METHOD AND DEVICE FOR DATING CAMERA IMAGES

Abstract

A method for dating images obtained by at least one camera equipping a vehicle includes acquiring a reference signal including time information and generating a modulated signal in response to the reference signal. The modulated signal has at least one retiming pulse with a retiming period which that is different from a base period of the modulated signal. The method further includes, for each camera acquiring images at a frequency depending on the frequency of the modulated signal, each image being associated with a timestamp provided by the camera, and determining the time difference between the timestamps of two successive images of the camera. If the time difference determined between said timestamps is different from the base period of the modulated signal, the method assigns a reference date to said images depending on the time information of the reference signal.

Claims

1. A method for dating images obtained by at least one camera equipping a vehicle, said method comprising the steps consisting in: acquiring a reference signal including time information, generating a modulated signal in response to the reference signal, said modulated signal having at least one retiming pulse having a retiming period (ΔT) which is different from a base period of the modulated signal, and for each camera: acquiring images at a frequency depending on the frequency of the modulated signal, each image being associated with a timestamp provided by the camera, and determining a time difference between the timestamps of two successive images of the camera and, if the time difference determined between said timestamps is different from the base period of the modulated signal, assigning a reference date to said images depending on the time information of the reference signal.

2. The method according to claim 1, wherein the modulated signal comprises a plurality of pulses having a same base period, the retiming pulse having a period which is less than or greater than said base period.

3. The method according to claim 1, wherein the reference signal includes at least one reference pulse, a rising edge of the retiming pulse of the modulated signal being time offset from a rising edge of the reference pulse of the reference signal, said time offset between the two rising edges being equal to a retiming period or to the retiming period plus a fixed number of periods by default.

4. The method according to claim 1, wherein, for each camera, the step consisting of acquiring images is performed at each pulse of said modulated signal.

5. The method according to claim 1, wherein the reference signal is associated with an NMEA type data frame comprising data relating to a date and a schedule of transmission of the reference signal.

6. The method according to claim 1, wherein the modulated signal is generated using a digital phase-locked loop.

7. The method according to claim 1, wherein, for each camera, the step consisting in determining the time difference between the timestamps of two successive images is carried out by a computer.

8. The method according to claim 1, wherein the modulated signal is generated by an electronic card connected to a global positioning system.

9. A computer program including instructions for the execution of a method according to claim 1 when said program is executed by a processor.

10. Information storage means, removable or not, partially or totally readable by a computer or a microprocessor including code instructions of a computer program for executing each of the steps of the method according to claim 1.

11. A device for dating images obtained by at least one camera equipping a vehicle, comprising: means configured to transmit a reference signal including time information, an electronic card connected to the means for transmitting the reference signal and configured to generate a modulated signal in response to the reference signal, said modulated signal having at least one retiming pulse having a retiming period (ΔT) which is different from a base period of the modulated signal, wherein each camera is connected to the electronic card and is configured to acquire images at a frequency depending on the frequency of the modulated signal, each image being associated with a timestamp provided by the camera, and said device further comprising a computer connected, on the one hand, to each camera and, on the other hand, to the means for transmitting the reference signal and configured to determine a time difference between the timestamps of two successive images of the camera and, if the time difference determined between said timestamps is different from the base period of the modulated signal, assigning a reference date to said images depending on the time information of the reference signal.

12. The method of claim 1, wherein the reference signal is transmitted by a global positioning system equipping said vehicle.

13. The method according to claim 4, wherein, for each camera, the step of acquiring images is performed at each rising edge of said pulses.

Description

BRIEF DESCRIPTION OF FIGURES

[0049] FIG. 1 is a schematic representation of an exemplary embodiment of the device according to the invention,

[0050] FIG. 2 is a schematic representation of the signals produced by the device of FIG. 1,

[0051] FIG. 3 represents an example of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0052] FIGS. 1 and 2 illustrate a device 100, according to one embodiment of the invention, intended to be arranged in a vehicle, for example a land vehicle. The vehicle is equipped with two cameras 101.sub.1 and 101.sub.2 to help in the navigation of the vehicle and in the exploration of the environment of the vehicle.

[0053] The device 100 comprises an inertial unit 102 equipped with a global positioning system 104, for example of the GPS (“Global Positioning System”) or GNSS (“Global Navigation Satellite System”) type.

[0054] The global positioning system 104 is adapted to transmit a reference signal 202, in particular a pulse per second (“PPS”) signal, associated with time information, for example an NMEA frame bearing a date and schedule of transmission of the “PPS” reference signal 202. The “PPS” reference signal 202 comprises a reference pulse 204.

[0055] The device 100 also comprises an electronic card 106, for example of the Arduino® type, having an input connected to the global positioning system 104. The electronic card can have one or a plurality of outputs, at least two of the outputs being connected to cameras 101. Of course, there may be additional outputs which are not connected to cameras 101. Moreover, the vehicle can comprise more than two cameras and the electronic card 106 can be connected to all or part of the cameras. Furthermore, the electronic card 106 can have a single output connected to each of the cameras 101 or to a single camera 101.

[0056] The electronic card 106 is configured to produce at each of the outputs thereof connected to a camera 101, a modulated signal 208 having a predetermined frequency, for example a frequency which is equal to the acquisition frequency of one of the cameras 101. Alternatively, the frequency of the modulated signal can be greater than the acquisition frequency of one or each camera 101. By way of example, the frequency of the modulated signal 208 is equal to 20 Hz. The modulated signal 208 comprises a retiming pulse 210 having a rising edge 212 which is time offset from a base period of the modulated signal, such that the retiming pulse has a retiming period which is different from the base period. This retiming pulse can occur just after the rising edge 206 of the reference pulse 204. The duration of the retiming period ΔT, which is different from the base period, is predetermined. The retiming period ΔT is for example greater than the base period of the modulated signal 208. Alternatively, the retiming period ΔT may be less than the base period of the modulated signal 208. The retiming period ΔT is by example equal to 52 ms. Alternatively, the retiming pulse 210 may be offset from a falling edge or another point of the PPS reference signal 202.

[0057] The vehicle can comprise two cameras 101 forming a stereo head arranged in a front portion of the vehicle having an image acquisition frequency of 20 Hz. The vehicle can also comprise a camera 101 arranged in a rear portion of the vehicle and configured to reading plates or road signs for example, and having an image acquisition frequency of 10 Hz.

[0058] The output(s) of the electronic card 106 can be connected to the connectors for triggering the cameras 101.

[0059] The electronic card 106 may implement a digital phase-locked loop to create the signal 208.

[0060] The electronic card 106 is configured to trigger an acquisition of the images 214 by the cameras 101 depending on the modulated signal 208. For example, each of the cameras 101 captures an image at each rising edge of the modulated signal 208.

[0061] The cameras 101 can be any type of camera, for example infrared cameras, thermal cameras, matrix cameras, linear cameras, etc.

[0062] Each of the cameras 101.sub.1 and 101.sub.2 comprises an internal clock 103.sub.1 and 103.sub.2 configured to associate a timestamp with the images 214 taken by said camera. The internal clocks 103.sub.1 and 103.sub.2 can be desynchronised with each other.

[0063] The device 100 comprises a computer 108 connected to the inertial unit 102 and is configured to receive the PPS reference signal 202 from the global positioning system. The computer 108 is also connected to each of the cameras 101 and is configured to receive the images 214 captured by each of the cameras 101.

[0064] The computer 108 receives from the global positioning system an NMEA type data frame. The NMEA frame comprises an RMC frame carrying information relating to the date of transmission of the PPS reference signal, for example the year, the month and the day, and a GGA frame carrying information relating to the schedule of transmission of the PPS reference signal, for example the hour, the minutes, the seconds and possibly the milliseconds.

[0065] The computer 108 is further configured to determine a difference between the consecutive image timestamps 214.sub.i and 214.sub.i+1. When the computer 108 determines a timestamp difference which is different from the base period, a reference date determined by the time information carried by the PPS reference signal is assigned to the image 214.sub.i+1, for example by the date and the schedule carried by the NMEA frame. Reference dates are also assigned to the images preceding and/or following the image 214.sub.i+1 according to the reference date of the image 214.sub.i+1. Thus, the device 100 allows dating the images of the cameras 101 with a standard connection and therefore without requiring a specific connection between the two cameras. This device also allows compensating for the drift or a poor configuration of the internal clocks 103 of the cameras 101. The device also allows compensating for the latencies due to the acquisition of the images and their transmission to the computer. Furthermore, the device allows dating the images even in the case of loss of an image. The determination of the difference between the timestamps of the acquired images allows finding the dates of the images as soon as the offset corresponding to the retiming pulse is detected. For example, the device 100 allows dating the images with an accuracy of less than 1 ms.

[0066] FIG. 3 represents an example of a method 300 which can be implemented by the device 100.

[0067] The method 300 is provided for dating the images obtained by one or more cameras equipping a vehicle, for example an autonomous vehicle.

[0068] The method 300 comprises:

[0069] a step 302 consisting in acquiring a reference signal including time information transmitted by a global positioning system equipping the vehicle, and

[0070] a step 304 consisting in generating a modulated signal in response to the reference signal, said modulated signal having at least one retiming pulse having a retiming period which is different from the base period of the modulated signal.

[0071] The reference signal may be the signal 202 of FIG. 2. The time information may be an NMEA data frame. The global positioning system may be the positioning system 104 of FIG. 1. For example, the modulated signal can be the modulated signal 208 of FIG. 2.

[0072] Furthermore, step 304 can be executed by an electronic card, for example the electronic card 106 of FIG. 1.

[0073] The method 300 also comprises, for each camera: [0074] a step 306 consisting in acquiring images at a frequency depending on the frequency of the modulated signal, each image being associated with a timestamp provided by the camera, [0075] a step 308 consisting in determining the time difference between the timestamps of two successive images of the camera and, if the time difference determined between said timestamps is different from, for example, greater than or equal to the retiming period, assigning a reference date to said images depending on the time information of the reference signal.

[0076] For example, the cameras can be the cameras 101 of FIG. 1. The method can comprise, for each camera, a step consisting in capturing an image for each rising edge of the modulated signal.

[0077] The timestamp provided by the camera can be obtained by an internal clock of said camera. Step 308 can be executed by a computer, for example the computer 108 of FIG. 1.