ppmtosixel

Updated: 1 August 2023
Table Of Contents

NAME

ppmtosixel - convert a PPM image to DEC sixel format

SYNOPSIS

ppmtosixel [-raw] [-margin] [-7bit] [ppmfile]

DESCRIPTION

This program is part of Netpbm.

ppmtosixel reads a PPM image as input and produces sixel commands (SIX) as output. The output is formatted for color printing (e.g. for a DEC LJ250 color inkjet printer) or for color display on DEC VT terminals and terminal emulators (VT240 and beyond).

If RGB values from the PPM file do not have maxval=100, ppmtosixel rescales them to maxval 100. A printer control header and a color assignment table begin the SIX file. Image data is in a compressed format by default. A printer control footer ends the image file.

OPTIONS

In addition to the options common to all programs based on libnetpbm (most notably -quiet, see Common Options), ppmtosixel recognizes the following command line options:

-raw: If you specify this, 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 slower.
-margin: If you don't specify -margin, the image will start at the left margin (of the window, paper, or whatever). If you do specify -margin, a 1.5 inch left margin will offset the image.
-7bit: If you don't specify -7bit, each control code will be expressed as a single, 8-bit "C1" character. If you do specify -7bit, each control code will be expressed using two, 7-bit "C0" characters. (See C0 and C1 control codes for more information.) In other words, -7bit produces more portable sixel files, and its absence produces smaller sixel files.
This option was new in Netpbm 11.04 (September 2023).

PRINTING

Generally, sixel files must reach the printer unfiltered. Use the lpr -x option or cat filename > /dev/tty0?.

LIMITATIONS

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.