Memory usage hits the roof - why?

ecce

I've wrote a kind of picture-resize-script (uses GD). My site is hosted by one.com, I don't have full control over the webbserver wich makes debugging pretty limited.

This is the case: The script looks though a folder with pictures in it, randomizes four pictures and creates small thumbnail of them. It then merges these four thumbnail to one picture. This script works fine on most folders, but some makes the script bail out, leaving a fatal error message saying I use more than 16 MB of memory. This is the piece of code where it happens:

//Resize and merge
$im_final = imagecreatetruecolor(162, 122);
imagefill($im_final, 2, 2, imagecolorallocate($im_final, 255, 255, 255));


$im_src = imagecreatefromjpeg("../pics/pic_archive/".$dir."/".$files[1][$arr[0]]) or die("Could not open file.");
imagecopyresampled($im_final, $im_src, 0, 0, 0, 0, $width, $height, imagesx($im_src), imagesy($im_src));
imagedestroy($im_src);

/*$im_src = imagecreatefromjpeg("../pics/pic_archive/".$dir."/".$files[1][$arr[1]]) or die("Could not open file.");
imagecopyresampled($im_final, $im_src, 82, 0, 0, 0, $width, $height, imagesx($im_src), imagesy($im_src));
imagedestroy($im_src);

$im_src = imagecreatefromjpeg("../pics/pic_archive/".$dir."/".$files[1][$arr[2]]) or die("Could not open file.");
imagecopyresampled($im_final, $im_src, 0, 62, 0, 0, $width, $height, imagesx($im_src), imagesy($im_src));
*/
$im_src = imagecreatefromjpeg("../pics/pic_archive/".$dir."/".$files[1][$arr[3]]) or die("Could not open file.");
imagecopyresampled($im_final, $im_src, 82, 62, 0, 0, $width, $height, imagesx($im_src), imagesy($im_src));

imagedestroy($im_src);

return $im_final;

As you can see some lines are commented out and just two thumbnails are created instead of four. This makes the script use less than 16M. I've tried using imagedestroy($im_src) to free up memory but it makes no difference at all.

The pictures are taken with a normal digital camera at 2M and use normal JPEG compression. Four of them are about 1M in total size.

What makes the script hit the roof like that?

MarkR

The amount of memory required to load a JPEG is not affected by the size of the JPEG, but the size of the image.

As the image needs to be uncompressed into memory, the memory requirement is the total for the raw image data, i.e. width height 3 bytes.

For a digital camera image, this can easily exceed 10Mb even if the original jpeg is just 500k.

Mark

Weedpacket

Well, the filesize might be 1MB, but obviously they can't be manipulated if they're still JPEG-compressed - so the filesize is irrelevant.

If the images have two million pixels, then at three bytes per pixel, that's six million bytes per image; four images makes for twenty four million bytes. On top of that of course is memory usage for everything else that's going on.

Have you tried using imagedestroy() after each image?

ecce

Yes I have tried using imagedestroy() and as said, it didn't change a thing. What bothers me is that the memory consumed seems to be builing up as more pictures are handeled. Two images is always OK, but when the third one comes in the script bails out. When the first image is done with that memory could be freed up, and so, if one image is ok to resize all four shouldn't be a problem. But it doesn't seem to work that way.

Weedpacket

ecce wrote:
When the first image is done with that memory could be freed up,

Well that what should happen when you call imagedestroy(); it's possible that the GD library has a leak somewhere so that imagedestroy() isn't effective, but I'd be surprised if it's as big as that (three 2-megapixel images makes for eighteen million bytes.... so imagedestroy would have to be leaking so much memory that it doesn't actually free anything at all). Remember that, GD being a non-PHP library, its resources lie outside PHP's own memory management.

I've tinkered a bit here (with four ~3M-pixel images). With imagedestroy() after each image memory consumption bounces between 22MB and 6MB. Leaving one call to imagedestroy() out sees consumption go up to 37MB until the next call to imagedestroy(), after which it goes back to bouncing between 22MB and 6MB. I do note that in your posted code you don't call imagedestroy() after the third image.