Resizing images in PHP with GD and Imagick

One task that is quite often required in websites and web applications is resizing of images for thumbnails or any other purpose. In PHP there’s a number of different ways you can approach image resizing each of which has it’s own advantages and disadvantages. In this post we will be using the GD and Imagick PHP extensions to resize images and comparing the differences.

When creating thumbnails there’s a few decisions that are required before you start coding. You need to decide on the width and height of your thumbnails, you need to decide whether you want your images to be cropped to fit your specified dimensions or not and you need to decide on an image format. In the examples below we will be showing how to resizing both using the “crop” method and without cropping.

So let’s launch into this article with a very brief look at the GD PHP extension.

GD is the more commonly used extension for PHP. It is generally easy to install (`yum install php-gd` on Fedora, CentOS etc or `sudo apt-get php5-gd` on ubuntu etc). It has quite extensive documentation with examples and as it is more commonly used there’s a lot more web content available for it.

The disadvantages of GD are that it is slower and more memory intensive. Overall it has slightly less functionality and can be more complex to use.
Let’s take a look at a quick resizing example. In this example we have a jpeg image that we are going to resize to be 150×150 pixels. We are not worried about the format of the image so we won’t be changing it.

function resize_image($file, $w, $h, $crop=FALSE) {
    list($width, $height) = getimagesize($file);
    $r = $width / $height;
    if ($crop) {
        if ($width > $height) {
            $width = ceil($width-($width*($r-$w/$h)));
        } else {
            $height = ceil($height-($height*($r-$w/$h)));
        $newwidth = $w;
        $newheight = $h;
    } else {
        if ($w/$h > $r) {
            $newwidth = $h*$r;
            $newheight = $h;
        } else {
            $newheight = $w/$r;
            $newwidth = $w;
    $src = imagecreatefromjpeg($file);
    $dst = imagecreatetruecolor($newwidth, $newheight);
    imagecopyresampled($dst, $src, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);

    return $dst;

$img = resize_image(‘/path/to/some/image.jpg’, 150, 150);

Resizing images with GD requires that you create a new image and copy the re-sampled section to it. This means that any EXIF data contained in the image will be lost. Note that in the code above we are not actually doing anything with the image. You could either output it directly to the browser or save it to a file using the imagejpeg function.

On the other hand, the Imagick PECL extension has it’s own advantages and disadvantages.

Imagick is the less frequently used PECL extension for the ImageMagick project. ImageMagick is a free suite of tools used for image creation and manipulation supporting over 100 different image formats. It is typically a command line tool but also has interfaces available for a number of different programming languages (including PHP).

The Imagick extension essentially provides an API for all of the functionality available in the `convert` command line tool. Imagick is fast, uses less memory and has some powerful functionality available. Quite often Imagick is a lot easier to use (once you figure out how), your code may end up smaller and cleaner.

The down side of using this extension is that the documentation is extremely limited and there are next to no examples available on the web. Installation can often be a painful task as well although it should just be a matter of running the command `pecl install imagick`.

So now let’s move on to an example. As above we are resizing a jpeg image to 150×150 pixels.

function resize_image($file, $w, $h, $crop=FALSE) {
    $img = new Imagick($file);
    if ($crop) {
        $img->cropThumbnailImage($w, $h);
    } else {
        $img->thumbnailImage($w, $h, TRUE);

    return $img;
resize_image(‘/path/to/some/image.jpg’, 150, 150);

As you can see the Imagick code is much less complex. It doesn’t duplicate the image so it uses less memory and doesn’t lose the image EXIF data. Again note that in the code we are not actually doing anything with the image. You could save it to a file using the writeImage method or output it directly to the browser.

As mentioned, depending on your purpose there is advantages and disadvantages to using both GD and Imagick. It is really just a matter of deciding what you need to do and determining which will work best for you.

As usual all comments are welcomed. I’d love to hear your thoughts and preferences relating using either GD or Imagick. Additionally if you have any specific image manipulation requests let us know and we will do our best to answer your questions.

That’s all for now.

  • Elvik

    Hello, I use imagick crop() and then resize() function but when resizing the image lose quality, is there a way to keep image quality? I try this, but doesn't work! =(

    $im = new Imagick($o_img);
    $im->cropImage($src_w, $src_h, $src_x, $src_y);
    $im->resizeImage($dst_w, $dst_h,imagick::FILTER_LANCZOS ,0);

  • Viswanath Ct

    Helpful! Thx :)

  • anonymous

    Thank you very much boss ,, i'll switch from using GD to Imagick !!

  • Learning PHP

    Nice!  I found a page that shows how to put changed images into a database - mySQL and PDO at:

  • pegiejot

    Good post, thank

blog comments powered by Disqus