The NetTuts.com site has continued their series covering the use of the GD functionality in PHP to manipulate images with a new tutorial posted today. In this second part of the series they focus in on resizing and manipulating images.

In my previous tutorial, we discussed basic image manipulation using the PHP GD library. In that tutorial, I gave a brief introduction to the library and showed you how to load images from a file or create them from scratch in PHP. After that, we learned how to crop, rotate, scale and flip an image using GD. I covered the imagefilter() function to apply different filters to image resources loaded in the script. I also mentioned some useful functions in GD like imagesx() and imagesy() to get the width and height of the loaded image.

By the end of my last GD tutorial, you learned how to use the library to automate basic tasks like resizing all images in a directory or applying filters like grayscale on them before saving the final result. [...] In this tutorial, we will learn about many more useful functions in GD and how they can be used to automate more of our image manipulation tasks.

They start by looking at the imageconvolution function and the use of a "convolution matrix" and how it can be useful to blur, sharpen, emboss, or detect edges on an image. It then covers the functions used to copy images and alter the end result by changing contrast or converting to grayscale. Finally, the author shows how to use the GD functionality to dynamically add a watermark to the image and output the result to a new file.