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
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,
Some of the display programs, and the
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
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
- This comment is used by
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
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
for more information.
program expects to see this comment.
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.