NAME

        PNG driver - driver to create PNG and PPM images.
       (drivers)

DESCRIPTION

       The  PNG  driver  generates  PNG  and  PPM images from GRASS display commands.  Per default PNG files are
       written with this driver. It is started as 'pseudo' monitor (image file instead) and  when  stopped,  all
       output from previously used display commands are written to the PNG image file.

USAGE

   Environment variables
       Several environment variables affect the operation of the PNG driver.
              GRASS_WIDTH=xxx
              the width of the image map (default is 640).
              GRASS_HEIGHT=yyy
              the height of the image map (default is 480).
              GRASS_PNGFILE=filename
              the  filename  to  put  the resulting image in, default is map.png.  If you set GRASS_PNGFILE 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_PNGFILE to a filename which ends in ".bmp", a 32-bpp BMP
              file will be created (these are not readable by some older viewers).

              GRASS_BACKGROUNDCOLOR=RRGGBB
              specifies the background color to use in RGB notation (hex values). Default is 000000 (black).
              GRASS_TRANSPARENT=[TRUE|FALSE]
              sets transparent background on (TRUE) or off (FALSE, default).
              GRASS_TRUECOLOR=[TRUE|FALSE]
              sets true-color support
              GRASS_PNG_COMPRESSION=[0|1|9]
              compression level of PNG files (0 = none, 1 = fastest, 9 = best, default is 6)
              GRASS_PNG_AUTO_WRITE=[TRUE|FALSE]
              if set to TRUE, the image file will be written  after  each  operation  (i.e.  whenever  a  client
              disconnects), rather than only being written out when the driver terminates.
              GRASS_PNG_READ
              if TRUE, the PNG driver will initialize the image from the contents of GRASS_PNGFILE.
              GRASS_PNG_MAPPED
              if  TRUE, the PNG driver will map GRASS_PNGFILE as its framebuffer, rather than using memory. This
              only works with BMP files.
              GRASS_RENDER_IMMEDIATE=[TRUE|FALSE]
              tells the raster library to use its built-in PNG driver rather  than  connecting  to  an  external
              monitor process using sockets. If TRUE, there is no need to run d.mon start=PNG.

   Example
       Define driver settings (here: bash shell syntax)
       export GRASS_RENDER_IMMEDIATE=TRUE
       export GRASS_TRUECOLOR=TRUE
        Start up the driver
       d.mon start=PNG
        Display raster map and vector polygons
       d.rast somerastermap
       d.vect somevectormap color=red
         Stop  the  driver  subsequently.  This  will  write  a file named map.png to be created in your current
       directory:
       d.mon stop=PNG

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 PNG raster map is defined by the map extents. Use g.region -p to get the number of
       rows and cols and use the environment variables to set the PNG 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

        Display drivers
       HTMLMAP driver, PostScript driver, XDRIVER
       d.frame, d.mon, d.rast, d.vect

AUTHOR

       Original version: Per Henrik Johansen  NORGIT AS
       Rewritten by: Glynn Clements, 2003

       Last changed: $Date: 2012-03-02 21:22:34 -0800 (Fri, 02 Mar 2012) $

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       © 2003-2013 GRASS Development Team