Lossless compression for x-ray mammogram images
A. Abu-Hajar, Ravi T. Sankar · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2003
This paper presents a lossless coding that is designed for 16-bit high-resolution x-ray images. The proposed algorithm uses non-linear histogram-based mapping that eliminates the gaps in the histogram before applying wavelet transform. The mapping is designed to reduce the magnitude of the wavelet coefficients, especially in the high frequency subbands. Reducing the magnitude of the coefficients in the high frequency subbands provides more compression as the high frequency subbands occupy most of the image area. This paper shows that the energy of all the subbands is being reduced after eliminating the gaps in the histogram, and hence the magnitudes of the coefficients are being reduced. To further exploit this property, the image is segmented into 64×64 blocks, and the gaps in the histograms of each block are independently eliminated, and then each block is independently coded using SPIHT. Since the mapping is non-linear, look-up tables are transmitted to the decoder as part of the overhead information. Experimental results show that the compression in bit per pixel (bpp) of the proposed algorithm does not only exceed wavelet-based SPHIT and JPEG 2000 but also it exceeds the state-of-the-art context-based JPEG-LS.