Illumination device comprising a light source and an optical reflector, and associated electronic device

Abstract

An illumination device (1) is proposed, comprising a light source (100) and an optical reflector (200). The light source has a principal direction of illumination defining an optical axis (OA). The optical reflector comprises two sections. The first section (210) has a first wall (211) extending at least partially around the light source to a first height (H1) in the direction of the optical axis. This first wall is convergent in the direction of light propagation. The second section (220) has a second reflective wall (221) extending from the first wall to a second height (H2) in the direction of the optical axis so as to reflect light rays from the light source. This second wall is divergent in the direction of light propagation. An electronic device comprising such an illumination device is also described. Figure 2 (for the abstract)

Description

Title of the invention: Illumination device comprising a light source and an optical reflector, and associated electronic device technical field

[0001] The present invention relates to the technical field of imaging, and in particular to the illumination of a scene observed by an image sensor.

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

[0003] It also relates to an electronic device comprising an image capture unit and such an illumination device.

[0004] The invention finds a particularly advantageous application in the illumination of the passenger compartment of a motor vehicle for driver surveillance cameras. Technological background

[0005] Driver monitoring cameras (known as DMS, for "Driver Monitoring System") are being used more and more frequently in the passenger compartment of motor vehicles. In this context, it is known to couple an image capture unit to an illumination device in order to maintain sufficient brightness regardless of ambient light.

[0006] The images captured by these devices are then analyzed by image processing algorithms to extract the relevant information.

[0007] In order to improve the performance of image processing algorithms, the requirements for image quality are becoming increasingly stringent. One of the parameters that can improve the quality of captured images is the uniformity of the scene illumination produced by the lighting device.

[0008] Conventionally, the light sources of illumination devices consist of one or more LEDs operating in the infrared range. LEDs generally have a Gaussian profile. The use of such light sources results in non-uniform illumination of the vehicle's interior.

[0009] To increase the performance of current image processing algorithms, it is recommended that the scene illumination not exceed a contrast of about 20% over the camera's field of view.

[0010] One solution for standardizing the illumination of a light source is to add an optical component such as a diffuser.

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

[0012] Another solution is to use a reflector surrounding the light source and allowing the peripheral rays of the source and out of the field of view of the image capture unit to be reflected towards an area of ​​interest in the vehicle's interior within the field of view of the image capture unit in such a way as to uniform the illumination.

[0013] This solution, although effective, leads to other sources of image degradation by redirecting stray light, in particular rays that are very inclined at the exit of the light source, to the image capture unit. Summary of the invention

[0014] In this context, an illumination device is provided comprising a light source and an optical reflector, the light source having a principal direction of illumination defining an optical axis and the optical reflector comprising two sections.

[0015] It is proposed here that the first section comprises a first wall extending at least partly around the light source over a first height in the direction of the optical axis, the first wall being convergent in the direction of propagation of the light.

[0016] This first wall, by its convergence, prevents the propagation of stray light in the illumination device. Indeed, the rays emitted at the base of the light source, being highly inclined, can be reflected (specular or diffuse reflection) in the opposite direction to the propagation of the light.

[0017] The second section comprises a second reflective wall extending from the first wall to a second height in the direction of the optical axis so as to reflect light rays emanating from the light source. The second wall diverges in the direction of light propagation.

[0018] The second wall makes it possible to reflect the peripheral light from the light source towards an area of ​​interest in the passenger compartment of the vehicle and thus to create a uniform illumination.

[0019] According to one embodiment, the optical reflector comprises a third section having a third reflective wall which extends over a third height in the direction of the optical axis, in the continuation of the second wall of the second section.

[0020] Furthermore, the third wall of the third section may have a third angle of inclination relative to the optical axis of less than 5°.

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

[0022] In addition, the first wall and the second wall each comprise two pairs of two faces positioned such that the two faces of a pair are opposite each other, on each side of the light source.

[0023] The faces of the sections can be flat.

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

[0025] Preferably, the light source is an LED emitting in the infrared, and the walls of the sections are reflective in the infrared.

[0026] The invention also relates to an electronic device comprising an image capture unit and an illumination device as described above configured to illuminate the field of view of the image capture unit.

[0027] The different features, variants and embodiments of the invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive. Brief description of the figures

[0028] In addition, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0029] [Fig.1] is a simulation of stray light within an electronic device as known from the prior art.

[0030] [Fig.2] is a schematic cross-sectional representation of the illumination device according to one embodiment of the invention,

[0031] [Fig.3] is a schematic perspective representation of the illumination device of the [Fig.2],

[0032] [Fig.4] is a schematic representation of an electronic device comprising the lighting device of the [Fig.2],

[0033] [Fig.5] is a schematic cross-sectional representation of the illumination device according to a different embodiment than that of [Fig.2],

[0034] [Fig.6] is a simulation of the illumination generated by a light source classic,

[0035] [Fig.7] is a simulation of the illumination generated by the illumination device of the [Fig.2], and

[0036] [Fig.8] is a graph representing the average and maximum illumination corresponding to the stray light entering the camera for the electronic device of [Fig.4] and for the electronic device of [Fig.1] as known from the prior art.

[0037] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references. Detailed description

[0038] A conventional electronic driver monitoring device 500 in the passenger compartment of a vehicle, as known in the prior art, is shown in [Fig. 1]. It comprises a conventional illumination device 520, as known in the prior art, and an image capture unit 510. The conventional illumination device 520 comprises a light source 521 and a conventional optical reflector 522. Here, the light source 521 is an infrared LED. The conventional optical reflector 522 is a continuous frustoconical reflective wall surrounding the light source 521.

[0039] The image capture unit 510 includes a camera and allows the capture of a scene illuminated by the conventional illumination device 520. The conventional electronic device 520 also includes a protective window 530. This protective window can be made of glass or plastic.

[0040] In [Fig. 1], stray light rays are shown. Stray light rays include light rays that are emitted by the light source 521 and reach the image capture unit 510 without having illuminated the scene.

[0041] The majority of the stray light rays are rays which are reflected inside the window 530 of the conventional electronic device 500 to the image capture unit 510, without being able to exit the conventional electronic device 500.

[0042] The simulation of these rays shows that a large majority of these parasitic light rays are very inclined rays at the exit of the light source 521 and are reflected by the conventional optical reflector 522 in its portion closest to the light source.

[0043] This part of the illumination contributes little to the illumination of the scene, and therefore generates more loss of uniformity via stray rays than contribution to illumination.

[0044] In [Fig.2], an illumination device 1 according to an embodiment proposed by the invention is shown in cross-section. It comprises a light source 100 and an optical reflector 200. This same illumination device 1 is shown in perspective in [Fig.3].

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

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

[0047] The first section 210, closest to the light source 100, comprises a first wall 211. The first wall 211 comprises four faces surrounding the light source 100 and facing each other in pairs.

[0048] The faces are flat here. They can be trapezoidal in shape.

[0049] The faces are inclined so that the surface defined by the first segment 210 (in section orthogonal to the optical axis OA) decreases in the direction of light propagation. In other words, the faces converge towards the optical axis in the direction of light propagation. The faces can be symmetrical with respect to the optical axis OA.

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

[0051] The faces are reflective here. In this way, highly inclined rays from the light source 100, such as those creating stray light in the example of [Fig. 1], will be reflected in the opposite direction to the propagation of the light, towards the light source 100 itself. For example, the reflection is specular here.

[0052] Thus, when used with an image capture unit, as described below with reference to [Fig.4], the stray light will not exit the illumination device 1 and will therefore not propagate to the image capture unit.

[0053] The faces 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. Here, the faces are reflective at least in the infrared.

[0054] Highly inclined rays are defined as rays forming an angle with the optical axis between an angle ALPHA1 and 90°. The angle ALPHA1 is the angle between the optical axis OA and the ray furthest from the optical axis OA not reflected by the first segment 210.

[0055] In another embodiment, the reflection of light on the first section is a diffuse reflection.

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

[0057] The second section 220 extends in continuity with the first section 210. The second section 220 comprises a second wall 221. The second wall 221 comprises four reflective faces, each extending in continuity with a corresponding face of the first section 210. The faces are arranged in two pairs. In each pair, the faces are positioned opposite each other.

[0058] The faces are flat here. They can be trapezoidal in shape.

[0059] Unlike the first section 210, the faces are inclined so that the surface defined by the second section 220 (in cross-section orthogonal to the optical axis OA) increases in the direction of light propagation. In other words, the faces diverge from the optical axis in the direction of light propagation.

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

[0061] This second section 220 reflects a portion of the rays from the light source 100 and forming an angle with the optical axis between ALPHA1 and an angle ALPHA2. The angle ALPHA2 is defined as the angle between the optical axis OA and the ray furthest from the optical axis OA not reflected by the second section.

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

[0063] The faces are flat here. They can be trapezoidal in shape.

[0064] A third angle of inclination is defined as the angle of inclination of the faces of the third section 230 with respect to the optical axis OA.

[0065] This third section 230 reflects a portion of the rays from the light source 100, forming an angle with the optical axis between ALPHA2 and an angle ALPHA3. Angle ALPHA3 is defined as the angle between the optical axis OA and the ray furthest from the optical axis OA not reflected by the third section 230.

[0066] For example, for a light source emitting a cone of light emission forming an angle between 50° and 80° with the optical axis, angle ALPHA 1 can be between 55° and 65° and / or angle ALPHA2 can be between 32° and 48° and / or angle ALPHA3 can be between 25° and 40°.

[0067] The faces of the second section 220 and / or third section 230 are here reflective in the infrared.

[0068] The second section 220 and the third section 230 make it possible to create more uniform illumination by reflecting the most inclined rays which are not in the field of view of the image capture unit towards areas of interest which lack illumination in the field of view of the image capture unit.

[0069] For example, in the case of a 100 Gaussian light source, which is the case of the LED here, the outermost rays will be reflected towards the peripheral areas of the central peak of illumination or the edges of the field of view of the image capture unit.

[0070] In [Fig. 2], several light rays emanating from the light source 100 are observed. The rays represented by solid lines have an angle of inclination less than ALPHA3 and are not reflected. The light rays represented by dashed lines are reflected by the second section 220. The reflected rays represented by dashed lines are reflected by the third section 230. The rays represented by dashed and dashed lines thus compensate for the Gaussian distribution of the LED by bringing luminous flux back to the edges of the field.

[0071] Furthermore, the optical reflector 200 can be produced by standard industrial processes such as injection molding followed by the deposition of a reflective coating by physical vapor deposition (or PVD for "Physical Vapor Deposition") or galvanizing.

[0072] Figure 4 shows an electronic device 2 according to an embodiment of the invention. The electronic device 2 comprises the illumination device 1 of Figures 2 and 3 and described above. It also comprises an image capture unit 20 and a control unit 30 coupled to the illumination 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 captures images of the environment in front of it, in this case, a portion of the vehicle's interior. For example, the field of view of the image capture unit 20 is directed towards the driver's usual position. 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 (when the driver is in his usual position) a level of unfitness to drive (for example a level of distraction or a level of drowsiness) by means of the analysis of the captured image.

[0075] To avoid disturbing people near the electronic device and to ensure consistent use of the image capture function day and night, the light source 100 can operate in the infrared range, which is invisible to the human eye. The image capture unit 20 operates in at least the same wavelength range as the light source 100. In this case, the image capture unit 20 operates only in the infrared. Alternatively, the image capture unit can operate in both the infrared and visible ranges.

[0076] To improve the performance of the captured image analysis, it is preferable that the uniformity of the lighting be such that the illumination contrast is less than 20%. This means that two points in the field of view of the image capture unit 20 must receive an illumination difference of less than 20%.

[0077] The angles of inclination and the heights of the faces of the sections were calculated by numerical simulation to meet this objective.

[0078] The first section 210 can have a first height H1 on the optical axis of between 1 and 1.5 mm. Here the first height H1 is 1.3 mm. The absolute value of the first angle of inclination THETA1 of the first section 210 with respect to the optical axis (OA) can be between 8 and 15°. Here the absolute value of the first angle of inclination is 10°.

[0079] The second section 220 can have a second height H2 on the optical axis of between 2 and 5 mm. Here the second height H2 is 3 mm. The absolute value of the second angle of inclination THETA2 of the second section 220 with respect to the optical axis (OA) can be between 8 and 15°. Here the absolute value of the second angle of inclination is 10°.

[0080] The third section 230 can have a third height H3 on the optical axis of between 0.8 and 1.5 mm. Here the third height H3 is 1 mm. The absolute value of the third angle of inclination of the third section 230 with respect to the optical axis (OA) can be less than 5°. Here the absolute value of the third angle of inclination is 1°.

[0081] For better runiformity of the source, the inclination of the faces of the third section 230 could be zero. However, in order to more easily manufacture the optical reflector 200, which is generally molded, it is preferable for the faces of the third section 230 to be slightly inclined.

[0082] These values ​​are dependent on the light source 100 and the configuration of the image capture unit 20. They are given here as an indication and are not limiting.

[0083] The electronic device 2 here comprises an outer casing 40 and a removable cover 42. The outer casing 40 provides mechanical support for the components relative to each other. The removable cover 42 allows easy access to the interior of the electronic device 2.

[0084] The electronic device 2 also includes a printed circuit board 50 on which the light source 100 and the control unit 30 are mounted. The optical reflector 200 is fixed here by means of mounting clips 4L

[0085] Alternatively, the illumination device 1 could be entirely fixed directly onto the printed circuit board 50.

[0086] In [Fig. 5], an illumination device 1 according to another embodiment of the invention is shown. The illumination device 1 here comprises a light source 100 and an optical reflector 200. The light source 100 can be a The source has Gaussian illumination, such as an LED. The optical reflector 200 here comprises two sections.

[0087] The first section 210 comprises converging faces and limits the propagation of stray light. The second section 220 comprises diverging faces and evens out the illumination in the same way as described above.

[0088] Fig. 6 represents a simulation 110 of the illumination generated by the light source 100 used in the illumination device 1. A Gaussian distribution of light is observed.

[0089] Figure 7 represents a second simulation 120 of the illumination generated by the Illumination device 1 of [Fig.2]. Thanks to the optical reflector 200, the peripheral light rays are bent around the light peak, thus generating uniform illumination over a wider field of view.

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

[0091] Fig. 8 represents a graph showing the average (Avg. Irrad) and maximum (Max. Irrad) illumination due to stray light as a percentage relative to a standard value at camera input for the electronic device of Fig. 4 (Inv. DMS) and for the conventional electronic device of Fig. 1 comprising a conventional illumination device (Std. DMS).

[0092] It is observed that the stray light is weaker when using the electronic device of [Fig.4] as defined here than for the conventional electronic device of [Fig.1] comprising a conventional illumination device.

Claims

Demands

1. Illumination device (1) comprising a light source (100) and an optical reflector (200), the light source (100) having a principal direction of illumination defining an optical axis (OA), the optical reflector (200) comprising two sections, the first section (210) comprising a first wall (211) extending at least partially around the light source (100) over a first height (H1) in the direction of the optical axis (OA), the first wall (211) being convergent in the direction of propagation of light, the second section (220) comprising a second reflective wall (221) extending in line with the first wall (211) over a second height (H2) in the direction of the optical axis (OA) so as to reflect light rays from the light source, the second wall (221) being divergent in the direction of propagation of light,and wherein the first wall (211) of the first section (210) of the optical reflector (200) is reflective.

2. Illumination device (1) according to claim 1, wherein the optical reflector (200) comprises a third section (230) having a third reflective wall (231) which extends over a third height (H3) in the direction of the optical axis, in the continuation of the second wall of the second section.

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

4. Illumination device (1) according to any one of claims 1 to 3, wherein the first wall (211) and the second wall (221) of the optical reflector (200) each comprise at least one pair of two faces.

5. Illumination device (1) according to claim 4, wherein the first wall (211) and the second wall (221) each comprise two pairs of two faces positioned such that the two faces of a pair are opposite each other, on each side of the light source (100).

6. Illumination device (1) according to any one of claims 4 or 5, wherein the faces are flat.

7. Illumination device (1) according to any one of claims 1 to 6, wherein the light source (100) is an LED emitting in

8. the infrared, and in which the walls (211, 221) of the sections (210, 220) are reflective in the infrared. Electronic device (2) comprising an image capture unit (20) and an illumination device (1) according to any one of the preceding claims configured to illuminate the field of view of the image capture unit (20).

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