GIF (Graphics Interchange Format)
GIF is a widely supported format for raster graphics, defined by
Compuserve, Inc. The program
xv (by John Bradley,
firstname.lastname@example.org) can be used to display GIF files on UNIX and
VMS workstations. PGPLOT uses the GIF87a variant, with up to 8 bits
per pixel (256 colors).
The GIF specification incorporates the Lempel-Zev-Welch (LZW)
compression algorithm which is the subject of a patent awarded to
Unisys. Use of this technology, and in particular creation of GIF
format files using this PGPLOT device driver, may require a license
- Device type code
/GIF (landscape orientation),
/VGIF (portrait orientation).
- Default file name
A GIF file can contain only a single image, so for multi-page plots
PGPLOT creates additional files. If the supplied file name contains
the character #, the file name is derived by replacing this
character with the current page number. If the supplied file name does not
contain a #, PGPLOT appends an underscore and the page number for the
second and subsequent pages, e.g.,
PGBEG file name: File names used:
pgplot#.gif pgplot1.gif, pgplot2.gif, pgplot3.gif, ...
pgplot.gif pgplot.gif, pgplot.gif_2, pgplot.gif_3, ...
If the supplied file name is ``-'', the output is sent to the standard
output stream, so that it can, for example, be piped into a viewing
program. This will only work for single-page plots.
- Default view surface dimensions
- /GIF: 850 by 680 pixels (nominally 10.0 by 8.0 inches)
/VGIF: 680 by 850 pixels (nominally 8.0 by 10.0 inches)
These defaults can be overridden by specifying environment
variables, or by calling routine PGPAP. The maximum size is limited
only by available memory.
- PGPLOT assumes that the device resolution is 85 pixels/inch, but
the actual resolution will vary depending on the display device.
- Color capability
- Color indices 0--255 are accepted, with standard defaults for color
indices 0--15. If the color representation of a color index is changed,
it affects all pixels drawn in that color on the current page.
- Input capability
- Environment variables
PGPLOT_GIF_WIDTH : width of image in pixels (default 850)
PGPLOT_GIF_HEIGHT : height of image in pixels (default 680)
- File format
- GIF files are binary files.
- Remko Scharroo, Tim Pearson, 1994.
Transparent Background Images
The GIF87a images produced by PGPLOT do not have a way of specifying a
transparent background. You can mark the background as transparent if
you convert the file to GIF89a format using giftrans and
specify that color index 0 should be transparent.
To use giftrans, just type
giftrans -t index GIF87a-file > GIF89a-file
This converts the GIF87a-file to a GIF89a-file, with the
index entry in the colormap made transparent. Invoke giftrans
-? option to see a complete usage description.