How to interpret the histogram?

[tafletcher]

I am new to digital photography. I've seen alot of talk about histograms. How can I intrepret the histogram that results in a great image?

[PacAce]

Unfortunately, the histogram will not tell you whether the image you have is going to be great or not. The histogram only tells you what the distribution is of the different light levels that make up your image.

To learn more about histograms, check out these sites:

http://www.sphoto.com/techinfo/histograms/histograms.htm

http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

[robertwgross]

There are lots of tutorials on histograms.

In a nutshell, the lines at the left are the dark tones and blacks. The lines at the right are the bright tones and whites. There are mid-tones in the middle.

If your histogram shows everything bunched up at the left, then chances are you have an underexposed image. If it shows everything bunched up at the right, then you have an overexposed image. Lots of good images have lines spread all over, from almost black to almost white. However, there is no law that says that all images must have that to be good.

---Bob Gross---

[Steven M. Anthony]

To build on Bob's comment, think of the histogram as a way to spot poorly exposed images. If you see a large (high) spike at the extreme left of the histogram, that means your image has recorded lots of pure black--i.e., no shadow detail will be present in the pixels making up that spike*. If you have a large (high) spike on the extreme right of the histogram, you have a lot of pure white--i.e., no highlight detail will be present in the pixels making up that spike*.

Whether that's completely bad depends on what you are shooting. A shot of a spot-lit stage will have spike on the left. But that is to be expected, because that's the effect the lighting director was likely trying to achieve--a scene where you see the performer and nothing else. I'm sure there are scenes that will naturaly have some blown out areas--but I'm too tired to think of any!

Important to keep in mind is that if you shoot in RAW format, the preview on your camera's LCD will not be an accurate representation of the images "RAW" histogram. The one you see on the LCD is constructed from the jpeg (and post processed in-camera) your camera makes from the raw file. So it might clip more highlights and shadows than the RAW file will show. So if you have small areas of flashing pixels on your LCD, it's probably not a problem.

* for all those experienced in the ways of ACR (Adobe Camera Raw): yes, it is possible you might find some color info in those spikes--but I thought that too advanced for a beginner's question, and probably more than I could give a good answer to, too!