30
How to proceed:
Set GrabCount to number of
frames used to calculate
shading image
Set
BuildImage
to "true"
Poll
SHGD_Control register until
Busy and BuildImage flags
have been reset automatically
Figure 27 automatic generation of a shading image
L
The maximum value of GRAB_COUNT depends on the type of camera and the number
of existing frame buffers. GRAB_COUNT is also automatically corrected to the power
of two.
L
The SHDG_CTRL register should not be queried at very short intervals, because each
query delays the generation of the shading image. A good interval time is 500 ms.
The following pictures clarify the process of automatic generation of correction data.
The line profiles were created using MVTEC’s “ActivVision Tools”.
Figure 28 Source image with non-uniform illumination
On the left you see the source image with non-uniform illumination. The line view in
the picture on the right clearly shows the brightness level falling off to the right.
The correction sequence controlled via “Directcontrol” uses the average of 16 frames
(10H) to calculate the correction frame. By unfocussing the lens high-frequency image