User`s manual

Basic Operation & Standard Features
3-26 BASLER A620
f
DRAFT
3.9 Corrections for Sensor Characteristics
The Basler engineering team used its extensive experience to build in corrections for some of the
characteristics exhibited by the sensor used in A620
f cameras. The result is a camera that
produces good image quality under normal conditions especially when compared to competitive
cameras with the same sensor. Some of the corrections made on the A620
f include:
• Fixed pattern noise correction via a calculated offset map.
• Correction for odd/even pixel mismatch that could be caused by the two banks of column
amplifiers used in the camera’s sensor.
• Compensation for the drift in sensor offset that could be caused by temperature variation in
the camera’s environment.
Even though the corrections included in the camera produce good image quality under normal
conditions, two undesirable effects may still be exhibited when the camera is operated under
extreme conditions. The first is a shutter efficiency effect and the second is a dark signal non-
uniformity effect.
Shutter Efficiency
Under some extreme conditions, such as when the camera is set for full resolution, a shutter
setting less than 50 and the lighting is very bright and continuous, the sensor’s electronic shutter
does not “close” efficiently. In these situations, after the normal exposure time is complete, the
pixels will continue to expose slightly during sensor readout. This causes the pixel values in
captured images to be higher at the bottom and lower at the top and the images will appear light
at the bottom and dark at the top.
The amount of unwanted exposure that will occur during readout depends on the brightness of the
light source and the ratio of the sensor readout time to the integration time. The effect will be most
noticeable when images are captured with a combination of a large AOI, bright lighting and a short
exposure time. Using smaller AOIs decreases the sensor readout time and minimizes the effect.
A recommended work around for the shutter efficiency effect is to use flash lighting that is bright
during the sensor’s normal exposure time and dark during sensor readout.
DSNU
At shutter settings of approximately 200 or less, the dark signal non-uniformity (DSNU)
characteristics of the sensor have no effect on the image. At shutter settings above 200, DSNU
begins to have an effect and the effect increases as the shutter setting is increased. At very high
shutter settings, the effect of DSNU may become apparent in captured images. The DSNU effect
becomes more noticeable at high gain settings, when the camera is operating in higher
temperature environments and the sensor gets hot, or when the camera is set for a 16 bit output
mode.
The effect of DSNU is usually described as “white spots” or “hot spots”, i.e., some pixels appear
lighter than they should be.