Dynamic Images / Serverside JPEG

[jamesl]

  I'm having a small ordeal with a site and people uploading large images (Often over 1MB). I can't rely on client side size restrictions, so that leaves me with two choices... to recompress into JPEG before sending to the client, or compressing and resizing on upload. I know it's possible, but I don't know how (Probably a rewrite rule), but I've seen sites that when an image is loaded, it instead takes you to a page which shows the image along with copyright information, a banner, the whatnot. Though, this would make things easier, I'd rather compress the files on upload. What would be best and how would I do it?

[redbullmarky]

do you mean like a thumbnail, just a bigger version?

[jamesl]

  Well I'd like to be able to do a thumbnail version, the main concern is people uploading large, uncompressed files, which get used for the MySpace equivalent of a display pic. When you have 10 1.5MB pictures on a page when they are being shrunk in HTML, it kind of causes... lag? Haha.

[redbullmarky]

ok, might be worth taking a look for thumbnail scripts anyway, but generally it involves [url=http://uk.php.net/gd]GD library[/url] to open, resize and display the smaller version. What its ability is to handle HUGE images is, I couldnt tell you...

[jamesl]

Jesus, das alot of stars... anyway, yeah, I figured I could just use the GD Library... Can you scale proportionally using the library? Seeing as I don't want images being square if they are rectangular.

[redbullmarky]

yeah - generally, to keep the quality, the function you're after is [url=http://www.php.net/imagecopyresampled]imagecopyresampled[/url]. it takes box coordinates of the source, box coordinates for the destnation, and voila.
the working out comes seperately, but generally follows something like this:

[code]
<?php
$filename = "test.jpg";
$w = 200; // max width
$h = 200; // max height

//first open the file
$im = imagecreatefromjpeg($filename);

// get its width/height
$sx = imagesx($im);
$sy = imagesy($im);

// work out the scale. $w would be initially set to the max width, $h to the max height
$scale = min($w/$sx, $h/$sy);

// send the necessary headers to the browser:
header("Content-type: image/jpeg");

// scale < 1 means it needs resizing as too big
if ($scale<1)
{
// work out the new width/height
$newwidth = $scale * $sx;
$newheight = $scale * $sy;

// create a 'canvas' for it
$im2 = imagecreatetruecolor($newwidth, $newheight);

// do the copying and send to browser
imagecopyresampled($im2, $im, 0, 0, 0, 0, $newwidth, $newheight, $sx, $sy);
imagejpeg($im2);

// clean up
imagedestroy($im);
imagedestroy($im2);
}
else
{
imagejpeg($im);
imagedestroy($im);
}
?>
[/code]