bionic (1) pngdriver.1grass.gz

PNG DISPLAY DRIVER

       PNG display driver to create PNG, PPM, or BMP images.

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 Cairo driver is not available.

USAGE

   Environment variables
       The PNG driver can be enabled by setting GRASS_RENDER_IMMEDIATE variable, eg.
       export GRASS_RENDER_IMMEDIATE=png
       Several environment variables affect the operation of the PNG driver:

           •   GRASS_RENDER_WIDTH=xxx
               the width of the image map (default is 640).

           •   GRASS_RENDER_HEIGHT=yyy
               the height of the image map (default is 480).

           •   GRASS_RENDER_BACKGROUNDCOLOR=RRGGBB
               specifies the background color to use in RGB notation (hex or R:G:B  values).  Named  colors  are
               also supported. Default is FFFFFF (white).

           •   GRASS_RENDER_TRANSPARENT=[TRUE|FALSE]
               sets transparent background on (TRUE) or off (FALSE, default).

           •   GRASS_RENDER_TRUECOLOR=[TRUE|FALSE]
               sets true-color support. Default is TRUE.

           •   GRASS_RENDER_FILE=filename
               the  filename to put the resulting image in, default is map.png.  If you set GRASS_RENDER_FILE to
               a filename which ends in ".ppm", 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 ".bmp", a 32-bpp
               BMP file will be created (these are not readable by some older viewers).

           •   GRASS_RENDER_FILE_COMPRESSION=[0|1|9]
               compression level of PNG files (0 = none, 1 = fastest, 9 = best, default is 6)

           •   GRASS_RENDER_FILE_READ
               if TRUE, the PNG driver will initialize the image from the contents of GRASS_RENDER_FILE.

           •   GRASS_RENDER_FILE_MAPPED
               if TRUE, the PNG driver will map GRASS_RENDER_FILE as its framebuffer, rather than using  memory.
               This only works with BMP files.

   Example
       export GRASS_RENDER_IMMEDIATE=png
       export GRASS_RENDER_TRUECOLOR=TRUE
       g.region raster=elevation
       d.rast elevation
       d.vect roadsmajor color=red
       This writes a file named map.png in your current directory.

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’s worth it).

       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.

       Further PNG file processing (e.g. quantization to 1 bit for monochrome images) can be done with  pnmquant
       of the netpbm tools.

SEE ALSO

        Cairo driver, PS driver, HTML driver, variables
       d.rast, d.vect, d.mon, d.erase, d.redraw

AUTHOR

       Original version: Per Henrik Johansen <phj (at) norgit.no>
       Rewritten by: Glynn Clements, 2003

       Last changed: $Date: 2014-12-19 22:17:36 +0100 (Fri, 19 Dec 2014) $

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       © 2003-2018 GRASS Development Team, GRASS GIS 7.4.0 Reference Manual