Error Inhomogeneity of Wavelet Image Compression

Despite the popularity of wavelet-based image compression, its error inhomogeneity-the error that is different for even and odd pixel locations, has not been previously analyzed and formally addressed. The difference on PSNR performance can be substantial, up to 3.4 dB for some images and compression ratios. In this paper, we show that the error inhomogeneity is caused by asymmetrical filtering of quantization errors after the upsampling step in wavelet synthesis process. We also develop a model that also allows predicting the amount of inhomogeneity for a given wavelet. Furthermore, we show how to redesign wavelet filters to reduce the error inhomogeneity.