Pyrocam III
HR
User Guide
Document No. 50361-001
Rev E
7/18/2017
Page 37
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 25,600 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 on 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. Spiricon will also provide you with a pair of files
that contain these tables upon request. These files form a backup source in case you
