Basler Vision Technologies Sprint Series, Руководство пользователя

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Features
Basler sprint Mono Cameras 121
6.3 Shading Correction
In theory, when a digital camera captures an image of a uniform object, the pixel values output from
the camera should be uniform. In practice, however, variations in optics and lighting and small
variations in the sensor’s performance can cause the camera output to be non-uniform even when
it is capturing images of a uniform object. The camera is equipped with a shading correction feature
that allows it to correct the captured image for variations caused by optics, lighting, and sensor
variations. There are two types of shading correction available on the camera, DSNU shading
correction and PRNU shading correction. You can set the camera to do only DSNU correction, to
do only PRNU correction, or to do both types of correction.
DSNU Shading Correction
When a line scan camera with a digital sensor captures a line in complete darkness, all of the pixel
values in the line should be near zero and they should be equal. In practice, slight variations in the
performance of the pixels in the sensor will cause some variation in the pixel values output from the
camera when the camera is capturing lines in darkness. This type of variation is know as Dark
Signal Non-uniformity (DSNU). DSNU shading correction corrects for the variations caused by
DSNU.
PRNU Shading Correction
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 in the
pixel values output from the camera. This type of variation is know as Photo Response Non-
uniformity (PRNU). The PRNU shading correction feature on the camera can correct for the
variations caused by PRNU.
The Factory Shading Value File and the User Shading Value File
To perform DSNU and PRNU shading correction, the camera needs a set of DSNU and PRNU
shading correction values. The camera has two files in its nonvolatile memory where it stores the
values that it needs to perform shading correction.
The first shading values file is called the "factoryshading" file. This file contains a complete
collection of the values needed to perform both DSNU shading correction and PRNU shading
correction. The values in this file are generated during the camera’s factory setup procedure and
they essentially serve as default shading values. The values in the factory file are optimized for
performing shading correction with "standard" optics and lighting. Using the factory settings will give
you reasonable DSNU and PRNU shading correction performance in most situations. The factory
shading values file is in a protected area of the camera’s memory and can’t be changed. One
advantage of the factory values is that they serve as a good default.