Contrast Enhancement Using Bi-Histogram Equalization With Brightness Preservation

Contrast enhancement is an important factor in the image preprocessing step. One of the widely accepted contrast enhancement method is the histogram equalization. Although histogram equalization achieves comparatively better performance on almost all types of image, global histogram equalization sometimes produces excessive visual deterioration. A new extension of bi-histogram equalization called Bi-Histogram Equalization with Neighborhood Metric (BHENM). First, large histogram bins that cause washout artifacts are divided into sub-bins using neighborhood metrics, the same intensities of the original image are arranged by neighboring information. Then the histogram of the original image is separated into two sub-histogram based on the mean of the histogram of the original image; the sub-histogram are equalized independently using refined histogram equalization, which produces flatter histogram. BHENM simultaneously preserved the brightness and enhanced the local contrast of the original image. Simulation result shows better brightness preservation.