Canon FB630U ユーザーズマニュアル

You can adjust the gamma curve with two slide bars, one for contrast and one for
brightness.  Use this method to adjust an image before scanning if it is slightly out of
focus or too dark.

You cannot use this feature with a Black & White (Line), color or high definition
color file that has been set with ColorSync™.

Contrast is the difference between the lightest light and the darkest dark in the
image.  A high contrast setting creates a great difference between light and dark
shades, and there is a very sharp distinction between light and dark areas of the
image.  A low contrast setting creates a small differnce between light and dark
shades and the distinction between light and dark areas of the image are not so
obvious.

If the image appears slightly out of focus, increase the contrast settting for a
sharper image.  However, if the contrast setting is too high, shadows will blacken
and the highlights will wash out.

Brightness is the overall lightness or darkness of an image without changing the
contrast.  Adjust the brightness setting to change the overall lightness or darkness
of the entire image.  However, if the brightness setting is too high, the highlights
will wash out, and if too low the shadows will blacken.

Contrast = 128 (Normal)

Contrast = 100

Contrast = 170

Brightness = 128 (Normal)

Brightness = 80

Brightness = 190