Picture Dictionary- Histogram:
Ever wonder what that black and white graph is that sometimes shows up on your camera’s LCD screen? It’s called a histogram, and it’s essentially a representation of the contrast and dynamic range in each image. The histogram shows a range of 0-255 with the value of zero being black and white valued at 255. You’ll find the ‘true white’ illustrated at the far right of the graph and the ‘true black’ on the far left. A well-exposed image will show points close to both ends.