Cylindrical to planar image mapping using scanline coherence

• US 5,396,583 A
• Filed: 10/13/1992
• Issued: 03/07/1995
• Est. Priority Date: 10/13/1992
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Miller, Gavin S. P., Chen, Shenchang E.
• Primary Examiner(s): Zimmerman, Mark K.
• Assistant Examiner(s): SMITH, MICHAEL
• Application Number:
  US07/959,716
• Time in Patent Office: 875 Days
• Field of Search: 395/127, 395/129, 395/130, 395/125, 395/126, 345/19, 345/126
• US Class Current: 345/427
• CPC Class Codes: G06T 15/04 Texture mapping
• CPC Class Codes: G06T 3/073 Transforming surfaces of revolution to planar images, e.g. cylindrical surfaces to planar images

Abstract

A method and apparatus for generating perspective views of a scene. With a viewing position at the center of to be cylindrical environment map, different views can be obtained by rotating the viewing direction either horizontally or vertically. The horizontal construction method of the present invention generally involves the steps of: determining the portion of the cylindrical map to be viewed; vertically interpolating pixel values in the portion of the cylindrical map to be viewed and mapping to a viewing plane; and displaying the viewing plane. The vertical construction method of the present invention generally involves the steps of: determining the portion of the cylindrical map to be viewed; vertically interpolating pixel values in the portion of the cylindrical map robe viewed and mapping to a vertical plane; horizontally interpolating pixel values in the vertical plane and mapping to the viewing plane; and displaying the viewing plane.

Claims

1. In a computer controlled display system, a method for displaying perspective corrected portions of an environment map comprising the steps of:

a) providing a cylindrical environment map, said cylindrical environment map comprised of a plurality of pixel shading values ordered in a first plurality of scanlines;

b) identifying a first portion of said cylindrical environment map;

c) mapping said first portion to a viewing plane having a second plurality of pixel shading values ordered in a second plurality of scanlines, said mapping including determining a plurality of scaling factors and applying the scaling factor corresponding to a scanline of said first plurality of scanlines to each pixel shading value in said scanline to obtain said second plurality of pixel shading values, said viewing plane having pre-determined dimensions; and

d) displaying said viewing plane.

2. The method as recited in claim 1 wherein said step of mapping said first portion to a viewing plane is further comprised of the step of minimizing aliasing effects by:

interpolating each scanline of said first plurality of scanlines to construct said second plurality of scanlines for said viewing plane; and

interpolating each scanline of said first plurality of scanlines to define pixel shading values for scanlines of said viewing plane.

3. The method as recited in claim 2 is further comprised of the steps of:

detecting that a different horizontal view is requested;

identifying a second portion of said cylindrical environment map;

mapping said second portion to said viewing plane by scaling pixel shading values of said second portion to said pre-determined dimensions of said viewing plane; and

displaying said viewing plane.

4. The method as recited in claim 1 wherein said method is further comprised of the steps of:

determining a view is requested which requires rotation in a vertical direction;

identifying a second portion of said cylindrical image to be viewed;

mapping said second portion to a vertical plane by scaling pixel shading values of said second portion to pre-determined dimensions of said vertical plane;

mapping said vertical plane mapping to a rotated viewing plane; and

displaying said rotated viewing plane.

5. The method as recited in claim 4 wherein said step of mapping said vertical plane mapping to said rotated viewing plane is further comprised of the step of scaling pixel shading values of said second portion along a horizontal axis.

6. The method as recited in claim 1 wherein said step of displaying said viewing plane is further comprised of the step of mapping said viewing plane to a coordinate system, said coordinate system associated with a viewing device on which said viewing plane will be displayed.

7. In a computer controlled display system, a method for displaying perspective views of a cylindrical environment map, said cylindrical environment map comprised of a plurality of pixel shading values, said method comprising the steps of:

a) determining a viewpoint from which to view said cylindrical environment map;

b) identifying a rotation direction;

c) if said rotation direction is horizontal, performing the steps of;

identifying a first portion of said cylindrical environment map to be viewed, said first portion having a plurality of vertical scanlines;

identifying a first viewing plane;

scaling said first portion vertically to said viewing plane by generating a first plurality of scaling factors and

applying the scaling factor corresponding to each of said plurality of vertical scanlines to each of said plurality of vertical scanlines;

mapping said first viewing plane to a coordinate system associated with a viewing device on which said perspective view will be displayed;

d) if said rotation direction is vertical, performing the steps of;

identifying a second portion of said cylindrical

environment map to be viewed, said second portion having a plurality of scanlines;

identifying a vertical plane corresponding to said second portion and said vertical rotation;

scaling said second portion vertically to said vertical plane by generating a second plurality of scaling factors and applying the scaling factor corresponding to each of said plurality of scanlines to each of said plurality of scanlines;

identifying a second viewing plane;

scaling said vertical plane horizontally to said second viewing plane;

mapping said second viewing plane to a coordinate system associated with a viewing device on which said perspective view will be displayed.

8. The method as recited in claim 7 wherein said step of scaling said first portion vertically to said viewing plane is comprised of the steps of:

determining a first vertical scaling factor for each vertical scanline of said first portion of said cylindrical environment map;

for each pixel in each vertical scanline of said first portion, applying the corresponding first vertical scaling factor to a pixel shading value for said pixel and inserting in a corresponding pixel location of a corresponding vertical scanline of said first viewing plane.

9. The method as recited in claim 7 wherein said step of generating a first plurality of scaling factors is performed by generating a constant value for each scaling factor of said first plurality of scaling factors based on the relationship of the radius of said cylindrical environment map, the distance from the viewpoint and the first viewing plane.

10. The method as recited in claim 9 wherein said step of scaling said second portion vertically to said vertical plane is comprised of the steps of:

determining a second vertical scaling factor for each vertical scanline of said second portion;

for each pixel in each vertical scanline of said second portion, applying the corresponding second vertical scaling factor to a pixel shading value for said pixel and inserting in a corresponding pixel location of a corresponding vertical scanline of said vertical plane.

11. The method as recited in claim 7 wherein said step of generating a second plurality of scaling factors is performed by generating a constant value for each scaling factor of said second plurality of scaling factors based on the relationship of the radius of said cylindrical environment map, the distance from the viewpoint and the vertical plane and the angular coordinate of said vertical scanline of said vertical plane.

12. The method as recited in claim 11 wherein said step of scaling said vertical plane horizontally to said second viewing plane is comprised of the steps of:

determining a horizontal scaling factor for each horizontal scanline of said vertical plane;

for each pixel in each horizontal scanline of said vertical plane, applying the corresponding horizontal scaling factor to a pixel shading value for said pixel and inserting in a corresponding pixel location of a corresponding horizontal scanline of said vertical plane.

13. The method as recited in claim 12 wherein said step of determining a horizontal scaling factor for each horizontal scanline of said vertical plane is performed by a perspective division between coordinate pixel addresses of said vertical plane and said second viewing plane.

14. A computer controlled display system for generating perspective views of a cylindrical environment map, said system comprising:

a) first storage means for storing said cylindrical environment map;

b) second storage means for storing pixel shading values;

c) a display means for displaying a perspective view, said display means coupled to said second storage means;

d) means for identifying a portion of said cylindrical environment map to be displayed;

e) horizontal scaling means coupled to said means for identifying a portion of said cylindrical environment map to be displayed and said second storage means, said horizontal scaling means for generating pixel shading values on a horizontal scanline by determining a plurality of horizontal scaling factors and applying the scaling factor corresponding to a horizontal scanline of said plurality of horizontal scanlines to each pixel shading value in said horizontal scanline; and

f) vertical scaling means coupled to said means for identifying a portion of said cylindrical environment map to be displayed and said second storage means, said vertical scaling means for generating pixel shading values on a vertical scanline by determining a plurality of vertical scaling factors and applying the scaling factor corresponding to a vertical scanline of said plurality of vertical scanlines to each pixel shading value in said vertical scanline.

15. The computer controlled display system as recited in claim 14 wherein said horizontal scaling means is further comprised of:

means for generating a uniform horizontal scaling factor for each horizontal scanline; and

means for applying said uniform horizontal scaling factor to pixel shading values of horizontal scanlines from a portion of said cylindrical environment map and storing in said second storage means.

16. The computer controlled display system as recited in claim 14 wherein said vertical scaling means is further comprised of:

means for generating a uniform vertical scaling factor for each vertical scanline; and

means for applying said uniform vertical scaling factor to pixel shading values of vertical scanlines from a portion of said cylindrical environment map and storing in said second storage means.

17. The computer controlled display system as recited in claim 14 is further comprised of a means for generating anti-aliased pixel values coupled to said horizontal scaling means and said vertical scaling means.