How to Use a Histogram in Photography
Professional photographers use histograms before, during and after taking pictures in order to adjust their camera settings and retake the photo or alter a photograph. A histogram represents the relationship of the pixels in a digital photograph and their various levels of darkness and light. Most histograms use shades of black and white to differentiate between light and dark in a photograph but you can view them for color images as well as black and white images.
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Instructions
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Take a photograph with a digital camera and switch the camera mode to show the histogram during the middle of your shoot. There are two main times a histogram can offer assistance; during the shoot and later, while viewing your photographs on a computer.
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Look at the histogram that represents the photo you just took. You will notice a thumbnail of the photograph and a small box with a graph. The left side of the graph represents the darkest portions of the photograph and the right side shows the areas of lightness or white. In between are graduating shades of light or midtones.
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Use the histogram as a measure to determine if the photograph you just took is overexposed or underexposed. The graph should register lower on the ends and feature a gradual curve in the middle. A graph with too many dark tones will show a large area on the left of the histogram. A photograph with blown-out highlights will have a large area on the right side.
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Adjust your camera settings and retake the photograph to get the correct exposure. Digital cameras that have histograms also have adjustable shutter and aperture settings that allow the photographer to reduce or increase the light that comes in the lens. A faster shutter reduces the light while a slower shutter will increase it.
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Lighten or darken a photograph after you take it by using special graphic software that produces its own histogram. Open a photo taken from a digital camera or use a scanned photograph. Programs like Adobe Photoshop offer various methods of manipulating the histogram in order to light or darken portions of the image (see Resources).
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Click and drag the sliders beneath the histogram in a graphic program. Three arrows appear on a bar beneath the graph. By dragging the right arrow to the left, the highlighted portions of the image will darken. If you drag the left arrow to the right, the darkest areas will get lighter. You can adjust the midtones by dragging the middle arrow in either direction.
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Prepare to lose some resolution when you adjust the sliders on a histogram. As the pixels change, the photograph may become blurry or grainy. Use your judgment to find a workable compromise.
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Tips & Warnings
If you’re using a high end digital camera, store the images in an uncompressed format by choosing the TIFF mode. You may alter histograms taken in this mode later with special graphic software without losing resolution.
Resources
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