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Creating transparent PNG 24bit background, how?

Posted: Wed Jul 18, 2007 8:20 am
by kaisellgren
Hi,

I have tried PHP manual scripts without luck.

My latest try:

Code: Select all

<?php

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

// something to get a white background with black border
$back = imagecolorallocatealpha($image, 200, 200, 200);
$border = imagecolorallocate($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);
?>
It says cannot output image or something. It's because the $back = imagecolorallocatealpha should not be alpha.

How do I create a transparent PNG with alpha. I DO NOT want a background. I'd like to be able to mouse right click the image and save to my cpu and when I put it on any image, it will be transparent.

Posted: Wed Jul 18, 2007 10:07 am
by onion2k
In $back = imagecolorallocatealpha($image, 200, 200, 200); .. you've not specified an alpha level.

I'd recommend using the imagecreatetruecolortransparent() function from http://www.phpgd.com/scripts.php?script=27 .