Full-scene antialiasing using improved supersampling techniques

• US 6,128,000 A
• Filed: 10/15/1997
• Issued: 10/03/2000
• Est. Priority Date: 10/15/1997
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: McCormack, Joel J., Jouppi, Norman P.
• Primary Examiner(s): CHANG, KENT WU
• Application Number:
  US08/958,129
• Time in Patent Office: 1,084 Days
• Field of Search: 345/150, 345/152, 345/147-149, 345/136-138, 345/431, 345/432, 345/433
• US Class Current: 345/614
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77
• CPC Class Codes: G06T 11/40 Filling a planar surface by adding surface attributes, e.g. colour or texture
• CPC Class Codes: G06T 15/10 Geometric effects

Abstract

A method and an apparatus reduces aliasing artifacts in images defined by pixels. A pixel is partitioned into subpixel locations from which sample points are selected. A fragment of the image is determined to be visible at at least one of the sample points. A fragment value associated with that fragment is stored. Each sample point at which the fragment is visible is linked to the stored fragment value. A color of the pixel is computed from the stored fragment values to reduce the aliasing artifacts in the image.

Claims

1. A computerized method for rendering an image defined by pixels, the pixels having an allocated memory, the method comprising the steps of:

selecting subpixel positions in a pixel as sample points;

storing a fragment value associated with a fragment of the image, the fragment covering at least one of the sample points;

linking each covered sample point to the stored fragment value to enable the generation of a color of the pixel using the fragment value;

processing a new fragment having a new fragment value, the new fragment being visible at one or more of the sample points of the pixel; and

replacing the stored fragment value with the new fragment value.

2. The method of claim 1 wherein the step of linking includes the steps of:

associating an index with each covered sample point; and

storing a value in each index that points to the stored fragment value.

3. The method of claim 1 wherein the step of linking includes the steps of:

associating a bit pattern with the stored fragment value, the bit pattern having a sequence of bits, each bit in the sequence being associated with one of the sample points; and

storing a value in each bit, the value in each bit indicating whether or not the sample point associated with that bit is covered by the fragment.

4. The method of claim 1 further comprising the step of:

partitioning the pixel into an array of subpixel positions, the array having N rows and N columns where N is an integer greater than one; and

wherein each selected sample point is in a different row and in a different column than every other sample point in that pixel.

5. The method of claim 1 wherein there are fewer sample points than subpixel positions in the pixel.

6. The method of claim 1, wherein:

the memory allocated to the pixels is allocated for storing a predetermined number of fragment values, the predetermined number being less than the number of sample points in the pixel.

7. The method of claim 1, further comprising the step of:

computing a color for the pixel using the new fragment value and each stored fragment value before replacing the stored fragment value with the new fragment value.

8. The method of claim 1, further comprising the step of:

reducing a number of sample points for the pixel when storing a fragment value associated with a subsequent fragment would exceed an amount of memory available for the pixel.

9. The method of claim 1, further comprising the steps of:

selecting subpixel positions in a second pixel as sample points; and

linking one of the sample points of the second pixel to the stored fragment value.

10. The method of claim 1, further comprising the steps of:

determining whether the memory allocated to the pixel is available for storing the new fragment value before storing the new fragment value; and

responsive to there not being enough memory allocated to the pixel for storing the new fragment value;

replacing the stored fragment value with the new fragment value.

11. The method of claim 10, wherein determining whether the memory allocated to the pixel is available for storing the new fragment value includes the step of:

counting links to each previously stored fragment value.

12. A method for reducing aliasing artifacts in an image defined by pixels comprising the steps of:

selecting subpixel positions in a pixel as sample points;

determining that a new fragment of the image is visible at one or more of the sample points of the pixel, the new fragment having a new fragment value;

allocating addresses of memory for the pixel for storing a predetermined number of fragment values;

replacing a selected one of the stored fragment values with the new fragment value if the predetermined number of fragment values are already stored in the allocated memory when the new fragment is determined to be visible, otherwise, storing the new fragment value;

linking each sample point of the pixel at which the new fragment is visible to the stored new fragment value to enable the generation of a color of the pixel using the fragment value, the generated color improving the perceived quality of the image by reducing aliasing artifacts.

13. A method for rendering an image defined by pixels comprising the steps of:

determining that a fragment of the image is visible at a subpixel position of a pixel, the fragment having fragment data;

storing the fragment data;

associating a bit pattern with the stored fragment data, the bit pattern having a bit value that indicates the subpixel position is associated with the stored fragment data, to enable the generation of a color of the pixel using the fragment data;

processing a new fragment having new fragment data, the new fragment being visible at one or more of the subpixel positions of the pixel; and

replacing the stored fragment data with the new fragment data.

14. An apparatus for rendering an image defined by pixels comprising:

means for selecting subpixel positions in a pixel as sample points;

means for storing a fragment value associated with a fragment of the image, the fragment covering one or more of the sample points in the pixel; and

means for linking each covered sample point to the stored fragment value to enable the generation of a color of the pixel using the fragment value, the generated color improving the perceived quality of the image by reducing aliasing artifacts;

means for processing a new fragment having a new fragment value, the new fragment being visible at one or more of the sample points of the pixel; and

means for replacing the stored fragment value with the new fragment value.

15. An apparatus for rendering an image defined by pixels, the apparatus comprising:

a graphics device configured to select subpixel positions in a pixel as sample points;

memory, coupled to the graphics device, for storing a fragment value associated with a fragment of the image, the fragment covering one or more of the sample points in the pixel, the graphics device linking each covered sample point of the pixel to the stored fragment value to enable the generation of a color of the pixel using the fragment value; and

wherein;

the graphics device is further configured to replace the stored fragment value with a new fragment value, the new fragment value being associated with a new fragment.