ALLIED Vision Technologies Marlin F-201 - Manual (Page 84)

Description of the data path
MARLIN Technical Manual V2.4.0
84
Shading correction
Shading correction is used to compensate for non-homogeneities caused by
lighting or optical characteristics within specified ranges.
To correct a frame, a multiplier from 1...2 is calculated for each pixel in
1/256 steps: this allows for shading to be compensated by up to 50 %.
Besides generating shading data off-line and downloading it to the camera,
the camera allows correction data to be generated automatically in the cam-
era itself.
How to store shading image
After generating the shading image in the camera, it can be uploaded to the
host computer for nonvolatile storage purposes.
The following pictures describe the process of automatic generation of cor-
rection data. The line profiles were created using MVTEC's ActivVision Tools.
• On the left you see the source image with non-uniform illumination.
• The graph on the right clearly shows the brightness level falling off to
the right.
By defocusing the lens, high-frequency image data are removed from the
source image, therefore its not included in the shading image.
Note
L
• Shading correction does not support the mirror func-
tion.
• If you use shading correction, don’t change the mirror
function.
Figure 42: Shading correction: Source image with non-uniform illumination