imagecolorsforindex

(PHP 4, PHP 5)

imagecolorsforindex — カラーインデックスからカラーを取得する

説明

array imagecolorsforindex ( resource $image , int $index )

指定したインデックスに対する色を取得します。

パラメータ

image: imagecreatetruecolor() のような画像作成関数が返す画像リソース。
index: 色インデックス。

返り値

指定したカラーインデックス index に対して適当な値からなる red、green、blue をキーとする連想配列を返します。

例

例1 imagecolorsforindex() の例


<?php

// 画像をオープンします
$im = imagecreatefrompng('nexen.png');

// 色を取得します
$start_x = 40;
$start_y = 50;
$color_index = imagecolorat($im, $start_x, $start_y);

// 可読形式にします
$color_tran = imagecolorsforindex($im, $color_index);

// どんな内容でしょう?
print_r($color_tran);

?>

上の例の出力は、たとえば以下のようになります。

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

参考

imagecolorstotal

imagecolorset

Last updated: Fri, 10 Oct 2008

add a note User Contributed Notes
imagecolorsforindex

hofstadler dot andi at gmx dot at
08-Oct-2008 04:36


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);

}

?>

matrebatre
08-Aug-2008 03:11


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().

derek at idreams dot co dot uk
01-Dec-2007 05:45


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 );

  }

}

?>

joe dot scylla at gmail dot com
28-Nov-2007 11:35


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;

?>

tim at leethost dot com
10-Sep-2007 02:01


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);

}

?>

slepichev at yahoo dot com
06-Sep-2007 07:50


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);

     }

?>

admin at phpgfx dot com
27-Aug-2007 01:54


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 );

    }

}



?>

adspeed.com
24-Aug-2005 08:05


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

strozek(a)deas()harvard()edu
26-Jun-2004 05:32


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)

m4551 at abasoft dot it
24-Apr-2004 01:23


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);

    }

}

add a note

imagecolorstotal

imagecolorset

Last updated: Fri, 10 Oct 2008