H is for Histogram

The word histogram strikes fear in the hearts of many a photographer - beginner and seasoned alike. It's that graph that you can see on the LCD screen on the back of your camera that looks painfully like those you saw in the statistics class that you nearly failed. I'm here to dispel the paralysis you feel just thinking about it. The histogram is your friend.

Let me over simplify an explanation so that you can begin to use it as the tool it really is. Here are 10 things to help you understand and use a histogram.

A histogram is a graph that shows the tones within a photograph, with dark/black being on the left and bright/white being on the right.
The height of any point on the graph indicates the amount of pixels at any particular level of darkness or brightness.
Just like in football "clipping" is bad, in this case clipped pixels.
When a histogram shows pixels climbing either end of the graph, they are clipped which means:
- details in those tones are lost,
- the appearance of the image will most likely be degraded, and
- the photograph is incorrectly exposed
"Expose to the right." There is more data in bright pixels than dark ones, so a graph favoring the righthand side is a good thing.
Clipping or blowing out highlights (brights) is a sin in digital photography, so expose an image to the right but NOT the far right.
If there's a line climbing the right hand side of the graph looking like it's heading for the stars, the highlights are blown - the data is gone. What can a photographer do?
Adjust the exposure in camera. Reduce the brightness in an image by stopping down - move the Exposure Compensation (+/-) in the negative direction until clipping is no longer a major issue. As you move the EV, the histogram will move left.
Avoid clipped shadows as well. There is less data in "dark" pixels; if you expose to the right you'll avoid ugly noise in the shadows.
Histograms can be really handy when you're shooting in bright light and can't see the image in the LCD screen; it enables you to reach every photographer's goal - a well exposed photograph in-camera.