METHOD FOR VISUALIZING A LASER SPOT IN A CORRECTED COLOR IMAGE AND IMAGE DETECTION DEVICE IMPLEMENTING THE METHOD

Abstract

The invention provides an image detection device for visualizing a laser spot on a color image. The device comprises a photosite array and a microfilter array including four distinct types of microfilters, the first three types of which exhibit transmission in two spectral ranges, and the fourth type of which exhibits transmission in only one of the two spectral ranges. The device further includes a band-stop optical filter in a sub-domain of a second spectral range.The device is configured to construct (301) an image for each type of microfilter; correct (302) each image resulting from a first type of microfilter by subtracting coefficient-weighted pixel values ​​from the image resulting from the fourth type of microfilter; obtain (303) a color image from the corrected images; detect (304) a laser spot in the image resulting from the fourth type of microfilter; and insert (305) the laser spot into the color image. Figure to be published with the abstract: Fig. 3.

Description

Title of the invention: Method for visualizing a laser spot in a corrected color image and image detection device implementing the method. Technical field

[0001] The present invention relates to the field of image sensors and more particularly to a method for visualizing a color image of a scene as well as a laser spot generated by an infrared laser pointer and present in said scene. STATE OF PRIOR ART

[0002] Silicon CMOS image sensors have the advantage of being mass-produced at low cost. They have recognized applications in color image detection, thanks to their detection sensitivity in the visible spectral range, at wavelengths from 400 nm to 780 nm. To obtain a color image, an array of colored microfilters, such as a Bayer filter, is usually placed in front of an array of photosites in the image sensor. The microfilter array generally comprises three types of colored filters, for example, red, green, and blue filters. A color image can then be constructed by taking into account, for each pixel of the image, the signal levels received by the photosites through the different types of colored filters.

[0003] In order to obtain a color image with good color fidelity, in other words, an image whose apparent colors are as close as possible to the colors of the imaged scene as perceived by the human eye, it is necessary to isolate signals from radiation with wavelengths in the visible spectrum from signals from radiation with wavelengths outside the visible range, for example by preventing the detection of infrared radiation by the photosites. However, the spectral detection range of a silicon CMOS sensor extends, due to the intrinsic band gap energy of silicon, into the near-infrared, at wavelengths beyond 780 nm. Furthermore, the filters in the microfilter array generally have a transmission profile that also extends into the near-infrared, due to design constraints of the microfilters.Colorimetric fidelity can then be increased by using an additional low-pass filter, allowing the stopping or cutting off of radiation in the near-infrared, with a wavelength greater than 780 nm.

[0004] In certain contexts, and particularly in a military application context, it is useful to visualize a laser spot generated by an infrared laser pointer and present in a scene, for example, for reasons of stealth. Detecting such a laser spot requires detecting optical radiation located in a spectral range of the infrared, for example, in a spectral range between 800 and 1000 nm wavelength. The use of such a low-pass filter, which stops radiation in the near-infrared, therefore prevents the detection of the laser spot.

[0005] Document FR 3 039 290 describes a method for visualizing a laser spot in the infrared range, requiring detection of a scene in several spectral bands exhibiting spectral continuity. However, the described method does not allow for obtaining a color image or improving its colorimetric fidelity.

[0006] It is therefore desirable to overcome these drawbacks of the prior art.

[0007] In particular, it is desirable to provide a solution that allows visualization of a laser spot in the infrared range, while also enabling the acquisition of a color image and improving the color fidelity of said color image compared to the imaged scene. It is also desirable to provide a low-cost solution implemented by a single image sensor. Finally, it is desirable to provide a solution that avoids spatial misalignment between the image of the laser spot and the image of the scene, and more specifically, avoids the introduction of alignment bias between the image of the laser spot and the image of the scene. Description of the invention

[0008] An object of the present invention is to provide an image detection device for visualizing a laser spot on a color image. The image detection device is a CMOS sensor comprising a photosite array, which itself comprises a microfilter array arranged so that each photosite faces a microfilter of the microfilter array, and a lens configured to produce an image of a scene on the photosite array. The microfilter array comprises at least four types of microfilters, each with a different spectral transmission range. At least three of these microfilter types each have a spectral transmission range within a first spectral domain and a second spectral domain, while the spectral transmission range of a fourth type of microfilter is entirely within the second spectral domain.The image detection device further includes a band-stop optical filter with an extinction spectral range extending into a first spectral subdomain of the second spectral domain, and includes a processing unit with electronic circuitry configured to: construct an image associated with each type of microfilter and having a predetermined number of pixels, each pixel of the image comprising a representative value. of a signal level detected by a photosite associated with said type of microfilter or interpolated from signal levels detected by photosites associated with said type of microfilter; correct each image associated with one of the at least three first types of microfilters, by subtracting, from the value of each pixel at a determined position in said image, the value of the pixel at said determined position of the image associated with the filter of the fourth type, said value being weighted by a coefficient specific to the type of microfilter associated with each corrected image; obtain a color image from the set of corrected images each associated with one of the at least three first types of microfilters; detect a laser spot having a predetermined shape in the image associated with the fourth type of microfilter and insert the laser spot into the color image obtained.

[0009] According to a particular embodiment, the image detection device further comprises a filtering optical system having a first transmission rate in the first spectral domain and a second transmission rate, distinct from the first transmission rate, in the second spectral domain.

[0010] According to a particular embodiment, the image detection device further comprises a filtering optical system having a variable and adjustable spectral transmission width in the second spectral domain, said filtering optical system being configured to cut off received optical radiation outside of said spectral transmission width in the second spectral domain.

[0011] According to a particular embodiment, the device is dimensioned to obtain a focusing task, in the plane of the photosite matrix, of dimension greater than the dimension of at least two photosites.

[0012] The invention also relates to a method for visualizing a laser spot on a color image, the method being implemented by an image detection device, of the CMOS sensor type, comprising a photosite array, comprising a microfilter array arranged such that each photosite is positioned opposite a microfilter of the microfilter array, and comprising a lens configured to produce an image of a scene on the photosite array. The microfilter array comprises at least four types of microfilters, each having a different spectral transmission range, with at least three of the first types of microfilters each having a spectral transmission range within a first spectral domain and a second spectral domain, and the spectral transmission range of a fourth type of microfilter being solely within the second spectral domain.The image detection device further includes a band-stop optical filter having a spectral extinction range extending into a first spectral subdomain of the second spectral domain, and includes steps implemented by a processing unit of the image detection device, . to: construct an image associated with each type of microfilter and having a predetermined number of pixels, each pixel of the image comprising a value representative of a signal level detected by a photosite associated with said type of microfilter or interpolated from signal levels detected by photosites associated with said type of microfilter; correct each image associated with one of the first three types of microfilters, by subtracting, from the value of each pixel at a determined position in said image, the value of the pixel at said determined position of the image associated with the filter of the fourth type, said value being weighted by a coefficient specific to the type of microfilter associated with each corrected image; obtain a color image from the set of corrected images each associated with one of the first three types of microfilters;detect a laser spot with a predetermined shape in the image associated with the fourth type of microfilter and insert the laser spot into the resulting color image. Brief description of the drawings

[0013] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of at least one exemplary embodiment, said description being made in relation to the accompanying drawings, among which:

[0014] [Fig-1] schematically illustrates an image detection device;

[0015] [Fig.2] schematically illustrates an example of a microfilter matrix of the device image detection;

[0016] [Fig. 3] schematically illustrates a method for visualizing a laser spot in a corrected color image; and

[0017] [Fig.4] schematically illustrates an example of a hardware platform adapted to implement an image detection device processing unit.

[0018] DETAILED DESCRIPTION OF IMPROVEMENTS

[0019] Figure 1 schematically illustrates an image detection device 1. The image detection device 1 is a CMOS sensor and comprises a photosite array 101. Each photosite is a unit for detecting the received optical radiation and is configured to transform said optical radiation into an electrical signal. The photosite thus detects a signal level representative of a light intensity and converts it into electrical form in order to transmit it, for example, to a processing unit 105 (described below).

[0020] The image detection device 1 further comprises a microfilter array 102 arranged such that each microfilter faces a photosite of the photosite array 101. In one embodiment, each microfilter faces a single photosite. Alternatively, each microfilter faces to a plurality of photosites, for example, facing two photosites. The microfilter array 102 is arranged in front of the photosite array. The term "in front" is defined here relative to a direction 110 of incidence of the optical radiation detected by the photosites. Preferably, the microfilter array 102 comprises as many microfilters as there are photosites in the photosite array 101, and each photosite in the photosite array 101 is associated with a microfilter.

[0021] The microfilter array 102 comprises at least four types of microfilters, each with a different spectral transmission range. A different spectral transmission range means that the transmission levels in at least a portion of the spectral transmission range differ between two types of microfilters. A spectral transmission range of a filter element is defined as the spectral range at which the transmission level exceeds a predefined transmission threshold, or the spectral range at which the normalized transmission level, relative to a maximum transmission level achieved by the filter, exceeds a predefined percentage, for example, greater than 20%. A spectral transmission range is not necessarily continuous and may thus include several disjoint spectral bands in which the transmission level exceeds the predefined transmission threshold.

[0022] At least three of the first types of microfilters in the microfilter array 102 have a spectral transmission range in the visible and near-infrared regions. The visible region is defined by a wavelength range between 400 nm and 780 nm. The near-infrared region is defined by a wavelength range between 780 nm and 1000 nm. Within the visible region, the spectral transmission range differs for each of the first three types of microfilters so as to allow the detection of optical radiation of distinct colors.

[0023] A fourth type of microfilters of the microfilter matrix 102 has a spectral transmission range contained only in the near-infrared range.

[0024] Fig. 2 schematically illustrates an example of a 102 microfilter matrix, comprising 16 microfilters distributed according to a periodic pattern of 4x4 microfilters.

[0025] According to this example, the microfilter matrix 102 comprises four types of microfilters. The first three types of microfilters include a first type of microfilter, called a red microfilter R, a second type of microfilter, called a green microfilter V, and a third type of microfilter, called a blue microfilter B. The fourth type of microfilter is an infrared microfilter IR.

[0026] In the visible spectrum, the spectral transmission range of the red microfilter R extends, for example, from 580 nm to 700 nm wavelength, the spectral range The transmission range of the green microfilter (V) extends, for example, from 500 nm to 600 nm wavelength, and the spectral transmission range of the blue microfilter (B) extends, for example, from 400 nm to 500 nm. The first types of microfilters—red (R), green (V), and blue (B)—are presented here as examples, but microfilters with other spectral transmission ranges can be used alternatively or in addition, such as cyan, magenta, or yellow microfilters.

[0027] In the near-infrared range, each of the first three or more types of microfilters exhibits a distinct transmission profile. A transmission profile is defined by the transmission level of the microfilter as a function of wavelength.

[0028] The near-infrared region is divided into a first spectral sub-region of the near-infrared, located, for example, between 780 nm and 800 nm wavelength, and a second spectral sub-region of the near-infrared, located, for example, between 800 nm and 1000 nm wavelength. In the first spectral sub-region of the near-infrared, the transmission profiles of the first three or more types of filters differ from one another. In contrast, in the second spectral sub-region of the near-infrared, the transmission profiles of these first three or more types of filters are proportional to one another.

[0029] The fourth type of microfilter, called the infrared (IR) microfilter, of the microfilter array 102 exhibits a transmission lower than the predefined transmission threshold in the visible spectral range and thus has a spectral transmission range limited to the near-infrared range. The infrared (IR) microfilters exhibit a transmission profile proportional to the transmission profiles of the red (R), green (V), and blue (B) microfilters in the second spectral sub-domain of the infrared. The transmission profile of the infrared (IR) microfilters may differ from the transmission profiles of the red (R), green (V), and blue (V) microfilters in the first spectral sub-domain of the infrared.

[0030] The filters of each of the types of microfilters are distributed regularly on the microfilter matrix 102. According to the example illustrated in [Fig.2], the microfilter matrix 102 comprises eight green V microfilters, two blue B microfilters, two red R microfilters and four infrared IR microfilters.

[0031] Returning to [Fig. 1], the image detection device 1 further comprises a lens 103 for producing an image of the observed scene on the photosite array 101. The lens is located in front of the microfilter array 102. Moreover, the microfilter array 102 is arranged between the lens 103 and the photosite array 101 in such a position that all the optical radiation detected by each photosite is transmitted through the microfilter located opposite said photosite. The microfilter array 102 is preferentially deposited on the photosite array 101, that is to say, in contact with the photosite array 101.

[0032] According to one embodiment, the image detection device 1 is dimensioned to obtain a focusing task, in the plane of the photosite matrix 101, with a dimension greater than the dimension of a single photosite, and preferably covering a plurality of photosites, for example, covering 2 to 4 photosites. Thus, each optical signal is received through several types of microfilters. Spectrum aliasing effects resulting from the presence of different types of microfilters facing contiguous photosites can then be avoided.

[0033] The image detection device 1 further comprises a band-stop optical filter 104 having an extinction spectral range extending at least to the first near-infrared spectral subdomain, for example, between 780 nm and 800 nm wavelength. An extinction spectral range is defined as a spectral range at which the filter's transmission level is below the predefined transmission threshold. In one embodiment, the extinction spectral range of the band-stop optical filter 104 extends below the first near-infrared spectral subdomain, for example, between 700 nm and 800 nm, but not below the highest transmission wavelength, in the visible range, of the first types of microfilters, for example, not below 700 nm when using red R microfilters.According to one embodiment, the spectral extinction range of the optical bandstop filter 104 can extend beyond the first near-infrared spectral subdomain, for example beyond 800 nm, but cannot extend to the highest wavelength of the second near-infrared spectral subdomain, for example 1000 nm, so that at least some of the radiation received in the second near-infrared spectral subdomain can be detected by the photosites.

[0034] The band-stop optical filter 104 is arranged to face all the photosites of the photosite array 101. The band-stop optical filter 104 is integrated into the image detection device 1 and located between the imaged scene and the photosite array 101. In one embodiment, the band-stop optical filter 104 is positioned in front of the lens 103. In another embodiment, the band-stop optical filter 104 is integrated into the lens 103, for example, by selecting a suitable material or by means of a surface treatment. The band-stop optical filter 104 thus prevents any radiation with wavelengths belonging to the first spectral subdomain of the near-infrared from being detected by the photosites of the photosite array 101.

[0035] The image detection device 1 includes the processing unit 105 configured to receive, for each photosite of the photosite array 101, information representative of a signal level detected by that photosite. Each piece of information representative of a signal level is received in association with a The position of the photosite in the photosite matrix 101 is further associated with a microfilter type in the microfilter matrix 102, for example using a lookup table stored in the memory of the processing unit 105, which associates each position in the photosite matrix with a microfilter type. The position of a photosite is, for example, defined by coordinates such as a row number and a column number.

[0036] The processing unit 105 is further configured to process the received information representative of signal levels and to construct an image from said signal levels. In general, the processing unit comprises electronic circuitry configured to implement the steps of the image detection process described in [Fig. 3].

[0037] According to one embodiment, the image detection device 1 further comprises a filtering optical system 106. The filtering optical system 106 has a first transmission level in the visible range, for example between 400 nm and 780 nm wavelength, and a second transmission level, distinct from the first transmission level, in the second spectral subdomain of the near-infrared, for example between 800 nm and 1000 nm wavelength. The first and second transmission levels are determined so as to compensate for a difference in average light intensity received in the visible range on the one hand and in the second spectral subdomain of the near-infrared on the other.The relative difference between the first and second transmission levels is determined, for example, prior to viewing a scene by taking into account estimated brightness parameters associated with the scene's observation context, on the one hand, and the emission intensity of an infrared laser pointer generating a laser spot, on the other. The optical filtering system 106 thus makes it possible to detect a laser spot simultaneously with a scene in which the laser spot is located, even when the light intensity emitted by the laser spot is low compared to the detected light intensity emitted by the scene, or vice versa.

[0038] In one embodiment, the optical filtering system 106 comprises one or more additional optical filters for adjusting the first transmission level relative to the second transmission level. The optical filtering system 106 is integrated into the image detection device 1 and located between the imaged scene and the photosite array 101. In one embodiment, the optical filtering system 106 is arranged in front of the band-stop filter 104, as illustrated in [Fig. 1], but can alternatively be arranged in front of the lens 103, between the lens 103 and the microfilter array 102, or integrated into the lens by a surface treatment, for example. In another embodiment, the optical filtering system 106 is contained within the optical band-stop filter 104, which comprises levels distinct transmission in the visible range and in the second spectral sub-range of the near-infrared.

[0039] Alternatively, the first and second transmission levels are equivalent, but the spectral transmission width in the second near-infrared spectral subdomain is variable and can be broadened or narrowed to compensate for a difference in average light intensity received in the visible range on the one hand and in the second near-infrared spectral subdomain on the other. According to one example, the optical filtering system 106 comprises a first high-pass interference filter, with a first cutoff wavelength located in the second near-infrared spectral subdomain, and a second low-pass interference filter, with a second cutoff wavelength located in the second near-infrared spectral subdomain and greater than the first cutoff wavelength.The spectral transmission width in the second spectral subdomain is therefore delimited by the first and second cutoff wavelengths. It is then possible to vary this spectral transmission width by tilting the first and / or second interference filter by a specific angle. This spectral transmission width then compensates for the difference in average light intensity received in the visible range on the one hand and in the second near-infrared spectral subdomain on the other.

[0040] Figure 3 schematically illustrates a method for visualizing a laser spot in a corrected color image. The visualization method is implemented by the image detection device 1 and comprises processing steps, implemented by the processing unit 105, based on information representing signal levels detected by the photosites of the photosite array 101 and received from said photosite array in electrical form. Each piece of information representing a signal level detected by a photosite is associated with a photosite position in the photosite array 101 and with a type of microfilter through which said signal is detected.

[0041] In a first step 301, the processing unit 105 constructs a first image associated with each type of microfilter. Each constructed image has a predetermined number of pixels, so that all the first images have the same number of pixels.

[0042] The processing unit 105 determines, for each piece of information representing a signal level detected by a photosite, a pixel value representing, for example, an intensity level to be displayed on a screen. Each pixel value is thus proportional to the signal level detected by a photosite, and is associated in in addition to the position of said photosite and the type of microfilter through which the signal was received.

[0043] The processing unit 105 performs, for each type of microfilter, a reconstruction operation, classically called demosaicing, so that each first image includes as many pixel values ​​as there are pixels, and preferably as many pixel values ​​as there are photosites in the photosite matrix 101.

[0044] For example, for each type of microfilter, the processing unit 105 determines the positions in the photosite matrix 101 for which a pixel value associated with that microfilter type is determined from a detected signal level. For each position in the photosite matrix 101 for which no pixel value associated with that microfilter type is determined, the processing unit 105 then determines a pixel value, called the interpolated pixel value, by interpolating determined pixel values, that is, values ​​representative of signal levels actually detected, and associated with that microfilter type. For example, an interpolated pixel value is obtained, for a microfilter type and at a given position, from the pixel values ​​associated with the n closest positions to the determined position, where n is an integer. The interpolation of the pixel values ​​can be linear or nonlinear.

[0045] According to one embodiment, the processing unit 105 performs the reconstruction operation from the received information representative of detected signal levels and then converts each detected signal level and each interpolated signal level into a pixel value.

[0046] In a subsequent step 302, the processing unit 105 corrects each image associated with one of the first three types of microfilters in order to limit the effect produced by the detection of an optical radiation component located outside the visible range, by the photosites.

[0047] Since the image detection device 1 includes the bandstop filter 104 having a spectral extinction range in the first subdomain of the near-infrared, the component of the optical radiation detected in said first subdomain is therefore zero or negligible compared to the total optical radiation received.

[0048] In the absence of the band-stop filter 104, the signal Sq j detected by a photosite associated with a first type i of microfilter, i being an integer between 1 and the total number of first types of microfilters, comprises a radiation component (or signal) Svjsibie j in the visible range and a radiation component Sir j in the near-infrared range and can thus be written:

[0049] Sqj = Svisibief i + Sj# i

[0050] The radiation component in the near-infrared spectral domain is the combination of the radiation components Sjri y and S[R2 i respectively in the first near-infrared spectral subdomain and in the second near-infrared spectral subdomain:

[0051] SIRj=SIRli+S lîvzf 1

[0052] Thus, the presence of the band-stop filter 104, which stops the radiation component in the first near-infrared spectral subdomain and therefore prevents it from being received by each photosite, results in the detection, by a photosite associated with a first type i of microfilter, of SRi radiation such that:

[0053] SRj — Syisibiç i + SjR2t j

[0054] It is then necessary, in order to obtain only the visible radiation component S i in the visible spectrum and thus increase the colorimetric fidelity of the image, to subtract, from the optical radiation detected by a photosite associated with a first type i of microfilter, the radiation component SjR2 i in the second spectral subdomain of the infrared:

[0055] S visible, i ^DJ ” ^IR2., i

[0056] Now, the radiation component SjR2 i in the second near-infrared spectral subdomain received by each first type i of microfilter is considered to be proportional to the optical radiation component in the second near-infrared spectral subdomain received by the fourth type of microfilter and denoted SIR2 JR ■

[0057] SIR2jR ~

[0058] kj being a proportionality factor specific to the first type i of microfilter in question.

[0059] Furthermore, the SRjR radiation detected by a photosite associated with the fourth type of microfilter does not include a radiation component in the first near-infrared spectral subdomain due to the presence of the 104 bandstop filter, nor a radiation component in the visible range due to the intrinsic spectral transmission range of the fourth type of microfilter. The SDIR radiation detected by a photosite associated with the fourth type of microfilter therefore includes only the optical radiation component in the second near-infrared spectral subdomain. SRjR2jR can be written as:

[0060] SDIR = SIR2jR

[0061] Thus, to limit the effect of the radiation component in the second near-infrared spectral subdomain received by a photosite associated with a first type i of microfilter, it is possible to subtract, from the optical radiation Spj detected by said photosite, the radiation Spj# detected by a photosite of the same coordinates in the photosite matrix, and associated with the fourth type of microfilter:

[0062] Svisibiej = Spj- Sfp>2,i ^î^Sdjr

[0063] To perform a correction aimed at limiting the effect produced on a color image by the detection of a radiation component located outside the visible range, the processing unit 105 therefore subtracts, pixel by pixel, from the pixel value of each first image associated with one of the first three or more types of microfilters, a value obtained by weighting, by the coefficient kj_ specific to the first type i of microfilter associated with the corrected image, the pixel value of the image associated with the fourth type filter. The processing unit 105 performs the subtraction for each pixel defined by its position (i.e., its coordinates) in the image.

[0064] The coefficient ki specific to each type i of microfilter is determined prior to the implementation of the visualization process, for example during a calibration step, and stored in the memory of the processing unit 105. The coefficients k are independent of the observed scene. Each coefficient kj is defined as the proportionality coefficient, in the second near-infrared spectral subdomain, between a photosite detection profile associated with one of the first three or more types of microfilters and a photosite detection profile associated with the fourth type of microfilter. It is thus possible to obtain pixel values, for each of the first three or more types of microfilters, that are as faithful as possible to the optical radiation received, in the visible range, by the photosites, and thus to increase the colorimetric fidelity of a color image compared to the imaged scene.

[0065] In a subsequent step 303, the processing unit 105 constructs a color image from the set of corrected images, each associated with one of the first three types of microfilters. For example, for a microfilter array 102 comprising red R, green G, and blue B microfilters, the processing unit 105 determines, for each pixel identified by its position in an image, a triplet of pixel values ​​comprising the values ​​of said pixel from each image associated with the red R, green G, and blue B microfilters. Each triplet of pixel values ​​corresponds to a predefined color. The processing unit 105 can then transmit the predefined color corresponding to each pixel to a display device. The processing unit 105 can further perform color correction and / or white balance operations.

[0066] In a subsequent step 304, the processing unit 105 detects, in the first image associated with the fourth type of microfilter, i.e., associated with the infrared (IR) microfilter, a laser spot emitted by an infrared laser pointer. The spectral emission range of the infrared laser pointer lies within the second spectral subdomain of the near-infrared, which ensures that the laser spot is present in said first image associated with the infrared (IR) microfilter. The laser spot is detected by detecting a predetermined shape within a specific spectral range, for example, by implementing at least one image processing operation such as thresholding, local contrast expansion, and frequency filtering.The detection of the laser spot from an infrared laser pointer differs from detection implemented using a conventional decamouflage algorithm, which searches for spectral singularities of undetermined shapes among a set of different spectral bands. According to the method of the present invention, the detection of the laser spot from an infrared laser pointer, on the other hand, involves searching for a predetermined shape within a specific spectral band corresponding to the second spectral subdomain of the near-infrared. The predetermined shape, which corresponds to the shape of the laser spot, is, for example, a Gaussian, pseudo-Gaussian, rotationally symmetric beam, or even a shape without rotational symmetry when the laser beam is shaped by beam-shaping techniques.

[0067] According to one embodiment, the optical filtering system 106 as described in relation to [Fig. 1] is inserted into the image detection device 1 in order to adjust the average light intensity received from the laser spot relative to the average intensity received from the scene. Indeed, the detection of the laser spot can be limited when the light intensity emitted by the laser spot is low compared to the light intensity emitted by the scene, for example, due to saturation of the detection of the photosites, associated with the infrared (IR) microfilters, by the light intensity received from the scene, or due to a light intensity received from the laser spot that is too low to be distinguished from a noise level of said photosites.The insertion of the optical filtering system 106 makes it possible to overcome these limitations in the detection of the laser spot, with, for example, the first transmission level, in the visible range, being lower than the second transmission level, in the second sub-range of the near-infrared.

[0068] Conversely, when the light intensity emitted by the laser spot is too high compared to the light intensity emitted by the scene, the light intensity received by the photosites associated with the first types of microfilters from the scene may be too low compared to a noise level of said photosites, or said photosites may be saturated in an area corresponding to the laser spot, preventing then to visualize at least part of the scene. The insertion of the optical filtering system 106 makes it possible to overcome this limitation of visualizing the scene, with for example the first level of transmission, in the visible domain, higher than the second level of transmission, in the second subdomain of the near-infrared, or with a spectral transmission width in the second subdomain of the near-infrared narrowed compared to the total width of the second spectral subdomain of the near-infrared.

[0069] In a subsequent step 305, the processing unit 105 inserts the laser spot into the constructed color image. The laser spot is inserted, for example, by replacing pixels in the color image with pixels in the same position in the image associated with the fourth type of microfilter and containing the detected laser spot. According to another example, said pixels of the color image and the image associated with the fourth type of microfilter are blended.

[0070] It is thus possible to obtain an image of a scene exhibiting good color fidelity and comprising an image of a laser spot emitted by an infrared laser pointer and observable within the scene. Furthermore, the image of the laser spot does not exhibit any spatial offset relative to the scene image, since both the laser spot and the scene are imaged by a single image detection device 1, in other words, by a single sensor. A pixel coordinate in the scene image and in the laser spot image therefore corresponds to a single direction in object space. Consequently, no alignment bias between the spot image and the scene image is introduced by the visualization method of the present invention.

[0071] Fig. 4 schematically illustrates an example of a hardware platform enabling the implementation, in the form of electronic circuitry, of the processing unit 105.

[0072] The hardware platform comprises, connected by a communication bus 410: a processor or CPU (Central Processing Unit) 401; a random-access memory (RAM) 402; a read-only memory 403, for example of type ROM (Read Only Memory) or EEPROM (Electrically-Erasable Programmable ROM), such as Flash memory; a storage unit, such as a hard disk drive (HDD) 404, or a storage media reader, such as an SD card reader (Secure Digital); and an I / F interface manager 405.

[0073] The I / f interface manager 405 allows the processing unit 105 to interact with the photosite array 101, as well as with a display device if necessary.

[0074] The processor 401 is capable of executing instructions loaded into RAM 402 from ROM 403, external memory, a storage medium (such as an SD card), or a communication network. When the Once the hardware platform is powered on, the 401 processor is able to read instructions from RAM 402 and execute them. These instructions form a computer program, causing the 401 processor to implement all or part of the steps and processes described herein.

[0075] All or part of the steps, processes, and operations described herein can thus be implemented in software form by executing a set of instructions by a programmable machine, for example, a DSP (Digital Signal Processor) or a microcontroller, or be implemented in hardware form by a dedicated machine or electronic component (chip) or a dedicated set of electronic components (chipset), for example, an FPGA (Field Programmable Gate Array) or ASIC (Application-Specific Integrated Circuit). Generally, the processing unit 105 comprises electronic circuitry adapted and configured to implement the processes and steps described herein.

Claims

1. Demands Image detection device (1) for visualizing a laser spot on a color image, the image detection device being of the CMOS sensor type, comprising a photosite array (101), comprising a microfilter array (102) arranged so that each photosite is positioned opposite a microfilter of the microfilter array (102) and comprising a lens (103) configured to produce an image of a scene on the photosite array (101), the image detection device (1) being characterized in that the microfilter array (102) comprises at least four types of microfilters (R, G, B, IR) each having a different spectral transmission range, at least three first types of microfilters (R, G, B) each having a spectral transmission range in a first spectral domain and in a second spectral domain,the spectral transmission range of a fourth type of microfilter (IR) being contained only in the second spectral domain, in that the image detection device (1) further comprises a band-stop optical filter (104) having an extinction spectral range extending in a first spectral subdomain of the second spectral domain, and in that it comprises a processing unit (105) comprising electronic circuitry configured for:, - construct (301) an image associated with each type of microfilter and having a predetermined number of pixels, each pixel of the image comprising a value representative of a signal level detected by a photosite associated with said type of microfilter or interpolated from signal levels detected by photosites associated with said type of microfilter, - correct (302) each image associated with one of the first three or more types of microfilters, by subtracting, from the value of each pixel at a determined position in said image, the value of the pixel at said determined position in the image associated with the filter of the fourth type, said value being weighted by a coefficient specific to the type of microfilter associated with each corrected image, - obtain (303) a color image from the set of corrected images each associated with one of the at least three first types of microfilters, - detect (304) a laser spot having a predetermined shape in the image associated with the fourth type of microfilter and insert (305) the laser spot into the color image obtained, the image detection device further comprising an optical filtering system (106) having a first transmission rate in the first spectral domain and a second transmission rate, distinct from the first transmission rate, in the second spectral domain.

2. Image detection device according to claim 1, the device being dimensioned to obtain a focusing task, in the plane of the photosite matrix (101), of dimension greater than the dimension of at least two photosites.

3. A method for visualizing a laser spot on a color image, the method being implemented by an image detection device (1), of the CMOS sensor type, comprising a photosite array (101), comprising a microfilter array (102) arranged so that each photosite is positioned opposite a microfilter of the microfilter array, and comprising a lens (103) configured to produce an image of a scene on the photosite array (101), the method being characterized in that the microfilter array comprises at least four types of microfilters, each having a different spectral transmission range, at least three first types of microfilters each having a spectral transmission range within a first spectral domain and a second spectral domain, the spectral transmission range of a fourth type of microfilter being solely within the second spectral domain,in that the image detection device further comprises a band-stop optical filter having a spectral extinction range extending in a first spectral subdomain of the second spectral domain, in that the image detection device further comprises a filtering optical system (106) having a first transmission rate in the first spectral domain and a second rate, transmission rate, distinct from the first transmission rate, in the second spectral domain, and in that the process includes steps implemented by a processing unit of the image detection device, of: - construct (301) an image associated with each type of microfilter and having a predetermined number of pixels, each pixel of the image comprising a value representative of a signal level detected by a photosite associated with said type of microfilter or interpolated from signal levels detected by photosites associated with said type of microfilter, - correct (302) each image associated with one of the first three or more types of microfilters, by subtracting, from the value of each pixel at a determined position in said image, the value of the pixel at said determined position in the image associated with the filter of the fourth type, said value being weighted by a coefficient specific to the type of microfilter associated with each corrected image, - to obtain (303) a color image from the set of corrected images, each associated with one of the first three types of microfilters, - detect (304) a laser spot having a predetermined shape in the image associated with the fourth type of microfilter and insert (305) the laser spot into the color image obtained.

Images