Teledyne 4M User Manual page 43

Falcon2 4M, 8M, and 12M Camera User's Manual 43
An important note on w indow blemishes:
When flat field correction is p erform ed , w ind ow cleanliness is p aram ou nt. The figu re below show s an
exam p le of w hat can hap p en if a blem ish is p resent on the sensor w ind ow w hen flat field correction is
p erform ed . The blem ish w ill cast a shad ow on the w afer. FFC w ill com p ensate for this shad ow by
increasing the gain. Essentially FFC w ill create a w hite sp ot to com p ensate for the d ark sp ot (shad ow ). As
long as the angle of the incid ent light rem ains u nchanged then FFC w orks w ell. H ow ever w hen the angle
of incid ence changes significantly (i.e. w hen a lens is ad d ed ) then the shad ow w ill shift and FFC w ill
m akes things w orse by not correcting the new shad ow (d ark sp ot) and overcorrecting w here the shad ow
u sed to be (w hite sp ot). While the d ark sp ot can be p otentially cle aned , the w hite sp ot is an FFC artifact
that can only be corrected by another FFC calibration.
Figure 15: Sp ectral d istribu tion of light sou rce u sed d u ring calibration of color cam eras only. This
corresp ond s rou ghly to a 5200 K color tem p eratu re.
Teledyne DALSA 03-032-20107-01