Table of Contents
GIMP (GNU Image Manipulation Program) is a very powerful program for the processing of pixel graphics. GIMP is the first choice for retouching or modifying photographs and other image files. Once you are familiar enough with the program, you will even be able to create entire images from scratch. An average user, however, will not need all of the powerful functions of GIMP. It can even be used for free-style painting. All tools, such as brush, pencil, or airbrush, are available (see Figure 23.1: “The GIMP Toolbox: The Default Window”). Frequent users of these features should definitely consider acquiring a graphics tablet.
Taking into account the power and performance of GIMP and the prices for commercial `professional' graphics programs, it soon becomes evident that the GNU Image Manipulation Program is a phenomenal gift to the Linux community. As with so many Linux programs, GIMP is under constant development.
UThis introduction cannot cover the whole range of features. The official GIMP manual has 924 pages and is available on the Internet at http://manual.gimp.org. Unfortunately, some of its descriptions and illustrations are outdated, because GIMP has undergone extensive development since the manual was written. The internal help system, still under development, also provides valuable assistance to the new user.
The version included in this distribution and discussed in this manual is the most recent release of the stable 1.2 series. The unstable GIMP 1.3 series is not intended for regular users. It is only intended for those involved in developing GIMP itself.
GIMP has been designed for processing pixel graphics. These images consist of small blocks of color that together create the entire image. A full-screen image on a monitor with an 800×600 resolution has exactly that number of pixels — 480,000 individual pixels. Considering this, it is not surprising that image files are generally quite bulky. In addition to the coordinates of each pixel, the color information is stored. With an image of 800×600 pixels, it is easy to get more than one MB of data. From the outset, therefore, much time and energy has been invested in developing compression procedures that squeeze the amount of information together. Some well-known graphics file formats for pixel images include:
The native GIMP format. It supports the layer technique discussed later and other specific GIMP functions. If you have created an image using GIMP-specific settings and save it in a different file format, information is lost.
A format without compression used by Microsoft Windows. An advantage of this format is that graphics can be loaded and saved very quickly, but this positive aspect is outweighed by the file size.
The Graphics Interchange Format has been specially developed for data transfer on the Internet and has special features to support this. For licensing reasons, many programs are no longer able to support this format. One special feature of GIF is the animated Gif, a GIF file in which several images are stored. In an Internet browser, these individual images are displayed so quickly one after the other that the impression of a moving image is created. GIF, despite its limitations, is popular predominantly because it allows transparency.
The Portable Network Graphics is a popular replacement for the GIF format. It can generate the same quality of compressed files without loss of information and is freely available. It allows a better form of transparency, but is not yet fully supported by all Internet browsers.
This format is used by the professional Adobe Photoshop application and supports the multilayer technique.
The Tagged Image File Format is another method of saving files in the professional arena. It is particularly popular in the printing business.
The compression method of the Joint Photographic Experts Group allows a highly efficient reduction of image files. Depending on the compression factor, image information is lost. Nevertheless, it is an ideal file format for images on the Internet.
Always save an XCF version of images you create. This makes future modifications much easier.
Unlike pixel graphics, vector graphics do not store information for all individual pixels. Instead, they store information about how image points, lines, or areas are grouped together. A line that runs horizontally across the screen, representing a total of 800 pixels, only needs four information units: the coordinates of the starting point, the coordinates of the end point, the information that these two points are connected by a line, and, possibly, the color of the line. With four coordinates and four lines connecting them, easily create a rectangle. The fact that this rectangle is filled with a specific color basically requires just one more information unit. In this way, even complex images can be represented with relatively little basic information. The drawing application of OpenOffice.org, for example, uses this format.