Image compression based on union of DCT and wavelet transform

摘要

A union of DCT (discrete cosine transform) and wavelet transform can generate a much sparser representation of the digital image signal than either of them alone. After the block-based DCT, the coefficients are rearranged into a number of frequency groups such that the coefficients locating at the same coordinate in all transform blocks are in one group. Then, one or more such groups are further decomposed by wavelet transform. After quantization, each frequency group is divided into squares. The squares are identified and encoded as either all-zero or not-all-zero. Inside those not-all-zero squares, the coefficients are encoded bit-plane by bit-plane in a 2-dimensional quaternary reaching pattern. Compared to existing peer systems, the compression performance is improved up to 30%, especially in high quality cases. For lossless compression, the image data is decomposed by a union of a reversible DCT approximant and a reversible wavelet transform. Besides, the coefficients are quantized by a remnant-preserved, partial quantization scheme. The lossless compression performance is improved about 20% against JPEG2000.