BWTHRESH(1)

NAME

bwthresh - threshold a black-and-white bw file into intensity bins

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SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO
AUTHOR
COPYRIGHT
BUG REPORTS

SYNOPSIS

bwthresh [-h | -?] _val_... < file.bw > output.bw

bwthresh reads a stream of black-and-white data in bw(5) format from standard input, quantizes each pixel value against the supplied threshold values, and writes the resulting bw(5) data to standard output.

Given n threshold values, the grayscale range 0-255 is divided evenly into n+1 output bins. Each input pixel is compared against the thresholds in order: the first threshold the pixel is less than selects its bin, and the pixel is replaced by that bin’s representative intensity. Bin i (for i from 0 to n-1) is assigned the value 256 * i / n, and the final bin is assigned 255.

The threshold values are positional arguments. They must be integers in the range 0-255, given in strictly increasing order, and no more than 255 may be supplied.

OPTIONS

-h, -?: Print a usage message and exit. Recognized only when given as the sole argument.
val…: One or more threshold values. Each must be an integer between 0 and 255 inclusive, and the values must be listed in strictly increasing order.

EXAMPLES

Example 1. Posterize an image into three intensity levels

pix-bw photo.pix | bwthresh 85 170 > poster.bw

Convert a color pix(5) image to grayscale with pix-bw(1), then collapse it to three flat intensity levels: pixels below 85 become 0 (black), pixels below 170 become 128 (mid-gray), and the rest become 255 (white). This is a quick way to produce a hard-edged, posterized mask from a continuous-tone image.

Example 2. Binarize an image at a single threshold

bwthresh 128 < input.bw > mask.bw

With a single threshold, every pixel below 128 becomes 0 and every pixel at or above 128 becomes 255, yielding a pure black-and-white mask.