Method and apparatus for generating non-homogenous fog

• US 6,064,392 A
• Filed: 03/16/1998
• Issued: 05/16/2000
• Est. Priority Date: 03/16/1998
• Status: Expired due to Term

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Oak Technology Partners (Qualcomm, Inc.)
• Inventors: Rohner, Michel A.
• Primary Examiner(s): Powell, Mark R.
• Assistant Examiner(s): GOOD JOHNSON, MOTILEWA
• Application Number:
  US09/042,595
• Time in Patent Office: 792 Days
• Field of Search: 345/426, 345/431, 345/432
• US Class Current: 345/426
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77

Abstract

The present invention simulates the effect of non-homogenous fog in computer graphics images. The non-homogenous fog visibility equation includes four parameters. A distance scaling parameter K1. A variable fog parameter K2. A normalization constant K3, and a scaling constant K4. The visibility at a sample point can be determined using the visibility equation: ##EQU1## where Z_ns is a normalized and scaled image distance which is equal to (K4*K1*Z)+(K4*K2). To improve computational efficiency the visibility function can be evaluated using a lookup table. The lookup table of the present invention has an efficient addressing scheme and a minimum number of output steps. The visibility function can be expressed as a function of a fog ratio and a fog distance. The fog distance is a distance from the viewpoint to the point where the visibility is reduced to 37% of full visibility. The fog ratio is the square root of the ratio of "near fog" density to "far fog" density. The visibility function expressed as a function of fog ratio and fog distance is ##EQU2##

Claims

1. A method of generating linear fog effects in an image on a display using a computer system comprising the steps of:

defining a start position for a linear fog model;

defining an end position for said linear fog model;

computing a fog distance, wherein said fog distance is a distance from a first reference position to a second reference position at which visibility is a predetermined value, said fog distance being equal to (0.63*end position)+(0.37*start position);

determining a fog ratio comprising a ratio of a fog density at said first reference position to a fog density at said second reference position beyond the fog distance;

computing a distance, D, from a sample point on an object to be displayed, to said first reference position;

determining a visibility value at said sample point, wherein said visibility value is equal to ##EQU56## wherein K5 is a curve fitting parameter;

mixing a fog color and a background color to obtain a pixel color based on at least one of said visibility values.

2. The method of claim 1 wherein said step of determining a fog ratio comprises computing a fog ratio equal to ##EQU57##

3. The method of claim 2 wherein K5 approximately equal to 0.9.

4. The method of claim 1 further comprising the step of interpolating a visibility value for a pixel based upon visibility values from a plurality of sample points.