Researches On High Efficiency Rate Control For Embodied Image Coding

Embedded wavelet coding technique is a main method for image coding, in which, EBCOT (Embedded Block Coding with Optimized Truncation) is an algorithm with highest performance at present, which is composed of Tier-1 and Tier-2 (short for T₁ and T₂) encoder. Because of good restored image and random access for coding stream, the algorithm becomes the first choices in practice.In the image coding field, the design of high performance image coder is always the goal that many relative researchers pursue. In the paper, Rate control of embedded block coding is studied in deep, especially on rate control algorithm and its implementation with high efficiency and performance. The creatively rate control algorithmes with low computation, low memory usage and high efficiency for hardware implementation are presented in the paper, which have been applied to real coding system successfully. The followings are main content of this paper:1. A fast algorithm for T₂ encoder in JPEG2000 suitable for hardware implementation is presented in this paper. By reducing the calculational complexity of the rate-distortion slope estimate and simplifying the design of optimized truncation and Tag Tree encoding in code stream organization, the difficulty and the resource of hardware implementation for T₂ encoder is reduced, and the parallelizability of the JPEG2000 hardware system is enhanced. The final code stream is accorded with the standard format of JPEG2000 and the loss of image quality is little.2. An adaptive rate control algorithm based on significant priority is presented for embedded block coding with optimized truncation. The coding passes of all coding block are evaluated by different significant priority according to the bit-planes the pass located in and the coding type, which are encoded by T₁ encoder in the significant priority order. T₂ encoder sends feedback to control the coding depth by the accumulated bit rate and complete the rate-distortion optimization truncation. The proposed scheme can efficiently reduce the cost of computation and memory usagc, which is suitable for hardware implementation.3. A novel wavelet decomposition framework is presented for multi-spectral image coding based on ROI Coding of EBCOT. After normal wavelet transform, the vertical wavelet decomposition is introduced for ROI which include the multi-spectral information in the high frequency subband, not for the background region. It can concentrate the enegy of spectra and enhance the coding result of ROI.4. After the elaborate analysis for the problem of rate pre-allocation for the remote sensing image JPEG2000 multi-image tiles encoding, a novel rate pre-allocation algorithm based on code block prediction is presented to eliminate influence of the reconstructed image quality using equal allocation. After wavelet transform and quantification, a prediction module is introduced to estimate the entropy of EBCOT code block within available bit plane, then using the summation estimate entropy of each image tile to allocate the rate for each image tile. The proposed algorithm matches the code mode of JPEG2000, with little loss of images quality especially for the image whose object has the characteristic of precinct convergence.5. Wavelet transform hardware module, space orientable tree hardware module and T₂ encoder hardware module for SHPIT and JPEG2000 are implemented. And a common net interface is implemented in coder for data exchange with external network.