This thesis proposes a novel chroma keying method based on stereo images, which can be applied to post-process the alpha matte generated by any existing matting approach.Given a pair of stereo images, a new matting Laplacian matrix is constructed based on the affinities between matching pixels and their neighbors from two frames. Based on the new matting Laplacian matrix, a new cost function is also formulated to estimate alpha values of the reference image through the propagation between stereo images.To avoid over-smoothing during propagation, a united window with an adaptive size is used in the Laplacian matrix to overcome the dilemma between the inadequate propagation caused by small size windows and the over-smoothness triggered by large size windows.Moreover, an optional pre-processing is presented. When it comes to the foreground object with strong reflection, based on the histogram statistics, the initial alpha values of the particular unknown pixels can be refined before the proposed post-processing method. In addition, a ground truth generation method is developed for chroma keying.Visual quality comparisons between the original mattes produced by existing approaches and the results post-processed by the proposed method show that our method can effectively enhance the quality of alpha mattes. Also, objective quality comparisons demonstrate that our proposed algorithm can significantly reduce the errors of alpha mattes.ii Acknowledgements I would like to thank my supervisor, Professor Jiying Zhao, for his guidance and providing me the chance to conduct the research on chroma keying. I greatly appreciate his patience and confidence in my research work.