Basler L800k, User Manual, Page: 66 / 168

Operation and Features
3-26 BASLER L800
k
Draft
With the CCT+
With the CCT+ (see Section 4.1 ), you use the Shading Mode parameter in the Image
Enhancement parameters group to enable DSNU shading correction.
By Setting CSRs
You enable DSNU shading correction by writing a value to the Mode field of the Shading Mode
CSR (see page
4-39 ).
Section 4.2.2 explains CSRs and Section 4.3.1 explains using read/write commands.
3.9.1.3 PRNU Shading Correction
In theory, when a line scan camera with a digital sensor captures a line with the camera viewing
a uniform, light-colored target in bright light, all of the pixel values in the line should be near their
maximum gray value and they should be equal. In practice, slight variations in the performance of
the pixels in the sensor, variations in the optics and variations in the lighting will cause some
variation the pixel values output from the camera. This variation is know as Photo Response Non-
uniformity (PRNU). The PRNU shading correction feature on
L800
k
cameras can correct for the
variations caused by PRNU.
Generating a Set of PRNU Shading Values
Before you can use PRNU shading correction, you must generate a set of PRNU shading
correction values. To generate a set of values, perform the following steps:
1. Place a uniform white or light colored target in the field of view of the camera. Adjust your
lighting, optics, line rate, exposure mode, exposure time, gain and camera temperature as
you would for normal system operation.
2. Capture several lines and examine the pixel values returned from the camera. The pixel
values for the brightest pixels should be about 90 to 95% of maximum.
a) If the pixel values for the brightest pixels are at 90 to 95% of maximum, go on to step 3.
b) If the pixel values for the brightest pixels are not at 90 to 95% of maximum adjust your
lighting and/or lens aperture setting to achieve 90 to 95%.
c) If you can not achieve 90 to 95% output by adjusting the lighting and/or aperture, then
adjust the gain setting to achieve the correct output.
3. Capture several lines and examine the pixel values in each line. In each line, the values for
the darkest pixels must not be less 1/2 of the values for the lightest pixels in the line. (If the
values for the darkest pixels are less than 1/2 of the value for the lightest pixels, the camera
will not be able to fully correct for shading variations.)
a) If the values for the darkest pixels are not less than 1/2 of the value for the lightest pixels,
go on to step 4.
b) If the values for the darkest pixels are less than 1/2 of the value for the lightest pixels, it
usually indicates extreme variations in lighting or poor quality optics. Make corrections as
required.
4. Begin capturing lines either by generating an ExTrig signal to trigger line capture or by setting
the camera for free-run exposure.