Reference Manual
Chapter
4
IVC-2D
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123
Matching
Reference label.
Label with defect.
Difference image.
There are four options for the difference image:
1.
Diff
The absolute value of the intensity difference in each pixel. This option is prefer-
able if the pattern’s mean intensity is part of the inspection purpose.
2.
Normalized diff
Like the Diff mode, but compensated for changes in mean intensity and contrast.
This option is preferable if uniform contrast variations shall be disregarded. (It is
not effective to remove local illumination changes in the image.)
3.
Diff with edge suppression
Like the Diff mode, but less sensitive to edge artifacts from the pattern.
4.
Normalized diff with edge suppression
Like the Normalized diff mode, but less sensitive to edge artifacts from the pat-
tern.
To high-light small defects on a pattern visually, for example in an HMI or demo, the follow-
ing steps can be used:
1.
Enable the parameter Create Pattern ROI
2.
Generate the difference image with option Normalized diff with edge suppression
3.
Locate the defects in the difference image by using Blob Finder. Optionally, pre-
process further with Erode and/or Stretch Gray
4.
FOR each blob/defect, use the Blob Analyzer to create a blob ROI
5.
Inside the FOR loop, draw the blob ROI by using Draw ROI
High-lighted defects for HMI display or demo purposes.
An advanced use of the difference image is to enhance features by suppressing back-
ground print, for example increasing robustness of a barcode application.