XSHOWGIF(1) XSHOWGIF(1)
27 April 1990
NAME
xshowgif - load gif images into an X11 window
SYNOPSIS
xshowgif [global_options] {[image_options] image ...}
DESCRIPTION
Xshowgif displays gif images in a X11 window.
Xshowgif is a pared down version of Jim Frost's (jimf@saber.com)
xloadimage program. Unlike xloadimage this program only displays GIF
files in a X11 Window. Support for alternate image types and loading
images into the root window have been removed. These features were
removed so the program could support some additional GIF file features
that cannot be supported in conjunction with these other features such
as display of multiple GIF images in a file.
If an image is larger then the window, you may move the image around
in the window by dragging with the left mouse button. The cursor will
indicate which directions you may drag, if any. You may exit the
window by typing 'q', 'Q' or '^C' when the keyboard focus is on the
window. If more then one image is specified on the command line, 'N'
moves you to the next gif file, while 'P' moves you to the previous
gif file. If the gif file contains more then one image 'n' moves you
to the next image in the gif file. If there are no more images in the
file, 'n' moves to the next file on the command line.
If the destination display cannot support the number of colors in the
image, the image will be dithered (monochrome destination) or have its
colormap reduced (color destination) as appropriate. This can also be
done forcibly with the -halftone and -colors options.
A variety of image manipulations can be specified, including
brightening, clipping, dithering, depth-reduction, and zooming. Most
of these manipulations have simple implementations; speed was opted
for above accuracy.
A wide variety of common image manipulations can be done by mixing and
matching the available options. See the section entitled HINTS FOR
GOOD IMAGE DISPLAYS for some ideas.
GLOBAL OPTIONS
The following options affect the global operation of xshowgif. They
may be specified anywhere on the command line.
-border color
This sets the background portion of the window which is not
covered by any images to be color.
-display display_name
X11 display name to send the image(s) to.
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27 April 1990
-geometry WxH[{+-X}{+-}Y]
This sets the size of the window onto which the images are
loaded to a different value than the size of the image. This
can be used to reduce the size of the destination window.
-help Displays a short summary of xshowgif command line syntax.
-quiet Forces xshowgif to be quiet. Normally xshowgif will display
the image size and colormap depth.
-verbose
Causes xshowgif to be talkative, telling you and any special
processing that it has to do.
-version
Print the version number and patchlevel of this version of
xshowgif.
The following options may preceed each image. These options are local
to the image they preceed.
-background color
Use color as the background color instead of the default (usually
white but this depends on the image type) if you are transferring
a monochrome image to a color display.
-brighten percentage
Specify a percentage multiplier for a color image's colormap. A
value of more than 100 will brighten an image, one of less than
100 will darken it.
-colors n
Specify the maximum number of colors to use in the image. This
is a way to forcibly reduce the depth of an image.
-clip X,Y,W,H
Clip the image before loading it. X and Y define the upper-left
corner of the clip area, and W and H define the extents of the
area. A zero value for W or H will be interpreted as the
remainder of the image.
-dither
Dither a color image to monochrome. This algorithm is very
trivial; the -halftone option may look better if you don't mind
the blown-up image.
-foreground color
Use color as the foreground color instead of black if you are
transferring a monochrome image to a color display. This can
also be used to invert the foreground and background colors of a
monochrome image.
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XSHOWGIF(1) XSHOWGIF(1)
27 April 1990
-halftone
Force halftone dithering of a color image when displaying on a
monochrome display. This happens by default when viewing color
images on a monochrome display. This option is ignored on
monochrome images. This dithering algorithm blows an image up by
sixteen times; if you don't like this, the -dither option will
not blow the image up (but won't look as nice).
-name image_name
Force the next argument to be treated as an image name. This is
useful if the name of the image is -dither, for instance.
-xzoom percentage
Zoom the X axis of an image by percentage. A number greater than
100 will expand the image, one smaller will compress it. A zero
value will be ignored.
-yzoom percentage
Zoom the Y axis of an image by percentage. See -xzoom for more
information.
-zoom percentage
Zoom both the X and Y axes by percentage. See -xzoom for more
information. Technically the percentage actually zoomed is the
square of the number supplied since the zoom is to both axes, but
I opted for consistency instead of accuracy.
EXAMPLES
To double the size of an image:
xshowgif -zoom 200 my.gif
To halve the size of an image:
xshowgif -zoom 50 my.gif
To brighten a dark image:
xshowgif -brighten 150 my.gif
To darken a bright image:
xshowgif -brighten 50 my.gif
HINTS FOR GOOD IMAGE DISPLAYS
Since images are likely to come from a variety of sources, they may be
in a variety of aspect ratios which may not be supported by your
display. The -xzoom and -yzoom options can be used to change the
aspect ratio of an image before display. If you use these options, it
is recommended that you increase the size of one of the dimensions
instead of shrinking the other, since shrinking looses detail. For
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XSHOWGIF(1) XSHOWGIF(1)
27 April 1990
instance, many GIF images have an X:Y ratio of about 2:1. You can
correct this for viewing on a 1:1 display with either -xzoom 50 or
-yzoom 200 (reduce X axis to 50% of its size and expand Y axis to 200%
of its size, respectively) but the latter should be used so no detail
is lost in the conversion.
One common complaint is that xshowgif does not have a -reverse
function for inverting monochrome images. In fact, this function is a
special-case of the foreground and background coloring options. To
invert an image with a black foreground and white background (which is
standard), use -foreground white -background black. This will work on
both color and monochrome displays.
AUTHOR
Modifications to xloadimage by
Richard J. Greco
Intel Scientific Computers
rjg@isc.intel.com
Xloadimage was written by
Jim Frost
Saber Software
jimf@saber.com
Other contributing people include Barry Shein (bzs@std.com), Kirk
Johnson (tuna@athena.mit.edu), Mark Snitily (zok!mark@apple.com), W.
David Higgins (wdh@mkt.csd.harris.com), and Dave Nelson
(daven@gauss.llnl.gov).
COPYRIGHT
Copyright (c) 1989, 1990 Jim Frost and others.
Xshowgif is a derivitive work of xloadimage by Jim Frost et. al. and
is subject to all copyright restrictions of xloadimage.
Xloadimage is copywritten material with a very loose copyright
allowing unlimited modification and distribution if the copyright
notices are left intact. Various portions are copywritten by various
people, but all use a modification of the MIT copyright notice.
Please check the source for complete copyright information. The
intent is to keep the source free, not to stifle its distribution, so
please write to me if you have any questions.
BUGS
Zooming dithered images, especially downwards, is UGLY.
The dithering algorithm used by -dither could be better, and both
-dither and -halftone assume that a color's brightness is the sum of
its RGB values, which is not correct but has the advantage of being
simple and fast.
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XSHOWGIF(1) XSHOWGIF(1)
27 April 1990
Images can come in a variety of aspect ratios. Xshowgif cannot detect
what aspect ratio the particular image being loaded has, nor the
aspect ratio of the destination display, so images with differing
aspect ratios from the destination display will appear distorted. See
HINTS FOR GOOD IMAGE DISPLAYS for more information.
Only PseudoColor, GrayScale, StaticColor, and StaticGray visuals are
supported. These are the most common visuals so this isn't usually a
problem.
Some window managers do not correctly handle window size requests. In
particular, many versions of the twm window manager use the MaxSize
hint instead of the PSize hint, causing images which are larger than
the screen to display in a window larger than the screen, something
which is normally avoided. Some versions of twm also ignore the
MaxSize argument's real function, to limit the maximum size of the
window, and allow the window to be resized larger than the image. If
this happens, xshowgif merely places the image in the upper-left
corner of the window and uses the zero-value'ed pixel for any space
which is not covered by the image. This behavior is less-than-
graceful but so are window managers which are cruel enough to ignore
such details.
The order in which operations are performed on an image is independent
of the order in which they were specified on the command line.
Wherever possible I tried to order operations in such a way as to look
the best possible (zooming before dithering, for instance) or to
increase speed (zooming downward before compressing, for instance).
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