3.3. System validation
3.3.1. Gain control
Gain profiles shown in Fig. 6 demonstrate effects of ambient
lighting. A high gain corresponds to low ambient light intensity.
The intensity for incandescent lighting shows a constant rate of
rise from 400 to about 520 nm and then plateaus. For fluorescent
lighting, there are peaks in gain that correspond to wavelengths
where relative intensity of ambient lighting is low. The peaks at
475, 520, and 675 nm correspond to the default wavelengths for
auto cycling. Gains rise again for wavelengths below 475 nm; how-
ever, there is spillover of reflected energy from the LEDs up to
around 465 nm that precludes using these lower wavelengths for
fluorescence imaging. The peak at around 570 nm suggests that
570 nm could also be a candidate wavelength for fluorescence
imaging depending on target response characteristics. The time
needed to acquire the necessary images and to calculate a new gain
profile is approximately 40 s.
Fig. 7 demonstrates the ability of a gain profile to normalize
measured intensity across wavelengths. Spectral responses using
a white HDPE cutting board as the target were acquired using fixed
camera gains of 0 and 4, and the HDPE Fluorescent gain array in
Fig. 6.