LOCALIZED, ADAPTIVE VIDEO CONTRAST ENHANCEMENT USING CONTROLLED HISTOGRAM EQUALIZATION

An adaptive histogram equalization-based approach improves contrast in a video signal. For each video frame, the histogram of the pixel luminance values is calculated. The calculated histogram is divided into three programmably-sized regions that are equalized independently of each other. The equalization is performed in a controlled fashion by clamping the peaks of the histogram thereby ensuring limited stretching of sharp peaks. The equalized values are averaged with the original pixel values with a weighting factor that is different for the three regions chosen such that the darker regions are enhanced more than the brighter ones. To ensure smooth enhancement, programmable guard band regions can be defined between the three divisions of the histogram. The statistics calculated from one frame may be used to enhance the next frame to eliminate the need for frame buffers. Many of the calculations may be performed in the inactive time between two frames.