PNG driver

## 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.

## USAGE

### Environment variables

Several environment variables effect 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.
- 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)
- 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.

### Example

1. Start up the driver

                d.mon start=PNG
                d.mon select=PNG

2. Display raster map and vector polygons

                d.rast somerastermap
                d.vect map=somevectormap color=red

3. 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 info-zip 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

XDRIVER, d.mon, d.rast, d.vect

## AUTHOR

Original version: Per Henrik Johansen
phj@norgit.no
NORGIT AS

Rewritten by Glynn Clements, 2003

Last changed: $Date: 2004/12/06 09:45:17 $