Illumination device comprising light source and optical reflector, and related electronic device

Abstract

The invention relates to a lighting device (1) comprising a light source (100) having a main lighting direction defining an optical axis (OA) and an optical reflector (200) comprising two sections, a first section (210) comprising a first wall (211) extending at least partially around the light source at a first height (H1) in the direction of the optical axis, the first wall converging in the direction of propagation of the light, and a second section (210) comprising a second wall (211) extending at least partially around the light source at a second height (H2) in the direction of the optical axis. The second section (220) comprises a second reflective wall (221) and extends in the continuation of the first wall in the direction of the optical axis by a second height (H2) in order to reflect the light from the light source, the second wall diverging in the direction of propagation of the light.

Description

Technical Field

[0001] The present invention relates to the field of imaging techniques, and more particularly to illuminating a scene observed by an image sensor.

[0002] The present invention particularly relates to an illumination device including a light source and an optical reflector.

[0003] The present invention also relates to an electronic device including an image acquisition unit and such an illumination device.

[0004] The present invention finds a particularly advantageous application in the illumination inside a motor vehicle, which is beneficial for a camera monitoring the driver. Background Art

[0005] Cameras for monitoring the driver inside a motor vehicle are being used more and more frequently, and are more widely known by their abbreviation DMS, which stands for Driver Monitoring System. In particular, in such cases, it is known to connect an image capture unit to an illumination device in order to maintain a sufficient light level independent of the ambient light level.

[0006] The images captured by these devices are then analyzed by image processing algorithms capable of extracting relevant information therefrom.

[0007] In order to improve the performance of image processing algorithms, the requirements for image quality are becoming increasingly strict. One of the parameters for improving the quality of the captured images is the uniformity of the scene illumination generated by the illumination device.

[0008] Traditionally, the light source of the illumination device consists of one or more infrared light-emitting diodes. LEDs typically have a Gaussian distribution. The use of such a light source results in non-uniform illumination inside the vehicle.

[0009] In order to improve the performance of current image processing algorithms, it is recommended that the illumination of the scene within the camera's field of view should not exceed a contrast of about 20%.

[0010] One solution for improving the uniformity of the light source illumination is to add optical components such as diffusers.

[0011] However, this solution results in a significant loss of light intensity, leading to a loss of efficiency of the illumination device and a reduction in the quality of the captured images.

[0012] Another solution is to use a reflector surrounding the light source, which is capable of reflecting the peripheral light from the light source located outside the field of view of the image acquisition device towards the area of interest inside the vehicle that does not fall within the field of view of the image acquisition device, so as to make the illumination more uniform.

[0013] Although this solution is effective, it results in other sources of image degradation due to the redirection of parasitic light, especially the light rays that leave the light source and have a large tilt angle until the image capture unit. Summary of the Invention

[0014] In this case, there is provided an illumination device including a light source and an optical reflector. The light source has a main illumination direction defining an optical axis, and the optical reflector includes two sections.

[0015] It is proposed here that the first section should include a first wall that at least partially surrounds the light source and extends in the direction of the optical axis at a first height, and the first wall converges in the direction of light propagation.

[0016] Due to its converging property, the first wall can avoid parasitic light from propagating into the illumination device. Specifically, light rays emitted at the base of the light source and having a very large tilt angle may be reflected (by specular reflection or diffuse reflection) in a direction opposite to the direction of light propagation.

[0017] The second section includes a second wall that is reflective and extends in the direction of the optical axis at a second height in the continuation of the first wall to reflect light rays from the light source. The second wall diverges in the direction of light propagation.

[0018] The second wall can reflect peripheral light from the light source towards an area of interest inside the vehicle, thereby producing uniform illumination.

[0019] According to one embodiment, the optical reflector includes a third section, and the third section includes a reflective third wall that extends in the direction of the optical axis at a third height in the continuation of the second wall of the second section.

[0020] In addition, the third wall of the third section may have a third tilt angle less than 5° with respect to the optical axis.

[0021] In one embodiment, each of the first wall and the second wall of the optical reflector includes at least a pair of two faces.

[0022] In addition, each of the first wall and the second wall includes two pairs of two faces, and the two faces positioned as a pair face each other, with one face on each side of the light source.

[0023] The faces of the section may be planar.

[0024] In one embodiment, the wall of the first section of the optical reflector is reflective.

[0025] Preferably, the light source is an LED that emits infrared rays, and the walls of the section are reflective in infrared rays.

[0026] The present invention also relates to an electronic device including an image acquisition unit and the illumination device as described above, and the illumination device is configured to illuminate the field of view of the image acquisition unit.

[0027] The various features, variations, and embodiments of the present invention can be related to each other through various combinations, provided that they are not mutually incompatible or mutually exclusive. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In addition, various other features of the present invention will become apparent from the accompanying description provided with reference to the drawings, which illustrate non-limiting embodiments of the present invention, in which:

[0029] Figure 1 is an analog of parasitic light within an electronic device known in the prior art;

[0030] Figure 2 is a functional cross-sectional schematic diagram of a lighting device according to an embodiment of the present invention;

[0031] Figure 3 is Figure 2 a perspective functional schematic diagram of the lighting device shown;

[0032] Figure 4 is a functional schematic diagram of an electronic device including Figure 2 the lighting device shown;

[0033] Figure 5 is a cross-sectional functional schematic diagram of a lighting device according to an embodiment different from Figure 2 ;

[0034] Figure 6 is an illumination simulation generated by a conventional light source;

[0035] Figure 7 is Figure 2 an illumination simulation generated by the lighting device shown; and

[0036] Figure 8 is a graph of the average illumination and maximum illumination corresponding to parasitic light entering a camera for Figure 4 an electronic device known in the prior art and Figure 1 an electronic device.

[0037] Note that in these figures, structural and / or functional elements common to various variations may have the same reference numerals. DETAILED DESCRIPTION

[0038] A conventional electronic device 500 in the prior art for monitoring a driver inside a vehicle, such as Figure 1 ​​​​​​​​As shown. It includes a conventional lighting device 520 known in the prior art and an image capture unit 510. The conventional lighting device 520 includes a light source 521 and a conventional optical reflector 522. In this case, the light source 521 is an infrared LED. The conventional optical reflector 522 is a frustum-shaped reflective wall that is continuous and surrounds the light source 521.

[0039] The image capture unit 510 includes a camera and is capable of capturing a scene illuminated by the conventional lighting device 520. The conventional electronic device 520 also includes a protective external lens 530. The protective external lens can be made of glass or plastic.

[0040] Figure 1 Depicts parasitic light rays. The parasitic light rays include light rays emitted by the light source 521 that reach the image capture unit 510 without illuminating the scene.

[0041] Most of the parasitic light rays are light rays that are reflected from the inside of the external lens 530 of the conventional electronic device 500 to reach the image capture unit 510 but cannot leave the conventional electronic device 500.

[0042] Simulation of these light rays shows that most of these parasitic light rays have a very large tilt angle when leaving the light source 521 and are reflected by the conventional optical reflector 522 at the part closest to the light source.

[0043] This part of the illumination contributes little to the illuminance of the scene. Therefore, compared with the loss of uniformity caused by additional illumination, the loss of uniformity caused by parasitic light rays is even more.

[0044] The cross-section of the lighting device 1 according to an embodiment proposed by the present invention is as Figure 2 shown. The device includes a light source 100 and an optical reflector 200. This same lighting device 1 is shown in Figure 3 a perspective view.

[0045] For example, the light source 100 can be an LED. The light source 100 defines an optical axis OA. The optical axis OA is the main illumination direction of the light source, that is, the direction with the maximum luminous intensity, for example. The reflector can be oriented such that its main axis coincides with the optical axis OA.

[0046] The optical reflector 200 here includes a first section 210, a second section 220, and a third section 230.

[0047] The first section 210 closest to the light source 100 includes a first wall 211. The first wall 211 includes four faces that surround the light source 100 and face each other in pairs.

[0048] The faces in this example are planar. They can be trapezoidal.

[0049] The surfaces are inclined in such a way that the surface defined by the first section 210 (in a section perpendicular to the optical axis OA) decreases in the direction of propagation of light. In other words, these surfaces converge towards the optical axis in the direction of propagation of light. These surfaces may be symmetric with respect to the optical axis OA.

[0050] The first inclination angle THETA1 is defined as the inclination angle of the surface of the first section 210 with respect to the optical axis OA.

[0051] The surfaces in this case are reflective. Thus, light rays emitted from the light source 100 at a very large inclination angle, for example the light rays that generate parasitic light in the example of Figure 1 will be reflected in a direction opposite to the direction of light propagation towards the light source 100 itself. For example, the reflection in this case is specular reflection.

[0052] Therefore, when used together with the image acquisition device described below with reference to Figure 4 no parasitic light will be emitted from the lighting device 1 and thus will not propagate to the image acquisition device.

[0053] The surfaces are reflective at least in the wavelength range emitted by the light source 100 and / or in the wavelength range of the image capture unit. In this case, these surfaces are reflective at least in the infrared.

[0054] Light rays with a very large inclination angle are defined as light rays that form an angle of ALPHA1 to 90° with the optical axis. The angle ALPHA1 is the angle between the optical axis OA and the light ray that is not reflected by the first section 210 and is the farthest from the optical axis OA.

[0055] In another embodiment, the light reflected from the first section is diffuse reflection.

[0056] Alternatively, these surfaces may be absorptive in the wavelength range emitted by the light source 100. In this case, the light rays are absorbed and do not propagate to the image capture unit.

[0057] The second section 220 extends continuously with the first section 210. The second section 220 includes a second wall 221. The second wall 221 includes four reflective surfaces, each of which extends continuously with the corresponding surface of the first section 210. These surfaces are arranged in two pairs. In each pair, the surfaces are positioned facing each other.

[0058] The surfaces in this case are planar. They may be trapezoidal.

[0059] Different from the first section 210, the surfaces are inclined in such a way that the surface defined by the second section 220 (in a section orthogonal to the optical axis OA) increases in the direction of propagation of light. In other words, these surfaces diverge from the optical axis in the direction of propagation of light.

[0060] The second tilt angle THETA2 is defined as the tilt angle of the face of the second section 220 with respect to the optical axis OA. The first tilt angle THETA1 and the second tilt angle THETA2 have opposite signs.

[0061] The second section 220 reflects some of the light rays originating from the light source 100 and forms an angle with the optical axis that is included between ALPHA1 and ALPHA2. The angle ALPHA2 is defined as the angle between the optical axis OA and the light ray that is farthest from the optical axis OA and not reflected by the second section.

[0062] The third section 230 extends continuously with the second section 220. The third section 230 includes a third wall 231. The third wall 231 of the third section 230 includes four faces, each of which extends continuously with the corresponding face of the second section 220. These faces are arranged in two pairs. In each pair, the faces are positioned to face each other.

[0063] The faces in this case are planar. They can be trapezoidal.

[0064] The third tilt angle is defined as the tilt angle of the face of the third section 230 with respect to the optical axis OA.

[0065] The third section 230 reflects some of the light rays originating from the light source 100 and forms an angle with the optical axis that is included between ALPHA2 and ALPHA3. The angle ALPHA3 is defined as the angle between the optical axis OA and the light ray that is farthest from the optical axis OA and not reflected by the third section 230.

[0066] For example, for a light source that emits an emission light cone at an angle of 50° to 80° with respect to the optical axis, the angle ALPHA1 can be included between 55° and 65°, and / or the angle ALPHA2 can be included between 32° and 48°, and / or the angle ALPHA3 can be included between 25° and 40°.

[0067] In this case, the surfaces of the second section 220 and / or the third section 230 are reflective in the infrared.

[0068] The second section 220 and the third section 230 make it possible to produce more uniform illumination by reflecting the light rays with the maximum tilt angle that are not located within the field of view of the image capture unit towards the region of interest lacking sufficient illumination within the field of view of the image capture unit.

[0069] For example, in the case of a Gaussian light source 100, i.e., the LED used here, the outermost light rays are reflected towards the peripheral region of the central illumination spike or the edge of the field of view of the image capture unit.

[0070] In Figure 2Several rays from the light source 100 can be seen. The rays shown as solid lines have an inclination angle smaller than ALPHA3 and are not reflected. The rays shown as dashed lines are reflected by the second section 220. The reflected rays shown as dashed lines are reflected by the third section 230. The rays shown as dashed and dash-dotted lines can thus compensate for the Gaussian distribution of the LED by returning some light flux to the edges of the field of view.

[0071] In addition, the optical reflector 200 can be produced using standard industrial processes such as injection molding and then applying a reflective coating by physical vapor deposition (PVD) or galvanized deposition.

[0072] Figure 4 An electronic device 2 according to an embodiment of the present invention is depicted. The electronic device 2 includes Figure 2 and Figure 3 the lighting device 1, which has been described above. It also includes an image capture unit 20 and a control unit 30 coupled to the lighting device 1 and the image capture unit 20. The electronic device 2 can be placed in a motor vehicle, for example, to form a driver monitoring system.

[0073] The image capture unit 20 can capture an image of the environment it faces, which in this case is part of the interior of a motor vehicle. For example, the field of view of the image capture unit 20 is directed towards the normal position of the driver. The image capture unit 20 can be a camera and capture the entire scene illuminated by the lighting device 1. The control unit 30 is configured to analyze the captured image.

[0074] The control unit can be designed to determine, by analyzing the captured image, the degree of unfitness for driving (such as the degree of distraction or drowsiness) when the driver is in the normal driving position.

[0075] To avoid discomfort to the people near the electronic device and to make the image capture process the same during the day and at night, the light source 100 can operate in the infrared because infrared light is invisible to the human eye. The image capture unit 20 operates at least in the same wavelength range as the light source 100. In this case, the image capture unit 20 operates only in the infrared. As an alternative, the image capture unit can operate in the infrared and visible light.

[0076] To improve the performance of the process of analyzing the captured image, the lighting uniformity is preferably such that the lighting contrast is less than 20%. This means that two points in the field of view of the image capture unit 20 must receive a lighting difference of less than 20%.

[0077] To achieve this, the inclination angles and surface heights of the sections have been calculated by numerical simulation.

[0078] The first section 210 is included between 1 and 1.5 mm along the optical axis at a first height H1. In this case, the first height H1 is 1.3 mm. The absolute value of the first tilt angle THETA1 of the first section 210 with respect to the optical axis (OA) is included between 8° and 15°. In this example, the absolute value of the first tilt angle is 10°.

[0079] The second section 220 is included between 2 and 5 mm along the optical axis at a second height H2. In this case, the second height H2 is 3 mm. The absolute value of the second tilt angle THETA2 of the second section 220 with respect to the optical axis (OA) is included between 8 and 15°. In this example, the absolute value of the second tilt angle is 10°.

[0080] The third section 230 is included between 0.8 and 1.5 mm along the optical axis at a third height H3. In this case, the third height H3 is 1 mm. The absolute value of the third tilt angle of the third section 230 with respect to the optical axis (OA) is less than 5°. In this example, the absolute value of the third tilt angle is 1°.

[0081] In order to obtain better light source uniformity results, the inclination of the surface of the third section 230 can be zero. However, in order to make the generally molded optical reflector 200 easier to manufacture, it is preferred that the surface of the third section 230 is slightly inclined.

[0082] These values depend on the construction of the light source 100 and the image acquisition device 20. They are given here in a non - limiting manner.

[0083] In this case, the electronic device 2 includes a housing 40 and a removable cover 42. The housing 40 mechanically holds the various components relative to each other. The removable cover 42 provides easy access to the interior of the electronic device 2.

[0084] The electronic device 2 further includes a printed circuit 50, on which the light source 100 and the control unit 30 are mounted. In this case, the optical reflector 200 is attached using a fixing clip 41.

[0085] As a variant, the lighting device 1 can be directly attached to the printed circuit 50 completely.

[0086] Figure 5 The lighting device 1 according to another embodiment of the present invention is depicted. In this case, the lighting device 1 includes a light source 100 and an optical reflector 200. The light source 100 can be a light source with Gaussian illumination, such as an LED. In this case, the optical reflector 200 includes two sections.

[0087] The first section 210 has a converging surface and limits the propagation of parasitic light. The second section 220 has a diverging surface and makes the illumination more uniform in the same manner as described above.

[0088] Figure 6 Depicts a simulation 110 of the illumination produced by the light source 100 used in the illumination device 1. A Gaussian distribution of light can be seen.

[0089] Figure 7 Depicts the Figure 2 second simulation 120 of the illumination produced by the illumination device 1. Due to the optical reflector 200, the peripheral light rays fold back around the light spike, thus producing a uniform illumination over a wider field of view.

[0090] Figure 7 Depicts the area 300 (commonly referred to as the "headbox") corresponding to the possible position of the driver's head. It can be seen that the simulated illumination here is uniform over a field of view wide enough to fully illuminate the aforementioned area 300.

[0091] Figure 8 Shown is Figure 4 the electronic device (Inv. DMS) and the Figure 1 conventional electronic device (Std. DMS) equipped with a conventional illumination device, a percentage comparison curve of the average illumination (Avg. Irrad) and the maximum illumination (Max. Irrad) caused by parasitic light with respect to the standard value entering the camera.

[0092] It can be seen that there is less parasitic light when using Figure 1 the electronic device defined in Figure 4 compared to using a conventional electronic device including a conventional illumination device.

Claims

1. A lighting device (1) comprising a light source (100) and an optical reflector (200), the light source (100) having a main illumination direction defining an optical axis (OA), the optical reflector (200) comprising two sections, a first section (210) comprising a first wall (211) that at least partially surrounds the light source (100) and extends in the direction of the optical axis (OA) at a first height (H1), the first wall (211) converging in the light propagation direction, and a second section (220) comprising a second wall (221) that is reflective and extends in the direction of the optical axis (OA) at a second height (H2) in a continuation of the first wall (211) so as to reflect light rays from the light source, the second wall (221) diverging in the light propagation direction.

2. The lighting device (1) according to claim 1, wherein, The optical reflector (200) includes a third section (230), the third section including a reflective third wall (231) that extends in the direction of the optical axis at a third height (H3) in a continuation of the second wall of the second section.

3. The lighting device (1) according to claim 2, wherein, The third wall (231) of the third section (230) has a third tilt angle of less than 5° relative to the optical axis.

4. The lighting device (1) according to any one of claims 1 to 3, wherein, Each of the first wall (211) and the second wall (221) of the optical reflector (200) includes at least a pair of two faces.

5. The lighting device (1) according to claim 4, wherein, Each of the first wall (211) and the second wall (221) includes two pairs of two faces, the two pairs of two faces being positioned such that the two faces of a pair face each other, with one face on each side of the light source (100).

6. The lighting device (1) according to any one of claims 4 or 5, wherein, The faces are planar.

7. The lighting device (1) according to any one of claims 1 to 6, wherein, The first wall (211) of the first section (210) of the optical reflector (200) is reflective.

8. The lighting device (1) according to any one of claims 1 to 7, wherein, The light source (100) is an LED that emits infrared rays, and wherein the walls (211, 221) of the sections (210, 220) are reflective in infrared rays.

9. An electronic device (2) comprising an image capture unit (20) and a lighting device (1) according to any one of the preceding claims, the lighting device being configured to illuminate the field of view of the image capture unit (20).

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