Most image corrections can be diagnosed by looking at a histogram displayed on the monitor as a guide when adjusting the camera settings to capture the picture.

Each pixel in an image can be set to any of 256 levels of brightness from pure black (0) to pure white (255). Histogram graphs the levels of brightness in the image and brightness distribution.

The horizontal axis represents the range of brightness from 0 255 left to right. more highligts mean strong taller right side.

Think of it as a line with 256 spaces on which to stack pixels of the same brightness.

The vertical axis represents the number of pixels with each of the 256 brightness values.

The higher the line coming up from the horizontal axis, the more pixels there are at that level of brightness. To read the histogram, you look at the distribution of pixels.