DE102009024961B4 - Method and device for evaluating headlights - Google Patents

Abstract

Method for recording the luminance field of vehicle headlights (1), in which a luminance measuring camera, hereinafter referred to as camera (2), arranged above the road area (4) illuminated by the vehicle headlight (1), through the surface of the road from a view from above (5) Detects light reflected to the camera (2) and, according to the pixel grid of the digital image sensor of the camera (2), determines a resolved raster image differentiated according to the luminance, from which, knowing the geometric dimensions of the camera location and the optical properties of the lens and image sensor an illuminance field reflected from the road (5) to the camera (2) is determined, the vehicle headlight (1) and camera (2) being moved relative to one another along the emission axis (A) of the vehicle headlight (1), successively by the camera (2) detectable illumination areas (3) are measured and subsequently can be combined to form an overall image of the luminance field of the vehicle headlight (1).

Description

The invention relates to a method and a device for evaluating headlights with regard to their luminance and / or illuminance and / or light intensity distribution in a vehicle environment that is as realistic as possible. The measurement of light intensity and distribution of a headlight from the is already known DE 2 239 959 A , whereby the light intensity is individually detected as a function of location by means of a large number of areally distributed intensity sensors. Furthermore, a camera can be provided which detects the position of the headlight to be tested in relation to the intensity sensors, so that corrections to the measurement setup are possible. A large number of intensity sensors are required for the measurement, whereby the light distribution can only be determined selectively.
The measurement of the light intensity distribution by means of goniometry is also previously known. With a correspondingly comparable resolution, goniometric measurements are very time-consuming, since a point cloud is determined step by step over two angular coordinates. Furthermore, the calculation of the luminance or illuminance takes place under the assumption of idealized simplified road conditions. A real measurement cannot be made with it.

From the EP 1 953 520 A2 A device for aligning a vehicle environment sensor or headlight is known in which a camera enables the alignment of an auxiliary adjustment device, such as a device detecting a light distribution from headlights, relative to the measuring station coordinate system, in particular to the vehicle axis, based on measuring points.

From the GB 2 076 174 A a height-adjustable device for testing vehicle lamps is known, which determines the light distribution in the beam path of the emitted light.

From the DE 197 04 427 A1 a device for regulating the range of headlights of vehicles is known, in which two light bundles shaped as spots are emitted at a defined distance in front of the vehicle, which are detected by an electro-optical sensor device arranged in the vehicle.

The object of the invention is to determine a high-resolution luminance or illuminance field or a light intensity distribution of a headlight with little expenditure of time.

This object is achieved for the method according to the invention by the features of claim 1 and for the device by the features of claim 5. Further advantageous refinements are listed in the subclaims and the description.
According to the invention, the method for recording the luminance field of vehicle headlights detects the illuminated road areas via a luminance measuring camera arranged above, hereinafter referred to as luminance camera or camera for short, from a view from above. The direction of observation is preferably perpendicular to the road surface. The light reflected by the surface of the road to the camera is captured by the lens and a resolved raster image that is differentiated according to the incident light intensity is generated in accordance with the pixel grid of the digital image sensor of the camera. The individual pixels reflect the smallest sections of the illuminated street. Knowing the geometric dimensions of the camera location, especially the height above the road and the optical properties of the lens - e.g. B. opening angle and the properties of the image sensor - grid, number of pixels, etc. - an illuminance field reflected from the road to the camera is determined. The vehicle headlight and camera are moved relative to one another along the emission axis of the vehicle headlight between successive measurements. In this way, successive illumination areas that can be recorded by the camera are measured. The individual illumination areas are then combined to form an overall image of the luminance field of the vehicle headlight. Due to the arrangement of the camera above the illuminated road area, the illumination area that can be captured by the camera can be captured with high resolution. The relative movement between the headlight and the camera between the measurements makes it possible to achieve a high-resolution overall image with just a few measurements. Assuming a typical camera location 8 m above the street and an image resolution of a modern luminance camera of at least 1000 × 1000 pixels and a lens aperture angle of 30 °, this corresponds to a field of view of 4.3 m × 4.3 m from a height of 8 m Resolution of 4 mm x 4 mm. At a measuring distance of 65 m, where the cut-off line touches the ground, this corresponds to an angular resolution that is better than 0.0001 ° compared to the measuring resolution of 0.01 ° of a conventional photogoniometer. Taking into account the measurement duration and measurement resolution, photogoniometric measurements with a measurement resolution of 0.1 ° are common. This in turn corresponds to a resolution of more than 10 m by 65 m. Furthermore, a significantly lower number of measurement steps is required, which is reflected in a reduction in time. Another advantage of the camera measurement vertically from above is the observation angle, which changes only slightly due to the lens expansion, which only affects the light intensity measurement little influenced. Furthermore, directed reflections of the headlight, the angle of incidence of which corresponds to the angle of radiation, are not reflected to the camera. Only diffusely scattered light is measured with it. The degree of reflection of the surface must be known, but only depends on the beam angle of the vehicle headlight to the road. The illuminance E⊥ is calculated from the measured luminance L: E⊥ = q⊥ L The luminance coefficient q⊥ is generally a function that depends heavily on four parameters: the horizontal and vertical angles of incidence and the horizontal and vertical viewing angles. This function is also dependent on the road conditions and has to be determined for each lane, which is very time-consuming. From the proposed perspective, the function is practically only slightly dependent on the horizontal angle of incidence. In practice, from this perspective, a reference measurement of the horizontal illuminance only needs to be carried out at one point with a photometer for each luminance recording in order to obtain q⊥ = E⊥ / L. This factor can be used to convert the entire luminance image, since the changes in q⊥ after the angles are small (cf. 4th ). This means that the method can be used for any homogeneous subsurface without prior measurement of its reflective properties. Problems that arise because, for example, a wet road dries slowly during the measurement and thus its reflection properties also change over time, do not apply, since the reference measurement is carried out immediately before or after the luminance recording (exposure time: several seconds) and thus in a few seconds is completed. One result is in 5 shown.

In an advantageous embodiment, the vehicle headlight is arranged in a stationary manner during the measurement and is not moved between the measurements. The successive illumination areas that can be detected by the camera are detected one after the other by a movement and thus repositioning of the camera between the measurements, with successive different road areas being measured. The alignment and positioning of the headlight can advantageously remain the same while the camera is moved along the emission axis between the measurements.
Alternatively, the camera is arranged in a stationary manner during the measurement and successive illumination areas are recorded by moving the headlight between the measurements. The headlight position and / or alignment is changed between the measurements, the same road area being measured by the camera in each case. In an advantageous manner, the degree of reflection of the surface remains the same, so that in the subsequent conversion into the illuminance, a degree of reflection that differs when the camera is moved along the emission axis is omitted as a source of error.

In one embodiment of the method, the beam angle of the headlight remains the same and the mobile headlight is moved along its emission axis between the measurements so that the fixed camera records different luminance distributions on the same road section. This method is advantageous if a correspondingly long measuring section (typically 65 m for low beam and 120 m for high beam images) is available. If a measurement is carried out in a closed room, which has advantages in terms of accuracy due to the constant ambient conditions, a measurement tunnel with a measurable distance of at least 120 m is required. Alternatively, you can work with shorter measuring tunnels by adjusting the headlight. To measure a high beam image, the headlight is changed in its height above the road and the height changed from the normal vehicle position is then taken into account when recording the luminance distribution, with the luminance recorded by the camera in the observed illumination area being converted accordingly. If you look at a single light beam from the headlight, the point of impact of the beam on the road changes when the headlight is adjusted in height, and thus the angle of observation changes when the observer is stationary. This change does not apply to vertical observation from above. The conversion from the shortened luminance image to the realistic one takes place via the luminous intensity distribution using the photometric distance law (pEg): $$\begin{array}{l}\begin{array}{l}\mathrm{L.}\left(verk\ddot{u}rzt\right)=\frac{1}{q_{\perp }}{\mathrm{E.}}_{\perp }\left(verk\ddot{u}rzt\right)\\ \underset{p\mathrm{E.}G:\mathrm{E.}=\frac{\mathrm{I.}}{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="DE102009024961B4\_0002.png,DE102009024961B4\_0003.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}}{{\displaystyle \Rightarrow }}\\ \mathrm{L.}\left(verk\ddot{u}rzt\right)=\frac{1}{q_{\perp }}\frac{1}{r^2\left(verk\ddot{u}rzt\right)}\mathrm{I.}\\ \iff \\ \mathrm{I.}=\mathrm{L.}\left(verk\ddot{u}rzt\right)q_{\perp }{r}^2\left(verk\ddot{u}rzt\right)\\ \underset{\mathrm{I.}einsetzenin}{{\displaystyle \to }}\end{array}\hfill \\ \mathrm{L.}\left(real\right)=\frac{1}{q_{\perp }}\frac{1}{r^2\left(real\right)}\mathrm{I.}\hfill \end{array}$$

• ein Scheinwerfer hat die eigentliche Höhe 0,65 m. Ein Lichtstrahl trifft in 50 m auf die Straße. Dann ist nach dem Satz des Pythagoras r(real) = 50,00 m. Wird der Scheinwerfer auf 0,30 m abgesenkt, ist r(verkürzt) = 23,08 m. Mit Hilfe eines Bildverarbeitungsprogrammes kann die Umrechnung pixelweise erfolgen. Das photometrische Entfernungsgesetz ist eine Näherung für große r im Bezug zu dem Scheinwerferdurchmesser. Daher sollte die Vermessung des Nahfeldes in realer Scheinwerfereinstellung erfolgen und nur das über den Tunnel hinausgehende Fernfeld über das beschriebene Verfahren gewonnen werden. Ein größerer Effekt hat ein Verkippen um δ des Scheinwerfers nach unten. Dann muss zusätzlich in der Bildverarbeitung der sich ändernde Einstrahlwinkel berücksichtigt werden, was in q⊥ erfasst wird. Die Transformation r(gedreht) -> r(real) verkompliziert sich marginal: r(gedreht) = Höhe Scheinwerfer/cos(α + δ) -> r(real) = Höhe Scheinwerfer/cos(α), α eigentlicher Einstrahlwinkel.

Here L (shortened) is the measured value. r (abbreviated) is the distance between the lamp and the point of incidence of the light beam on the road and is known from the geometry for each point on the road. Using the actual distance r (real) one obtains the actual luminance or illuminance distribution L, B (real). As an an example:

• a headlight is actually 0.65 m high and a beam of light hits the road at 50 m. Then according to the Pythagorean theorem r (real) = 50.00 m. If the headlight is lowered to 0.30 m, r (shortened) = 23.08 m. The conversion can be done pixel by pixel with the help of an image processing program. The photometric distance law is an approximation for large r in relation to the headlight diameter. For this reason, the near field should be measured with the real headlight setting and only the far field going beyond the tunnel should be obtained using the method described. Tilting the headlight down by δ has a greater effect. Then the changing angle of incidence must also be taken into account in the image processing, which is recorded in q⊥. The transformation r (rotated) -> r (real) is marginally complicated: r (rotated) = height of headlight / cos (α + δ) -> r (real) = height of headlight / cos (α), α actual angle of incidence.

According to the invention, the device for recording the luminance field of vehicle headlights has a commercially available luminance camera which is arranged above the road area illuminated by the vehicle headlight, the light reflected by the road to the camera being detectable from above. A digital image sensor with a corresponding pixel grid generates a resolved and differentiated grid image at the camera output according to the incident light intensity. An image processing unit is then connected to the camera. The structure is designed in such a way that the vehicle headlight and camera can be moved relative to one another along the emission axis of the vehicle headlight. Here, in a first alternative arrangement, the camera is attached to a movable holder and, with regard to its position relative to the headlight, can be moved along its emission axis.
In an advantageous embodiment, the device for recording the luminance field is arranged in a room with walls that absorb scattered light, the camera being movable on a rail system along the emission axis of the headlight. The rail system, which is preferably arranged on the ceiling, offers the advantage of faster, automated measurements.

In a second alternative embodiment, the headlight is moved along its emission axis and the camera position remains fixed. The headlight can be moved accordingly with a slide construction which ensures an exact assignment.
In all embodiments, headlights mounted individually on holders can be measured, whereby these can also be measured in their installation position permanently mounted in the vehicle, which is not possible with a photogoniometric measurement.

The invention is described below using an exemplary embodiment.

• 1 eine schematische Darstellung des Messaufbaus in einer Ansicht von oben, bei welcher zwischen den Messungen die Kamera verfahren wird,
• 2a, b eine schematische Darstellung des Messaufbaus, bei welcher zwischen den Messungen der Scheinwerfer entlang seiner Abstrahlachse verfahren wird,
• 3a, b eine schematische Darstellung des Messaufbaus, bei welchem zwischen den Messungen der Scheinwerfer in seiner Höhe über der Straße verfahren wird.

Here show:

• 1 a schematic representation of the measurement setup in a view from above, in which the camera is moved between the measurements,
• 2a, b a schematic representation of the measurement setup, in which the headlight is moved along its emission axis between measurements,
• 3a, b a schematic representation of the measurement setup, in which between the measurements the headlight is moved in its height above the road.

In 1 is a vehicle headlight 1 shown, which is a street area 4th along a road 5 illuminates. A camera 2 is arranged on a movable bracket in such a way that it is supported by the camera 2 detectable illumination areas 3 can capture from above. The camera 2 is many times higher than the headlight above the road. The movement of the camera 2 takes place along the emission axis A. of the vehicle headlight 1 .

2a and b show a structure similar to that of FIG 1 described, wherein identical parts are provided with the same reference numerals. Deviating from 1 a relative movement of the headlight to that by the camera occurs between two successive measurements 2 detectable illumination area. 2a and 2 B each represent the moment of an individual measurement, while the vehicle headlights are taken between the recordings 1 along the emission axis A. was moved.

3 a and b show the measurement setup in a side view. If the camera position is identical, the height between the measurements H of the headlight over the street 5 varies. The camera position remains unchanged in this example, but can also be changed. An advantageous embodiment is a number of consecutive from the camera 2 detectable illumination areas 3 by moving the camera position and after adjusting the height H of the vehicle headlight 1 above the surface of the road 5 to measure the same area again and to convert it into the required high beam field.

4th shows the horizontal luminance coefficient q⊥ of a road in dry and wet conditions. In the method described, a reference measurement of q⊥ is included for each luminance image. The angle of incidence results from the distance between the headlight and the center of the corresponding road section and the height of the headlight.

5 shows a composite luminance image from a vertical direction of observation. A reference measurement was used to determine q⊥ per image; the luminance is obtained by multiplying the individual luminance image by the corresponding factor q⊥. The individual images were taken with the LMK 98-4 color measuring system from FA. TechnoTeam recorded and processed with the software LMK 2000 of the FA TechnoTeam. The displayed scale and the individual images were also created with the LMK2000 software from FA TechnoTeam.

List of reference symbols

1

Vehicle headlights

2

camera

3

Illumination area that can be captured by the camera

4th

illuminated street area

5

Street

A.

Emission axis

H

Vehicle headlight height 1

Claims (7)

Method for recording the luminance field of vehicle headlights (1), in which a luminance measuring camera, hereinafter referred to as camera (2), arranged above the road area (4) illuminated by the vehicle headlight (1), through the surface of the road from above (5) detects light reflected to the camera (2) and, according to the pixel grid of the digital image sensor of the camera (2), determines a resolved raster image differentiated according to the luminance, from which, knowing the geometric dimensions of the camera location and the optical properties of the lens and image sensor an illuminance field reflected from the road (5) to the camera (2) is determined, the vehicle headlight (1) and camera (2) being moved relative to one another along the emission axis (A) of the vehicle headlight (1), successively by the camera (2) detectable illumination areas (3) are measured and subsequently can be combined to form an overall image of the luminance field of the vehicle headlight (1). Procedure according to Claim 1 , characterized in that the vehicle headlight (1) is stationary during the measurement and the successive illumination areas (3) that can be captured by the camera (2) are captured one after the other by a movement and thus repositioning of the camera (2) between the measurements, with successive different sections of the road (5) are measured. Procedure according to Claim 1 , characterized in that the camera (2) is stationary during the measurement and the successive illumination areas (3) are detected by a movement of the vehicle headlight (1), the same section of the road (5) being measured in each case. Procedure according to Claim 1 o. 3, characterized in that the vehicle headlight (1) is moved along the emission axis (A) and / or its height above the surface of the road (5) is changed. Device for recording the luminance field of vehicle headlights (1), in which a camera (2) is arranged over the road area (4) illuminated by the vehicle headlight (1), through which the road (5) to the Camera (2) reflected light can be detected, and according to the pixel grid of the digital image sensor of the camera (2) a resolved raster image differentiated according to the luminance is present at its output, which is subsequently switched on to an image processing unit, whereby the vehicle headlights (1) and camera (2 ) are movable relative to one another along the emission axis (A) of the vehicle headlight (1). Device according to Claim 5 , characterized in that the camera (2) is attached to a movable holder and is movable with respect to its position relative to the vehicle headlight (1) along its emission axis (A). Device according to Claim 6 , characterized in that the device for recording the luminance field is arranged in a room with walls that absorb scattered light, the camera (2) being movable on a rail system along the emission axis (A) of the vehicle headlight (1).

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