Method for adjusting setpoint values for a digital lighting unit of a motor vehicle

Description

[0001] The invention relates to lighting modules for motor vehicles. In particular, the invention relates to control methods for such modules involving matrix light sources.

[0002] A light-emitting diode, LED, is a semiconductor electronic component capable of emitting light when passed through it by an electric current having at least a threshold intensity. In the automotive field, LED technology is increasingly used for various light signaling solutions. LED matrices are particularly interesting in the field of automotive lighting. Matrix light sources can be used for "leveling" type functions, i.e., adjustment of the height of the emitted light beam, depending on the vehicle's attitude and the road profile.Other applications include DBL ("Digital Bending Light"), which corresponds to the adjustment of the direction of the emitted light beam, to follow the road in the horizontal plane, ADB ("Adaptive Driving Beam"), which corresponds to an anti-glare function that generates shadow zones in the light beam emitted by a main beam headlight so as not to disturb other road users, but also functions for projecting patterns on the ground using the pixelated light beam. The contours of the shadow zones must be well defined and reproducible by a lighting device in order to comply with current regulations.

[0003] It is known to use light sources of different types of technologies for the lighting applications mentioned. This is for example the monolithic technology, according to which a large plurality of elementary sources of LED type, equivalent to pixels, are etched in a common semiconductor substrate. Integrated electrical connections make it possible to activate the pixels independently of each other. Another known technology is that of microLEDs, which generates a matrix of LEDs of small dimensions, typically less than 150µm. There are also micro-mirror type modules, DMD (Digital Micro-Mirror Device), which involve a projection technology using an intensity modulator on a uniform beam.Micro-mirrors, whose position is controlled by means of piezoelectric elements, are oriented so as to selectively reflect an incident light beam, so that each micro-mirror corresponds to an elementary source of the pixel matrix thus generated. The light from a source is directed onto the micro-mirror matrix by an optic.

[0004] The light emitted by a matrix light source passes through an optic comprising at least one optical lens, 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 homogeneous. Typically a central zone is capable of projecting at a high resolution, while the resolution progressively decreases at the edges of the field of view of the light source, which can have a significant aperture of the order of 35°. Projecting precise contours in areas of lower resolution (i.e. at the edges of the field of view) is therefore difficult or even impossible using known solutions. The result of projecting a precise contour or pattern in such an area is generally a blurred or distorted contour or pattern.

[0005] The invention aims to overcome at least one of the problems posed by the prior art. In particular, the invention aims to propose a method which can increase the precision of projected patterns or contours using a matrix light source and an associated optical system, without having to resort to a more complex or expensive optical system.

[0006] According to a first aspect of the invention, a method for adapting 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 remarkable in that it comprises a step of applying, by means of a calculation unit, digital filtering to the digital setpoint before relaying the filtered digital setpoint to the lighting unit. The digital filtering anticipates geometric aberrations induced by said optical system during the projection of a digital setpoint.

[0007] Preferably, the digital lighting setpoint may comprise an elementary light intensity setpoint for each elementary light source of the matrix light source. The digital filtering may preferably comprise a selective reduction of the elementary light intensity setspoints according to predetermined elementary setpoint filtering values.

[0008] Said filtering comprises the application of a dedicated digital filter for each of the elementary light instructions, said dedicated digital filter anticipating the geometric aberrations induced by said optical system on the projected pixels which are part of a spatial neighborhood of the projected pixel corresponding to said elementary light instruction.

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

[0010] Preferably, said filtering may comprise the application of a dedicated digital filter for each column or line of elementary light instructions, said dedicated digital filter anticipating the geometric aberrations induced by said optical system on the projected columns or lines of pixels which are part of the spatial neighborhood of the projected column or line of pixels corresponding to said column or line of elementary light instructions.

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

[0012] Preferably, the method may comprise the prior steps for each elementary light source of the matrix light source: i) determining the spatial light distribution of the projected pixel through the optical system when the elementary light source is commanded to emit at maximum output; ii) determining, by means of a calculator, a factor or a reduction value of the maximum output such that the reduced emission output produces a spatial light distribution which illuminates the pixels in the vicinity of the projected pixel at maximum at a predetermined brightness level; iii) associating the factor or the reduction value with the position of said light source in the matrix light source, and recording it in a memory element as an elementary setpoint filter value for a corresponding elementary setpoint.

[0013] Preliminary steps i)-iii) can preferably be carried out once for each row or column of elementary light sources.

[0014] According to another aspect of the invention, a lighting device for a motor vehicle is provided. The lighting device comprises a digital lighting unit having a matrix light source composed of elementary light sources and an optical system. The device further comprises a data receiving unit for receiving a lighting setpoint. The lighting device is remarkable in that it comprises a calculation unit configured to adapt a lighting setpoint received in accordance with a method according to one aspect of the invention. The lighting device further comprises a control unit for controlling the lighting unit in accordance with the filtered lighting setpoint.

[0015] Preferably, the control unit and / or the computing unit may comprise a microcontroller element or a data processor programmed by means of a computer program suitable for carrying out said method.

[0016] The arrangement of the optical system may preferably be such that the light emitted by the elementary light sources of the lighting unit passes through it. The optical system may preferably comprise at least one optical lens

[0017] The data receiving unit may preferably comprise a network interface capable of receiving / sending data on a data bus internal to the motor vehicle. For example, the bus may be a "Controller Area Network" type bus, CAN, Ethernet, a Gigabit Multimedia Serial Link, GMSL, or a Low Voltage Differential Signaling, LVDS, technology bus, such as an FPD-Link III bus.

[0018] The matrix light source may preferably comprise a monolithic source, comprising elementary electroluminescent light sources with semiconductor elements etched in a common substrate and activatable independently of each other.

[0019] The matrix light source may preferably comprise a micro LED type matrix, comprising a matrix of elementary sources produced by light-emitting diodes, LEDs, of small dimensions, typically less than 150 µm.

[0020] The matrix light source may preferably comprise a micro-mirror device, DMD, ("Digital Micromirror Device"), in which an elementary source comprises a micro-mirror of a matrix, which selectively reflects an incident light beam depending on its position.

[0021] According to yet another aspect of the invention, a computer program comprising a sequence of instructions is provided, which, when executed by a processor, cause the processor to implement a method according to one aspect of the invention.

[0022] According to another aspect of the invention, a non-transitory computer-readable storage medium is provided, said medium storing a computer program according to the preceding aspect of the invention.

[0023] By using the aspects according to the invention, it becomes possible to preemptively anticipate geometric aberrations induced in an image projected by an optical system (such as distortions or blurring). This is achieved using a digital process, preferably implemented by computer software. The solution therefore does not require the use of more expensive optics which would generate less distortion. This approach makes it possible to keep the production cost of the proposed lighting device relatively stable, while significantly improving its optical behavior. This improvement is all the more useful when the lighting device performs an "Adaptive Driving Beam" (ADB) type function, which requires the projection of precise contours and patterns, while requiring less brightness.

[0024] Other features and advantages of the present invention will be better understood with the aid of the description of the examples and the drawings among which: there Fig. 1 is an illustration of a method in accordance with a preferred embodiment of the invention; Fig. 2 is an illustration of the spatial light distribution of a pixel projected by a lighting unit in accordance with a preferred embodiment of the invention; Fig. 3 is a schematic illustration of a lighting device in accordance with a preferred embodiment of the invention.

[0025] Unless specifically indicated otherwise, 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 in a non-limiting manner.

[0026] The description focuses on the elements of a lighting module for a motor vehicle that are necessary for understanding the invention. Other elements, which are known to be part of such modules, will not be mentioned or described in detail. For example, the presence and operation of a converter circuit involved in the power supply of a matrix light source, known per se, will not be described in detail.

[0027] A matrix light source can generate a large number of elementary light sources, for example several thousand electroluminescent light sources with a semiconductor element, of the LED type. 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 typically associated with such a matrix light source. Typically, the central part of a projected image has a high resolution, while the regions at the edge of the image have a degraded resolution. It has been observed that in a high-definition central zone (corresponding to approximately -11° to 11° of aperture), the light emitted by an elementary source produces a projected pixel, and also contributes to the brightness of approximately two neighboring pixels.The light emitted by an elementary source in an average area (corresponding to about + / - 11 to 14) produces one projected pixel, and also contributes to the brightness of about four neighboring pixels. In a low-resolution border area, the light emitted from a single elementary source produces one projected pixel, and at the same time contributes to the brightness of about eight pixels in its vicinity. The spatial distribution of the light emitted by an elementary source of the matrix light source is therefore not homogeneous for all the elementary sources that compose the matrix light source, but it depends on the location of the elementary source relative to the optical system, even if the characteristics of the elementary sources are otherwise equivalent.It has also been observed that the spatial distribution of the light emitted by an elementary light source depends on its operating efficiency: at 100% efficiency (always on), the light produced is likely to contribute to the illumination of a greater number of neighboring pixels than at a lower efficiency. A blurring effect of the projected light beam or geometric aberration induced by the optical system can therefore be at least partially counteracted by reducing the light intensity of an elementary light source. The efficiency of a light-emitting diode type light source can, in a known manner, be influenced by controlling its power supply using a pulse width modulation (PWM) signal, which is characterized by a duty cycle representative of the desired efficiency.The invention uses his observations to implement a method that limits the optical aberrations generated by the lighting unit.

[0028] The illustration of the figure 1 shows the provision of a digital lighting setpoint 10 intended to be projected by a digital lighting unit 100. The digital setpoint comprises for example an image of which each pixel 12 comprises a light intensity value, which must ideally 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 micro-mirror device or other matrix light sources known in the art. The digital lighting unit 100 also comprises an optical system comprising at least one optical lens 120, arranged downstream of the matrix light source, following the direction of the emitted light.A computing unit 130, such as a processor or a microcontroller element programmed for this purpose, applies a digital filtering F to the original digital setpoint 10, thus producing a filtered digital setpoint F(10). The latter is relayed to the lighting unit and finally projected using 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 induced by the optical system 120. It should be noted that a projected pixel P(12) corresponds to a spatial distribution of light, having a maximum intensity at the center and a decreasing bell-shaped shape in its vicinity. The filter F depends on the distribution generated for each elementary light source 112 by the optical system 120.

[0029] According to a preferred embodiment of the invention, the value of each pixel 12 of the original setpoint 10 is adapted by the calculation unit 130 according to a predetermined reduction factor or value forming part of the data of the filter F. Each of these elementary setpoint filtering values ​​is chosen so as to limit the impact of the spatial distribution of light emitted for a given pixel P(12) on its neighboring pixels. According to a preferred embodiment, the horizontal behavior of a matrix source is almost homogeneous. In such a case, an elementary setpoint filtering value is chosen for each column of the original setpoint 10, thus limiting the calculation needs of the calculation unit 130.

[0030] There figure 2 shows how the elementary setpoint filtering values ​​are obtained according to a preferred embodiment, without the invention being limited to this example. The vertical axis shows pixel references or equivalently elementary light source / column references. The horizontal axis shows a percentage of brightness relative to a maximum normalization intensity. Here, the pixel with index X is considered. When the light source X operates at a duty cycle of 100%, the area under the “PWM 100%” curve represents the entirety of the emitted light, while the shape of the curve shows the spatial distribution of this emission.The values ​​shown for the neighboring pixels / columns X+1 (12%), X+2 (4%), X+3 (0%, enhanced to a minimum of 1% shown in dotted lines) represent predetermined brightness threshold values ​​that the spatial light distribution of pixel X must meet to ensure a projection with reduced geometric aberrations. These values ​​can be determined either empirically by precise measurements or by computer simulation methods. They depend on the matrix light source used, the characteristics of the elementary light sources, as well as the optical system used.

[0031] It becomes apparent that a brightness setting equivalent to 100% for the elementary light source of index X implies excessively high brightness levels for all neighboring pixels. In order to fully comply with the imposed constraints, an efficiency of 50% must be applied to the pixel of index X, if the original setting indicates 100%. The corresponding weight of 0.5 is stored in a memory element as an elementary setting filter value for each setting of index X. The filter values ​​can be refined for other intensities of the pixel of index X. This process is performed once, for all elementary light sources, or for all columns of elementary sources. The process produces the filter values ​​F for the lighting unit in question.It should be noted that the elementary setpoint filtering values ​​are not homogeneous for all elementary light sources, since their location relative to the optical system 120 has a major impact on the light distribution they produce.

[0032] Once all these elementary setpoint filtering weights or values ​​have been identified, the filter application step is preferably implemented by the following algorithm: for all pixels i, j of the original setpoint:

[0033] In which I t represents the original setpoint 10, I p represents the filtered instruction F(10), W c is the vector of filter weights of column "c", and i min is a lower threshold value that prevents the algorithm from ending up setting all intensities to 0. The value min value allows to retain the worst case among all the neighboring pixels, that is to say the neighboring pixel most impacted by pixel X. In the example given, for a given pixel, 10 neighboring columns are adapted by the algorithm, since 10 columns are likely to be impacted by the spatial distribution of the light emitted by this given pixel. It goes without saying that these data are to be adapted according to the application and the characteristics of the light sources / optical systems considered, without departing from the scope of the present invention.

[0034] There figure 3schematically shows a lighting device 20 according to a preferred embodiment of the invention. It comprises a digital lighting unit 100 having a matrix light source composed of elementary light sources as well as an optical system. A data reception unit 140 is capable of receiving a lighting instruction 10, in the form of a digital image on a data bus of a motor vehicle. Typically the instruction comes from a central control module of the vehicle. The device comprises a microcontroller element 130 configured to adapt each received lighting instruction 10 in accordance with the method which has just been described. The device further comprises a control unit 150 intended to control the lighting unit 100 in accordance with the filtered lighting instruction F(10).To do this, the duty cycle of a pulse width modulated control signal is preferably adapted to reflect the filtered setpoint values ​​F(10).

[0035] It goes without saying that the embodiments described do not limit the scope of protection of the invention. By using the description just given, other embodiments are conceivable without departing from the scope of the present invention.

[0036] The scope of protection is determined by the claims.

Claims

1. A method for adapting a digital lighting setpoint (10) intended to be projected by a digital lighting unit (100) of a motor vehicle, comprising a matrix light source (110) and an optical system (120), characterized in that the method comprises a step of applying, by way of a computing unit (130), digital filtering (F) to the digital setpoint (10) before relaying the filtered digital setpoint (F(10)) to the lighting unit (100), said digital filtering (F) anticipating geometric aberrations induced by said optical system (120) during the projection P(10) of a digital setpoint, characterized in that the said filtering (F) comprises applying a dedicated digital filter for each of the elementary light setpoints (12), said dedicated digital filter anticipating the geometric aberrations induced by said optical system (120) on the projected pixels that form part of a spatial neighborhood of the projected pixel P(12) corresponding to said elementary light setpoint (12).

2. The method as claimed in claim 1, characterized in that the digital lighting setpoint (10) comprises an elementary light intensity setpoint (12) for each elementary light source (112) of the matrix light source (110), and in that the digital filtering comprises selectively reducing the elementary light intensity setpoints (12) in accordance with predetermined elementary setpoint filtering values (F).

3. The method according to one of claims 1 or 2, characterized in that said filtering (F) comprises applying a dedicated digital filter for each column or row of elementary light setpoints (12), said dedicated digital filter anticipating the geometric aberrations induced by said optical system (120) on the projected columns or rows of pixels that form part of the spatial neighborhood of the projected column or row of pixels corresponding to said column or row of elementary light setpoints.

4. The method as claimed in one of claims 1 to 3, characterized in that the lighting setpoint comprises a digital image having a resolution at least equal to the projection resolution of the lighting device.

5. The method as claimed in one of claims 1 to 4, characterized in that it comprises the following preliminary steps for each elementary light source (112) of the matrix light source (110): i. determining the spatial light distribution P(12) of the pixel projected through the optical system (120) when the elementary light source (112) is controlled so as to emit at a maximum output; ii. determining, by way of a computer, a reduction factor or value of the maximum output, such that the reduced emission output produces a spatial light distribution that illuminates the pixels in the neighborhood of the projected pixel P(12) at most to a predetermined degree of brightness; iii) associating the reduction factor or value with the position of said light source (112) in the matrix light source (110), and storing it in a memory element as elementary setpoint filtering value (F) for a corresponding elementary setpoint (12).

6. The method as claimed in claim 5, characterized in that the preliminary steps are 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) having a matrix light source (110) composed of elementary light sources (112) as well as an optical system (120), the device (20) furthermore comprising a data reception unit (140) intended to receive a lighting setpoint (10), characterized in that the device comprises a computing unit (130) configured so as to adapt a received lighting setpoint (10) in accordance with the method as claimed in one of claims 1 to 6, the lighting device furthermore comprising a control unit (150) intended to control the lighting unit (100) in accordance with the filtered lighting setpoint F(10).

8. A computer program comprising a sequence of instructions which, when they are executed by a processor, result in the processor implementing a method as claimed in one of claims 1 to 6.

9. A non-transitory computer-readable storage medium, said medium storing a computer program as claimed in claim 8.