Local Contrast Enhancement Utilizing Bidirectional Switching Equalization Of Separated And Clipped Sub-Histograms
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Date
2014-09
Authors
Hoo, Seng Chun
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Abstract
Digital image contrast enhancement methods that are based on histogram equalization (HE) technique are useful for the use in consumer electronic products due to their simple implementation. However, almost all the suggested enhancement methods are using global processing technique, which does not emphasize local contents. Therefore, a novel local histogram equalization method, which is Local Contrast Enhancement Utilizing Bidirectional Switching Equalization of Separated and Clipped Sub-Histograms (LCE-BSESCS) has been proposed. This proposed method is an extension to Brightness Preserving Bi-Histogram Equalization (BBHE) and Bi-Histogram Equalization with a Plateau Limit (BHEPL). LCE-BSESCS is similar to BBHE in terms of using the same mean-separation methodology. Unlike BBHE that uses global average intensity value as the splitting point, the local splitting point in LCE-BSESCS is the average intensity value from the samples within the contextual region. In addition, similar to BHEPL, LCE-BSESCS clip the histogram with a threshold value obtained using the average value from sub-histogram. However, unlike BHEPL, a switching approach has been used. This switching approach reduces the processing time as the transfer function is calculated from one sub-histogram only instead of two sub-histograms. The implementation of LCE-BSESCS method starts by first defining the contextual region, and then followed by creating local histogram, separating the histogram into two sub-histograms, clipping the corresponding sub-histogram, creating the bidirectional intensity switching mapping function and finally mapping the center pixel. From the analysis for all the methods evaluated, LCE-BSESCS has the lowest value for Mean Brightness Error (i.e. 3.4570) and Speckle Noise Strength (i.e. 6.4639).
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Digital image contrast enhancement methods , are useful for the use in consumer electronic products