Epson GT-6500 EN - Manual (Page 28)

Gamma correction
Gamma correction is a function that adjusts the light intensity so it
matches the output device.
Although an image may display clearly on your CRT display, your
printer may not produce it the same way. Since image reproduction
depends on the output device (CRT, printer, etc.), gamma correction
adjusts the light intensity so the image is faithfully reproduced on the
output device you are using. The term gamma refers to the ratio
between the input and output light intensity.
Display A Display B
Printer A Printer B Printer C
1-14 Overview