Shad-o-Scan User Manual, Rev04
43
Shad-o-Scan 3001/4501 X-Ray Detector
Teledyne DALSA
Example 1: to update the actual dark reference map, for example to correct for
changing detector temperature conditions, set
FFC New Dark Weight
to 20 and
Snap
a
few dark images every 5-10 minutes.
Example 2: to create a fully new dark reference map, for example when the
integration time is significantly changed, first set
FFC New Dark Weight
to 100 and
Snap
a dark image to overwrite the old dark reference map. Then set
FFC New Dark
Weight
to 10 and
Snap
at least 32 dark images to average out the random noise in the
dark image.
Ensure that the detector is not exposed to X-rays during capturing of new dark images, as
this will significantly impact the usability of the updated dark reference map and the
quality of the FFC operation.
Disable DPC while creating new or updated dark and gain reference maps for FFC. This will
ensure that FFC will deliver optimal results.
Volatile memory space of the detector is limited. This may cause a Gain/Dark map
selection issue with map 3 when all customer maps (map 0
–
map 3) are used for Full
Resolution modes.
After changing the
Factory/Customer Map Select
mode, the detector needs to transfer the
selected Factory/Customer Maps to volatile memory. When this process is finished, the
detector’s network conn
ection needs to be re-established.
FFC and/or DPC processing will be disabled in case not all reference maps for the selected
mode are available or the wrong map is selected in
Manual Map Select
mode. The
FFC
Processing
and/or
DPC Processing
field will show
Not Active.
FFC Calculation
The pixel value after FFC correction, FFCVal(x,y), is given by the following formula:
FFCValue(x,y) Pixel value after FFC
PixelVal(x,y) Pixel value in raw image
DarkVal(x,y) Pixel value in Dark map
GainVal(x,y) Pixel value in Gain map
UnityGainFactor
Value in map representing unity gain, as a power of 2
Offset
Fixed value added to prevent noise clipping
File Format
The file format of a dark and gain maps are as follows: A header indicates the
specification of the dark or gain map. The 32 bytes header format is described below:
