How to Save Your Work in GIMP
Save your files the same way you save them in any program, by using the File menu. File > Save As saves your images in the default GIMP file format, which is .xcf. This is not a standard image file format, but a special native GIMP format. Use the .xcf format as your master save format because it preserves layers, channels, paths, transparency, and other editing data. This allows you to go back and easily re-edit your images without having to start over, and without losing your editing options.
When you are finished editing, you then need to export your image to a standard format (File > Export) such as .jpg, .png, .gif, .psd, or .tiff. If you plan to use your images on the Web, .jpg and .gif work well because you get good image quality in the smallest file size. Another good Web format—.png—supports transparency (unlike .jpg). If you need very large file sizes for printing images or for high-quality archiving, go with .tiff file format.To learn more, Wikipedia's Image file formats is a good reference.
All About Image Cropping
Figure 4: A cute pic that's prime for cropping.
Select the Crop tool, which looks like an X-Acto knife, and use it to select the part of the image you want to keep. Like most of GIMP's tools, the crop tool is forgiving, and has corner handles so that you can tweak it until you have it just right. Then press the Enter or Return key to make the crop and, as always, if you don't like it you can undo it.
In fact, GIMP provides an Undo History in the right-hand dock; just look at top row of tabs for the one with the yellow undo arrow. You can use this to go directly to any point in your undo history, including all the way back to the beginning. Figure 5 shows the improved version.
Figure 5: The cropped—and improved—goat and bear.
This photo was taken on a gloomy wet day, so I brightened it with Colors > Brightness-Contrast. First I increased the contrast to brighten the colors and sharpen the image, and I kicked the brightness level up a bit to bring out the white a little more. Then I used the Smudge tool to blur out the cars in the background. As a general rule, when you want to make colors richer and images appear sharper try increasing the contrast first.
Resizing Images in GIMP
When you want to make images larger or smaller, go to Image > Scale Image. Note the little chain link to the right of the Width and Height settings; by default these are linked so that when you change one the other automatically changes to stay in proportion. If you want to control them separately, click the chain to un-link them. Don't make images larger unless you have no other option, because that magnifies pixels and the results usually look bad.
GIMP's printing dialog is pretty nice, and it allows you to make and preview all kinds of finicky adjustments without wasting ink and paper. You can set the paper type and size, color modes, number of copies, scaling, borders, and print borderless. You'll get the best results with an inkjet photo printer that uses separate ink cartridges for each color, such as black, cyan, magenta, and yellow, and by selecting the correct paper type.
You'll be a lot happier with GIMP if you refer to the good documentation. My favorite GIMP books are Beginning GIMP: From Novice to Professional, by Akkana Peck, and The Book of GIMP: A Complete Guide to Nearly Everything by Olivier Lecarme and Karine Delvare. Visit GIMP documentation for more documentation and how-tos.
Carla Schroder is the author of The Book of Audacity, Linux Cookbook, Linux Networking Cookbook,and hundreds of Linux how-to articles. She's the former managing editor of Linux Planet and Linux Today.
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