imagdiff(1) General Commands Manual imagdiff(1)
NAME
imagdiff - compare two image files and writes differences to a third
file file.
SYNOPSIS
imagdiff [-h(elp)] [-f fuzz_dist] [-m mode] oldfile newfile deltafile
DESCRIPTION
imagdiff reads in any two image files readable by Imlib2 and write out
a "delta" image file that represents the differences between the two
files.
OPTIONS
-h Print help and quit.
-f fuzz_dist
When performing a grayscale difference analysis, any pixel
values within the distance specified by -f option are considered
equal. This option has no effect on a color difference
analysis. The default value is 1.
-m mode
Set of the mode of the difference analysis. At present, five
modes are available, as described in the MODES section. The
default mode is 1.
MODES
1 Grayscale: In this mode, both input images are converted to
grayscale. Any pixels that are darker (when comparing old to
new) are highlighted in BLUE, and any pixels that are brighter
are highlighted in RED. [On a B&W drawing with a white
background, this results in additions being highlighted in BLUE,
and subtractions being highlighted in RED.] If one of the two
input images is missing, a blank all-white image will be created
as a substitute.
2 Grayscale (lightened): This works much like the Grayscale
analysis of mode 1, except that all unchanged pixels are shifted
halfway towards white. This makes it easier to identify changes
on an image where the background is predominantly white. If one
of the two input images is missing, a blank all-white image will
be created as a substitute.
3 Grayscale (darkened): This works much like the Grayscale
analysis of mode 1, except that all unchanged pixels are shifted
halfway towards black. This makes it easier to identify changes
on an image where the background is predominantly black. If one
of the two input images is missing, a blank all-black image will
be created as a substitute.
4 Color: Here, the differences between the two images are
computed on a per-RED, per-GREEN, and per-BLUE basis and are
shifted and scaled such that unchanged pixels will show up as
50% gray. If one of the two input images is missing, a blank
50% gray image will be created as a substitute.
5 Color (stretched): Again, differences between the two images
are computed on a per-channel and are shifted that unchanged
pixels will show up as 50% gray, but here the scaling is
maximimized to emphasize differences. If one of the two input
images is missing, a blank 50% gray image will be created as a
substitute.
NOTES
The compare and gm compare utilities (found within the ImageMagick and
GraphicsMagick suites, respectively) can be utilized to perform a
similar analysis. However, imagdiff has been optimized for black-and-
white images and runs faster because of the underlying Imlib2 engine.
CAVEATS
Metadata found in the input files (including resolution information) is
discarded. Also, the Imlib2 export routine makes no attempts at
colorspace reduction or otherwise optimizing the output image. If
saving to a PNG file, consider using pngrecolor (or even opt-png) to
reduce the filesize.
SEE ALSO
compare(1), gm(1), opt-png(1), pngrecolor(1)
COPYRIGHT
Copyright (C) 2019-2025 by Brian Lindholm. This program is free
software; you can use it, redistribute it, and/or modify it under the
terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
littleutils 2025 Mar 22 imagdiff(1)
littleutils 1.2.8 - Generated Sun Oct 19 09:12:24 CDT 2025