DE102022104041B3 - Arrangement and method for taking pictures - Google Patents

Abstract

The creation of the point correspondences for obtaining a distance image is facilitated by the arrangement and by the method for recording images of a surface with two cameras in a stereo arrangement. Polarized lighting in a special arrangement and polarization orientation is used, as well as simple polarization filters with a special orientation in the respective beam path to the image recorders of the cameras. Advantages for the creation of point correspondences: It is possible to evaluate both locally and proportionately mixed diffuse and specular reflecting surfaces without knowing the distribution of these material properties on the surface. Highlights appear at the same surface location in the two cameras. Cast shadow areas only appear in one of the two cameras and can be removed from the correspondence determination in advance. The picture can be taken with a single shot and thus also with fast movement (camera or surface).

Description

The invention relates to an arrangement and a method for recording images of an object surface using a first camera and a second camera in a stereo arrangement. The images can be used to obtain a distance image. Distance images encode the distance of the points of the scene's surface (object points or background points) from the sensor (generally a camera) or the elevation of these points relative to a plane, in contrast to conventional images that encode gray values or colors. The pixels of a distance image therefore contain distance information (e.g. distance or height) of the associated object point that is displayed in each case. It is a classic computer vision problem.

Technical applications can be found in mechanical engineering, robotics including service robotics, electronics production, archaeology, the clothing industry, biometrics, medicine and reverse engineering.

The aim is, for example, the 3D acquisition of the fine or coarse structure or waviness or bending of a component or the localization of surface defects or an assembly control or the determination of the position of one or more objects of known geometry in a scene (example: "picking in the box ").

The invention can be applied to a wide variety of surface characteristics, including mixed ones, from fully diffuse (Lambert's reflection) to matt, weakly glossy (e.g. paper), glossy (e.g. metallically glossy in various degrees of roughness) to partially reflective. The more shiny a surface, the narrower the reflection lobe. Knowledge of the Bidirectional Reflectance Distribution Function (BRDF) is not assumed. Fully reflective surfaces or large surface areas without a diffuse component are not considered here; deflectometry methods are suitable for this.

The methods and arrangements described here are used for triangulation with cameras in a stereo arrangement to obtain a distance image. In stereo methods, objects recorded from different camera positions are shifted and/or distorted in the images in relation to one another due to the system, which ultimately contains the distance information to be found. With stereo methods, the most difficult problem is determining the correspondence of the pixels, i.e. the assignment of the pixels of one camera to the corresponding ones of the other camera. If the correspondence is known, a distance image can be calculated using triangulation if the recording geometry is known.

Triangulation is known state of the art, there is extensive, old and new literature on correspondence determination, the correspondence determination has not yet been satisfactorily solved in numerous applications. The description of this invention focuses on measures to simplify the determination of correspondence.

To determine the correspondence, features at a point P1 in an image from the camera C1 are compared with features at a point P2 in an image from the camera C2. The features are derived from data provided by the camera at pixels P1 in the image from camera C1 and P2 in the image from camera C2 (P1/P2) or there in small image sections (windows). In the course of the correspondence determination, quality values are determined for correspondence hypotheses P1/P2, which result from the comparison of the characteristics of P1 with those of P2.

In order to facilitate the correspondence determination, various methods based on structured light are known. Disadvantageously, these methods require a structured light projection device.

If the transmitter and receiver are interchanged, the bidirectional reflection distribution (BRDF) is retained according to the Helmholtz reciprocity. Various approaches are based on this and work with two cameras C1 and C2 and two point light sources or almost point light sources L1 and L2. In this case, L1 is either real or virtual in the optical axis of C1 and L2 is either real or virtual in the optical axis of C2. Or L1 is in close proximity to C1 and L2 is in close proximity to C2 ( U.S. 7,623,701 B2 , U.S. 7,769,205 B2 , U.S. 7,574,067 B2 , U.S. 2015/0281676 A1 ). If an image is recorded with C1 with illumination L2, and conversely an image is recorded with C2 with illumination L1, then with brilliant reflection at a surface point P the gray values of the corresponding points of P are the same.

Yuqi Ding, Yu Ji, Mingyuan Zhou, Sing Bing Kang, Jinwei Ye: "Polarimetric Helmholtz Stereopsis", published in Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV), 2021, pp. 5017-5026, relates to a Stereo arrangement based on Helmholtz reciprocity, in which an object that is irradiated with a polarized light source is imaged with a polarization camera. Two camera recordings are made, for the second camera recording the Camera position and the position of the light source relative to the first camera recording are mechanically reversed by means of a rotary wheel. The radiation reflected by the object is broken down into three components.

These solutions have the disadvantage that they cannot work for Lambertian or near Lambertian reflection. With Lambertian reflection, the luminance depends on the lighting and is independent of the viewing direction. The reason for this can be found in DE 10 2019 105 358 B4 (0037). If, in the case of Lambertian reflection, the lighting and viewing angles are interchanged at a point with unequal lighting and viewing angles, a different impression of brightness is obtained.

After DE 10 2019 105 358 B4 the lights occupy a larger space or can be distributed in a special way over a larger space. In addition, an image with an illumination LX is recorded with each of the two cameras, it being possible for LX=L1 or LX=L2 to apply. Images of L1 can also be taken with C1 and images of L2 can also be taken with C2 (see eg 0081). Through these measures, the ability to be evaluated is achieved in a larger surface area and the ability to be evaluated is also facilitated in the case of Lambertian reflection.

Both with punctual illuminations, as well as extended illuminations DE 10 2019 105 358 B4 A difficulty remains when light from L1 is reflected in specular to C1 or light from L2 in specular is reflected to C2. The difficulty will increase based on the description below 2 explained. A disadvantage here is that in this situation it is not possible to separate the gloss component and the diffuse component in a simple manner.

The Post-Released DE 10 2021 121 121 A1 relates to a device for determining geometric properties of a surface by means of polarized light which is directed onto a surface and two polarization cameras in a stereo arrangement which can distinguish between the polarized and unpolarized components, these components being recorded under different lighting geometries.

The object of the present invention is to at least partially eliminate the disadvantages mentioned.

The object is achieved according to the invention by arrangements and methods with the features of the independent patent claims. Preferred refinements and developments of the invention result from the dependent patent claims.

• 1 eine bekannte Anordnung mit zwei Kameras und zwei Punktlichtquellen,
• 2 ein Problem der bekannten Anordnung bei Rückstrahlung im Glanz,
• 3a, b die Wirkung der erfindungsgemäßen Lösung für den Glanzanteil,
• 4a, b die Wirkung der erfindungsgemäßen Lösung für den Glanzanteil, bei dezentral liegendem Oberflächenpunkt,
• 5 die Lösung gemäß der Erfindung bei Rückstrahlung im Glanz,
• 6a, b die Wirkung der erfindungsgemäßen Lösung für den Diffusanteil bei asymmetrischer Beleuchtung,
• 7 die Wirkung der erfindungsgemäßen Lösung für den Diffusanteil bei symmetrischer Beleuchtung,
• 8 eine ringförmige Beleuchtung,
• 9 eine Auswertung der Schlagschattenbildung, und
• 10 die Bildaufnahme mit einem einzigen Schuss, bei bunten Oberflächen.

The invention is described in more detail using the following embodiments with associated figures. It shows:

• 1 a well-known arrangement with two cameras and two point light sources,
• 2 a problem of the known arrangement with reflection in the gloss,
• 3a, b the effect of the solution according to the invention on the gloss component,
• 4a, b the effect of the solution according to the invention for the gloss component, with a decentralized surface point,
• 5 the solution according to the invention in retroreflection in luster,
• 6a, b the effect of the solution according to the invention for the diffuse component with asymmetric lighting,
• 7 the effect of the solution according to the invention for the diffuse component with symmetrical lighting,
• 8th a ring lighting,
• 9 an evaluation of the cast shadow formation, and
• 10 the image acquisition with a single shot, with colored surfaces.

When incident light is reflected off a surface, part of the incident light is usually specularly reflected and another part of the incident light is diffusely reflected. In order to keep the explanation of the process principles simple, a binary distinction is made in the following between diffusely reflecting and specularly reflecting reflection components, i.e. only the diffuse component or the gloss component is considered in each case. These proportions vary on the surface i.a. locally. In practice, of course, intermediate stages and locally continuous transitions are also possible.

The reflecting component depends on the angle at which the light falls and on the angle at which the camera is aimed at the surface. In the following, “in the specular angle” means that “angle of incidence = angle of reflection” applies to reflection. Depending on the width of the reflection lobe, a reflection with a gloss component also takes place at angles that deviate more or less from it.

Both gray value image cameras and color image cameras can be used for the invention become. In order to make the description simpler and easier to understand, the examples are initially based on greyscale cameras, and the generalization to color image cameras is given at the end.

Preliminary remarks on the figures: The lights and cameras that are active in the situation described are drawn with thick lines, the others with thin lines. The drawings describe the principle and are not to scale. This also applies to the positioning of the lights; the position of the lights had to be shifted somewhat unrealistically in some cases in order to be able to accommodate various arrows so that they could be distinguished from one another.

The explanation in the figures is done for the sake of easier understanding with point light sources (incandescent lamp symbols), the statements are also based on almost point-shaped light sources and extended light sources DE 10 2019 105 358 B4 applicable.

1 shows the known arrangement with two cameras C1 and C2 and two point light sources L1 and L2, which are located in the immediate vicinity of C1 and C2. An image of surface 1 is recorded with C1 illuminated with L2 (C1, L2 drawn with thick lines). R3 is the effective reflection lobe. Correspondingly, an image with illumination L1 is also recorded with C2. In the case of a glossy reflection at a surface point P, the gray values of the corresponding points of P in C1 and C2 are the same.

2 shows the above-mentioned difficulty when light is reflected from L1 in specularity to C1 ("reflection"). The Helmholtz reciprocity applies here to L1/C1. If on the one hand an image is recorded with C1 with illumination L2 and on the other hand an image with C2 with illumination L1, the gray values of the corresponding points in C1 and C2 are both zero with narrow reflection lobes. That wouldn't be particularly disturbing if it were only selectively so, but that can definitely be the case over a large area on the surface 1. One is therefore dependent on the diffuse component here. Since the luminance with Lambertian reflection depends on the lighting and is independent of the viewing direction, the diffuse component is the same in both cameras with the same lighting. If you take the lighting L1 for this, the diffuse component appears in C2, but the diffuse component is superimposed in C1 by the strongly specular reflection from L1. On the other hand, the same applies to L2/C2.

In contrast to the prior art, the invention presented here uses polarized illumination in a special arrangement and polarization direction and assignment to the cameras, as well as simple polarization filters with a special polarization direction in the respective beam path to the image recorders (image sensors) of the cameras. Simple linear filters are sufficient as polarization filters; alternatively, circular filters can also be used (with a suitable sequence of linear filters/Lambda quarter plate).

To create a distance image of a surface 1 using two cameras C1 and C2 in a stereo arrangement and with two lights, the two lights L1 and L2 are arranged such that when rays from the first light L1 are reflected on a surface point P at the glancing angle to the second camera C2 , rays from the second illumination L2 are also reflected at least approximately at the same surface point P in the glancing angle to the first camera C1.

The arrangement is characterized by
that in the beam path of each camera there is a polarization filter, each with a polarization direction, the polarization direction of the first camera rC1, and the polarization direction of the second camera rC2,
and that the illumination L1 works with a first polarization direction rL1 and the second further illumination L2 works with a second polarization direction rL2,
and that the camera and illumination polarization directions are oriented such that light from L1 specularly reflected at the surface toward camera C1 is substantially blocked at Rc1 and light from L2 specularly reflected at the surface toward camera C2 is essentially blocked at Rc2.
and that light specularly reflected from L1 to C2 is substantially transmitted at Rc2 and light specularly reflected from L2 to C1 is substantially transmitted at Rc1.

The polarization filters can be located in the beam path of the cameras in front of the lens or in the lens or between the lens and the image recorder of the respective camera. The polarization filters according to the invention in the beam path of the cameras are also implemented in polarization cameras with their (typically 2×2) pixel polarization filter arrangements of different polarization directions, in which the pixels of a single, selected polarization direction can be detected.

The polarization directions are set up and fixed when configuring the system or in the event of a service case according to the conditions described and are retained for different surfaces during operation. For the last condition (L1 to C2 and L2 to C1) it is advantageous to use a central point of the entire evaluation area and an average surface inclination to be expected there.

Explanation of the gloss content

3a and 3b show the solution for the gloss component, with the reflection lobes R3. At 3a Camera C1 and lighting L2 are active at 3b camera C2 and lighting L1 are active. is viewed in 3a/b a central point P of the surface. In this case, the gloss components are the same in both cameras, since this light component, reflected from L1 to C2, is essentially transmitted and the light component, reflected from L2 to C1, is essentially transmitted.

If a surface point is decentralized, as in the 4a and 4b (from the viewer's direction of 4a/b backwards or forwards), then with specular reflection from L1 to C2, the polarization direction is rotated by an angle and from L2 to C1 by the same angle, only with the opposite sign (seen from the direction of the viewing camera). Due to the filters rC1/rC2, this results in a weakening of the gloss component, but this weakening is the same for both cameras, since the angles of rotation are the same in terms of amount.

Regarding the directions of polarization drawn in the figures: The directions of polarization of the corresponding polarization filters are drawn in both for the illuminations and for the cameras; for the sake of clarity, the figures simply distinguish between HOR, horizontally hatched, and VER, vertically hatched. This corresponds to the following special case: with VER, the direction of polarization lies at least approximately in the plane of incidence for a central point, with HOR transversely to it. Here, the plane of incidence is spanned by the incident beam and the perpendicular to a surface element. The same applies to the polarization direction arrows R3 drawn horizontally/vertically. In 4a/b the symbolic directional arrows 3 are shown rotated with a rotated direction of polarization.

The only important thing is that the polarized components of L1 in C1 are essentially blocked by the filters, as are the polarized components of L2 in C2. Conversely, in C1 the polarized components of L2 are essentially transmitted, as are the polarized components of L1 in C2.

So you can rotate all HOR filters as well as all VER filters by e.g. 45 degrees and achieve the same desired effects.

You won't always get full pass or block, but the effects are enough to get the desired results.

5 shows the elimination of the above problem when light from L1 is reflected to C1 in the gloss. The filter rC1 prevents the polarized light from reaching C1 from L1.

If L1 and C1 are close together, the reflection will match 5 a specular reflection at a plane perpendicular to the polarized illuminating beam. In the case of specular back-reflection, there is a phase jump, but the direction of polarization is retained and thus the blocking by the polarization filter rC 1, which is transverse to the direction of polarization, is only slightly weakened if L1/ C1 are further apart.

Using polarized lighting in order to then partially remove the polarized component from the evaluation in the cameras seems absurd at first glance. The advantages become clear when you look at this in the context of the diffuse component.

Explanation of the diffuse portion

In general, when polarized light hits a Lambertian diffuse reflecting surface, it becomes depolarized. When L1 is illuminated, part of the diffusely reflected, i.e. depolarized, component passes through the polarization filter rC1. The same applies to L2 and rC2.

6a shows the diffuse component R2 when illuminated by L1. As mentioned above, in the case of diffuse reflection, the luminance is independent of the viewing direction and is therefore in principle the same for both cameras. The diffuse component is indicated in the figures by the circle R2. The star symbol 2 is intended to indicate unpolarized light. The arrow symbol 3 is intended to indicate polarized light. The two polarization filters rC1 and rC2 allow the same part of the diffuse part that is the same for both cameras. This applies to any tilt angle of the surface 1 at the reflecting point.

6b shows the situation when illuminated by L2. Here the illumination angle is flatter and the diffuse light component is correspondingly weaker, indicated by the in 6b smaller circle R2.

7 shows the diffuse component for a symmetrical situation, i.e. symmetrical lighting/camera position. It should be noted that in a symmetrical situation, if the specular parts L1/C2 and L2/C1 are equal ( 3 and 4 ), at locally isotro pen surfaces, the diffuse components L1/C1, L1/C2, L2/C1, L2/C2 are all the same (the same angle of incidence in terms of amount).

The first illumination L1 is advantageously located in a ring around the optical axis of the first camera C1, see FIG. 8th , and the second illumination L2 annularly around the optical axis of the second camera C2. The conditions for using the Helmholtz reciprocity (illumination L1/2 on the optical axis of C1/2) are thus well approximated.

To determine the correspondences:

• Mit Kamera C1 („links“) unter Beleuchtung von L1 („links“), kurz Livonli.
• Mit Kamera C1 („links“) unter Beleuchtung von L2 („rechts“), kurz Livonre.
• Mit Kamera C2 („rechts“) unter Beleuchtung von L1 („links“), kurz Revonli.
• Mit Kamera C2 („rechts“) unter Beleuchtung von L2 („rechts“), kurz Revonre.

For the sake of clarity, we assume that 4 separate images are taken:

• With camera C1 (“left”) under illumination of L1 (“left”), Livonli for short.
• With camera C1 (“left”) under illumination of L2 (“right”), Livonre for short.
• With camera C2 (“right”) under illumination of L1 (“left”), Revonli for short.
• With camera C2 (“right”) under illumination of L2 (“right”), Revonre for short.

$$\mathbf{Livonre}=\mathbf{Livonre}\text{glanz}+\mathbf{Livonre}\text{diffus},$$

etc.For each of these images there is a gloss component and a diffuse component, in short Livonli gloss, Livonli diffuse, Livonre gloss, etc.
with $$\mathbf{Livonli}=\mathbf{Livonli}\text{shine}+\mathbf{Livonli}\text{diffuse},$$

$$\mathbf{Livonre}=\mathbf{Livonre}\text{shine}+\mathbf{Livonre}\text{diffuse},$$

Etc.

und analog: $$\begin{array}{l}\mathbf{Revonli}+\mathbf{Revonre}\\ =\mathbf{Revonli}\text{glanz}+\mathbf{revonli}\text{diffus}+\mathbf{Revonre}\text{diffus}.\end{array}$$

Due to Livoni gloss=0, Revonre gloss=0 (blocking by crossed polarization directions rL1 and rC1, as well as rL2 and rC2) applies $$\begin{array}{l}\mathbf{Livonre}+\mathbf{Livonli}\\ =\mathbf{Livonre}\text{shine}+\mathbf{Livonre}\text{diffuse}+\mathbf{Livonli}\text{diffuse},\end{array}$$

and by analogy: $$\begin{array}{l}\mathbf{Revonli}+\mathbf{revenge}\\ =\mathbf{Revonli}\text{shine}+\mathbf{revonli}\text{diffuse}+\mathbf{revenge}\text{diffuse}.\end{array}$$

wegen Revonlidiffus=Livonreglanz
und
Revonlidiffus=Livonlidiffus (diffus, gleiche Beleuchtung, also unabh. von Betrachtungsrichtung), und
Livonrediffus=Revonrediffus (diffus, gleiche Beleuchtung, also unabh. von Betrachtungsrichtung).With that applies $$\mathbf{Livonre}+\mathbf{Livonli}=\mathbf{Revonli}+\mathbf{revenge}$$

because of Revonlidiffuse=Livonreglanz
and
Revonlidiffus=Livonlidiffus (diffuse, same lighting, i.e. independent of viewing direction), and
Livonrediffus=Revonrediffus (diffuse, same lighting, i.e. independent of viewing direction).

These two images (Livonre+Livonli) and (Revonli+Revonre) are advantageously used to determine correspondence, which can be done using known methods.

It is simply sufficient to leave both lights L1 and L2 switched on in order to record the sum of Livonre + Livonli in C1 and at the same time the sum of Revonli + Revonre in C2. It is thus possible to take a picture with a single shot.

However, if from the in the DE 10 2019 105 358 B4 , description too 23 If the method explained for the evaluation of cast shadows is to be used, a separate evaluation of Livonre and Revonli appears necessary.

For single shot image acquisition:

9 shows the evaluation of the cast shadow formation accordingly DE 10 2019 105 358 B4 , 23 ; L2 is switched on to determine the cast shadow areas 4 visible in camera C1, which are not visible in camera C2 and therefore cannot contribute to the determination of correspondence. Symmetrically to this, L1 is switched on to determine the cast shadow areas visible in camera C2, which are not visible in camera C1 and therefore cannot contribute to the correspondence determination. This is done by evaluating Livonre and Revonli at separate times. With this temporal separation, 2 shots are therefore required.

To evaluate the formation of hard shadows, the image can be recorded with a single shot on achromatic surfaces by separating them by color. For this purpose, the lights L1 and L2 can be operated with different colors F1 and F2, respectively, and the two cameras are color cameras that are able to separate these two colors.

• Die Beleuchtung L1 erfolgt mit zwei Spektralbereichen, sL0 und SL1. Die Beleuchtung L2 erfolgt mit zwei Spektralbereichen, sL0 und sL2. Die Kamera C1 kann nach der Bildaufnahme in einem Spektralbereich sC0 arbeiten, der mit Spektralbereich sL0 überlappt und in einem Spektralbereich sC2, der mit Spektralbereich sL2 überlappt. Die Kamera C2 kann nach der Bildaufnahme in dem Spektralbereich sC0 arbeiten und in einem Spektralbereich sC1, der mit Spektralbereich sL1 überlappt. Dabei überlappen sich die Spektralbereiche sL1 und sC0 nicht oder nur wenig, ebenso die Spektralbereiche sL2 und sC0.

Image acquisition with a single shot is also possible with colored surfaces as follows, see 10 :

• The illumination L1 takes place with two spectral ranges, sL0 and SL1. The lighting L2 takes place with two spectral ranges, sL0 and sL2. After the image recording, the camera C1 can work in a spectral range sC0 that overlaps with spectral range sL0 and in a spectral range sC2 that overlaps with spectral range sL2. The camera C2 can post of the image recording work in the spectral range sC0 and in a spectral range sC1 that overlaps with the spectral range sL1. The spectral ranges sL1 and sC0 do not overlap, or only slightly, as do the spectral ranges sL2 and sC0.

And the spectral ranges sL1 and sC2 do not overlap, or only slightly, as do the spectral ranges sL2 and sC1.

Technically, lighting spectral ranges sL0, sL1 and sL2 can be realized preferably by assembling narrow-band light-emitting diodes, as in 10 indicated by arrows; With conventional color cameras, the spectral ranges sC0, sC1 and sC2 are broadband ranges, as in 10 indicated by curves.

The images recorded by the cameras C1 and C2 can be further processed to determine the cast shadow. For this purpose, camera C1 further processes the image recorded by it in the spectral range sC2 and camera C2 further processes the image recorded by it in the spectral range sC1. Under the circumstances described, the drop shadow areas appear black or nearly black in the images captured by the two cameras. This makes it easy to determine the shadow areas.

Here it must be ensured that the parts of the surface that are visible in both cameras still deliver, albeit small, parts that can still be evaluated, otherwise these parts of the surface also appear black and are therefore indistinguishable from the hard shadow areas. Depending on the surface color, a subtractive color mixture can take place on the surface parts visible in both cameras, so that they also appear black. Fortunately, the phenomenon that the gloss component is reflected without color mixing, and the gloss component is let through by the polarization filters in the operating mode relevant here (light from L1 to C2 and from L2 to C1) is fortunate.

When using multispectral cameras, the requirements for the spectral ranges can be met very well, with the specified spectral ranges not having to be contiguous, i.e. they can consist of disjunctive individual ranges.

General Benefits

According to the invention, distance images of a surface are made possible by means of stereo analysis without movement (the laser light section requires movement that must be synchronized with the signal processing), without complex pattern projection devices, with lighting units that are easy to implement and with inexpensive, easily available on the market Standard greyscale or color cameras. With the same arrangement, it is possible to evaluate both locally and proportionately mixed diffuse and specular reflecting surfaces without knowing how these material properties are distributed on the surface.

For physical reasons, time-of-flight systems have accuracy limits, regardless of the size of the image field and the camera resolution, even for small image fields; in contrast to this, the achievable accuracy can in principle be increased at will with increasing camera resolution and/or by "stitching" several small image fields.

Highlights, otherwise very disturbing, since with conventional stereo in the two cameras i.a. appearing at different surface locations, appearing at the same surface location here. An otherwise serious problem with shiny spots becomes an advantage.

In conventional stereo, drop shadows are sometimes visible in both cameras, sometimes only in one, and if visible in both cameras, they generally appear with different brightness. And they are difficult to distinguish from dark surface regions visible in both cameras. Cast shadows therefore represent a major problem with conventional stereo. With the arrangement according to the invention, cast shadow areas only appear in one of the two cameras and can be removed from the correspondence determination in advance.

It is possible to take a picture with a single shot and can therefore also take place with fast movement (camera or surface).

Further variants of the invention

Color:

Color cameras can be used to advantage for colored surfaces: Instead of comparing individual gray values or the contents of gray value windows when determining correspondence, you only need to compare the color values or contents of color value windows, e.g. the red-green-blue values. In the case of colored surfaces, this simplifies the evaluation compared to pure intensity evaluation and improves the result.

Special camera types:

Of course, HDR cameras can also be used to expand the dynamic range.

The invention is not limited to the use of 2D cameras, but line cameras, ie cameras in which only one or very few directly or closely adjacent lines are scanned, can also be used without modifications.

Multiple Camera Pairs:

The previous considerations relate to only one single stereo camera pair. With several pairs of cameras, a separate distance image can be created for each pair of cameras. Several distance images can be merged using known methods to form a common distance image, which results in an increase in accuracy and/or an enlargement of the evaluation area (“stitching”).

Evaluation unit:

The image evaluation of the spectral components can be carried out in at least one of the two cameras C1, C2 ("intelligent cameras") or take place in an evaluation unit separate from the cameras, such as a PC, or in an evaluation unit to which only the image sensors of the cameras are connected. It is in this sense that "camera C.... can work in a spectral range... after the image has been recorded" and "camera C... processes the image it has recorded".

Claims (12)

Arrangement for recording images of a surface (1) by means of a first camera (C1) for recording at least one first image of the surface (1) and a second camera (C2) for recording at least one second image of the surface (1) in a stereo arrangement and with a first illumination (L1) and a second illumination (L2), the first illumination (L1) and the second illumination (L2) being arranged such that when rays from the first illumination (L1) hit a surface point (P) are reflected in the glancing angle to the second camera (C2), rays from the second illumination (L2) are reflected on at least approximately the same surface point (P) in the glancing angle to the first camera (C1), characterized in that in the beam path of the first camera (C1) a first polarization filter with a first polarization direction (rC1) is positioned and in the beam path of the second camera (C2) a second polarization filter with a second polarization direction ng (rC2) and that the first illumination (L1) can operate with a first polarization direction (rL1) and the second illumination (L2) can operate with a second polarization direction (rL2), and that the camera and illumination polarization directions are oriented such that light from the first illumination (L1) specularly reflected at the surface downstream of the first camera (C1) is substantially blocked by the first polarizing filter (rC1) and that light from the second illumination (L2 ) specularly reflected at the surface after the second camera (C2) is substantially blocked by the second polarizing filter (rC2), and that light specularly reflected by the first illuminator (L1) after the second camera (C2). is substantially transmitted by the second polarizing filter (rC2), and light specularly reflected by the second illumination (L2) after the first camera (C1) at the first pole Arization filter is essentially allowed to pass. arrangement according to claim 1 , wherein the first illumination (L1) is arranged annularly around the optical axis of the first camera (C1) and the second illumination (L2) is arranged annularly around the optical axis of the second camera (C2). Arrangement according to one of the preceding claims, characterized in that the first lighting (L1) can be operated with a first color (F1) and the second lighting (L2) with a second color (F2) different from the first color (F1) and the two cameras (C1, C2) are color cameras capable of separating the two colors (F1 and F2). arrangement according to claim 1 or 2 , characterized in that - the first lighting (L1) can be operated with a general lighting spectral range (sL0) and a first special lighting spectral range (sL1), - the second lighting (L2) with the general lighting spectral range (sL0) and a second special lighting spectral range ( sL2) can be operated, - an evaluation of at least one first image recorded by the first camera (C1) in a general camera spectral range (sC0) that overlaps with the general illumination spectral range (sL0), and in a second camera spectral range (sC2) that overlaps with the second illumination spectral range (sL2), and - an evaluation of at least one second image recorded by the second camera (C2) in the general camera spectral range (sC0) and in a first camera spectral range (sC1) which overlaps with the first illumination spectral range (sL1), - the first illumination spectral range (sL1) and the general camera spectral range (sC0) overlapping only slightly or not at all , and wherein the second illumination spectral range (sL2) and the general camera spectral range (sC0) do not overlap one another or only slightly, - and wherein the first illumination spectral range (sL1) and the second camera spectral range (sC2) do not overlap one another or only slightly, and the second illumination spectral range (sL2) and the first camera spectral range (sC1) overlap only slightly or not at all. Arrangement according to one of the preceding claims, further comprising a device for obtaining corresponding point pairs with respect to points on the object surface (1) from the at least one first image and the at least one second image. Arrangement according to one of the preceding claims, further comprising a device for obtaining a distance image of the object surface (1) from the at least one first image and the at least one second image. Method for recording images of a surface (1) by means of a first camera (C1) and a second camera (C2) in a stereo arrangement and with a first illumination (L1) and a second illumination (L2), the first illumination (L1) and the second illumination (L2) are arranged such that when rays from the first illumination (L1) are reflected on a surface point (P) in the glancing angle to the second camera (C2), rays from the second illumination (L2) on at least approximately the same Surface point (P) are reflected in the specular angle to the first camera (C1), characterized in that a first polarization filter with a first polarization direction (rC1) is positioned in the beam path of the first camera (C1) and a second one is positioned in the beam path of the second camera (C2). Polarization filter with a second polarization direction (rC2) is positioned, and that the first illumination (L1) with a first polarization direction (rL1) works and the z far illumination (L2) operates with a second polarization direction (rL2), and that the camera and illumination polarization directions are oriented such that light from the first illumination (L1) specularly reflecting at the surface downstream of the first camera (C1). is substantially blocked by the first polarizing filter (rC1), and that light from the second illumination (L2) specularly reflected at the surface downstream of the second camera (C2) is substantially blocked by the second polarizing filter (rC2). and that light specularly reflected by the first illumination (L1) after the second camera (C2) is substantially transmitted by the second polarizing filter (rC2), and light reflected by the second illumination (L2) after the first camera (C1) is specularly reflected, is essentially transmitted through the first polarization filter, and that with the first camera (C1) at least a first image of the surface (1) au f is taken and with the second camera (C2) at least a second image of the surface (1) is recorded. procedure after claim 7 , wherein the first illumination (L1) is arranged annularly around the optical axis of the first camera (C1) and the second illumination (L2) is arranged annularly around the optical axis of the second camera (C2). procedure after claim 7 or 8th , characterized in that the first lighting (L1) is operated with a first color (F1) and the second lighting (L2) with a second color (F2) different from the first color (F1) and the two cameras (C1, C2) Are color cameras capable of separating the two colors (F1 and F2). procedure after claim 7 or 8th , characterized in that - the first lighting (L1) is operated with a general lighting spectral range (sL0) and a first special lighting spectral range (sL1), - the second lighting (L2) with the general lighting spectral range (sL0) and a second special lighting spectral range ( sL2) is operated, - the at least one first image recorded by the first camera (C1) is fed to an evaluation in a general camera spectral range (sC0) which overlaps with the general illumination spectral range (sL0), and in a second camera spectral range (sC2) , which overlaps with the second illumination spectral range (sL2), - the at least one second image recorded by the second camera (C2) is fed to the evaluation in the general camera spectral range (sC0) and in a first camera spectral range (sC1), which coincides with the first illumination spectral range (sL1) overlaps, - wherein the first illumination spectra lrange (sL1) and the general camera spectral range (sC0) do not or only slightly overlap, and wherein the second illumination spectral range (sL2) and the general camera spectral range (sC0) do not overlap one another or only slightly, - and the first illumination spectral range (sL1) and the second camera spectral range (sC2) do not overlap one another or only slightly, and the second illumination spectral range (sL2) and the first camera spectral range (sC1) do not or only slightly overlap. Procedure according to one of Claims 7 until 10 , characterized in that the at least one first image and the at least one second image are used to obtain corresponding pairs of points with respect to points on the object surface (1). Procedure according to one of Claims 7 until 11 , characterized in that the at least one first image and the at least one second image are used to obtain a distance image of the object surface (1).

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