The human visual system is very sensitive to contrast in images, which is the difference in the color and brightness of different objects. Besides, the human eye is a miraculous system that can feel intensities at the 1016 light levels [4]. No wonder some sensors could mess up the image data.
When analyzing images, it is very useful to draw their histograms. They simply show you the lightness distribution of a digital image. In order to do that, you need to count the number of pixels with the exact lightness and plot that as a distribution graph. This gives us a great insight into the dynamic range of an image.
When a camera picture has been captured with a very narrow light range, it gets difficult to see the details in the shadowed areas or other areas with poor local contrast. Fortunately, there's a technique to spread frequencies for uniform intensity distribution, which is called histogram equalization. The following image shows the same picture with their respective...