Digital Photo Management In Linux, Part 2 - page 2
Open a photo in editing mode. Your first job is to crop the image if it needs it. Check out the Aspect Image Ratio Crop in the Transform menu because this is an extremely useful tool. First select your aspect ratio. If you're making prints, 2:3 is for 4"x6" prints, 4:5 is for 8"x10", and 5:7 is for 5"x7" prints. Then try out different Composition Guides. Golden Mean, Golden Spirals, Harmonious Triangles, and Rule of Thirds are all standard devices for figuring out the best composition for an image. (Read your Digikam manual for more good information on these.) You might be surprised by how much an image is improved with a bit of smart cropping. Setting the aspect ratio lets you safely drag and resize your selected crop area without accidentally changing the ratio.
For freehand cropping, use Transform -> Crop. First select what you want to keep, then click Crop. Transform -> Resize makes your picture bigger or smaller without cropping.
Now go to the Fix menu. You'll see Red Eye Reduction in the top-level menu, which is a nice convenience. First select the region of your photo that contains the red eyes, then you can choose either mild or aggressive reduction.
Both Blur and Sharpen present nice large before-and-after previews. The Blur feature is nice for portraits- having too much sharpness is not friendly to most faces.
The Sharpen feature improves a slightly blurry picture, but using it too much makes the picture look fake.
Fix -> Colors is where the real action takes place. The first three commands are the most commonly-used ones for most folks: Brightness/Contrast/Gamma, Hue/Saturation/Brightness, and Color Balance. But before you go on a spree, try the Auto Color Correction feature. This is a great tool that gives you five different profiles to try. It displays the usual previews, and you can always hit the Undo button if you don't like the results. (For extra insurance you can work from a copy.) Note that whatever settings you make on these will be preserved, so when you open a new image to edit you'll start with whatever settings you applied before. Click the Default button to return to zero.
Brightness/Contrast/Gamma is for correcting exposures. Usually this is a good first stop, because correcting exposures often corrects apparent color problems too. It's also a cool way to boost the dramatic value of an image. For example, try increasing the contrast and knocking the brightness down a few notches. On images with a shallow depth of field, the in-focus parts will appear to leap out at you, more details seem apparent, and colors appear more more intense.
Hue/Saturation/Brightness are good for pictures that appear washed-out, or overdone. Turn up the Saturation and turn down the Brightness to rescue washed-out colors. My Canon 30D freaks out a bit with big splashes of bright red, like a close-up of a red geranium. It displays as an oversaturated, detail-poor red blob. Turning down the Saturation brings out the details and sharpness.
Color Balance can be tricky, because you're changing the colors. But it's the power tool for fixing skin tones and other color-balance problems. Remember that anything you do can be undone. It's a lot better than the olden days of chemicals, films, and photographic papers- second chances cost money back then.