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5.8 Test Images
5.8.2 LFSR
The LFSR (Linear Feedback Shift Register) test image outputs a constant pattern with a
pseudo-random grey level sequence containing every possible grey level that is repeated for
every row. The LFSR test pattern was chosen because it leads to a very high data toggling rate,
which stresses the interface electronic and the cable connection.
Figure 5.22: LFSR (linear feedback shift register) test image
In the histogram you can see that the number of pixels of all grey values are the same.
Please refer to application note [AN026] for the calculation and the values of the LFSR test
image.
5.8.3 Troubleshooting using the LFSR
To control the quality of your complete imaging system enable the LFSR mode, set the camera
window to 1024 x 1024 pixels (x=0 and y=0) and check the histogram. The camera window can
also be set to a multiple of this resolution (e.g. 2048 x 2048 or 4096 x 3072) if the camera
model supports this resolution. If your image acquisition application does not provide a
real-time histogram, store the image and use an image viewing tool (e.g. ImageJ) to display
the histogram.
In the LFSR (linear feedback shift register) mode the camera generates a constant
pseudo-random test pattern containing all grey levels. If the data transmission is correctly
received, the histogram of the image will be flat (Fig. 5.23). On the other hand, a non-flat
histogram (Fig. 5.24) indicates problems, that may be caused either by a defective camera, by
problems in the acquisition software or in the transmission path.
In robots applications, the stress that is applied to the camera cable is especially high due to
the fast movement of the robot arm. For such applications, special drag chain capable cables
are available. Please contact the Photonfocus Support for consulting expertise.
MAN066 12/2018 V1.1
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