PHP : Function Reference : Image Functions : imagecolorallocatealpha PHP Examples Tutorials References

Example 990. Example of using imagecolorallocatealpha()

<?php

$size = 300;
$image=imagecreatetruecolor($size, $size);

// something to get a white background with black border
$back = imagecolorallocate($image, 255, 255, 255);
$border = imagecolorallocate($image, 0, 0, 0);
imagefilledrectangle($image, 0, 0, $size - 1, $size - 1, $back);
imagerectangle($image, 0, 0, $size - 1, $size - 1, $border);

$yellow_x = 100;
$yellow_y = 75;
$red_x    = 120;
$red_y    = 165;
$blue_x   = 187;
$blue_y   = 125;
$radius   = 150;

// allocate colors with alpha values
$yellow = imagecolorallocatealpha($image, 255, 255, 0, 75);
$red    = imagecolorallocatealpha($image, 255, 0, 0, 75);
$blue   = imagecolorallocatealpha($image, 0, 0, 255, 75);

// drawing 3 overlapped circle
imagefilledellipse($image, $yellow_x, $yellow_y, $radius, $radius, $yellow);
imagefilledellipse($image, $red_x, $red_y, $radius, $radius, $red);
imagefilledellipse($image, $blue_x, $blue_y, $radius, $radius, $blue);

// don't forget to output a correct header!
header('Content-type: image/png');

// and finally, output the result
imagepng($image);
imagedestroy($image);
?>

The above example will output something similar to:

Code Examples / Notes » imagecolorallocatealpha

If you only wish to extract the alpha value for a color, you can simply extract it like so: <?php $color = imagecolorat($im, 50, 50); $alpha = $color >> 24; ?> It actually shifts off the first 24 bits (where 8x3 are used for each color), and returns the remaining 7 allocated bits (commonly used for alpha)

Check out this Source, it's a little funny feature showing you, for what imagecolorallocatealpha() is used: <?php $im=imagecreatetruecolor(300,300); $white=imagecolorallocate($im,255,255,255); imagefilledrectangle($im,0,0,imagesx($im),imagesy($im),$white); for($i=0;$i<256;$i=$i+10) { $col=imagecolorallocatealpha($im,$i,$i,$i,ceil(rand(0,127))); imagefilledellipse($im,$i,$i,$i,$i,$col); } header("content-type: image/png"); imagepng($im); ?>

imagecolorallocatealpha

Allocate a color for an image (PHP 4 >= 4.3.2, PHP 5)
int imagecolorallocatealpha ( resource image, int red, int green, int blue, int alpha )

Example 990. Example of using imagecolorallocatealpha()

Code Examples / Notes » imagecolorallocatealpha

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imagecolorallocatealpha

Allocate a color for an image (PHP 4 >= 4.3.2, PHP 5) int imagecolorallocatealpha ( resource image, int red, int green, int blue, int alpha )

Example 990. Example of using imagecolorallocatealpha()

Code Examples / Notes » imagecolorallocatealpha

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Allocate a color for an image (PHP 4 >= 4.3.2, PHP 5)
int imagecolorallocatealpha ( resource image, int red, int green, int blue, int alpha )