Study On A Method Of Image Enlargement And Application In Video Communications

In the field of multimedia communications, generally there are three means to improve the efficiency and quality of image communications. The first is to widen the bandwidth of communication network, the second is to compress the digital image with coding algorithm, and the third is to cut down the size of original image at the transmitter while carrying out inverse operation at the receptor. The last one is the focus in this paper. An effective method of image enlargement has been discussed and put into application in the multimedia image communications.There are many methods for image enlargement, among which Proximal Evaluation is the simplest. In this method, the value of every inserted pixel equals to that of its closest compeer in the original image, and the characteristic of frequency response in the diagonal direction is fine. But there is mosaic impact in the enlarged picture because this method can't adequately attenuate the vertical frequency off the Base Band in the horizontal and vertical direction. The other way called Double Linear Interposition makes sufficient attenuation of repeating frequency, eliminates the mosaic impact and thereby improves the quality of enlargement picture. But this method requires that the value of every pixel be equal to the weighted sum of the value of those pixels next to it. Since the complexity involved, it is hard to implement the algorithm with hardware system.Taking into account that the quality of enlarged picture should meet the directional sensitivity of human vision and that the enlargement algorithm should be convenient for hardware to implement, an enlargement method called AdjacentDiffusion, that well matches characteristics of human vision, is studied in this paper. With Adjacent Diffusion, by means of simple coordinate transformation of pixels, which especially benefits for hardware implementation, a fairly good enlargement quality can be obtained. Furthermore, the design of hardware implementation of Adjacent Diffusion, with programmable logic device CPLD, is discussed, and programs with VHDL language, which describe main functions of the hardware system, are also given.At the end of this paper, the comparison and analysis among pictures with different methods of image enlargement, which have been mentioned in this paper, are given.