Fred's web page - My technical reports

On appearance-based methods

[Lab06] (download: pdf)

Frédéric Labrosse. Appearance-based heading estimation: the visual compass. Technical Report UWA-DCS-06-048, Department of Computer Science, University of Wales, Aberystwyth, January 2006.

In this report we present an algorithm to estimate the heading of a robot relative to a heading specified at the beginning of the process. This is done by computing the rotation of the robot between successive panoramic images, grabbed on the robot while it moves, using a sub-symbolic method to match the images. The context of the work is Simultaneous Localisation And Mapping (SLAM) in unstructured and unmodified environments. As such, very little assumptions are made about the environment; the few made are much more reasonable and less constraining than the ones usually made in such work.
The algorithm's performance depends on the value of a number of parameters, values being determined to provide overall good performance of the system. The performance is evaluated in different situations (trajectories and environments) with the same parameters and the results show that the method performs adequately for its intended use. In particular, the error is shown to be drifting slowly, in fact much slower than un-processed inertial sensors, thus only requiring un-frequent re-alignment, for example when re-localising in a topological map.

On image representation

[Lab00] (download: ps.gz, pdf)

Frédéric Labrosse. Towards Continuous Image Representations. Technical Report, Department of Mathematical Sciences, Computing Group, University of Bath, UK, April 2000.

In the cinema industry, special effects performed during post-production generally use pixel based versions of the movie frames. Although this type of representation is easy to obtain, it has problems like the amount of data and processing difficulties. (How do you remove an object in an image when its outline is not well defined because of the blur naturally present in the image?)
We propose to use continuous, i.e. vectorial, representations. They are indeed easy to manipulate and it has been shown that they can be used to render very high resolution images, which is necessary for cinema, in affordable times.
In this report, we address a first step towards such representations: the extraction from images of smooth continuous contours at sub-pixel accuracy and some ways of representing their interior. The sub-pixel accuracy is necessary to obtain representations that are resolution independent.
Images are decomposed into structural regions that correspond to specified image characteristics. This is done using standard relaxation labelling. Information taken at different stage during the relaxation is used to extract structural contours. Sub-pixel accuracy is obtained by using snakes as well as the blur present in images (because of the acquisition process). We propose solutions, adapted to our context, to often mentioned problems of snakes, namely initialisation, parameter determination, and instability.
The interior of the structural regions must be represented to allow the rendering of images as close as possible to the original ones. We propose here two schemes, one using a single colour for each region, the second sampling the original image to allow smoothly varying colour in each region.

On object modelling

See also my publications