The Research On Motion Estimation And Wavelet Methods In Video Compression

Image is the main approach to obtain information, and image compression is crucial to process,store and transmit digital image. Motion estimation and compensation play a virtual role in video compression coding to reduce temporal redundancies. This dissertation focuses on the motion estimation algorithm in spatial and wavelet domain,also investigated are the applications of wavelet transform in image compression. The main research of this dissertation is listed as follows:Based upon the motion characteristics of the subjects in spatial domain, an adaptive motion estimation (MV) algorithm, imposing of an alterable search pattern and an adaptive model for starting point prediction is proposed. According to the integrality and the motion continuity of the object, the parameters of the prediction model can be modified corresponding to the variation of the correlation amongest the adjacent blocks to minish the difference between the prediction result and the best MV. The alterable search pattern can improve searching efficiency by adjusting its size and shape according to the grads of the sum of absolute differences (SAD), which reflects the motion characteristics of the adjacent blocks. Experiment results demonstrate that the proposed algorithm outperforms the other fast motion estimation algorithms presented in this dissertation in terms of PSNR,search speed and subjective quality of the reconstruct image.An initial MV prediction approach together with a cross search motion estimation algorithm is presented. Combined with full search in low subband, a more accurate initial MV can be obtained from the prediction approach with little computational cost overhead, by utilizing multiresolution characteristic of wavelet transform and temporal/spatial correlation between the blocks. Due to the subbands coefficients characteristic, the cross search is performed only along the horizontal or vertical direction after low-band-shift. Search results can approximate the best MV by adjusting cross searching center continually. Motion estimation is performed by the level of the wavelet transform, and the search range is confined to the 4 subbands of the reference frames at the same transform level. AS a result, the MV searched is the best one at the current resolution, which can insure the optimality of reconstruct image quality under the current data received. The simulation results validate the prediction approach and the search algorithm. On basis of the impact on reconstruct image PSNR, brought by update step in motion compensation temporal filtering (MCTF), a content adaptive invert motion compensation (IMC) algorithm is proposed. When the update step is skipped, the energy gain factors will change correspondingly in both of the high and low subbands at encoder side. By useing the SAD calculation method of a simple scalar quantizer with independent coding of the source samples, the PSNR fluctuation can be figured out between even and odd frames whether the update step is skipped. Additionally, the ways to select MV for IMC is studied on principle of MV invertible between prediction and update step. Simulations illustrate the improvement in PSNR of reconstruct image by the proposed way. Furthermore, a content adaptive IMC algorithm in MCTF, composed of two estimation models, is put forth to reduce the ghosting artifacts. One model is based on characteristic of subbands coefficients for low activity region estimation, and the other is to estimate the MV accuracy in high subbands from the energy after ME. Artifacts, caused by inaccuracy ME or update step, can be reduced effectively by the estimation models. Experiment results verify the efficiency of the adaptive IMC algorithm.A high efficiency and low power dissipation VLSI architecture is designed for two-dimensional discrete wavelet transform (2D-DWT). In the separable lifting-scheme based 2D-DWT architecture, data dispatch is optimized in both row and column processor. Scanning in zigzag order, the processors can work in parallel via few temporal buffers to store the data filtered by column processor, leading to improvement of data transform speed and hardware utilization factor. By the optimization of data dispatch in column processor, only one read or one write operation are necessary per clock for temporal buffer, so the bandwidth of memory access can be reduced to 50 percents in contrast to one read and one write in usual case. As a result, the line buffer can be single-port RAM instead of two-port RAM, and the chip area and power dissipation can be decreased sufficiently. After demonstrated in FPGA, the implementation is synthesized with HJTC 0.18μm cell library, and layout has been designed for tape out. The CMOS chip demonstrates the VLSI architecture and its implementation.Finally, an image compression scheme,including DSP for multimedia process,2D-DWT transformer,video camera and network transmission, is designed for the rotary kiln alumina production. Compression experiments are carried out to compress and reconstruct the flame image in rotary keln under different PSNR condition at various spatial and temporal resolutions. The coal particles region can be identified accurately at very low bitrate. Experiment results show the validity of the scheme proposed for flame image compression in rotary keln.