Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1997-10-15
2001-03-20
Powell, Mark R. (Department: 2779)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
C345S428000, C345S422000
Reexamination Certificate
active
06204859
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to computer graphics, and more particularly to a method and apparatus for producing composite colors images defined by subpixel resolution.
BACKGROUND
Many computer graphics systems use pixels to define images. The pixels are arranged on a display screen as an rectangular array of points. Aliasing occurs because the pixels have a discrete nature. Artifacts can appear when an entire pixel is given a light intensity or color based upon an insufficient sample of points within that pixel. To reduce aliasing effects in images, the pixels can be sampled at subpixel locations within the pixel. Each of the subpixel sample locations contributes color data that can be used to generate the composite color of that pixel. However, some graphics systems may limit the amount of memory for storing subsample color data for each pixel. Thus, such graphic systems must carefully select which color data are stored so that these systems can still accurately produce a composite color for each pixel.
Hence, there is a need for a method and an apparatus that, for each pixel, can make color selections and replacements without introducing unsatisfactory artifacts into a displayed image.
SUMMARY OF THE INVENTION
In accordance to the present invention, an objective is to provide an apparatus and method for determining colors of pixels. Another objective is to operate effectively within memory constraints for storing pixel data by selecting the fragment data that contributes to the color of a given pixel, which can be from fragments of different objects or surfaces of the image, while minimizing noticeable color differences for the pixel and avoiding the introduction of unsatisfactory artifacts.
The present invention resides in a method and an apparatus for determining a color of a pixel. In terms of the method, the invention stores up to a predetermined number of fragment values for the pixel. Each stored fragment value is associated with a fragment of an image that is visible in that pixel. A new fragment is determined to be visible in the pixel with at least one other fragment with a stored fragment value still being visible in the pixel. The fragment value of one of the visible fragments is discarded to determine which fragment values are stored and subsequently used to generate the color of the pixel.
In one aspect of the method, the discarded fragment value is the new fragment value of the new fragment. In another aspect, the discarded fragment value is one of the stored fragment values.
In yet another aspect, the new fragment is part of a different surface of the image than each of the fragments associated with a stored fragment value.
In still another aspect, the method selects for discarding the stored fragment value with the Z-depth value that is larger than the Z-depth value of each other stored fragment value, and replaces that fragment value with the new fragment value. The greater the Z-depth value, the farther the associated fragment is from the viewer of the image.
In still yet another aspect, the method selects for discarding the stored fragment value with the color value that produces a numerically smaller color difference than the color value of each other stored fragment value when compared to the color value of the new fragment value. Discarding the fragment value that produces the smallest color difference minimizes any noticeable color change for the pixel.
In still another aspect, the two above aspects of the method can be used to discard the new fragment.
In terms of the apparatus, the invention comprises a memory and a graphics device. The memory stores up to a predetermined number of fragment values for a given pixel. Each stored fragment value is associated with a fragment of an image that is visible in that pixel. The graphics device determines that a new fragment is visible in the pixel with at least one other fragment with a stored fragment value still being visible in the pixel. The graphics device discards the fragment value of one of the visible fragments to determine which fragment values can be used to generate the color of the pixel.
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Chang Chun-Fa
Jouppi Norman P.
McCormack Joel J.
Digital Equipment Corporation
Good-Johnson Motilewa
Pennie & Edmonds LLP
Powell Mark R.
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