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