Image processing
4.2 Code verification
SIMATIC MV420 / SIMATIC MV440
64 Operating Instructions, 04/2013, A5E02371045-06
4.2.6.2 Calibrating the reflectance
Procedure
Calibrate the reflectance as follows:
1. Place the calibration plate in the viewing range of the reader.
2. Position the data matrix (with approximately 80% contrast) in the center below the reader
to achieve uniform lighting.
Note: If, during processing, the code to be read is always positioned in a region below the
reader that is clearly offset from the center, you should also position the data matrix in
this region. See also Normalizing the reader (Page 63) .
3. Enter the val
ues for contrast and maximum reflectance specified on the calibration card in
the appropriate boxes.
4. Start the calibration and, if necessary, follow the instructions for eliminating errors.
The following values are now calculated:
– Cell scaling:
The calibration card has a fixed cell size. From this, the calibration function calculates
the image scaling in milli-inches (mil) per pixel.
– Avg. gray scale value:
During calibration, a mean light histogram of the code is calculated. The mean light is
the average value of the background when the background and foreground are
separated by the minimum variance.
– Histogram peak low:
The peak value of the brightness of the image background.
– Histogram peak high:
The peak value of the brightness of the image foreground.
Recommended cell sizes for verification of 2D codes
Camera resolution Min. cell size Max. cell size
(16 x 16 cells)
Max. cell size
(32 x 32 cells)
640 x 480 pixels
(SIMATIC MV440 SR)
10 mil 30 mil 15 mil
1024 x 768 pixels
(SIMATIC MV440 HR)
7 mil 50 mil 25 mil
1600 x 1200 pixels
(SIMATIC MV440 UR)
4 mil 90 mil 45 mil
Calibration code takes
up approximately half
the image height.
Target size:
Min. 10 pixels/cell
Calibration code represented with 10 pixels/cell.
Target size: Max. 80 % of the image height
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