Optimizing the capacity of distortion-freewatermarking on palette images
Yongdong Wu, Qiming Li, Feng Bao · 2008
In a palette image file, each color is pointed by at least one palette entry and each pixel is represented with one of the color pointers. Since many palette images use a portion of palette entries only, this paper presents a distortion-free watermarking on palette images by exploiting the unused entries. It allocates x palette entries to one color such that each pixel of the color is able to embed log2x bits. In order to achieve high embedding capacity, we formulate the relationship among embedding capacity, color occurrence, and unused palette entries. By solving the formula and allocating the palette entries in a sub-optimal manner, the present scheme provides a roughly optimal capacity. Our experiment demonstrates that the present scheme is of high watermarking capacity.