Dalsa PC-30-02K80-R, Manual

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Piranha Color Camera User’s Manual 35
DALSA 03-032-10211-03 9/27/2007
The trilinear CCD sensor used in the Piranha Color camera has three linear arrays for
Red (R), Green (G) and Blue (B) color channel, respectively. The inter-array spacing
between color channels is 3 lines apart centre-to-centre. Because of the spacing between
the linear arrays, each array will have a slightly different view of an object that is passing
before the camera. Therefore, for each exposure, each color array in the sensor captures
an image of a slightly different area on the object.
The spatial correction process is used to properly reconstruct the full color (RGB) image
of the object. For example, assuming that the following parameters are used:
The system uses a magnification of 1/10, i.e., an area of 0.1 mm x 0.1 mm on the object
will have an image of 10 µm x 10 µm on the sensor;
The encoder is set to have a step of 0.1 mm in the movement of the web; i.e., the image
on the sensor will move 10 µm for each step of the encoder;
The image is line captured at each step of the encoder;
The moving object A from the view of line of Red channel to that of Green channel is 3
steps, i.e.:
3 steps x 0.1 mm/step x 1/10 magnification = 30 µm movement of the image on the
sensor.
There are 3 more steps to move the image of object A further from the Green channel
to the Blue channel.
To properly reconstruct the full RGB image of the object A, the user needs to combine
the Red channel data captured at line capture #0 with Green data captured at capture
#3 and Blue data captured at capture #6. A parameter
Line Delay is used to specify
which line captures should be combined to properly reconstruct the image. In the
above case, the
Line Delay is 3. In general,
Inter-array spacing (30 µm or 42 µm)
Line Delay = -----------------------------------------------------
Step of encoder (µm) x magnification
Red Tap 2
Red Tap
1
Blue Tap
1
Green Tap 2
Green Tap
1
30 µm (4k)
42 µm (2k)
30 µm (4k)
42 µm (2k)
The three color lines are
separated
30 µm (4k) or 42 µm (2k) apart
center to
center.