Perceptually tuned subband coder for JPEG

Abstract

This paper presents a perceptually tuned subband image coder, which selectively operates on the subbands of an image to achieve good compression ratio. The proposed encoder divides an image into 8 × 8 sub-images and subsequently decomposes each sub-image into four subbands. A just noticeable distortion (JND) model is employed to remove all the perceptually insignificant subbands from the sub-images. The remaining subbands are processed by the subband discrete cosine transform (SBDCT). This reduces the computational cost of the SBDCT without introducing perceptible distortion. To further reduce the perceptual redundancy in the image, an image-dependent quantization matrix is computed from the JND profile of the image. Our simulation results indicate that our proposed encoder outperforms the JPEG baseline coder at bit rates from 0.25 to 0.9 bpp.