Gamma Adjustments; Histogram Techniques - Canon CanoScan FB 1200S User Manual

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If you have a high-contrast image, or a black and white continuous tone
photograph that needs minor adjustment, the brightness and contrast
settings can improve the image.
If you have an image with multiple tones, such as most color images, the
brightness and contrast settings may not provide the desired results. The
Gamma, Histogram, and Special Tone Curves, which let you adjust the
midtone range and contrast as well as individual color ranges, may give you
more satisfying results.

Gamma Adjustments

The Gamma curve tool adjusts the midtones in an image in relation to
themselves. Adjusting the gamma setting can improve the visibility of color
and grayscale images, particularly ones with many midtones. Gamma values
above 1.00 lighten the midtones of an image, and values below 1.00 darken
the midtones. The gamma settings can range from 0.10 and 10.00, but for
most color photographs, the range is between 1.00 and 2.00. The
photographs scanned for the illustrations in this manual had many dark
midtones in the background, so a lower setting was used to enhance the
background.

Histogram Techniques

The histogram displays a graph of all the pixels in the image, sorted by tone.
The darkest pixels are grouped to the left, the midtone pixels in the middle,
and lightest tone pixels to the right. The triangular sliders at the bottom of the
histogram reflect the default settings of Black-Point 0, Mid-point 128, and
White-point 255.
The histogram tools let you change the distribution of dark-tone, midtone,
and white-tone pixels in your image, to correct the image. Any changes you
make are immediately displayed in the preview image.
Chapter 5
Scanning Techniques
65
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