Mastering OpenCV 3 - Second Edition

Histogram equalization

We can easily perform histogram equalization to improve the contrast and brightness of an image, using the equalizeHist() function. Sometimes this will make the image look strange, but in general it should improve the brightness and contrast and help face detection. The equalizeHist() function is used as follows:

    // Standardize the brightness & contrast, such as 
    // to improve dark images. 
    Mat equalizedImg; 
    equalizeHist(inputImg, equalizedImg);