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Description of the data path
OSCAR Technical Manual V2.4.0
75
Automatic generation of correction data
Requirements
Shading correction compensates for non-homogeneities by giving all pixels
the same gray value as the brightest pixel. This means that only the back-
ground must be visible and the brightest pixel has a gray value of less than
255 when automatic generation of shading data is started.
It may be necessary to use a neutral white reference, e.g. a piece of paper
instead of the real image.
Algorithm
After the start of automatic generation, the camera pulls in the number of
frames set in the GRAB_COUNT register. Recommended values are 4, 8 or 16.
An arithmetic mean value is calculated from them (to reduce noise).
After this, a search is made for the brightest pixel in the mean value frame.
The brightest pixel(s) remain unchanged. A factor is then calculated for each
pixel to be multiplied by, giving it the gray value of the brightest pixel.
All of these multipliers are saved in a shading reference image. The time
required for this process depends on the number of frames to be calculated
and on the resolution of the image.
Correction alone can compensate for shading by up to 50% and relies on
12 bit pixel data to avoid the generation of missing codes.
Thus the output after the shading correction has potentially 11-bit accuracy.
How to proceed:
Figure 33: Automatic generation of a shading image
Set GrabCount to # of
desired frames
Set BuildImage Flag to true
Poll SHGD_Control
Register until Busy and
BuildImage Flag are
resetted