Image compression by a time enhanced self organizing map

This paper presents the promising results of an innovative modification of the Kohonen's algorithm, the time enhanced self-organizing map (TESOM), when used for low bitrate image compression. The time enhanced map is used in this paper to learn codebooks of subimages, in a similar way as other classical algorithms based on LVQ or SOM do, but taking advantage of the fact that it learns the sequence order of the input data (i.e. subimages) during the training phase. The codebook learned by the new proposed algorithm TESOM presents the advantage that the vicinity of the codes in the output map is not only established by their visual similarity, as in SOM, but also by the sequential order of the subimages during the training phase. Since this sequential order of the subimages determines the vicinity of the codes, the increment of the representative code of two consecutive subimages has been proved to have a lover Entropy and can therefore be codified by a lower bit rate. The advantage of the proposed algorithm is thoroughly evaluated and quantified over a set of experiments, which include several images, used in different ways in the training phase for codebook design and in the compression phase, and a variety of parameters.