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Item Method for Calculation of Sky Light Luminance Aiming at an Interactive Architectural Design(Blackwell Science Ltd and the Eurographics Association, 1996) Dobashi, Yoshinori; Kaneda, Kazufumi; Yamashita, Hideo; Nishita, TomoyukiRecently, computer graphics are frequently used for both architectural design and visual environmental assessment. Using computer graphics, designers can easily compare the effect of the natural light on their architectural designs under various conditions, such as different times of day, seasons, atmospheric conditions (clear or overcast sky) or building wall materials. In traditional methods of calculating the luminance due to sky light, however, all calculation must be performed from scratch if such conditions undergo change. Therefore, to compare the architectural designs under different conditions, a great deal of time has to be spent on generating the images.This paper proposes a new method of quickly generating images of an outdoor scene, taking into account glossy specular reflection, even if such conditions change. In this method, luminance due to sky light is expressed by a series of basis functions, and basis luminances corresponding to each basis function are precalculated and stored in a compressed form in the preprocess. Once the basis luminances are calculated, the luminance due to sky light can be quickly calculated by the weighted sum of the basis luminances. Several examples of an architectural design demonstrate the usefulness of the proposed method.Item Modeling of Skylight and Rendering of Outdoor Scenes(Blackwell Science Ltd and the Eurographics Association, 1993) Tadamura, Katsumi; Nakamae, Eihachiro; Kaneda, Kazufumi; Baba, Masashi; Yamashita, Hideo and Nishita, TomoyukiPhotorealistic animated images are extremely effective for pre-evaluating visual impact of city renewal and construction of tall buildings. In order to generate a photorealistic image not only the direct sunlight but also skylight must be considered.This paper proposes a method of high-fidelity image generation for photorealistic outdoor scenes based on the following ideas: * 1The intensity distribution of skylight taking account of scattering and absorption due to particles in the atmosphere which coincides with CIE standard skylight luminance functions is sought, and realistic images considering about spectrum distribution of skylight for any altitude of the sun can be easily and accurately displayed. * 2A rectangular parallelepiped with a specialized distribution of intensity simulating the skylight is introduced for efficient calculation of illumination due to skylight, and by employing a graphics hardware calculation of the skylight illuminance taking into account shadow effects is obtained with high efficiency- these techniques can be used to generate sequences of images, making animations possible at far lower calculation cost than previous methods.Item A Projection Mapping System onto a Human Body for Medical Applications(The Eurographics Association, 2019) Fukuhara, Ryo; Kaneda, Kazufumi; Tamaki, Toru; Raytchev, Bisser; Higaki, Toru; Nishimoto, Soh; Sotsuka, Yohei; Fusiello, Andrea and Bimber, OliverIn breast reconstructive surgery where patient's abdominal fat and blood vessels are transplanted to the breast, it is very important to identify the course of the blood vessels inside the abdomen. In this paper, we propose a system for projecting blood vessels extracted from computer tomography angiography (CTA) on a patient's abdominal surface to support the breast reconstructive surgery. The proposed system detects the position and orientation of a projector automatically using an image captured by a camera mounted with the projector and is able to project the exact course of the blood vessels onto an abdominal skin from an arbitrary direction. An experiment using an abdominal model fabricated from patient's CTA data with a 3D printer demonstrates the usefulness of the proposed system.Item A Quick Rendering Method Using Basis Functions for Interactive Lighting Design(Blackwell Science Ltd and the Eurographics Association, 1995) Dobashi, Yoshinori; Kaneda, Kazufumi; Nakatani, Hideki; Yamashita, Hideo; Nishita, TomoyukiWhen designing interior lighting effects, it is desirable to compare a variety of lighting designs involving different lighting devices and directions of light. It is, however, time-consuming to generate images with many different lighting parameters, taking interreflection into account, because all luminances must be calculated and recalculated. This makes it difficult to design lighting effects interactively. To address this problem, this paper proposes a method of quickly generating images of a given scene illustrating an interreflective environment illuminated by sources with arbitrary luminous intensity distributions. In the proposed method, the luminous intensity ditribution is expressed with basis functions. The proposed method uses a series of spherical harmonic functions as basis functions, and calculates in advance each intensity on surfaces lit by the light sources whose luminous intensity distribution are the same as the spherical harmonic functions. The proposed method makes it possible to generate images so quickly that we can change the luminous intensity distribution interactively. Combining the proposed method with an interactive walk-through that employs intensity mapping, an interactive system for lighting design is implemented. The usefulness of the proposed method is demonstrated by its application to interactive lighting design, where many images are generated by altering lighting devices and/or direction of light.Item Perceptually Based Afterimage Synthesis(The Eurographics Association, 2012) Mikamo, Michihiro; Slomp, Marcos; Raytchev, Bisser; Tamaki, Toru; Kaneda, Kazufumi; Carlos Andujar and Enrico PuppoAfterimages comprise a common, recurring perceptual phenomenon experienced in a daily-basis. Afterimages are best realized when staring at some high intensity light source (i.e., a light bulb) and then shifting the ocular focus to other less luminous portions of the scene: a temporary “ghost” image of that strong intensity remains imprinted on the retina. During the time the afterimage stays active, several exquisite color gradations appear and fade. Although research on the topic has been moderately active in ophthalmology and vision domains, no definitive model has been devised. Furthermore, no afterimage simulation seems to have yet been investigated in computer graphics. In this paper we attempt to introduce the topic to the field and therefore widen the research spectrum of computer graphics. The proposed technique is based on psychophysical and physiological evidence, addressing the color transitions and the duration of the effect. The method is also fast and suitable for real-time applications. Our stance towards afterimages is more than just curiosity on this peculiar effect: we believe that its understanding and proper simulation can assist on relevant tasks such as urban and road engineering for safer pedestrian and vehicle mobility at adverse lighting conditions.Item A Tone Reproduction Operator for All Luminance Ranges Considering Human Color Perception(The Eurographics Association, 2014) Mikamo, Michihiro; Raytchev, Bisser; Tamaki, Toru; Kaneda, Kazufumi; Eric Galin and Michael WandIn this paper, we present a novel tone reproduction operator that is able to handle the color shift that occurs in photopic, mesopic, and scotopic vision, using a model based on a two-stage model of human color vision and psychophysical data obtained from measurements of human color perception. Since conventional methods are limited to generating images under a certain visual condition, it is difficult to apply just one operator to deal with scenes with continuous change within a wide luminance range, such as various scenes in movies. To overcome this problem, we have developed a model based on psychophysical data involving wavelength discrimination within a wide luminance range, which provides us with clues about the change of color perception. That is, the spectral sensitivity shifts toward the short wavelengths and decreases according to the adaptation light levels. By integrating the wavelength discrimination into our model, the proposed operator enables us to compute the transition of color perception under a wide range of viewing conditions.Item Skylight for Interior Lighting Design(Blackwell Science Ltd and the Eurographics Association, 1994) Dobashi, Yoshinori; Kaneda, Kazufumi; Nakashima, Takanobu; Yamashita, Hideo; Nishita, Tomoyuki and Tadamura, KastumiIt is inevitable for indoor lighting design to render a room lit by natural light, especially for an atelier or an indoor pool where there are many windows. This paper proposes a method for calculating the illuminance due to natural light, i.e. direct sunlight and skylight, passing through transparent planes such as window glass. The proposed method makes it possible to efficiently calculate such illuminance accurately, because it takes into account both non-uniform luminous intensity distribution of skylight and the distribution of transparency of glass according to incident angles of light. Several examples including the lighting design in an indoor pool, are shown to demonstrate the usefulness of the proposed method.