February 22, 2019

The Graphics Lab on Your Linux Desktop - page 2

A Wealth of Graphics Tools

  • August 1, 2000
  • By Michael Hall

The GNU Image Manipulation Program (The GIMP) is considered one of the best examples of open source development around, especially where desktop applications are concerned. It's stable, versatile, extensible, and feature-packed. A lot of sites in the Linux community owe their graphical flair to the GIMP, and it's proven to be a killer app for many: it offers a level of functionality comparable to Photoshop for free. (A screenshot is at the right.)

The GIMP provides not only excellent "paint" tools, but a comprehensive set of filters (or plug-ins), plus embedded scripting (via the Scheme-like Script-Fu, Perl, or Python). There are some issues where the user interface is concerned, but they're centered around how easy it is to get to the incredible number of tools available: the GIMP is still a fairly easy program to pick up, even if it is cumbersome to use at times.

Most distributions include the GIMP, though many are still using the older 1.0 series of releases. The project is currently well on its way to version 1.2, however, which includes quite a few changes in functionality and includes some usability tweaks.

Helix Code packages a current developer's version of the GIMP as part of their GNOME release. The Debian Helix Code packages currently includes version 1.1.24. Since Helix Code builds their releases around the unstable (Woody) release of Debian, you may need to pay a visit to the Debian package archive to meet some dependencies. Specifically, the GIMP depends on a version of aalib found in Woody.

If you aren't using Helix Code, and your distribution doesn't have a very current version of the GIMP, you can always visit the project's download page.

There's a lot to play with in the GIMP, but we're going to concern ourselves with the parts you can use to clean up or manipulate your digital photographs.

Basic Manipulation
The GIMP, despite its huge number of plug-ins and scripts, provides a lot of very simple and basic tools for working with an image that can go a long way to helping simple photographs look pretty nice. A good place to start is with the "Image" menu, which you can access by right-clicking anywhere in a photo you're working on.

The Image menu contains tools for manipulating color balance, contrast and brightness, and the hue and saturation of an image. These are all essential to tweaking out environmental factors you couldn't control when you took the picture, or to help out cameras with odd characteristics, such as the tendency to cast everything with a blue tint. My own camera, for instance, has a black & white image mode that introduces some purple in the shading... by using the Desaturate option under the Image/Colors menu I'm able to remove that purple quickly and easily. You can also use the Desaturate tool to striking effect by simply selecting an area of the image using the Smart Scissors or Bezier Curve tool and selectively desaturate (remove the color from) the area you selected.

Another useful option located under Image/Colors menu is the Filterpack tool, which allows you to manipulate the hue, color, and saturation of the image interactively, by presenting thumbnail previews of the results of any changes. The tool is very flexible in that it allows you to select which elements of the picture you'd like to work with: the highlights, midtones, or shadows. This is a great tool for working on pictures afflicted with poor lighting, murky shadows, or uneven bright spots.

Once you've cleaned up your photo with the basic tools, there's still plenty you can do with it using the GIMP. Here's a quick list of other tools that are especially useful with digital photos:

In the Toolbox
The Dodge and Burn Tool: This tool is located on the bottom row of the main window of the GIMP, and looks like a small paddle. Dodging and burning are basic skills for every darkroom technician and they can save an unevenly lit photo. The GIMP provides a digital equivalent to waving a paddle (or finger, or piece of paper) between the enlarger light and photo paper. This tool is a good one to use with a fuzzier-edged brush.

The Blur/Sharpen Tool: Also located on the bottom row of the GIMP toolbox, this tool allows you to selectively blur and sharpen parts of the image using the brush you've selected. Because most digital cameras are little better than point-and-shoots, this tool comes in handy if your camera set your depth of field a little too deep, or if there's an element of the photo you'd like to deemphasize a little.

Using Script-Fu
Script-Fu is an extension to the GIMP that allows users to develop scripts that automate sequences of plug-ins and enhancements to an image. There are plenty of scripts included with the base GIMP distribution.

If you're looking to add some effects to your pictures, right-clicking on the picture and selecting "Script-Fu" and then "Decor" will present you with several scripts that range from adding a bevel to the image to adding simulated coffee stains or rendering the image in sepia tones.

Use these scripts carefully--the GIMP has an 'undo' option, but it treats scripts for what they are: a series of distinct commands. By default, the GIMP allows you to undo up to your last five commands. Most script-fu scripts perform many more operations on your image than that. If you're offered the opportunity to "work on a copy" of the image, take it. If you mess things up too badly, by right clicking on the image, selecting 'File' and then selecting 'Revert', you can restore the picture to its state when you first loaded it from disk.

Some Filters
In addition to basic tools and scripts, the GIMP packs a bunch of image filters. In particular, check out the filters offered under Enhance. One allows you to clean out digital artifacts like speckling, another enhances the overall sharpness of the image, and another allows you to reduce the overall sharpness.

If you're interested in preparing your pictures for display on a web page, the Web section of the filters menu offers tools to create image maps and prepare images for clean conversion from RGB to indexed palettes.

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