Riso HC5500 Series User Manual page 62

Details
Adjusts the Gamma value for each colour of RGB.
Click [Details] to display a check mark and click the [Change details] button to display the
[Gamma control Details change] window.
You can click
A smaller value makes lighter images and a larger value makes darker images.
The initial setting is 0.
This item is different from the general concept of Gamma control.
)p.2-18
2-20
or to adjust the value from -25 to +25.