feature image expose_v0.2

Overview

The feature-image-expose software is used for image exposure correction. The exposure correction is performed through statistical quantities modification of the image histogram. The process simply fit the statistical quantities of the chromatic values according on the provided parameters.

In addition, this software allows also to display the histogram statistical quantities on the standard output for analysis purpose.

Usage

The feature-image-expose software expect the following parameters. Starting with the execution switches :

--set -e

If this execution switch is provided, the software performs the
histogram correction and write the result on the specified
output image file.

--get -g

If this switch is provided, the software analysis the image
histogram value and display them on the standard output. The
image is then left unchanged.

The stream arguments and parameters are :

--input -i

Path of the input image.

--output -o

Path of the output image if the '--set' is provided.

Exposure correction arguments and parameters are :

--mean -m

Mean of the chromatic values of the desired output image.

--stdd -s

Standard deviation of the chromatic values of the desired output
image.

Demonstration

Considering m_img as the input image histogram mean and s_img as the histogram standard deviation, the exposure correction proceed to the following correction :

        H' = ( ( H - m_img ) s_img^-1 ) s_cor + m_cor

where m_cor and s_cor are the provided mean and standard deviation, respectively, H being the image histogram. In other word, the correction transform the histogram in order to align its mean and standard deviation to the provided values.

Considering the following rectilinear image extracted from a panorama taken using an Eyesis4Pi camera in Geneva :

and asking the histogram statistical quantities leads the the following output :

172.829
70.3792

Asking for an exposure correction using respectively 192 and 96 as mean and standard deviation produce the following image result :

Providing 128 as mean and 70 as standard deviation, the following result image is obtained :

One understand easily that exposure correction can lead to strong image deterioration. Both mean and standard deviation used should not differ to much from the original image statistical quantities.

Compilation

The software binary can be build using its specific makefile by simply typing in its base directory :

$ make clean && make build [OPENMP=false]

The binary is placed in the local bin directory and is not copied in the main bin directory. To generate the documentation, use the command :

$ make clean-documentation && make documentation

To install or uninstall the binaries on the local computer, use the commands :

# make install
# make uninstall