Hardware manual

OCR Impact Reference Guide
Datalogic Automation Inc. 3-186
• Characters must have at least a one pixel column of vertical separation between them. If they overlap
vertically, then they can not be read. However, if the characters are on a fixed pitch, then the "Maxi-
mum Character Width" parameter can be used to force them to break apart. In some cases, filter pre-
processing can also be used to separate characters. Characters should be a minimum of twenty-eight
pixels high for best results.
Reading Characters
When you click Run, the tool will read the characters within the ROI. Any unread characters show up as the
Substitution Character in the output string. If any character can not be read or does not match the verification
string (if there is one), then the "Successful Read" output is False. You can adjust the input parameters if you
get too many mismatches or unreadable characters. You can also add unreadable characters to the Font
Library, if desired.
As the tool verifies each output character against the verification string, it searches toward the right in the
verification string until it finds a match. If it finds a match, then it reports the character as successfully read
in the “Character Success List” output. This allows it to skip over missing characters in the image and still
verify the remaining characters. If it reaches the end of the verification string without finding a match, then
it treats the character as an extra character by reporting it as a failure in the “Character Success List” output
and skips over it in the matching process so that the next character in the output string can still match the
next character in the verification string.
Verification
Use the "Verify String" input value to verify that the output string is the expected string. If any character
does not match the verification string, then the "Successful Read" output is False. The "Verify String" can
also be used as a training string. If, during verification, a part fails, you can stop and train on that image and
the tool will use the verification string.
Font Library Tab
The Font Library tab displays all the characters that the OCR tool has been trained to recognize. Select a
character to type a new name for a character, click the Delete Character icon to delete a character, or click
the Delete All Character icon to delete all the characters.
Threshold Types
Adaptive Threshold - Bright Characters
This sets the upper and lower thresholds automatically based on all the grey levels in the ROI. The lower
threshold is set to a value somewhere in the valley between the bright pixel and the dark pixel peaks. The
exact value depends on the statistics of the two peaks. The upper threshold is set to 100%. Bright pixels are
thus considered in-range. This setting is best used when looking for a bright part of an image with non-uni-
form grey levels. In this example, the lower threshold would be approximately 50% and the upper threshold
100%.
Adaptive Threshold - Dark Characters
Threshold
Range
Lower
Threshold
Upper
Threshold
0100