今泉 祥子

In this paper, we propose a novel encryption method for JPEG bitstreams in which encrypted data can preserve the JPEG file format with the same size as that without encryption. Accordingly, data encrypted with the method can be decoded without any modification of header information by using a standard JPEG decoder. In addition, the method makes two contributions that conventional methods allowing bitstream-level encryption do not: spatially partial encryption and block-permutation-based encryption. To achieve this, we propose using a code called restart marker for the first time, which can be inserted at regular intervals between minimum coded units (MCUs) for encryption. This allows us to define extended blocks separated by restart markers, so the two contributions are possible with restart markers. In experiments, the effectiveness of the method is verified in terms of file size preservation and the visibility of encrypted images.

This paper proposes an extended method for reversible color tone control for blue and red tones. Our previous method has an issue in that there are cases where the intensity of enhancement cannot be flexibly controlled. In contrast, the proposed method can gradually improve the intensity by increasing the correction coefficients, regardless of the image features. This is because the method defines one reference area where the correction coefficients are determined, one each for blue and red tones, while the previous method defines a common reference area for both tones. Owing to this, the method also provides independent control for blue and red tones. In our experiments, we clarify the above advantages of the method. Additionally, we also discuss the influence of the data-embedding process, which is necessary to store recovery information, on the output image quality.