imagecolorallocatealpha

imagecolorallocatealpha

Allocate a color for an image

 **imagecolorallocatealpha** GdImage $image int $red int $green int $blue int $alpha

behaves identically to
with the addition of the transparency

parameter . imagecolorallocatealpha``imagecolorallocate``alpha

The , and parameters are integers between 0 and 255 or hexadecimals between 0x00 and 0xFF. redgd.value.red

greengd.value.green

bluegd.value.blue

alpha A value between and . indicates completely opaque while indicates completely transparent. 0``127``0``127

red``green``blue

A color identifier or false if the allocation failed.

**Voorbeeld: Example of using **

<?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);
?>

**Voorbeeld: Convert typical alpha values for use with **

Usually alpha values of  designate fully transparent pixels,
and the alpha channel has 8 bits. To convert such alpha values to be compatible
with , some simple arithmetic is
sufficient:

0``imagecolorallocatealpha

<?php
$alpha8 = 0; // fully transparent
var_dump(127 - ($alpha8 >> 1));
$alpha8 = 255; // fully opaque
var_dump(127 - ($alpha8 >> 1));
?>

int(127)
int(0)

imagecolorallocate``imagecolordeallocate