DE102016202181A1 - Lighting for a 3D camera - Google Patents

Abstract

Device for beam shaping so that the scene dynamic range is minimized.

Description

The invention relates to a lighting for a 3D camera according to the preamble of the independent claims.

A 3D camera should include all systems that detect 3D data from an actively lit scene, such as systems with structured light and / or Time of Flight (TOF) systems, in particular, light-time camera systems, which measure distances directly from the camera Determine the light transit time or gain the light transit time from the phase shift of an emitted and received radiation. As a light transit time or 3D cameras in particular PMD cameras with photonic mixer detectors (PMD) are suitable, as in the DE 197 04 496 A1 described and, for example, by the company 'ifm electronic GmbH' or 'PMD Technologies GmbH' as O3D camera or as a CamBoard relate. In particular, the PMD camera allows a flexible arrangement of the light source and the detector, which can be arranged both in a housing and separately.

In the 2D or general illumination range, beamformings exist which are designed to illuminate scenes uniformly; so z. B. modified the light emission of LED street lights by attaching optics so that streets and / or sidewalks are homogeneously illuminated and not to be illuminated areas (private land, etc.) are omitted. This beam shaping is essentially oriented at the distances or square distance variations occurring at the place of use.

In the 2D camera sector, high dynamic ranges are often achieved by means of several exposures with different exposure times (so-called HDR recordings - high dynamic range). This is at the expense of frame rate and energy consumption; also motion blur can arise.

In the case of 3D cameras with active illumination (for example, time-modulated with ToF or spatially modulated with structured light), much higher dynamic ranges are required within the image area. In addition to the quadratic dependence of the distance variation, the vignetting of the objective or the relative sensitivity (relative illumination - RI) of the 3D camera, the expected angle-dependent reflectivities are to be considered here. Furthermore, aspects such as the eye safety of lasers or LEDs must be considered.

HDR recordings based on several individual recordings with different integration times are particularly unfavorable for 3D recordings because they reduce the frame rate, increase the computational effort and lead to so-called motion artifacts. H. In particular, the edges of objects lie on different pixels in the different, temporally successive recordings and are difficult to evaluate.

3D ToF camera illuminators that illuminate areas outside the image area may be affected by measured value corruption due to multipath propagation (eg, reflections), i. H. A target is irradiated both directly and via at least one second path - for example in the form of directed (eg window panes) or undirected, diffuse reflections.

The object of the invention is to make a 3D camera system more robust with respect to dynamic changes.

The object is achieved in an advantageous manner by the illumination according to the invention for a 3D camera according to the preamble of the independent claims.

The problem is solved according to the invention in that the radiation of an active illumination of a 3D camera is shaped in such a way that the effective dynamic range is minimized in the case of a 3D image.

Advantageous is a lighting module ( 10 ) for a 3D camera ( 20 ) in which a beam shaping of the illumination module is designed such that an intensity dynamic of one of the 3D camera ( 20 ) of detected light, preferably including camera system parameters, is minimized.

Preferably, the beam shaping is configured such that the light component outside the image area to be detected becomes minimal.

Preferably, the beam shaping is realized by means of lenses or diffusers, in particular via emitters or emitter arrays, for example VCSEL.

Similarly, the beam shaping can be done by means of several different light sources.

In a further embodiment, the beam shaping takes place via different emitters with a small emission angle.

It is particularly useful to additionally design the beam shaping in such a way that the emission power is limited as a function of the angle.

This procedure is particularly advantageous if, for example, an eye and / or skin safety must be ensured.

Equally advantageous is a 3D camera system ( 1 ) with the aforementioned lighting module ( 10 ) is provided, in which in particular in addition to the beam shaping of the illumination camera system parameters are adjusted to minimize the intensity dynamics.

The spatial intensity variation is not only suitable for time-modulated 3d-ToF illumination, but also for 3d-structured-light illumination. Ie. the dot pattern of a "structured-light" generator has an intensity envelope as mentioned above.

The invention will be explained in more detail by means of embodiments with reference to the drawings.

Show it:

1 schematically a light transit time camera system,

2 a 1 / cos ⁴ illumination profile for a 60 ° × 46 ° field of view

3 a 1 / cos ³ illumination profile for an 80 ° × 60 ° image field

4 a 1 / cos ³ illumination profile for a 120 ° × 80 ° field of view

In the following description of the preferred embodiments, like reference characters designate like or similar components.

1 shows a measurement situation for an optical distance measurement with a light time camera, as for example from the DE 197 04 496 A1 is known.

The light transit time camera system 1 includes a lighting or a lighting module 10 with a light source 12 and associated beam shaping optics 15 as well as a receiving unit or light runtime camera 20 with a receiving optics 25 and a light transit time sensor 22 ,

The light transit time sensor 22 has at least one time-of-flight pixel, preferably also a pixel array, and is designed in particular as a PMD sensor. The receiving optics 25 typically consists of improving the imaging characteristics of multiple optical elements. The beam shaping optics 15 the lighting 10 may be formed for example as a reflector or lens optics. In a very simple embodiment, if necessary, optical elements can also be dispensed with both on the receiving side and on the transmitting side.

The measurement principle of this arrangement is essentially based on the fact that, based on the phase shift of the emitted and received light, the transit time and thus the distance covered by the received light can be determined. For this purpose, the light source 12 and the light transit time sensor 22 via a modulator 30 together with a specific modulation signal M ₀ with a base phase position φ ₀ applied. In the example shown is also between the modulator 30 and the light source 12 a phase shifter 35 provided with the base phase φ _{0 of} the modulation signal M _{0 of} the light source 12 can be moved by defined phase positions φ _var . For typical phase measurements, phase positions of φ _var = 0 °, 90 °, 180 °, 270 ° are preferably used.

The light source transmits according to the set modulation signal 12 an intensity-modulated signal S _p1 with the first phase position p1 or p1 = φ ₀ + φ _var . This signal S _p1 or the electromagnetic radiation is in the illustrated case of an object 40 reflects and hits due to the distance traveled corresponding phase-shifted Δφ (t _L ) with a second phase position p2 = φ ₀ + φ _var + Δφ (t _L ) as a received signal S _p2 on the light transit time sensor 22 , In the time of flight sensor 22 the modulation signal M _{0 is} mixed with the received signal S _p2 , wherein the phase shift or the object distance d is determined from the resulting signal.

As illumination source or light source 12 are preferably infrared light emitting diodes. Of course, other radiation sources in other frequency ranges are conceivable, in particular, light sources in the visible frequency range are also considered.

In order to detect a scene with a high dynamic range, it is provided according to the invention that the radiation of an active illumination of a 3D camera is shaped in such a way that the effective dynamic range is minimized in a 3D image.

• – Laterale zu erwartende Reflektivitäten in der Szene Dies können z. B. einfache hell-dunkel Bereiche diffus reflektiernder, aber auch der Glanz/spiegelnde Reflektivität von Zielen sein (siehe auch BSDF-bidirectional scattering distribution function, oder auch bidirectional reflectance distribution function).
• – a priori bekannte Abstandsunterschiede im Bildbereich: z. B. 1/cos^2(\phi) Abstandszunahme bei senkrechter Betrachtung einer ebenen Fläche; oder z. B. Einschränkungen der maximal möglichen Abstände, wenn die 3d-Kamera z. B. trotz horizontaler Ausrichtung Teile von Boden oder Decke erfasst.
• – Beachtung der Vignettierung des Objektivs bzw. der gesamten beobachtungs-winkelabhängigen relativen Empfindlichtkeit der Kamera (kann z. B. auch der chief ray angle (CRA) mismatch mit umfassen, wenn der CRA des Objektivs nicht zum Design-CRA von Mikrolinsen auf dem Sensor passt).
• – Beachtung von Augensicherheitskriterien, insbesondere bei Verwendung von sogenannten „engineered diffusers” d. h. Limitierung der Abstrahlleistung in gewisse Richtungen, wenn der Grenzwert der maximal zulässigen Bestrahlungsleistung überschritten würde; z. B. wenn die zu emittierende Leistung in diese Richtung insbesondere bei Beachtung der virtuellen/reellen Quellengröße aufgrund des Betrachtungswinkels des Emitters zu groß wird. Extrembeispiel: ein planer Diffusor oder Emitter, welcher in alle Richtungen gemäß IEC 60825-1 die maximal mögliche Laserleistung für eine gewisse Laserklasse (z. B. Laserklasse 1) emittieren soll, hätte ein cos-förmigen Abstrahlprofil.
• – Außerhalb des Bildbereiches ist jegliche Emission zu vermeiden, um ungewolltes Streulicht von außerhalb des Bildbereiches und auch Mehrwegeausbreitung des aktiven 3d Kamerabeleuchtung zu vermeiden.

The following variables are considered:

• - Lateral expected reflectivities in the scene. B. simple light-dark areas diffuse reflecting, but also the gloss / specular reflectivity of targets (see also BSDF bidirectional scattering distribution function, or bidirectional reflectance distribution function).
• - a priori known distance differences in the image area: z. B. 1 / cos ^ 2 (\ phi) distance increase when viewed perpendicularly a flat surface; or z. B. Limitations of the maximum possible distances when the 3d camera z. B. detected despite horizontal alignment parts of the floor or ceiling.
• - Observe the vignetting of the lens or the total viewing angle-dependent relative sensitivity of the camera (may include, for example, the chief ray angle (CRA) mismatch, if the CRA of the lens is not the design CRA of microlenses on the sensor fits).
• - Observance of eye safety criteria, in particular when using so-called "engineered diffusers", ie limitation of the radiation power in certain directions if the limit value of the maximum permissible irradiation power were exceeded; z. For example, if the power to be emitted in this direction becomes too large, in particular if the virtual / real source size is taken into account because of the viewing angle of the emitter. Extreme example: a planar diffuser or emitter, which in all directions according to IEC 60825-1 The maximum possible laser power for a certain laser class (eg laser class 1) should emit, would have a cos-shaped radiation profile.
• - Outside of the image area, any emission should be avoided to avoid unwanted stray light from outside the image area and also multipath propagation of the active 3d camera lighting.

z(θ, ϕ)

= erwartete/vorab bekannte/maximal mögliche Bildabstände

RI(θ, ϕ)

= relative Empfindlichkeit des Kamerasystems

R(θ, ϕ)

= Reflektivität der erwarteten/vorab bekannten Ziele

With:

z (θ, φ)

= expected / previously known / maximum possible image distances

RI (θ, φ)

= relative sensitivity of the camera system

R (θ, φ)

= Reflectivity of the expected / previously known goals

In 2 a possible example of a beam profile is shown. For the measurement of a highly diffusely reflecting, flat target using a camera system which has only sensitivity limitations due to the vignetting of an uncorrected objective, typically a radially symmetrical illumination corresponding to 1 / cos ⁴ (φ) is advantageous. The example shown is calculated for an image field of 60 ° × 46 °. Due to the intensity peaks in the edge region, the vignetting of the lens can be compensated advantageous.

Since it is usually attempted to correct strong vignetting in lenses, at least in part by appropriate designs, an in 3 shown 1 / cos ³ (φ) -like intensity curve of the illumination represent a compromise between the vignetting uncorrected and well-corrected lenses. in the In the case illustrated, the elevation of the border areas was also limited in order to ensure eye safety.

When using planar diffusers, such as diffractive optical elements (DOE), holographic optical elements (HOE) or so-called "engineered diffusers", one also encounters the problem that the real or virtual source size becomes smaller and smaller as the viewing angle increases Therefore, the maximum allowable irradiation limit (MCC) will be reached earlier with increasing angle. In such a case, the radiated intensities in the respective directions should not simply be limited to a constant value, but should be more limited according to the source size; The above formulas then change to:

A corresponding example is in 3 shown.

LIST OF REFERENCE NUMBERS

1

Time of flight camera system

10

Lighting, lighting module

12

light source

20

Receiver, light time camera

22

Transit Time Sensor

30

modulator

35

Phase shifter, lighting phase shifter

40

object

φ, Δφ (t _L )

term-related phase shift

φ _var

phasing

φ ₀

base phase

M ₀

modulation signal

p1

first phase

p2

second phase

Sp1

Transmission signal with first phase

sp2

Received signal with second phase

d

subject Distance

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19704496 A1 [0002, 0027]

Cited non-patent literature

• IEC 60825-1 [0034]

Claims (9)

Lighting module ( 10 ) for a 3D camera ( 20 ) in which a beam shaping of the illumination module is designed so that an intensity dynamic of one of the 3D camera ( 20 ) of detected light is minimized. Lighting module ( 10 ) according to claim 1, wherein the beam shaping is designed such that the light component outside the image area to be detected becomes minimal. Lighting module ( 10 ) according to one of the preceding claims, in which the beam shaping is effected by means of lenses or diffusers. Lighting module ( 10 ) according to one of the preceding claims, in which the beam shaping takes place via emitters or emitter arrays. Lighting module ( 10 ) according to one of the preceding claims, in which the beam shaping takes place by means of a plurality of different light sources Lighting module ( 10 ) according to claim 5, wherein the beam shaping is carried out by aligning different emitters with a small emission angle. Lighting module ( 10 ) according to any one of the preceding claims, wherein the beam shaping is additionally designed so that the emission power is limited depending on the angle. 3D camera system ( 1 ) with a lighting module ( 10 ) according to any one of the preceding claims. 3D camera system ( 1 ) according to claim 8, wherein in addition to the beam shaping of the illumination camera system parameters are adapted to minimize the intensity dynamics.

Images