Note: For PL-A and PL-B Cameras Only
Flat Field Correction (FFC) is a technique for reducing the effects of sensor pattern noise (FPN Fixed Pattern Noise, and PRNU – Photo-Response Non-Uniformity) and lighting non-uniformities. The camera comes with factory calibrated FFC parameters. A customer site-specific FFC calibration can be performed using an FFC field tool called the FFC Wizard. The following figure shows a block diagram of the FFC algorithm. An offset and gain are applied to the incoming pixel to generate a corrected pixel. The offset and gain are derived from the dark field and flat field obtained during FFC calibration.
When to Use
A FFC calibration should be done in the field when you want to optimize the image quality for your application and camera settings. The FFC calibration that Pixelink supplies corrects for the sensor pattern noise, but does not correct for lighting or lenses. The reason for this is that lighting is very application specific. FFC is also dependent on several camera settings. Settings such as gain, integration time and brightness all have an impact on the FFC values applied to an image.
Another point to consider is that all digital cameras are temperature dependent. Thus you should allow the camera to settle at its steady-state operating temperature prior to performing a FFC calibration.
When Not to Use
A given FFC calibration can improve an image over a range of camera settings, but once outside the range (and this range is application specific) the FFC may actually make the image worse. For example, if a user calibrates FFC at a gain of 0dB, using a 1ms integration time, and then uses the camera at a gain of 18dB and 1000ms integration time, FFC will no longer improve the image.
How to Use
In the Pixelink Capture OEM application, the LUT and FFC tab allows the user to disable and enable FFC. The FFC Wizard is used to perform a site and camera setting specific FFC calibration. You need to pay careful attention to the FFC Wizard messages during the first FFC calibration. For example, the Wizard requires that the camera settings be stored in Channel 1 prior to the calibration
You need to store the parameters in the memory channel prior to performing field FFC calibration. This pop up window, shown above, is obtained through the Camera Save Camera Settings Menus.
The duration of the FFC calibration is sensor size dependent, but typically takes several minutes to complete. The figure below shows the first pop-up window in the FFC Wizard.