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Viewing Direction:
The textures were placed on a turn table, and recordings were made
for aspects of 0, 60, 120, and 180 degrees (conditions -, r60, r120, r180).
The last recording is mainly to validate noise
robustness for texture analysis algorithms.
Four cameras were used, enumerated c1..c4, three perpendicular to the
light bow at 0 degrees azimuth and 80, 60, 40 degrees altitude, being c1, c2,
c3, respectively. Furthermore, one is mounted at 60 degrees azimuth and 60
degrees altitude, being c4. For the latter camera, aspect is rotated by 60
degrees to have an identical view as camera c2, effectively rotating the
illumination bow by 60 degrees.
Combined with five illumination
directions and one semi-hemispherical illumination, a sparse sampling of the
BTF is obtained.
Illumination Direction:
Each object was recorded with only one out of five lights turned on,
yielding five different illumination angles (conditions l1-l5).
Furthermore, turning on all lights (condition l8)
yields a sort of hemispherical illumination, although
restricted to a more narrow illumination sector than true
hemisphere.
Note that, for camera c4, the texture was rotated such that the
same aspect is viewed as for camera c2. This can be considered as the lighting
position being turned 60 degrees towards the camera. Hence, cameras c2 and c4
view the same aspect of the texture, but light direction has shifted by 60
degrees in azimuth.
Further note, for camera c1 viewing the material almost perfectly from above,
the recordings of the rotated versions of the material correspond to azimuthal
rotation of the light source (after correction of the image orientation).
Illumination Color:
Each texture was recorded with 3075K illumination color temperature, at which the cameras were white balanced. One image for each camera is recorded with all lights turned on, at a reddish spectrum of 2175K color temperature (condition i).