Allied Vision Technologies AVT Marlin, Техническое руководство, Страница: 91 / 247

Description of the data path
MARLIN Technical Manual V2.4.0
91
DSNU & blemish correction
(MARLIN F-131B only)
In order to further reduce the dark signal non uniformity (DSNU) of the
CMOS sensor to levels similar to CCD sensors, the MARLIN F-131B is equipped
with a special
DSNU reduction function , extending the shading correction.
The DSNU function applies an additive correction to every pixel in order to
equalize the dark level of the pixels. This function also enables correction of
single and double blemished pixels by replacing them with their neighbor-
hood pixels. DSNU and blemish pixel correction are generated simultaneously
but can be switched on/off separately.
The following screenshots demonstrate how it works:
On the left picture (without correction) it can be seen that over the complete
field of view there is a certain spread of the histogram, indicating non uni-
form dark pixels and blemished pixel(s) with brightness around 192(
Δ
). With
pure DSNU correction the spread is considerably smaller.
The table below shows the advanced register map, required to control this
functionality.
Having generated the correction data it is possible to separately control the
blemish pixel correction with the help of the following register:
The effect of the additional blemish correction can be demonstrated with the
next screenshot. Not only is the spread now smaller, there are also no pixels
above a considerably lower grey level (
Δ
at. app. 96 in this case).
Figure 48: Effect of DSNU correction
Note
L
Configuration
To configure this feature in an advanced register:
• See Table 112: Advanced register: DSNU on page 218.
• Table 113: Advanced register: Blemish on page 219