Image capture device and monitoring system for a driver of a motor vehicle

Abstract

The invention relates to an image capture device (1) comprising a matrix (10) of photosensitive elements (100), each photosensitive element comprising a photosensitive surface (110) and light collecting means (120), arranged on the photosensitive surface, arranged to convey light coming from an external scene onto the photosensitive surface, at least one of the photosensitive elements being sensitive to a given wavelength range in the infrared domain. According to the invention, the collecting means of said photosensitive element are shaped to convey the light onto only a portion (110A) of the photosensitive surface of said photosensitive element. Figure for abstract: Fig. 2

Description

Title of the invention: Image capture device and system for monitoring a driver of a motor vehicle Technical field

[0001] The present invention relates generally to the technical field of image capture.

[0002] It relates more particularly to an image capture device.

[0003] It also relates to a system for monitoring a driver of a motor vehicle. Technological background

[0004] Driver monitoring systems (better known by the English acronym DMS for "driver monitoring system") traditionally operate in the infrared or near infrared range. This makes it possible, for example, to operate at night with an infrared light source, which therefore does not dazzle the driver, or to detect the driver's eyes through sunglasses. In this context, a driver monitoring system generally comprises an image capture device sensitive to infrared light.

[0005] The sharpness of the images produced by the image capture device is, however, quite poor. Indeed, infrared photons, which carry less energy than visible photons, propagate quite far in the photosensitive semiconductor material. Thus, the light received by a photosensitive element, i.e. by a pixel of the detector of the image capture device, can be detected by the neighboring photosensitive element (a phenomenon known in English as “pixel cross-talk”), which generates a blurred image.

[0006] This low sharpness is a problem for the accuracy of driver monitoring algorithms. Summary of the invention

[0007] In this context, the present invention proposes an image capture device comprising a matrix of photosensitive elements, each photosensitive element comprising a photosensitive surface and light collecting means, arranged on the photosensitive surface, arranged to convey light coming from an external scene onto the photosensitive surface, at least one of the photosensitive elements being sensitive to a given wavelength range in the infrared domain, the collecting means of said photosensitive element being shaped to convey the light onto only a portion of the photosensitive surface of said photosensitive element.

[0008] Thus, thanks to the invention, the surface area of ​​the photosensitive element which actually receives light is less than the total photosensitive surface area of ​​the photosensitive element. This is equivalent to structurally reducing the photosensitive surface area of ​​the photosensitive element.

[0009] Using only a portion of the photosensitive surface has the effect of reducing the overall sensitivity of the image capture device (since less light is collected by the photosensitive elements) in exchange for an increase in image sharpness. This increase in sharpness is particularly interesting for driver monitoring algorithms that need to perceive details.

[0010] Other advantageous and non-limiting characteristics of the device according to the invention, taken individually or in all technically possible combinations, are the following: - said means for collecting said photosensitive element are shaped to convey light over less than 80% of the photosensitive surface of said photosensitive element; - said means for collecting said photosensitive element are shaped to convey light over less than 65% of the photosensitive surface of said photosensitive element; - said means for collecting said photosensitive element are shaped to convey light over less than 50% of the photosensitive surface of said photosensitive element; - said means for collecting said photosensitive element comprise a lens arranged opposite the photosensitive surface of said photosensitive element, the lens having a shape designed to converge the light only on said part; - the lens has a size smaller than that of the photosensitive surface of said photosensitive element; - said means for collecting said photosensitive element comprise a light blocking element arranged opposite a periphery of the photosensitive surface of said photosensitive element; - the blocking element comprises at least one of: a mask in contact with an outer layer of said photosensitive element and; a wall extending between the photosensitive surface of said photosensitive element and the outer layer of said photosensitive element; - said photosensitive element is sensitive only to a wavelength range between 900 nm and 980 nm; - a plurality of the photosensitive elements are sensitive to a range of lengths given wave of the infrared domain.

[0011] The invention also relates to a system for monitoring a driver of a motor vehicle comprising an image capture device as described above and an infrared light source.

[0012] Thus, remarkably, the relative reduction in overall sensitivity of the image capture device is compensated by the use of a light source which ensures sufficient illumination of the scene, i.e. here of the passenger compartment of the motor vehicle.

[0013] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Description of the invention

[0014] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0015] In the attached drawings:

[0016] [Fig-1] is a schematic representation of a monitoring system of a driver of a motor vehicle according to the invention,

[0017] [Fig.2] is a schematic side view of three photosensitive elements of an image capture device according to the invention,

[0018] [Fig.3] is a schematic top view representation of a photosensitive surface of a photosensitive element of [Fig.2].

[0019] An image capture device 1 according to the invention is shown in [Fig.l]. The image capture device 1 operates at least partly in the infrared range and preferably in the near infrared range which is for example defined by wavelengths between 700 nm and 2000 nm. This means that the image capture device 1 is adapted to generate images on the basis of wavelengths in the infrared range. The image capture device 1 is for example an infrared camera.

[0020] As shown in [Fig.l], the image capture device 1 is intended to be part of a monitoring system 3 for a driver of a motor vehicle. The monitoring system 3 also comprises a light source 2. The light source 2 is arranged in the passenger compartment of the motor vehicle so as to illuminate the driver's face. The light source 2 is designed to emit light in a wavelength range to which the image capture device 1 is sensitive, i.e. here to emit infrared light. The light source 2 is thus an infrared light source such as an infrared diode. The images produced by the image capture device 1 can then be processed by driver monitoring algorithms, implemented by the monitoring system 3 (which also includes computer processing means not shown in [Fig.l]), in order to provide functions such as controlling the vehicle brakes when a high level of driver distraction or drowsiness is detected.

[0021] The image capture device 1 comprises a matrix 10 of photosensitive elements 100, also called pixels. As shown in [Fig.l], the matrix 10 of photosensitive elements 100 is substantially planar. It is placed at the image plane of the image capture device 1, which also comprises a set of optical devices designed to converge the light from the external scene, coming in particular from the driver's face, onto the matrix 10 of photosensitive elements 100 (only some of the photosensitive elements are schematically represented in [Fig.l]).

[0022] The matrix 10 comprises for example 1000 by 1000 photosensitive elements 100. Three of the photosensitive elements 100 of the matrix 10 are shown in detail in [Fig. 2], they are separated by dotted lines. In the example of [Fig. 2], all the photosensitive elements 100 are sensitive to a given wavelength range of the infrared domain, i.e. a predetermined wavelength interval of the infrared domain. Preferably, they are sensitive only to said given wavelength range of the infrared domain. This means for example that their quantum efficiency is less than 5% outside said given wavelength range of the infrared domain.

[0023] Said given wavelength range of the infrared domain extends for example from 900 nm to 980 nm. The light source 2 can then be a diode emitting mainly light at 940 nm.

[0024] Alternatively, only some of the photosensitive elements of the matrix, for example one out of four, may be sensitive to said given wavelength range of the infrared domain. The others are then sensitive to given wavelength ranges of the visible domain typically corresponding to red, green and blue. The image capture device is then for example a so-called “RGB-IR” camera (according to the English acronym for Red Green Blue - InfraRed, i.e. Red Green Blue - InfraRed).

[0025] As shown in the figures, the photosensitive elements 100 are all identical (they are all infrared pixels), apart from their position within the matrix 10. The description which follows is therefore made with reference to only one of these photosensitive elements.

[0026] As shown in [Fig.2], the photosensitive element 100 comprises a photosensitive surface 110 and light collecting means 120, arranged on the surface photosensitive 110.

[0027] The photosensitive surface 110 corresponds to a surface, here the one facing the external scene, of a photosensitive block 111 made of semiconductor material, such as silicon, adapted to convert photons into electrical signals. When a photon is incident on the photosensitive surface 110, it penetrates more or less deeply into the thickness of the photosensitive block 111 and is detected by means of an electronic circuit.

[0028] In the example of [Fig. 2], the photosensitive block 111 here forms, with appropriate electrical connections (not shown), a photodiode. The photosensitive surface 110 thus corresponds here to the light collection surface of the photodiode. As shown in [Fig. 2], each photosensitive element 100 also comprises, in addition to the photosensitive block 111, a storage element 130 designed to temporarily store the electrical signal generated by the photosensitive block 111 and one or more compartments 140 provided for passing electronic circuits. Here, the matrix 10 of photosensitive elements is of the CMOS type.

[0029] In a variant not shown, when the entire surface of the matrix is ​​sensitive to light (typically when it is of the “full frame” CCD type), the size of each photosensitive surface is equal to the surface of the matrix divided by the number of photosensitive elements that it comprises. For example, when the matrix has a surface area of ​​25 mm2 and 1000 by 1000 photosensitive elements, the photosensitive surface area of ​​each photosensitive element is 25 pm2.

[0030] As shown in [Fig. 3], the photosensitive surface 110 here has a square shape. The photosensitive surface 110 has a surface area which is for example between 9 pm2 and 25 pm2.

[0031] The collecting means 120 of the photosensitive element 100 are arranged to convey the light coming from the external scene onto the photosensitive surface 110. Here, the term “convey” means the act of conducting, that is to say transmitting at least partially, the light which is incident on said collecting means 120 to the photosensitive surface 110 on which they are arranged.

[0032] As shown in [Fig.2], the collection means 120 comprise in particular a structural element 121, a filter 122, and a protective layer 123.

[0033] The structural element 121 rises from the photosensitive surface 100. Here it rests on the photosensitive surface, it is therefore in contact with it. The separating element 121 is made of a material at least partially transparent to said given wavelength range of the infrared domain, for example silica. The structural element 121 acts as a support for the filter 122 and the protective layer 123. It affects little, preferably as little as possible, the path of the light passing through it.

[0034] The filter 122 extends opposite the photosensitive surface 110, here parallel to the latter as shown in [Fig.2]. The filter 122 is here an infrared filter transmitting mainly, preferably exclusively, the wavelengths included in said given wavelength range of the infrared domain. This makes it possible to make the photosensitive element 100 specifically sensitive to the infrared domain although the photosensitive block 111 made of semiconductor material can be sensitive to a wide range of wavelengths.

[0035] The protective layer 123 also extends opposite the photosensitive surface 110, here substantially parallel to the latter as shown in [Fig. 2]. The protective layer 123 is made of a material at least partially transparent to said given wavelength range, for example made of plastic material or glass. The protective layer 123 here forms an external layer of the photosensitive element 100.

[0036] The collecting means 120 of the photosensitive element 100 are more specifically shaped to convey the light to a first part 110A only of the photosensitive surface 110 of the photosensitive element 100. The first part 110A delimits a part or portion only of the photosensitive surface 110. In other words, it is provided that a second part 110B, of non-zero surface, of the photosensitive surface 110 of the photosensitive element 100 does not receive light. The collecting means 120 are thus shaped so that the light from the external scene selectively illuminates the first part 110A of the photosensitive surface 110, that is to say only the first part 110A (and not the second part 110B).

[0037] As [Fig. 3] clearly shows, the second part 110B of the photosensitive surface 110 is complementary to the first part 110A in the sense that the union of the two forms the entirety of the photosensitive surface 110. The first part 110A of the photosensitive surface 110 receiving light is here a central part, which is distant (here equidistant) from the edges of the photosensitive surface 110, which is also square in shape. In the example of [Fig. 3], the second part 110B forms a strip, the periphery of which is also square, surrounding the first part 110A. Other surface distributions between the first and second parts are obviously possible. Each of the first and second parts can also comprise several separate sub-parts.

[0038] Increasing the surface area of ​​the second part 110B of the photosensitive surface 110, and therefore reducing that of the first part 110A, advantageously makes it possible to increase the sharpness of the infrared images (image property commonly defined by the English term “sharpness”). Thus, the first part 110A of the photosensitive surface 110 represents for example less than 80% of the surface area of ​​the photosensitive surface 110, or even less than 65% of the surface area of ​​the photosensitive surface 110, or even less than 50% of the surface area of ​​the photosensitive surface 110. This increase is made however to the detriment of the sensitivity of the infrared images, that is to say of their overall intensity. In the example of [Fig.3], the modulation transfer function of the photosensitive element 100 depends on the ratio of the width L1 of the first part 110A to the width L2 of the photosensitive surface 110.

[0039] As shown in [Fig.2], the collection means 120 comprise several devices allowing the specific illumination of the first part 110A, namely: a lens 124; a mask 125; and a wall 126. Of course, the collection means 120 may comprise only one or two of these devices.

[0040] The lens 124 is arranged opposite the photosensitive surface 110. As shown schematically in [Fig. 2], the lens 124 has a shape designed to converge the light (represented by the rays RI in solid lines) only on the first part 110A of the photosensitive surface 110. The lens 124 is here formed with the protective layer 123 in the sense that it constitutes a part of the protective layer 123. The lens 124 is here delimited by a flat face 123A of the protective layer 123, substantially parallel to the photosensitive surface 110, and a convex face 123B of the protective layer 123, opposite the flat face 123A. The convex face 123B is thus oriented towards the external scene, it is intended to receive the light coming from this scene.

[0041] The lens 124 here has a generally spherical cap shape in the sense that the periphery of the convex face 123B is circular. The lens 124 preferably has a size smaller than that of the photosensitive surface 110. This means, for example, that, parallel to the photosensitive surface 110, the convex face 123B is less extensive than the photosensitive surface 110 which it overhangs.

[0042] To increase the convergence effect of the lens 124, it may be provided to increase the curvature of the convex face 123B.

[0043] The mask 125 and the wall 126 each form a light-blocking element. Indeed, unlike the lens 121, which shapes the light, the mask 125 and the wall 126 block, for example by absorbing them, a portion of the light. Here, the mask 125 and the wall 126 are arranged on the periphery of the photosensitive element 100. The periphery of the photosensitive element 100 corresponds to its edges, that is to say where the photosensitive element 100 is adjacent to the other photosensitive elements 100 or to the edges of the matrix 10. In [Fig. 2], this blocked portion of the light is represented by the rays R2 in dotted lines.

[0044] As shown in [Fig. 2], the mask 125 here comprises a thin layer of an opaque material, for example black in color. The mask 125 is for example formed by a layer of paint applied directly to the protective layer 123, which makes it particularly simple to produce. Of course, the mask 125 can be made of other materials, for example plastic.

[0045] As shown in [Fig. 2], the mask 125 covers the entire protective layer 123 except for its convex face 123B. However, the mask 125 may partially cover the convex face 123B of the protective layer 123 or, on the contrary, extend at a distance from the convex face 123B. The mask 125 acts here as a diaphragm limiting the quantity of light that can reach the photosensitive surface.

[0046] As shown in [Fig.2], the wall 126 extends between the photosensitive surface 110 and the protective layer 123. The wall 126 is made of an opaque material.

[0047] The wall 126 here has the shape of a hollow cylinder (two sides of which are facing each other and are visible in [Fig. 2]) with a square section. The wall 126 thus forms a conduit with a reduced section relative to the photosensitive surface 110, which makes it possible to channel the light towards the first part 110A of the photosensitive surface 110. Here, the wall 126 at least partially overhangs the second part 110B of the photosensitive surface 110.

[0048] The present invention is in no way limited to the embodiment described and shown, but those skilled in the art will be able to provide any variant in accordance with the invention.

[0049] For example, when the image capture device comprises infrared pixels and color pixels, for example when it is an RGB-IR camera, some of the filters can selectively transmit wavelength ranges corresponding to visible light, for example red, green and blue.

[0050] The lens could be an element added to the protective layer.

[0051] The mask could in contact with the protective layer on the side of the flat face of the protective layer. The mask could, for example, be placed between the protective layer and the filter.

[0052] The wall may have any shape suitable for at least partially hiding the second part of the photosensitive surface. The wall may have a variable height between the photosensitive surface and the protective layer. It may, for example, extend to the photosensitive block. It may have sections of different shapes, for example a circular section. It may also comprise several sub-walls distinct from one another. As a further variant, the collection means may not comprise a wall.

Claims

Claims

1. Image capture device (1) comprising an array (10) of photosensitive elements (100), each photosensitive element (100) comprising a photosensitive surface (110) and light collecting means (120), arranged on the photosensitive surface (110), arranged to convey light coming from an external scene onto the photosensitive surface (110), at least one of the photosensitive elements (100) being sensitive to a given wavelength range of the infrared domain, characterized in that the collecting means (120) of said photosensitive element (100) are shaped to convey the light onto only a portion (110A) of the photosensitive surface (110) of said photosensitive element (100).

2. An image capturing device (1) according to claim 1, wherein said collecting means (120) of said photosensitive element (100) are shaped to convey light over less than 80% of the photosensitive surface (110) of said photosensitive element (100).

3. An image capturing device (1) according to claim 1 or 2, wherein said collecting means (120) of said photosensitive element (100) are shaped to convey light over less than 65% of the photosensitive surface (110) of said photosensitive element (100).

4. An image capturing device (1) according to one of claims 1 to 3, wherein said collecting means (120) of said photosensitive element (100) are shaped to convey light over less than 50% of the photosensitive surface (110) of said photosensitive element (100).

5. An image capturing device (1) according to one of claims 1 to 4, wherein said collecting means (120) of said photosensitive element (100) comprises a lens (124) arranged opposite the photosensitive surface (110) of said photosensitive element (100), the lens (124) having a shape designed to converge the light only on said portion (110A).

6. An image capturing device (1) according to claim 5, wherein the lens (124) has a size smaller than that of the photosensitive surface (110) of said photosensitive element (100).

7. An image capturing device (1) according to one of claims 1 to 6, wherein said collecting means (120) of said photosensitive element (100) comprises a light blocking element disposed opposite a periphery of the photosensitive surface (110) of said photosensitive element (100).

8. An image capturing device (1) according to claim 7, wherein the blocking element comprises at least one of: a mask (125) in contact with an outer layer (123) of said photosensitive element (100) and; a wall (126) extending between the photosensitive surface (110) of said photosensitive element (100) and the outer layer (123) of said photosensitive element (100).

9. An image capturing device (1) according to one of claims 1 to 8, wherein said photosensitive element (100) is sensitive only to a wavelength range between 900 nm and 980 nm.

10. Monitoring system (3) for a driver of a motor vehicle comprising an image capture device (1) according to one of claims 1 to 9 and an infrared light source (2).

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