Digital image measurement method, as an extension of Particle Image Velocimetry of single phase flow measurement, was investigated for application to air water two phase flows. The method has strong potential ability in measuring bubble geometrical features and moving velocities for complex bubble motion in aerated water flow. Both diluted and dense bubble rising flows are measured using the digital image method. Measured bubble shapes and sizes, and bubble velocities are affected by threshold selection for binary image. Several algorithms for selecting threshold are compared and methods for calculating the time averaged void fraction are discussed. Digital image measurement method, as an extension of Particle Image Velocimetry of single phase flow measurement, was investigated for application to air water two phase flows. The method has strong potential ability in measuring bubble geometrical features and moving velocities for complex bubble motion in aerated water Both diluted and dense bubble rising flows are measured using the digital image method. Several algorithms for selecting threshold are compared and methods for calculating the time averaged void fraction are discussed.