System for monitoring the interior and / or exterior of a vehicle with two acquisition devices, and associated method and computer program product

Abstract

System for monitoring the interior and / or exterior of a vehicle with two acquisition devices, and associated method and computer program product The present invention relates to a system (10) for monitoring the interior and / or exterior of a vehicle (12), comprising: - a first acquisition device (14) capable of acquiring a first series of images at a first acquisition frequency, - a second acquisition device (16) capable of acquiring a second series of images at a second acquisition frequency lower than the first acquisition frequency, and - a control unit (18) capable of: - receiving the series of images, - timestamping each image with a respective timestamp time, and - associating each image of the second series with an image of the first series having the timestamp time closest to the timestamp time of said image of the second series.The invention further relates to an associated method and computer program product. Figure for abstract: Fig 1.

Description

Title of the invention: System for monitoring the interior and / or exterior of a vehicle with two acquisition devices, and associated method and computer program product

[0001] The present invention relates to a system for monitoring the interior and / or exterior of a vehicle comprising a first acquisition device and a second acquisition device, having different acquisition frequencies, an associated computer program product and method.

[0002] Such a system serves, for example, to acquire two types of information from a single scene, and thus to superimpose this information, for example to superimpose an image of the visible face of an occupant, in particular the driver, and a thermal image of said face, so that a control unit is able to automatically regulate the temperature of the heating, ventilation and air conditioning system. This makes it possible in particular to improve the comfort of the occupant, but also safety, in particular for the driver, for example by avoiding the effects of drowsiness due to an unsuitable temperature.

[0003] To superimpose the information, a link is made between the images acquired by the two acquisition devices.

[0004] However, with different acquisition frequencies, it is not easy to synchronize the images acquired by the two acquisition devices.

[0005] Document WO 2018 / 194759 describes a method for controlling the exposure and synchronization of asymmetric acquisition devices.

[0006] This document teaches determining the difference between the exposure time of a first of the devices and the exposure time of the second device, and generating a signal to synchronize the acquisition of the images of the two acquisition devices based on this difference.

[0007] Thus, this document teaches how to modify the acquisition carried out by the devices, so as to synchronize the devices as such.

[0008] However, some acquisition devices do not allow the acquisition to be modulated, and acquire images at a given frequency, so that this method could not be applied to them.

[0009] Furthermore, even if the devices were compatible, this potentially means that one of the sensors, called fast, acquires fewer images or signals than it could in order to be synchronized with the other sensor, whereas the images or signals from the fast sensor are likely to be analyzed independently of the images from the other sensor, so that it could be interesting to have more images of the fast sensor.

[0010] Finally, the assembly for synchronizing the two acquisition devices complicates the design of the hardware and increases costs.

[0011] The aim of the invention is then to propose a simple system making it possible to synchronize images acquired at different frequencies.

[0012] To this end, the invention relates to a system for monitoring the interior and / or exterior of a vehicle, the monitoring system comprising:

[0013] - a first acquisition device capable of acquiring a first series of images of the interior and / or exterior of the vehicle at a first acquisition frequency,

[0014] - a second acquisition device capable of acquiring a second series of images from inside and / or outside the vehicle at a second acquisition frequency, the second acquisition frequency being lower than the first acquisition frequency, and

[0015] - a control unit capable of:

[0016] - receive the first series of images and the second series of images,

[0017] - timestamp each image of the first series of images and each image of the second series of images with respective timestamp time, and

[0018] - associate each image of the second series of images with a respective image of the first series of images, said respective image of the first series of images having, among the images of the first series of images, the respective timestamp time closest to the respective timestamp time of said image of the second series of images.

[0019] The control unit then makes it possible to associate with each image acquired by the slowest acquisition device, an image from the fastest acquisition device, and thus, to allow exploitation of the synchronized images, without modifying the operation of the acquisition devices.

[0020] According to other advantageous aspects of the invention, the system comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0021] - the first acquisition device is a camera operating in the lengths visible and near infrared waves, and / or the second acquisition device is a thermal camera;

[0022] - the first acquisition device is capable of acquiring each image of the first series of images with an exposure during a respective first exposure interval, the respective timestamp time of each image of the first series of images being the median time of the first exposure interval of said image, the second acquisition device being capable of acquiring each image of the second series of images with an exposure during a second exposure interval respective, the respective timestamp time of each image of the second series of images being the median time of the second exposure interval of said image;

[0023] - the respective first exposure intervals have the same first duration, and the respective second exposure intervals have the same second duration;

[0024] - the control unit is able to select, for each image of the second series of images, the two images of the first series of images having the respective timestamp time closest on either side of the timestamp time of said image of the second series of images, comparing the respective differences, for the selected images, between the timestamp time of said image of the second series of images and the timestamp time of each selected image, and associating with said image of the second series of images the selected image whose difference between the timestamp time of said image of the second series of images and the timestamp time of said selected image is the smallest;

[0025] - the control unit is capable of, when the difference between the timestamp time of said image of the second series of images and the timestamp time of each selected image is identical, associating with said image of the second series of images the selected image having a most recent timestamp time;

[0026] - the second acquisition device is capable of acquiring each image of the second series of images with an exposure during a respective second exposure interval, the control unit being able to select, for each image of the second series of images, the image or images of the first series of images having a timestamp time included in the corresponding second exposure interval, and to associate with said image of the second series of images the selected image, in the event of uniqueness, or, otherwise, the selected image whose difference between the timestamp time of said image of the second series of images and the timestamp time of said selected image is the smallest among the selected images;

[0027] - the control unit comprises a circular buffer memory and is capable of receiving the first set of images and the second set of images in the circular buffer;

[0028] - the system is a vehicle interior monitoring system.

[0029] The invention also relates to a method for monitoring the interior and / or exterior of a vehicle comprising the following steps:

[0030] - acquisition of a first series of images of the interior and / or exterior of the vehicle by a first acquisition device at a first acquisition frequency,

[0031] - acquisition of a second series of images of the interior and / or exterior of the vehicle by a second acquisition at a second acquisition frequency, the second acquisition frequency being lower than the first acquisition frequency,

[0032] - reception by a reception module of the first series of images and the second series of images,

[0033] - timestamping by a timestamping module of each image of the first series of images and each image of the second series of images with a respective timestamp time, and

[0034] - association by a synchronization module of each image of the second series of images to a respective image of the first series of images, said respective image of the first series of images having, among the images of the first series of images, the respective timestamp time closest to the respective timestamp time of said image of the second series of images.

[0035] The invention also relates to a computer program product comprising software instructions suitable for, when implemented by computer, implementing the steps of receiving, timestamping and associating a monitoring method as previously described.

[0036] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0037] [Fig-1] [Fig.l] is a schematic representation of a surveillance system according to one embodiment of the invention,

[0038] [Fig.2] [Fig.2] is a schematic representation of the steps of the monitoring method according to one embodiment of the invention, and

[0039] [Fig.3] [Fig.3] is a schematic representation of an example of implementation of the method according to an embodiment of the invention.

[0040] An example of a monitoring system 10, in particular of the interior and / or exterior, here, for example of the interior, of a vehicle 12, is shown in [Fig.l].

[0041] The monitoring system 10 comprises a first acquisition device 14, a second acquisition device 16 and a control unit 18.

[0042] The first acquisition device 14 is capable of acquiring a first series of images of the interior and / or exterior, here, for example of the interior, of the vehicle 12 at a first acquisition frequency.

[0043] The first acquisition frequency is, for example, between 10 Hz and 120 Hz.

[0044] More particularly, the first acquisition device 14 has a first acquisition field 20 comprising a part of the interior and / or the exterior, here, for example, of the interior, of the vehicle.

[0045] The first acquisition field 20 comprises, for example, the location of the face of an occupant, preferably of a driver of the vehicle in the driving position.

[0046] The first acquisition device 14 is, for example, a camera operating in the visible and near infrared wavelengths, for example operating for a range of wavelengths corresponding to the range from 300 nm to 1100 nm.

[0047] The first acquisition device 14 is here capable of acquiring each image of the first series of images with an exposure during a respective first exposure interval Expl, shown in [Fig.3].

[0048] The respective first exposure intervals here have the same first duration, for example between 3 ms and 150 ms.

[0049] The second acquisition device 16 is capable of acquiring a second series of images of the interior and / or exterior, here, for example of the interior, of the vehicle 12 at a second acquisition frequency.

[0050] The second acquisition frequency is lower than the first acquisition frequency.

[0051] The second acquisition frequency is, for example, between 1 Hz and 10 Hz.

[0052] More particularly, the second acquisition device 16 has a second acquisition field 22 comprising a part of the interior and / or the exterior, here, for example, of the interior, of the vehicle.

[0053] The second acquisition field 22 comprises, for example, the location of the face of an occupant, preferably of a driver of the vehicle in the driving position.

[0054] The second acquisition field 22 is, for example, similar to the first acquisition field 20 to within 10%.

[0055] The second acquisition device 16 is, for example, a thermal camera.

[0056] The second acquisition device 16 is here capable of acquiring each image of the second series of images with exposure during a respective second exposure interval Exp2.

[0057] The respective second exposure intervals here have the same second duration, for example between 50 ms and 300 ms.

[0058] The second duration is, for example, greater than the first duration.

[0059] Each of the first acquisition device 14 and the second acquisition device 16 is provided with a clock, so that, for each acquisition of an image, the exposure interval is dated.

[0060] The clocks of the first acquisition device 14 and of the second acquisition device 16 are, for example, here, synchronized.

[0061] Alternatively, the offset between the clocks is known.

[0062] The control unit 18 comprises a reception module 24, a timestamp module 26 and a synchronization module 28.

[0063] The time stamping module 26 is connected to the reception module 24.

[0064] The synchronization module 28 is connected to the time stamping module 26.

[0065] In the example shown, the control unit 18 comprises, as an optional addition, an analysis module 30 and, possibly, an action module 32.

[0066] Where appropriate, the analysis module 30 is connected to the synchronization module 28, and where appropriate, the action module 32 is connected to the analysis module 30.

[0067] In the example of [Fig.l], the control unit 18 comprises an information processing unit formed for example of a memory and a processor associated with the memory.

[0068] The control unit 18 also has a circular buffer memory, also called a “buffer ring”.

[0069] The control unit 18, more particularly the reception module 24, is capable of receiving the first series of images and the second series of images from the first acquisition device 14 and from the second acquisition device 16, and here the exposure interval of each of the images of the first series and the second series of images.

[0070] The control unit 18, more particularly the reception module 24, is connected to the first acquisition device 14 and to the second acquisition device 16, more particularly by wire or by remote connection.

[0071] The control unit 18 is capable of receiving the first series of images and the second series of images in its memory, more particularly in the circular buffer memory.

[0072] The control unit 18, more particularly the timestamping module 26, is capable of timestamping each image of the first series of images and each image of the second series of images with a respective timestamp time, more particularly the images received in the circular buffer memory.

[0073] The respective timestamp time tl of each image of the first series of images is, for example, here the median time of the first exposure interval of said image.

[0074] The respective timestamp time t2 of each image of the second series of images is, for example, here the median time of the second exposure interval of said image.

[0075] In the case where the median time does not correspond to a unit of time, but for example here to a half-unit of time, as shown here for the second series of images, then the median time is, for example, the time corresponding to the truncated unit of time.

[0076] Alternatively, the median time is, for example, rounded to the nearest unit of time.

[0077] Thus, the control unit 18, more particularly the time-stamping module 26, is capable of calculating the median time of the first or second exposure interval for each of the images of the first series of images and of the second series of images, received in the circular buffer memory, and of assigning to each of the images said respective calculated median time.

[0078] The control unit 18, more particularly the synchronization module 28, is capable of associating each image of the second series of images with a respective image of the first series of images, said respective image of the first series of images having, among the images of the first series of images, the respective timestamp time t1 closest to the respective timestamp time t2 of said image of the second series of images.

[0079] In a first embodiment, the control unit 18, more particularly the synchronization module 28, is able to select, for each image of the second series of images, the two images of the first series of images having the respective timestamp time t1 closest on either side of the timestamp time t2 of said image of the second series of images.

[0080] In the example of [Fig. 3], for the first image of the second series of images, the control unit 18 thus selects the first image and the second image of the first series of images; for the second image of the second series of images, the control unit 18 selects the second image and the third image of the first series of images, etc.

[0081] Then, the control unit 18, more particularly the synchronization module 28, is able to compare the respective differences, for the selected images, between the timestamp time t2 of said image of the second series of images and the timestamp time t1 of each selected image.

[0082] In the example of [Fig.3], for the first image of the second series of images, the differences corresponding to the intervals referenced Aa and Ap are compared.

[0083] Here, the difference is smaller between the first image of the first series and the first image of the second series than between the second image of the first series and the first image of the second series.

[0084] Then, the control unit 18, more particularly the synchronization module 28, is able to associate with said image of the second series of images the selected image whose difference between the timestamp time t2 of said image of the second series of images and the timestamp time t1 of said selected image is the smallest.

[0085] In the example of [Fig.3], the first image of the second series is associated with the first image of the first series; the second image of the second series is associated with the third image of the first series.

[0086] When the difference between the timestamp time of said image of the second series of images and the timestamp time of each selected image is identical, the control unit 18, more particularly the synchronization module 28, is, for example, able to associate with said image of the second series of images the selected image having a most recent timestamp time.

[0087] In a second alternative embodiment, the control unit 18, more particularly the synchronization module 28, is able to select, for each image of the second series of images, the two images of the first series of images having the respective timestamp time closest on either side of the timestamp time of said image of the second series of images, similarly to the first embodiment.

[0088] Then, the control unit 18, more particularly the synchronization module 28, is able to compare the timestamp time t1 of the selected images with the second exposure interval Exp2 of said image of the second series of images, and to exclude any first selected image whose timestamp time is outside the second exposure interval of said image of the second series of images.

[0089] For example, in the example of [Fig. 3], for the first image of the second series of images, the control unit 18 does not exclude any of the selected images because the first image and the second image of the first series of images have a timestamp time tl included in the exposure interval Exp2 of the first image of the second series. For the second image of the second series of images, the control unit 18 excludes the second image of the first series because its timestamp time at the time unit (t) 18 is outside the interval between 24 and 34 time units (t).

[0090] Then, the control unit 18, more particularly the synchronization module 28, is able to associate with said image of the second series of images:

[0091] - the selected image not excluded, if only one of the selected images is excluded,

[0092] - the selected image whose difference between the timestamp time of said image of the second series of images and the timestamp time of said selected image is the lowest among the selected images, if no selected image is excluded, or

[0093] - no image if both selected images are excluded.

[0094] In the second case, when the difference between the timestamp time of said image of the second series of images and the timestamp time of each selected image is identical, the control unit 18, more particularly the synchronization module 28, is, for example, capable of associating with said image of the second series of images the selected image having a most recent timestamp time.

[0095] In the example of [Fig.3], the first image of the second series is associated the first image of the first series after comparing the respective differences, similarly to the first embodiment. The second image of the second series is associated with the third image of the first series, since the second image of the first series was previously excluded.

[0096] In a third alternative embodiment, the control unit 18, more particularly the synchronization module 28, is capable of selecting, for each image of the second series of images, the image(s) of the first series of images having a timestamp time t1 included in the second corresponding exposure interval Exp2.

[0097] In the example of [Fig. 3], for the first image of the second series of images, the control unit 18 thus selects the first image and the second image of the first series of images; for the second image of the second series of images, the control unit 18 selects only the third image of the first series of images, etc.

[0098] Then, the control unit 18, more particularly the synchronization module 28, is able to associate with said image of the second series of images the selected image, in the case of uniqueness, or, otherwise, the selected image whose difference between the timestamp time of said image of the second series of images and the timestamp time of said selected image is the smallest among the selected images.

[0099] In the second case, when the difference between the timestamp time of said image of the second series of images and the timestamp time of each selected image is identical, the control unit 18, more particularly the synchronization module 28, is, for example, capable of associating with said image of the second series of images the selected image having a most recent timestamp time.

[0100] In the example of [Fig.3], the first image of the second series is associated with the first image of the first series after comparison of the respective differences, similarly to the first embodiment. The second image of the second series is associated with the third image of the first series of images, since it is the only image selected.

[0101] This therefore makes it possible to associate with each image of the acquisition device at the lowest frequency an image acquired during the corresponding exposure interval of the other acquisition device, where appropriate, so that these images are subsequently considered to have been acquired at an identical or similar time.

[0102] For example, each thermal image of the driver's face is associated with a visible image of said face.

[0103] In a particular embodiment, the control unit 18, more particularly the analysis module 30, is then capable of carrying out any method of analysis of these images.

[0104] For example, the control unit 18, more particularly the analysis module 30, is able to obtain, for each image of the second series, at least a second piece of information from said image and at least a first piece of information from the image of the associated first series, the first and second pieces of information characterizing comparable areas for the associated images.

[0105] The control unit 18, more particularly the analysis module 30, is, for example, capable of carrying out an image analysis so as to recognize areas of interest on the images of the first series.

[0106] For example, the control unit obtains information regarding the temperature on the thermal images and information regarding the locations of at least one notable area of ​​the driver's face on the images from the first acquisition device.

[0107] By superimposing the two types of information which are considered comparable, the control unit is then able to deduce the temperature of at least one given area of ​​the face and / or an upper part of the body of an occupant, for example the driver, for example the forehead, the nose, the hands, etc.

[0108] This makes it possible in particular to detect whether the driver has an abnormal temperature.

[0109] Indeed, the temperature of a person's face varies depending on the area. For example, the nose is generally cooler than the forehead.

[0110] Thus, by using both thermal images and visible images, it is possible to know the temperature of a given zone, in particular an area considered representative, for example, of the internal temperature of the conductor.

[0111] Where appropriate, the action module 32 is capable of sending an action and / or alarm and / or alert signal as a function of the first and second information.

[0112] For example, a threshold temperature is defined.

[0113] When the temperature of at least one given area of ​​the driver's face exceeds the threshold temperature, then the action module 32 is able to send an action and / or alarm and / or alert signal.

[0114] The action module 32 is, for example, connected to a central control system, the action signal comprising, for example, an instruction to open the window near the driver and / or an air conditioning system.

[0115] The action module 32 is, for example, connected to an audible and / or visual alarm system, the alarm signal comprising, for example, an instruction to emit an audible and / or visual signal.

[0116] The action module 32 is, for example, connected to a communication system, the alert signal comprising, for example, an alert message.

[0117] Thus, this makes it possible to either take actions or issue an alarm or send an alert when a driver has a temperature that is too high.

[0118] Indeed, a driver's temperature that is too high is correlated with an increased risk of drowsiness at the wheel.

[0119] In the example of [Fig. 1], the reception module 24, the timestamp module 26 and the synchronization module 28, as well as, as an optional addition, the analysis module 30 and the action module 32, are each produced in the form of software, or a software brick, executable by the processor. The memory of the control unit is then capable of storing reception software, timestamp software, and synchronization software, as well as, as an optional addition, analysis software and action software. The processor is then capable of executing each of the software among the reception software, the timestamp software, and the synchronization software, as well as, as an optional addition, the analysis software and the action software.

[0120] In a variant not shown, the reception module 24, the time-stamping module 26 and the synchronization module 28, as well as, as an optional addition, the analysis module 30 and the action module 32, are each produced in the form of a programmable logic component, such as an FPGA (Field Programmable Gate Array), or an integrated circuit, such as an ASIC (Application Specific In-tegrated Circuit).

[0121] When the control unit 18 is produced in the form of one or more software programs, that is to say in the form of a computer program, also called a computer program product, it is furthermore capable of being recorded on a medium, not shown, readable by a computer. The computer-readable medium is for example a medium capable of storing electronic instructions and of being coupled to a bus of a computer system. By way of example, the readable medium is an optical disk, a magneto-optical disk, a ROM memory, a RAM memory, any type of non-volatile memory (for example FLASH or NVRAM) or a magnetic card. A computer program comprising software instructions is then stored on the readable medium.

[0122] A method for monitoring the interior and / or exterior, here, for example the interior, of a vehicle will now be described with reference to [Fig.2].

[0123] The monitoring method is, for example, implemented here by a monitoring system 10 such as that described with reference to [Fig.l].

[0124] The monitoring method comprises the following steps:

[0125] - acquisition 110 of a first series of images of the interior and / or the exterior, here, for example from inside the vehicle by a first acquisition device 14 at a first acquisition frequency,

[0126] - acquisition 112 of a second series of images of the interior and / or exterior, here, for example from inside the vehicle by a second acquisition frequency 16 at a second acquisition frequency, the second acquisition frequency being lower at the first acquisition frequency,

[0127] - reception 114 by a reception module 24 of the first series of images and the second series of images, more specifically in a circular buffer,

[0128] - timestamp 116 by a timestamp module 26 of each image of the first image series and each image of the second image series with a respective timestamp time tl, t2, and

[0129] - association 118 by a synchronization module 28 of each image of the second series of images to a respective image of the first series of images, said respective image of the first series of images having, among the images of the first series of images, the respective timestamp time closest to the respective timestamp time of said image of the second series of images.

[0130] Here, during the reception step, the reception module further receives the exposure interval Expl, Exp2 of each of the images of the first series and the second series of images, each interval being associated with the corresponding image.

[0131] In the timestamping step, the timestamping module calculates, for example, the median time of the first or second exposure interval Expl, Exp2 for each of the images of the first series of images and of the second series of images received, and to timestamp each of the images with said respective calculated median time, as the respective timestamp time tl, t2.

[0132] During the association step, the synchronization module 28 implements, for example, the sub-steps according to the first embodiment described with regard to the system.

[0133] Alternatively, the synchronization module 28 implements, for example, the sub-steps according to the second or third embodiment described with regard to the system.

[0134] At the end of the association step 118, each image from the acquisition device at the lowest frequency is associated with an image from the other acquisition device, so that these images are subsequently considered to have been acquired at an identical or comparable time.

[0135] In a particular embodiment, the monitoring method further comprises an analysis step 120, here by the analysis module, and possibly an action and / or alarm and / or alert step 122, here by the action module.

[0136] The analysis step 120 comprises, for example, an analysis of the images of the first series and the second associated series.

[0137] For example, the analysis module 30 obtains for each image of the second series, at least a second piece of information from said image and at least a first piece of information from the image of the associated first series, the first and second pieces of information characterizing comparable zones for the associated images.

[0138] The analysis module 30 carries out, for example, an image analysis so as to re- know areas of interest in the images of the first series.

[0139] For example, the analysis module calculates, from the associated images of the first series and the second series, information concerning the temperature on the images of the second acquisition device and information concerning the locations of at least one notable area of ​​the driver's face on the images of the first acquisition device.

[0140] The analysis module then deduces, for example, the temperature of at least one given area of ​​the face and / or an upper part of the body of an occupant, for example the driver, for example the forehead, the nose, the hands, etc.

[0141] In a particular embodiment, the action and / or alarm and / or alert step 122 comprises the emission of an action and / or alarm and / or alert signal as a function of the first and second information.

[0142] For example, a threshold temperature is defined.

[0143] When the temperature of at least one given area of ​​the driver's face exceeds the threshold temperature, then the action module 32 sends an action and / or alarm and / or alert signal.

[0144] The signal comprises, for example, an instruction to open the window near the driver and / or an air conditioning system; and / or an instruction to emit an audible and / or visual signal; and / or an alert message, as described in more detail with respect to the system.

[0145] The present monitoring systems and methods thus make it possible to synchronize images acquired by acquisition devices which are not synchronized with each other, and thus to have the possibility of carrying out cross-image analyses, considering that the associated images were acquired substantially at the same time.

[0146] Such a method does not require adaptation of the physical system and can be carried out by simple processing after acquisition.

Claims

Claims

1. A system (10) for monitoring the interior and / or exterior of a vehicle (12), the monitoring system (10) comprising: - a first acquisition device (14) capable of acquiring a first series of images of the interior and / or exterior of the vehicle (12) at a first acquisition frequency, - a second acquisition device (16) capable of acquiring a second series of images of the interior and / or exterior of the vehicle (12) at a second acquisition frequency, the second acquisition frequency being lower than the first acquisition frequency, and - a control unit (18) capable of: - receiving the first series of images and the second series of images, - timestamping each image of the first series of images and each image of the second series of images with a respective timestamp time (t1, t2), and - associating each image of the second series of images with a respective image of the first series of images,said respective image of the first series of images having, among the images of the first series of images, the respective timestamp time (tl) closest to the respective timestamp time of said image (t2) of the second series of images.,

2. A surveillance system according to claim 1, wherein the first acquisition device (14) is a camera operating in the visible and near infrared wavelengths, and / or the second acquisition device (16) is a thermal camera.

3. A monitoring system according to claim 1 or 2, wherein the first acquisition device (14) is adapted to acquire each image of the first series of images with an exposure during a respective first exposure interval (Expl), the respective timestamp time (tl) of each image of the first series of images being the median time of the first exposure interval (Expl) of said image, the second acquisition device (16) being adapted to acquire each image of the second series of images with an exposure during a respective second exposure interval (Exp2), the respective timestamp time (t2) of each image of the second series of images being the median time of the second exposure interval (Exp2) of said image.

4. A monitoring system according to claim 3, wherein the respective first exposure intervals (Expl) have the same first duration, and the respective second exposure intervals (Exp2) have the same second duration.

5. Surveillance system according to any one of claims 1 to 4, wherein the control unit (18) is capable of selecting, for each image of the second series of images, the two images of the first series of images having the respective timestamp time (tl) closest on either side of the timestamp time (t2) of said image of the second series of images, of comparing the respective differences, for the selected images, between the timestamp time (t2) of said image of the second series of images and the timestamp time (tl) of each selected image, and of associating with said image of the second series of images the selected image whose difference between the timestamp time (t2) of said image of the second series of images and the timestamp time (tl) of said selected image is the smallest.

6. Surveillance system according to claim 5, wherein, the control unit is capable of, when the difference between the timestamp time (t2) of said image of the second series of images and the timestamp time (tl) of each selected image is identical, associating with said image of the second series of images the selected image having a most recent timestamp time (tl).

7. Surveillance system according to any one of claims 1 to 4, wherein the second acquisition device (16) is capable of acquiring each image of the second series of images with an exposure during a respective second exposure interval (Exp2), the control unit being capable of selecting, for each image of the second series of images, the image or images of the first series of images having a timestamp time (tl) included in the corresponding second exposure interval (Exp2), and of associating with said image of the second series of images the selected image, in the case of uniqueness, or, otherwise, the selected image whose difference between the timestamp time (t2) of said image of the second series of images and the timestamp time (tl) of said selected image is the smallest among the selected images.

8. A monitoring system according to any one of claims 1 to 7, wherein the control unit (18) comprises a buffer memory circular and is adapted to receive the first series of images and the second series of images in the circular buffer.

9. A monitoring system according to any preceding claim, wherein the monitoring system is a vehicle interior monitoring system.

10. Method for monitoring the interior and / or exterior of a vehicle (12) comprising the following steps: - acquisition (110) of a first series of images of the interior and / or exterior of the vehicle (12) by a first acquisition device (14) at a first acquisition frequency, - acquisition (112) of a second series of images of the interior and / or exterior of the vehicle by a second acquisition device (16) at a second acquisition frequency, the second acquisition frequency being lower than the first acquisition frequency, - reception (114) by a reception module (24) of the first series of images and the second series of images, - timestamping (116) by a timestamping module (26) of each image of the first series of images and each image of the second series of images with a respective timestamping time (t1, t2),and - association (118) by a synchronization module (28) of each image of the second series of images with a respective image of the first series of images, said respective image of the first series of images having, among the images of the first series of images, the respective timestamp time (tl) closest to the respective timestamp time (t2) of said image of the second series of images.,

11. A computer program product comprising software instructions suitable, when implemented by computer, for implementing the steps of receiving, timestamping and associating a monitoring method according to claim 10.

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