Graphics Muse

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## ImageMagick Overview

After months of procrastination, I finally got around to taking a closer look at the ImageMagick set of tools from John Cristy and E.I. DuPont De Nemours and Company Incorporated. I've had a number of readers write and ask me about the program, what I thought of it and how does it work, etc. Its time to address some of those issues.
ImageMagick is a graphics manipulation tool along the lines of XV or the GIMP that runs on a variety of Unix systems, including Linux, along with MS and Macintosh platforms. The package is available in source or binary distributions from http://www.wizards.dupont.com/cristy/ImageMagick.html. I downloaded the binary package which was a gzipped tar file of the installation package using relative paths. Since the package attempts to place the binaries and some other files under the /usr/X11R6 directory tree, and I only install system files there (everything else goes under /usr/local), I had to unpack the file in a local directory tree, change the name of the X11R6 directory to local, recreate the tar file and then unpack it as root from the root (/) directory. Other than this, the installation of the binary package was painless.
The distribution comes with a set of 9 tools that allow both interactive and command line editing of images:

1. display
2. import
3. animate
4. montage
5. convert
6. mogrify
7. identify
8. combine
9. xtp

All of the tools come with well written man pages and honor the -? command line option to get usage summaries.
The first of these, display, is an interactive program that uses X Windows. The interface is consists of a single, columnar set of buttons, each of which opens a menu, and a viewing window. Figure 1 shows the default image window and the menu box.
The image window will dither images to fit on the display based on the hardware support you are using.
The menu buttons are simple to use - just click on one to see the options available for that menu. The top level menu options are:

- File - file functions
- Edit - undo, redo, etc.
- View - affects image size
- Transform - rotations, shear, flip, crop, etc.
- Enhance - brightness, hue, saturation, etc.
- Effects - despeckle, sharpen, blur, solarize, etc.
- F/X - swirl, implode, oil painting, etc.
- Image Edit - add borders and frames, edit colors, etc.
- Miscellany - image info, slide show, histogram, etc.
- Help - extensive help system, including some HTML based documentation

Under File the options include such things as a Print function (using Postscript, so you'll want to make sure you have Ghostscript installed first), New, Open, Next, Former, and Visual Directory, among others. The Visual Directory appears much like the Open option in that both provide a File Selection box from which to choose an image. I'm not certain if I was using it correctly, however, since I got the feeling the visual directory is supposed to be similar to XV's visual schnauzer.
The Effects and F/X menus are similar in that both provide access to features that manipulate the image, much like XV's algorithms or the GIMP's plug-ins. I found the Shade function interesting in that it turned the 2D planet into a slightly 3D image by adding shadows in the appropriate places. Most of the functions are similar to the features found in the stock GIMP distribution but there are a few more than what XV provides in its algorithms menu.
The number of features of the display program is attractive, but as an image editing tool for artists it is a step or two behind the ease of use of the GIMP. Some of the effects features are a little nicer than what is currently available for the GIMP, however. And the annotate feature, which allows you to insert text into an image, does provide a reasonable font previewer. Still, the GIMP is a more sophisticated end-user interface. During my brief testing of display I had multiple lock ups on my Linux 1.2.13 box, but that may be due to older libc. I also noticed that display appeared to run a bit slow in refreshing the image window. Redraws of the windowing toolkit (looks a bit like Tk or Motif, but I'm not certain what it is really) were really slow. Again, this may be due to my slightly older Linux system.
Beyond the graphical interface, the other 8 programs in the distribution are command line oriented. From what I can gather this is what makes ImageMagick a valuable addition to the Linux graphics artists toolchest. Each of the commands serves a general purpose but handles that purpose with an extensive array of options. As a group these tools can be used to automate the handling of images for display on web pages quite nicely. I think that many of the features builtin into the display program are covered by these command line interfaces, but I also found a few features that I think display may not handle.
Import is used to do screen captures of windows or rectangular regions of your monitors display. You can specify an window ID or name or you can use import interactively by using the mouse to specify the window or region to capture. Options include allowing capture of the window manager frame, dithering and cropping the image before saving. The output file format depends on the filename extension used for the saved file or by prefixing the filename with the file type followed by a colon, such as ps:output_image. By default import will save the file as an Encapsulated Postscript file.
Animate will take a series of images in just about any format and display them as an animation. As with most animation software the quality of the animation will depend on the number and type of images, the speed of the computer and the memory available to process the images. Since I didn't have a series of images to experiment with I wasn't able to really look into this particular tool.
Montage allows you to create a single image built from a series of other images. Input images are scaled to fit a specified tile size, a square of 120x120 by default, and then places the images side by side in a series of rows. By default 5 tiles are used in a row and 4 rows are produced. If more than 20 images are supplied then additional output montages are produced. You can specify a larger number of tiles to use for a single montage, and thus the number of input images to use, with the -tile option. Montage offers a large set of options. The page size can be set so that the postscript output will fit on various paper sizes. You can set the gamma level for the output files, crop and dither the input images, provide an ornamental frame around the output image, and where to place an image inside a tile if it doesn't fill the entire tile region (this is known as where the image will gravitate within the tile). Input files can be identified with labels using various fonts. 3D shadows can be added to input images as well as a textured backdrop in the tile areas and borders not covered by input images.
Convert and Identify are complimentary programs. Identify can be used to determine, based on the files magic number, the image format of a particular file. Along with the file type information such as the size of the file, whether or not it is colormapped, and the number of colors in the image are also printed. Convert takes an image in one format and converts it to another file using a different, specified format. The format type can be specified just as with import, with a prefix or suffix denoting the format of the input and output types. Convert can also read Unix compressed (.Z suffixed) image files, but does not write the converted image as a compressed file. Multipage or multipart images are converted with output files using the filename with a scene number for a suffix. This is a modifiable option, however. You can embed a printf() style formatting string in the output file name to sequentially number the images and still include the format type as a suffix.
Mogrify manipulates images the way the Effects and F/X menu options in display do. This tool takes an input file and processes it based on the options specified and in the order they are specified. Since options are processed in the order they are presented on the command line, it is possible to set a series of options to be globally applied to a series of images, then change one or more of these options for individual images - all from a single command line. Mogrify permits scripting and batch processing of images. XV can do this to some extent, but I've never used it that way and the number of processing functions is greater in mogrify. The GIMP has a scripting interface, but batch processing has to go through Net-FU (a network based interface). NetPBM provides only command line interfaces, but you have to script a series of programs together to get the same effect you get from mogrify. Image Alchemy, a commercial product for image processing from Handmade Software, appears to be the only real match for the way mogrify functions for batch processing.
Finally, the ImageMagick tool set includes an extra feature - xtp - which allows for network transfer of files simiilar to the way ftp works. According to the ImageMagick web site, xtp doesn't require any interactive commands so file transfers can more easily be batch processed.
Beyond the base tools, John Christy and E.I. Dupont De Nemours and Company also provide a plug-in package called the ImageMagick Plug-In. This appears to be (although I'm not quite clear about it) the shared image libraries for a number of popular image file formats. It is basically equivalent to what libgr provides except that the ImageMagick libraries include support for MPEG files. There are also a number of programs in the Plug-In packages, including a TIFF thumbnail generator and the cjpeg and djpeg tools for compressing and decompressing images to and from the JPEG format. Most of the tools in the Plug-in package are related to TIFF handling.
As you can see the ImageMagick tools cover a lot of ground. I didn't get to comparing the quality of the images from ImageMagick versus XV or NetPBM so this review is really just an introduction to the toolset. But the tools are obviously high quality, feature rich, and well documented. The developers announce frequent updates and additions which is better than what you generally hear of XV or NetPBM. If you've used XV, the GIMP or NetPBM and find these might not quite fill all your needs you owe it to yourself to take a look at ImageMagick. No graphics fanatics arsenal of tools is ever complete and no tool can handle every need. Its important to keep aware of the tools that are available. ImageMagick is a tool that deserves serious consideration for your collection of graphics tools for Linux.

© 1997 by Michael J. Hammel