create_thumbnail.php

function create_thumbnail($max_width, $max_height, $source_file, $dst_dir)
{
    $imgsize = getimagesize($source_file);
    $width = $imgsize[0];
    $height = $imgsize[1];
    $mime = $imgsize['mime'];
 
    switch ($mime) {
        case 'image/png':
            $image_create = 'imagecreatefrompng';
            $image = 'imagepng';
            $quality = 9;
            break;
 
        case 'image/jpeg':
            $image_create = 'imagecreatefromjpeg';
            $image = 'imagejpeg';
            $quality = 100;
            break;
 
        default:
            return false;
            break;
    }
    
    $dst_img = imagecreatetruecolor($max_width, $max_height);
    imagealphablending($dst_img, false);
    imagesavealpha($dst_img, true);
    $src_img = $image_create($source_file);
     
    $width_new = $height * $max_width / $max_height;
    $height_new = $width * $max_height / $max_width;
    // If the new width is greater than the actual width of the image, then the height is too large and the rest cut off, or vice versa
    if ($width_new > $width) {
        // Cut point by height
        $h_point = (($height - $height_new) / 2);
        // Copy image
        imagecopyresampled($dst_img, $src_img, 0, 0, 0, $h_point, $max_width, $max_height, $width, $height_new);
    } else {
        // Cut point by width
        $w_point = (($width - $width_new) / 2);
        imagecopyresampled($dst_img, $src_img, 0, 0, $w_point, 0, $max_width, $max_height, $width_new, $height);
    }
     
    $image($dst_img, $dst_dir, $quality);
 
    if ($dst_img) {
        imagedestroy($dst_img);
    }
    if ($src_img) {
        imagedestroy($src_img);
    }
}