Grid Based Method for Computing DCT Coefficients in Arbitrary Rectangle Region

At present, almost all digital images are transferred to the compressed format for storing and communication reason, in which the discrete cosine transform (DCT) based compression method remains an effective and important way for image compression because of the effort from JPEG. It is considerable to introduce image processing techniques such as feature extraction, pattern recognition and image indexing to the compressed image domain. In these image processing techniques, they all involve operations on arbitrary regions in images. So it is critical to find an effective way to calculate the DCT coefficients in arbitrary regions. To this end, we propose a grid based approach to find the most suitable relationship between DCT coefficients in 8*8 macro-blocks and arbitrary rectangle region. Experiment result reveals that the proposed method has a lower computational complexity than the butterfly algorithm (BA) when computing the DCT coefficients in arbitrary rectangle region.