Method for adjusting the set point of a digital lighting unit of a motor vehicle

Abstract

The invention relates to a method for adjusting the setpoint of a digital lighting unit intended to be projected by a digital lighting unit of a motor vehicle, the digital lighting unit comprising a matrix light source and an optical system. The method comprises the step of applying digital filtering to the digital setpoint. The filter used is able to anticipate geometrical aberrations caused by the optical system when projecting the digital setpoint.

Description

Technical Field

[0001] The present invention relates to a lighting module for a motor vehicle. In particular, the present invention relates to a control method for such a module involving a matrix light source. Background Art

[0002] A light emitting diode (LED) is a semiconductor electronic component capable of emitting light when it is subjected to an electric current having at least a threshold intensity. In the automotive sector, LED technology is increasingly used for many light signaling solutions. LED matrices are particularly popular in the field of automotive lighting. Matrix light sources can be used for “leveling” type functions, i.e. to adjust the height of the emitted light beam according to the attitude of the vehicle and the contour of the road. Other applications include DBL (“Digital Bending Light”), which corresponds to adjusting the direction of the emitted light beam so as to follow the road in the horizontal plane, ADB (“Adaptive Driving Beam”), which corresponds to an anti-glare function that generates a shadow area in the beam emitted by the high beam so as not to interfere with other road users, and functions for projecting patterns on the ground using a pixelated light beam. The contours of the shadow area must be well defined and reproduced by the lighting device in order to comply with the provisions of the current regulations.

[0003] It is a known practice to use light sources with different types of technology for the aforementioned lighting applications. This can include, for example, monolithic technology, according to which a large number of LED-type basic sources equivalent to pixels are etched into a common semiconductor substrate. Integrated electrical connections allow pixels to be activated independently of each other. Another known technology is the technology of micro-LEDs, which produces a small-sized LED matrix of typically less than 150 μm. There are also modules of the micro-mirror or DMD (“digital micro-mirror device”) type, which involve projection technology using an intensity modulator on a uniform light beam. The micro-mirrors whose positions are controlled by piezoelectric elements are oriented to selectively reflect the incident light beam so that each micro-mirror corresponds to the basic source of the pixel matrix thus generated. The light from the light source is directed onto the micro-mirror matrix by an optical device.

[0004] The light emitted by the matrix light source passes through an optical device comprising at least one optical lens in order to project the desired contour in front of the motor vehicle. However, for a given matrix light source and an associated output optical system, the response of the elementary light sources of the matrix through the optical system is not uniform. Typically, the central area can be projected with high resolution, while the resolution gradually decreases towards the edge of the field of view of the light source, which can also have a large aperture of the order of 35°. Therefore, using known solutions, the projection of precise contours in areas of lower resolution (i.e., at the edge of the field of view) is difficult or even impossible. The result of projecting a precise contour or pattern in such an area is usually a blurred or significantly distorted contour or pattern. Summary of the invention

[0005] An object of the present invention is to overcome at least one of the problems caused by the prior art. In particular, the present invention aims to propose a method that can increase the accuracy of patterns or contours projected by a matrix light source and an associated optical system without using more complex or more expensive optical systems.

[0006] According to a first aspect of the invention, a method for adjusting a digital lighting setpoint intended to be projected by a digital lighting unit of a motor vehicle is proposed. The lighting unit comprises a matrix light source and an optical system. The method is noteworthy in that it comprises a step of applying a digital filtering to the digital setpoint by a calculation unit before transmitting the filtered digital setpoint to the lighting unit. The digital filtering anticipates geometrical aberrations caused by the optical system during projection of the digital setpoint.

[0007] Preferably, the digital lighting set point may comprise a basic light intensity set point for each basic light source of the matrix light source.The digital filtering may preferably comprise selectively reducing the basic light intensity set point in dependence on a predetermined basic set point filter value.

[0008] Preferably, the filtering may comprise applying for each basic light set point a dedicated digital filter, said dedicated digital filter anticipating geometric aberrations induced by the optical system on projection pixels forming part of a spatial neighbourhood of the projection pixel corresponding to the basic light set point.

[0009] The neighborhood of a pixel may for example cover a predetermined number of pixels around the pixel. Alternatively, it may cover all pixels within a circle of a predetermined radius.

[0010] Preferably, the filtering may comprise applying to each column or row of basic light set points a dedicated digital filter, the dedicated digital filter anticipating geometric aberrations induced by the optical system on the projected columns or rows of pixels forming part of a spatial neighbourhood of the projected columns or rows of pixels corresponding to the column or row of basic light set points.

[0011] The lighting setpoints may preferably comprise a digital image having a resolution at least equal to the projection resolution of the lighting device.

[0012] Preferably, the method may comprise the following preliminary steps for each elementary light source of the matrix light source:

[0013] i) determining a spatial light distribution of a pixel projected through the optical system when the primary light source is controlled to emit at maximum output;

[0014] ii) determining by a computer a reduction factor or value of the maximum output such that the reduced emission output produces a spatial light distribution that illuminates pixels in a neighborhood of the projected pixel at most with a predetermined brightness level;

[0015] iii) Associating a reduction factor or value with the position of said light source in the matrix light source and storing it in a memory element as a basic set point filter value for the corresponding basic set point.

[0016] Preferably, the preliminary steps i) to iii) are performed once for each row or column of elementary light sources.

[0017] According to another aspect of the invention, a lighting device for a motor vehicle is proposed. The lighting device comprises a digital lighting unit having a matrix light source consisting of elementary light sources and an optical system. The device further comprises a data receiving unit for receiving a lighting set point. The lighting device is noteworthy in that it comprises a calculation unit configured to adjust the received lighting set point according to a method according to one aspect of the invention. The lighting device further comprises a control unit for controlling the lighting unit according to the filtered lighting set point.

[0018] Preferably, the control unit and / or the computing unit may comprise a microcontroller element or a data processor which is programmed with a suitable computer program in order to perform the method.

[0019] The optical system may preferably be arranged such that light emitted by the primary light source of the lighting unit passes therethrough. The optical system may preferably comprise at least one optical lens.

[0020] The data receiving unit may preferably include a network interface capable of receiving / sending data via a data bus inside the motor vehicle. For example, the bus may be a CAN (Controller Area Network) bus, an Ethernet bus, a Gigabit Multimedia Serial Link (GMSL) type bus, or a bus using Low Voltage Differential Signaling (LVDS) technology, such as an FPD-Link III bus.

[0021] The matrix light source may preferably comprise a monolithic light source comprising a primary light emitting light source having semiconductor elements which are etched into a common substrate and which can be activated independently of each other.

[0022] The matrix light source may preferably comprise a micro-LED type matrix comprising a matrix of elementary sources generated by light emitting diodes LED of small size (typically less than 150 μm).

[0023] The matrix light source may preferably comprise a micromirror device DMD (Digital Micromirror Device), wherein the elementary sources comprise micromirrors in a matrix which selectively reflect an incident light beam depending on its position.

[0024] According to a further aspect of the invention, a computer program is proposed comprising a sequence of instructions which, when executed by a processor, causes the processor to implement a method according to an aspect of the invention.

[0025] According to another aspect of the present invention, a non-transitory computer-readable storage medium is proposed, the medium storing a computer program according to the aforementioned aspect of the present invention.

[0026] By using aspects according to the invention, it is possible to anticipate in advance the geometrical aberrations (such as distortion or blur) induced in the image projected by the optical system. This is achieved using a digital method preferably implemented by computer software. Therefore, the solution does not require the use of more expensive optics that would produce less distortion. This approach makes it possible to keep the production costs of the proposed lighting device relatively stable while clearly improving its optical behavior. This improvement is all the more useful when the lighting device performs an "adaptive driving beam" or ADB function, which requires the projection of precise contours and patterns while requiring lower brightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other features and advantages of the present invention will be better understood from the description of embodiments and the accompanying drawings, in which:

[0028] Figure 1 is a diagrammatic representation of a method according to a preferred embodiment of the present invention;

[0029] Figure 2 is a graphical representation of the spatial light distribution of a pixel projected by a lighting unit according to a preferred embodiment of the present invention;

[0030] Figure 3 is a schematic diagram of a lighting device according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0031] Unless otherwise stated, technical features described in detail for a given embodiment may be combined with technical features described in the context of other embodiments described by way of example and not limitation.

[0032] This description focuses on the elements of a lighting module for a motor vehicle that are necessary for understanding the invention. Other elements that form part of such a module in a known manner will not be mentioned or described in detail. For example, the presence and operation of a converter circuit (known per se) involved in supplying power to a matrix light source will not be described in detail.

[0033] A matrix light source can generate a large number of elementary light sources of the LED type, for example, thousands of light sources based on electroluminescent semiconductor elements. Such a light source can cover a large field of view of the order of 35°. In a lighting device for a motor vehicle, an optical system comprising at least one optical lens is usually associated with such a matrix light source. Typically, the central part of the projected image has a high resolution, while the image edge area has a lower resolution. It has been observed that in the high-definition central area (corresponding to approximately -11° to 11° of the aperture), the light emitted by the elementary source generates a projected pixel and also contributes to the brightness of approximately two adjacent pixels. The light emitted by the elementary source in the average area (corresponding to approximately + / -11 to 14) generates a projected pixel and also contributes to the brightness of approximately four adjacent pixels. In the low-resolution edge area, the light emitted from a single elementary source generates one projected pixel and simultaneously contributes to the brightness of approximately eight pixels near it. Therefore, the spatial distribution of the light emitted by the elementary sources of the matrix light source is not uniform for all elementary sources constituting the matrix light source, but depends on the position of the elementary source relative to the optical system, even if the characteristics of the elementary source are otherwise the same. It has also been observed that the spatial distribution of the light emitted by an elementary light source depends on its operating output: at 100% output (always switched on), the light produced tends to contribute to the illumination of a greater number of adjacent pixels than at a lower output. Blurring effects or geometric aberration effects of the projected light beam caused by the optical system can therefore be at least partially offset by reducing the light intensity of the elementary light source. The output of a light emitting diode light source can be influenced in a known manner by driving its current supply via a pulse width modulation or PWM signal characterized by a duty cycle representative of the desired output. The present invention uses these observations to implement a method for limiting the optical aberrations produced by the lighting unit.

[0034] Figure 1The diagram of shows the provision of a digital lighting set point 10 intended to be projected by a digital lighting unit 100. The digital set point comprises, for example, an image, wherein each pixel 12 comprises a light intensity value, which ideally should be reproduced by a corresponding elementary light source 112 of a matrix light source 110 of the digital lighting unit 100. The matrix source 110 may comprise a monolithic source, a digital micromirror device or other matrix light sources known in the art. The digital lighting unit 100 further comprises an optical system comprising at least one optical lens 120 arranged downstream of the matrix light source along the direction of emitted light. A computing unit 130, such as a processor or microcontroller element programmed for this purpose, applies a digital filtering F to the raw digital set point 10, thereby generating a filtered digital set point F(10). The latter is transmitted to the lighting unit and finally projected by the matrix light source 110 and the optical system. The result is a projected image P(10). The filtering step makes it possible to anticipate geometric aberrations caused by the optical system 120. It should be noted that the projected pixel P(12) corresponds to a spatial distribution of light, having a maximum intensity at the center and a decreasing bell-shaped tendency in the vicinity thereof. The filter F depends on the distribution generated by the optical system 120 for each elementary light source 112 .

[0035] According to a preferred embodiment of the invention, the calculation unit 130 adjusts the value of each pixel 12 of the raw set point 10 according to a predetermined reduction factor or value forming part of the data of the filter F. Each of these basic set point filter values ​​is selected so as to limit the impact of the spatial distribution of the light emitted for a given pixel P (12) on its neighboring pixels. According to a preferred embodiment, the horizontal behavior of the matrix source is substantially uniform. In this case, a basic set point filter value is selected for each column of the raw set point 10, thereby limiting the calculation requirements of the calculation unit 130.

[0036] Figure 2 It is shown how the basic set point filter values ​​are obtained according to a preferred embodiment, however the invention is not limited to this example. The vertical axis shows the reference of the pixel or the reference of the source / column of the equivalent basic light source. The horizontal axis shows the percentage of brightness relative to the maximum normalized intensity. Consider here the pixel marked with X. When the light source X is operated with a duty cycle of 100%, the area under the curve "PWM100%" represents all the emitted light, while the trend of the curve shows the spatial distribution of this emission. The values ​​indicated for the neighboring pixels / columns X+1 (12%), X+2 (4%), X+3 (0%, rising to a minimum value of 1%, shown in dotted lines) represent the predetermined brightness thresholds that the spatial light distribution of the pixel X must comply with in order to guarantee a projection with reduced geometric aberrations. These values ​​can be determined empirically by precise measurements or by computer simulation methods. They depend on the characteristics of the matrix light source used, the basic light source and the optical system used.

[0037] It is obvious that for the elementary light sources denoted X, a set point equal to 100% brightness involves too high brightness levels for all neighboring pixels. In order to comply with all imposed constraints, if the original set point indicates 100%, an output of 50% should be applied to the pixel denoted X. A corresponding weight of 0.5 is stored in the memory element as a basic set point filter value for each set point denoted X. The filter values ​​may be refined for other intensities of the pixel denoted X. The method is performed once for all elementary light sources or for a column of all elementary light sources. The method generates a filter value F for the lighting unit in question. It should be noted that the basic set point filter values ​​are not uniform for all elementary light sources, since their position relative to the optical system 120 has a major influence on the light distribution they produce.

[0038] Once all of these weights or base set point filter values ​​have been identified, the step of applying the filter is preferably accomplished by the following algorithm.

[0039] For all pixels i, j of the original set point

[0040] min value =1;

[0041] For all k in the range [-5, ..., 5],

[0042] If k = 0,

[0043] Then value = I t (i, j)

[0044] otherwise

[0045] value = I t (i+k,j)*W c (k)

[0046] If value < i Min

[0047] Then value = i Min

[0048] If value < min value

[0049] min value =value(value);

[0050] I p (i+k, j)=min value .

[0051] Among them I t Indicates the original set point 10, I prepresents the filtered set point F(10), W c is the vector of filter weights for column “c”, and i min is the lower threshold to prevent the algorithm from eventually setting all intensities to 0. The value min value This makes it possible to retain the worst case of all the neighboring pixels, that is to say the neighboring pixels most affected by pixel X. In the example given, for a given pixel, 10 neighboring columns are adjusted by the algorithm, since the 10 columns are susceptible to the spatial distribution of the light emitted by this given pixel. It goes without saying that these data should be adjusted according to the application and to the characteristics of the light source / optical system considered, without departing from the scope of the invention.

[0052] Figure 3 A lighting device 20 according to a preferred embodiment of the invention is schematically shown. It comprises a digital lighting unit 100 having a matrix light source consisting of elementary light sources and an optical system. A data receiving unit 140 is capable of receiving lighting set points 10 in the form of a digital image via a data bus of a motor vehicle. Typically, the set points come from a central control module of the vehicle. The device comprises a microcontroller element 130, which is configured to adjust each received lighting set point 10 according to the method described above. The device further comprises a control unit 150 for controlling the lighting unit 100 according to the filtered lighting set point F(10). To this end, the duty cycle of the pulse width modulated control signal is preferably adjusted so as to reflect the filtered set point value F(10).

[0053] It goes without saying that the described embodiments do not limit the scope of protection of the invention. By referring to the description that has just been given, other embodiments can be envisaged without departing from the scope of the invention.

[0054] The scope of protection is defined by the claims.

Claims

1. A method for adjusting a digital lighting setpoint (10) intended to be projected by a digital lighting unit (100) of a motor vehicle, the digital lighting unit (100) comprising a matrix light source (110) and an optical system (120), characterized in that The method comprises the following steps: applying a digital filter (F) to the digital lighting set point (10) by means of a calculation unit (130) before transmitting the filtered digital set point (F(10)) to the digital lighting unit (100), the digital filter (F) anticipating geometric aberrations caused by the optical system (120) during projection (P(10)) of the digital set point, The digital filtering (F) comprises applying a dedicated digital filter for each column or each row of the basic light intensity set point (12), the dedicated digital filter anticipating geometric aberrations induced by the optical system (120) on the columns or rows of transmitted pixels forming part of a spatial neighborhood of the columns or rows of transmitted pixels corresponding to the columns or rows of the basic light intensity set point (12).

2. The method according to claim 1, characterized in that The digital lighting set point (10) comprises a basic light intensity set point (12) for each basic light source (112) of the matrix light source (110), and the digital filtering comprises selectively reducing the basic light intensity set point (12) according to a predetermined basic set point filter value.

3. The method according to claim 1 or 2, characterized in that: The digital filtering (F) comprises applying, for each basic light intensity set point (12), a dedicated digital filter which anticipates geometric aberrations induced by the optical system (120) on projected pixels forming part of a spatial neighborhood of the projected pixel (P(12)) corresponding to the basic light intensity set point (12).

4. The method according to claim 1 or 2, characterized in that: The digital lighting setpoint comprises a digital image having a resolution at least equal to a projection resolution of the lighting device.

5. The method according to claim 1 or 2, characterized in that: The method comprises the following preliminary steps for each elementary light source (112) of the matrix light source (110): i. determining the spatial light distribution of a pixel (P(12)) projected by the optical system (120) when the primary light source (112) is controlled to emit at maximum output; ii. determining by a computer a reduction factor or value of the maximum output such that the reduced emission output produces a spatial light distribution that illuminates pixels in a neighborhood of the projected pixel (P(12)) at most with a predetermined degree of brightness; iii. associating a reduction factor or value with the position of said elementary light source (112) in the matrix light source (110) and storing it in a memory element as an elementary set point filter value for a corresponding elementary light intensity set point (12).

6. The method according to claim 5, characterized in that The preparatory step is performed once for each row or column of elementary light sources.

7. A lighting device (20) for a motor vehicle, comprising a digital lighting unit (100), the digital lighting unit (100) having a matrix light source (110) consisting of elementary light sources (112) and an optical system (120), the lighting device (20) further comprising a data receiving unit (140) for receiving a digital lighting set point (10), characterized in that: The device comprises a computing unit (130) configured to adjust a received digital lighting set point (10) according to a method according to any one of claims 1 to 6, and the lighting device further comprises a control unit (150) for controlling the digital lighting unit (100) according to a filtered digital set point (F(10)).

8. A non-transitory computer-readable storage medium storing a computer program comprising a sequence of instructions which, when executed by a processor, cause the processor to implement the method according to any one of claims 1 to 6.

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