- This paper presents an automated digital image processing (DIP) algorithm called Volumetricsbased Global Minima (VGM) thresholding algorithm for processing asphalt concrete (AC) X-ray computed tomography (CT) images. It utilizes known volumetric properties of AC mixtures as the main criterion for establishing the air-mastic and mastic-aggregate gray scale boundary thresholds. Several DIP techniques were utilized to characterize the AC microstructure. It is well demonstrated that the VGM processed images are significantly improved compared to the raw X-ray CT images. It can be concluded that VGM thresholding algorithm was shown to be a major improvement over the largely manual/subjective techniques used in the past.