Rockwell Automation 5370-OCR2 PAK - Manual (Page 58)

Chapter 5
Creating and Editing Fonts
5–23
•
Variations in print density
Changes in print density can reduce the contrast between characters and
the background. This is usually not a problem if sufficient contrast exists
in the first place, which can be achieved by ensuring that the lighting is
even across the field of view, and by adjusting the camera’s light
references.
Important: Variations in print density can also compensated for by using
the CVIM2 Image Tool to preprocess the image for the OCR Tool. Refer
to Appendix B for more information.
When the characters become darker or lighter, the characters in the
thresholded image tend to grow or shrink. The system will accommodate
this if there is a sufficiently wide border of don’t-care pixels around the
edge of the character in the taught character pattern.
•
Size changes
Minor changes in character size can be accommodated by leaving a
sufficiently wide border of don’t-care pixels around the edge of the
character in the taught character pattern. Major changes in character size
require changing the character size of the OCR Tool using the Rescale
option, and cannot be accommodated from one image to the next.
•
Smudges
Smudges appear as extra ink or dark material in the region of the
characters. Major smudges will be rejected, but the system can allow for
minor smudges if the character correlation percentage is reduced.
•
Background contrast changes
Often when a product changeover occurs, the material on which the
characters are printed changes. If the change in contrast is too large, it
may be necessary to adjust the OCR Tool’s threshold. This can be
performed during a changeover, but not from one image to the next.
Important: Background contrast changes can also compensated for
using the CVIM2 Image Tool to preprocess the image for the OCR Tool.
Refer to Appendix B for more information.