Standard Compression Techniques Research Articles

A Novel Approach to Lossy Real-Time Image Compression: Hierarchical Data Reorganization on a Low-Cost Massively Parallel System

This paper discusses an innovative real-time oriented image compression system, based on a simple algorithm designed explicitly to be implemented on a low-cost SIMD computer architecture featuring a much lower power consumption than traditional DSPs or dedicated hardware. For this reason the considered approach is suitable to be integrated on portable systems, where power consumption is a critical design issue. The algorithm, based on a hierarchical decomposition of the input image, has been tested on a special purpose SIMD system, PAPRICA, exploiting its features such as its massive parallelism and its capability to operate on local data as well as to handle hierarchical data structures. According to the proposed approach, the quality of the decompressed image can be traded for a lower power consumption as well as a higher processing speed. A comparison between the discussed algorithm and the standard JPEG compression technique is also presented.

Lossless compression of multispectral image data

While spatial correlations are adequately exploited by standard lossless image compression techniques, little success has been attained in exploiting spectral correlations when dealing with multispectral image data. The authors present some new lossless image compression techniques that capture spectral correlations as well as spatial correlation in a simple and elegant manner. The schemes are based on the notion of a prediction tree, which defines a noncausal prediction model for an image. The authors present a backward adaptive technique and a forward adaptive technique. They then give a computationally efficient way of approximating the backward adaptive technique. The approximation gives good results and is extremely easy to compute. Simulation results show that for high spectral resolution images, significant savings can be made by using spectral correlations in addition to spatial correlations. Furthermore, the increase in complexity incurred in order to make these gains is minimal. >

Error Sensitivity of CCITT Standard Facsimile Coding Techniques

The CCITT has defined Group 3 facsimile apparatus as that which digitally transmits an ISO A4 document over a switched telephone circuit in approximately one minute. Data compression is employed to achieve the reduced transmission time. Study Group XIV of the CCITT has drafted Recommendation T.4 to achieve compatibility between Group 3 facsimile devices. The standard data compression technique specified by T.4 is a one-dimensional coding scheme in which runlengths are encoded using a modified Huffman code (MHC). The recommendation also includes an optional twodimensional compression technique known as the modified READ code (MRC). It is recognized that the switched telephone network is prone to error when transmitting digital data at the standard T.4 data rate of 4800 bits/s. This paper evaluates the error sensitivity of the MHC and MRC when operating over a typical telephone circuit. The error sensitivity analysis is accomplished by means of computer simulation. The error performance of the two coding techniques is analyzed both quantitatively and qualitatively. The quantitative analysis is accomplished using the error sensitivity factor which represents the average number of incorrect pels in the output document caused by a transmission error. The qualitative analysis is based upon viewing actual error-contaminated images generated in the simulation process. Two separate analyses have been performed. First, error sensitivity data for both the MHC and MRC are developed under identical operational conditions, and their relative performance is discussed. In the second part four different techniques for processing the received facsimile signal (MRC), to minimize the subjective effect of transmission errors, are analyzed.