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Bug #23177 imagecreatefromgd2 consumes too much memory
Submitted: 2003-04-12 07:59 UTC Modified: 2003-04-15 21:18 UTC
From: alberty at neptunelabs dot de Assigned:
Status: Not a bug Package: GD related
PHP Version: 4CVS-2003-04-12 (stable) OS: i686-pc-linux-gnu
Private report: No CVE-ID: None
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From: alberty at neptunelabs dot de
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 [2003-04-12 07:59 UTC] alberty at neptunelabs dot de 
Hi,

i've found a bug with handling gd2 images.

The problem is affected with the bundled libgd (2.0.12).

I've convert an image (4932x3543 pixel) with the pngtogd2 tool:

./pngtogd2 mytestpic.png mytestpic.gd2 4932 2

My memory limit is (php.ini):
memory_limit = 162M 

The script:
<?php
$filename='mytestpic.gd2';
$image=imagecreatefromgd2($filename);
?>


results an wrong error message:

Fatal error: Allowed memory size of 169869312 bytes exhausted at (null):0 (tried to allocate 22581552 bytes) 

At first, 22581552 bytes is only the filesize of the mytestpic.gd2 file.

Also it shouldn be a problem to load an image with 4932x3543 pixel, because this image need no more
than 69896304 bytes (3+1 channels).


Regards,

Steve

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 [2003-04-14 19:47 UTC] iliaa@php.net 
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

The memory allocation is:
width * height * channels, which in your case would be upwards of 200megs.
 [2003-04-15 02:04 UTC] alberty at neptunelabs dot de 
Hi Ilia,

you have declared this bug report #23177 as bogus,
but I don?t understand your calculation:

4932 x 3543 x 3 = 50 MB
4932 x 3543 x 4 = 67 MB

Also you ignore the reported wrong error display in php:
>> (tried to allocate 22581552 bytes)
= 22 MB ?!

Your calculation is only correct if you reserve an integer for each channel instead of a byte.

Best regards,

-- 
Steve Alberty
 [2003-04-15 21:18 UTC] iliaa@php.net 
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

First of all the 162 memory limit was exausted not in one allocation, but a fair number of them. GD is not exactly memory friendly and can create many temporary & permanent buffers while reading the image from disk.
Consider gdImageCreateTrueColor() (internal GD function)
one of this things this function will do before even doing a single calculation is allocate:
(length * 4) * 2
(width * 2 * length)

These  two allocations alone already took some 39.5 megs

Keep in mind that while this is happening your png image had too been loaded to memory and is taking up a few dosen megs (at least).
 
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