A DCT-Domain Video Alignment Technique for MPEG Sequences

An image/video registration technique for multiple compressed video inputs such as MPEG sequences is investigated. The proposed technique is based on the matching of discrete cosine transform (DCT) coefficients and motion vectors. First, the I frame of each input sequence is separated into the background and moving objects. For the background, coarse edge features are extracted by applying edge detectors of different characteristics to the luminance DC coefficients. Each detector generates a difference map for a single background. A threshold is determined for each difference map to produce a binary map. Then, alignment parameters are determined using the binary maps of input images generated by the same detector. For the moving object, alignment parameters can be finetuned by the motion information of all frames in the same group of pictures (GOP). Finally, the actual displacement in the pixel domain is estimated by the weighted average of alignment parameters from all background detectors and refinement parameters from motion information. It is shown by experimental results that the proposed method reduces the computational cost of image/video registration significantly in comparison with the traditional pixel domain registration techniques while achieving certain quality of composition