3—Basic Operation of the Tau 640 and GUI
Tau 640 User’s Manual
3-12
June 2011
TAU-0640-00-10, version 110
Flat-Field-Correction Mode:
Tau 640 includes 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 640 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. The second set of Auto FCC parameters labeled
Low Gain
apply to Tau 640-P cameras with the auto gain switch enabled.
Note
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 whenever the
Do FFC
button
is clicked. At camera temperature excursions beyond 0°C and 40 °C, a
Do FFC
command is recommended in order to maintain image quality.
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.
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.
