The Quick Start Guide to the GIMP, Part 3

This month we learn how to use the Image Window and layers in building our images with the GIMP, a Linux power tool for the graphics artist.
A Quick Look At Filters

The GIMP is designed around the concept of external programs which handle much of the detailed work of the application, such as file I/O and image processing. The latter are commonly referred to as image filters since they filter the pixels in an image to produce an interesting effect.

To access the filters you use the Image Window's pop-down menu. The top level of this menu holds the Filters submenu. Under this submenu you will find an array of options including such categories as Artistic, Blur, Edge Detect, Render and many others. Each category has one or more filters associated with it.

Filters can operate on an image without any further user input, but most require the setting of variable parameters. When the filter is selected the GIMP launches the external program and opens a communications path to it. The plug-in filter then requests a dialog box with any number of buttons, menus, sliders or other window features. Each of the configurable items in the dialog has a default value so the user can simply accept the defaults and have the filter process the image. Many of the filters provide preview windows to give the user an idea of how the image will look after the filter is applied based on the configuration the user has selected. Since some processing can potentially take quite a bit of time to complete, some filters allow the preview to be turned off.

It is impossible to discuss the breadth and detail of the available filters in this one article. I plan on writing some tips for using these filters in the future, either to be presented in the “Graphics Muse” column in the Linux Gazette or on my GIMP web pages. In the meantime, I'll just mention a few of my favorites.

The IFS Compose plug-in is a nifty little tool for creating fractal images. Fractals have been around for some time and many people have grown a little tired of the same old Mandelbrot sets, but this is different. The fractals are actually a set of three Serpinski triangles that can be rotated, scaled, stretched and colored. The transformation of each of these can, when done properly, create some very realistic looking foliage or very artistic backdrops. A nice feature of this plug-in is that it keeps track of its settings between invocations.

The Cubism and Mosaic Plug-Ins (“Filters->Artistic->Cubism” and “Filters->Artistic->Mosaic”) offer some unusual effects. The Mosaic plug-in can produce images that appear as though they have been tiled using square and randomly edged 3D tiles. Cubism applies rectangular patches using the colors of the current layer and user-defined sizes and distributions. You can think of Cubism as “applying rectangular order” to a layer. Use of Cubism will cause a layer to be changed drastically so you might wish to duplicate a layer before applying this filter.

The Whirl and Pinch Filter (“Filters->Distorts->Whirl and Pinch”) creates swirled patterns on the selected area or layer, much like having the image as the surface of a liquid in which you swirl your finger. The amount of swirl or pinch can be user defined, and a preview of the effect is available from the filters dialog window.

The SuperNova Filter (“Filters->Image->SuperNova”) creates a bright sun-like section in the current layer. The Sun has spokes extending out from the center. The color and radius of the sun, the number of spokes, and the position of the sun within the layer are all user definable parameters for this filter. It is often useful to apply this filter on a transparent layer (with the “Keep Transparency” toggle turned off) and then add or subtract it from underlying layers.

And then...

There are lots of other filters, and the number of ways in which they can be used is endless. Next month I'll cover the Toolbox in its entirety, explaining what each icon is and how it is used. I'll also cover more details on creating and using selections as well as how to add and manipulate text within your images.


Michael J. Hammel ( a Computer Science graduate of Texas Tech University,is a software developer specializing in X/Motif living in Denver, Colorado. He writes the monthly Graphics Muse column in Linux Gazette, maintains the Linux Graphics mini-HOWTO, helps administer the Internet Ray Tracing Competition ( and coauthored the text The Unix Web Server Book, published by Ventana Press. His outside interests include running, basketball, Thai food, gardening and dogs.