See DYNAMIC RANGE
The image histogram on your camera’s LCD display tells you everything you need to know about the brightness range in your subject and whether your camera can capture it. The histogram is a graphical representation of the tones in your picture, showing the number of pixels at different brightness levels from pure black (on the left of the scale) to pure white (on the right). The ‘shadows’ in your picture are roughly the left quarter of the overall brightness range. With average subjects the histogram peaks in the midtones, though histogram shapes will vary wildly (see overleaf). The ‘highlights’ are in the right quarter of the brightness range. The dynamic range of the scene you’re photographing is shown by the width of the histogram. The dynamic range your camera can record, is shown by the width of the histogram scale. If the histogram won’t fit, it’s a warning sign.