Ned Greene and Michael Kass. Approximating Visibility with Environment Maps. Technical Report 41, Apple Computer, Inc., 1994.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....Examples of exact visibility representations are the aspect graph [20] or the visibility skeleton [9] and exact shadow boundaries [3, 8, 23, 27] As mentioned above, they are impractical for complex scenes. Point sampling algorithms calculate visibility up to the accuracy of the display resolution [5, 7, 13]. One sample ray is sent into the scene and the obtained visible surface is reused over an area (e.g. a pixel or solid angle on the hemisphere) Today s most widely used approach is a hardware accelerated z buffer [2] or its variants, the hierarchical z buffer [14] and hierarchical occlusion maps ....

Greene, Ned "Approximating Visibility with Environment Maps," Graphics Interface '86, pp 108-114.

....previously rendered or digitized views. Creating a light eld does not require any explicit geometry or illumination information of the scene, and thus bypasses the modeling problem. Compared to other image based rendering techniques such as Apple s QuickTime VR[3] or view interpolation [4, 5, 6, 7, 8, 9, 10], light eld rendering is simple, robust, and allows more freedom in the range of possible views. Created from images captured at a number of camera positions, a light eld is a collection of light rays owing through space. The four dimensional structure of a light eld and the high sampling ....

N. Greene and M. Kass, Approximating Visibility with Environment Maps, Apple Technical Report, November 1994.

....some form of explicit or implicit per pixel depth information to the reference images, restrictions on translation can be removed. Systems developed by Greene and Kass, Chen and Williams, and McMillan and Bishop take this approach. I will describe each of these systems in turn. 27 Greene and Kass [Greene94] develop an approach for walkthroughs of static scenes which is a hybrid between geometric rendering and image based rendering. Because image based representations are prone to occlusion errors caused by objects close to the viewpoint, they separate the geometry for a given reference viewpoint ....

Ned Greene and Michael Kass. Approximating visibility with environment maps. Technical Report #41, Apple Computer, November 1994.

.... were optically or electronically processed to obtain 360 degree viewing [1] 9] A project called Navigation used a grid of panoramas for sailing simulation [10] Real time reprojection of environment maps was used to visualize surrounding scenes and to create interactive walkthrough [11] [12]. A hardware method for environment map look up was implemented for a virtual reality system [13] While rendering an environment map is trivial with a computer, creating it from photographic images requires extra work. Greene and Heckbert described a technique of compositing multiple image ....

....quantized to the nearest grid point to approximate the motion (figure 2) However, this approach requires a larger number of environment maps to be stored in order to obtain smooth motion. A more desirable approach may be the view interpolation method [18] or the approximate visibility method [12], which generates new views from a coarse grid of environment maps. Instead of constraining the movement to the grid points, the nearby environment maps are interpolated to generate a smooth path. Figure 2. An unconstrained camera path and an approximated path along the grid lines. 3.4 Camera ....

Greene, NandM. Kass. Approximating Visibility with Environment Maps. Technical Report No. 41. Apple Computer, Inc.

....to navigate discretely from location to location, and while at each location continuously change the viewing direction. The major limitation of rendering systems based on environment maps is that the viewpoint is fixed. One way to relax this fixed position constraint is to use view interpolation [Chen93, Greene94, Fuchs94, McMillan95a, McMillan95b, Narayanan95]. Most of these methods require a depth value for each pixel in the environment map, which is easily provided if the environment maps are synthetic images. Given the depth value it is possible to reproject points in the environment map from different vantage points to warp between multiple images. ....

Greene, N. and Kass, M., "Approximating Visibility with Environment Maps," Apple Technical Report No. 41, November, 1994.

....a subset of the scene visible from a specified viewing region [AIRE91, TELL92] Only the potentially visible objects are processed in the walkthrough time. This approach does not completely solve the problem because there may be viewing regions from which all objects are visible. Greene and Kass[GREE93] developed a method to approximate the visibility at a location from adjacent environment maps. The environment maps are Z buffered images rendered from a set of discrete viewpoints in 3D space. Each environment map shows a complete view of the scene from a point. An environment map can take the ....

Greene, N. and M. Kass. Approximating Visibility with Environment Maps. Technical Report 41, 1993, Apple Computer, Inc.

....issues in detail. The algorithm is demonstrated on pre rendered synthetic imagery. A later system [28] used a 3D cylindrical to planar warp for acquired imagery. Similar warping calculations have been used to accelerate ray tracing of animations and stereo pairs [1, 2, 7] Greene and Kass [15] generated simplified image like representations of a scene by retaining only those polygons which were visible in a Z buffered image from the reference viewpoint. To minimize cracking, polygons which occupied a pixel in this image but whose true projected screen space area was smaller than a ....

....and a separate affine or 2D projective warp is applied to each layer. Different layers can also then be re rendered at different rates. This technique is an alternative to a full 3D warp. Variations on it are used by Talisman [36] Regan and Pose (priority rendering) 30] and by Greene and Kass [15]. This last system actually renders the near geometry in the standard fashion into every derived frame only the far geometry is represented in image form. The texture based simplification systems mentioned earlier [3, 32] can also be considered to be layered systems. 3.5 Predictive Tracking ....

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Ned Greene and Michael Kass. Approximating visibility with environment maps. Technical Report #41, Apple Computer, November 1994.

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Ned Greene and Michael Kass. Approximating Visibility with Environment Maps. Technical Report 41, Apple Computer, Inc., 1994.

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N. Greene and M. Kass, Approximating Visibility with Environment Maps, Apple Technical Report, November 1994.

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