Content progressive coding of limited bits/pixel images

We propose a new lossless context based method for content progressive coding of limited bits/pixel images, such as maps, company logos, etc., common on the WWW. Progressive encoding is done by separating the image into content layers based on color level or predefined information. By introducing skip-pixel coding the number of pixels encoded in each layer is reduced by using information from already coded layers. This approach is combined with efficient template based context bi-level coding, context collapsing methods for multi-level images and arithmetic coding. With our new method we are thus able to outperform existing coding schemes and in addition provide progressive coding. Compared to GIF we are able to reduce the compressed size with a factor of up to 3