For each couple of chains a colineation is obtained. Different problems occur during the chain matching process. As the chains are generally not decomposed the same way in both images, problems of split and merge have to be taken into account. Furthermore, due to the noise in the images, the computation of the colineations can be unstable. This unstability is reduced by using the fundamental matrix to constrain the computation of the colineation.
Results become much better but some problems still remain in some cases.
In this approach, color caracteristics are extracted globally on the whole image. A vector of these characteristics indexes every image of the database. A query is performed by comparing the distances between the characteristic vector of the given sketch with the characteristic vectors of the images contained in the database. The other approach focuses on the decomposition of the images into regions and the geometric dependencies between them. Images are first cut into regions of homogenous color.