Resize images with PHP, support PNG, JPG

function resize($newWidth, $targetFile, $originalFile) {

    $info = getimagesize($originalFile);
    $mime = $info['mime'];

    switch ($mime) {
            case 'image/jpeg':
                    $image_create_func = 'imagecreatefromjpeg';
                    $image_save_func = 'imagejpeg';
                    $new_image_ext = 'jpg';
                    break;

            case 'image/png':
                    $image_create_func = 'imagecreatefrompng';
                    $image_save_func = 'imagepng';
                    $new_image_ext = 'png';
                    break;

            case 'image/gif':
                    $image_create_func = 'imagecreatefromgif';
                    $image_save_func = 'imagegif';
                    $new_image_ext = 'gif';
                    break;

            default: 
                    throw new Exception('Unknown image type.');
    }

    $img = $image_create_func($originalFile);
    list($width, $height) = getimagesize($originalFile);

    $newHeight = ($height / $width) * $newWidth;
    $tmp = imagecreatetruecolor($newWidth, $newHeight);
    imagecopyresampled($tmp, $img, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);

    if (file_exists($targetFile)) {
            unlink($targetFile);
    }
    $image_save_func($tmp, "$targetFile.$new_image_ext");
}

I've written a class that will do just that and is nice and easy to use. It's called
PHP Image Magician

$magicianObj = new imageLib('racecar.jpg');
$magicianObj -> resizeImage(100, 200);
$magicianObj -> saveImage('racecar_convertd.png', 100);

It supports Read and Write (including converting) the following formats

• jpg
• png
• gif
• bmp

And can read only

• psd's

Example

// Include PHP Image Magician library
require_once('php_image_magician.php');

// Open JPG image
$magicianObj = new imageLib('racecar.jpg');

// Resize to best fit then crop
$magicianObj -> resizeImage(100, 200, 'crop');

// Save resized image as a PNG
$magicianObj -> saveImage('racecar_small.png');