Abstract: Raw cotton impurities test technology is the key and difficult point at home and abroad in recent years. In order to detect the raw impurity rate, this paper puts forward a kind of method that uses the three channels of RGB digital image to get impurities. This method can make full use of all kinds of information provided by color images than the method that converts color images to gray images directly. This method firstly extracts gray image of three channels of raw cotton RGB image, then preprocesses the images, after threshold segmentation and mathematical morphology processing, finally calculates impurities area and impurity rate.

Key words: raw cotton impurities, RGB color image, image processing, impurities rate