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Now showing 1 - 6 of 6
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    Cross Scan Buffer and its Applications
    (Blackwell Science Ltd and the Eurographics Association, 1994) Tanaka, Toshimitsu; Takahashi, Tokiichiro
    We propose the Cross Scanline Buffer which preserves the result of hidden surface removal as performed by the Cross Scanline Algorithm. The Cross Scan Buffer reduces image re-generation time and eliminates aliasing artifacts even if the image is arbitrarily scaled. Perfect anti-aliasing is achieved because the Cross Scanline Algorithm analytically determines visible polygonal surfaces and divides them into sets of triangles and trapezia. The Cross Scan Buffer supports the various applications that currently use the conventional buffering methods for anti-aliasing. This paper introduces and tests three applications: image scaling, shadow creation, and texture mapping. Experimental results verify that the Cross Scan Buffer is very powerful yet efficient.
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    Cross Scanline Algorithm
    (Eurographics Association, 1990) Tanaka, Toshimitsu; Talcahashi, Tokiichiro
    This paper proposes a new hidden surface removal algorithm which is based on the scanline algorithm but scans in two directions, horizontally and vertically. Named the cross scanline algorithm, it can efficiently detect all polygons and calculate their exact projected areas in each pixel even if the polygons are much smaller than the pixel. Comparisons with the regular sub-scanlines algorithm show that high quality anti-aliased images can be generated.
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    Shading with Area Light Sources
    (Eurographics Association, 1991) Tanaka, Toshimitsu; Takahashi, Tokiichiro
    This paper derives a shading model for area light sources which covers both diffuse and specular reflection. The shading model assumes ideally diffuse polygonal light sources and uses Phong’s reflection model. The model can accurately integrate the intensities of diffuse and specular reflection without simulating an area light source as an array of point light sources. To simplify the reflection integration, each light source is transformed from the Cartesian coordinate system into the polar system. The light source is projected onto a unit sphere and then triangulated along great circles of the unit sphere. Finally, the integration value is calculated by polynomial approximation. Since our method can accurately integrate both diffuse and specular reflection, it can generate images that are more photorealistic than conventional methods. Because point light sources are not employed, highlight roughness is completely suppressed. Several images are presented that show the advantages of our method.
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    Painting-like Image Emphasis based on Human Vision Systems
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Tanaka, Toshimitsu; Ohnishi, Noboru
    Regional image emphasis is often evident in paintings and illustrations. This technique increases local contrast while reducing global contrast by amplifying image intensity on shadowed surfaces, reducing intensity on illuminated surfaces, and then expanding contrast at intensity edges. The effects are assumed to result from the visual processing needed to interpolate the real world onto canvas. Therefore, we propose an intensity emphasis method based on human vision. This method simulates the adaptation of photoreceptor cells and the lateral inhibition of receptive fields. These attributes of a vision system are realized by computation of relative intensity and differential intensity in small areas.The proposed method can successfully generate painting-like artifacts, which greatly improves the perception of visual elements displayed in an image. Since the method efficiently reduces the dynamic range of images, it can be used for displaying highlighted images on standard graphic monitors. Experiments on a computer-generated image and a photograph confirm the advantages of our method.
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    Fast Shadowing Algorithm for Linear Light Sources
    (Blackwell Science Ltd and the Eurographics Association, 1995) Tanaka, Toshimitsu; Takahashi, Tokiichiro
    This paper presents a fast shadowing algorithm for linear light sources that uses a ray-oriented buffer. Space segmentation by the buffer guarantees that if a point is included in a subspace, all light rays toward the point are also contained in the subspace. Each cell of the buffer stores a list of objects that lie within or intersect the subspace allocated to the cell. Therefore, candidate objects, those that may cast shadows onto a point, are determined by referring to the cell where the point is mapped. In addition, whether each candidate object actually casts shadows or not is tested with the bounding-volume of the shadow space to reduce the number of objects subjected to expensive light clipping. The bounding-volumes are also stored in the buffer. For efficiently generating the ray-oriented buffer, we present the cylindrical scan-conversion algorithm. The algorithm preconverts objects surfaces to trapezia to decrease the light clipping cost, then connects the trapezia to the buffer cells.Due to the above improvements, our algorithm achieves over 10 times faster shadow generation compared to the conventional methods. Experimental results confirm that our method can generate realistic images with soft shadows in a few minutes.
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    Fast Analytic Shading and Shadowing for Area Light Sources
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Tanaka, Toshimitsu; Takahashi, Tokiichiro
    This paper describes a fast analytic algorithm that generates exact highlights and soft shadows from area light sources. In order to realize fast shadowing, we propose the ray-oriented buffer which segments 3D space by following light rays from polygonal sources. Each cell of the buffer stores objects that intersect a related subspace. Candidate objects which may cast shadows onto a point are selected by referring to the buffer. The candidates are then tested with their shadow bounding volumes to suppress objects that never occlude light sources.In addition, we propose the cross scanline clipping algorithm. It quickly determines the exact regions of uncovered area light sources with simple silhouette generation. Both diffuse and specular reflections are computed by integrating light rays from the uncovered sources. Experimental results confirm the high performance of the proposed method.