Balluff MATRIX VISION mvBlueNAOS, Technical Manual

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1.18 Use Cases 157
No oscillation occurs, regardless of DC ambient vs. AC indoor light.
This operation mode is known as flicker-free or flicker-less operation.
What it mainly does is to adjust the frame frequency to precisely the frequency of the power line. Usually the
line frequency is very stable and therefore is the harmonic frequency difference of the two signals are very slow;
probably in the range of
<
0.1 Hz.
The fact that we do not know the phase relation between the two frequencies means that we scan the alternating
ambient light source with our camera. The shorter the exposure time, the more we see a slow change in brightness.
Using AutoExposure/AutoGain can completely eliminate this change because the frequency of change is very low.
That means it will be legal if we calculate a brightness difference in one picture and apply it for the next one, because
the change is also valid in the next one; as we fulfill the Nyquist theorem.
If we use an arbitrary scanning frequency like 20 fps or whatever your algorithm and data flow is accepting, is wrong
in this aspect and leads to oscillations and undesired flicker.
Pointing to a 60 Hz display with flashing backlight an oscillation of 10 Hz can be seen of course.
Figure 3: wxPropView - Intensity plot while pointing the camera to a 60 Hz display
1.18.2.3.3 Conclusion
To avoid oscillations, it is necessary to adapt the camera frequency to the frequency of AC light. When using auto
expose a flicker-free mode (timer based external trigger) is needed. If the camera is used throughout the world it
is necessary that the frequency of AC light can be set in the software and the software adapts the camera to this
specific environment.
1.18.2.4 Working with binning / decimation
With binning / decimation it is possible to combine / reduce adjacent pixels vertically and/or horizontally. Depending
on the sensor, up to 16 adjacent pixels can be combined / reduced.
See also
https://www.matrix-vision.com/manuals/SDK_CPP/Binning_modes.png
To optimize the sensor speed, the firmware will check if the binning / decimation functionality is provided by the
sensor. If it is available it will use the sensor for binning / decimation, if not, binning / decimation will be processed
in the camera's FPGA.
If a binning / decimation combination is not possible, the following note will be displayed:
In this case no acquired images will be displayed until you have changed the settings.
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