Method for digitally rendering skin or like materials

• US 7,536,047 B2
• Filed: 11/17/2003
• Issued: 05/19/2009
• Est. Priority Date: 11/15/2002
• Status: Active Grant

• Current Assignee: Warner Bros Entertainment Incorporated (Warner Bros. Discovery, Inc.)
• Original Assignee: Warner Bros Entertainment Incorporated (Warner Bros. Discovery, Inc.)
• Inventors: Borshukov, George, Lewis, John P.
• Primary Examiner(s): Bella; Matthew C
• Assistant Examiner(s): LIEW, ALEX KOK SOON
• Application Number:
  US10/715,777
• Publication Number:
  US 20040150642A1
• Time in Patent Office: 2,010 Days
• Field of Search: None
• US Class Current: 382/154
• CPC Class Codes: G06T 13/80 2D [Two Dimensional] animation, e.g. using sprites
• CPC Class Codes: G06T 15/20 Perspective computation
• CPC Class Codes: G06T 17/00 Three dimensional [3D] modelling, e.g. data description of 3D objects
• CPC Class Codes: G06T 2200/08 involving all processing steps from image acquisition to 3D model generation
• CPC Class Codes: G06T 2210/61 Scene description
• CPC Class Codes: G06T 7/55 from multiple images
• CPC Class Codes: H04N 5/262 Studio circuits, e.g. for mixing, switching-over, change of character of image, other special effects ; Cameras specially adapted for the electronic generation of special effects

Abstract

A computationally efficient method for rendering skin tissue to achieve lifelike results includes application of a blurring algorithm to a two-dimensional light map. The algorithm is compact and is not derived from complex mathematical models of subsurface scattering in translucent materials, and yet achieves results similar to more complex models. The method includes receiving three-dimensional surface geometry relating to a digital object and other information for defining modeled light reflected from the surface, generating a two-dimensional matrix of light intensity values mapped to the surface geometry, blurring the matrix using a compact algorithm, and rendering the object using the blurred light intensity values.

Claims

1. A method for rendering a digital object, the method comprising:

receiving information defining a digital object, wherein the digital object comprises a computer-generated three-dimensional surface geometry to be rendered to produce an appearance of translucent skin material, and wherein the information is sufficient for defining modeled light reflected from the surface geometry of the digital object in a modeled light environment;

generating, using a simple reflectance model, a two-dimensional light intensity matrix representing diffuse reflection from a modeled color-neutral surface of the digital object in the modeled light environment exclusive of sub-surface scattering effects, each matrix entry being a lumel representing a modeled light intensity correlated to a mapped unique surface element of the digital object, using a processor;

blurring the light intensity matrix, thereby producing a blurred matrix; and

rendering the digital object, using matrix entries from the blurred matrix to determine pixel intensity values for the digital object combined with a color map representing specular surface reflection from a modeled non-neutral surface of the digital object in the modeled light environment, to produce an appearance simulating subsurface scattering in the translucent skin material.

2. The method of claim 1, wherein the generating step further comprises computing a modeled light intensity for each matrix entry using detailed skin topographical data.

3. The method of claim 2, wherein the generating step further comprises processing the detailed skin topographical data in the form of a bump map.

4. The method of claim 2, further comprising obtaining the detailed skin topographical data by measuring a three-dimensional structure of a skin surface sample.

5. The method of claim 1, wherein the rendering step further comprises using color values from a color map to determine pixel color values for the digital object.

6. The method of claim 1, wherein the rendering step further comprises determining the pixel intensity values by mip-mapping the blurred light intensity matrix.

7. The method of claim 6, further comprising generating a color map comprising a two-dimensional matrix, wherein each matrix entry of the color map represents a color of the unique surface element of the digital object.

8. The method of claim 1, wherein the blurring step further comprises convolving the light intensity matrix.

9. The method of claim 1, wherein the blurring step further comprises processing the light intensity matrix using a Fast Fourier Transform function.

10. The method of claim 1, wherein the blurring step further comprises executing a blurring algorithm of the form e⁻

x^2+y2)/σ

, where x and y are the horizontal and vertical widths, respectively, of the blur kernel in number of lumels, e is the base of the natural logarithm, and σ

is a spreading parameter.

11. The method of claim 1, wherein the generating step further comprises generating a light intensity matrix for each of three color separation channels.

12. The method of claim 11, wherein the blurring step further comprises blurring the light intensity map for each channel according to the general expression

I_x,y=V_x,y·

I_0,0;

where I_x,y is a blurred value of each (x,y)_th lumel, V_x,y is an attenuation factor for each (x,y)_th lumel defining a blur kernel having a predetermined width, and I_0,0 is an unblurred value of each (x,y)_th lumel of the light intensity map.

13. The method of claim 12, wherein the blurring step further comprises computing the blur kernel

V_x,y=1/(√

{square root over (x²+y²)}+1)^PRGB

separately for each channel, wherein x and y are computed over the range of −

h_RGB to h_RGB, h_RGB is a corresponding h_R, h_G, or h_B halfwidth of the blur kernel for each channel, and P_RGB is a corresponding P_R, P_G, or P_B power factor for each channel.

14. The method of claim 12, wherein the blurring step further comprises computing V_x,y using a corresponding value of P_R, P_G, and P_B for each respective color channel within a range of 2 to 4.

15. The method of claim 12, wherein the blurring step further comprises computing V_x,y over a halfwidth h_RGB determined by

16. A system for rendering a digital object, the system comprising a memory holding a two-dimensional light intensity matrix representing diffuse reflection from a modeled color-neutral surface of the digital object in a modeled light environment without subsurface scattering effects, each matrix entry being a lumel representing a modeled light intensity correlated to a mapped unique surface element of the digital object, wherein the light intensity matrix is a blurred matrix;

and

a processor operatively coupled to the memory, whereby the processor determines pixel intensity values for rendering the digital object using matrix entries from the blurred matrix combined with a color map representing specular surface reflection from a modeled color non-neutral surface of the digital object, to provide a rendered appearance of the digital object emulating subsurface scattering in a translucent skin material.

17. The system of claim 16, wherein the processor determines values of each matrix entry of the blurred matrix using an unblurred light intensity matrix and a blurring algorithm.

18. The system of claim 16, wherein the memory further holds a two-dimensional color map of the digital object, and wherein the processor determines pixel color values for rendering the digital object using the color map.

19. The system of claim 16, wherein the memory further holds a two-dimensional bump map, the bump map describing fine surface variation between surfaces of the digital object and a modeled 3D geometry of the digital object.

20. The system of claim 19, wherein the processor calculates a two-dimensional unblurred light intensity matrix using the bump map and a modeled light environment.