One big advantage to shooting digitally is the ability to view a histogram in the LCD screen on the back of your camera body. A histogram is a graph of the data in your image displaying shadows on the left and highlights on the
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Plugged up
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Blown out
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right. You can use a histogram to evaluate the tonal distribution in your digital photos. Once you view the histogram you can determine if you need to make additional exposures at alternate settings to get a better image. To utilize this feature, simply program your camera to display a histogram immediately after exposure. Having this immediate feedback will result in a much higher success rate.
When evaluating a histogram, the primary concern is clipping or loss of data due to underexposure or overexposure. When a histogram 'hits the wall' to the left, the image is underexposed. If the histogram is heavy on the right the image is overexposed. This indicates that you should change exposure settings to get a more balanced exposure for your image.
The histogram displayed on the camera represents the information of an image in a converted JPEG state even if you are shooting in RAW. Because RAW is so flexible, you will not know what the histogram of a RAW file will look like until it has been processed. Many digital cameras will allow you to set JPEG contrast to a low setting, which reduces the likelihood of clipping and provides a better RAW preview.
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Some problems, low hi
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Good histogram
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If you shoot RAW files, you will not only have more data (16-bit as opposed to 12- or 8-bit), you will also have the option of processing it yourself with a RAW converter rather than having the camera process it for you. Adobe Photoshop CS and higher has a built in RAW converter. The RAW files you shoot will have more data in the highlights than is indicated by the histogram. Typically there are many more bits of data in the highlights than the shadows because data in the shadows tends to be noisier and of lower quality. For these reasons, in RAW format, favor overexposure rather than underexposure; you will be amazed at how much highlight detail you can recover. Assuming your photo has a 6-stop dynamic range (there are 6 f-stops between the darkest and lightest parts of the photo) the progression looks like this from dark to light: 64, 128, 256, 512, 1024, 2048. Having this numerical evaluation, from the camera to the computer, makes digital photography an understandable science as well as an art.
John Paul Caponigro is an internationally respected fine artist, author of Adobe Photoshop Master Class, and a member of the Photoshop Hall of Fame.
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