Pyrocam IV Operator’s Manual Document No. 50337-001 Rev F 2/21/2017 Page 38
APPENDIX D – GAIN CORRECTION
Gain Correction Overview
This procedure will assume that the user is familiar with the operation of the Pyrocam.
This procedure will outline how to go about creating a gain correction table for
downloading to the Pyrocam. This table will be permanently stored in your Pyrocam’s flash
memory. How to save the table to a file is also described.
Pulsed and Chopped
The following procedure is common for both Chopped and Pulsed operating modes.
However, the Pyrocam can store separate gain correction tables, one for Chopped mode
and one for Pulsed mode. The table being loaded or saved is based on the setting of the
Chopped / Pulsed selector. Only one mode can be in effect at a time.
What is Gain Correction?
A gain correction table is a list of correction factors for each of the 102,400 pixels that
form the Pyrocam imager array. The object of this table is to cancel out local response
variations in the detector array, yielding a more uniform response overall. Gain
correction table factors are limited to a range of 0.50 to 2.00. Thus pixels whose
response is less than ½ of the mean response cannot be successfully gain corrected.
Such pixels should be dealt with using Bad Pixel Correction. In general, pixels that
deviate significantly from the mean response should be treated as bad pixels. See
APPENDIX C.
NOTE: The relationship between bad pixel correction and gain correction is important to
understand. Bad pixel correction is usually turned on. Bad pixel correction has a
lesser impact on overall camera throughput performance than gain correction does.
This is because bad pixel correction deals with a small number of pixels, while gain
correction affects every pixel. In pulsed mode (above ~35Hz) you will see a
slowdown in camera frame rate output, especially at the higher pulse rates.
Setup
Performing an accurate gain correction requires the detector to be uniformly illuminated
at a relatively high level of intensity. If such a source of illumination is not available, it is
best to not attempt to build a gain correction table. If this is the case, results will
probably be worse than the normal detector’s non-uniformity.
Factory Gain Correction Files
Most Pyrocams will come with a factory installed chopped mode gain correction table
stored in its Flash memory. However, no pulsed mode gain correction table is supplied.
This is because the gain correction affect is dependent upon pulse width and pulse rate
timing. If a pulsed gain correction file is supplied, it will be a null file, meaning it contains
a gain correction table that tells the Pyrocam that it is not fitted with a gain correction
table. If the null file is downloaded to the Pyrocam, the Gain Correction on/off button
will appear disabled (gray), meaning the Pyrocam has no gain correction table loaded.
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