A study on two-layer coding for animation images

A coding scheme specifically designed for animation images is proposed. Taking the characteristics of animation images into account, lines and homogeneous color regions are extracted from animation images. Lines and contours of the homogeneous color regions are approximated by straightline and spline functions. We found that smoothing operations are effective to extract homogeneous regions from background images. A connected filter is used for the smoothing operation while keeping edges of the original image correctly. Precise approximation of the contours is also required. For this purpose, we propose to use dynamic programming with a feedback algorithm. As a result, an animation image can be represented by two layers; significant points as a base layer, and discrete cosine transform (DCT) blocks for an additional layer. For the compensation of the loss caused by the smoothing operation, the DCT is applied to the difference between the original images and lines and homogeneous color regions images. High-quality images can be obtained by adding this differential data to the approximated images.