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Hierarchical progressive image coding controlled by a region based approach

This paper presents a progressive image coding technique in which a rough preview image is enhanced with the zerotree encoding of the residual image in the wavelet domain. The preview image is achieved with a region based approach that gives a basic description of the scene with a very high compression ratio. As a second stage, the residual between the original image and the preview is decomposed using a wavelet transform, and it is encoded for a progressive transmission. The wavelet coefficients are selected from the coarsest to the finest level of resolution, using a mask obtained from the image preview. Such a mask sets the importance of the coefficients on the basis of their distance from the contours of the regions of the preview. A modified zerotree approach is used to progressively encode the weighted coefficients until significant texture is introduced in the image and the required quality is achieved. Moreover, if an image with very good quality is required, the resulting reconstruction error is encoded by means of vector quantization and transmitted over the channel. The proposed method is compared to progressive JPEG, and it gives similar results at low compression ratios and far better results at higher ones.