Computer recognition of occluded curved line drawings
Abstract
A computer program has been designed to interpret scenes from PEANUTS
cartoons, viewing each scene as a two-dimensional representation of
an event in the three-dimensional world. Characters are identified
by name, their orientation and body position is described, and their
relationship to other objects in the scene is indicated. This
research is seen as an investigation of the problems in recognising
flexible non-geometric objects which are subject to self-occlusion as
well as occlusion by other objects. A hierarchy of models containing both shape and relational
information has been developed to deal with the flexible cartoon
bodies. Although the region is the basic unit used in the analysis,
the hierarchy makes use of intermediate models to group individual
regions into larger more meaningful functional units. These
structures may be shared at a higher level in the hierarchy.
Knowledge of model similarities may be applied to select alternative
models and conserve some results of an incorrect model application.
The various groupings account for differences among the characters or
modifications in appearance due to changes in attitude. Context
information plays a key role in the selection of models to deal with
ambiguous shapes. By emphasising relationships between regions, the
need for a precise description of shape is reduced. Occlusion interferes with the model-based analysis by obscuring the
essential features required by the models. Both the perceived shape
of the regions and the inter-relationships between them are altered.
An heuristic based on the analysis of line junctions is used to
confirm occlusion as the cause of the failure of a model-to-region
match. This heuristic, an extension of the T-joint techniques of
polyhedral domains, deals with "curved" junctions and can be applied
to cases of multi-layered occlusion. The heuristic was found to be
most effective in dealing with occlusion between separate objects;
standard instances of self-occlusion were more effectively handled at
the model level. This thesis describes the development of the program, structuring the
discussion around three main problem areas: models, occlusion, and
the control aspects of the system. Relevant portions of the
programs analyses are used to illustrate each problem area.