A novel technique for data hiding in color paletted images

The size of an uncompressed image depends on the resolution of the image and the number of colors in it. Gray-scale images typically contain 256 or fewer gray levels. In a color image, the color of each pixel is represented by three bytes, one each for red, blue and green. This leads to a potential of more than 16 million colors. However, the eye can discern only about 10,000 distinct colors. Moreover, common images usually contain fewer colors. Many images, therefore, contain much fewer colors, which form a palette. Many file formats treat the information in such a color image as a table containing the palette and individual pixels as pointers to that table. In this paper, a novel technique for hiding data using the palettes of color images is proposed. The technique can be implemented without interfering with the image data, by using unused entries or visually indistinguishable colors in the image palette.