Syntax:
set terminal pbm {<fontsize>} {<colormode>}
where <fontsize> is small, medium, or large and <colormode> is monochrome, gray or color. Default size is 640 pixels wide and 480 pixels high. The output for monochrome is a portable bitmap (one bit per pixel). The output for gray is a portable graymap (three bits per pixel). The output for color is a portable pixmap (color, four bits per pixel). The output of these drivers can be used with Jef Poskanzer's excellent PBMPLUS package which provides programs to convert the above PBMPLUS formats to GIF, TIFF, MacPaint, Macintosh PICT, PCX, X11 bitmap and many others.
Examples:
set term pbm small
set size 2,2
set term pbm color medium