Lab 7: Reflectance and photometric stereo

8%

c428/615, Martin Jagersand

Submit code and report electronically through the upload link on the e-Class course webpage.
Marks may be given for any of the questions in the assignment, so please answer them all
(many only require a one sentence answer).
Demo: In your lab session.

Objectives

Understand radiometry notions (radiance, irradiance, BRDF). How does image colors relate to light and surface properties ? Understant the use of shading in shape reconstruction.

Exercise 1 : Scene radiance (2%)

Does the brightness that a wall appear to the eye depends on the distance of the viewer to the wall ? Explain.

Exercise 2 : Radiosity (2%)

Explain the white out phenomena : On a cloudy winter day, we can't perceive the shape of the snow covered terrain Why ?

(Hint: derive the surface radiance equation assuming that the sky has uniform radiance and the surface has Lambertian uniform albedo).

Exercise 3: Photometric stereo (4%)

Implement a photometric stereo algorithm that recovers the integrated depth map and albedo map from shading in three images. Make sure that the resulting surface is integrable.

First try the algorithm for reconstructing a synthetic sphere. It is possible to reconstruct only the pixels that are visible in all three images.

Light position:
sphere0 (0 0 1)
sphere1 (0.5547 0 0.8321)
sphere2 (-0.4851 -0.4851 0.7276)

Then apply the algorithm to any one of the two sets of real images (dog sequence or snowman sequence). Ignore the shadows.

Light position:
dog0 (0.2316 0.1035 0.9673)
dog1 (-0.215 0.138 0.967)
dog2 ( -0.04 -0.19 0.98)

Light position:
snowman0 (-0.11 0.28 0.95)
snowman1 (0.39 0.20 0.90)
snowman2 (-0.05 -0.06 0.997)