Block-based DCT and wavelet selective coding for arbitrary-shaped images

Images usually have quite different properties place by place. This variation of local properties may affect the coding efficiency when utilizing a fixed coding method. In this paper, a new coding method which selects Discrete Cosine Transform (DCT) or Wavelet Transform (WLT) block by block adaptively according to the local properties of the image to achieve high coding efficiency, is proposed. A separable WLT, which gives higher coding efficiency and can be treated in the same manner as DCT, is proposed to simplify the hardware/software implementation. And an adaptive scanning method associated with the separable WLT, which achieves high coding efficiency by scanning the corresponding coefficients with large values across the resolution first to shorten the zero-run, is also proposed. Furthermore, for coding of arbitrary-shaped images with block-based DCT and WLT, a new padding technique based on the concept of making boundary blocks smooth is proposed. These new coding methods are verified through the simulation in comparison with the MPEG-4 Verification Model. The simulation results show the improvement of PSNR up to 2 dB.