I.R.I.S. IRIScan Pro 3 Wi-Fi User Guide - Manual (Page 51)

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Brightness Adjusts the lightness or darkness of an image. The higher the value,
the brighter the image. Drag the slider to the right or left to increase
or decrease the brightness. The range is from –100 to +100.
Contrast Adjusts the range between the darkest and the lightest shades in the
image. The higher the contrast, the bigger the different grayscale.
Drag the slider to the right or left to increase or decrease the
contrast. The range is from –100 to +100.
Brightness: -50 Brightness: 0
(Normal)
Brightness: +50
Contrast: -50 Contrast: 0
(Normal)
Contrast: +50