BWDIFF(1)

NAME

bwdiff - compare two black and white files

On this page

SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO
AUTHOR
COPYRIGHT
BUG REPORTS

SYNOPSIS

bwdiff [-b] [-m | -g | -l | -e | -n] file1 file2

bwdiff compares two black and white bw(5) format files and writes the results to standard output. By default, bwdiff records the differences as offsets from a neutral, half-intensity grey (128). The written value is brighter than this neutral grey by an amount proportional to the signed difference between the pixels in file1 and file2. Pixels that are brighter in file1 than in file2 will be brighter than the neutral grey, while pixels that are dimmer in file1 than in file2 will be dimmer. This difference is divided by two to fit the 0 to 255 output range.

bwdiff accepts -'' as a synonym for standard input, and .'' as a synonym for the platform’s null device.

Note that this program also produces useful results on color pix(5) files.

OPTIONS

-m: Calculates the magnitude of the difference. No offset or division is applied. Brighter pixels indicate larger differences in value, and black indicates no difference.
-g: Greater-than relational operation. Outputs a full-white (255) pixel if the value of the pixel in file1 is greater than the corresponding pixel in file2. Cannot be combined with other relational flags.
-l: Less-than relational operation. Outputs a full-white (255) pixel if the value of the pixel in file1 is less than the corresponding pixel in file2. Cannot be combined with other relational flags.
-e: Equal-to relational operation. Outputs a full-white (255) pixel if the value of the pixel in file1 is equal to the corresponding pixel in file2. Cannot be combined with other relational flags.
-n: Not-equal-to relational operation. Outputs a full-white (255) pixel if the value of the pixel in file1 is not equal to the corresponding pixel in file2. Cannot be combined with other relational flags.
-b: Sets the background to the corresponding pixels of file1 at a lowered intensity instead of the default black background. This option only applies when using one of the relational operation flags (-g, -l, -e, or -n).

EXAMPLES

Example 1. Basic Difference

To find the difference between two black and white images:

bwdiff image1.bw image2.bw > diff.bw

Example 2. Relational Operation on Color Images

Suppose you ran pixstat(1) on a file and found the modes to be red=107, green=93, blue=70. You can display those pixels whose colors are exactly at these values by comparing the file against a solid color stream:

gencolor 107 93 70 | bwdiff -e file.pix - | pix-fb