SVS-Vistek 926.15hr387*XGE Series, User Manual

Page: 36 / 122

SVS-VISTEK
Feature description 36
5.2.7 Shading Correction
The interactions between objects, illumination, and the camera lens might
lead to a non-uniform flatfield in brightness. Shading describes the non-
uniformity of brightness from one edge to the other or center towards
edge(s).
This shading can be caused by non-uniform illumination, non-uniform
camera sensitivity, vignetting of the lens, or even dirt and dust on glass
surfaces (lens).
Shading correction is a procedure to create a flatfield image out of a
non-uniform image regardless of the reasons of the non-uniformity.
Before doing shading correction, make sure your lens is clean and in
perfect condition. If the lens is not clean or the lighting not uniform, the
algorithm tries to compensate these as well – resulting in a wrong shading
table and visible artifacts, loss of details or local noise in the final image.
In theory there are several ways to correct shading:
>
In the host computer: Significant loss of dynamic range, colour
ruptures
>
In the camera, digital: better (smoother) shading than on the
computer side (10 or 12 bit), loss of dyn range
>
In the camera, analog: Change gain/offset locally on sensor to get
optimum shading correction with only small changes in dynamic
range
Figure 4: Original and shading corrected image