Steganography is a technique to hide a secret data into stego-data for secret communications. In the steganography, it is important to suppress a degradation of the stego-image for data hiding. The stego-image of the steganographic method is divided into full-color images and palette-based images. In this paper, we propose a new multi-bit steganographic method for the palette-based images. In the case of embedding for palette-based images, there are two characteristics described below. (1) Embedding degradation is not remarkable because palette-based images have been degraded due to color quantization and error-diffusion processes. (2) The embedding error tends to greater than full-color images due to usable colors are few. In the proposed method, representative colors of the palette-based image are sorted and their index numbers are replaced so that the embedding error becomes small. The proposed method suppresses the degradation of the cover-image by dispersing the embedding coordinates. We verify the effectiveness of our method through experiments using palette-based color images.
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