Histogram is a graphical display on the camera that shows the exposure. It shows the details of the image such as shadows, the extent of brightness and if any area in the image is black or white. Histograms are of great help in underwater photography as it is not easy to accurately read the exposure of the image on the LCD screen. This graphical histogram is also known as tonal range of a photo.
The tonal range of the image is graphed on the basis of its brightness value. Tones to the right of the screen are light whereas the one’s to the left are dark. There is no correct histogram technique, as different levels of brightness are displayed for different images.