Content Based Image Retrieval Using a Metric in a Perceptual Colour Space

The aim of the present work is building an evaluation method for the similarity between colour hues. The method is defined by studying the attribution process, by human subjects, of colour hue couple to similarity classes (from ‘very similar’ to ‘little similar’). From the study of these categorical judgements it is derived that the relation between the hue and the colour similarity is ‘not-isometric’ and greatly depends on the colour category. This result allows to extract representative functions for the three colour of the subtractive system: Red, Yellow, Blue. Besides we used a new method for segmenting the colour, based on the similarity with the main colours. Our method defines a quaternary tree structure, named ‘Similarity Quad-Tree’; it is capable of extracting, from the whole image, the belonging degree to the Red, Yellow and Blue colours and their similarity with the reference colour. The check on the method applicability has given good results both: in the user satisfaction and in the computation. The approach may be viewed as a simple and fast indexing method.