A color ratio based image retrieval for e-catalog image databases

Most of the content-based image retrieval systems are based on RGB color space. Using the average amount of red, green, and blue is appropriate for natural images. But, for the case of e-catalog images, the number of colors for a given catalog image is only a few and the average color of an image is meaningless to customers. This paper presents a color comparison scheme based on the HSI color ratio to improve the accuracy of retrieval on e-catalog images. We have divided hue by 30 degrees, resulting in 12 colors. By considering saturation and intensity, and eliminating some duplicate combinations, we further divided each hue into 15 categories, thus resulting in 186 representative colors which is quite smaller than 1.7 million colors of 24 bit RGB case. The resulting 186-element HSI histogram is represented using presence bitmap, vector(186 bit) and ratio vector(93 bytes). For the e-catalog images, most of the presence vector bits are 0 since there are only a few colors. We have implemented the prototype retrieval system and showed the usefulness of the proposed system by comparing measures such as precision and search speed with RGB histogram based schemes.