);
}
?>

down

derek at idreams dot co dot uk ¶

17 years ago


The earlier microsoft sepia example seemed to have a factor in which made it pinky... here is a modified example which uses just the Microsoft sepia (as per the wiki sepia entry)

<?
function imagetosepia(&$img) {
  if (!($t = imagecolorstotal($img))) {
    $t = 256;
    imagetruecolortopalette($img, true, $t);
  }
  $total = imagecolorstotal( $img );
  for ( $i = 0; $i < $total; $i++ ) {
    $index = imagecolorsforindex( $img, $i );
    $red = ( $index["red"] * 0.393 + $index["green"] * 0.769 + $index["blue"] * 0.189 );
    $green = ( $index["red"] * 0.349 + $index["green"] * 0.686 + $index["blue"] * 0.168 ); 
    $blue = ( $index["red"] * 0.272 + $index["green"] * 0.534 + $index["blue"] * 0.131 ); 
    if ($red > 255) { $red = 255; }
    if ($green > 255) { $green = 255; }
    if ($blue > 255) { $blue = 255; }
    imagecolorset( $img, $i, $red, $green, $blue );
  }
}
?>

down

admin at phpgfx dot com ¶

17 years ago


this is a sepia filter using microsoft's definition

<?php

function imagesepia( $img ) {
    $total = imagecolorstotal( $img );
    for ( $i = 0; $i < $total; $i++ ) {
        $index = imagecolorsforindex( $img, $i );
        $red = ( $index["red"] * 0.393 + $index["green"] * 0.769 + $index["blue"] * 0.189 ) / 1.351;
        $green = ( $index["red"] * 0.349 + $index["green"] * 0.686 + $index["blue"] * 0.168 ) / 1.203;
        $blue = ( $index["red"] * 0.272 + $index["green"] * 0.534 + $index["blue"] * 0.131 ) / 2.140;
        imagecolorset( $img, $i, $red, $green, $blue );
    }
}

?>

down

adspeed.com ¶

19 years ago


To correct m4551 at abasoft dot it example:

ImageTrueColorToPalette($im,1,$t);

might give less colors than $t, so the for loop should call "$i<ImageColorsTotal($im)" instead of "$i<$t" just to be sure, or you'll get the warning: Color index [0-9] out of range

down

strozek(a)deas()harvard()edu ¶

20 years ago


Regarding m4551's method of conversion -- the actual CCIR-approved RGB-to-grayscale conversion is as follows:

grayscale component = 0.2125*R + 0.7154*G + 0.0721*B

(cf. CCIR Recommendation 709 for modern monitors)

down

m4551 at abasoft dot it ¶

20 years ago


here's a function to greyscale an image even from a truecolor source (jpeg or png).

slightly poor quality, but very fast...

function imagegreyscale(&$img, $dither=1) {    
    if (!($t = imagecolorstotal($img))) {
        $t = 256;
        imagetruecolortopalette($img, $dither, $t);    
    }
    for ($c = 0; $c < $t; $c++) {    
        $col = imagecolorsforindex($img, $c);
        $min = min($col['red'],$col['green'],$col['blue']);
        $max = max($col['red'],$col['green'],$col['blue']);
        $i = ($max+$min)/2;
        imagecolorset($img, $c, $i, $i, $i);
    }
}

down

-1

tim at leethost dot com ¶

17 years ago


Here's a better grayscale, sepia, and general tinting function.  This function is better because:

1) Works with true color images (the other sepia code didn't).
2) Provides a more gooder grayscale conversion (yes, I said "more gooder").  The other grayscale code used imagetruecolortopalette, which just doesn't work well for grayscale conversion.
3) The other sepia code was really colorful, a little too much for my taste.  This function allows you to optionally set the tinting of the grayscale to anything you wish.
4) Single function for grayscale, sepia, and any other tinting you can dream up.

Here's some examples:

imagegrayscaletint ($img);  // Grayscale, no tinting
imagegrayscaletint ($img,304,242,209);  // What I use for sepia
imagegrayscaletint ($img,0,0,255);  // A berry blue image

The RGB values for tinting are normally from 0 to 255.  But, you can use values larger than 255 to lighten and "burn" the image.  The sepia example above does this a little, the below example provides a better example of lightening the image and burning the light areas out a little:

imagegrayscaletint ($img,400,400,400);  // Lighten image
imagegrayscaletint ($img,127,127,127);  // Darken image

<?
function imagegrayscaletint (&$img, $tint_r = 255, $tint_g = 255, $tint_b = 255) {
  $width = imagesx($img); $height = imagesy($img);
  $dest = imagecreate ($width, $height);
  for ($i=0; $i<256; $i++) imagecolorallocate ($dest, $i, $i, $i);
  imagecopyresized ($dest, $img, 0, 0, 0, 0, $width, $height, $width, $height);
  for ($i = 0; $i < 256; $i++) imagecolorset ($dest, $i, min($i * abs($tint_r) / 255, 255), min($i * abs($tint_g) / 255, 255), min($i * abs($tint_b) / 255, 255));
  $img = imagecreate ($width, $height);
  imagecopy ($img, $dest, 0, 0, 0, 0, $width, $height);
  imagedestroy ($dest);
}
?>

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