Often overlooked by beginning photographers, the digital camera histogram display is used to measure the picture’s tonal range from dark to light with black on the left end and white on the right end. The middle section represents mid tones. An underexposed photo has overly dark areas with the graph skewing to the left, while an overexposed photo has blown-out areas with the graph skewing to the right.
Why the Histogram Display is a Useful Tool to Have for Good Photographs
Although some photographers might prefer underexposed or overexposed photos for the effect they are going for, such as silhouettes, generally most prefer a perfectly exposed photo since there is no loss of detail in the image. For instance, a photo of a crumbled paper does not reveal any creases but only its outline as a white, obscure object. This overexposure is measured by extreme values on the right.
A histogram helps photographers take pictures that are closer to their expectations and imaginations since they use it as a reference point to increase or decrease the exposure by way of shutter speed, f-stop, ISO—the three DSLR basics—or a different metering mode.
The LCD screen is too small to accurately decipher whether the exposure of a photo is off or not and since a 15 inch monitor is not readily available, the histogram comes in handy. Most, if not all, DSLRs have a highlight alert system where the overexposed areas will blink on the histogram. Check the camera’s instruction manual for specific information.
Is There a Perfect Histogram Shape to Look for In an Image?
There is no such thing as a perfect histogram. Naturally bright objects like snow or light bulbs can create peaks and spikes on the right of the histogram even though the photo is exposed correctly. But in general, a good histogram has an even spread of tones peaking in the middle while tapering off towards the edges. Just remember to look out for dramatic peaks on either end of the histogram when examining an image.
While one can use programs like Photoshop or Lightroom to correct a photo, it’s better to get it right the first time and retain the original detail. Understanding histograms also helps when editing photos on the computer. A helpful hint when checking for a correctly exposed photo is to make sure the whites in the photo are pure white instead of pale yellow or another off-color.