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Bug #20847 subimages made from transparent images aren' transparent
Submitted: 2002-12-05 17:49 UTC Modified: 2002-12-05 19:19 UTC
From: gid at gifpaste dot net Assigned: pajoye (profile)
Status: Closed Package: GD related
PHP Version: 4.3.0RC2 OS: Debian (sid) Linux 2.4.20
Private report: No CVE-ID: None
 [2002-12-05 17:49 UTC] gid at gifpaste dot net
I'm running 4.3.0RC2 with the built in gd library.

What I'm trying to do is create a transparent subimage from a series of pngs that have an 8 bit alpha channel.  I then can resize the subimage, rotate it, whatever over another photograph.

I realize there's the imagecolortransparent() function so you can specify one color on your image as transparent, but this does not help the case when you want full 8-bit transparency.

Expected results:  The subimage should have an 8-bit alpha channel like the png's that's it's created from and should be transparent when imagecopy()'d over the photoimage.

Actual results:  I get a black box where I tried to copy the image.

Web page source:  http://pimpbot.qooqle.com/gid/php_bug1/
(example png and jpg images I used are loacated here)

Example source:
<?
// load photo image
$photo_img = imagecreatefromjpeg('images/kittybath.jpg');
imagealphablending($photo_img, TRUE);

// load just one letter for now to test
// this is a transparent png with an 8 bit alpha channel
$letter_img = imagecreatefrompng('images/S.png');
imagealphablending($letter_img, TRUE);
$x = imagesx($letter_img);
$y = imagesy($letter_img);

// create the words image, same size as the letter for now
// this is also referred to as the subimage, it should also have an 8 bit alpha channel
// like the letter_img
$words_img = imagecreate($x, $y);
imagepalettecopy($words_img, $letter_img);
imagealphablending($words_img, TRUE);

// copy letter image onto words image
imagecopy($words_img, $letter_img, 0, 0, 0, 0, $x, $y);

// now that we have the words image, we can resize it, rotate it, etc
// but we won't do that for now to keep things simple

// copy words image onto photo image
imagecopy($photo_img, $words_img, 50, 50, 0, 0, $x, $y);

// write out new image
imagejpeg($photo_img, 'images/new.jpg', 90);
?>

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 [2002-12-05 17:52 UTC] gid at gifpaste dot net
Additional note:  If I try to directly copy the transparent png image over the photo image, it works like a charm, it's only when I need to create an intermediate subimage that it doesn't work.
 [2002-12-05 19:19 UTC] pajoye@php.net
Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit http://www.php.net/support.php as this bug system is not the
appropriate forum for asking support questions. 

Thank you for your interest in PHP.

hello,

You may use color to draw something in a image, not only alpha channels. Paint program shows you a black/gray for ot as a convenience.

Try to redraw your letter with real color (even with transparancy) and it will work.

Thank's for your report.

pierre



 
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