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PHP imagecolorallocatealpha - Allocate Color and Transparency for an Image

PHP Image Processing

imagecolorallocatealpha — Allocate a color and transparency for an image.

Syntax

int imagecolorallocatealpha ( resource $image , int $red , int $green , int $blue , int $alpha )

The behavior of imagecolorallocatealpha() is identical to imagecolorallocate(), but with an additional transparency parameter alpha, which ranges from 0 to 127. 0 represents fully opaque, and 127 represents fully transparent.

Returns FALSE if allocation fails.

Note: This function requires GD 2.0.1 or later (recommended 2.0.28 and later).

Example

<?php
$size = 300;
$image = imagecreatetruecolor($size, $size);

// Draw a square with a white background and 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 some 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);

// Draw three overlapping circles
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 the correct header!
header('Content-type: image/png');

// Finally output the result
imagepng($image);
imagedestroy($image);
?>

The above example outputs an image as follows:

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