Dalsa Piranha4 User Manual page 106

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Use a white material that has no texture, such as a non glossy plastic.
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If you must use white paper, make sure it is moving during the calibration process. If
you do not do this, your image will have vertical stripes.
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Another way to prevent the vertical stripes is to slightly defocus the lens while the
calibration is performing and then to refocus the lens once it has finished.
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Calibration is easily performed using the 'cpa' command.
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The cpa command has 3 parameters.
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The first parameter is a selection between:
▪
▪
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We recommend that the second option is used to correct for any image non uniformity
due to the lens and setup.
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The second parameter is the number of lines you want to average over. Use a value of
4096 to achieve the best average.
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The third parameter is the 12-bit target value you want to achieve after calibration.
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The cpa command takes several seconds to complete. The slower the line rate, the longer it will
take.
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On completion of the 'cpa' command, you should see an image from the camera that is flat field
corrected with the lens at the target level you set.
You are now ready to evaluate the image quality of the P4 camera under your operating conditions.
'0' – Per pixel FFC calibration
'1' – A low pass FFC calibration