Fraunhofer Institute for Factory Operation
Image-based Marking Analysis and Evaluation
Automatic and Objective Inspection of Marking Quality
A number of subjective impressions characterize a marking’s quality and valence. Variances in the production process influence not only readability but also a product’s overall impression, often considerably. An inspection is essential whenever consistently high quality must be ensured. Important evaluation criteria of a marking’s quality are the attributes of completeness, contrast, sharpness and homogeneity. The results of quality evaluations by inspectors are subjective.
The Fraunhofer IFF in Magdeburg has developed a new image-based system that automatically and objectively inspects the important attributes of marking quality.
System
The system employs a complex multi-dimensional attribute space consisting of the contrast, homogeneity, completeness, lettering and edge width a marking’s graphic and textual to objectively analyze and evaluate a marking’s quality. A weighting of the different attributes objectively reproduces the subjective perception of quality. Findings from the physiology of human perception are used for the weighting.
The inspected marking is specified by vector graphics, thus facilitating high flexibility. The algorithm for the evaluation of marking quality functions based on contour, i.e. regardless of whether targets are letters, characters or other symbols. First, the target marking is reconciled with the test specimen's actual image to detect and evaluate the individual elements. To do so, the image elements are selected automatically and disturbing influences such as the camera lens’s distortion are corrected. Finally, a best fit algorithm positions the processed test specimen's image elements over the target image. In the process, the translation, rotation and scaling between target and actual contours are ascertained and corrected so that the measured and the predefined elements can be compared directly and differences detected easily.
System Features
- Objective inspection based on weighted attributes
- Evaluation of completeness, contrast, sharpness and homogeneity
- Specification of inspected markings as vector graphics
- Certified repeatability and reproducibility (Gage R&R tests)
- Suitability for in-line quality assurance of a wide variety of marking systems