Showing papers on "Alpha compositing published in 1998"

Visibility sorting and compositing without splitting for image layer decompositions

Abstract: We present an efficient algorithm for visibility sorting a set of moving geometric objects into a sequence of image layers which are composited to produce the final image. Instead of splitting the geometry as in previous visibility approaches, we detect mutual occluders and resolve them using an appropriate image compositing expression or merge them into a single layer. Such an algorithm has many applications in computer graphics; we demonstrate two: rendering acceleration using image interpolation and visibility-correct depth of field using image blurring. We propose a new, incremental method for identifying mutually occluding sets of objects and computing a visibility sort among these sets. Occlusion queries are accelerated by testing on convex bounding hulls; less conservative tests are also discussed. Kd-trees formed by combinations of directions in object or image space provide an initial cull on potential occluders, and incremental collision detection algorithms are adapted to resolve pairwise occlusions, when necessary. Mutual occluders are further analyzed to generate an image compositing expression; in the case of nonbinary occlusion cycles, an expression can always be generated without merging the objects into a single layer. Results demonstrate that the algorithm is practical for real-time animation of scenes involving hundreds of objects each comprising hundreds or thousands of polygons. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation Display algorithms. Additional

System and method for performing blending using an over sampling buffer

Abstract: The present invention provides an alpha blending unit that is able to perform alpha blending on sub-samples of a pixel in an efficient manner. The alpha blending unit preferably comprises a plurality of registers for storing a source color, a blending value, and a plurality of destination sub-sample values, multipliers, adders, an accumulator and a divider. The alpha blending unit advantageously sums the destination sub-sample values and then divides them by the number of sub-samples to generate a combined destination color value. This combined destination color value along with the source color and a blending value are then provided to the multipliers, and adders to generate a new destination color value for the pixel.

Jim Blinn's corner: dirty pixels

Abstract: 1. The World's Largest Easter Egg and What Came Out of It 2. What We Need Around Here Is More Aliasing 3. Return of the Jaggy 4. How Many Different Curves Are There? 5. Dirty Pixels 6. Cubic Curve Update 7. Triage Tables 8. The Wonderful World of Video 9. Uppers and Downers 10. Uppers and Downers, Part II 11. The World of Digital Video 12. How I Spent My Summer Vacation-1976 13. NTSC: Nice Technology, Super Color 14. What's the Deal with the DCT? 15. Quantization Error and Dithering 16. Compositing-Theory 17. "Composting"-Practice 18. How to Attend a SIGGRAPH Conference 19. Three Wrongs Make a Right 20. Fun with Premultiplied Alpha

Compositing digital images

Abstract: Most computer graphics pictures have been computed all at once, so that the rendering program takes care of all computations relating to the overlap of objects. There are several applications, however, where elements must be rendered separately, relying on compositing techniques for the anti-aliased accumulation of the full image. This paper presents the case for four-channel pictures, demonstrating that a matte component can be computed similarly to the color channels. The paper discusses guidelines for the generation of elements and the arithmetic for their arbitrary compositing.

Pixel masks for screen-door transparency

Abstract: Rendering objects transparently gives additional insight in complex and overlapping structures. However, traditional techniques for the rendering of transparent objects such as alpha blending are not very well suited for the rendering of multiple transparent objects in dynamic scenes. Screen door transparency is a technique to render transparent objects in a simple and efficient way: no sorting is required and intersecting polygons can be handled without further preprocessing. With this technique, polygons are rendered through a mask: only where the mask is present, pixels are set. However, artifacts such as incorrect opacities and distracting patterns can easily occur if the masks are not carefully designed. The requirements on the masks are considered. Next, three algorithms are presented for the generation of pixel masks. One algorithm is designed for the creation of small (e.g. 4/spl times/4) masks. The other two algorithms can be used for the creation of larger masks (e.g. 32/spl times/32). For each of these algorithms, results are presented and discussed.

Architecture of a coprocessor module for image compositing

Abstract: This paper proposes the architecture of a coprocesssor module for image compositing. The emerging MPEG-4 standard for multimedia applications allows script-based compositing of audiovisual scenes from multiple audio and visual objects. This involves the composition of the output frame by alpha-blending of Video Object Planes (VOPs). A coprocessor architecture is presented, that works in parallel to an MPEG-4 video- and audio-decoder, and performs computation and bandwidth intensive low-level algorithms for image compositing. The processor has on-chip memories that allow preload of data before it is accessed. VHDL implementation and synthesis for a 0.5/spl mu/ process show an estimate of 100 MHz achievable clock-frequency and 10 k gates for arithmetic and control circuitry which results in roughly 5 mm/sup 2/ silicon area. Overall performance is sufficient to compose more than 5 full-screen VOPs with a background of size 704/spl times/576 each at 30 Hz.

Pixel clustering for improved graphics throughput

Abstract: A 3-D graphics system combines a software programmed setup processor, a 3-D pipeline, and a software programmed back end processor. The setup processor performs 'setup' on polygons for the 3-D pipeline. The 3-D pipeline rasterizes the polygons to create pixels. The back end processor performs back end processing, such as Z-buffering and alpha blending on the pixels. In one embodiment, the throughput of the 3-D graphics system is increased by clusterizing the pixels before back end processing. Specifically, a clusterizer combines pixels into clusters that can be processed by the back end processors without data coherency problems. Furthermore, the pixels are selected for a cluster to minimize memory latency and access times. In one embodiments, clusters are filled with fill addresses by a cluster filler. The filled addresses generated by the cluster filler, do not cause potential hazards in the back end processor.

Method and device for generating three-dimensional image

Abstract: (57) [Summary] In a computer three-dimensional image, in addition to the conventional perspective method, a more natural and effective three-dimensional image is provided. A transparency designating means for setting greater transparency for each object as the distance from the viewpoint is smaller. 4 and an image synthesizing unit 15 that performs hidden surface processing on the image of each object to which transparency has been added by the image generating unit and the transparency designating unit while considering transparency, and synthesizes the image into one image. , Can provide a more natural and effective three-dimensional image.

Digital still camera with composite image display function

Abstract: PROBLEM TO BE SOLVED: To confirm prior to photographing the composition ratio on a digital still camera, having an image composting function to set its composition ratio. SOLUTION: An image selected by an image selecting means 22 is read out of a storage means 23 and inputted to an image compositing means 26. An image-pickup means 24 picks up a current image and inputs it to the image compositing means 26. While the means 26 composites an image of both the images displays their composited image on a display means 27, a compositing ratio setting means 25 sets the composite ratio of the selected image and current image.

An array processor architecture with parallel data cache for image rendering and compositing

Abstract: This paper proposes a new array architecture for MPEG-4 image compositing and 3D rendering. The emerging MPEG-4 standard for multimedia applications allows VRML-like script-based compositing of audio-visual scenes from multiple audio and visual objects. MPEG-4 supports both natural (video) and synthetic (3D) visual objects or a combination of both. Objects can be manipulated e.g. positioned, rotated, warped or duplicated by user interaction. A coprocessor architecture is presented, that works in parallel to an MPEG-4 video and audio-decoder and a floating-point geometry-processor. It performs computation and bandwidth intensive low-level tasks for image compositing and rasterization. The processor consists of a SIMD array of 16 identical DSPs to reach the required processing power for real-time image warping, alpha-blending, z-buffering and phong-shading. The processor has an object-oriented parallel cache architecture with 2D virtual address space (e.g. textures) that allows concurrent and conflict-free access to shared image data objects for all 16 DSPs.

Image blending by feature overwrite

Abstract: This paper describes a new image compositing algorithm that can properly blend images whose features have a high aspect ratio. Although several techniques have been used in image compositing, none of them works well for images whose features have a high aspect ratio. This compositing algorithm is a simulation on 2D projected space, of the physical phenomena of underlying 3D models. Our algorithm consists of the three steps. First, the images are composited using a multiresolution technique. Second, the features of each image are extracted. Finally, the features are overwritten to the composited image. This method makes it possible to composite hair or fur naturally.

An Evolving Approach to Computer Graphics Courses in Computer Science

Abstract: in the field. Topics in this course include the process of presenting 3D images on a 2D surface (projections and viewing; Z-buffers), developing and presenting realistic images (texture maps, environment maps, antialiasing, alpha channel, lighting models), and managing the viewing device (scan conversion, clipping). The second course is close to the concepts and algorithms course described in [BRO 88] and [OHL 86], frequently taught now as the first computer graphics course, but is not the kind of course in specialized techniques or systems that is sometimes considered as an advanced course [OWE 92]. Recent developments in computer graphics APIs permit us to take a new approach to teaching a first graphics course that parallels a first computer programming course. This first graphics course, and a second course that could follow it, are briefly described and are placed in the context of current graphics courses. New Opportunities in Graphics Courses There are two reasons students study computer graphics: to be able to do computer graphics programming, either on the job or for personal work, or to understand computer graphics deeply in order to build a graphics-focused career. Few computer science programs can develop separate courses for these two kinds of students because the faculty and equipment resources needed are too scarce. Thus we must consider courses that serve both purposes. An analogy might be useful. This analogy is the general programming environment, in which students learn programming through a high-level language (and the trend has been to move the level of the language upwards as the field has matured) and later learn the details of how program execution works. In a more diagrammatic form: Computer is: Problem Solving + Language