Fast 2D discrete cosine transform on compressed image in restricted quadtree and shading format

Given a compressed image in the restricted quadtree and shading format, this paper presents a fast algorithm for computing 2D discrete cosine transform (DCT) on the compressed grey image directly without the need to decompress the compressed image. The proposed new DCT algorithm takes O(K²logK+N²) time where the decompressed image is of size N×N and K denotes the number of nodes in the restricted quadtree. Since commonly K<N, the proposed algorithm is faster than the indirect method by decompressing the compressed image first, then applying the conventional DCT algorithm on the decompressed image. The indirect method takes O(N²logN) time.     

An improved no-search fractal image coding method based on a fitting plane

In this paper a fast and efficient no-search fractal image coding method based on a modified gray-level transform which uses a fitting plane is presented. The improved gray-level transform can reduce the minimum matching error between a given range block and its corresponding domain block, and thus, it can enhance the possibility of successful domain-range matching. In comparison with our previous scheme which uses an adaptive plane, the improved scheme results in a considerable acceleration of the encoding process, decreases the compression ratio and improves the quality of the reconstructed images in the meanwhile. Comparing with Furao’s no-search scheme, our improved scheme can get higher PSNR at higher bpp and almost the same PSNR at lower bpp. Although it uses more transform coefficients, such a fitting plane method can speed up the encoding process with the quality of the reconstructed images improved.     

Thinning algorithms based on quadtree and octree representations

Thinning is a critical pre-processing step to obtain skeletons for pattern analysis. Quadtree and octree are hierarchical data representations in image processing and computer graphics. In this paper, we present new 2-D area-based and 3-D surface-based thinning algorithms for directly converting quadtree and octree representations to skeletons. The computational complexity of our thinning algorithm for a 2-D or a 3-D image with each length N is respectively O(N²) or O(N³), which is more efficient than the existing algorithms of O(N³) or O(N⁴). Furthermore, our thinning algorithms can lessen boundary noise spurs and are suited for parallel implementation.     

Efficient quadtree based block-shift filtering for deblocking and deringing

The existing implementations of block-shift based filtering algorithms for deblocking are hard to achieve good smoothing performance and low computation complexity simultaneously due to their fixed block size and small shifting range. In this paper, we propose to integrate quadtree (QT) decomposition with the block-shift filtering for deblocking. By incorporating the QT decomposition, we can easily find the locations of uniform regions and determine the corresponding suitable block sizes. The variable block sizes generated by the QT decomposition facilitate the later block-shift filtering with low computational cost. In addition, large block based shift filtering can provide better deblocking results because the smoothing range of large blocks spans over the conventional 8 × 8 block size. Furthermore, we extend the proposed QT based block-shifting algorithm for deringing JPEG2000 coded images. Experimental results show the superior performance of our proposed algorithms.     

Multiband segmentation based on a hierarchical Markov model

We develop a new multiscale Markov segmentation model for multiband images. Using quadtree multiple resolution analysis of a multiband image, we use both inter- and intra-scale spatial Markov statistical dependencies. Bayesian inference is used to assess the appropriate number of segments. We exemplify the excellent results which can be obtained with this approach using synthetic images, and in two case studies involving multiband astronomical image sets.     

一种基于改进四叉树的GIS空间选择查询算法——以ESRI SHAPE格式文件为例

该文通过对原有四叉树在结点分裂和索引对象的结点分配方法方面进行改进,使索引对象被合理地并且不重复地分配到四叉树中的各个树结点中,减少了信息冗余,结点分布更加合理,从而提高整个索引树的搜索效率。并以ESRISHAPE格式文件为例,详细探讨了改进的四叉树在地理信息系统(GIS)的空间选择查询(包括点查询和开窗查询)中的应用与实现算法。实践表明,该算法逻辑清晰,实现简单,查询高效,具有实用价值。