Reflectance and Texture of Real-World Surfaces
KRISTIN J. DANAColumbia University
BRAM VAN GINNEKENUtrecht UniversitySHREE K. NAYAR
Columbia UniversityJAN J. KOENDERINK
Utrecht University
ACM Transactions on Graphics, Vol. 18, No. 1, January 1999
Overview
• Introduce BRDF and BTF
• BTF Texture Gathering Technique
• CUReT Database
• BTF Applications
• Future Work
• Pretty Pictures
Bidirectional Reflectance Distribution Function (BRDF)
• Nicodemus [1970] and Nicodemus et al. [1977]
• Coarse scale level– local surface variations are
subpixel– local intensity is uniform
• Bidirectional:1. Camera Angle2. Light Angle
• “Objects look differently when viewed from different angles, and when illuminated from different directions”
Bidirectional Texture Function (BTF)
• Fine scale level– Surface variations give rise to local intensity
variations
• Bidirectional:1.Camera Angle
2.Light Angle
• “Objects look differently when viewed from different angles, and when illuminated from different directions”
BRDF vs. BTF
Why do we need BTFs?• Traditional 2-D texture synthesis and texture-mapping do not take into account the
change in texture appearance as the viewing and illumination directions change– A single digital image of a rough surface is mapped onto a 3-D object and the
appearance of roughness is usually lost or distorted• Bump-mapping [Blinn 1977, 1978] preserves some of the appearance of
roughness– knowledge of the surface shape is required– shadows cast from the local surface relief are not rendered
• ray tracing can be used– exact geometry of the surface must be known– high computational cost
• solid texturing: combine a volumetric texture synthesis with volume rendering techniques
– computationally intensive– applicable for a limited variety of textures.
• BTF database– “potential exists for 3-D texturing algorithms using images, without the need for a
volumetric texture model or surface synthesis procedure”
BTF: Where do we start?• Already BRDF databases
• Employ new techniques to create BTF database
• Pull Together:– Robot– Lamp– PC– Photometer– Video camera
Texture Gathering Technique
• Fixed light source– Halogen bulb with a Fresnel lens (single-
beam focusing)
• Camera moves through 7 positions– 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, 157.5°
from light source
• Texture sample moves through multiple orientations– Robot arm orients sample normal along
vertices of quarter-sphere facing the light source
Texture Gathering Technique
• At each camera position, texture is captured with its normal along quarter-sphere vertices
• Not all vertices captured at each position– At position 7, only a few
normals are actually visible to the camera
Quarter-Sphere Orientations: Camera Positions
Texture Gathering Technique
• Sample lies in xs–ys plane with its global normal pointing in the direction of zs
• Each circular marker represents a distinct illumination direction
• For each of these illumination directions, the sample is imaged from seven viewing directions
Quarter-Sphere Orientations: Illumination Directions
Texture Gathering Technique
• Textures that have grids or grains
• Measurements are repeated rotating sample about zs by either 45° or 90° depending on the structure of the anisotropy
• Examples: – Linen (square grid)
rotated 45°– Corduroy (vertical lines)
rotated 90 °
Special Case: Anisotropic Textures
Texture Gathering Technique
• Relate radiance to pixel values• Use Kodak standard card
image for every sample measured.
• Letting r denote the total radiance and p denote the average pixel value, a linear relationship was found
• Data with significant pixel underflow (pixel values near 0) or overflow (pixel values near 255) were not used.
Control Considerations
End Product
• 205 images for each sample
• 640 x 480 pixels• 24 bits per pixel (8 bits per
RGB channel).• Database total: over
14,000 images (61 samples, 205 measurements per sample, plus 205 additional measurements for anisotropic samples)
• CUReT Database:www.cs.columbia.edu/CAVE/curet/
Camera Position Images
1 55
2 48
3 39
4 28
5 19
6 12
7 4
Total 205
Columbia-Utrecht Reflectance and Texture Database (CUReT)
BTF Applications
• Top row– Two images of “plaster_b” with
different illumination and viewing directions
• Bottom row– Spatial spectrum of “plaster_b” with
zero frequency at the center and brighter regions corresponding to higher magnitudes
– Notice orientation change due to change of illumination direction causing change in shadow direction.
• Computer vision:– Texture recognition algorithms often
based on spectral content of image textures
– BTF should be considered for recognition of real-world surfaces
Sample 11: “plaster_b”
BTF Applications• BTF texture gathering
technique allows easy gathering of BRDF data– Pros:
• Simple system• Simultaneously gather
BRDF and BTF measurements
– Cons:• Not as accurate as
traditional BRDF measurement systems
Future Work
Synthesizing Bidirectional Texture Functions for Real-World Surfaces
Xinguo Liu, Yizhou Yu, Heung-Yeung Shum• 3 Step approach to synthetically generate BTFs
1. Recovers approximate 3D geometry of surface details using a shape-from-shading approach
2. Generates a novel version of the geometric details with the same statistical properties as the sample surface
3. Uses an “appearance preserving procedure” to synthesize novel images under various viewing/lighting settings, defining a novel BTF
Show me some BTF pictures!!!
• 13 images per sample used from database collection of 205– 1 image of frontal view– 12 oblique views
• Use averaging of three pixels at the section borders to reduce the appearance of seams
Pretty Pictures
Traditional2-D texture-mapping
BTF3-D texture-mapping
Sample 11 (plaster)
Pretty Pictures
Traditional2-D texture-mapping
BTF3-D texture-mapping
Sample 8 (pebbles)
Pretty Pictures
Traditional2-D texture-mapping
BTF3-D texture-mapping
Sample 45 (concrete)
Pretty Pictures
Traditional2-D texture-mapping
BTF3-D texture-mapping
Sample 28 (crumpled paper)
Pretty Pictures
Traditional2-D texture-mapping
BTF3-D texture-mapping
Sample 19 (plush rug)
Pretty Pictures
Traditional2-D texture-mapping
BTF3-D texture-mapping
Sample 56 (wood) (anisotropic)
fine
