What's the most efficient way to resize large images in PHP?
I'm currently using the GD function imagecopyresampled to take high resolution images, and cleanly resize them down to a size for web viewing (roughly 700 pixels wide by 700 pixels tall).
This works great on small (under 2 MB) photos and the entire resize operation takes less than a second on the server. However, the site will eventually service photographers who may be uploading images up to 10 MB in size (or images up to 5000x4000 pixels in size).
Doing this kind of resize operation with large images tends to increase the memory usage by a very large margin (larger images can spike the memory usage for the script past 80 MB). Is there any way to make this resize operation more efficient? Should I be using an alternate image library such as ImageMagick?
Right now, the resize code looks something like this
function makeThumbnail($sourcefile, $endfile, $thumbwidth, $thumbheight, $quality){
// Takes the sourcefile (path/to/image.jpg) and makes a thumbnail from it
// and places it at endfile (path/to/thumb.jpg).
// Load image and get image size.
$img = imagecreatefromjpeg($sourcefile);
$width = imagesx( $img );
$height = imagesy( $img );
if ($width > $height) {
$newwidth = $thumbwidth;
$divisor = $width / $thumbwidth;
$newheight = floor( $height / $divisor);
}
else {
$newheight = $thumbheight;
$divisor = $height / $thumbheight;
$newwidth = floor( $width / $divisor );
}
// Create a new temporary image.
$tmpimg = imagecreatetruecolor( $newwidth, $newheight );
// Copy and resize old image into new image.
imagecopyresampled( $tmpimg, $img, 0, 0, 0, 0, $newwidth, $newheight, $width, $height );
// Save thumbnail into a file.
imagejpeg( $tmpimg, $endfile, $quality);
// release the memory
imagedestroy($tmpimg);
imagedestroy($img);