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Gamma Correction Illustrated


Gamma correction can be used to correct a variety of exposure problems. This page illustrates some of the ways gamma correction can be used.

Gamma correction factors are always greater than zero. A correction factor greater than one can be considered a "positive gamma correction" since it adds light to the picture. Gamma correction factors less than one, on the other hand, subtract light from the picture, and can therefore be considered "negative gamma correction."

A gamma correction factor greater than one will lighten dark parts of the picture without excessively lightening the bright ones. This is useful for fixing underexposed images. It can also be used successfully on pictures with a lot of backlighting to bring out detail in the foreground.

original underexposed image
Original Image
image with gamma 3.0 correction
Gamma 3.0 Correction

While a gamma correction may yield an image that is technically correct, it is sometimes desirable to not apply the correction, to achieve an artistic effect.

original underexposed image
Original Image
image with gamma 3.0 correction
Gamma 2.0 Correction

Click here to see the 1024x768 published version of the above picture.

A gamma correction factor less than one will darken light parts of the picture without excessively darkening the shadows. This can be used to fix washed out (over exposed) pictures.

original overexposed image
Original Image
image with gamma 0.5 correction
Gamma 0.5 Correction

Sometimes different gamma corrections need to be applied to different parts of the picture. For the result to be a believeable image, the photographer truly has to be an artist: Finding the boundaries between the parts of the picture that need to be lightened and the ones needing darkening is relatively easy. The difficulty comes from making the boundaries disappear in a natural looking way so the viewer doesn't realize the picture has been manipulated.

original image with complex exposure problems
Original Image
image with positive and negative gamma correction
Gamma 1.5 Shadow Correction
Gamma 0.5 Cloud Correction

Click here to see the 1024x768 published version of the last picture.

 

 
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Featured Photos

Moonlit Snowscape, Harvard, Mass., Picture for December 29, 2007
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Moonlit Snowscape, Harvard, Mass.

Moonrise on Christmas Eve 2007 was a spectacular sight: Climbing through scudding clouds, the luminous orb carried an almost magical air into the evening soon after sunset. December's blanket of snow had been rained on earlier in the week, and the arctic air that followed encrusted the landscape in a tough reflective shell of frozen waves and patterns. If you saw the Moon that night, you will surely remember it...

Display Date:   December 29, 2007
Photographer: Fred Koschara
Image Date: December 24, 2007
Camera: Sony F-717
 
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Winter Sunset Lighthouse, Cape Elizabeth, Maine, Picture for February 6, 2008
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Winter Sunset Lighthouse, Cape Elizabeth, Maine
Display Date:   February 6, 2008
Photographer: Fred Koschara
Image Date: January 30, 2008
Camera: Sony F-717
 
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April Weather, Boylston Street, Picture for October 27, 2004
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April Weather, Boylston Street
Display Date:
 October 27, 2004
Photographer:
 Fred Koschara
Image Date:
 April 14, 2004
Camera:
 Sony F-717
 
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