Sun Microsystems, Inc.

Stuart C Wells

Grant J Williamson

James Van Loo

Mukund Bhakta

Jack R McKeown

Dawn M Wallner

James V Loo

Jack R Mckeown

The method and apparatus of the present invention takes into consideration that the eye is more sensitive to intensity variations at low levels of intensity than at high levels of intensity and produces higher quality dithered images by employing a sectioned or piecewise linear quantization strategy which sacrifices the fineness of interval spacing at the high end of the intensity scale in order to achieve greater accuracy of reproduction at the low end. The input intensity values are divided into a plurality of sub-ranges indicative of low intensities and high intensities. The number of input intensity levels allocated to the low intensity sub-ranges is small and the number of quantized or output intensity levels allocated to the low intensity sub-ranges is large compared to those allocated to the high intensity sub-ranges such that the interval spacing at the low intensity sub-ranges is small to provide greater accuracy at the low intensity levels where the eye is most sensitive.

Method and apparatus for non-linear dithering of digital images

A method and apparatus for dithering vectors in which the dither matrix is aligned to the vector and not to the display coordinate space. The dither matrix is aligned to the vector according to the major axis of the vector. In a preferred embodiment the dither matrix is rectangular in shape to correspond to the shape of the vector. The vector aligned dither matrix ensures that the individual pixels which make up the vector are dithered with elements more likely to simulate the original intermediate intensities.

Method and apparatus for vector aligned dithering

An adaptive shading method is utilized to generate shaded images in real time. The technique to shade the image is determined according to the curvature of the surface, the variation of the light vector across the surface, and the variation of the eye vector across the surface. The color or intensity is first computed at each of the vertices of the polygon. A series of tests are then performed to determine the order equation that is to be used to interpolate the color or intensity across the polygon between the vertices. Using this technique, polygons having a slight or no curvature and an infinite light source (thus being the simplest form of shading), will use an extremely fast, low order equation to interpolate across the polygon. Polygons, having a high degree of curvature and/or positional light source will utilize, as necessary, a higher order equation which requires additional computation time but produces desirable shading results.

Method and apparatus for adaptive Phong shading

In the method and apparatus of the present invention, dithered images are composited with separately rendered undithered images. The dithered image is first transformed back to its unquantized state to include the full range of intensity values by performing a back-transforming process which translates the quantized or dithered value back to its original intensity value. The back transformed dithered image is then combined with the separately rendered, but undithered image using the technique of compositing. The composited image is then dithered to a quantized representation are stored in the frame buffer for subsequent display.

Method and apparatus for the dithering of antialiased vectors

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.

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Santa Clara, CA, United States of America

Stuart C Wells