19 December 1985 Entropy-Constant Image Enhancement by Histogram Transformation
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Image enhancement techniques are described for increasing visual contrast in an intensity range (or ranges) of interest. Enhancement is accomplished by histogram transformation where (except for quantization error) there is no change in entropy between the input and output images. This preservation of entropy is desired for some applications where it is imperative that no artifacts be introduced - as may result from such enhancement techniques as spatial filtering and adaptive histogram transformation. The contribution of this work is toward the compilation and organization of useful image enhancement techniques and toward an understanding of matching particular transformations with the desired purposes. Two types of methods for obtaining histogram transformations are distinguished here. In one type the output histogram is specified as a ramp-shaped function, and the transformation is found. This type is useful for automatically enhancing low or high intensity ranges, and for histogram equalization. For the second type, the general form of the transformation function is defined to be a third order polynomial function, which is specified by the choice of the intensity region of interest and the desired amount of contrast enhancement. This type is useful for interactive enhancement. Examples are shown which illustrate where each of the transformations is applicable, and what results are obtained from such transformations.
© (1985) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Lawrence O' Gorman, Lawrence O' Gorman, Lynne Shapiro Brotman, Lynne Shapiro Brotman, } "Entropy-Constant Image Enhancement by Histogram Transformation", Proc. SPIE 0575, Applications of Digital Image Processing VIII, (19 December 1985); doi: 10.1117/12.966493; https://doi.org/10.1117/12.966493


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