Low bit rate color image coding with adaptive encoding of wavelet coefficients

We report the performance of the embedded zerotree wavelet (EZW) using successive-approximation quantization and an adaptive arithmetic coding for effective reduction in bit rates while maintaining high visual quality of reconstructed color images. For 24 bit color images, excellent visual quality is maintained upto a bit rate reduction to approximately 0.48 bpp by EZW yielding a compression ratio (CR) of 50:1. Further bit rate reduction to 0.375 bpp results in a visible degradation by EZW, as is the case when using the adaptive vector quantizer AFLC-VQ. However, the bit rate reduction by AFLC-VQ was computed from the quantizer output and did not include any subsequent entropy coding. Therefore entropy coding of the multi-resolution codebooks generated by adaptive vector quantization of the wavelet coefficients in the AFLC-VQ scheme should reduce the bit rate to at least 0.36 bpp (CR 67:1) at the desired quality currently obtainable at 0.48 bpp by EZW.