WHAT IS A HISTOGRAM?
A display of all the information in your image, running from dark on the left to light on the right, a histogram is a quick way to identify whether your image is well exposed. Peaks bunched up at either end signify an image with large dark or light portions, and those that vanish off the edge are clipped to pure white or black, with no detail discernible in them by even the keenest eye. Adjustments such as “Levels” or “Curves” can be seen working on the histogram, as their effect is to change the position of tones. Increase the brightness of an image dramatically, and you’ll see the peaks bunch up at the right-hand side. A well-exposed image has data in almost every part of the histogram, with a smooth curve peaking in the middle considered ideal.