Scaling and cropping an image to the specified size using PHP GD

imagescalecrop.php

<?php
/**
 * Loads an image into a GD resource and scales/crops it to the given target size.
 * 
 * @param string $filename The file name of the image.
 * @param string $mime The mime type of the image.
 * @param string $target_size The target size.
 * 
 * @throws Exception When the image MimeType is invalid.
 * 
 * @return resource The GD image resource.
 * 
 * @author Dennis Degryse
 */
imagescalecrop($filename, $mime, $target_size) {
    // validate the mime type
    $valid_formats = ['jpeg', 'gif', 'png', 'bmp', 'wbmp', 'webp', 'xbm'];
    list($mime_type, $mime_format) = expode('/', $mime);
    
    if ($mime_type !== 'image' || !in_array($mime_format) {
        throw new \Exception('Invalid image.');
    }
    
    $img = call_user_func("imagecreatefrom$mime_format", $filename);
    
    $factor = max(array_map(function($td, $d) { return $td / $d; }, $target_size, $size = imagegetsize($filename)));
    $new_size = array_map(function($d) use($factor) { return $d * $factor; }, $size);
    $offset = array_map(function($d, $td) { return ($d - $td) / 2}, $new_size);
    
    imagescale($img, $new_size[0], $new_size[1]);
    imagecrop($img, [ $offset[0], $offset[1], $target_size[0], $target_size[1] ]);
    
    return $img;
}