Compress image file using PHP imagejpeg() function

compressImage.php

<?php

/**
 * Sample to compress image file in PHP.
 * 
 * This will compress all files in *input* directory and store the result in *output* directory.
 * 
 * To run this code, PHP extension *gd* should be enabled.
 * 
 * Syntax
 * ```shell
 *    php compressImage.php
 * ```
 */

// Get files in directory input, ignore '.' and '..'.
$files = array_diff(scandir('input'), ['.', '..']);

// Convert files to output/small_<input name>.jpeg
foreach ($files as $file) {
    compress("input/$file", "output/small_{$file}.jpeg", 40);
}

/**
 * Compress image file to jpeg file.
 * 
 * The source code is from https://stackoverflow.com/questions/11418594/how-to-reduce-the-image-size-without-losing-quality-in-php/19404938#19404938
 * 
 * @param string $source Image file of type jpeg/gif/png
 * @param string $destination Output image
 * @param float $quality Ratio to compress image, between 1 to 100.
 */
function compress($source, $destination, $quality)
{
    $info = getimagesize($source);

    if ($info['mime'] == 'image/jpeg') 
        $image = imagecreatefromjpeg($source);

    elseif ($info['mime'] == 'image/gif') 
        $image = imagecreatefromgif($source);

    elseif ($info['mime'] == 'image/png') 
        $image = imagecreatefrompng($source);

    imagejpeg($image, $destination, $quality);

    return $destination;
}