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Reference Manual ATOM one SSM500
advanced feature that requires the right measurement equipment to be setup correctly
(see setup instructions at the end of this chapter).
The lens shading correction uses a correction function to increase the gain in the outer
image areas. The parameter k configures the natural vignetting compensation (cos4
compensation), a higher value will result in a higher compensation. The parameters offset
and slope configure the artificial vignetting compensation. If the value for offset is
increased, the radius where the compensation starts will be increased (moved to the
image border). The higher the slope, the stronger is the compensation. The values k and
slope range from 0.0 to 2.0, the offset from 0.0 to 1.0.
Please note that all values have to be passed as fixed point numbers in Q2.30 format, that
means a value of 0.67 equals: 0.67 * 2^30 = 719407022
Value
Minimal
Maximal
Default
Comment
Enable
0
1
0
Enables or disables the lens shading
correction module
K
0.0
(0)
2.0
(2147483648)
0
Corrects natural vignetting, has to be
given in Q2.30 fixed point format
Offset
0.0
(0)
1.0
(1073741824)
0
Corrects artificial vignetting, has to be
given in Q2.30 fixed point format
Slope
0.0
(0)
2.0
(2147483648)
0
Corrects artificial vignetting, has to be
given in Q2.30 fixed point format
To setup the lens shading correction, follow these steps:
1. Point the camera at a homogeneous light source.
2. Connect the camera to a wave monitor and select a line in the middle of the image,
you should see a decrease in luminescence towards the edges of the image.
3. Enable lens shading correction, start with the parameters K, Offset and Slope set to
0.
4. Now turn up the K factor, this should correct the lens shading in the middle area of
the image, the edges will probably still be not ideally illuminated. Make sure to not
overcompensate, this will create a wavelike appearance of the luminescence on the
monitor.
5. Set the Offset to 0.5 and set to slope to a high value like 1.5, you should now clearly
see where the compensation starts. Now adjust the slope until you hit the point
where the luminescence starts decreasing. Finally decrease the slope until the
result is not overcompensated anymore.
6. Make fine adjustments until you are satisfied with the result.
Please note that, depending on the optical lens used, the aperture and focal length have
influence on the lens shading, so you should use your default setup for configuring the
compensation. Also it might be helpful to turn of the auto exposure during the setup.
