WO2016084067A1

WO2016084067A1 - Stereoscopic acquisition module for use in 3d scanners and/or displaying pseudo 3d video

Info

Publication number: WO2016084067A1
Application number: PCT/IL2015/051126
Authority: WO
Inventors: Uri Neta; Or Ramot
Original assignee: A. B. Imaging Solutions Ltd
Priority date: 2014-11-27
Filing date: 2015-11-22
Publication date: 2016-06-02

Abstract

A 3D scanner has a stereoscopic acquisition module for acquiring a stereoscopic 2D image frame stream of a scanned 3D surface of a 3D object. The scanner also having a 3D surface processing module for processing said stereoscopic 2D image frame stream for generating a 3D surface file modelling the scanned 3D surface of the 3D object; and a pseudo 3D video processing module for converting said stereoscopic 2D image frame stream to a pseudo 3D video stream of the scanned 3D surface of the 3D object for display on a pseudo 3D video display device.

Description

STEREOSCOPIC ACQUISITION MODULE FOR USE IN 3D SCANNERS AND/OR DISPLAYING PSEUDO 3D VIDEO

Field of the Invention

The invention relates to stereoscopic acquisition modules for acquiring stereoscopic 2D image frame streams for possibly use in 3D scanners and possibly displaying pseudo 3D video.

Background of the Invention

Stereoscopic acquisition modules are employed for acquiring two stereoscopic 2D image frame streams for generating a 3D surface file of a scanned surface of a 3D object in 3D scanners. Possibly such acquired stereoscopic 2D images may be used also for displaying pseudo 3D video streams on pseudo 3D video display devices. Such a pseudo 3D impression of a scanned objected may be derived by viewing stereoscopic 2D images of the object recorded from two perspectives and then possibly using special projection hardware and/or eyewear to provide a pseudo 3D illusion of depth.

The scanned surface can be an external surface of an opaque object or an internal surface of an object covered by a transparent material, for example, perspex. Each stereoscopic 2D image frame is typically acquired at an included acute angle at a pre-detennined working distance from a 3D object such that each stereoscopic 2D image frame includes two different images with an overlap region. The two different images of a stereoscopic image are commonly referred to as a left image and a right image.

Conventional stereoscopic acquisition modules are implemented as follows: First, two spaced apart cameras angled toward a 3D object thereby enabling simultaneous acquiring a left image frame and a right image frame. Second, a single camera with an optical train for simultaneously imaging a 3D object from two different directions for simultaneously acquiring a left image frame and a right image frame. And third, a single camera with an optical train for imaging a 3D object from two different directions for consecutive acquiring of a left image frame and a right image frame.

3D scanners employ a 3D surface processing module to calculate depth information from the overlap region of a stereoscopic 2D image for preparing a 3D point cloud for the corresponding overlap region of the scanned surface of a 3D object. 3D scanners acquire a stereoscopic 2D image frame stream, such that respective consecutive stereoscopic 2D image frames have considerable overlap to preclude gaps in adjacent 3D point clouds which could lead to defects in a 3D surface file of a scanned surface of a 3D object. 3D surface processing modules statistically stitch 3D point clouds of consecutive overlap regions in an iterative process called alignment or registration to generate a 3D surface file modelling a scanned 3D surface of a 3D object.

Pseudo 3D video may employs a pseudo 3D video processing module for converting a stereoscopic 2D image frame stream to a pseudo 3D video stream for display on a pseudo 3D video display device. The pseudo 3D video processing module may convert each stereoscopic 2D image frame into a single pseudo 3D video frame. Implementation of a pseudo 3D video processing module is described in an article entitled FPGA-Based System Combines Two Video Streams to Provide 3D Video. The article is available online at htrp://www.analog.com/libraty/analogdialogue/archives/47- 12/stereo_video.html.

Summary of the Invention

In one aspect, the present invention may be directed towards stereoscopic acquisition modules for acquiring stereoscopic 2D images of a 3D object. The stereoscopic acquisition modules may for example include an optical system having a double telecentric lens with an entrance lens, an intermediate aperture, and an exit lens and a splitting prism deployed in front of the entrance lens relative to a common focal point of the double telecentric lens. The splitting prism acts to split inbound optical rays such that the double telecentric lens images a 3D object from two different observation directions. The stereoscopic acquisition module of an embodiment of the present invention can be readily implemented in a 3D scanner for scanning a surface of a 3D object for generating a 3D surface file modelling the scanned 3D surface of the 3D object. Alternatively, the stereoscopic acquisition module can be readily implemented for displaying a pseudo 3D video of the 3D object on pseudo 3D video display devices including pseudo 3D monitors, pseudo 3D projectors, and pseudo 3D goggles.

In another aspect, possibly combinable with the former aspect, an embodiment of the present invention may be based on the realization that 3D scanners employing stereoscopic scanning can additionally include an onboard pseudo 3D video processing module for converting a stereoscopic 2D image frame stream to a pseudo 3D video stream for display on a pseudo 3D video display device instead displaying a conventional 2D video, thereby affording a more intuitive stereoscopic visualization for a user.

The 3D scanners in some embodiments therefore may have the dual functionality of generating 3D surface files of scanned surfaces of 3D objects and providing pseudo 3D video streams for display on pseudo 3D video display devices. The onboard pseudo 3D video processing module can output a pseudo 3D video stream in one or more standard pseudo 3D video formats including side-by-side, top bottom, interlace, flip page, and the like. The pseudo 3D video stream can be displayed on conventional pseudo 3D video display devices including inter alia pseudo 3D monitors, pseudo 3D projectors, and pseudo 3D goggles.

The present invention is technology agnostic insofar as it is applicable to 3D scanners employing stereoscopic scanning irrespective of the actual implementation of the stereoscopic scanning. One conventional implementation of stereoscopic scanning includes two cameras differently angled toward a 3D object thereby enabling simultaneously acquiring a left image frame and a right image frame. Another conventional implementation of stereoscopic scanning includes a single camera with an optical train for simultaneously imaging a 3D object from two different directions for simultaneous acquiring a left image frame and a right image frame. Yet another conventional implementation of stereoscopic scanning includes a single camera with an optical train for imaging a 3D object from two different directions for consecutively acquiring of a left image frame and a right image frame.

The present invention in its various aspects can be implemented as new 3D scanners with onboard pseudo 3D video processing modules. Alternatively, the present invention can be implemented by retrofitting existing 3D scanners with pseudo 3D video processing modules to provide the additional functionality of pseudo 3D video.

Brief Description of Drawings

In order to understand the invention and to see how it can be carried out in practice, preferred embodiments will now be described, by way of non- liiniting examples only, with reference to the accompanying drawings in which similar parts are likewise numbered, and in which:

Fig. 1 is a schematic diagram of the use of a conventional stereoscopic acquisition module in a 3D scanner and/or displaying a pseudo 3D video on a pseudo 3D display device;

Fig. 2 is a schematic diagram of a stereoscopic acquisition module in accordance with one embodiment of the present invention for use in a similar manner as a conventional stereoscopic acquisition module;

Figs. 3A to 3B are perspective and side views of splitting prisms according to various embodiments of the invention of the stereoscopic acquisition module of Figure 2;

Fig. 4 is a schematic diagram of a stereoscopic acquisition module in accordance with another embodiment of the present invention;

Fig. 5A is an optical ray diagram showing the imaging of a left 2D image of the stereoscopic 2D image of the Figure 2 stereoscopic acquisition module; Fig. 5B is an optical ray diagram showing the imaging of a right 2D image of the stereoscopic 2D image of the Figure 2 stereoscopic acquisition module;

Fig. 6 is a schematic diagram of a conventional 3D scanner for generating a 3D surface file modelling a scanned 3D surface of a 3D object and displaying a 2D video stream on a 2D video display device; and

Fig. 7 is a schematic diagram of an embodiment of a 3D scanner for generating a 3D surface file modelling a scanned 3D surface of a 3D object and displaying a pseudo 3D video stream on a pseudo 3D video display device.

Detailed Description of the Drawings

Figure 1 shows a stereoscopic acquisition module 100 having an optical axis 101 and designed for scanning a 3D object O for capturing a stereoscopic 2D image frame stream 102. The stereoscopic acquisition module 100 can be incorporated in a 3D scanner generally denoted 200 including a 3D surface processing module 201 for processing the stereoscopic 2D image frame stream

102 to generate a 3D surface file 202 modelling a scanned 3D surface of the 3D object O. Alternatively, the stereoscopic 2D image frame stream 102 can be processed by a pseudo 3D video processing module 300 for converting the stereoscopic 2D image frame stream 102 to a pseudo 3D video stream 301 for display on a pseudo 3D video display device 302.

The stereoscopic 2D image frame stream 102 includes left image frames

103 and right image frames 104. The left image frames 103 and the right image frames 104 include an overlap region. The stereoscopic acquisition module 100 can include a single camera or a pair of cameras for capturing the stereoscopic 2D image frame stream 102 depending on the implementation of the stereoscopic acquisition module 100. Suitable cameras include inter alia Ximea's MQ042xG-CM-PCA commercially available from Ximea, Germany.

Figure 2 shows an embodiment of a stereoscopic acquisition module 400 having an optical axis 401 and also designed for capturing a stereoscopic 2D image frame stream 402 of the 3D object O. The stereoscopic 2D image frame stream 402 includes left images 402 A and right images 402B. The stereoscopic acquisition module 400 includes an optical system 405 and an imaging module 404 deployed co-axial on the optical axis 401. The optical system 405 includes a double telecentric lens having an entrance lens 407 and an exit lens 408 spaced apart therefrom.

The entrance lens 407 has a focal length FL1, a front focal plane FFP1 and a back focal plane BFP 1. The exit lens 408 has a focal length FL2, a front focal plane FFP2 and a back focal plane BFP2. The object O is placed at the front focal plane FFP1. The imaging module 404 is deployed at the back focal plane BFP2.

The entrance lens 407 's back focal plane BFP1 coincide with the exit lens 408 's front focal plane FFP2 at a common focal point CFP. The optical system 400 includes an aperture 409 (indicated in Figs. 5A, 5B) at the common focal point CFP and a splitting prism 411, embodiments of which are also shown in Figures 3. The splitting prism 411 is in front of the entrance lens 407 relative to common focal point CFP and is deployed adjacent the entrance lens 407.

The splitting prism 411 includes a forward first entrance surface 412 inclined tapering axially forwardly towards the optical axis 401 and a rear first exit surface 413 perpendicular to the optical axis 401. The splitting prism 411 further includes a forward second entrance surface 414 inclined tapering axially forwardly towards the optical axis 401 and a rear second exit surface 416 perpendicular to the optical axis 401. The first entrance surface 412 and the second entrance surface 414 subtend to form therebetween a large (possibly included) obtuse angle a in the range of about 174° ± 3°.

An illumination module (not shown) possibly of and on the 3D scanner may be provided with means for illuminating e.g. a dentition with visible and/or infrared illumination. With attention drawn to Fig. 3C, possible inbound beams from such visible and e.g. infrared illumination are illustrated aniving from left to right. Since inbound beams of different wave length when passing through the boundary into the prism 411 will break a different angles, the focal point of the IR inbound rays may be different than the focal point of the visible inbound rays. Such, difference in focal point may be useful in accordance with an aspect of the invention for inspecting 3D objects of different depth, such as inspecting with the visible light an upper part of a tooth while with the IR light a lower part of the tooth adjacent the gum.

With attention drawn to Fig. 3B, an embodiment of prism 411 is illustrated as being an achromatic prism made possibly of two layers or materials in order to control location of the focal points of such different inbound wave lengths, to possibly bring them closer one to the other. Here, the focal point of the inbound IR rays are illustrated brought closer to those of the visible light, however any other manipulation may be possible such as to bring the focal point of the visible light closer to that of the IR light. Preferably in such an achromatic prism, the refractive index n2 of the forward layer of the prism may be smaller than the refractive index nl of the more rear layer in order to control the inbound light in the desired manner.

In an aspect of the present invention, designing prism 411 to include its tapering slanting surfaces located as its forward entrance - allows better control of inbound incoming rays of light since such incoming light only exhibits one refraction in direction on entrance into the prisms while not exhibiting any refraction while exiting the prism in the rear direction.

Figure 4 shows an alternative embodiment of a stereoscopic acquisition module 417 similar in construction and operation as the stereoscopic acquisition module 417 such that similar parts are likewise numbered. The latter 417 differs from the former 400 insofar as the latter 417 includes a mirror 418 disposed between the exit lens 408 and the imaging module 404 such that the imaging module 404 is not co-axial with the optical axis 401.

The operation of the stereoscopic acquisition module 400 is now described with reference to Figures 5 A and 5B. Figure 5 A shows a first inbound or incidence parallel beam 430 passing through the first entrance surface 412, the first exit surface 413 and the pinhole aperture 409 to form a first outbound parallel beam 431 to form an image 432 of the left images 402A on the imaging module 404. Figure 5B shows a second inbound parallel beam 440 passing through the second entrance surface 414, the second exit surface 416 and the pinhole aperture 409 to form a second outbound parallel beam 441 to form an image 442 of the right images 402B on the imaging module 404. The second outbound beam 441 arrives from a different direction (i.e. a different view of object O) than the first outbound beam 431 such the two images 432 and 442 constitute a stereoscopic 2D image.

Figure 6 shows a conventional 3D scanner 1000 for stereoscopic scanning a 3D object 1001 to generate a 3D surface file 1002 of a scanned 3D surface of the 3D object 1001. The 3D scanner 1000 includes a stereoscopic acquisition module 1003 for capturing a stereoscopic 2D image frame stream 1004 of the scanned 3D surface of the 3D object 1001. The stereoscopic acquisition module 1003 can include a single camera or a pair of cameras for capturing the stereoscopic 2D image frame stream 1004 depending on the implementation of the stereoscopic acquisition module 1003. Suitable cameras include inter alia Ximea's MQ042xG-CM-PCA commercially available from Ximea, Germany, www.ximea.com. The stereoscopic 2D image frame stream 1004 includes left image frames 1006 and right image frames 1007. The left image frames 1006 and the right image frames 1007 include an overlap region. The 3D scanner 1000 includes a 3D surface processing module 1008 for processing the stereoscopic 2D image frame stream 1004 to generate the 3D surface file 1002. The 3D scanner 1000 displays a 2D video stream of the right image frames 1007 on a 2D video display device 1009.

Figure 7 shows a 3D scanner 2000 generally similar in construction and use as the 3D scanner 1000 and therefore similar parts are likewise numbered. The 3D scanner 2000 may include a stereoscopic acquisition module as discussed with respect to module 1003 or any other type stereoscopic acquisition module such as the embodiment of the stereoscopic acquisition module 400 of the present invention. The 3D scanner 2000 differs from the 3D scanner 1000 insofar as the latter 2000 additionally includes an onboard pseudo 3D video processing module 1111 for converting the stereoscopic 2D image frame stream 1004 to a pseudo 3D video stream 1112 of the scanned 3D surface of the 3D object 1001 for display on a pseudo 3D video display device 1113. The onboard pseudo 3D video processing module 1111 converts each stereoscopic 2D image frame into a single pseudo 3D video frame. Implementation of a pseudo 3D video processing module is described in an article entitled FPGA-Based System Combines Two Video Streams to Provide 3D Video. The article is available online at http ://www. analog, com/library/analogdialogue/archives/47- 12/stereo_video.html

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications, and other applications of the invention can be made within the scope of the appended claims.

Claims

CLAIMS:

1. A 3D scanner comprising:

a stereoscopic acquisition module for acquiring a stereoscopic 2D image frame stream of a scanned 3D object;

a 3D surface processing module for processing said stereoscopic 2D image frame stream for generating a 3D surface file modelling the scanned 3D object; and

a pseudo 3D video processing module for converting said stereoscopic 2D image frame stream to a pseudo 3D video stream of the scanned 3D object for display on a pseudo 3D video display device.

2. The 3D scanner of claim 1, wherein the stereoscopic acquisition module having an optical axis and comprising:

an optical system including

i) a double telecentric lens deployed along the optical axis and having an entrance lens and an exit lens spaced apart from said entrance lens, said entrance lens having a front focal plane and a back focal plane, said exit lens having a front focal plane and a back focal plane, said entrance lens' back focal plane coinciding with said exit lens' front focal plane at a common focal point,

ii) an aperture at said common focal point, and

iii) a splitting prism deployed along the optical axis in front of said entrance lens relative to said common focal point and adjacent said entrance lens; and

an imaging module at said exit lens' back focal plane for capturing a stereoscopic 2D image of the surface of the 3D object deployed at said entrance lens' front focal plane.

3. The 3D scanner of claim 2, wherein the splitting prism is an achromatic prism comprising a rear portion with a first refractive index nl and a front portion with a second refractive index n2 different from nl.

4. The 3D scanner of claim 3, wherein n2 is smaller than nl.

5. The 3D scanner of claim 3, wherein nl is smaller than n2.

6. The 3D scanner of any one of claims 1 to 5 and further comprising an illumination module adapted to illuminate the 3D object with rays of different wavelength simultaneously or sequentially.

7. The 3D scanner of any one of claims 2 to 6, wherein the prism comprising front first and second entrance surfaces and at least one rear exit surface, the front entrance surfaces converging in the front direction towards the optical axis and the rear exit surface being perpendicular to the optical axis.

8. A method for scanning a 3D object comprising the steps of:

providing a stereoscopic acquisition module for acquiring a stereoscopic 2D image frame stream of the 3D object;

processing said stereoscopic 2D image frame stream for generating a 3D surface file modelling the 3D object; and

converting said stereoscopic 2D image frame stream to a pseudo 3D video stream of the scanned 3D object for display on a pseudo 3D video display device.

9. The method of claim 8 and comprising a step of providing eyewear means to a viewer of the pseudo 3D video display device, wherein viewing the pseudo 3D video display device with eyewear provides the viewer with a pseudo 3D illusion of depth of the scanned 3D.

10. The method of any one of claims 8 or 9, wherein the stereoscopic acquisition module having an optical axis and comprising:

an optical system including

ii) an aperture at said common focal point, and iii) a splitting prism deployed along the optical axis in front of said entrance lens relative to said common focal point and adjacent said entrance lens; and

11. The method of claim 10, wherein the splitting prism is an achromatic prism comprising a rear portion with a first refractive index nl and a front portion with a second refractive index n2 different from nl.

12. The method of claim 10, wherein n2 is smaller than nl.

13. The method of claim 10, wherein nl is smaller than n2.

14. The method of any one of claims 8 to 13 and further comprising an illumination module adapted to illuminate the 3D object with rays of different wavelength.

15. The method of any one of claims 10 to 14, wherein the prism comprising front first and second entrance surfaces and at least one rear exit surface, the front entrance surfaces converging in the front direction towards the optical axis and the rear exit surface being perpendicular to the optical axis.