映像情報メディア学会誌

An efficient key generating method that uses recursive hash chains is proposed for hierarchical access control. The proposed method introduces recursive hash chains for reducing the number of managed keys. In addition to decreasing this number down to one, regardless of the number of the controlled targets and their depth, the number of keys delivered to a user by using the proposed method is equal to or less than that in conventional methods.

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Physical motion features that cause a difference in the perceived rhythmic sense of a dancer were identified. We compared the rhythmical movements of Latin American and Japanese people to find such features. A 2-D motion capture system was used to measure rhythmical movement, and two motion features were identified. The first was the phase shift of the rotational angles between the hips and chest, and the second was the phase shift between the hips' rotational angle and horizontal position. A psychophysical study demonstrated whether these features affected the perceived rhythmic sense of a dancer. The results showed that both motion features significantly affected perceived sense, and one of them also affected how a viewer guessed the home country or area of a dancer. Consequently, the rhythmic sense of a virtual character can be controlled easily by adding and removing features to and from the character's synthesized motion.

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We describe an unbeatable rock-scissors-paper (janken) game system which defeats the opponent without fail and never has any delay in the presentation of the hand. This system recognizes the shape of the opponent's hand with pictures taken by a 60-fps camera and displays the hand form that can win a game on the screen before the opponent completes their hand form. When a 60-fps camera used, the whole process, which includes image acquisition, preprocessing the image, recognition of the hand shape and a display of the winning hand form, is done within about 16 msec. The optimal display time is decided on the basis of experience, recognition of the hand form and the time needed to present one of the three symbols without giving the opponent, who has average reactions a feeling of delay.

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Recently many live performances have featured the use of information technologies, for example, projecting visual images. We created a new Noh-style stage performance based on traditional forms combined with a modern arrangement using information technologies. In the performance, we had virtual actors presented by CG animation act on the Noh stage. We used human motion data obtained by a motion capture system to create the movements of the virtual actors and had them act with the real actors. We describe the method of projection in a traditional Noh theater, the creation of virtual actors using 3D-motion data, and the method of controlling virtual actors.

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