Syntax:
set terminal pbm {<fontsize>} {<mode>} {size <x>,<y>}
where 5#5fontsize6#6 is small, medium, or large and 5#5mode6#6 is monochrome, gray or color. The default plot size is 640 pixels wide and 480 pixels high.
The output of the pbm driver depends upon 5#5mode6#6: 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