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A program that compares two images using a perceptually based image metric.

Build status Static analysis status

Copyright (C) 2006-2011 Yangli Hector Yee

Copyright (C) 2011-2016 Steven Myint, Jeff Terrace

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, 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 in the file LICENSE.

Build Instructions

  1. Download CMake from if you do not already have it on your system.

  2. Download FreeImage from
    • On OS X with MacPorts: port install freeimage
    • On OS X with Brew: brew install freeimage
    • On Ubuntu: apt-get install libfreeimage-dev
  3. Type:

    $ make
  4. To specify the install directory, use:

    $ make install DESTDIR="/home/me/mydist"


Command line:

Usage: perceptualdiff image1 image2

Compares image1 and image2 using a perceptually based image metric.

  --verbose         Turn on verbose mode
  --fov deg         Field of view in degrees [0.1, 89.9] (default: 45.0)
  --threshold p     Number of pixels p below which differences are ignored
  --gamma g         Value to convert rgb into linear space (default: 2.2)
  --luminance l     White luminance (default: 100.0 cdm^-2)
  --luminance-only  Only consider luminance; ignore chroma (color) in the
  --color-factor    How much of color to use [0.0, 1.0] (default: 1.0)
  --down-sample     How many powers of two to down sample the image
                    (default: 0)
  --scale           Scale images to match each other's dimensions
  --sum-errors      Print a sum of the luminance and color differences
  --output o        Write difference to the file o
  --version         Print version

Check that perceptualdiff is built with OpenMP support:

$ ./perceptualdiff | grep -i openmp
OpenMP status: enabled


  • Hector Yee, project administrator and originator -
  • Scott Corley, for png file IO code.
  • Tobias Sauerwein, for make install, package_source Cmake configuration.
  • Cairo Team, for bugfixes.
  • Jim Tilander, rewrote the IO to use FreeImage.
  • Steven Myint, for OpenMP support and bug fixes.
  • Jeff Terrace, for better FreeImage support and new command-line options.

Version History

  • 1.0 - Initial distribution
  • 1.0.1 - Fixed off by one convolution error and libpng interface to 1.2.8
  • 1.0.2 - [jt] Converted the loading and saving routines to use FreeImage
  • 1.1 - Added colorfactor and downsample options. Also always output difference file if requested. Always print out differing pixels even if the test passes.
  • 1.1.1 - Turn off color test in low lighting conditions.
  • 1.1.2 - Add OpenMP parallel processing support and fix bugs.
  • 1.2 - Add --sum-errors, use more standard option style, and fix bugs.
  • 1.3 - Add MSVC compatibility.
  • 1.4 - Detect differences due to the alpha channel. This was lost in 1.0.2 when FreeImage was introduced.
  • 2.0 - Support usage as a library.
  • 2.1 - Allow accessing stats directly when used as a library.

Usage as a library

#include <perceptualdiff/metric.h>
#include <perceptualdiff/rgba_image.h>

int main()
    const auto a = pdiff::read_from_file("a.png");
    const auto b = pdiff::read_from_file("b.png");

    const bool same = pdiff::yee_compare(*a, *b);



A program that compares two images using a perceptually based image metric








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