Epson ES-1000C Reference Manual page 132

Explanation:
This command sets the brightness level of the scanned image data.
Seven values for i are available: 00 , 01 , 02 , 03 , FF , FE and
H H H H H H,
FD .
H
The graph below shows the differences between the brightness
settings when gamma correction is set for the CRT Display A setting.
Note:
The brightness parameter is not available if a user-defined gamma
correction table (see ESC Z) is selected.
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Command Reference