Canon CS-S 4.3 manual Gamma Adjustments, Histogram Techniques

CONTENTS		Chapter 5	59
		Scanning Techniques
GLOSSARY
INDEX
	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.

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