Recently, several systems have appeared for the content-based retrieval of images. The QBIC system [FFN 
93] provides for the retrieval of images by color, texture and shape. It supports two classes of color content - global and local. In the QBIC system the extraction of local regions is handled manually by requiring a person to draw region boundaries using a mouse. Both the global and local color information is represented by mean color and color histogram. The QBIC system also uses a quadratic distance metric for comparing histograms. Because the quadratic distance measure is very computationally intensive, the mean color distance is used as a pre-filter for color queries [HSE 95].