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Histogram equalisation (HE) is widely used to enhance the image contrast but it tends to over-enhance the image background brightness. Improvement schemes have been introduced to reduce this defect of the conventional HE, but the over-enhancement of the background brightness is still obvious. A novel approach of nonlinear HE is presented, which is able to enhance the image contrast while preserving the background brightness for images with well-defined background brightness.
Tan et al. (Thu,) studied this question.