Comparison of Hartley and Cas-Cas transforms in medical image compression

The Hartley and Cas-Cas transforms which are discrete and real-to-real, are compared in terms of times taken, compression ratios and quality of the reconstructed image, for the purpose of comparing their suitability for transform domain compression applications. A thresholding method for quantization is introduced where threshold values are adaptively selected according to the correlation factor of each block of equally divided blocks in the image. Additionally in some pixels it was found advantageous to code by retaining only the sign bit. Preliminary results suggest that compression ratios of 10-15 to 1 were readily achievable for projection radiographs with no subjective loss of image quality. The fast Cas-Cas transform ran about 25% faster than the Hartley transform with equal output quality