NAME

pbmreduce - read a PBM image and reduce it N times

SYNOPSIS

pbmreduce [-floyd|-fs|-threshold] [-value val] [-randomseed=integer] N [pbmfile]

You can abbreviate any option to its shortest unique prefix.

DESCRIPTION

This program is part of Netpbm(1).

pbmreduce reads a PBM image as input and reduces it by a factor of N, producing a PBM image as output.

pbmreduce duplicates a lot of the functionality of pamditherbw; you could do something like pamscale | pamditherbw, but pbmreduce is a lot faster.

You can use pbmreduce to "re-halftone" an image. Let's say you have a scanner that only produces black&white, not grayscale, and it does a terrible job of halftoning (most b&w scanners fit this description). One way to fix the halftoning is to scan at the highest possible resolution, say 300 dpi, and then reduce by a factor of three or so using pbmreduce. You can even correct the brightness of an image, by using the -value option.

OPTIONS

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

-threshold

By default, pbmreduce does the halftoning after the reduction via boustrophedonic Floyd-Steinberg error diffusion; however, you can use this option to specify simple thresholding. This gives better results when reducing line drawings.

-floyd, -fs

Specify the Floyd-Steinberg error diffusion method. This is the default.

-value

This option alters the thresholding value for all quantizations. It should be a real number between 0 and 1. Above 0.5 means darker images; below 0.5 means lighter.

-randomseed=integer