Image coding with mixed representations and visual masking

We propose a novel approach for low bit rate perceptually transparent image compression. It exploits both frequency and spatial visual masking effects and uses a combination of Fourier and wavelet transforms to encode different bands. Frequency domain masking is computed by using a fine to coarse analysis step. Spatial domain masking is computed either by using Girod's (1989) model or a coarse to fine analysis step that accurately computes local contrast. A discrete cosine transform is used in conjunction with frequency domain masking to encode the low frequency bands. The medium and high frequency bands are encoded using spatial domain masking and a wavelet transform. The encoding of these bands is based on a recursive selection of the important edges in each band. It uses cross-band prediction to minimize the bit rate. Experiments show the approach can achieve a very high quality to nearly transparent compression at bit rates of 0.2 to 0.4 bits/pixel.