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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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