PHP - Compress Image to Meet File Size Limit

I have to upload image files that meet a max width dimension and max file size.

I have the code that checks width size and resizes the image to meet the max image width.

However, when I am saving the file I can set the quality

imagejpeg( $imgObject , 'resized/50.jpg' , 50 ); //save image and set quality

What I would like to do is avoid setting a standard quality, as the images being submitted vary highly from quality and may be low to begin with.

The quality of the image should be set as high as possible without going over the max file size limit.

The only solution I have is to save several versions of the image at varying qualities, check each file size and pick the best one. This works but is very slow and process intensive.

Any suggestions on how this could be done better?

Thanks

Solution

Here is a way to achieve that. It does not save a file until it is satisfied that the file size will be lower than the specified maximum.

$original_file = 'original.jpg';
$resized_file = 'resized.jpg';
$max_file_size = '30000'; // maximum file size, in bytes

$original_image = imagecreatefromjpeg($original_file);

$image_quality = 100;

do {
    $temp_stream = fopen('php://temp', 'w+');
    $saved = imagejpeg($original_image, $temp_stream, $image_quality--);
    rewind($temp_stream);
    $fstat = fstat($temp_stream);
    fclose($temp_stream);

    $file_size = $fstat['size'];
}
while (($file_size > $max_file_size) && ($image_quality >= 0));

if (-1 == $image_quality) {
    echo "Unable to get the file that small. Best I could do was $file_size bytes at image quality 0.\n";
}
else {
    echo "Successfully resized $original_file to $file_size bytes using image quality $image_quality. Resized file saved as $resized_file.\n";
    imagejpeg($original_image, $resized_file, $image_quality + 1);
}

This requires no file to be written until you've successfully found the ideal compression ratio.

This loop starts with an $image_quality of 100, then counts downward trying each new value on a temporary in-memory buffer. If gets down to trying 0 and the file would still be too big, it returns an error message. Otherwise, if it gets to a value that works, it reports that and saves the new file using that image quality setting.

If you're feeling adventurous, you could implement a binary search algorithm to find the ideal compression ratio more quickly, but this quick-fix gives the same result, albeit possibly a tad slower.