<title>Image coding methods and their assessment</title>

Abstract

Image coding methods continue to be introduced without satisfactorily answering the question, "which compression method is best for a given set of conditions?" This paper provides a framework for comparing and contrasting seemingly unrelated methods and then addresses the remaining issue, "which metric should be used?" IMAGE COMPRESSION METHODS Generic image compression modelWe will first present a general model for image compression and decompression so that the many, seemingly unrelated, algorithms can be broken down into their constituent parts and compared.A general model for image data compression and decompression is illustrated in Fig. 1. In this model original pixels are processed in two steps. First the original pixels are passed through an encoder model which is designed to reduce the correlation typically found in the unprocessed image pixels. By 204

<title>Method for quality evaluation of the block-transform compressed images</title>

“…Common faults of MSB are that a slight shift of an image causes a large numerical error but no visual distortion and, conversely, a small spatially concentrated numerical error can be an important visual artifact [2,3]. It is common to normalize this distortion in some way to produce a dimensionless measure of quality and to describe the result in decibels.…”