Chia-Ying Chang and Shen-Chuan Tai
Zone system, dual-compensation technique, logarithmic transforma-tion, gamma transformation
Luminance is crucially important to the quality of images. Colour, details, and texture can be washed out when luminance is exceedingly bright or hidden when luminance is overly dark. Logarithmic and gamma transformations are two well-known methods to alter exposure values. Unfortunately, both of these methods involve compressing the dynamic range of the image. This paper proposes a simple method based on the zone system devised for film photography to provide two levels of image compensation for the adjustment of luminance. The zone system is used to determine the level luminance, whereupon two compensation strategies are applied to produce an optimized high key or low key images. Experimental results demonstrate the superior performance of the proposed compensation method over existing methods, according to the evaluation using histograms, contour plots, the universal quality index, and structural similarity.
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