Polynomial Texture Maps Dan Hazen CS 395 Advanced

Polynomial Texture Maps Dan Hazen CS 395: Advanced Computer Graphics January 22, 2002 Based on the paper: Malzbender, T. , Gelb, D. , Wolters, H. , “Polynomial Texture Maps”, Computer Graphics (SIGRAPH 01 PROCEEDINGS), August 2001. www. hpl. hp. com/ptm Northwestern University

Introduction What are Polynomial Texture Maps (PTM’s)? Image based texture maps used for more accurate texturization of fine details. Why use PTM’s? More Realistic Textures! Northwestern University

Background Bi-directional Texture Function: Northwestern University

Background Bi-directional Texture Function (Cont. ): Conventional BTF Northwestern University

Polynomial Texture Mapping Store coefficients at EACH TEXEL. Coefficients derived from series of photographs. L(u, v) = a 0(u, v)lu 2 + a 1(u, v)lv 2 + a 2(u, v)lulv + a 3(u, v)lu + a 4(u, v)lv + a 5(u, v) Northwestern University

Polynomial Texture Mapping (Cont. ) DEMO! Northwestern University

Polynomial Texture Mapping (Cont. ) Capture images using devices to get the coefficients Northwestern University

Polynomial Texture Mapping (cont. ) Storage Concerns: Best Case: Worst Case: 9 Bytes/Texel: 21 Bytes/Texel: 1 Byte: Red 1 Byte: Blue 1 Byte: Green 6 Bytes: Coefficient a 0 -5 1 Byte: Red 1 Byte: Blue 1 Byte: Green 6 Bytes: a 0 -5 Red 6 Bytes: a 0 -5 Blue 6 Bytes: a 0 -5 Green 500 x 500 Image: ~2. 2 Megs 500 x 500 Image: ~5. 1 Megs Northwestern University

PTM Applications Specular Highlighting Northwestern University

PTM Applications (Cont. ) Contrast Enhancement: Method 1 – Specular Highlights Original PTM Photo Reconstruction Specular PTM + Highlight Northwestern University

PTM Applications (Cont. ) Contrast Enhancement: Method 2 – Diffuse Gain Original Diffuse Photograph Gain = 1. 9 PTM Reconstruction Northwestern University

PTM Applications (Cont. ) Contrast Enhancement: Method 3 – Light Extrapolation Original Photograph Extrapolated PTM Reconstruction Northwestern University

PTM Applications (Cont. ) Video: http: //www. hpl. hp. com/ptm/ Northwestern University

PTM Applications (Cont. ) Northwestern University

PTM Applications (Cont. ) Northwestern University

PTM Applications (Cont. ) Northwestern University

PTM Applications (Cont. ) Northwestern University

PTM Applications (Cont. ) Northwestern University

PTM Applications (Cont. ) Northwestern University

PTM Advantages and Issues Advantages 1. Only images needed to form the texture 2. Texture maps maintain roughness 3. Neat lighting and viewing tricks 4. Efficient enough for interactive speeds once coefficients are obtained Issues 1. Storage Costs 2. Using biquadratic polynomial: in some cases may not be precise enough Northwestern University

PTM Research Expansion Suggestions for research expansion: • • Use a higher order polynomial for better representation Use basis functions to reduce storage costs Get rid of fixed camera constraint to get a higher number of free dimensions Add modeling surface opacity to the list of features Northwestern University

Conclusions • • • Polynomial Texture Maps (PTM’s) portray rough surfaces based on a set of input images Polynomial Texture Maps can be used for more than just interactively moving a light source around a texture; there are methods that improve image definition Easy to do in hardware but storage could be a problem QUESTIONS? Northwestern University