Method for acquiring a sequence of image parts and associated acquisition system

Abstract

The invention relates to a method for acquiring a sequence of images for viewing the pointing of a target by a laser designator, the laser designator emitting laser pulses towards the target and generating designation tasks, the method comprising the following steps: - acquiring (110) a designation image in a first exposure time window synchronized with an instant of emission of a laser pulse, said first exposure time window having a first duration; - determining (120) the designation task from the designation image; - acquiring (122) scene images in a second exposure time window taking place between two instants of emission of laser pulses, said second exposure time window having a second duration four times greater than the first duration; - superimposing (128) the designation task on the scene images;- repetition (130) of the previous steps. Figure to be published with the abstract: Figure 6;

Description

Title of the invention: Method for acquiring a sequence of image parts and associated acquisition system Technical field of the invention

[0001] The present invention relates to an improved method for acquiring a sequence of images or parts of images allowing the visualization of the laser pointing of a target using a dual-band imager. State of the prior art

[0002] Currently, many weapons are guided. One of the guidance modes is achieved using a laser designator (Semi Active Laser Guidance). The laser designator emits a time-coded laser beam at a given wavelength and at a particular frequency. The laser beam is directed at the target. The laser beam generates designation spots on the target. The weapon's seeker or guidance system knows the particular frequency of the laser designator. It detects the designation spots generated by the laser designator. A dual-band imager images the target and the designation spots generated by the laser beam to verify that the laser designator is indeed pointing at the target. Such an imager is described, for example, in document FR 3054893. This dual-band imager makes it possible to capture an optical signal that includes the wavelength of the laser designator and the infrared wavelengths.If the designator axis becomes misaligned with the target, the operator immediately notices this and re-aims the target with the designator. This allows the operator to constantly monitor its aiming. A laser designator uses a pulsed laser, which allows very high photon power levels to be achieved during designation with relatively low amounts of energy. The amount of energy received by a dual-band imager placed a few kilometers from the designated target is therefore very low compared to the infrared photon energy emitted by the scene and integrated by the optical sensor over periods of several milliseconds. The laser designation signal is then drowned in the photon noise generated by the scene. Conventional dual-band imagers therefore do not allow a scene to be imaged simultaneously with a laser designation spot when the laser designation target is located beyond a few hundred meters from the imager. Presentation of the invention

[0003] The aim of the present invention is to enable imaging with a dual-band imager of a scene as well as laser designation spots without the significant photonic noise during the acquisition of the scene compromising the visibility of the designation spot. An aim of the present invention is to eliminate any image or image residue that could have been detected as a bright spot or even a decoy. These goals are achieved with an innovative technique that simultaneously interweaves two photonic integration modes: an internally synchronized mode for scene acquisition and an externally synchronized mode for the laser designation spot. The scene acquisition mode is optimized to maximize the number of scene acquisitions. The laser designation spot acquisition mode is optimized to acquire the largest number of laser designation spots. Summary of the invention

[0004] The subject of the present invention is a method for acquiring a sequence of at least parts of images making it possible to visualize the pointing of a target by a laser designator, the laser designator being capable of emitting laser pulses in the direction of the target and of generating designation tasks, the laser pulses being emitted at an emission frequency and in a wavelength belonging to a first band of wavelengths, the acquisition method being implemented by an image acquisition system comprising a dual-band imager capable of capturing an optical signal in the first band of emission wavelengths and in the infrared, and a processing unit adapted to process the images acquired by the dual-band imager and to parameterize the dual-band imager, the method comprising at least one cycle, said cycle comprising the following steps: a) acquiring at least a portion of a designation image, said at least a portion of the designation image being acquired in a first exposure time window synchronized with an instant of emission of a laser pulse, said first exposure time window having a first exposure duration; b) determining the designation task or the position of the designation task from said at least one designation image portion; c) acquiring at least parts of scene images, said at least parts of scene images being acquired in a second exposure time window occurring between two laser pulse emission times, said second exposure time window having a second exposure duration, the second exposure duration being at least four times greater than the first exposure duration; (d) superimposing the designation task or the position of the designation task on at least parts of scene images; e) repeating steps a), b), c) and d) to obtain a sequence of at least parts of images.

[0005] The features set out in the following paragraphs may optionally be implemented. They may be implemented independently each other or in combination with each other: The first exposure time is less than 4 ms, preferably less than 1 ms. The second exposure time is greater than 4 ms, preferably between 8 and 40 ms. The method comprises a duration of less than 10 ms, preferably 5 ms between the start of the step of acquiring said at least one part of the designation image and the start of the step of acquiring at least parts of scene images. The method further comprises a preliminary step of configuring the dual-band camera by the processing unit so that the first exposure time windows are synchronized with the emission times of the laser pulses. The acquisition system further comprises a laser designator connected to the processing unit, and in which said parameterization step comprises the following steps: - transmission of the emission times of the laser pulses from the laser designator to the processing unit; - determination of the emission frequency and the times of generation of first exposure time windows so that each first exposure time window is temporally centered around a time of emission of a laser pulse, - transmission of the instants of generation of the first exposure time windows from the processing unit to the dual-band camera. The method further comprises the following steps: - acquisition of at least a part of a calibration image, said at least a part of a calibration image being acquired during a calibration time window subsequent to the first exposure time window, the calibration time window having a duration substantially equal to the first exposure duration, - subtracting said at least one part of a calibration image from said at least one part of a designation image to obtain at least one image part representing only the designation task, said at least one image part representing only the designation task being used as at least one designation image part to implement the step of determining the position of the designation task. The method comprises several cycles, and wherein the image portion representing only the designation task obtained during the subtraction step of the first cycle is added to the image portion representing only the designation task obtained during the subtraction step of the second cycle. The dual-band camera is capable of acquiring designation images comprising N rows and M columns, N and M being natural integers, and in which only a part of the designation image is acquired, said portion of the acquired designation image comprising between 50% and 10% of the N rows and the M columns. Advantageously, this windowing makes it possible to maintain a sufficiently high image acquisition frequency to allow smooth and non-jerky viewing of the image sequence. The dual-band camera is capable of acquiring scene images comprising N rows and M columns, N and M being natural integers, and in which only a portion of the scene image is acquired, said portion of the acquired scene image comprising between 100% and 30% of the N rows and M columns.

[0006] The invention also relates to a system for acquiring a sequence of at least parts of images making it possible to visualize the pointing of a target by a laser designator, the laser designator being capable of emitting laser pulses in the direction of the target and of generating designation tasks, the laser pulses being emitted at an emission frequency and at a wavelength belonging to a first band of wavelengths, the acquisition system comprising: - a dual-band imager capable of capturing an optical signal in the first wavelength band and in the infrared, the dual-band imager being capable of acquiring at least a portion of a designation image and at least portions of scene images, said at least a portion of a designation image being acquired in a first exposure time window synchronized with an emission of a laser pulse, said first exposure time window having a first exposure duration, said at least a portion of the scene images being acquired in a second exposure time window having a second exposure duration, the second exposure duration being at least four times greater than the first exposure duration; and - a processing unit adapted to process the at least one part of designation images and the at least parts of scene images to obtain a sequence of at least parts of images, the processing unit being able to determine the position of the designation task from said at least one part of designation image and to superimpose the position of the designation task on the at least parts of scene images. Brief description of the figures

[0007] [Fig-1] is a schematic view of the system for acquiring parts of images according to the present invention;

[0008] [Fig.2] is a diagram showing the field of view of the dual-band camera during of a first time window of exposure;

[0009] [Fig.3] is a diagram showing the field of view of the dual-band camera during of a calibration time window;

[0010] [Fig.4] is a diagram showing the field of view of the dual-band camera during a second exposure time window;

[0011] [Fig.5] is a diagram showing three superimposed timing diagrams representing respectively the emissions of the laser pulses over time, the time windows of exposure of the dual-band camera over time and the time windows of recording the images over time;

[0012] [Fig.6] is a diagram showing the steps of the method of acquiring a sequence of image parts according to the present invention

[0013] [Fig.7] is a diagram showing the sub-steps of an embodiment of the synchronization step of the acquisition method according to the present invention. Detailed description of the invention

[0014] With reference to [Fig.l], the system 2 for acquiring a sequence of images according to the present invention makes it possible to visualize and monitor the pointing of a target 4 using a laser designator 12.

[0015] This acquisition system 2 comprises a dual-band camera 6, a processing unit 8 connected to the dual-band camera and a display screen 10 connected to the processing unit. The display screen 10 makes it possible to view the images processed by the processing unit.

[0016] In the embodiment shown, the acquisition system 2 also comprises a laser designator 12 capable of generating laser pulses Ei, Ei+1 which, upon contact with a surface, cause designation spots Di, Di+1 to appear. The laser designator 12 is connected to the processing unit. The laser pulses Ei, Ei+1 have an emission frequency known to the weapon. This emission frequency can vary from one shot to another within a known frequency range. The laser designator is pointed in the direction of the target 4 by an operator. The laser pulses Ei, Ei+1 emitted by the operator generate designation spots Di on the pointed surface. These designation spots Di, Di+1 appear at a frequency corresponding to the emission frequency of the laser pulses Ei, Ei+1. The wavelength of the emitted laser pulses belongs to a first wavelength band XI captured by the dual-band camera.These Di designation tasks are captured by the dual-band imager.

[0017] In the embodiment shown, the laser designator 12 is connected by a wired connection to the processing unit 8. The laser designator is capable of transmitting to the processing unit 8 the emission times ti, ti+1 of the laser pulses via this wired connection. It can also transmit the emission frequency of the laser pulses.

[0018] According to a variant not shown, the laser designator 12 is an external laser designator. It is not connected to the processing unit. It is not part of the acquisition system. In this case, a detection system is used to determine the emission times and the emission frequency of the laser designator.

[0019] The dual-band camera 6 comprises a matrix of photo-detectors capable of capturing an optical signal in a first wavelength band XI comprising the emission wavelength of the laser designator and in a second wavelength band X2 included in the infrared range. The first wavelength band XI is a narrow band centered around 1064 nm or 1550 nm, depending on the type of designator used. In the present patent application, a wavelength band is considered narrow when it is less than 50 nm. The second wavelength band X2 is between 3 pm and 5 pm so as to be able to image the thermal radiation emitted by the various objects and bodies present in the field of vision of the dual-band camera and in particular the radiation emitted by the target. Another usable band is the LWIR band from 8 to 12 pm.

[0020] The dual-band camera 6 is directed towards the target 4.

[0021] The dual-band camera 6 is configured to acquire different types of images named differently depending on their acquisition characteristics. Thus, the dual-band camera 6 is suitable for acquiring designation images, calibration images and scene images.

[0022] The designation images 18 are acquired during first exposure time windows II shown in [Fig.5]. The first exposure time windows II are temporally synchronized with the emission times ti, ti+1 of the laser pulses Ei, Ei+1. The designation images 18 represent the designation task Di, Di+1 and at least a part of the target 4, as visible in [Fig.2].

[0023] The first exposure time windows II take place during a first exposure duration T1 of less than 1 ms. Preferably, the first exposure duration T1 is less than 4 ms. Advantageously, the first exposure duration T1 is less than 1 ms.

[0024] The calibration images 20 are acquired during calibration windows 1e shown in [Fig. 5]. The calibration windows 1e take place between two instants of laser pulse emissions. In particular, the calibration windows 1e are subsequent to the first exposure time windows II. The calibration windows 1e have the same duration as the first exposure time windows II. The calibration images 20 represent only the target 4, as visible in [Fig. 3].

[0025] The scene images 22 are acquired during second time windows exposure time 12. The scene images 22 represent only the target 4 as visible in [Fig.4]. The second exposure time windows 12 take place between two laser pulse emission times. In particular, the second exposure time windows 12 are subsequent to the calibration windows 1e. The second exposure time windows 12 each have a second exposure duration T2.

[0026] The second exposure time T2 is greater than the first exposure time. The second exposure time T2 is between 4 ms and 40 ms. The second exposure time T2 is that of the Normal Imaging mode.

[0027] The second exposure time T2 is longer than the first exposure time T1 so that the photodetector array integrates the light in the second wavelength band / .2. The integration time of the light in the first wavelength band is less than the integration time in the second wavelength band because the light power of the reflected laser pulses is greater than that of the infrared radiation emitted by the scene and by the target 4.

[0028] The first exposure duration T1 is pre-recorded and the second exposure duration T2 is close to that of the normal imaging mode in the dual-band camera 6. The generation times of the first time windows are configurable.

[0029] The dual-band camera 6 is capable of acquiring images 18, 20, 22 comprising N lines and M columns. These images 18, 20, 22 correspond to the field of vision of the dual-band camera.

[0030] The dual-band camera 6 can also window the acquired images. Thus, the dual-band camera 6 can acquire and record portions of images that are reduced in size compared to the field of view of the dual-band camera. In particular, the dual-band camera 6 can acquire portions 24 of designation images comprising approximately less than 25% of the rows and columns of the complete designation images. Advantageously, these portions of images are recorded more quickly in the memory 14 than complete images. Preferably, a portion 24 of a designation image comprises between 50% and 10% of the rows and columns of a complete image. An example of a portion 24 of a designation image is shown in [Fig. 2].

[0031] Similarly, the dual-band camera 6 can acquire calibration image portions 26. The calibration image portions 26 have the same size as the designation image portions. An example of a calibration image portion 26 is shown in [Fig.3].

[0032] Finally, the dual-band camera can acquire portions of scene images 28 comprising less than 60% of the rows and columns of a complete image. Preferably, the 28 scene image parts comprise between 80% and 40% of the rows and columns of a complete image. An example of a 28 scene image part is shown in [Fig.4].

[0033] The processing unit 8 comprises a processor and a memory 14 containing instructions for implementing the method for acquiring parts of images described below.

[0034] The processing unit 8 is capable of configuring the dual-band camera so that it generates the first exposure windows II synchronized with the emission times ti, ti+1 of the laser pulses Ei, Ei+1.

[0035] The processing unit 8 is capable of receiving the parts 24 of designation images, the parts 26 of calibration images and the parts 22 of scene images acquired by the dual-band camera, of processing these parts of images and of transmitting the processed parts of images to the display screen.

[0036] In particular, the processing unit 8 is adapted to locate the position of the designation task Di, Di+1 in a designation image. The processing unit is able to superimpose the position of the designation task on the scene images to make the position of the pointing of the laser designator appear on the scene images. For this purpose, the designation task Di or a pattern representing the designation task is superimposed on the scene images. This pattern can for example be a reticle 16.

[0037] With reference to the figure in figures 6 and 7, the method for acquiring a sequence of images according to the present invention begins with a preliminary step 100 of parameterizing the dual-band camera by the processing unit 8 so that the first exposure time windows II are synchronized with the emission times ti, ti+1 of the laser pulses Ei, Ei+1.

[0038] In the embodiment shown in [Fig.l] in which the dual-band camera is connected to the processing unit 8, this preliminary step comprises three sub-steps shown in [Fig.7].

[0039] During a step 102, the laser designator 12 transmits the emission times ti, ti+1 (or tops) of the laser pulses to the processing unit, via the wired link.

[0040] During a step 104, the processing unit 8 determines the emission frequency of the laser pulses Ei, Ei+1.

[0041] During a step 106, the processing unit 8 determines the instants of generation of first exposure time windows II so that each first exposure time window II is temporally centered around an instant ti of emission of a laser pulse Ei, as represented on the timing diagram of [Fig.5].

[0042] During a step 108, the processing unit 8 configures the dual-band camera 6 by transmitting to it the instants of generation of first time windows exhibition II.

[0043] Then, the laser designator 12 is pointed at the target 4. It emits laser pulses Ei, Ei+1 which generate designation spots Di, Di+1 on the pointed surface. The dual-band imager 6 is directed at the target 4 so that the target 4 and the designation spots are in its field of vision.

[0044] During a step 110, the dual-band imager 6 captures an optical signal during a first exposure time window Tl synchronized with an emission instant ti of a laser pulse Ei.

[0045] Since the dual-band camera knows the future emission times of the laser pulses Ei, Ei+1, the image capture can be carried out during a time window Tl having a short duration. Thus, the first exposure time window Tl has a duration of less than 1 ms. Since the duration of this window is short, the photometric noise of the dual-band imager is reduced.

[0046] The captured optical signal represents a part 24 of a designation image. This part 24 of the designation image represents the designation task Di and at least a part of the target, as visible in [Fig.2].

[0047] During a step 112, the optical signal representing the designation image part 24 is recorded in the memory 14 of the processing unit during a first recording time window RI. Advantageously, the first recording time window RI is short because only one part of the designation image has been recorded. Thus, for example for a captured image part comprising 25% of the lines and columns of the complete image, the duration of the first recording time window RI is reduced by approximately 75%. The duration of the first recording time window RI is for example less than 0.4 ms.

[0048] In the embodiment shown in [Fig. 3], the dual-band camera 6 operates in an “integrate then read” operating mode. The recording step takes place after the acquisition step. Alternatively, the dual-band camera 6 operates in an “integrate while read” operating mode.

[0049] Advantageously, the designation image part 24 is centered in the center of the designation image 18.

[0050] As a variant, the processing unit 8 is capable of determining a predicted position of the target 4 from the acquired images, and the part of the designation image is centered around the predicted position of the target.

[0051] During a step 114, the dual-band imager 6 acquires a calibration image portion 26 during a calibration time window 1c directly subsequent to the recording time window RL. The calibration time window 1c has the same duration Tl as the first exposure time window II. The calibration image part 26 has the same dimension as the designation image part 24.

[0052] During a step 116, the electro-optical signal representing the calibration image part 26 is recorded in the memory 14 of the processing unit during a recording time window Rc. Advantageously, the duration of the recording time window Rc is short because only one part of the calibration image is recorded.

[0053] During a step 118, the processing unit 8 subtracts the part 26 of the calibration image from the part 24 of the designation image to obtain at least one image part representing only the designation task.

[0054] Advantageously, this subtraction of image parts makes it possible to eliminate the fixed noise generated by the photodetector matrix. This subtraction also makes it possible to considerably reduce any residual image which would be detected despite the very short integration time.

[0055] During a step 120, the processing unit 8 determines the position of the designation task Di on the image part obtained during the step 118. The position of the designation task is recorded in the memory 14.

[0056] During a step 122, the dual-band camera 6 acquires parts 28 of scene images during a second time window 12. The second time window 12 has a second exposure duration T2. ​​The second exposure duration T2 is at least four times greater than the first exposure duration. The second exposure duration T2 is between 5 ms and 40 ms.

[0057] Advantageously, the duration D between the start of the step of acquiring the part 24 of the designation image and the start of the step of acquiring the parts 28 of scene images is less than 2.4 ms.

[0058] During a step 124, the parts 28 of scene images are recorded in the memory 14 during a second recording time window R2. The dual-band camera 6 may optionally acquire other parts of scene images during a new second time window 12 and record them during a new recording time window R2, as visible in [Fig. 5]. Thus, steps 122 and 124 may optionally be repeated one or more times.

[0059] During a step 126, the parts 28 of scene images are displayed on the display screen 10.

[0060] During a step 128, the position of the designation task Di, Di+1 determined during step 120 is superimposed on the parts 28 of scene images. For this purpose, either the designation task is superimposed on the parts 28 of scene images or a crosshair is superimposed on the scene images at the position of the designation task.

[0061] The dual-band camera 6 can optionally acquire other parts of scene images during a new second time window 12 and record them during a new recording time window R2, as visible in [Fig.5].

[0062] During a step 130, steps 110 to 128 are repeated during a second cycle.

[0063] Alternatively, during step 120, the image part obtained during the first time window II (step 118) is directly superimposed on the scene image parts obtained during the second time window (step 122)

[0064] When this variant is used, the image representing the designation task determined during the second cycle is added to the image representing the designation task acquired during the first cycle. A predefined number of images representing the designation task can thus be added to each other. Then, when this number is reached, the images representing the designation task are deleted from the memory. The position of the designation task is refreshed.

[0065] Alternatively, the method does not include a step 114 of acquiring a portion 26 of a calibration image, nor a step 118 of subtracting the portion 26 of a calibration image from a portion 24 of a designation image. In this case, the position of the designation task is directly determined on the portion of the designation image.

[0066] Alternatively, a complete designation image is acquired during step 110.

[0067] Alternatively, a complete calibration image is acquired during step 114.

[0068] Alternatively, during a step 118, the processing unit 8 subtracts the image from full calibration to full designation image.

[0069] Alternatively, complete scene images are acquired during step 122.

[0070] Alternatively, since the laser frequency is known to the system, the triggering is made from pulse n to see pulse n+1. Triggering is performed by the laser designator in standalone mode or, in external designation, a point detection device that detects the laser illumination and provides a synchronized signal.

[0071] According to one embodiment, steps 110, 120, 122, and 128 are successive.

Claims

Claims

1. Method for acquiring a sequence of at least parts of images making it possible to visualize the pointing of a target (4) by a laser designator (12), the laser designator (12) being capable of emitting laser pulses (Ei, Ei+1) in the direction of the target and of generating designation tasks (Di, Di+1), the laser pulses being emitted at an emission frequency and in a wavelength belonging to a first band (XI) of wavelengths, the acquisition method being implemented by an image acquisition system (2) comprising a dual-band imager (6) capable of capturing an optical signal in the first band (XI) of emission wavelengths and in the infrared, and a processing unit (8) adapted to process the images acquired by the dual-band imager and to parameterize the dual-band imager, the method comprising at least one cycle, said cycle including the following steps: a) acquisition (110) of at least one part (24) of a designation image, said at least one part (24) of designation image being acquired in a first exposure time window (II) synchronized with an instant (ti) of emission of a laser pulse, said first exposure time window (II) having a first exposure duration (Tl) of less than 4 ms, preferably of less than 1 ms; b) determining (120) the designation task (Di, Di+1) or the position of the designation task (Di, Di+1) from said at least one part (24) of designation image; c) acquisition (122) of at least parts (28) of scene images, said at least parts of scene images being acquired in a second exposure time window (12) taking place between two instants (ti, ti+1) of emission of laser pulses, said second exposure time window (12) having a second exposure duration (T2); the second exposure duration (T2) being at least four times greater than the first exposure duration (T1); d) superimposing (128) the designation task (Di, Di+1) or the position of the designation task on at least parts (28) of scene images; e) repeating (130) steps a), b), c) and d) to obtain a sequence of at least parts of images.

2. Acquisition method according to claim 1, in which the second exposure duration (T2) is greater than 4 ms, preferably between 8 and 40 ms.

3. Acquisition method according to any one of claims 1 and 2, which comprises a duration of less than 10 ms, preferably 5 ms between the start of the step of acquiring said at least one part (24) of designation image and the start of the step of acquiring at least parts (28) of scene images.

4. Acquisition method according to any one of claims 1 to 3, in which the method further comprises a prior step (100) of parameterizing the dual-band camera (6) by the processing unit (8) so that the first exposure time windows (II) are synchronized with the emission times (ti, ti+1) of the laser pulses (Ei, Ei+1).

5. Acquisition method according to claim 4, wherein the acquisition system further comprises a laser designator (12) connected to the processing unit (8), and wherein said parameterization step (100) comprises the following steps: - transmission (102) of the emission times (ti, ti+1) of the laser pulses from the laser designator (12) to the processing unit (8); - determination (104, 106) of the emission frequency and the generation times of first exposure time windows (II) so that each first exposure time window is centered temporally around an emission time (ti, ti+1) of a laser pulse, - transmission (108) of the generation times of first exposure time windows (II) from the processing unit (8) to the dual-band camera (6).

6. Acquisition method according to any one of claims 1 to 5, which further comprises the following steps: - acquisition (114) of at least one part (26) of a calibration image, said at least one part (26) of a calibration image being acquired during a calibration time window (le) subsequent to the first exposure time window (Tl), the calibration time window (le) having a duration substantially equal to the first exposure duration (Tl), - subtraction (118) of said at least one part (26) of a calibration image from said at least one part (24) of a designation image to obtain at least one image portion representing only the designation task, said at least one image portion representing only the designation task being used as at least one designation image portion (24) for implementing the step of determining the position of the designation task.

7. The acquisition method of claim 6, wherein the method comprises several cycles, and wherein the image portion representing only the designation task obtained during the subtraction step of the first cycle is added to the image portion representing only the designation task obtained during the subtraction step of the second cycle.

8. Acquisition method according to any one of claims 1 to 6, in which the dual-band camera (6) is capable of acquiring designation images (18) comprising N rows and M columns, N and M being natural integers, and in which only a part (24) of the designation image is acquired, said part (24) of the acquired designation image comprising between 50% and 10% of the N rows and the M columns. Advantageously, this windowing makes it possible to maintain an image acquisition frequency sufficiently high to allow smooth and non-jerky viewing of the image sequence.

9. Acquisition method according to any one of claims 1 to 6, wherein the dual-band camera (6) is capable of acquiring scene images (22) comprising N rows and M columns, N and M being natural integers, and wherein only a portion (28) of the scene image is acquired, said portion (28) of the acquired scene image comprising between 100% and 30% of the N rows and M columns.

10. System (2) for acquiring a sequence of at least parts of images making it possible to visualize the pointing of a target (4) by a laser designator (12), the laser designator (12) being capable of emitting laser pulses (Ei, Ei+1) in the direction of the target (4) and of generating designation tasks (Di, Di+1), the laser pulses being emitted at an emission frequency and at a wavelength belonging to a first wavelength band (XI), the acquisition system (2) comprising: - a dual-band imager (6) capable of capturing an optical signal in the first wavelength band (XI) and in the infrared, the dual-band imager (6) being capable of acquiring at least one part (18) of a designation image and at least parts (28) of images of scene, said at least one part (18) of a designation image being acquired in a first exposure time window (II) synchronized with an emission (ti, ti+1) of a laser pulse, said first exposure time window (II) having a first exposure duration (Tl) less than 4 ms, preferably less than 1 ms, said at least one part (28) of the scene images being acquired in a second exposure time window (12) having a second exposure duration (T2), the second exposure duration (T2) being at least four times greater than the first exposure duration (Tl); and - a processing unit (8) adapted to process the at least one part (24) of designation images and the at least parts (28) of scene images to obtain a sequence of at least parts of images, the processing unit (8) being able to determine the position of the designation task (Di, Di+1) from said at least one part (24) of designation image and to superimpose the position of the designation task on the at least parts (28) of scene images.

Images