Image scrambling is a method in which an original image turns into a visually degraded image. In this paper, we propose a new algo- rithm of hierarchical scrambling method for palette-based images using bitwise operation. The target pixels for scrambling were cho- sen randomly using a pseudo-random number generator and were transformed into their corresponding binary bits. Then, bitwise operation was applied to concatenate the target pixels and the corresponding random numbers to scramble the palette-based images. The images in the proposed method are more distorted than those in the conventional methods. We also introduce a hierarchical key assignment scheme for more secure and efficient communication. We carried out performance tests using standard images. This demonstrates that our method is superior to the conventional methods.

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We proposed a concept of ‘digital silica photography’ for long-term preservation. It stores digital photographic data with decode-free analog images inside a fused-silica plate using a femtosecond pulse laser. The digital data are written so as to be able to read out using a normal camera in order to guarantee future readability. The decode-free analog images will explain digital contents and reading method in the distant future. As a feasibility demonstration, photographic data of Ukiyo-e ( Japanese woodblock prints) were record- ed at 290 μm under the surface of a fused-silica plate with a density of 1,693 dpi. The decode-free analog image was made by a 1-bit error-diffusion dithering method. The digital data were successfully read out from a single-shot picture taken by a 24-M pixel camera with a macro lens. We also showed the potential of fire resistance through an annealing test at 1,000 ̊C.

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