Hour 16

Graphics Tools

In this hour you'll be introduced to a variety of graphics programs and utilities for Linux. This hour starts with a short discussion of different graphics formats you'll find on your system, then shows you how to convert graphics using filter programs and other graphic utilities. These programs are useful for creating, editing, and translating graphics imported from other computer systems.

You'll find a treasure trove of great graphics programs on this book's CD-ROM, and you're likely to be impressed with their usefulness and versatility. You'll be able to translate nearly any type of graphic, and will be able to perform sophisticated operations to transform your graphics files.

Understand Linux Graphics File Formats

There are many different types of graphics file formats, and examples of several types are installed in your system. You may already be familiar with several different formats, especially if you've used other computer operating systems. However, when you use Linux, expect to run into graphics files in formats you've never seen before.

Many files can be recognized by the filename's extension, or letters following

a period in the filename. For example, you may recognize .GIF, .PCX, .TIF, or .JPG as common extensions. In Linux, you'll also find files in formats such as .xbm or .xpm installed on your system. The /usr/X11R6/include/X11/bitmaps directory contains nearly 100 different bitmap files, and the /usr/X11R6/lib/X11/xfm directory contains more than 100 black-and-white bitmap icons, as well as more than 110 color pixmap icons.

Table 16.1 is a list of some of the graphics formats, along with relevant conversion programs you'll find on your system. To convert a graphic image from one format to another, see the manual page for the relevant conversion program.

Table 16.1. Linux graphics formats and conversion programs.

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Table 16.1. continued

Converting and Viewing Graphics

There are a number of ways to convert graphics files to different formats using the programs you'll find installed on your system. A number of painting or drawing programs discussed in this hour translate graphics. Many programs in Table 16.1 also work as filters in piped commands (see Hour 6, "Using the Shell," for details) to translate graphics.

You can use different combinations of these commands to convert files. The resulting files, which may display and print the same, usually aren't the same file size, so a side benefit of converting graphics may be to save disk space. Look at the following example:

# xwd >graphic.xwd

# xwdtopnm <graphic.xwd | pnmtotiff >graphic2.tiff

xwdtopnm: writing PPM file

pnmtotiff: computing colormap...

pnmtotiff: 6 colors found

# ls -l graphic.xwd graphic2.tiff

-rw-rw-r--   1 bball    bball      240380 Jan  5 15:15 graphic.xwd

-rw-rw-r--   1 bball    bball       15278 Jan  5 16:51 graphic2.tiff

The first command line uses the xwd client to create an X11 window dump graphic (after you select a window and press your left mouse button). Then the window dump file is converted to a portable anymap format, and this stream is fed into the pnmtotiff command to create a .tiff graphic. As you can see, the .tiff graphic file format is nearly 16 times smaller than the X11 window dump graphic.

There are also many graphics programs not listed in Table 16.1 that can be used to alter graphic images. For example, the pnmrotate, pnmsmooth, or pnmscale commands rotate, smooth, and resize graphic images. You can use a variety of these programs to not only convert graphics, but change their appearance or orientation.

If you're using pipes to convert a graphic, you also can change the image on the fly by applying these filter programs. The previous example, now has a filter inserted during the conversion:

# xwd >graphic.xwd

# xwdtopnm <graphic.xwd | pnmflip -topbottom | pnmtotiff >graphic.tiff

xwdtopnm: writing PPM file

pnmtotiff: computing colormap...

pnmtotiff: 6 colors found

Here a window dump is created, and then, using the pnmflip program, it is turned upside down and backwards before creating the .tiff version. Combinations of different filters achieve different effects.