FLIR Tau Camera TAU-0035-00-10 User Manual page 29

Tau User's Manual
Flat-Field-Correction Mode:
internal mechanisms for periodically improving image quality via
a process called flat-field correction (FFC). During FFC, a
shutter briefly blocks the detector array, presenting a uniform
temperature (a flat field) to every detector element. While
imaging the flat field, the camera updates correction
coefficients, resulting in a more uniform array output. The
analog video image is frozen during the entire process, which
takes less than a half second, and resumes automatically
thereafter. Repeating the FFC operation often prevents the
imagery from appearing "grainy". This is especially important
when the camera temperature is fluctuating, such as
immediately after turn-on or when ambient temperature is
drifting. FFC can be controlled manually at any time using the
Do FFC command button.
Tau provides three FFC modes:
Auto: In the Automatic FFC mode, the camera performs FFC whenever its
temperature changes by a specified amount or at the end of a specified period of time
(whichever comes first). When this mode is selected, input windows are available in
the FLIR Camera Controller GUI for specifying the temperature change and the
number of frames that trigger automatic FFC. The temperature change is specified in
degrees, with valid values in the range 0 to 100 in 0.1 degree increments. The time
period is specified in analog video frames (33ms NTSC, 40ms PAL), with valid values
in the range 0 to 30,000 frames. A setting of 0 frames for the FFC Interval will allow
the Tau camera to only perform an FFC based on the values in Temp change. The
second set of Auto FCC parameters labeled Low Gain apply to Tau-P Cameras with
the auto gain switch enabled.
Note
FLIR recommends using the factory default values for the two automatic-FFC parameters if
possible. These values were selected to maintain a high degree of image quality over all
camera operating conditions.
Manual: In Manual FFC mode, the camera does not perform FFC automatically based
on specified values of temperature change or expired time. The FFC will be performed
once upon startup then again using the internal shutter when the "Do FFC" button is
clicked.
Note
Large camera temperature excursions cause the camera to perform the FFC operation (even
with Manual FFC mode selected), typically at temperature crossings near 0°C and 40 °C.
External: In External FFC mode a uniform source (blackbody) must be placed in front
of the camera. The image of this uniform source will be subtracted from all
subsequent images. This feature is useful if there are lens or lens mount non-
uniformities that are not corrected by an internal FFC. The camera will not perform an
FFC process on startup if the saved state of the camera is External mode FFC.
Many customers have found that the palm of their hand or a table is an adequate
uniform source to perform an External FCC.
TAU-0035-00-10, version 150
3—Basic Operation of the Tau and GUI
Tau cameras include
June 2011 3-13