Syntax:
set terminal pbm {<fontsize>} {<mode>} {size <x>,<y>}
where <fontsize> is `small`, `medium`, or `large` and <mode> is `monochrome`, `gray` or `color`. The default plot size is 640 pixels wide and 480 pixels high. The output size is white-space padded to the nearest multiple of 8 pixels on both x and y. This empty space may be cropped later if needed.
The output of the `pbm` driver depends upon <mode>: `monochrome` produces a portable bitmap (one bit per pixel), `gray` a portable graymap (three bits per pixel) and `color` a portable pixmap (color, four bits per pixel).
The output of this driver can be used with various image conversion and manipulation utilities provided by NETPBM. Based on Jef Poskanzer's PBMPLUS package, NETPBM provides programs to convert the above PBM formats to GIF, TIFF, MacPaint, Macintosh PICT, PCX, X11 bitmap and many others. Complete information is available at http://netpbm.sourceforge.net/.
Examples:
set terminal pbm small monochrome # defaults
set terminal pbm color medium size 800,600
set output '| pnmrotate 45 | pnmtopng > tilted.png' # uses NETPBM"