Kodak Document Scanner 9500 with Image Manager Integrator Manual page 100

Brightness indicates that calibration is functioning correctly and is
Brightness
directly affected by threshold. Loss in brightness in a scanned
image may indicate a need to recalibrate the scanner or to alter
threshold values. Brightness is measured, using the step wedge,
by counting the number of black and white steps.
A-61122/A-61124 March 1999 E-27