This paper describes the procedure that has been developed for absolute porosity measurement using Image Analysis (IA). Because of the crumbly nature of the composite substrate, it was not possible to proceed with standard method. The IA conducted on Optical Microscopy did not show enough contrast between pores and other features to be automated. The IA conducted on Scanning Electron Microscopy (SEM) with back scattered electron imaging gives enough contrast for automatic threshold determination. The SEM magnification is a parameter to be considered because it filters the information. Three frames at 500X magnification are enough for measuring the porosity of homogeneous supersonic induction plasma sprayed 18 mm samples (thickness 50-100 µm). The established calibration almost shows a 1 to 1 ratio for the image analysis as measured porosity versus the Archimedean porosity. Application of this absolute porosity determination by IA can be found in the Functionally Graded Materials (FGM) which composition is not constant over the layer thickness.