.TH pngdriver 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH PNG DISPLAY DRIVER
\fIPNG display driver\fR to create PNG, PPM, or BMP images.
.SH DESCRIPTION
The PNG driver generates PNG, PPM, or BMP images from GRASS display
commands. Per default PNG files are written with this driver. This
driver is used by default if \fICairo
driver\fR is not available.
.SH USAGE
.SS Environment variables
The PNG driver can be enabled by setting \fBGRASS_RENDER_IMMEDIATE\fR
variable, eg.
.br
.nf
\fC
export GRASS_RENDER_IMMEDIATE=png
\fR
.fi
Several environment variables affect the operation of the PNG driver:
.RS 4n
.IP \(bu 4n
\fBGRASS_RENDER_WIDTH=xxx\fR
.br
the width of the image map (default is 640).
.IP \(bu 4n
\fBGRASS_RENDER_HEIGHT=yyy\fR
.br
the height of the image map (default is 480).
.IP \(bu 4n
\fBGRASS_RENDER_BACKGROUNDCOLOR=RRGGBB\fR
.br
specifies the background color to use in RGB notation (hex or
R:G:B values). Named colors are also supported. Default
is \fBFFFFFF\fR (white).
.IP \(bu 4n
\fBGRASS_RENDER_TRANSPARENT=[TRUE|FALSE]\fR
.br
sets transparent background on (TRUE) or off (FALSE, default).
.IP \(bu 4n
\fBGRASS_RENDER_TRUECOLOR=[TRUE|FALSE]\fR
.br
sets true\-color support. Default is TRUE.
.IP \(bu 4n
\fBGRASS_RENDER_FILE=filename\fR
.br
the filename to put the resulting image in, default is map.png.
If you set GRASS_RENDER_FILE to a filename which ends in \(dq.ppm\(dq, a PPM
file will be created (with alpha channel stored in a PGM image, if applicable).
If you set GRASS_RENDER_FILE to a filename which ends in \(dq.bmp\(dq, a 32\-bpp
BMP file will be created (these are not readable by some older viewers).
.IP \(bu 4n
\fBGRASS_RENDER_FILE_COMPRESSION=[0|1|9]\fR
.br
compression level of PNG files (0 = none, 1 = fastest, 9 = best, default is 6)
.IP \(bu 4n
\fBGRASS_RENDER_FILE_READ\fR
.br
if TRUE, the PNG driver will initialize the image from
the contents of GRASS_RENDER_FILE.
.IP \(bu 4n
\fBGRASS_RENDER_FILE_MAPPED\fR
.br
if TRUE, the PNG driver
will map GRASS_RENDER_FILE as its framebuffer, rather than using
memory. This only works with BMP files.
.RE
.SS Example
.br
.nf
\fC
export GRASS_RENDER_IMMEDIATE=png
export GRASS_RENDER_TRUECOLOR=TRUE
g.region raster=elevation
d.rast elevation
d.vect roadsmajor color=red
\fR
.fi
This writes a file named map.png in your current directory.
.SH NOTES
The PNG driver uses the libpng (see
the libpng home page) and
zlib (see the
zlib home page), all which needs to
be installed for the PNG driver to work (it\(cqs worth it).
.PP
The resolution of the output images is defined by current region
extents. Use g.region \-p to get the number of rows and cols
and use the environment variables to set the image size. If you would
like a larger image, multiply both rows and cols by the same whole
number to preserve the aspect ratio.
.PP
Further PNG file processing (e.g. quantization to 1 bit for monochrome
images) can be done with pnmquant of
the netpbm tools.
.SH SEE ALSO
\fI
Cairo driver,
PS driver,
HTML driver,
variables
.br
.br
d.rast,
d.vect,
d.mon,
d.erase,
d.redraw
\fR
.SH AUTHOR
Original version: Per Henrik Johansen <\fIphj (at)
norgit.no\fR>
.br
Rewritten by: Glynn Clements, 2003
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual