References in periodicals archive ?
For this, it was observed that using an algorithm with histogram technique (Autolevels, Contrast stretching, Histogram equalization) before the Retinex algorithm can lead to more accurate output images, when speaking about terms of visual quality.
Defining contrast stretching (CS) quantitatively with respect to the reference image (RI) for the different enhanced versions of the images is as given in the following:
Contrast stretching increases the dynamic range of gray levels in an image and it is one of the simplest technique for enhancing contrast [10].
Here [k.sub.0], [k.sub.1] and [k.sub.2] are the normal number that less than 1, [E.sub.s] and [[sigma].sub.s] are the local mean and standard deviation, [E.sub.g] and [[sigma].sub.g] are the global mean and standard deviation, X as gray scale amplification factor, [beta] and [gamma] for contrast stretching coefficients.