WO2007048929A1

WO2007048929A1 - Antiglare equipment and surveillance camera equipped with same

Info

Publication number: WO2007048929A1
Application number: PCT/FR2006/002402
Authority: WO
Inventors: David Batte; Karine Sophie Lepage; Olivier Descoubes; Jean-Loup Chretien
Original assignee: Tietronix Optics
Priority date: 2005-10-25
Filing date: 2006-10-25
Publication date: 2007-05-03
Also published as: EP1941305A1; FR2892588A1; FR2892588B3

Abstract

The invention concerns an antiglare equipment for a surveillance camera and a method for using such an equipment. It comprises image sensing means for controlling computing means, located proximate an active filter including an LCD screen and pointing in the same direction, the computing means being designed to compensate for parallax between the sensor and an input lens, and to control the darkening of the dazzling parts of said image. An output lens designed to form with the filter and the input lens an afocal system, with adjusting means of the order of 20 micrometers, is provided, the active filter being formed by superimposing mutually secured layers, including a first polarizer, a first protective binding layer, the LCD screen, a second protective binding layer and a second polarizer.

Description

ANTI-GLARE EQUIPMENT AND MONITORING CAMERA EQUIPPED WITH SUCH EQUIPMENT

The present invention relates to an anti-glare equipment and a camera provided with such an equipment of the type comprising an active filter (LCD), placed in the focal plane of an input objective, and having a filtering image controlled by a computer connected to a camera sensor placed in the vicinity of the active filter and pointing towards the same direction, said image having masking areas obscuring the dazzle areas.

It also relates to a method implementing such equipment.

It finds a particularly important application although not exclusive in the field of surveillance in punctually or accidentally very dazzling environment, with rapid deployment of the source, such as that of a rocket pad, or a track of jet aircraft, or to read license plates between headlights of burning cars.

Surveillance cameras are already known using an active filter or LCD modulator to overcome the most dazzling parts of an image.

Such cameras, however, have disadvantages. Indeed, they generally comprise optical devices that need to detect the parts saturated with the same lenses as those that will allow the image to be recovered _, to be processed for the active filter. If in this way, there is no risk of parallax effect and / or offset between filter and dazzled image, however, there are losses in brightness of the rest of the image in case of derivation of a portion of the light received by the lenses.

Attenuating devices are also known for masking the dazzling areas by screens optically placed in front of the image sensor and controlled by it.

Such devices, however, have a high degree of instability because of the loop-shaped optical array servocontrol which generates unacceptable oscillations if a correct response time is desired.

The present invention aims to overcome these disadvantages, by providing an equipment, a camera and an anti-glare process better than those previously known to the requirements of the practice, particularly in that it will allow a high opto-mechanical consistency between image and masking screen, even in case of strong glare, with optimized response time and little loss of information.

To do this, it combines a specific optical filter part, a high precision mechanical positioning, an eccentric sensor and calculation means arranged to control the obscuration of the screen so as to mask the dazzling images arranged to compensate for the parallax between eccentric sensor and input objective of the image to be processed.

This combination surprisingly allows a result particularly suitable for the detection of the immediate environment of the dazzling area, including when the latter is in motion or in strong acceleration, for example at speeds greater than 5m / s, or at accelerations greater than 2g, for a field of view of 40 ° .

For this purpose, the present invention essentially provides anti-glare equipment for a surveillance camera of a zone comprising an active filter comprising a liquid crystal type screen (LCD) placed in the focal plane of an entrance lens. an image of said zone, and computing means for controlling the obscuration of the screen so as to mask the dazzling portions of said image, characterized in that it comprises image sensor means adapted to control said computing means, placed in the vicinity of the active filter and pointing in the same direction, the computing means being arranged to compensate for the parallax between the sensor and the input lens, an output lens arranged to form with the filter and the objective of input an afocal system, said afocal system comprising means for adjusting the relative position of the objectives and the filter with an accuracy of less than about 20 micron s, and in that the active filter is formed of a superposition of layers joined together, comprising a first polarizer, a first protective bonding layer, the LCD type screen, a second protective bonding layer and a second polarizer. In advantageous embodiments, one and / or the other of the following provisions is also used:

- the afocal system is telecentric symmetry;

- The active filter further comprises, on either side, a first and a second antireflection glass layers located respectively and with respect to the optical path in front of the first polarizer and behind the second polarizer;

- The layers are secured together irremovably;

the screen is an LCD, DMD or MEMS screen whose cells are programmed according to a filtration algorithm Gi = f (Yi + k), arranged to block dazzling sources with a black level on said dazzling sources and to apply levels progressive gray around the source (s) to obtain a progressively attenuated image; the filtration algorithm is arranged to form a pixel blocking screen from a pre-established correspondence table stored in a memory of the computer.

The invention also provides a digital or analog surveillance camera equipped with equipment as described above.

It also proposes a method implementing the equipment and / or the camera described above.

The invention also proposes a method for producing an image on the sensor of a surveillance camera equipped with anti-glare equipment comprising an active filter comprising a liquid crystal screen (LCD) placed in the plane focal point of an input lens, characterized in that it comprises the following steps: the area or zones of saturated pixels are identified in the event of the image being dazzled by a first sensor placed in the vicinity of the active filter and pointing in the same direction, a filter matrix arranged to conceal the dazzling parts of said image is developed from calculations controlled by said first sensor so as to obtain said visible image on the sensor of the surveillance camera by compensating the parallax, the image being sensed by an optical path comprising an output lens arranged to form with the filter and an input lens an afocal system, the relative position of the lenses and the filter being made with a precision lower than in the order of 20 micron meter, and the active filter being formed of a superposition of layers joined together, comprising a first polarizer, a first bonding layer prote the LCD type screen, a second protective bonding layer and a second polarizer.

Advantageously, the filter matrix is developed according to a filtration algorithm Gi = f (Yi + k).

Also advantageously, the filter matrix is developed from a pre-established correspondence table stored in the computer's memory.

In another advantageous embodiment, the afocal system is telecentric symmetry and / or the layers of the filter are secured to one another immovably. The invention will be better understood on reading the following description of the embodiments given as non-limiting examples. The description refers to the accompanying drawings in which:

- Figure 1 shows a block diagram of the present invention.

FIGS. 2 and 3 illustrate examples of filtration curves obtained with a sensor and an LCD screen belonging to equipment according to the embodiment of the invention more particularly described here.

FIG. 4 gives, in section, an embodiment of the filter comprising an LCD liquid crystal screen according to the invention.

FIG. 5 represents an exemplary mounting of the polarizers according to one embodiment of the invention.

FIGS. 6, 7, 8 schematically show exemplary embodiments of the telecentric telecentric symmetrical camera system (FIG. 6) with telecentric non-symmetrical system (FIG. 7) (FIG. 8) for selective filtering according to embodiments of the invention.

- Figure 9 shows is a sectional view of an embodiment of the camera according to the invention.

FIG. 10 is an ellatized perspective view of an embodiment of an anti-glare equipment according to the invention.

Figure 1 shows an anti-glare equipment for camera 2 for monitoring an area in which there are objects 4 causing dazzling light. The equipment 1 comprises an active filter 5 comprising a liquid crystal screen 6 (LCD) placed in the focal plane (mixed line) 7 of an objective or optical input system 8 of an image of said zone 3 and objects 4 that it contains.

The equipment 1 further comprises sensor means 9 for example belonging to a small camera 10 provided with an optical system 11 input recovering the image of the zone 3 and objects 4, with a slight parallax due to the angle between light rays 12 which pass through the direction 13 of the rays attacking the main entry objective 8. The sensor means 9 are for example a charge coupled sensor (CCD) or CMOS type. This sensor is connected to a computer 14 programmed to compensate for the parallax and with a sufficient accuracy to, once homoté translation correction performed as described below through a simple algorithm calculation, allow the desired filtering.

More precisely, the parallax existing between the optical system 8 of the active filter 5 and the optical system 11 of the camera, implies an offset of the image seen by these systems, for an object 4 placed at a distance d. This offset is corrected by the calculator 14.

In the embodiment more particularly described here, by way of nonlimiting example, the computer performs the following functions:

- Modification of the image received by the camera, so that it is virtually perfectly superimposed on the image seen by the optical system of the active filter. calculation of the filtering image Gi (for each pixel i of the LCD screen) as a function of the luminance Yi + k of the pixels i read by the camera; this calculation can be of one of the following types:

• Gi≈f (Yi + k with O <_ k <, 4 which will be detailed below and which is a function of the luminosity of the pixels;

• LUT (correspondence table);

• Threshold: if Yi + k> Threshold 1, then Gi ≈ 0 (blocking); if Yi + k <Threshold 2, then Gi - 1 (passing).

By way of indication, an embodiment of the electronics of the computer 14 is now described below. This is for example composed of the following elements:

- A Power Supply Board, providing the necessary voltages to the Process Board (1.5V, 1.8V, 3.3V, 5V, 15V), from an external power supply that can vary from 9V to 24V.

Said Process Card which performs the following functions:

• acquisition of small camera images

• storing these images in RAM

• calculation of the masking image for the LCD screen, and generation of the signals necessary for its operation,

• memorization of user-defined parameters,

System management for example via RS232 interface,

• Programming of the calculator itself by external specific interface. - An interface circuit (not shown) with an external electronic system (computer).

The computer 14 is for example integrated in the same housing as the objective and the sensor of the camera 10, which integrates the sensor 9 (CCD, CMOS ...) itself connected to the process card.

We will now describe below the software functions of the process map according to the embodiment of the invention more particularly envisaged.

Basic functions

The basic functionality is to generate an image on the LCD 6, by applying black pixels to places of high intensity light sources (dazzling sources).

To do this, the computer 14 must sequentially:

1) Acquire the image from the small camera 10, the latter being placed in an optical axis 12 close to that 13 of the LCD 6. This image comprises for example 640 horizontal pixels 480 lines.

2) Store this image in memory known as SDRAM, in order to overcome any problem of asynchrony between the small camera 10.

3) Apply a filter function Gi, for each pixel of the screen of the LCD, function of each pixel Yi + k received, with 0 ^ k <_ 4 is Gi = f

(Yi + k), .Gi and Yi + k are here coded on 8 bits (256 levels).

This filtering function responds to all glare situations, blocking sources with a black level on the LCD screen, and applying "gray levels" around the source, in order to obtain a gradually attenuated image.

The algorithm used is here and for example a linear function directly proportional to the distance between the dazzled central pixel (s) which are completely obscured, and the pixel just about to be saturated, which is then attenuated linearly.

In other words, by further describing the function G, it refers to lines 2 and 3.

More precisely, and with reference to FIGS. 2 and 3, two embodiments of Gi function have been described.

It will be recalled first of all that, in the invention, each pixel i of the modulator (active filter 6, for example an LCD screen) is controlled individually by the computer 14.

Each pixel of the modulator is further characterized by:

its location in the filter: P (x, y), x being the row of pixels and y the column of pixels its transmission Gi: ratio between the luminous intensity received by the pixel and the light intensity transmitted or reflected by the pixel.

As we have seen, for each pixel, the transmission Gi is variable (from 0 to 1) and is defined by the computer according to the information received from the sensor.

This variable transmission makes it possible to obtain differential treatment, pixel by pixel, of the light sources according to their position or their intensity. This variable attenuation of the filter makes it possible to define the notion of Levels of Gray. A dazzling source is more or less attenuated by the modulator: totally attenuated (Black Level): a black task hides the dazzling source considered - not attenuated (White Level) partially attenuated (Gray Level): a gray and partially transparent task masks the source dazzling considered

This function (see above) can thus notably be of the type:

"linear

"logarithmic

"l / x

"LUT correspondence table

"At threshold, if Ni> Threshold 1, then Gi ≈ 1 (blocking), if Ni <Threshold 2, then G = O (passing)

In the case of a linear distribution (see Figure 2) the formula of these filters is the following: y = ENT [(ax + b)] with a = - (Ymax-Ymin) / Xtnax-Xmin b = Xmax + Ymax - Ymin xXmin Xmax - Xmin

Thus, for example, for an LCD (Ymax, Ymin) and a sensor ((Xmax, Xmin), respectively of value (220, 140) and (229, 22), it comes y≈ENTC- (220-140) / (229- ^λ 22 ') * x + 220 + (220-140) / (229- ^Λ 22') * ^Λ 22 ') The Xmin value in this formula is actually to be adapted for each interval

FIG. 2 shows on the abscissa the gray level of the sensor and on the ordinate the gray level of the LCD screen.

For the above values, the following gray-scale curve is shown at 20.

Another curve for a sensor sensitivity (Xmin) of 150 (instead of 22) is shown at 21.

A second nonlimiting example is also given with reference to FIG. 3. Here, it is a stepped algorithm that makes it possible to calculate the gray levels.

FIG. 3 shows the operation of a three-stage filter in the dynamics 160 and 200 (curve 22) of the gray levels of LCD for a dynamic sensor between 229 and 100. Advantageously, this filter can be smoothed (see FIG. curve 23).

This kind of step filter makes it possible to see the impact of the dynamics between gray levels between sensor and LCD.

4) Modify the image of the camera so that the sizes of the two images on the LCD (image of the optical system of the active filter and image coming from the camera) are identical.

5) Transmit this final image to the driver of the LCD screen, and also generate the synchronization signals necessary for the LCD and its driver.

All these treatments are done in real time, except the phase shift created by the asynchrony between the small camera and the LCD screen. Additional functions

In addition to these functions, the calculator provides:

1) A management of camera parameters (via a bus) in reading and writing:

2) A function modifying the image.

3) A loading of the filter curve.

4) Activation of a grid on the LCD screen.

5) An LCD display of the transparent type White or Black.

6) A reference of the version of the code XXXXX: command V

7) A memorization of the previous parameters (except G, B, N) in an EEPROM memory, via the bus.

These parameters are read at each power up, and assigned to each corresponding variable, and to the small camera for small camera settings.

Optional features

Three optional functions are, for example, also implemented on the computer processor's process card 14.

1) Control of the temperature of the LCD (in PWM mode) from a sensor and a heating circuit.

2) Composite video input to use an external analog camera.

3) Composite video output to control an external analog monitor.

FIG. 4 is a sectional view of the active filter 5.

In this embodiment, it consists of a block 30 comprising four layers 31, 32, 33, 34 of glass known as Neoceram, and two polarisers 35 and 36 sandwiched between the glass layers, one with vertical polarization and the other with horizontal polarization (see Fig. 5), the liquid crystal screen LCD 6 being centrally located as shown in Figure 4.

All these elements are secured together for example by gluing by being embedded in racks 37 and 38, irremovably, or by simple pressure being compressed between two cleats (not shown).

To allow the assembly of Neoceram lenses and polarizers, these elements must be ground. In particular, if these elements are in raw section, it will then be necessary to cut them with dimensions greater than 1 mm in relation to those desired, so that they can then be honed to the correct dimensions.

The two outer lenses 33 and 34 made of Neoceram N-Q are, for example, anti-reflective on one side.

Note more generally that the polarizers must be assembled crossed so that the assembly, once assembled, is "passing".

The axes of the two polarizers (parallel to one of the sides of the polarizer) are positioned at 90 ° +/- 0.2 ° 1 'from each other.

Advantageously, the axis 39 of the polarizer of the input lens side must be parallel to the width

(ie vertical). The axis 40 of the second polarizer 36 of the output objective side must be parallel to the length (i.e. horizontal).

In the embodiment world more particularly described here, the total thickness of the assembled assembly does not exceed 4mm, for example between 2 mm and 3 mm.

The assembly made is then positioned (see FIG. 9) in the support 41 of the filter 42, the latter being adjustable in lateral positioning parallel to the axis 43 of the camera 44 with adjustment means 45, for example screwed , allowing a precision of 20 20 μm.

The assembly must be placed in the support so that the connectors 46 of the web 47 connecting the LCD screen with the electronic card Process 48 of the type described above, can be connected to said electronic cards.

The telecentric afocal system 50 and its input and output objectives 51 and 52 will now be more specifically described with reference to FIGS. 7 to 9.

FIG. 6 shows a schematic view of the afocal optical system 50 containing the selective filtering plane 53 and a lens 54 which makes it possible to image the scene on the retina 55 of the surveillance camera.

The exit pupil of the afocal 52 then coincides with the entrance pupil of the objective 54 (FIG. 6).

More precisely, the afocal system is broken down into a first objective imaging the scene on the selective filtering plane 53, (non-telecentric in FIG. 7 and telecentric on line 8) and a relay lens 52 returning the image to infinity. and allowing the pupillary conjugation (FIG. 8) between the entrance pupil 58 and the exit pupil 59.

More precisely, the proposed solution for the afocal system is, according to the embodiment of the invention more particularly described here telecentric symmetrical type, and this with reference to Figures 8, 9 and 10.

In this case, the entrance pupil 57 coincides with the object focal plane of the imaging objective or entry objective 51. The pupil is thus rejected to infinity in the intermediate space. And the exit pupil 58 is therefore in the plane of the image focus of the exit lens or relay lens 52.

Since the relay objectives 52 and the imager 51 are identical, the magnification is -1 or 1.

To achieve a magnification of 1, the image must be returned to the outside or inside of the afocal system, not exhaustively, using lenses, prisms or cubes polarization separators. To have a perfect symmetry, one must work to grow one.

But a slight dissymmetry is possible to work on other magnifications.

Thanks to the use of a symmetrical afocal system, for the Imager 51 and Relay 52 objectives, the longitudinal chromaticism, the spherical aberration, the astigmatism and the field curvature are particularly well corrected, even if they have a less correct correction. other aberrations.

Indeed, the quality of the final image is preferred to the quality of the image in the selective filtering plan.

The telecentric systems commonly existing are telecentric object systems (where magnification is insensitive to the position of the object), telecentric image systems (where magnification is insensitive to the position of image), and telecentric object-image systems. They are mainly used for measurement applications (in machine vision, for example).

Here, with telecentricity as more particularly sought after, it has become apparent that the absence of a field lens at the level of selective filtering plane and the use of atypical symmetry of the optical system for the correction of aberrations makes it possible to surprisingly better modulator performance (LCD, DMD ...), thanks to the low incidence of rays.

Remember that the "principle of symmetry" allows the compensation of the produced aberrations.

The disadvantage, however, is that it requires excellent accuracy of the relative positioning between the LCD screen and the input (imager) and output (relay) objectives.

In the case of telecentric symmetric afocal, the plane of symmetry

The anti-glare equipment 60 is now going according to one embodiment.

The equipment 60 comprises an ocular frame 61 on which the objectives 51 and 52 are adapted to be locked. The filter block 62, constituted as described with reference to FIG. 4, is then placed so that the LCD screen 53 is interposed with precision with respect to the central focal plane of the symmetrical telecentric optic less than 20. μm, thanks to a screw adjustment system 63 known in itself.

A housing 64 is fixed to the frame 61, by means of screws 65 and contains the small camera 66 comprising the optics 61 known per se and the process card 68 as described above, itself powered by the map 69.

A superior shield 70 of parallelepiped shape covers the whole

Note finally that the afocal "telecentric symmetry" of the invention is obtained a high field on the retina 55 and a small number of apertures of the optical system with good image quality.

In addition, it is economical because the imaging objectives 51 and relay 52 are identical.

As is obvious and as also follows from the above, the present invention is not limited to the embodiments more particularly described. On the contrary, it embraces all the variants and in particular those where anti-glare equipment and surveillance camera are integral with each other, in the same housing and / or in a demountable and releasable manner.

Claims

Anti-dazzle equipment for a surveillance camera of a zone comprising an active filter comprising a liquid crystal type screen (LCD) placed in the focal plane of an image entry objective of said zone, and calculation means for controlling the obscuration of the screen so as to mask the dazzling parts of said image, characterized in that it comprises image-sensing means adapted to control said calculation means, placed in the vicinity of the active filter and pointing in the same direction, the calculation means being arranged to compensate for the parallax between the sensor and the input lens, an output lens arranged to form with the filter and the input lens an afocal system , said afocal system comprising means for adjusting the relative position of the objectives and the filter with a precision of less than about 20 microns, and in that the active filter is formed of a superpower layer of interconnected layers comprising a first polarizer, a first protective bonding layer, the LCD type screen, a second protective bonding layer and a second polarizer.

2. Equipment according to claim 1, characterized in that the afocal system is telecentric symmetry.

3. Equipment according to any one of the preceding claims, characterized in that the active filter further comprises, on both sides, first and second antireflection glass layers located respectively and with respect to the optical path, in front of the first polarizer and behind the second polarizer.

4. Equipment according to any one of the preceding claims, characterized in that the layers are joined together irremovably.

5. Equipment according to any one of the preceding claims, characterized in that the screen is an LCD, DMD or MEMS whose cells are programmed according to a filtration algorithm Gi = f (Yi + k), arranged to block the dazzling sources with a black level on dazzling sources and apply gradual gray levels around the source to get a gradually dimmed image.

6. Equipment according to any one of claims 1 to 4, characterized in that the filtering algorithm is arranged to form a pixel blocking screen from a pre-established correspondence table stored in a memory of the computer.

7. Digital surveillance camera, characterized in that it is equipped with equipment according to any one of the preceding claims.

A method of generating an image on the sensor of a surveillance camera equipped with anti-glare equipment comprising an active filter comprising a liquid crystal type (LCD) screen placed in the focal plane of a goal input, characterized in that it comprises the following steps: the area or zones of saturated pixels are identified in the event of dazzling of the image by a first sensor, placed in the vicinity of the active filter and pointing in the same direction a filter matrix arranged to conceal the dazzling portions of said image from a computation controlled by said first sensor is produced in order to obtain said visible image on the sensor of the surveillance camera, and the image is captured by a path optical lens comprising an output lens arranged to form with the filter and an input lens an afocal system, the relative position of the lenses and the filter being made with a precision of less than about 20 microns, and the active filter being formed of a superposition of layers joined together, comprising a first polarizer, a first protective bonding layer, the LCD type screen, a second layer of e protective connection and a second polarizer.

9. Method according to claim 8, characterized in that the filter matrix is developed according to a filtration algorithm Gi = f (Yi + k).

10. The method of claim 9, characterized in that one develops the filter matrix from a preset correspondence table stored in a memory of the computer.

11. Method according to any one of claims 8 to 10 characterized in that the afocal system is telecentric symmetry.

12. Method according to any one of claims 8 to 11 characterized in that the different layers of the filter are joined together irremovably.