Naoya Ogawa and Kazunori Umeda
Most methods for range measurement or three-dimensional shape reconstruction have required large equipment or a special environment. This paper proposes a method which obtains a range image easily in a general environment using only an off-the-shelf digital camera. Distance is calculated based on irradiance of scene lighted by the digital camera's flash using the fact that the intensity of reflected light of the flash is inversely proportional to the square of the distance from the object. Irradiance is obtained by subtracting an image without the flash from an image with the flash. The image without the flash is used to obtain the reflectance ratio at each pixel. The intensity of reflected light of the flash is affected by the inclination of object surface. A method to estimate the inclination at each pixel is proposed which uses the changes in the irradiance of adjacent pixels. Inclination is formulated as the function of the rate of change, and is calculated based on this rate, which is obtained easily from the image. Color information is obtained simultaneously because visible light is used. Assumptions in the method are that the object surface has no specular reflection and the flash is set at the center of the lens. Experiments show that a range image is obtained roughly and that appropriate distance is obtained for inclined surfaces.
Keywords: digital camera, flash, range measurement, reflectance ratio, normal of surface