Summary: \BeginparThis article gives an overview of a diverse selection of currently used second-generation image coding techniques. These techniques have been grouped into similar categories in order to allow a direct comparison among the varying methods. An attempt has been made, where possible, to expand upon and clarify the details given by the original authors. The relative merits ans shortcomings of each of the techniques are compared and contrasted.\Endpar (Provider: ACM) Review: \BeginparThis paper gives an overview of a diverse selection of currently used second-generation image coding techniques that incorporate properties of the human visual system (HVS). These techniques are grouped into categories in order to allow a direct comparison among the methods. The relative merits and shortcomings of each technique are compared and contrasted. The authors do not intend to cover every second-generation image coding technique, but rather to provide an introduction to the broad categories of existing techniques.\Endpar \BeginparThe paper is structured in seven sections, the first of which is an introduction. Section 2 describes some of the commonly used properties of the human visual system that have been incorporated into image coding systems: the frequency sensitivity of the HVS; its spatial and temporal frequency dependencies; its directional anisotropy, which is related to its decreasing sensitivity at high and low spatial frequencies; and its spatial and temporal masking.\Endpar \BeginparIn section 3 the authors describe some multiscale and pyramidal techniques, which operate on the original image and subsample it in order to produce various levels of image detail at progressively smaller scales. This idea exploits the eye{’}s ability to identify such levels of progressively smaller subsampled images; a mechanism is developed that can be used to identify common features that are present at various levels of detail. Three techniques are presented: one is based on the Laplacian pyramid as a method of image compression; one is similar to the Laplacian technique, but using the wavelet transform, which has advantages at low bit rates, since information at all scales is available for edges and regions; and one is a multiscale edge detection technique, in which the image is smoothed at various scales and edge points are detected by a first- or second-order differential operator.\Endpar \BeginparSection 4 presents techniques that employ directional filters as part of the coding process. Directional filtering has been employed as a modeling scheme in order to exploit the fact that the eye contains direction-sensitive neurons. The scheme can be applied directly to the original image or to the output of a feature separation stage, with different compression ratios.\Endpar \BeginparSection 5 describes techniques for coding images based on visual patterns. These techniques use the fact that the eye can decompose an image into a set of smaller visual patterns.\Endpar \BeginparSection 6 covers techniques based on segmentation, considering its three main steps: preprocessing, segmentation, and coding of contours and texture components. The modeling stage is based on the fact that the eye is good at identifying regions that appear similar and grouping them accordingly. The segmentation algorithm employed in the overall technique is responsible for separating the original image into regions. The modeling schemes can represent the contents of a region accurately and hence produce good images. In general, most of the segmentation techniques perform well for images that contain large areas of similar texture or intensity.\Endpar \BeginparSection 7, {“}Contour-Coding-Based Approaches,{”} presents two image coding techniques that use the notion that contours can be used solely in the coding process. These techniques make no attempt to model the content of a region; instead, they consider the image as composed of many separate contours and their properties that are used in the coding process. One lossy and one lossless method are described.\Endpar \BeginparThe last section is a complete summary. The authors provide a rich reference list, including more than 70 titles. They include many illustrations, which contribute to the reader{’}s understanding.\Endpar \BeginparThis is a useful overview of second-generation image coding techniques, especially for people involved in image processing.\Endpar (Provider: ACM)