Naokazu Aoki

Analysis of sharpness increase by image noise

Motivated by the reported increase in sharpness by image noise, we investigated how noise affects sharpness perception. We first used natural images of tree bark with different amounts of noise to see whether noise enhances sharpness. Although the result showed sharpness decreased as noise amount increased, some observers seemed to perceive more sharpness with increasing noise, while the others did not. We next used 1D and 2D uni-frequency patterns as stimuli in an attempt to reduce such variability in the judgment. The result showed, for higher frequency stimuli, sharpness decreased as the noise amount increased, while sharpness of the lower frequency stimuli increased at a certain noise level. From this result, we thought image noise might reduce sharpness at edges, but be able to improve sharpness of lower frequency component or texture in image. To prove this prediction, we experimented again with the natural image used in the first experiment. Stimuli were made by applying noise separately to edge or to texture part of the image. The result showed noise, when added to edge region, only decreased sharpness, whereas when added to texture, could improve sharpness. We think it is the interaction between noise and texture that sharpens image.

A key derivation scheme for hierarchical access control to JPEG 2000 coded images

This paper proposes a key derivation scheme to control access of JPEG 2000 (JP2) coded images, which consist of hierarchical scalability such as SNR, resolution levels, and so on. The proposed scheme simultaneously controls access to each level of scalability. The proposed scheme derives keys through hash chains, and each JP2 packet is enciphered with each individual key. By introducing combinations of a cyclic shift and a hash function, the proposed scheme manages only a single key for a JP2 image; whereas the conventional access control schemes having the above mentioned features manage multiple keys. The single managed key is not delivered to any user. The proposed scheme is also resilient to collusion attacks. Performance analysis shows the effectiveness of the proposed scheme.

Improvement of Multi-bit Information Embedding Algorithm for Palette-Based Images

We propose a new approach that is an improvement on the conventional of a multi-bit information embedding algorithm for palette-based images. The proposed method embeds secret information by changing the pixel values for each of the

Hierarchical Key Assignment Scheme for Multimedia Access Control with Modified Hash Chain

2^{k-2}+1

Hierarchical scrambling scheme for palette-based images

2k-2+1 pixels. Hence, our scheme can embed more information compared to the conventional method. Furthermore, the developed algorithm does not drastically change the pixel values with large color differences between before and after the changes. Therefore, it reduces the degradation of the image quality. Our experimental results show that the proposed scheme is superior to the conventional method.

Memory texture as a mechanism of improvement in preference by adding noise

In this paper, an efficient data hiding scheme for printed color images is proposed that visualizes on printed color images embedded data that is invisible on a monitor. We accomplished this scheme by using the differences of color gamut between a monitor and printer. The proposed scheme visualizes embedded data by converting one piece of color information, either L*, a*, or b*, to a fixed value when printing. This feature can be easily applied to copyright protection for printed images. Simulation results show the effectiveness of our scheme.

For Digitization of Photographic Books

We propose a key assignment scheme and applying it to control hierarchical access to multimedia content. By introducing a modified hash chain, the proposed scheme manages one key composed of a single segment. The managed key is not distributed to any users, providing security against key leakage. Collusion attacks are prevented by the order of key assignment. Our scheme also reduces the number of hash calculations. Analysis of performance demonstrated this scheme is valid.

Digital image improvement by adding noise: an example by a professional photographer

We propose an efficient tamper detection scheme for JPEG2000 codestreams. The proposed scheme embeds information while maintaining the scalability function of JPEG2000 and can detect tampered layers or tampered resolution levels for each decoded image quality level. Marker codes that delimit a JPEG2000 codestream must not be generated in the body data that possesses the image information. We can prevent new marker codes from being generated when embedding information into the JPEG2000 codestream. The experimental results show that our scheme can preserve the high quality of the embedded images.