LinuxConf.Au: GIMP Uncovered: Understanding Images and Image Editing
The majority of Linux users have probably tried editing their photographs with the GNU Image Manipulation Program (GIMP), and many are regular users. You may use GIMP on a regular basis, or you may be just starting out: but do you really feel like you understand the details?
In this tutorial, you'll get down and dirty with GIMP. No prior GIMP experience is required: beginners who haven't done any image editing at all are welcome. As we progress, I'll cover the hows and whys of each operation: intermediate GIMP users who use the application on a regular basis may find that they can work much more effectively by understanding some of the background behind GIMP's operation.
I'll start by covering some of the basics of photo manipulation. I'll discuss details of the different image formats: when should you use a JPEG, and when might it be better to use GIF? What's PNG good for? What about TIFF, ICO and BMP? I'll also discuss resolution versus pixel size, an area which causes a huge amount of confusion among users. How big should you make your image if you want to print it? What size should you use for web images, and what are some ways you can make your web images smaller without making them look bad? What are the differences between raster and vector formats, and how can you move between them?
Next, I'll cover layers. Layers are the heart of any GIMP operation beyond the basic photo crop, resize, scale, brightness and contrast operations, and an understanding of layers can make a huge difference to your image editing experience. For me, beginning to understand layers was the point where I stopped feeling like I was fighting GIMP and started to love it. Layers sound intimidating when you haven't used them before, but anyone can learn the basics in a few minutes -- a few simple examples will illustrate why they're useful and how to manage them.
I'll also cover selection: perhaps the most difficult, yet most important, aspect to manipulating photos and other pre-existing images. GIMP offers many different methods for selecting a part of an image -- so many that it's very easy to get confused and wonder what they all do and which one is most appropriate. I'll talk about which selection methods are best in common circumstances, how they relate to each other, and how to switch among them.
Finally, I'll introduce users to layer modes, an often ignored yet very powerful way of combining several images to get all sorts of interesting effects; and I'll discuss some of GIMP's useful built-in filters and plug-ins.