On image compression: a DWT-DCT algorithm

We propose a hybrid transform that performs one-level wavelet decomposition of any image and follows it with a discrete cosine transform (DCT) in its lowpass sub-band. It shows a definite improvement over the DCT-based JPEG coder performance, in that it allows for a wider range of compression ratios (CR) over which the coder PSNR performance is good while it requires far fewer computations. We show that even though the proposed transform has similarity to sub-band DCT, it outperforms sub-band DCT at low CR and is as good as the sub-band DCT at high CR