GB2147762A - An artifical binocular vision system - Google Patents

Abstract

Disclosed herein is a video camera assembly for an artifical stereopsis system wherein left and right video cameras (1 and 2) of equal principal distance (F) are mounted so that their photo.surfaces (3 or 4) are co-planar and are each scanned in lines parallel to the camera base (III - III), the principal points (7 or 8) of the left and right cameras being offset (OS) equally (to the left and right respectively) from the centre point (9 or 10) of each photo-surface; whereby the fields-of-view of the two cameras will coincide at the reference plane (V -V). <IMAGE>

Description

SPECIFICATION An artificial binocular vision system This invention relates to an artificial binocularthreedimensional vision system, hereinafter referred to as "an artificial stereopsis system". Stereopsis is a biological term used to denote binocular stereoscopic vision and the term is used herein to denote the analogous artificial process of binocularthreedimensional vision for robots and automation.

Such systems incorporate two synchronised image sensors and employ stereo image correlation for establishing relative or absolute spatial co-ordinates in three dimensions of visible objects.

Artificial stereopsis is an extension of a photogrammetric stereo image-correlation technique that has been developed as a rapid means of extracting three dimensional topographical information from aerial photographs (see, for example United States Patent Specification No. 3 659 939).

In the above-referred patent specification, and generally in photogrammetry, the video signals are corrected for both Y and X image displacements, of which only the X displacements are related to object dimensions. The Y displacements result from camera miss-orientation and their presence obscures the X displacements to be measured. The circuitry for Y correction is both expensive and, more importantly, slow.

It is an object of the present invention to provide an optical and geometrical arrangement to enable a pair of video cameras to produce signals that differ only in that X displacement due to the object distance (Z) to be determined.

The following definitions will apply: "WORKSPACE" as being all light-reflecting surfaces visible in the video camera's field-of-view including background (e.g. walls, doors, ceilings etc.). and foreground and intermediate objects of any kind; "OBJECTS" as being any part or content of the workspace separated from the background, whether moveable or not; "VIDEO CAMERA" as being any image sensing device that 1) employs a lens to focus an image of a workspace on a photo-surface and 2) produces an electrical signal descriptive of the image; "IMAGE" as being the optical system's projection of the workspace, including any objects present therein, on the photo-surface of a video camera; "PRINCIPAL POINT" as being the intercept of the image plane with the perpendicular from the projection centre of the camera;; "PRINCIPAL DISTANCE" as being the distance between the principal point and the projection centre; "PRINCIPAL PLANE" as being a plane containing the projection centres of a pair of cameras and parallel to the image plane; "CAMERA AXIS" as being the line through the centre point of the photo-surface and the projection centre of the camera; "REFERENCE PLANE" as being that plane parallel to the principal plane at the intercept of camera axes; "FIELD-OF-VIEW" as being the projection through the projection centre of the boundaries of the photo-surface onto the reference plane; "CAMERA BASE" as being the line connecting the projection centres of binocular cameras.

According to the present invention, a video camera assembly for an artificial stereopsis system consists of left and right hand video cameras, of equal principal distance and mounted so that their photo-surfaces are co-planar and are each scanned in lines parallel to the camera base, the principal points of the left and right cameras being offset equally (to the right and left respectively) from the centre point of each photo-surface; whereby the fields-of-view of the two cameras will coincide at the reference plane. The translational offset enables the image of the workspace to cover the photo-surface of each camera without introducing trapezoidal distortion arising out of the geometry of projection.

An artificial stereopsis system in accordance with the present invention will only correlate homologous image points as scanned by the video cameras; no correction is made for Y displacements both for simplicity and to speed real-time data processing.

The parameters of such a system enables the three-dimensional XYZ data to be calculated from the dx image displacement signal. For this to work, the input video signals have to be such that the only difference there can be between them will be due to the camera base giving views differing only in relative X-displacement of image details. Thus the time difference dt between the scanning of homologous image points in the left and right cameras is uniquely determined by the translational difference in the X-direction (dx); (dx = v.dt, where v is the image scanning velocity). Calculation of XYZ data is then a matter of a suitable algorithm based on the assembly's geometry and the dx data.

In a preferred embodiment of the invention, the two cameras are locked one to the other to prevent any relative movementtherebetween; although provision can be made to allow the cameras to be locked and unlocked for relative translational, lateral movement so that the eyebase can be changed without distortion of their angular relationship.

The invention is illustrated in the Drawing, which is a schematic diagram of a video camera assembly in accordance with the invention.

As shown, an assembly consists of left and right hand video cameras 1 & 2 arranged so that their photo-surfaces 3 & 4 respectively lie in the same image plane l-l. The projection centres 5 & 6 of the two cameras' lens systems each lie in the principal plane ll-ll, which is parallel to the image plane l-l. The principal distance F is the same for both cameras and, finally, it is arranged that both photo-surfaces 3 & 4 are scanned in lines parallel to the camera base Ill-Ill.

The lens system of each camera is offset towards a centre line IV-IV between the cameras. In precise optical terms, the principal points 7, 8 of the left and right cameras are offset equally (to the right and left respectively) by a distance OS from the centre point 9 or 10 of each photo-surface. The effect of this is that the field-of-view for each camera will coincide at the reference plane V-V. Specifically, the camera axis of each camera VI-VI and VII-VII respectively intercept at the reference plane V-V at point 11 and the limits oftheworkspace 12 for which images of objects therein will only differ in X displacement is indicated by the cross-hatching.

The parallel translational offset of the projection centre of each lens system enables the scheimflug condition to be met so that the reference plane will be sharply focussed over the entire photo-surface of each camera.

Each camera is constructed identically, one camera being rotated 180 degrees about its camera axis on installation, whilst arranging for its photosurface to be scanned in the same X direction as the other camera. The offset is usually fixed but, where cameras might be required to adapt to differing applications, the offset could be made variable.

In practice, a pair of solid state array video cameras are fitted to a mounting somewhat similar to an optical bench in that the relative positions of the two cameras can be adjusted to ensure that their photo-surfaces remain in the same plane and that the camera base is adjusted to the correct length for a particular application.

Claims (4)

1. Avideo camera assembly for an artificial stereopsis system consisting of left and right video cameras of equal principal distance and mounted so that their photo-surfaces are co-planar and are each scanned in lines parallel to the camera base, the principal points of the left and right cameras being offset equally (to the right and left respectively) from the centre point of each photo-surface; whereby the fields-of-view of the two cameras will coincide at the reference plane.

2. An assembly as claimed in claim 1, wherein the two cameras are locked to one another to prevent any relative movement therebetween.

3. An assembly as claimed in claim 2, wherein means are provided to enable the two cameras to be locked and unlocked for relative lateral movement; whereby the length of the camera base can be varied.

4. A video camera assembly for an artificial stereopsis system substantially as described with reference to or as shown by the Drawing.