Conventionally, there are various techniques in which an image of an arbitrary object is captured using a monocular camera, the distance to the object is measured, and a distance image of the object is generated. Technologies using such a distance image include, for example, a user interface that detects that the driving posture is abnormal, using a distance image of a driver who is driving a vehicle, and thus makes an alert and a user interface that detects the curvature of fingers in order to understand sign language and then operates.
As technologies for measuring the distance to an object, an image input device according to Japanese Laid-open Patent Publication No. 2004-328657 measures the distance on the basis of the intensity of reflection light that is reflected from an object by using a monocular camera and an illuminating unit that faces the object. Specifically, the image input device according to Japanese Laid-open Patent Publication No. 2004-328657 captures a first image while irradiating an object with light. The image input device then captures a second image without irradiating the object with light. On the basis of the difference in the reflection light intensity (distance difference) between the first image and the second image, the image input device then outputs a third image that is an image representing the intensity distribution of the reflection light, which is applied to the object, and that contains information on the depth of the object (distance information).
However, the above-described conventional technologies have a problem in that the distance to an object cannot be measured accurately.
Specifically, a diffuse reflection coefficient is usually necessary to measure the distance to an image. However, Japanese Laid-open Patent Publication No. 2004-328657 does not disclose a method for calculating a diffuse reflection coefficient of an object, which means that the diffuse reflection coefficient of the object has to be known. In other words, Japanese Laid-open Patent Publication No. 2004-328657 cannot be applied to an object for which the diffuse reflection coefficient is unknown and accordingly the distance to an object that has a shape difference in shape cannot be accurately measured.