Image Contrast Enhancement for Brightness Preservation Based on Dynamic Stretching

Image Contrast Enhancement for Brightness Preservation Based on Dynamic Stretching

Histogram equalization is an efficient process often employed in consumer electronic systems for
image contrast enhancement. In addition to an increase in contrast, it is also required to preserve
the mean brightness of an image in order to convey the true scene information to the viewer. A
conventional approach is to separate the image into sub-images and then process independently
by histogram equalization towards a modified profile. However, due to the variations in image
contents, the histogram separation threshold greatly influences the level of shift in mean
brightness with respect to the uniform histogram in the equalization process. Therefore, the
choice of a proper threshold, to separate the input image into sub-images, is very critical in order
to preserve the mean brightness of the output image. In this research work, a dynamic range
stretching approach is adopted to reduce the shift in output image mean brightness. Moreover,
the computationally efficient golden section search algorithm is applied to obtain a proper
separation into sub-images to preserve the mean brightness. Experiments were carried out on a
large number of color images of natural scenes.