Digital Photo Management In Linux, Part 2
By: Carla Schroder
Thursday, October 11, 2007 01:41:23 PM EST
URL: http://www.linuxplanet.com/linuxplanet/tutorials/6426/1/
Everything Depends
Last week we learned how to sanely organize our vast digital photo archives with Digikam. Today we'll look at Digikam's built-in editing tools. You'll be able to do a surprising amount of your editing work without ever leaving Digikam.
If you're familiar with old-fashioned film photography, you know that capturing an image with any sort of fidelity is a big game of "it depends." There are hundreds of factors that affect the appearance and quality of the final image- the quality of your camera, the type of film, the type of processing and papers used. Both color and black-and-white film processing are very malleable; you can achieve all kinds of affects with different developers, papers, and printing techniques.
With digital photography the malleability of images is magnified a thousand-fold. Start with the quality of your optics, then your camera's image sensor, then your computer's software, and if you make prints, the quality of your printer and printer drivers. To make matters even more interesting every computer monitor displays images differently, so what you see on the screen is hardly ever the same as what comes out of your printer. But despair not, for Linux has some excellent color management tools. I'll be writing about this in future installments; for now, check out LProf or Argyll for creating accurate color profiles for monitors, cameras, and scanners.
All of this flexibility lets you work however you prefer. I like to get the picture as right as possible in the camera and not have to bother with a lot of post-processing, so I rely on zoom lenses, precise exposures and bracketing, and careful focusing. Other people love spending hours on editing and tweaking; it's entirely up to you.
Cropping, Resizing, and Basic Fixes
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.
Limitations
The basic fixes we learned today apply to the entire image; you can't select a region of your photo and work only on that. You'll need a more deluxe image editor for that sort of fine-tuning.
That wraps up our two-part introduction to Digikam. Be sure to read the Digikam manual and visit the user's mailing list. Watch this space for future amazing digital photo editing howtos.
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