WO2002040940A1 - Apparatus and method for determining the three-dimensional shape of an object - Google Patents

Abstract

The invention relates to an apparatus for determining a three-dimensional shape of an object from a two-dimensional image, comprising a light source for illuminating the object, and a detector for forming an image of the illuminated object, wherein the light source emits a pattern of substantially needle-like light beams that are directed at the object, and wherein the detector forms an image of spots of light of the object thus illuminated by the light beams, and a processor is connected to the detector for reconstructing the shape of the object from the image of spots of light detected by the detector. The detector and the light source have a fixed position in relation to one another, the object is located between predetermined boundaries, and a mask is placed between the light source and the object for the formation of light rays, the mask being provided with an aperture pattern that is placed such that when the object is moved between the predetermined boundaries, the individual spots of the light spot image observed by the detector move along non-intersecting line sections.

Description

Apparatus and method for determining the three-dimensional shape of an object

The invention relates to an apparatus and method for determining a three-dimensional shape of an object from a two-dimensional image, wherein a light pattern is projected on the object and an image is formed of the illuminated object.

To this end usually a light source is used for illuminating the object and a camera for forming an image of the illuminated object .

Such a method is known from the article "One-Shot Active 3D Shape Acquisition" by the authors M. Proesmans, L. van Gool and A. Oosterlinck, 13th International Conference on Pattern Recognition, Vienna, August 25-29, 1996, Vol. Ill, pp. 336-340. In this known method a pattern of squares is projected on the object, and a relatively complicated algorithm is necessary to be able to reconstruct the original shape of the illuminated object from the image pattern observed by the camera. There is a need for such a reconstruction system for the purpose of, among other things, quality control of surfaces of products of the agricultural industry and the metal and car industry, for the purpose of dimensional stability control of products, and for the purpose of automatic recognition of faces, which is useful for the security sector and for forensic applications.

It is observed, that from US-A-5, 003, 166 a system is known for remote determination with regard to an object, using an image projected on the object. By means of a camera, this image and the deformation occurring therein is determined and processed in the distance determination. The subject of this publication is therefore not connected with the present invention.

From DE-A-43 04 815 an apparatus is known for determining a three-dimensional shape of an object from a two-dimensional image, which apparatus comprises a light

ω ω t to μ> μ> in o cπ o cπ o Ul

produces a pixel 9. This pixel 9 lies in the image plane 8 on a line section Ul, U2, whose extreme boundaries are determined by the actual boundaries 6 and 7 within which the object 3 is located. The invention produces, among other things, a solution for the problem that when there are several light beams illuminating the object 3, the ability to distinguish between the various pixels 9 in the image plane 8 of the camera threatens to become lost . Fig. 2A shows a front view of a mask that can be used for forming the parallel light beams. The apertures 10 in the mask 2 are grouped such that the relating line sections Ul, U2, as it were overlap yet do not intersect in the image plane 8 of the camera; this is shown in Figure 2B. This allows the pixels 9 in the image plane 8 to be distinguished from each other. As explained above, said line sections Ul, U2 correspond with a variation in the position of the respective object spot 5 of the object 3 between the boundaries 6 and 7. Fig. 2B shows that these line sections are determined and do not cross or intersect. This affords the possibility to directly use the position of the pixel 9 formed in the image plane 8 of the camera that corresponds with the object point 5, for the determination of the position taken up by this object point 5 in the space. For each object point 5 of the object 3 illuminated via the mask 1 by the light source 2, the position is determined on the basis of the position that the pixel 9 occupies in the image plane 8 of the camera on the respective line Ul, U2, after which said position is subsequently used for deriving for each object point 5 the spatial location where the respective light beam meets the object 3. This spatial location in relation with the boundaries 6 and 7 within which the object 3 is located, is unambiguously determined by the spot that the pixel 9 occupies on the line U1-U2. A simple calculation therefore allows said spatial location to. be derived from the location of the pixel 9 on the line section U1-U2. It is then possible to use for all light spots of the image plane 8 the spatial location of the respective object points 5 pertaining thereto and determined as described above in an integral compilation for the determination of the form of the object 3.

Incidentally, it is remarked that according to the invention the system and the method are also very well suited to be used with more than one camera in order to obtain a greater accuracy when determining the shape of the object.

Claims

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for each individual spot of the light spot image the position it takes in the line section pertaining to that spot, and subsequently deriving therefrom for each position the spatial location where the respective light beam meets the object, after which for all spots of the light spot image the respective spatial locations are compiled for the determination of the shape of the object.