EP3365866A1

EP3365866A1 - System adapted for providing an operator with augmented visibility and associated method

Info

Publication number: EP3365866A1
Application number: EP16787785.1A
Authority: EP
Inventors: Etienne Payot; Jérôme ARTAUD
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2015-10-22
Filing date: 2016-10-21
Publication date: 2018-08-29
Also published as: FR3042882A1; FR3042882B1; CA3001668A1; WO2017068141A1; US20180300856A1; CN108369727A; IL258758A

Abstract

The invention relates to a system adapted for providing an operator with augmented visibility, useful in particular to aid aircraft piloting, comprising at least one sensor able to capture image data in a given spectral band and a central calculation unit able to process the image data captured and to transmit them to a display unit. This system comprises: - at least one high-resolution sensor (20) able to acquire image data forming a digital image (10) in a spectral band including at least all or part of the band visible to the human eye, of first spatial resolution, and of strictly finer angular capture resolution than the angular resolution of the human eye, and - a nonlinear processing module (22) adapted to produce a change in spatial resolution while preserving bright points of said digital image acquired (10) so as to obtain a digital image (h) to be displayed of second spatial resolution which is lower than the first spatial resolution.

Description

System adapted to provide an operator with increased visibility and associated method

The present invention relates to a system adapted to provide an operator with increased visibility, which can be used in particular for assisting aircraft control, as well as an associated method.

The invention is in the field of augmented vision systems (EVS), which are imaging systems intended to provide an operator with an image of the environment improved by compared to a human perception, this image can be presented through a display head up (or HUD for "head-up display" in English) or on a display screen (display called "head down").

These EVS systems have applications in particular in the field of aircraft piloting assistance, especially in the approach and landing phase, but also taxiing and takeoff, in case of low visibility due to environmental conditions and / or degraded weather.

Indeed, in the aeronautical field, it is usual to mark the runways of landing / landing of the airports thanks to markings, in particular light markings, as for example the approach ramp, the luminous markings of edge and center of track .

In order to guarantee safety in the field of air transport, there are regulations imposing a given runway visual range to engage a landing approach for example. Runaway Visual Range (RVR) is defined as the distance up to which an aircraft pilot, placed in the centreline of the runway, can see by his natural vision the marks or the lights which delimit the track or which mark the axis of this one. The RVR is generally evaluated by an automatic calculation integrating the instrumental measurements relating to the transmission coefficient of the atmosphere and the background luminance and information on the intensity of the lighting. For example, for a so-called CAT 1 for Category 1 approach, the regulation imposes a minimum RVR value of 550 meters to initiate an approach, other requirements have to be met otherwise, and the regulation allows to descend to a decision height (DH) at least 200ft (200ft), the height at which the pilot must discern visual references to descend below the DH decision height. Such a visual range is difficult to obtain in certain degraded meteorological conditions which can make the lighting markings undetectable by the pilot at the decision height DH. EVS systems have been designed, in particular to remedy this problem and improve the natural vision of flight crews and extend landing capabilities in conditions of degraded visibility. The regulation allows, in the example cited above, to go down to 10Oft if the necessary visual references could be discerned by the pilot at 200ft with the help of an EVS and even if this is not the case. not discernible by the human eye.

EVS systems are currently known comprising image sensors in the infrared spectral band using the spectral bands of 3 to 5μηι or 8 to 14 μηι and in the spectral band SWIR for "Short Wave Infra Red" of signals electromagnetic wave which extends from 1 μηι to 2.5μηι. The purpose of using sensors in the SWIR spectral band is to optimize the detection capabilities of incandescent lamps commonly used to mark tracks.

However, recent lighting uses new light emitting diode (LED) lighting techniques, which have no emission beyond a wavelength of 1 μηι.

The patent application WO 2009/128065 A1 describes an EVS system comprising a plurality of sensors able to operate in various spectral bands, comprising the NIR spectral band for "Near Infra-Red" of electromagnetic signals of wavelength extending from 0.7μηι at 1 .0μηι, and the spectral band of visible light which extends from 0.4μηι to 0.7μηι. This system mergers the image data acquired by the different sensors. The spectral bands to be fused are selected according to the previously identified meteorological conditions and the nature of the light markings to be detected.

However, in addition to its computational complexity and its high manufacturing cost, such a system has performance limited to the performance of the best spectral bands present in the equipment. In addition, it is not possible to predict the system performance, ie the gain in visibility relative to the human eye, because this gain varies depending on the weather and atmospheric conditions, the luminance background and intensity of light markings. Therefore, it is not easy, with such a system, to predict whether for a given RVR value, the system will achieve the performance required to initiate and complete the landing.

In the following, the angular resolution is defined as being the elementary field of view of a pixel of an image sensor detector. It is generally considered that the angular resolution of the human eye is about 0.8 arc minutes, or 0.0135 ° (or 0.00029 radians). Likewise in what follows, a high spatial resolution will designate a fine angular resolution, thus a small resolution angle / field of view. The object of the invention is to overcome the disadvantages of the prior art mentioned above.

For this purpose, the invention proposes, according to a first aspect, a system adapted to provide an operator with increased visibility, intended for the purpose of piloting an aircraft, comprising at least one sensor capable of acquiring image data. in a given spectral band and a central processing unit able to process the acquired image data and to transmit the processed image data for displaying a digital image on a display unit.

This system comprises:

at least one high-resolution sensor capable of acquiring image data forming a digital image in a spectral band including at least all or part of the spectral band corresponding to the electromagnetic signals visible to the human eye, of first spatial resolution, and angular resolution of capture strictly finer than the angular resolution of the human eye, and

- A non-linear processing module adapted to achieve a spatial resolution change while preserving bright spots of said acquired digital image to obtain a digital image to display second spatial resolution less than the first spatial resolution.

Advantageously, the system of the invention is an EVS system using at least one sensor (orientable or fixed) of very fine angular resolution and significantly better than that of the eye in the visible spectral band, which allows:

• to have significantly improved range of detection of lighting markings compared to the eye,

• to be adapted to LED lighting,

• to be able to quantify its performance in relation to the visual range of the human eye, regardless of any variation in weather and atmospheric conditions.

In addition, the proposed system is less expensive in hardware and requires less computational resources than a system based on sensors adapted to operate in several different spectral bands.

The system according to the invention may have one or more of the following characteristics, taken independently or in all their technically acceptable combinations.

Each digital image is defined by a matrix of pixels, each pixel having an associated value, said value being even higher when a pixel is glossy, and the nonlinear processing module is able to apply a nonlinear filtering has a block of pixels of the digital image acquired to determine a corresponding pixel value in the digital image to be displayed, said non-linear filtering taking into account, for a block of pixels of the acquired digital image, at least the maximum value said block of pixels.

Non-linear filtering involves associating with a pixel of the digital image to display a value calculated from values above a predetermined threshold of the corresponding block of pixels of the acquired digital image.

Alternatively, the nonlinear filtering involves associating with a pixel of the digital image to display a value calculated from a given number of the highest values of the block of pixels.

The system includes a plurality of high resolution juxtaposed sensors.

The system comprises a high-definition sensor, adapted to be positioned in a position for acquiring image data along a line of sight, and displacement members of said sensor, making it possible to move the angle of sight of this sensor.

The high-resolution sensor capable of acquiring digital image data is a first sensor in a first spectral band corresponding to the signals visible to the human eye, the system further comprising a second sensor capable of acquiring second digital image data. in a second spectral band different from the first spectral band.

The second spectral band belongs to the field of infrared electromagnetic waves of wavelength between 3 and 14 micrometers.

The system further comprises an image processing module adapted to effect a merger between said digital image to be displayed and the second digital image data acquired by the second sensor.

The angular capture resolution is strictly finer than the angular resolution of the human eye, by a factor greater than or equal to 3.

According to a second aspect, the invention proposes a method adapted to provide an operator with increased visibility, intended for use in aircraft piloting, implemented by a system comprising at least one sensor capable of acquiring data from aircraft. image in a given spectral band and a central processing unit adapted to process the acquired image data and to transmit the processed image data for displaying a digital image on a display unit. The method comprises the following steps:

acquisition of the image data forming a digital image in a spectral band including at least all or part of the spectral band corresponding to the electromagnetic signals visible to the human eye, of first spatial resolution, and angular resolution of capture strictly finer than the angular resolution of the human eye, and

- Applying a non-linear processing adapted to achieve a spatial resolution change while preserving bright spots of said acquired digital image to obtain a digital image to display second spatial resolution less than the first spatial resolution.

Since the advantages of the method are similar to the advantages of the system briefly described above, they are not recalled here.

The process according to the invention may have one or more of the following characteristics, taken independently or in all their technically acceptable combinations.

Each digital image is defined by a matrix of pixels, each pixel having an associated value, said value being even higher when a pixel is shiny, and the nonlinear processing comprises the application of a nonlinear filtering a block of pixels of the acquired digital image for determining a corresponding pixel value in the digital image to be displayed, said non-linear filtering taking into account at least the maximum value of said block of pixels.

According to one variant, the value associated with the pixel of the digital image to be displayed is calculated from a given number of the highest values of the block of pixels.

The method includes another step of acquiring second digital image data in a second spectral band different from the first spectral band.

The method includes a step of merging the second resolution digital image obtained by nonlinear processing with the second digital image data.

Other features and advantages of the invention will emerge from the description given below, by way of indication and in no way limiting, with reference to the appended figures, among which:

FIG. 1 schematically represents an aircraft approaching a track marked by light markings;

FIG. 2 diagrammatically illustrates an augmented vision system according to a first embodiment; FIG. 3 schematically illustrates two images of different spatial resolutions;

- Figure 4 schematically illustrates an augmented vision system according to a second embodiment.

The invention will be described in its application to aircraft flight control, it being understood that it is not limited to this application.

Indeed, the invention finds applications more generally in any context in which an increased vision compared to the human vision of an operator is useful, for example for controlling other types of devices.

Figure 1 schematically illustrates an application context of the invention, which is the landing of an aircraft.

In the example of FIG. 1, an aircraft 2 is on landing approach on a landing field 4, comprising a landing runway 6.

The landing strip is marked by various markers 8, 10, 12, 16, 18. For example, the markers 8 are markers of the center of the track, the markers 10, 12 are light markers of the edge of the track, arranged Regularly along its entire length, the markers 16 are runway threshold markers and the markers 18 are approach ramp markers.

The markers 8, 10, 12, 16, 18 emit at least in the spectral band visible to the eye by the operator and some can be made by LED lamps and others by incandescent lamps .

Advantageously, the aircraft 2 is equipped with a system 14 adapted to provide the pilot with increased vision.

It should be noted that the system 14 is shown schematically in Figure 1, and that it is in practice made of several elements that are positioned at different locations or grouped together, as explained in more detail below.

According to a first embodiment illustrated schematically in FIG. 2, a system 14 according to the invention comprises an image sensor 20 in the spectral band of the electromagnetic radiation or signals visible to the human eye, of wavelength between 0.4μηι to 0.7μηι but can in a variant go up to 1 μηι.

In a variant, the image sensor 20 operates in a spectral band comprising only a part of the spectral band of the electromagnetic signals visible to the human eye.

The sensor 20 is a high resolution sensor, making it possible to obtain a level of angular resolution of shooting that is finer than the human eye. The digital image acquired by the sensor 20 has an associated spatial resolution, the spatial resolution being defined as the number of image data or pixels per unit length. Each pixel has an associated radiometry value, also called intensity value.

Preferably, the sensor 20 is such that the ratio K between the angular resolution of the human eye and the angular image acquisition resolution is greater than or equal to 3. The digital image acquired by such a sensor is said on -resolved because it has angular resolution finer than the angular resolution achievable by the human eye.

The sensor 20 makes it possible to capture, along a line of sight, a field of view of maximum angle Θ preferably of the order of 35 ° to 40 °.

Preferably, the sensor 20 is a CMOS sensor ("Complementarity Metal-Oxide Semiconductor"), composed of photodiodes, whose manufacturing cost is moderate.

Alternatively, the sensor 20 is a CCD (Charge Coupled Device) or uses any other sensor technology.

In an alternative embodiment, in order to acquire image data corresponding to the angle of view field Θ, the sensor 20 is replaced by a plurality of angle-of-view sensors smaller than Θ, juxtaposed and adapted capturing image data corresponding to adjacent fields of view or having an overlapping portion.

In another alternative embodiment, the high resolution sensor 20 has a field of view of angle smaller than the desired angle, thus a narrower field of view, but this sensor 20 is made movable by displacement members, allowing it to be rotated so as to cover a wide field of view of the order of Θ. For example, such displacement members are formed by an articulated or fixed connection associated with a motor. In this embodiment, the sensor 20 is steerable.

In practice, in the case of use for aircraft piloting aid 2, the sensor 20 is placed for example at the front of the fuselage of the aircraft.

Advantageously, as explained in detail below, the capture of an overbooked image makes it possible to improve the visibility of the light markings with a quantifiable performance, even in conditions of reduced visibility.

For example, a fog-reducing weather condition is schematically illustrated by a cloud 21 in FIG. At the output of the sensor 20, an over-resolved digital image ₁₀ of first spatial resolution R ₀ is obtained, the image consisting of K ^* L pixels, for example 5120 ^* 4096. The digital image is defined by a matrix of pixel values.

The data of the over-resolved digital image ₁₀ , of first spatial resolution R ₀ , are transmitted to a non-linear processing module 22, for example via a data bus connected to the output of the sensor 20. non-linear processing 22 is implemented by a not shown programmable device, for example an on-board computer, comprising one or more processors able to execute calculations and computer program code instructions when they are powered up.

In a variant, the programmable device implementing the non-linear processing module 22, as well as any other calculation module, is implemented by an integrated circuit of the FPGA type or by a dedicated integrated circuit of ASIC type.

The processing carried out by the nonlinear processing module 22 makes it possible to go from the first image ₁₀ of the first spatial resolution R ₀ to a digital image of second spatial resolution R _1; less than the first spatial resolution R ₀ , while preserving contrast points of the image, in particular bright spots (or points of positive contrast) of the image.

Points of contrast are called points or pixels whose associated value is clearly greater or substantially less than the average value of the pixels of the neighborhood, for example greater than 3 times the standard deviation of the pixels of this neighborhood.

The points whose associated value is much higher than the surrounding values are bright points, the contrast is positive.

The points whose associated value is significantly lower than the surrounding values are dark points, the contrast is negative.

It should be noted that with a conventional resolution sensor, not over-resolved, it is possible to miss points of strong contrast (positive or negative) due to the resolution of the sensor.

The processing performed by the nonlinear processing module 22 makes it possible to maintain positive contrast points in the digital image of second spatial resolution less than the first resolution.

FIG. 3 illustrates two such images ₁₀ and 1 with a resolution factor equal to 3 between the first resolution R ₀ and the second resolution. Thus, a block B of 3 × 3 pixels of the digital image ₁₀ corresponds to a pixel P of the image . The correspondence is a spatial correspondence in the respective matrices, as shown in Figure 3.

More generally, a block of MxN pixels of the image ₁₀ , corresponds to a pixel of the image. In the preferred embodiment, the nonlinear processing applied by the module 22 to pass from a block B, containing pixels (Bi _j ), {= 3x ₁ + k, j = 3x j _l + k, k € {0,1,2}} of the image ₁₀ at the pixel P i _j of the image consists in associating with the pixel Pn ^ the maximum value of the pixels of the block MxN of the image ₁₀ :

P _Wi = max (fl _(J )

Thus, advantageously, the gain provided by the over-resolution of the image ₁₀ acquired by the sensor 20 is preserved. The maximum intensity emitted by the luminous markings, captured by the over-resolved image acquisition, is preserved in the second resolution digital image.

Advantageously, the non-linear processing module is adapted to retain the detected light spots, in other words to preserve the brightest points of the block, because in fact the more a point is shiny, the higher the associated value in the image digital is high.

The applied nonlinear processing preserves the bright spots but does not preserve the dark spots, as only the brightest points are of interest for the intended piloting application.

In a variant, the nonlinear processing module 22 applies other nonlinear treatments of filtering type that retain the maximum values or that process the pixels according to their rank. Filtering on overlapping windows can also be considered.

For example, for a given block, the values of the block pixels greater than a threshold S are retained. The threshold S can be set or dynamically calculated, for example, being the average increased by 2 or 3 times the standard deviation of pixel values of the block. All the values retained, which are the values of the brightest pixels of the block according to the chosen criterion, are then used to obtain the final value of the pixel of the second resolution digital image. For example, an average of the values retained, therefore greater than threshold S, of the block considered, is calculated and assigned as the final value of the corresponding pixel in the second resolution digital image

In another example, the values of the pixels of a block considered are ordered in descending order of the values and the 2 (or 3) most important values are retained. The values retained, which are the values of the brightest pixels of the block according to the chosen criterion, are then used to obtain the final value of the pixel of the second resolution digital image. For example, an average of the values retained. of the block considered, is calculated and assigned as the final value of the corresponding pixel in the second resolution digital image.

At the output of the non-linear processing module 22, the digital image of second spatial resolution Ri less than the resolution R ₀ is transmitted to an image processing module 24, able to apply conventional processing, for example correction of radiometry, geometric alignment in view of the display of the image on a display unit 26, for example a screen.

In one embodiment, the processing modules 22 and 24 are applied by the same onboard computer.

In one embodiment, the display is performed by incrustation on a display screen 26, located at the sight of a flight operator, called head-up display.

The second resolution is preferably chosen according to the display resolution of the display screen 26, for example a "head-up" display. Alternatively, a "head-down" display screen, for example located on the dashboard, is used.

Advantageously, such a head-up display makes it possible to present to the operator an augmented vision of the reality that he can perceive naturally, and thus to help him for the piloting operations.

Thus, a visualization method adapted to provide an operator with an augmented vision according to the invention comprises a first step of acquiring a first digital image of first spatial resolution by a high resolution sensor able to acquire image data in a spectral band corresponding to the signals visible by the human eye, with a level of angular resolution of capture strictly greater than the level of angular resolution of the human eye.

This first step is followed by a non-linear processing step making it possible to obtain a second image of second spatial resolution R ₂ , less than the first spatial resolution and of second angular resolution adapted to the resolution of the display device.

Preferably, the factor between the angular resolution of capture and the angular resolution of the human eye is greater than or equal to 3, that is to say that the angular resolution of capture is at least 3 times finer than the resolution angular of the human eye.

Advantageously, the performance of the proposed system is computable, regardless of weather conditions. Indeed, a meteorological condition is characterized by an absorption coefficient σ in a given spectral band.

According to Beer-Lambert-Bouguer's law, the intensity changes as a function of the distance X and the absorption coefficient σ in the following way: l (X) = l ₀ · β ^χ ρ (-σ (Χ -

Where X ₀ is a reference distance to which the intensity l ₀ of a beacon is associated.

Taking into account a variation of the angular resolution, where a is the angular resolution of the pixel for an EVS equipment using the method of the invention and ore _f is the angular resolution of the pixel for a reference EVS equipment using an equivalent angular resolution at the display resolution, we obtain:

l (X) = l ₀ · ε ^χ ρ (-σ (Χ -

Under meteorological conditions leading to an extinction coefficient of 0.01 m- ¹ , for example:

• the same signal-to-noise ratio for luminous markings at 500 m with an angular resolution reference sensor oc _ref and at 1000 m with an angular resolution sensor refined by a factor of 25 (a = oc _ref / 25), c ' that is, a higher resolution level of a factor of 25 leads to a gain in range of a factor of 2,

• the same signal-to-noise ratio for luminous markings at 800 m with an angular resolution reference sensor oc _ref and at 1000m with an angular resolution sensor refined by a factor of between 3 and 4 (a = a _ref / 3 , 5), that is to say that a level of resolution higher by a factor of 3.5 leads to a gain in range of 25%.

Therefore, it is demonstrated that a higher level of angular resolution makes it possible to quantifiably reduce the range of detection provided by EVS equipment.

In a variant of this first embodiment, the system of the invention is an EVS system using at least one sensor (orientable or fixed) of very fine angular resolution in a spectral band different from that of the eye, which allows to have significantly improved lighting range detection range performance compared to an EVS system having a resolution of the class of that of the eye in this same spectral band.

A second embodiment of a system 30 adapted to provide increased vision according to the invention is illustrated in FIG. 4.

The system 30 comprises, in addition to the first sensor 20 capable of acquiring images of very high spatial resolution in the visible spectral band, and the processing unit 22 described above, constituting a first imaging channel, a second sensor 32 capable of acquire the images ₂ in a different spectral band than the visible spectral range, preferably in the infrared spectral range.

Preferably, the spatial resolution of the images 1 ₂ acquired by the sensor 32 is substantially equal to the second spatial resolution R ₂ of the images obtained at the output of the nonlinear processing module 22.

The acquisition by this second sensor 32 forms a second imaging path.

The system 30 also comprises a processing module 34 adapted to perform the fusion of the images and 1 ₂ , corresponding to the same field of view, by applying in particular, with techniques known in the field of image processing, a radiometry control on each of the channels, a geometric alignment for rendering the images and ₂ superimposable and a pixel-to-pixel addition.

The processing module 34 is also adapted to perform any image correction for display.

In practice, the processing module 34 is implemented by a not shown programmable device, for example an on-board computer, comprising one or more processors capable of executing calculations and instructions of computer program code when they are put under control. voltage.

The processing module 34 implements a step of merging between the second resolution digital image obtained by non-linear processing performed during the non-linear processing step by the module 22, and the second digital image data. ₂ acquired by the sensor 32.

The resulting merged image is then transmitted to a display unit 26, analogous to the display unit 26 described above with reference to FIG. 2, for example a display for overlay and display.

Advantageously, the proposed system makes it possible to acquire an image of first spatial resolution which is over-resolved, which makes it possible to capture positive contrast points, that is to say points which are shiny with respect to their neighborhood, and of preserve these positive contrast points in the digital image of second spatial resolution, lower than the first resolution. In the end, a second resolution digital image space for display and operation is obtained, but this image includes gloss information that could not have been captured with an image acquisition at said second spatial resolution.

Claims

1. - System adapted to provide an operator with increased visibility, for use in aircraft piloting, comprising at least one sensor capable of acquiring image data in a given spectral band and a central processing unit able to process the acquired image data and transmitting the processed image data for displaying a digital image on a display unit,

characterized in that it comprises:

at least one high-resolution sensor (20) capable of acquiring image data forming a digital image (l ₀ ) in a spectral band including at least all or part of the spectral band corresponding to the electromagnetic signals visible to the human eye , of first spatial resolution, and angular resolution level of capture strictly finer than the angular resolution of the human eye, and

a nonlinear processing module adapted to perform a spatial resolution change while preserving bright spots of said acquired digital image (l ₀ ) to obtain a digital image (h) to display a second spatial resolution less than the first spatial resolution.

2. - System according to claim 1, wherein each digital image is defined by a matrix of pixels, each pixel having an associated value, said value being even higher than a pixel is glossy, characterized in that the module (22) is capable of applying a nonlinear filtering to a block of pixels of the acquired digital image to determine a corresponding pixel value in the digital image to be displayed, said nonlinear filtering preserving the bright points and taking into account, for a block of pixels of the acquired digital image, at least the maximum value of said block of pixels.

3. - System according to claim 2, characterized in that said non-linear filtering preserving the bright spots consists of associating with a pixel of the digital image to display a value calculated from the values greater than a predetermined threshold of the block of corresponding pixels of the acquired digital image.

4. - System according to claim 2, characterized in that said non-linear filtering preserving the bright spots consists in associating with a pixel of the digital image to be displayed a value calculated from a given number of the highest values. the corresponding pixel block of the acquired digital image.

5. - System according to one of claims 1 to 4, characterized in that it comprises a plurality of juxtaposed high resolution sensors.

6. - System according to one of claims 1 to 4, characterized in that it comprises a high-definition sensor, adapted to be positioned in a position for acquiring image data along a line of sight, and organs displacement of said sensor, for moving the viewing angle of the sensor.

7. - System according to any one of claims 1 to 6, wherein said high resolution sensor (20) capable of acquiring digital image data is a first sensor in a first spectral band corresponding to the signals visible by the eye human, characterized in that it further comprises a second sensor (32) adapted to acquire second digital image data in a second spectral band different from the first spectral band.

8. - System according to claim 7, characterized in that said second spectral band belongs to the field of infrared electromagnetic waves of wavelength between 3 and 14 microns.

9. - System according to any one of claims 7 or 8, characterized in that it further comprises an image processing module (34) adapted to perform a merger between said digital image to be displayed and the second data d digital image acquired by the second sensor.

10. - System according to any one of claims 1 to 9, characterized in that the angular resolution of capture is strictly finer than the angular resolution of the human eye by a factor greater than or equal to 3.

1 1. - A method adapted to provide an operator with increased visibility, for use in aircraft piloting, implemented by a system comprising at least one sensor capable of acquiring image data in a given spectral band and a unit a central processing unit adapted to process the acquired image data and to transmit the processed image data for displaying a digital image on a display unit,

characterized in that it comprises steps of: - acquisition of the image data forming a digital image in a spectral band including at least all or part of the spectral band corresponding to the electromagnetic signals visible to the human eye, of first spatial resolution, and angular resolution resolution strictly finer than the angular resolution of the human eye, and

12. - The method of claim 1 1, wherein each digital image is defined by a matrix of pixels, each pixel having an associated value, said value being higher as a pixel is shiny, characterized in that the non-linear processing includes applying a non-linear filtering to a block of pixels of the acquired digital image to determine a corresponding pixel value in the digital image to be displayed, said non-linear filtering taking into account at the minus the maximum value of said block of pixels.

13. - Method according to claim 12, characterized in that said non-linear filtering comprises associating with a pixel of the digital image to be displayed a value calculated from values greater than a predetermined threshold of the block of corresponding pixels of de the digital image acquired.

14. - Method according to claim 12, characterized in that said nonlinear filtering comprises associating with a pixel of the digital image to be displayed a value calculated from a given number of the highest values of the block of pixels. corresponding of the acquired digital image.

15. - Method according to any one of claims 1 1 to 14, characterized in that it comprises another step of acquiring second digital image data in a second spectral band different from the first spectral band.

16. - Method according to claim 15, characterized in that it comprises a step of merging between the second resolution digital image obtained by non-linear processing and the second digital image data.