The Utah Raster Toolkit is a collection of programs and C routines for dealing with raster images commonly encountered in computer graphics. A device and system independent image format stores images and information about them. Called the RLE(5) format, it uses run length encoding to reduce storage space for most images.

The programs (tools) currently included in the toolkit are listed above, together with a short description of each one. Most of the tools read one or more input RLE files and produce an output RLE file. Some generate RLE files from other information, and some read RLE files and produce output of a different form.

An input file is almost always specified by mentioning its name on the command line. Some commands, usually those which take an indefinite

introduce the input file name. If the input file name is absent the tool will usually read from the standard input. An input file name of "-" also signals that the input should be taken from the standard input.

On Unix systems, there are two other specially treated file name forms. A file name starting with the character '|' will be passed to sh(1) to run as a command. The output from the command will be read by the tool. A file whose name ends in ".Z" (and which does not begin with a '|') will be decompressed by the compress(1) program. Both of these options supply input to the tool through a pipe. Consequently, certain programs (those that must read their input twice) cannot take advantage of these features. This is noted in the manual pages for the affected commands.

An output file is almost always specified using the option -o outfile. If the option is missing, or if outfile is "-", then the output will be written to the standard output.

On Unix systems, the special file name forms above may also be used for output files. File names starting with '|' are taken as a command to which the tool output will be sent. If the file name ends in ".Z", then compress will be used to produce a compressed output file.

Several images may be concatenated together into a single file, and most of the tools will properly process all the images. Those that will not are noted in their respective man pages.

Picture comments. Images stored in RLE(5) form may have attached comments. There are some comments that are interpreted, created or manipulated by certain of the tools. In the list below, a word enclosed in <> is a place-holder for a value. The <> do not appear in the actual comment.

image_gamma=<float number>
Images are sometimes computed with a particular ``gamma'' value -- that is, the pixel values in the image are related to the actual intensity by a power law, pixel_value=intensity^image_gamma. Some of the display programs, and the buildmap(3) function will look for this comment and automatically build a "compensation table" to transform the pixel values back to true intensity values.
display_gamma=<float number>
The display_gamma is just 1/ image_gamma. That is, it is the ``gamma'' of the display for which the image was computed. If an image_gamma comment is not present, but a display_gamma is, the displayed image will be gamma corrected as above. The to8(1) program produces a display_gamma comment.
The length of the colormap stored in the RLE header must be power of two. However, the number of useful entries in the colormap may be smaller than this. This comment can be used to tell some of the display programs ( getx11(1), in particular) how many of the colormap entries are used. The assumption is that entries 0 - colormap_length-1 are used. This comment is produced by mcut(1), rlequant(1), and rledither(1).
This comment is used by getx11(1) to set the window title. If present, the comment is used instead of the file name. (No other programs currently pay attention to this comment.) The comments IMAGE_TITLE, title, and TITLE are also recognized, in that order. No programs produce this comment.
All toolkit programs (with the exception of rleaddcom(1)) create or add to a HISTORY comment. Each tool appends a line to this comment that contains its command line arguments and the time it was run. Thus, the image contains a history of all the things that were done to it. No programs interpret this comment.
This comment should be present in a file stored in ``exponential'' form. See unexp(1) and float_to_exp(3) for more information. The unexp(1) program expects to see this comment.

compress(1), sh(1), RLE(5).

Many people contributed to the Utah Raster Toolkit. It started out life as part of the Alpha_1 system. This manual page was written by Spencer W. Thomas, University of Michigan.