UMAX Technologies Astra 2000U - Manual (Page 56)

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Highlight Bar
This setting defines the lightest (whitest) tones in the scanned
image. If you broaden the range that includes the highlight points,
the pixels within the newly specified range are be remapped
allowing you to see more details in a color/gray image.
Moving the slider on the scroll bar to the left increases the
brightness. Moving it to the right decreases the brightness. The
default setting is 255. The maximum highlight setting is 255; the
minimum is 1 (which is White).
Shadow Bar
The Shadow bar defines the darkest tones in the scanned image.
Moving the slider on the scroll bar to the left increases the
brightness in shadowed areas. Moving it to the right decreases the
brightness in shadowed areas. The default setting is 0. The
maximum shadow setting is 254 (which is Black), the minimum is
0.
Gamma Bar
The gamma bar alters the mid-range gray tones in the scanned
image. All optical devices, such as monitors and scanners, have
some variance in their light sensitivity characteristics. To get a
scanned image with good results, VistaScan provides Gamma
adjustment capabilities so you can compensate for this variance in
your scanner.
Moving the slider on the scroll bar to the right increases the
brightness of the mid-range gray tones. Moving it to the left
decreases the brightness of the mid-range gray tones. The default
setting is 1.2.
Reset Button
Click the Reset button to cancel the changes and return the value to
the default setting.