Method and system for reliable 3D shape extraction of metal surface

1. A method of extracting a three-dimensional (3D) shape, the method of comprising:

irradiating a target object simultaneously with a first set and a second set of polarized lights, each set comprising at least three polarized lights of a distinct wavelengths and the second set of polarized lights having at least three polarized lights of the same wavelengths as the first set of polarized lights, wherein the first set of polarized lights being polarized in a direction different from the second set of polarized lights;

operating a processor to determine whether the target object is in a moving state or in a stationary state;

acquiring two sets of two-dimensional (2D) images via two discrete cameras, each set of two-dimensional (2D) images from each one of the two discrete cameras comprising at least three two-dimensional (2D) images, in which each of the two-dimensional (2D) images is generated from the distinct polarized lights among the corresponding polarized lights of the first set and the second set of the polarized lights reflected on an outer surface of the target object;

operating the processor to select at least three two-dimensional (2D) images among the two sets of two-dimensional (2D) images excluding two-dimensional (2D) images generated from direct reflected light; and

operating the processor to synthesize said at least three of the selected two-dimensional (2D) images by a photometric stereo method.

2. The method of claim 1 , wherein the first set of polarized lights are linearly polarized lights, and the second set of polarized lights are linearly polarized in a direction orthogonal to the first set of polarized lights.

3. A system for extracting a three-dimensional (3D) shape of a target object, the system comprising:

a first light source emitting at least three polarized lights of distinct wavelengths on to an outer surface of the target object and a second light source emitting at least three polarized lights of the same wavelengths as the polarized lights of the first light source on to an outer surface of the target object, the first light source and the second light source emitting their polarized lights to the outer surface of the target object at the same time, wherein the polarized lights of the first light source being polarized in a different direction from the polarized lights of the second light source;

two cameras;

a processor; and

a non-transitory memory storing a set of instructions executable by the processor, when executed:

the processor activates the two cameras to acquire two-dimensional (2D) images, each two-dimensional (2D) image corresponding to a distinct polarized lights of the first light source and the second light source; and

the processor selects at least three two-dimensional (2D) images among the two-dimensional (2D) images other than two-dimensional (2D) images obtained from direct reflected light, and synthesizes the selected three images by a photometric method to extract a 3D shape of the surface of the target object.

4. The system of claim 3 , wherein the polarized lights of the first light source are linearly polarized, and wherein the polarized lights of the second light source are linearly polarized in a direction orthogonal to the polarized lights of the first light source.

5. The system of claim 3 , wherein each of the two cameras is provided with a linear polarizing filter of transmitting a linearly polarized light in a corresponding direction.

6. The system of claim 3 , wherein each of the two cameras is provided with a circular polarizing filter, wherein linear polarizing filter portions of the circular polarizing filters are arranged to be orthogonal to each other.

7. The system of claim 3 , wherein a first camera of the two cameras is provided with a linear polarizing filter and a second camera of the two cameras is provided with a circular polarizing filter of which a linear polarizing filter portion of the circular polarizing filter is arranged to be orthogonal to the linear polarizing filter of the first camera.