ppmtosixel – convert a portable pixmap into DEC sixel format
ppmtosixel [-raw] [-margin] [ppmfile]
Reads a portable pixmap as input. Produces sixel commands (SIX) as
output. The output is formatted for color printing, e.g. for a DEC
LJ250 color inkjet printer.
If RGB values from the PPM file do not have maxval=100, the RGB values
are rescaled. A printer control header and a color assignment table
begin the SIX file. Image data is written in a compressed format by
default. A printer control footer ends the image file.
-raw If specified, each pixel will be explicitly described in the
image file. If -raw is not specified, output will default to
compressed format in which identical adjacent pixels are
replaced by “repeat pixel” commands. A raw file is often an
order of magnitude larger than a compressed file and prints much
If -margin is not specified, the image will be start at the left
margin (of the window, paper, or whatever). If -margin is spec‐
ified, a 1.5 inch left margin will offset the image.
Generally, sixel files must reach the printer unfiltered. Use the lpr
-x option or cat filename > /dev/tty0?.
Upon rescaling, truncation of the least significant bits of RGB values
may result in poor color conversion. If the original PPM maxval was
greater than 100, rescaling also reduces the image depth. While the
actual RGB values from the ppm file are more or less retained, the
color palette of the LJ250 may not match the colors on your screen.
This seems to be a printer limitation.
Copyright (C) 1991 by Rick Vinci.
26 April 1991 ppmtosixel