In this paper, we propose an extended reversible data hiding method for palette-based images that enhances payload security. In a previous method, multiple index colors appear in duplicate in a color palette as a result of the data hiding process. This leads to the locations where payload bits have been embedded being disclosed, so the security for the payload is weakened. In contrast, the proposed method configures a new approximate color for each target color without reducing the total number of index colors. Consequently, this method can derive high-quality marked images while maintaining the security of payload bits. Experimental results show the effectiveness of the proposed method in terms of image quality using peak signal to noise ratio (PSNR)/structural similarity (SSIM) and the number of reduced colors.

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We fabricated an electrochromic device with a cellulose substrate impregnated with a dimethyl terephthalate-based electrochromic solution. By cutting the cellulose substrate into a shape of an alphabetical letter, we succeeded in displaying an electrochromic letter. The simple fabri- cation and the biodegradable cellulose substrate potentially contribute to the sustainability-oriented development.

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