The linearity of the MIDI detector is an indicator if the quality of
its response curve. The pipeline calculate the coefficients of the
polynomial fit of the average pixel value (over a windowed area) of the
detector for 3 different configurations (image, prism and grism). The
polynomial fit is:
I(t) = A_0 + A_1 * t + A_2 * t^2, where I is the detector level in
ADU and t the time in millisecond.