Workshop in UP1, DIKU
January 16, 2002: Workshop in UP1, DIKU.
10-11: Mads Nielsen, ITU: "Random Walk of Linear Maps: an Application to Warping of 2D Images."
11-12: Benny Lautrup, Niels Bohr Institute, KU: "Random Walks of Linear Maps: An Analytical Solution."
14-15: Peter Giblin, University of Liverpool
15-16: Lewis Griffin, Guys Hospital, London, "Metamerism in Spatial Vision"
Metamerism effects spatial vision i.e. for any given pattern of
responses of visual neurons, there is a large
metamery class of images that could have caused it. The term `feature
detection' acknowledges the belief that a visual
system should somehow proceed from initial quantitative measurements
(e.g. linear neuron responses) to categorical
qualitative descriptors (e.g. dark blob on the light side of a convex
edge). This step is complex even when applied to single
images, so the prospect of developing a theory that applies to vast
metamery classes of possible images is dismaying.
Koenderink  has pioneered a strategy that solves both problems:
identifying a unique simple iconic image within each
metamery class. This dispenses with the need to deal with the full
metamery class, and since the iconic images are simple
the extraction of qualitative structure will be facilitated.
The correct rule for selecting from a metamery class remains
unknown, though candidates have been explored [2,
3]. We have examined six new candidate rules based upon minimizing norms
of the luminance or the gradient magnitude.
We have also explored a further rule based on choosing the most likely
(ML) explanation within a metamery class. This we
approach by calculating (on the basis of a natural image collection) the
most likely explanation of 1st order structure in 1D
and 2D. Finally, we consider to what degree there is coincidence between
the norm and ML approaches. We find such
coincidence plausible though our best candidate (the total variation
norm) has clear shortcomings.
- Koenderink JJ (1993) What is a feature?, J. Intell. Syst.
- Tagliati E & Griffin LD (2001) Features in Scale Space: Progress on
the 2D 2nd Order Jet, In: Scale-Space and
Morphology in Computer Vision vol. 2106 (M Kerckhove, ed.),
Springer, pp. 51-62.
- Koenderink JJ & van Doorn AJ (1996) Metamerism in complete sets of
image operators, In: Advances in Image
Understanding '96, pp. 113-129.