2.2.1. Gain
Autogain is disabled in the camera to ease comparison of results
across locations and time. To maximize dynamic range in images,
the exposure time is normally the inverse of the frame rate
(default: 15 frames per s) with a small adjustment made for data
transfer timing. An automated routine allows an array of gains to
be calculated and stored at 5 nm intervals from 400 to 720 nm,
inclusive. The routine adjusts the gain at a particular wavelength
until the average pixel intensity of the center region of the image
is just less than a selected threshold, normally 1024. The points
used to define the coordinates of the center region are the points
one-third and two-thirds the distance along the horizontal and
vertical image dimensions. The camera directly supports integer
gains of 0–32. Negative gains are implemented in software by
using a hardware gain of zero and reducing exposure time using
the empirically-derived formula: