Low Smear - Basler A102K User Manual

3.5 Low Smear

In applications where a CCD sensor is
under constant illumination, high-
contrast images
unwanted effect that converts dark
pixels into brighter ones. This effect is
commonly called "smearing".
With the help of the Low Smear
feature on the A102
reduced in the upper part of the
image. The effect of the Low Smear
feature is illustrated in Figure 3-9.
The left image was captured without
the low smear feature. There is
smearing both in the upper and lower
part of the image.
The right image was captured with low
smear active. There is no smearing in
the upper part of the image.
Smearing is caused by two things:
• an unwanted post-exposure of the pixels when they are being moved out through the vertical
shift registers. Only those pixels located above the area of exposure on the CCD array which
must pass the light source during shift-out are subject to post-exposure. For this reason,
post-exposure only produces smearing in the lower part of the image. (Remember that the
lens causes the image on the sensor to be inverted, so the lower part of the image is at the
top of the sensor.)
• an unwanted existing accumulation of charges in those shift registers which have passed
points of constant illumination during the previous frame transfer and have thus been
exposed before they receive the next pixels. These unwanted charges add to the next pixels
when these pixels are shifted from the sensor cells into the vertical shift registers. This
causes smearing in the upper part of the image.
The amount of unwanted charges accumulated in the shift registers grows with the amount of
exposure. For that reason, smearing does not appear under short-term illumination such as flash
light. It only appears under constant illumination.
The Low Smear feature cannot be activated or deactivated. It is active all of the time. To use this
feature to its best advantage, the frame rate must not exceed a maximum setting. The setting can
be calculated using the below equations.
First, you need to calculate the frame transfer time based on the height of the area of interest (AOI)
using this formula:
T(f) =
where:
k
BASLER A102
may show an
, smearing is
k
ξ
Ε
646.5 µs + 1040 AOIH –
T(f) = frame transfer time
AOIH = number of lines in the AOI
DRAFT
Figure 3-9: Full Smear (left), Low Smear (right)
⌠ ζ ξ Ε
Φ
12.04 µs + AOIH
Operation and Features
Φ ⌠ ζ
+ 1 64.22 µs
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