[visionlist] Post-doctoral fellowship, VISIONTRAIN project, Helmholtz Institute, Utrecht University, the Netherlands

Sylvia Pont s.c.pont at phys.uu.nl
Mon Sep 11 08:01:19 GMT 2006

Post-doctoral fellowship, VISIONTRAIN project, 1 year, at the Helmholtz
Institute, Department of Physics and Astronomy, Utrecht University, in the

The post-doctoral fellow will work within the ecological optics group (prof.
Koenderink, Dr. Pont, Dr. van Doorn and three PhD students) and in
conjunction and in association with the VISIONTRAIN PhD student, Stefan
Karlsson (see http://www.phys.uu.nl/~wwwpm/HumPerc/index.html).

The aim is to extend our previous studies into illuminance flow (see below)
to 3D solid rough objects, with systematical variations of the shape,
surface roughness and light field. Concrete aims are to 1. test shape and
light field perception (psychophysics), and 2. compare the results of those
psychophysics studies with analyses of illuminance flow patterns (computer
vision), for those 3D objects.

For conditions and application procedures see

For further information about the VISIONTRAIN project see

For other inquiries please contact prof. Jan J. Koenderink
(j.j.koenderink at phys.uu.nl) or dr. Sylvia C. Pont (s.c.pont at phys.uu.nl).


Background information about previous studies:

In many scenes the light field is similar at different positions in the
scene because it is due to a single distant source. This induces similar
structures in the illuminance of objects at different positions in the
scene. Local light vectors can be decomposed into normal and tangential
components with respect to a surface. Lambertian ³shading² of the surface
depends upon the normal component only. The surface illuminance flow is
defined as the vector field of directions of the tangential light vector
components. Texture gradients over rough objects depend upon the tangential
components and reveal the illuminance flow. Using the finding that patches
of roughly uniform 3D texture reveal the local orientation of the
illumination we were able to map the global structure of the illuminance
flow. We found that it is a robust indicator of the light field and an
important entity for many subsequent inferences from the image such as shape
from shading. Furthermore, through psychophysical experiments we found that
human observers are able to estimate the local illumination orientation from
3D texture. The results of these experiments were in many regards similar to
estimates on the basis of our computer vision algorithm, using the squared
gradient or Hessian. Our latest psychophysics findings seem to point in the
direction that the squared gradient might be the effective stimulus for
estimating local illumination orientation from 3D textures on globally flat
surfaces by human observers. Our latest photometry and computer vision
studies shed light onto systematical effects on the illuminance orientation
estimates due to non-Lambertian reflectance, due to oblique viewing and due
to anisotropical surface structures.



Dr Sylvia C. Pont
Dept. of Physics and Astronomy
Physics of Man
Helmholtz Institute
Buys Ballot Laboratory 358
Princetonplein 5
3584 CC Utrecht
The Netherlands

Tel: +31 (0)30 253 2809
Email: s.c.pont at phys.uu.nl


More information about the visionlist mailing list