Image acquisition device and system for monitoring a motor vehicle driver

Abstract

The invention relates to an image acquisition device (1) comprising an array (10) of photosensitive elements (100), each photosensitive element comprising a photosensitive area (110) and a collection means (120) for collecting light, said collection means being disposed on said photosensitive area and being arranged to transmit light from an external scene onto said photosensitive area, at least one of said photosensitive elements being sensitive to a given wavelength range of the infrared domain. According to the invention, the collection means of said photosensitive element are shaped so as to transmit light only onto a portion (110A) of said photosensitive area of said photosensitive element.

Description

Technical Field

[0001] This invention relates to the field of image acquisition technology.

[0002] More specifically, the present invention relates to an image acquisition device.

[0003] The present invention also relates to a driver monitoring system for monitoring motor vehicle drivers. Background Technology

[0004] Driver-monitoring systems (DMS) typically operate in the infrared or near-infrared domain. For example, this allows for operation at night using infrared light sources, which, because of their infrared nature, do not dazzle the driver and can even detect the driver's eyes through sunglasses. In this context, driver-monitoring systems often include image acquisition devices sensitive to infrared light.

[0005] However, the images produced by image acquisition devices are quite poor in sharpness. Specifically, infrared photons carry less energy than visible photons and propagate quite deeply into the photosensitive semiconductor. Therefore, the light received by one pixel of a photosensitive element, i.e., the detector of the image acquisition device, may be detected by adjacent photosensitive elements (this effect is called pixel crosstalk), resulting in a blurred image.

[0006] This low resolution poses a problem for the accuracy of driver monitoring algorithms. Summary of the Invention

[0007] Against this backdrop, the present invention provides an image acquisition device comprising an array of photosensitive elements, each photosensitive element including a photosensitive region and a collecting device for collecting light, the collecting device being placed above the photosensitive region and arranged to transmit light from an external scene to the photosensitive region, at least one of the photosensitive elements being sensitive to a given wavelength range in the infrared domain, and the collecting device of the photosensitive element being shaped to transmit light to only a portion of the photosensitive region of the photosensitive element.

[0008] Therefore, with the help of this invention, the area in the photosensitive element that actually receives light is smaller than the total photosensitive area of ​​the photosensitive element. This is equivalent to structurally reducing the photosensitive area of ​​the photosensitive element.

[0009] Using only a portion of the photosensitive area reduces the overall sensitivity of the image acquisition device (because the photosensitive element collects less light), but in return, it improves image clarity. This improved clarity is particularly beneficial for driver monitoring algorithms that require the perception of details.

[0010] The following are other advantageous and non-limiting features of the device according to the invention, which may be implemented individually or in any technically feasible combination:

[0011] - The collecting device of the photosensitive element is shaped to transmit light to less than 80% of the photosensitive region of the photosensitive element;

[0012] - The collecting device of the photosensitive element is shaped to transmit light to less than 65% of the photosensitive region of the photosensitive element;

[0013] - The collecting device of the photosensitive element is shaped to transmit light to less than 50% of the photosensitive region of the photosensitive element;

[0014] - The collecting device of the photosensitive element includes a lens disposed facing the photosensitive region of the photosensitive element, the lens having a shape designed to converge light only to the portion thereof;

[0015] - The size of the lens is smaller than the size of the photosensitive area of ​​the photosensitive element;

[0016] -The collecting device of the photosensitive element includes a light-shielding element placed around the periphery of the photosensitive area facing the photosensitive element;

[0017] - The light-shielding element includes at least one of the following: a mask in contact with the outer layer of the photosensitive element; and a wall extending between the photosensitive region of the photosensitive element and the outer layer of the photosensitive element;

[0018] -The photosensitive element is only sensitive to wavelengths between 900 nm and 980 nm;

[0019] - The plurality of photosensitive elements are sensitive to a given wavelength range in the infrared domain.

[0020] The present invention also relates to a driver monitoring system for monitoring motor vehicle drivers, the driver monitoring system comprising the image acquisition device and infrared light source as described above.

[0021] Therefore, it is worth noting that the relative decrease in the overall sensitivity of the image acquisition device is compensated by using a light source that ensures adequate illumination of the scene, i.e., the passenger compartment of the motor vehicle.

[0022] Of course, various features, variations and embodiments of the present invention can be combined with each other in various combinations, as long as they are not incompatible or mutually exclusive. Attached Figure Description

[0023] The following description, taken with reference to the accompanying drawings which are given as non-limiting examples, will make it clear what the invention consists of and how it can be practiced.

[0024] In the attached diagram:

[0025] Figure 1 This is a schematic diagram of a driver monitoring system for monitoring motor vehicle drivers according to the present invention;

[0026] Figure 2 This is a schematic side view of three photosensitive elements of the image acquisition device according to the present invention;

[0027] Figure 3 Is it like this? Figure 2 A schematic top view of the photosensitive area of ​​the photosensitive element shown. Detailed Implementation

[0028] Figure 1 The image acquisition device 1 according to the present invention is shown. The image acquisition device 1 operates at least partially in the infrared domain, and preferably in the near-infrared domain, which is defined, for example, by wavelengths between 700 nm and 2000 nm. This means that the image acquisition device 1 is suitable for generating images based on wavelengths in the infrared domain. The image acquisition device 1 is, for example, an infrared camera.

[0029] like Figure 1 As shown, the image acquisition device 1 is intended to form part of a driver monitoring system 3 for monitoring motor vehicle drivers. The monitoring system 3 also includes a light source 2. The light source 2 is located in the passenger compartment of the motor vehicle to illuminate the driver's face. The light source 2 is designed to emit light within the wavelength range sensitive to the image acquisition device 1, specifically infrared light. Therefore, the light source 2 is an infrared light source, such as an infrared diode. The images generated by the image acquisition device 1 can then be processed by a driver monitoring algorithm implemented by the monitoring system 3 (the monitoring system 3 also includes...). Figure 1 (A computing processing device, not shown), to perform functions such as controlling the vehicle's brakes when a driver is detected to be highly distracted or drowsy.

[0030] The image acquisition device 1 includes an array 10 of photosensitive elements 100, which are also referred to as pixels. Figure 1 As shown, the array 10 of photosensitive elements 100 is generally planar. The array 10 is positioned in the image plane of the image acquisition device 1. The image acquisition device 1 also includes a set of optical devices designed to converge light from the external scene, particularly from the driver's face, onto the array 10 of photosensitive elements 100. Figure 1 Only some photosensitive elements are shown schematically in the image.

[0031] Array 10 includes, for example, 1000 × 1000 photosensitive elements 100. Figure 2The image shows in detail the three photosensitive elements 100 of array 10, separated by dashed lines. Figure 2 In the example, all photosensitive elements 100 are sensitive to a given wavelength range in the infrared domain, i.e., a predetermined wavelength interval in the infrared domain. Preferably, they are sensitive only to said given wavelength range in the infrared domain. This, for example, means that outside said given wavelength range in the infrared domain, their quantum efficiency is less than 5%.

[0032] The given wavelength range in the infrared range extends, for example, from 900 nm to 980 nm. The light source 2 could then be a diode that primarily emits light at 940 nm.

[0033] As a variation, only some photosensitive elements in the array, such as one out of every four, are sensitive to the given wavelength range in the infrared domain. The other photosensitive elements are then sensitive to a given wavelength range in the visible domain, which typically corresponds to red, green, and blue light. The image acquisition device is then, for example, a so-called RGB-IR camera (RGB-IR stands for Red Green Blue - Infrared).

[0034] As shown in the figure, all photosensitive elements 100 are identical except for their position in array 10 (they are all infrared pixels). Therefore, the following description refers to an individual photosensitive element among these photosensitive elements.

[0035] like Figure 2 As shown, the photosensitive element 100 includes a photosensitive region 110 and a light-collecting device 120, which is disposed above the photosensitive region 110.

[0036] The photosensitive region 110 corresponds to the surface of the photosensitive block 111 made of semiconductor (e.g., silicon), which is the surface facing the external scene. The photosensitive block 111 is adapted to convert photons into electrical signals. When a photon is incident on the photosensitive region 110, it penetrates more or less into the thickness of the photosensitive block 111 and is detected by means of electronic circuitry.

[0037] exist Figure 2 In this example, the photosensitive block 111, together with appropriate electrical connections (not shown), forms a photodiode. Therefore, the photosensitive region 110 here corresponds to the light-collecting region of the photodiode. Figure 2 As shown, in addition to the photosensitive block 111, each photosensitive element 100 also includes a storage element 130 designed to temporarily store the electrical signals generated by the photosensitive block 111, and one or more compartments 140 for the passage of electronic circuits. Here, the array 10 of photosensitive elements is of CMOS type.

[0038] In a variant not shown, when the entire area of ​​the array is light-sensitive (typically when it is a "full-frame" CCD type), the size of each photosensitive area is equal to the area of ​​the array divided by the number of photosensitive elements it contains. For example, when the array area is 25 mm² and has 1000 × 1000 photosensitive elements, the photosensitive area of ​​each photosensitive element is 25 μm².

[0039] like Figure 3 As shown, the photosensitive region 110 has a square shape. The photosensitive region 110 has an area, for example, between 9 μm² and 25 μm².

[0040] The collecting device 120 of the photosensitive element 100 is arranged to transmit light from the external scene to the photosensitive region 110. Here, the word "transmit" should be understood as conduction, that is, the light incident on the collecting device 120 is at least partially transmitted to the photosensitive region 110 above the collecting device 120.

[0041] like Figure 2 As shown, the collecting device 120 specifically includes a structural element 121, a filter 122, and a protective layer 123.

[0042] Structural element 121 protrudes from photosensitive region 100. It rests on and is thus in contact with the photosensitive region. Separating element 121 is made of a material that is at least partially transparent to the given wavelength range in the infrared domain, such as silicon dioxide. Structural element 121 serves as a carrier for filter 122 and protective layer 123. It has minimal, and preferably minimal, influence on the path of light passing through it.

[0043] The filter 122 is positioned opposite to the photosensitive area 110, and as follows: Figure 2 The image shown here is parallel to the latter. Filter 122 here is an infrared filter that primarily transmits, and preferably only transmits, wavelengths contained within the given wavelength range in the infrared domain. This allows the photosensitive element 100 to be particularly sensitive to the infrared domain, although the photosensitive block 111 made of semiconductors may be sensitive to a wide wavelength range.

[0044] The protective layer 123 is also disposed opposite to the photosensitive area 110, and as... Figure 2 The diagram shown here is substantially parallel to the latter. The protective layer 123 is made of a material that is at least partially transparent to the given wavelength range, such as plastic or glass. The protective layer 123 here forms the outer layer of the photosensitive element 100.

[0045] More specifically, the collecting device 120 of the photosensitive element 100 is configured to transmit light to only a first portion 110A of the photosensitive region 110 of the photosensitive element 100. The first portion 110A defines only a portion or segment of the photosensitive region 110. In other words, a second portion 110B of the photosensitive region 110 of the photosensitive element 100, having a non-zero area, does not receive light. Therefore, the collecting device 120 is configured to selectively illuminate the first portion 110A of the photosensitive region 110, i.e., only the first portion 110A is illuminated (while the second portion 110B is not illuminated).

[0046] like Figure 3 Clearly shown, the second portion 110B of the photosensitive region 110 is complementary to the first portion 110A, meaning that the union of these two portions forms the entire photosensitive region 110. The first portion 110A of the light-receiving photosensitive region 110 is here the central portion, which is equidistant from the edges of the also square photosensitive region 110. Figure 3 In the example, the second portion 110B forms a strip surrounding the first portion 110A, and the perimeter of this strip is also square. Of course, other area distributions for the first and second portions are also possible. Each of the first and second portions may also include multiple sub-parts that are separate from each other.

[0047] Increasing the area of ​​the second portion 110B of the photosensitive region 110, and thus reducing the area of ​​the first portion 110A, advantageously improves the sharpness of the infrared image. Therefore, the first portion 110A of the photosensitive region 110 occupies, for example, less than 80%, even less than 65%, or even less than 50% of the area of ​​the photosensitive region 110. However, this improvement comes at the cost of the sensitivity of the infrared image, i.e., its overall brightness. Figure 3 In the example, the modulation transfer function of the photosensitive element 100 depends on the ratio of the width L1 of the first portion 110A to the width L2 of the photosensitive region 110.

[0048] like Figure 2 As shown, the collecting device 120 includes a plurality of devices that allow specific illumination of the first portion 110A, namely: a lens 124; a mask 125; and a wall 126. Of course, the collecting device 120 may include only one or both of these devices.

[0049] Lens 124 is positioned opposite to photosensitive area 110. For example... Figure 2Schematably, lens 124 has a shape designed to converge light (represented by the ray R1 drawn in solid line) onto only a first portion 110A of photosensitive region 110. Lens 124 is formed here together with protective layer 123, meaning that lens 124 forms part of protective layer 123. Lens 124 is defined here by a flat surface 123A and a convex surface 123B of protective layer 123, the flat surface 123A being generally parallel to photosensitive region 110, and the convex surface 123B being opposite to flat surface 123A. Therefore, convex surface 123B is oriented towards the external scene and is designed to receive light from that scene.

[0050] Lens 124 has an overall spherical shape, meaning that the periphery of the convex surface 123B is circular. The size of lens 124 is preferably smaller than the size of the photosensitive region 110. This, for example, means that, viewed parallel to the photosensitive region 110, the extent of the convex surface 123B is smaller than that of the photosensitive region 110 located below it.

[0051] To enhance the converging effect of lens 124, the curvature of convex surface 123B can be increased.

[0052] Mask 125 and wall 126 each form an element for blocking light. Specifically, unlike lens 121 which shapes light, mask 125 and wall 126 block a portion of light, for example, by absorption. Here, mask 125 and wall 126 are placed around the periphery of photosensitive element 100. The periphery of photosensitive element 100 corresponds to its boundary, i.e., the position where photosensitive element 100 is adjacent to other photosensitive elements 100 or adjacent to the edge of array 10. Figure 2 In the diagram, the portion of light that is blocked is represented by the dashed ray R2.

[0053] like Figure 2 As shown, mask 125 comprises a thin layer of opaque material, such as a thin layer of black material. Mask 125 is formed, for example, by a layer of coating applied directly to protective layer 123, thus making its manufacture particularly simple. Of course, mask 125 can be made of other materials, such as plastic.

[0054] like Figure 2 As shown, mask 125 covers the entire protective layer 123 except for its convex surface 123B. However, mask 125 may partially cover the convex surface 123B of the protective layer 123, or conversely, be spaced apart from the convex surface 123B. Mask 125 serves here as an aperture to limit the amount of light that can reach the photosensitive region.

[0055] like Figure 2 As shown, wall 126 extends between photosensitive region 110 and protective layer 123. Wall 126 is made of opaque material.

[0056] Wall 126 here has a hollow columnar shape with a square cross-section. Figure 2 (The two opposite sides are visible in the image). Therefore, the wall 126 forms a conduit with a smaller cross-section than the photosensitive region 110, enabling light to be guided to the first portion 110A of the photosensitive region 110. Here, the wall 126 is at least partially located above the second portion 110B of the photosensitive region 110.

[0057] This invention is by no means limited to the embodiments described and shown, and those skilled in the art can add any variations thereto that conform to this invention.

[0058] For example, when an image acquisition device includes infrared pixels and color pixels, such as when it is an RGB-IR camera, some filters can selectively transmit wavelengths corresponding to visible light, such as red, green and blue light.

[0059] Lenses can be elements attached to a protective layer.

[0060] The mask can contact the protective layer on one side of its flat surface. For example, the mask can be positioned between the protective layer and the filter.

[0061] The wall can have any shape suitable for at least partially obscuring a second portion of the photosensitive area. The wall can have a variable height between the photosensitive area and the protective layer. For example, it can extend all the way to the photosensitive block. It can have a cross-section of different shapes, such as a circular cross-section. It can also include multiple sub-walls that are independent of each other. As yet another variation, the collecting device may not include the wall.

Claims

1. An image acquisition device (1) comprising an array (10) of photosensitive elements (100), each photosensitive element (100) comprising a photosensitive region (110) and a light-collecting device (120) disposed above the photosensitive region (110) and arranged to transmit light from an external scene to the photosensitive region (110), at least one of the photosensitive elements (100) being sensitive to a given wavelength range in the infrared domain. Its features are, The collecting device (120) of the photosensitive element (100) is shaped to transmit light to only a portion (110A) of the photosensitive region (110) of the photosensitive element (100).

2. The image acquisition device (1) according to claim 1. in, The collecting device (120) of the photosensitive element (100) is shaped to transmit light to less than 80% of the photosensitive region (110) of the photosensitive element (100).

3. The image acquisition device (1) according to claim 1 or 2, wherein, The collecting device (120) of the photosensitive element (100) is shaped to transmit light to less than 65% of the photosensitive region (110) of the photosensitive element (100).

4. The image acquisition device (1) according to any one of claims 1 to 3, wherein, The collecting device (120) of the photosensitive element (100) is shaped to transmit light to less than 50% of the photosensitive region (110) of the photosensitive element (100).

5. The image acquisition device (1) according to any one of claims 1 to 4, wherein, The collecting device (120) of the photosensitive element (100) includes a lens (124) disposed facing the photosensitive region (110) of the photosensitive element (100), the lens (124) having a shape designed to focus light only onto the portion (110A).

6. The image acquisition device (1) according to claim 5, wherein, The size of the lens (124) is smaller than the size of the photosensitive area (110) of the photosensitive element (100).

7. The image acquisition device (1) according to any one of claims 1 to 6, wherein, The collecting device (120) of the photosensitive element (100) includes a light-blocking element placed opposite the periphery of the photosensitive region (110) of the photosensitive element (100).

8. The image acquisition device (1) according to claim 7, wherein, The light-shielding element includes at least one of the following: a mask (125) in contact with the outer layer (123) of the photosensitive element (100); and a wall (126) extending between the photosensitive region (110) of the photosensitive element (100) and the outer layer (123) of the photosensitive element (100).

9. The image acquisition device (1) according to any one of claims 1 to 8, wherein, The photosensitive element (100) is only sensitive to wavelengths between 900 nm and 980 nm.

10. A driver monitoring system (3) for monitoring motor vehicle drivers, comprising an image acquisition device (1) and an infrared light source (2) according to any one of claims 1 to 9.

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