No matter which Linux distro you run, chances are it came with a magnificent little image editor called GIMP (GNU Image Manipulation Program). Unlike Paint and other free-with-your-OS image editors, GIMP is a full featured graphics app with a broad range of capabilities that rival those os Adobe Photoshop. (Note: GIMP does lack many features of its $749 rival, but it has the distinct advantage of costing absolutely nothing.) In this, our first of several posts about this powerful Linux app, we'll give you a quick-and-dirty intro to GIMP's most basic features. Note that there are multiple ways to accomplish these basic tasks in GIMP, but these methods require the fewest steps. In later tutorials, we'll show you more advanced (and more efficient) image editing techniques.
Crop an Image
Cropping in GIMP is fairly straightforward. To start, open an image and select the rectangle selector from the toolbox. Then place the cursor in one corner of the area you'd like to crop. (It's often easiest to start in the upper left corner, like reading a book.) Now drag the rectangle toward the opposite corner of your desired area. (If you started in the upper left corner, you'll be dragging toward the lower-right.) Once you're happy with the selected area, right-click in the box and choose Image > Crop Image.
Resize an Image (aka Scaling)
Like cropping, scaling is a simple operation in GIMP. Open your image and select Image > Scale Image from the menu. Enter the dimensions you want in the fields, and then click Scale to make it so. Easy peasy.
Alternatively, you can handle both cropping and resizing with the Crop and Resize tool located in the Tools > Transform Tools menu. It works similarly to the above examples, but for quick edits, we like the above methods more.
Fix Your Pics
You can manually adjust color, hue, and saturation easily in GIMP. In this image, my tortoise is looking a little hot in the Hawaiian sun, and I'd like to eliminate those washed out white spots from his shell. To do it, I'm going to modify the color balance in the highlights by clicking Tools > Color Tools > Color Balance and using the sliders to make small adjustments. Because I really only want to tone down the highlights at this point, I check the Highlights option at the top of the Adjust Color Balance dialog, and then I push the Yellow-Blue slider a little to the right. A small adjustment quickly removes most of the annoying white spots from the tortoise's shell without significantly altering the image's overall appearance. While I'm at it, I'm going to turn up the Red and Green just slightly to preserve the natural red tones of the soil and shell and preserve the bright greens of the surrounding grass. As long as you make small adjustments, the result maintains a natural look while bringing out more of the subject's fine details. You can also make adjustments to brightness, hue, and saturation in the same way, by choosing those options from the Tools > Color Tools menu.
That concludes this week's GIMP tutorial. This one was elementary, but in upcoming posts, we'll dig a lot deeper into this app's wide range of features, including working with paint tools to manipulate your images, using layers, and playing with the array of plug-ins and scripting tools that make GIMP such a powerful graphics tool.