Shad-o-Scan 3001/4501 User Manual (Draft)
45
Teledyne DALSA
How to Create a New Gain Map
To use FFC to correct for system specific spatial intensity variations, new Gain maps should be
created and uploaded to the detector as part of the factory system calibration routines.
For optimal gain correction, the Gain reference map should be created at an exposure of
approximately 25% of the full scale output signal.
To create a new Gain map:
•
Average at least 16 images captured by the detector, without any object placed in the X-
ray beam.
•
Subtract the average of at least 32 dark images, without X-ray exposure, using the same
integration time (or frame rate) as used for capturing the X-ray images above.
•
Determine the mean value of the image, in the region (ROI) where the signal value (X-
ray exposure) is highest.
•
For each pixel, divide this mean ROI value by the (averaged) X-ray exposed pixel value at
that position (as floating point).
•
Multiply the pixel values by 4096 (2
12
), the Unity Gain Factor.
•
Store the resulting pixel values (as 16-bit integer values) as the new Gain map, preceded
by the appropriate file header information.
