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Ch 3 – Preparing to Take a Picture
Image Setup Options
User’s Guide to the SPOT Cooled Color Digital Camera, 6/9/98
41
Gamma adjustment corrects an image by creating a new version of the original. To
create the new image, the Adjust Gamma (RGB) function reassigns the RGB values of
each pixel in the image according to the curve in the following graph:
Pixel Value - New Image
Pixel Value - Original Image
gamma = 1
gamma > 1
gamma < 1
full scale
full scale
0
0
The above graph demonstrates some of the basic principles of gamma adjustment:
§
Black (pixel value = 0) remains black at all gamma values.
§
White (pixel value = full scale) remains white at all gamma values.
§
Gamma values greater than one lift the darker areas of the original image into the
brighter areas of the new image.
§
A gamma curve is smooth: there are no unexpected jumps or cutoffs. This means that
when viewing a gamma adjusted image, you will be able to see the details (intensity
differences) in both the black and white areas of the image.
To use the Gamma Adjust option, follow these steps:
1.
Check the Gamma Adjust box on the Image Setup window.
2.
Enter a gamma value between .1 and 4.0. Although there is no formula for
determining a gamma value, gamma values are typically between 1.3 and 1.7
!
Note: Although the gamma adjust option is typically used to lighten the mid-tones
of an image, entering a value between .1 and 1 will darken the mid-tones.