WO2006067005A1

WO2006067005A1 - Device and method for influencing incident light on an image sensor

Info

Publication number: WO2006067005A1
Application number: PCT/EP2005/056067
Authority: WO
Inventors: Marc Giordani; Eladio Lopez; Dominique Marchal; Vincent Thominet
Original assignee: Robert Bosch Gmbh
Priority date: 2004-12-20
Filing date: 2005-11-18
Publication date: 2006-06-29
Also published as: DE102004061334A1

Abstract

The invention relates to a device and to a method which influences incident light on an image sensor (10), in particular in a motor vehicle. According to the invention, a camera and a controllable element (14) which is made of at least one cell having controllable, variable light transmission, are provided. Said element (14) is controlled in such a manner that super and/or overexposed image regions are attenuated.

Description

Device and method for influencing the incident on an image sensor

light

State of the art

The invention relates to a device and a method for influencing the light incident on an image sensor, in particular in conjunction with a camera system for motor vehicles.

Many applications use camera systems that capture images of an environment. From the recorded images are then derived, for example by means of image analysis reactions or the recorded image sequences stored. Particular fields of application are in the field of motor vehicles driver assistance systems or outside of the vehicle application video surveillance systems. An important aspect of such systems is that the images taken by the camera under different conditions such as

Daylight, at night or twilight or under special weather conditions must have sufficient quality for the application, in particular be evaluated. Of particular importance are measures that protect the camera from glare, overexposure, etc. This is especially true in connection with driver assistance systems for motor vehicles, in which glare can occur more frequently due to solar radiation and / or reflections.

The cameras used in the above applications typically include a lens and an image sensor and, as stated above, must be able to produce an image more adequate for the application To deliver quality under all conditions essential for the application. In particular, this also applies to glare or serious disturbances in the image, for example by direct view of the camera in the sun, glare from oncoming vehicles or reflections of vehicle lights on wet roads, etc. Characteristic of these situations is that the entire image or a

Part of it is overexposed, while in the case of overexposed portions of the image, other parts of the image are dark. In order to achieve images that can also be evaluated in the abovementioned situations, it must be possible to provide evaluable information in both low and bright illumination conditions. This results in the requirement for the camera system, a high dynamic

Cover exposure range, to avoid saturation of the pixels of the image sensor and to prevent interference of adjacent pixels.

From WO 99/62732 Al it is known to suppress blinding of the driver by means of darkenable areas on the windshield of a vehicle.

Advantages of the invention

By attaching at least one element with controllable light transmission in the detection range of the image sensor is advantageously a dynamic

Reducing the illumination or exposure of the sensor always provided when this reduction is necessary.

It is particularly advantageous that this can also be done with partial images, so that a reduction of the illumination or exposure intensity takes place only in the actually affected area of the image.

The use of electrically controllable elements with variable light transmission results in favorable installation conditions, so that no additional space is required. Furthermore, can be by the known elements a

Realize mass production with reasonable costs.

Further advantages will become apparent from the following description of exemplary embodiments or from the dependent claims. drawing

The invention is explained below with reference to the embodiments illustrated in the drawings. FIG. 1 shows a basic flow diagram for controlling a variable light transmission element in conjunction with a camera system. In the figures 2 to 6 different embodiments for the installation of a variable light transmission element are shown.

Figures 7 to 10 show various embodiments regarding the design of the element's controllable cell allocation and sensor areas (e.g., pixels) of the element

Image sensor.

Description of exemplary embodiments

In order to optimally exploit the sensitivity of the image sensor installed in the camera, it is necessary to find a way by which the incident light from overexposed areas of a recorded scene is dynamically, i. continuously or discretely changeable, can be limited. The basic idea is to fulfill this requirement by introducing elements with controllable light transmission into the optical path of the camera. Such controllable elements with variable

Translucency depending on an applied control signal are also known in the form of arrays consisting of several individually controllable cells. For example, for this purpose LCD elements, electrochromic elements (ECD) or suspended particles (SPD), which are defined when voltage is applied, are used.

In order to meet the above requirements, one or more of such elements, which constitute a set of individual variable light transmissive cells, at one or more selected locations suitable for achieving the camera's anti-glare protection, are placed in the optical Path introduced in front of the image sensor. The position and the size of the cells or the cell arrays is determined in such a way that the entire image area or the image area required for the corresponding application is covered. The position of the element (hereinafter also called VLT element (VLT = variable light transmission)) is in the optical path between the image sensor of the observed - A -

Scene. In a preferred embodiment, the element with variable light transmission is designed such that each pixel of the image sensor is associated with one or more cells of the controllable element with variable light transmission. In another advantageous embodiment, a cell is associated with multiple pixels, with multiple cells needed for the entire relevant image. During the

By operating the camera system, the translucency of the elements is dynamically adjusted, i. reduced if necessary to have no or only a few pixels of the image sensor that are in or near saturation. Depending on the technology used for the elements, the light transmittance may be continuous or only incrementally between a maximum and a minimum

Permeability level can be varied. For elements that can only assume two states, intermediate states, i. Conditions with a light transmission between the two extreme values realized by an arrangement of smaller cells is used. The number of cells in one or the other state results in the intermediate values for the

Translucency values of the cell cluster.

FIG. 1 shows a schematic representation of a block diagram with a flow chart, on which the basic procedure is illustrated. FIG. 1 shows the sensor 10 of a camera system as well as the optical light incidence path 12. Furthermore, an element 14 is provided which consists of at least one cell with controllable light transmission. This element 14 is inserted in the optical path 12 between the scene taken by the sensor and the sensor itself. The sensor is in the preferred embodiment part of a camera system for use in motor vehicles. The automatic control of the element 14 is carried out by a

Control system 16. This consists essentially of the modules Image Capture 18, Image Analysis 20 and Control 22. The process performed in the control system 16 is as follows. The image acquisition module 18 supplies image data of the sensor to the image analysis module 20 at a selected data rate, or in a predetermined image clock cycle. The maximum rate or the maximum clock depends on the used

Sensor technology, for example, whether the sensor is a CCD sensor or a CMOS sensor, and the possibly necessary integration time until the completion of the image acquisition. The image analysis module 20 includes an algorithm that computes a desired light transmittance of the corresponding controllable cell (s) for the acquired image transmitted by the acquisition module 18 or for subregions of the image associated with a corresponding cell or cells of the element 14 , This is preferably done by having a

Gray value distribution of the image or of partial areas of the image is determined. Thereupon, the center of gravity (or mean value) of this gray value distribution is determined and compared with a predetermined desired value. The deviation of the gray scale centroid from the desired value is then e.g. by means of a table in which the deviation is assigned to a value, into a control value for

Actuation of the corresponding cell (s) of the element 14 implemented. The desired value of the gray value distribution can also be dependent on the time of day and / or the global light conditions. It must also be considered that a certain amount of time elapses in the element 14 to achieve the desired light transmission values. This time constant, which depends mainly on the technology used for the element 14, is to be considered in the design of the control circuit shown in FIG. For color images, proceed according to the procedure described above.

The control value determined from the described manner, in the case of an element 14 consisting of several controllable cells, together with a value for the cells to be controlled (for example coordinate values), is fed to the control module 22. This converts the supplied value into corresponding drive signals for the affected cell (s).

Depending on the version, the element 14 consists of one or several, individually controllable cells with variable light transmission. Depending on the design, these cells are arranged, for example, in a rectangular array, ie in a matrix with identical or different rectangular cells, or in a type of honeycomb array, ie a matrix of identical hexagonal cells. The arrangement of the cells takes place in such a way that the selected areas of the image or the image sensor are covered, in particular an assignment of cells to one or more pixels of the image sensor. Another division of the cell array of the element 14 is also possible. Figures 2 to 6 show various configurations of an image acquisition system in a motor vehicle using a camera and an element of controllable light transmission consisting of one or more cells.

In this case, two main configurations are distinguished, namely a first, in which the

Element 14 is not part of the camera arrangement, and a second, in which the element 14 is part of the camera arrangement itself.

FIG. 2 shows a first exemplary embodiment. Shown is a windshield 24. Behind this windshield 24, a camera 26 is arranged, which essentially comprises a diaphragm 28, a lens 30 and an image sensor 32. Light 34 falls through the windshield 24 onto the camera aperture 28 and is imaged on the image sensor 32 in the camera via an objective 30. The image sensor 32, such as a CMOS image sensor, has a plurality of pixels that are excited by the incident light to produce image information. The image acquired in this way is then further processed as shown in FIG. Furthermore, in FIG. 2, directly in front of the image sensor, in one embodiment applied to the image sensor, a controllable element 36 is provided, which consists of one or more controllable cells. These cells are individually controlled and change their light transmission when activated. In this illustrated embodiment, the light transmitting element 36 is disposed inside the camera 26 in a plane immediately in front of the image sensor mounted at a focal point of the lens 30. In this configuration, in one embodiment, the variable light transmittance element is configured such that the light incident on each pixel of the image sensor can be affected by the corresponding upstream cell of the controllable light transmittance element. In the event that the cell boundaries of the element do not correspond exactly to the boundaries of the pixels, the light striking a pixel is affected by several associated cells.

FIGS. 8 to 10 show exemplary embodiments for the assignment of the cells of FIG

Elements with controllable light transmission and the pixels of the image sensor.

FIG. 8 shows a configuration in which the dimensions of the cells 36a of the variable light transmittance element (VLT cells) are identical to those of FIGS Sensor pixels 32a are. This results in a 1: 1 assignment of the cells to the pixels, which allows to control the incident light individually for each pixel.

FIG. 9 shows an embodiment in which the VLT cell dimensions are larger than those of the sensor pixels. In this case, there is an I: n assignment of the cells 36a (gray, white) to the pixels 32a. This controls the incident light for a cluster of neighboring pixels.

Another embodiment is shown in FIG. 10. In this embodiment, the cells of the VLT element 36 are arranged so that a specific distribution of the exposure fields is achieved. In this case, each VLT cell 36a (gray, white, dashed) allows controlling the incident light for a particular area of the sensor corresponding to a variable cluster of adjacent pixels 32a.

FIG. 3 shows a further exemplary embodiment for the arrangement of the element with controllable light transmission. In the embodiment of Figure 3, this element is still part of the camera assembly and is installed in the beam path. Figure 3 shows the incident light 34, which falls over the windshield 24 of the vehicle on the aperture 28 of the camera 26. There, the light is focused on the objective 30 and imaged on the image sensor 32 via an additional lens 38. The

VLT element 36 is arranged in the focal plane of the objective 30 and the lens 38. The additional lens 38 serves to construct an intermediate image of the image sensor plane in the focal plane of the camera lens. The arrangement of the VLT element 36 in this place has the advantage over the arrangement in Figure 2 of a higher expediency, in particular of a favorable construction. In this case, the same functionality as described in the embodiment of Figure 2 is achieved.

A further arrangement of the VLT element is shown in the exemplary embodiment of FIG. 4. Here too, light 34 is incident on the windshield of the vehicle 24 on the aperture 28 of a camera 26. The camera consists essentially of lens 30 and sensor element 32, as already illustrated with reference to FIG In this configuration, the VLT element 36 is arranged in the region of the aperture of the camera 26, preferably applied to the diaphragm (outside or inside). This makes it possible to modify the Lihttransmission locally in each point of the aperture. This affects the amount of light that reaches each sensor pixel. In this embodiment, by means of a single VLT cell covering the entire aperture and thus achieving control of the global exposure of the sensor. In another embodiment, multiple VLT cells are used to achieve variable aperture transmittance (so-called apodization, ie, enhancement of the resolving power of an optical layer through an absorbing layer in the entrance aperture). This allows a corresponding spatial filter effect to achieve, for example, improvements in image contrast.

In general, when arranging the VLT element 36 in the light path, it must be noted that the spatial filtering of the resulting image occurs as soon as the VLT element

Element 36 is not in the image, i. Sensor level or an optical conjugate plane is arranged.

Another embodiment for mounting the VLT element is shown in FIG. 5. In this case, the VLT element 36 is mounted on the inside of the windshield 24 of the vehicle, e.g. glued. The other elements correspond to the elements which have already been described with reference to FIG. In the exemplary embodiment illustrated in FIG. 5, the camera is arranged, for example, behind the rearview mirror on the windshield. In another embodiment, the camera is behind another pane of the vehicle, e.g. Rear window, side window, etc. Also in this case, it may be advantageous to attach the VLT element 36 to the inner surface of the window as shown in FIG.

Figure 6 shows a further embodiment in which the VLT element 36 in the windshield 24 of the motor vehicle (or in another disc of

Motor vehicle) is integrated.

In these configurations, it is achieved that the light incident on the associated sensor pixel is affected by a change in the transmissivity of the selected VLT cell. However, it should be noted that because of the overlap of the

Light rays that are incident on adjacent pixels, an attenuation of the exposure for a pixel or area of pixels partially affects the neighboring pixels or the neighboring areas. In this way, an influencing zone of the VLT cell 36 is formed in the sensor. FIG. 7 clarifies this. It shows an incident light beam 45 which is attenuated by a selected VLT cell 47 of the VLT element 36 which is mounted on the windshield 24. This light beam is imaged on the sensor 32 via the lens 30 of the camera. The associated pixel 49 detects less light according to the attenuation, but neighboring pixels are affected by the overlap of

Light rays also affected. This results in an influencing zone 50 on the sensor whose exposure is attenuated by the control of a VLT cell.

In another, not shown in the figures embodiment, the camera within a headlight or a tail light, for example, behind the outer lens, installed. In this case, the VLT element is integrated on the inside of the lens or in the lens itself. This configuration is analogous to that discussed above with reference to FIGS. 5 and 6.

As possible technologies for the VLT element will depend on the design and

Application field LCD elements, electrochromic elements (ECD) or elements with suspended matter, so-called Suspended Partical Devices (SPD) used. Criteria for selection are the range within which the light transmission can be varied, the resolution and dimensions of the VLT array and the dynamic properties of the element, such as the switching speed.

Claims

claims

1. A device for influencing the incident on an image sensor light, in particular in a motor vehicle, with an image sensor (32) and with an element (36) with controllable light transmission, characterized in that the element (36) is arranged such that on impinging the image sensor (32)

Light is at least partially attenuable.

2. Apparatus according to claim 1, characterized in that the element (36) consists of a plurality of cells which are individually controllable, and which are associated with one or more image sensor pixels.

3. Device according to one of the preceding claims, characterized in that the element (36) is mounted directly in front of the image sensor (32) and is applied thereto.

4. Device according to one of the preceding claims, characterized in that the image sensor (32) is part of a camera (26) and the element (36) is mounted in the beam path of the camera after the lens and in front of the sensor in a focal plane of the lens.

5. Apparatus according to claim 4, characterized in that an additional lens (38) is provided, which images an intermediate image on the image sensor (32) and in the plane of which the element (36) is arranged.

6. Device according to one of the preceding claims, characterized in that the element (36) is arranged in the region of the outer panel of the camera.

7. Device according to one of the preceding claims, characterized in that the camera (26) behind a disc or a lens, in particular the

Windscreen or a vehicle headlamp, wherein the element (36) is attached to the inside of the disc or lens or is integrated in the disc or lens.

8. Device according to one of the preceding claims, characterized in that the cells of the element (36) are designed such that a 1: 1 assignment of the cells and the image sensor pixels takes place, or that a l: n assignment takes place or that the cells selectable Regions of the image sensor (32) are assigned.

9. Device according to one of the preceding claims, characterized in that an image analysis module (20) is provided which on the basis of the image sensor (32) detected image generates control signals for the controllable element (14) with variable light transmission, such that a Overexposure or excessive exposure is avoided.

10. A method for influencing the light impinging on an image sensor, in particular in a motor vehicle, wherein an image sensor (32) takes a picture of a scene in front of him and wherein an element (14, 36), which consists of at least one cell with a controllable, variable light transmission is controlled, characterized in that by means of analysis of the

Image sensor (32) recorded image is determined whether at least one image area is too high or overexposed and wherein a control signal for the controllable element (14, 36) is generated when such an area was detected, such that the exposure of at least this area is reduced.