Tag: Image analysis

This talk focused on the combination of two technologies, Reflectance Transformation Imaging (RTI) and Image analysis. Much of the talk dealt with the application of these two technologies to evaluate accelerated aging or Oddy Test coupons in a quantitative manner. As the evaluation of Oddy tests has traditionally been subjective, making reproducibility problematic, I was particularly interested in the potential for quantitative analysis.
Reflectance Transformation Imaging (RTI) is a relatively inexpensive and simple tool that creates a mathematically synthesized image of an object’s surface from a series of image (typically ~36) lit from different angles and directions. The image produced by the RTI software can reveal visual information that is difficult to discern under normal conditions.
Image analysis software utilizes algorithms that enhance the visual separation of features and marks them for analysis, a process known as segmentation, thereby enabling those features to be quantified. The software used by the authors of this presentation was Image Pro Premier by Media Cybernetics, which has previously been used for thin section analysis of ceramics.
The authors used RTI and Image analysis in combination to evaluate Oddy test coupons. The process aided in visual assessment, improved the documentation of the results, and provided quantitative results. Adding RTI and Image analysis to the Oddy test protocol was not a cumbersome addition, requiring only ~ 20 minutes. It was noted that the type of coupon used made a big difference for this technique, as foil and bent coupons were not ideal since the added texture complicated interpretation of the results.
After exposure, the coupons were photographed and processed in batches by metal: silver, copper, and lead. A single image of the coupons was chosen from the RTI viewer and used for image analysis. A different protocol was used for each metal. The image of the lead coupons was converted to grayscale and the colors inverted, background, control, and corrosion areas were defined, and the “Smart Segmentation” tool used to separate and quantify them. The image of the copper coupons was not converted to grayscale and the variety of corrosion types were all treated the same by the segmentation process. The image of the silver coupons was converted to grayscale or pseudo-color to enhance differences before segmentation. The software allows for individual segmentation protocols to be saved and reused. The percentage of tarnished to untarnished surface could be calculated for each metal. Comparison with visual evaluation of test coupons yielded the following results:
Control or clear pass: 1-4% tarnish
Clear Fail: 45-100% tarnish
Pass for temporary use: 7 – 17% tarnish
The “temporary” category is particularly hard to judge when evaluating Oddy tests in the traditional manner, so this method seems to be especially useful in this case.
In addition to Oddy test results, RTI and image analysis were used by the authors to evaluate rapid corrosion tests and coating tests. In each case, like with the Oddy tests, the process provided good documentation as well as the possibility for quantitative results. The combination of these techniques seems to have great potential for a number of applications and their relative simplicity and inexpensiveness make them a great tool for institutions with limited analytical capabilities.