Exposure Characteristic Curves and Image Contrast

This interactive Java tutorial explores the relationship between the slope (often referred to as gamma) of characteristic curves exhibited by transparency and negative films and the amount of contrast produced by these films. Instructions for operation of the tutorial appear below the applet window.

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The tutorial initializes with a characteristic curve of a typical black & white film on the left side of the window and the image produced by that film on the window's right side. Use the slider to adjust the slope of the characteristic curve, which simultaneously produces a change in image contrast. As the slope is increased, so is image contrast. The Choose A Specimen pull-down menu allows a visitor to select between several images, and the Color Images radio button changes the image palette from black & white to color photomicrographs of the same specimen.

Characteristic curves exhibited by transparency films slope in the opposite direction from those obtained with negative films . This occurs because a short exposure (underexposure) produces very dense transparencies but thin negatives, and a long exposure (overexposure) yields thin transparencies but dense negatives. In addition, characteristic curves for transparency films have a much steeper slope than negative films, due to the fact that transparency films have more inherent contrast and a very narrow exposure latitude.

Contributing Authors

Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.

Kirill I. Tchourioukanov and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.