Showing papers on "Alpha compositing published in 1991"

Method and apparatus for rendering anti-aliased polygons

Abstract: A scan conversion process is performed on a polygon using a single pass technique. The pixels which comprise the edges and vertices of the polygon are first determined from the vertices which define the polygon. The alpha channel comprises either a sub-pixel mask associated with each pixel which indicates the amount and sub-pixel regions of coverage or a single value indicative of the percentage of coverage of a pixel. Furthermore, a z value indicative of the depth of each pixel is maintained. The pixels between the edge pixels of the polygon are then turned on, thereby filling the polygon. The pixels which comprise the polygon are then composited with the background pixels on a per pixel basis. The depth value of each pixel of the polygon (the z value) is used to determine the compositing equations to be used to composite each pixel of the polygon to the background. The compositing equations update the color of the pixel, the z buffer value of the background pixel and the sub-pixel mask to reflect the addition of information from the compositing of the pixel of the polygon into the background pixel. Through this method high quality anti-aliased polygons may be rendered without performing the time consuming process of sorting the polygons in depth order prior to compositing.

Image-Composition Architectures for Real-Time Image Generation

Abstract: This dissertation describes a new approach for high-speed image-generation based on image compositing Application software distributes the primitives of a graphics database over a homogeneous array of processors called renderers Each renderer transforms and rasterizes its primitives to form a full-sized image of its portion of the database A hardware datapath, called an image-composition network, composites the partial images into a single image of the entire scene Image-composition architectures are linearly scalable to arbitrary performance This property arises because: (1) renderers compute their subimages independently, and (2) an image-composition network can accommodate an arbitrary number of renderers, with constant bandwidth in each link of the network Because they are scalable, image-composition architectures promise to achieve much higher performance than existing commercial or experimental systems They are flexible as well, supporting a variety of primitive types and rendering algorithms Also, they are efficient, having approximately the same performance/price ratio as the underlying renderers Antialiasing is a special challenge for image-composition architectures The compositing method must retain primitive geometry within each pixel to avoid aliasing Two alternatives are explored in this dissertation: simple z-buffer compositing combined with supersampling, and A-buffer compositing This dissertation describes the properties of image-composition architectures and presents the design of a prototype z-buffer-based system called PixelFlow The PixelFlow design, using only proven technology, is expected to render 25 million triangles per second and 870 thousand antialiased triangles per second in a two-card-cage system Additional card cages can be added to achieve nearly linear increases in performance

A Physically Based Colour Model

Abstract: We propose an intuitively simple way of representing colour which has the additional virtue that, it permits mixing and overlaying of transparent and opaque paints to an arbitrary degree. Our approach is related to the earlier alpha channel model used for compositing. It includes this as a special case but has applications in many other areas, especially animation, paint programs and graphics libraries.