Color Conversion Formulae between RGB Color Space and HSI Color Space for Color Image Processing

The color space expressed by the three attributes of human color, hue, saturation, and lightness, is the HSI color space. In particular, in color image processing, preserving hue is required, therefore the HSI color space is used. Since color images are acquired and displayed in RGB color space, conversion with RGB color space is required for processing in HSI color space. The general HSI color space is defined by Gonzalez and Woods, but the color gamut is very different from the RGB color space. The larger the intensity value, the more inappropriate the saturation value. Thus, when the intensity and saturation are processed in this HSI color space, it is often the case that the processing result is located in outside the RGB color space or even if the processing result is in the RGB color space, it may not be an appropriate value. In this paper, RGB color space and CMY color space are used properly according to the value of the input signal, and processing is performed in the HSI color space converted from each space. After the processing in the HSI color space, we convert to the RGB color space by using a proposed method in this paper, in order to obtain the same processing result as the result of processing in the ideal HSI color space.