Detect JPEG image quality

Question

I allow users to upload images. However, I want to keep JPEG quality not more than 90%. What I plan to do is to detect the current quality: - If less than 90% do nothing - If mo

Answer 1

Here is a PHP function that tries all available methods of getting quality (that I know of):

/* Try to detect quality of jpeg.
   If not possible, nothing is returned (null). Otherwise quality is returned (int)
    */
function detectQualityOfJpg($filename)
{
    // Try Imagick extension
    if (extension_loaded('imagick') && class_exists('Imagick')) {
        $img = new Imagick($filename);

        // The required function is available as from PECL imagick v2.2.2
        if (method_exists($img, 'getImageCompressionQuality')) {
            return $img->getImageCompressionQuality();
        }
    }

    if (function_exists('shell_exec')) {

    // Try Imagick
        $quality = shell_exec("identify -format '%Q' " . $filename);
        if ($quality) {
            return intval($quality);
        }

        // Try GraphicsMagick
        $quality = shell_exec("gm identify -format '%Q' " . $filename);
        if ($quality) {
            return intval($quality);
        }
    }
}