XIIMUS 4K CL User Manual. Model: 4096CT. Version 1.4
4.2
Pixel correction unit
4.2.1 Description
The TVI XIIMUS series line scan cameras incorporate a user programmable real time pixel
correction unit, PCU. The PCU can be set up by downloading appropriate correction data via
the serial port to the camera.
The PCU can simultaneously perform white balancing, removal of pixel to pixel offsets
(PRNU & DSNU), lighting profile correction, removal of lens curvature and/or perform custom
operations on the output data of the camera.
4.2.2 Data
order
The correction data consist of 24 bits of data per colour pixel. Thus, for a full RGB-pixel the
user has to provide 72 bits of data. The data is sent to the camera via the RS-232 port
(Camera Link or separate 9-pin D-connector) starting with the first pixel in the line. Colours
are sent in RGB order to the camera. The start of the transmission to the camera is illustrated
below, each letter corresponds to one byte (8 bits) of data:
1 2
3
RRR GGG BBB
RRR GGG BBB
R..
Within a single colour pixel the data is ordered into a multiplier and an offset. The multiplier
consists of 14 bits and the offset of 10 bits. Thus, the three bytes that make up the correction
data for one colour pixel are internally divided on a bitwise level as follows:
R (byte 0)
R (byte 1)
R (byte 2)
Multiplier Offset
13
12
11
10
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
Please refer to the serial communication section of this document for additional information
on how to download correction data to the camera.
4.2.3 Correction
algorithm
The pixel correction unit (PCU) utilises a simple linear algorithm to correct the digital output
data of the camera. The formula below is used to correct all data once correction is enabled:
y
i
= (x
i
- b
i
)
x
a
i
y
i
= corrected output data
x
i
= camera raw data
b
i
= offset to be subtracted from the raw data
a
i
= multiplier for scaling of data
Since the offset
b
i
has a 10-bit range, it is possible to subtract greater values than the
camera dark level, which is typically around 40 DU. As an example, the user might want to
subtract the background of the image instead of the dark level.
© TVI Vision, 14 July 2006 page 12 ( 56 )