In the first part of this series, I introduced histograms: handy graphs generated by cameras and image-editing software that you can use to analyze a photo's exposure. Part 2 of this series will concentrate on using histograms as a tool for shooting better photographs.
Knowing what's wrong with your current exposure doesn't do you much good if you don't know how to fix your exposure. I'll s
What Is Exposure?
To understand exposure, sneak out of work right now and see a matinee at a movie theater. (If you get caught, tell your boss that it's professional development—part of your photography education.)
When the movie is over, leave the theater out of the back door. As you step from the dark movie theater into the bright afternoon light, you'll be momentarily blinded as your eyes adjust to the change in brightness. That's exposure.
Your eyes can adjust how much light they gather. If they gather too much, the world washes out to bright white. If they can't gather enough, you stumble around in the dark. To control how much light is gathered, the size of your pupil changes, opening wider to allow more light and closing down to reduce the amount of light.
Your camera works the same way. If there's too much light striking the sensor, the image has parts that are blown out to complete white. Too little light, and some parts will be complete black. In addition to losing detail in highlights and shadows when an image is over- or underexposed, the overall brightness of the photo can affect how colors look and the overall atmosphere of a scene.
(posted by Jennifer Apple for www.PhotoshopSupport.com)