A proposal of ambient light estimation methods for skin region detection

Many skin region detection methods have been proposed, and color information of the skin is an easy method to detect the skin region from the image. However, the color of the skin is not stable, because the illumination condition, especially the ambient light changes often. Usually, the color space is used to represent the skin color. Nevertheless, it is needed to adjust the parameters of the skin color in the color space for the ambient light change. In order to solve this problem, we propose two methods to detect skin region by estimating the color of the ambient light. In our method, the color of the ambient light is estimated by using one reference light. In the first method, the color of the ambient light is estimated by subtracting two images; an image taken under the unknown ambient light, and an image irradiated a reference light. To subtract these two images, the influence of the ambient light is suppressed. Then the color of the ambient light is estimated. However, irradiation of the reference light is required by changing the ambient light in this method. In the second method, the color of the ambient light is estimated by using the color of the object in the image. However, usually, there is not an object whose color is known. Thus the color of the object in the image is estimated by irradiating the reference light, first. If there is an immovable object in the image, for example the background, this method can estimate the color of the ambient light without irradiate the reference light again. In this paper, these two methods are described, and comparative experiments were conducted. By experimental results, we confirmed that the skin region was detected correctly under the several ambient light environments.