/Midway-Image-Equalization

Primary LanguageC++

#+AUTHOR Thierry Guillemot and Julie Delon #+DATE <2015-08-07 ven.>

About

Author
Thierry Guillemot <thierry.guillemot.work@gmail.com> and Julie Delon <julie.delon@parisdescartes.fr>
Copyright
(C) 2015 IPOL Image Processing On Line http://www.ipol.im/
Licence
GPL V3+

Overview

This source code provides an implementation of the “midway” image equalization, as described in IPOL, another program called ‘create_histogram.sh’ used to generate the histogram of all PNG images contained in a directory and a ‘launch.sh’ file to generate all the results presented in the paper.

The ‘bin/midway’ program reads two PNG images, then apply contrast changes to these images such that the output images have the same distributions (this is done channel by channel). This common distribution is built as the midway between the two original ones. If H1 and H2 are the cumulative histograms of the input images (for the considered channel), the midway histogram is defined as (0.5*(H1-1 + H2-1))-1. The contrast changes to be applied are thus respectively x -> 0.5*(x + H2-1 o H1 (x)) for the first image and x -> 0.5*(x + H1-1 o H2 (x)) for the second image. Both resulting images are written as PNG images.

The ‘create_histogram.sh’ compute the histograms of all the PNG images of a specified directory. Resulting histograms are written in SVG.

Only 8bit GRAY/RGB PNG images are handled.

Requirement

The code is written in ANSI C, and should compile on any system with an ANSI C compiler.

The libpng header and libraries and gnuplot programs are required on the system for compilation and execution. On Linux, just use your package manager to install it:

sudo apt-get install libpng
sudo apt-get install gnuplot

For more information, see http://www.libpng.org/pub/png/libpng.html

Compilation

Simply use the provided makefile, with the command ‘make’. The makefile will produce two programs called : ‘bin/midway’ and ‘bin/histogram’. The ‘midway’ program is used the midway equalization of two images. The ‘histogram’ program is used by ‘create_histogram.sh’ to compute the histogram of a directory.

Usage

midway

Description

The ‘bin/midway’ program is used to apply the midway equalization over two images. It takes 4 parameters with other optional:

bin/midway in1.png in2.png out1.png out2.png [options]
in1.png
first input image.
in2.png
second input image.
out1.png
first output image.
out2.png
second output image.

Options :

-dithering sigma
apply a Gaussian noise of standard deviation sigma before applying the midway equalization.
-verbose
activate the verbose mode

Usage examples

If you want to compute the midway equalization between the files ‘input/bat1.png’ and ‘input/bat2.png’ without dithering and save the resulting images into ‘out1.png’ and ‘out2.png’, you can use the command:

bin/midway input/bat1.png input/bat2.png out1.png out2.png

The command:

bin/midway input/nice1.png input/nice2.png out1.png out2.png -dithering 2

will compute the midway equalization of the files ‘input/nice1.png’ and ‘input/nice2.png’ with a dithering of sigma=2 and save the resulting images into ‘out1.png’ and ‘out2.png’.

create_histogram.sh

Description

The ‘create_histogram.sh’ program is used to compute the histogram of all PNG images contained in a directory. It takes 1 parameter with other optional:

./create_histogram.sh directory out.svg [options]
directory
directory containing PNG images

Options :

-cumulative
compute the normalized cumulative histogram

Usage example

To compute the normalized histogram of the directory input, you can use:

./create_histogram.sh input

To compute the normalized cumulative histogram of the directory input, you can use:

./create_histogram.sh input -cumulative

launch.sh

Description

The ‘launch.sh’ file is used to generate all the result presented in the paper. To launch it, just use the command To compute the normalized histogram of the directory input, you can use:

./launch.sh

About this file

Copyright 2015 IPOL Image Processing On Line http://www.ipol.im/ Author: Thierry Guillemot <thierry.guillemot@gmail.com> and Julie Delon <julie.delon@parisdescartes.fr>

Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved. This file is offered as-is, without any warranty.