[IPOL announce] new article: Midway Video Equalization

[announcements about the IPOL journal]

A new article is available in IPOL: http://www.ipol.im/pub/art/2017/181/

Javier Sánchez,
Midway Video Equalization,
Image Processing On Line, 7 (2017), pp. 65–80.
https://doi.org/10.5201/ipol.2017.181

Abstract
This article presents an implementation of the 'Midway Equalization' 
method for videos. This technique allows us to modify the image 
histograms so that they present similar luminances. We propose two 
algorithms: the first one based on histogram inversion and the second 
one on the sorting of images intensities. The former computes the 
histograms and then finds the contrast change functions by convolving 
the inverse histograms with a Gaussian function. The latter starts by 
sorting the pixels of each image by intensity; the temporal signals, 
composed of all gray levels of the same rank, are then convolved with a 
Gaussian function. In this sorting method, the resulting histograms are 
more similar and homogeneous. Nevertheless, the histogram strategy is 
faster and provides good results in general. The algorithms include a 
'dithering' option for reducing quantization artifacts. The whole 
implementation depends on a single parameter, the standard deviation, 
that is used for Gaussian convolutions. The experiments show several 
examples, including the quantization artifacts that appear in some 
situations and the benefits of dithering. We observe that these 
artifacts are usually more important in the histogram method.