Quantitative image analysis techniques for the evaluation of porosity

Levels of porosity, inclusions and corrosion in a material have traditionally been quantified qualitatively through visual inspection and rating systems. Such methods are largely subjective and often dependent on the interpretation of the evaluator. It is now possible with modern image analysis programs to make quantitative measurements, comparisons and evaluations of microstructural features, like micropores, inclusions and corrosion pits. This technical memorandum presents some of the basic image analysis techniques and procedures dealing with image collection, calibration and thresholding, and measurement and analysis. In addition, a typical application of these methods to measure gas porosity in welded specimens is presented.