Avision AVA3 400 - Manual (Page 41)

Scanner Operation
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Contrast: Adjusts the range between the darkest and the
lightest shades in the image. The higher the
contrast, the bigger the different gray scales.
Decrease your Contrast Normal Increase your Contrast
Gamma: Adjusts the midtone of the image without losing
details of the lightest and the darkest areas.
Gamma Value: 1.0 Gamma Value: 1.4 Gamma Value: 2.0