Linux Tools for Professional Photography
A lot of the tools in The GIMP, as well as other image editing programs, aren't needed for photographic work. Most of my time is spent using the Levels or Curves tools. The first adjustment I make is to the overall exposure, and the best tool for this is Levels. Never use the Brightness/Contrast tool, as it tends to clip values. Open the Levels tool and slide the black and white points right up to the point where data (height) is apparent. Adjust the middle slider to lighten or darken the overall image.
Cleaning up dust and scratches is the vital next step, and the Clone tool is perfect for this. Zoom in until the size of a dust spot is easily seen on the screen and then carefully scan the entire image. When you find a spot, select the Clone tool using a soft-edged brush that is slightly larger than the dust spot. Set the Clone Tool Options to 100% opacity and select aligned. Ctrl-click on an adjacent area to pick up an area to copy, release the Ctrl key and click directly on top of the spot. By using an opaque brush, the spot should be removed completely. The technique for removing scratches is similar, but you have to watch out for repeating patterns. With a little practice, you should be able to clone large sections without any telltale artifacts.
We now are ready to make a print. For me, the print is the final piece of art, and I spend a lot of time trying to create a print that really speaks to the viewer. I often will print out a picture 10–20 times, subtly making adjustments until I am happy with the image. I call this inkjet print my artist proof.
To prepare the image for printing, a few adjustments must be made that are specific to the print size. These adjustments are destructive, so save a copy of your image to a master file before getting started. First, resize the image by opening up the Scale Image dialog under The GIMP's Image menu. For inkjets I recommend 200PPI at your desired print size. Next, sharpen the image using the Unsharp Mask tool. Think of this as enhancing the edges in a photo. In case you're wondering why it's called unsharp, the name comes from the traditional photographic method of using a blurred (or unsharp) copy negative to increase the edge definition, and thus the perceived sharpness, of an image. Select Filter→Enhance→Unsharp Mask, and a dialog box appears with three sliders. Radius is how far away from the edge pixels are affected, Amount controls how much the pixels are changed and Threshold determines which edges are affected. To decide how much sharpening to apply, view the image at 100% and try a few settings. Unfortunately, Unsharp Mask does not yet have a preview, so you have to apply a setting, undo and repeat until you get the look you want. I am looking for the setting where the sharpening is barely obvious on my screen, generally starting with a radius of 1.0, a threshold of 3 and an amount of .75.
I use CUPS with Gimp-Print when printing to the Epson inkjets. Check the Gimp-Print Web page for instructions on getting this set up and running. By using Gimp-Print, all of the Epson-specific options are available in the Print menu. It also includes the Epson printer utility escputil, which allows for head cleaning and print alignment. Ideally, at this point we would be able to create an ICC profile for our printer; however, no software for Linux exists yet that does this. Instead, I recommend creating a standard set of adjustments using Gimp-Print's color adjust feature. To arrive at these adjustments, use a color test image such as the one we used for monitor calibration. Print the image, and look carefully at the results. You should be able to see details in the shadows and separation in the grayscale step tablet; the neutral and skin tones should not have a color bias. If this isn't the case, open the Print dialog box, select Image/Output Settings→Adjust Output and make the necessary changes. Repeat until your printout looks correct. Once you find a standard set of adjustments, write them down so you can use them as a starting point for future prints.
The moment of truth has finally arrived—will the final print match what we have been viewing on the screen? Print out the image and compare it to the image onscreen. They should be very similar, but something is fundamentally different about looking at a print vs. the screen. Study the image and see where improvements can be made, and continue making refinements in The GIMP until you are satisfied.