Event video sequence

Abstract

To facilitate power saving in an event-triggered camera.SOLUTION: In a monitoring camera 100, pre-event image frames are stored in raw format up to a time in which an event occurs. The power saving is achieved by deferring image processing for a pre-event video sequence. A post-event video sequence reduces the total power required by performing processing at a lower clock frequency.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to capturing and processing an event-started video sequence.

Background Art

[0002] Video cameras such as surveillance cameras or monitoring cameras are currently used in many different applications (both indoor and outdoor). Larger image sensors and other technological advancements have significantly improved the image quality of videos from such cameras, but at the same time, the video stream size, in other words, the bitrate, has also increased. Since both memory capacity and network bandwidth are limited resources, it is a common countermeasure to store or stream only videos that are started or triggered by events, rather than all videos.

[0003] The term, event, is used herein in its broadest sense, and thus an event can be considered to be anything that can justify the need for video documentation, and the term can include anything from when a door is forced open and a burglar alarm sounds to a visit by a care professional in a patient's home.

[0004] Often, it is also of interest not only to make the video available from the time the event starts, but also to record the video showing the monitored area or scene during the period immediately preceding the start of the event. This is generally solved by using a so-called pre-event buffer in which videos of recent time intervals are continuously recorded. When an event starts, the video recorded in the pre-event buffer is retrieved and included in the video clip showing the event. U.S. Patent No. 8,676,027 by the applicant of the present application discloses a method related to such a pre-event buffer in a camera.

[0005] Monitoring cameras can be mounted in various locations and often have one cable connection and another network access for power supply, or in the case of Power over Ethernet (PoE), they have both through a single connection. However, recently, body-worn cameras, often called body-attached cameras (BWCs), have seen increasing popularity. Body-worn cameras are used, for example, by police officers or security guards to capture video and other data during patrols and incidents. Such cameras are typically battery-powered. This means that the power available to body-worn cameras is much more limited than that for cameras mounted in fixed locations. Therefore, means and measures that are perfectly effective when used with cable-connected cameras, for example, cameras mounted in buildings, can be problematic with BWCs because much greater attention to power consumption is required. One challenge lies in the area of ​​event-initiated recording, where the use of a pre-event buffer requires the camera to continuously record video. This can rapidly drain the battery, and therefore improvements in this area are important. [Overview of the project]

[0006] The objective of the present invention is to promote power saving in cameras associated with event-triggered video.

[0007] According to the first aspect, a method for recording an event video sequence is presented, and the event video sequence is: - A pre-event video sequence including video showing the monitored scene during a predetermined period before event detection, and - Post-event video sequence containing video showing the monitored scene from the time of event detection. Includes, The method is, - A step of sequentially capturing image frames, - The newly acquired image frame is added to a set of pre-event image frames corresponding to a predetermined period, thereby continuously storing the newly acquired image frame in the pre-event buffer. - A step of receiving a first signal indicating that an event has been detected, - Upon receiving the first signal, 〇A step of interrupting the storage of newly captured image frames in the pre-event buffer, 〇A step of supplying the newly captured image frame to the image processing unit, The image processing unit performs image processing on newly acquired image frames. The steps include: storing the processed image frames in memory as a post-event video sequence, - A step of receiving a second signal indicating that the event has ended, - Upon receiving the second signal, ○ A step of interrupting the supply of newly acquired image frames to the image processing unit, The steps include: 〇 Supplying a set of image frames from the pre-event buffer to the image processing unit, The steps include: 〇 Performing image processing on a set of image frames within the image processing unit, The steps include: storing the processed set of image frames in memory as a pre-event video sequence; Includes.

[0008] By storing a set of image frames in the pre-event buffer without pre-processing them within the image processing unit, it is possible to achieve a substantial reduction in power consumption by the camera during periods when no events occur, while still allowing the creation of pre-event video sequences when needed, and providing valuable insights into the operations that occur during the period leading up to the reception of the first signal. By prioritizing the processing of the post-event video sequence over the processing of the set of pre-event image frames, it is possible to stream the post-event portion of the event video sequence from the camera for viewing by the user in real time or near real time. The pre-event video sequence, which shows the scene during the limited period leading up to the first signal, is then processed as soon as the second signal is received and the event ends, and can be viewed immediately thereafter.

[0009] In battery-powered cameras, delaying image processing of the set of images forming the pre-event video sequence until it is actually needed prevents unnecessary battery power consumption. Therefore, the battery will last longer, and the camera may be used for longer periods without needing to be recharged. This method is also useful in cameras where the total power draw needs to be kept within a certain limit and within a given power class for other reasons, such as when the camera is powered by a Power over Ethernet (PoE) connection. A possible disadvantage is that a larger pre-event buffer is required because image frames occupy more space in the case of raw (unprocessed) format compared to processed, especially encoded, format. However, in situations where power consumption reduction is critical, this method remains an attractive option.

[0010] Another effect of delaying processing and subsequent storage of the image in memory is that there are fewer read / write operations performed on the memory, which in turn extends the memory's lifespan.

[0011] Furthermore, delaying processing means that it may not be necessary to process image frames from the pre-event buffer at full frame rate; in other words, it can be tolerated that processing each image frame takes longer. This can allow for the use of more advanced image processing and encoding algorithms without adding more processing power. Allowing processing to be performed at a slower rate than full frame rate also means that processing can be done at a lower clock frequency, which reduces the total power required.

[0012] The method may further include the step of sequentially discarding the oldest image frame from the pre-event buffer as a newly captured image frame is stored, or in other words, a circular buffer (first-in, first-out, FIFO) memory can be used for the pre-event buffer. This provides an efficient option for storing the raw set of image frames that make up a possible pre-event video sequence.

[0013] The method may further include feeding a subset of the newly captured image data to an image processing unit before receiving the first signal. This subset of image data can be used, for example, to stream to a remote user to give an overall view of the scene during the entire visit to the scene by the person holding the camera. The subset of image data can be stored in memory for later use, either additionally or alternatively.

[0014] A subset of image data can be generated by spatially subsampling a newly captured image, thereby supplying the image processing unit with image frames having a reduced resolution compared to the newly captured image. Alternatively, a subset of image data can be generated by temporally subsampling a newly captured image frame, thereby supplying the image processing unit with a stream of image frames having a reduced frame rate compared to the frame rate of the newly captured image frame. Both alternative methods provide means for creating a subset that has only a very limited amount of image data while still allowing the overall appearance of the scene to be seen, and which can be processed in image processing without causing significant power consumption.

[0015] The step of storing newly captured image frames in the pre-event buffer may include compressing the image frames. This achieves more efficient storage of the raw set of image frames and allows a smaller pre-event buffer to be used for the same amount of image frames stored in the pre-event buffer. The compression used in this step would be a power-efficient compression such as run-length encoding or jpg encoding, which substantially reduces the size of the image frames without increasing the power consumed by the camera.

[0016] The method may further include feeding a set of image frames from the pre-event buffer to the image processing unit, and then resuming the continuous storage of newly captured image frames in the pre-event buffer. Thus, a new set of image frames becomes available, which can then form the basis for a new pre-event video sequence.

[0017] The steps for performing image processing may include one or more of the following: defective pixel correction, white balancing, demozaising, matrixing, gamma correction, sharpening, noise filtering, scaling, and encoding.

[0018] Delaying image encoding until the event occurs makes it possible to start both pre-event and post-event video sequences using intra-encoded frames (I-frames), which makes decoding and viewing the event video sequence much more convenient. In conventional solutions where the pre-event video sequence is encoded sequentially, there is little opportunity to control the encoding to ensure that the I-frames are encoded at the start of the event video sequence. When viewing conventional event video sequences, it is necessary to go back to the start of the encoded group of pictures (GOP), which can sometimes take about a minute when decoding and viewing the event video. In this method, since it is possible to start encoding the pre-event video sequence using I-frames, it becomes possible to start decoding and viewing just as the event video sequence begins.

[0019] The first signal can be received from an image analysis unit positioned to detect events in the monitored scene based on the captured image frames. Examples of processes used by such an image analysis unit include video motion detection, object recognition, foreground-background segmentation, and other methods for determining, based on the video image, that some type of event of interest is occurring in the scene.

[0020] Further or alternatively, the first signal can be received from an external event detection unit arranged to detect events within the monitored scene. The term "external" should be interpreted as being separated from the camera, such as being outside the camera, operating independently of the camera, or physically or logically separated from the camera. Such an external event detection unit can include sensors for detecting when a weapon is drawn from a holster, or movement sensors for detecting, for example, when a person holding the camera has fallen, been pushed, or started running. The external event detection unit can also include some kind of position measurement sensor, such as for receiving a GPS signal, to indicate that the camera has entered an area where it is necessary to record video. Other examples of events that can be detected by the external event detection unit are changes in the GPS connection or changes in the connection to a communication network, such as a change in the connection to a Wi-Fi network or a cellular network.

[0021] The external event detection unit can also include sensors, such as PIR sensors, radar, or lidar, that can detect movement or objects within the scene. In some cases, the external event detection unit can also be another camera. The other camera can be of the same type as the camera itself or can have a completely different configuration. As an example, if the camera using the method presented herein is a body-worn camera, the other camera can be another similar body-worn camera, or the other camera can be a monitoring camera mounted for monitoring the scene, such as a thermal camera or a visual camera. This camera can transmit the first signal to any body-worn camera in the vicinity.

[0022] As another option, audio or sound from the scene, such as the sound of gunfire or a loud scream, can be analyzed to find an indication that an event justifying video recording is occurring.

[0023] The second signal can be generated as a response to the first signal no longer being received. This may apply, for example, when the first signal is received from a motion sensor indicating that a person wearing the camera is running, and the sensor indicates that the person has stopped running.

[0024] Furthermore or alternatively, the second signal can be generated in response to a timer reaching a predetermined value, and the timer starts when the first signal is received. This can be useful in situations where it can be reliably assumed that any event that needs to be recorded on video will have a duration shorter than the predetermined value. The second signal can be generated by an external event detection unit based on some kind of data from any of the sensors used to generate the first signal or the absence of such data.

[0025] The method can further include the step of streaming the processed image frames of the post - event video sequence to a recipient when a first signal indicating that an event has been detected is received. Thus, a third party such as a security operator can be immediately notified that an event is occurring within the scene and can take appropriate actions such as sending a backup to the personnel within the scene. The video can be streamed to a remote server via, for example, a mobile phone network or other types of wireless networks. The security operator can view the streamed images by means of a video management system connected to the remote server.

[0026] According to a second aspect of the present invention, there is provided a monitoring camera configured to record an event video sequence, The event video sequence is - a pre - event video sequence including video showing the monitored scene during a predetermined period before event detection, and - Post-event video sequence containing video showing the monitored scene from the time of event detection. Includes, The camera is - An image acquisition unit configured to continuously capture image frames, - A pre-event buffer configured to continuously store newly acquired image frames by adding them to a set of pre-event image frames corresponding to a predetermined period, - An event unit configured to receive a first signal indicating that an event has been detected and a second signal indicating that the event has ended, - An image processing unit configured to process image frames, - Memory configured to store processed image frames Equipped with, Upon receiving the first signal, - The camera is configured to interrupt the storage of newly captured image frames in the pre-event buffer and to send the newly captured images to the image processing unit. - The image processing unit is configured to perform image processing on newly acquired image frames and store the processed images in memory as a post-event video sequence. Upon receiving the second signal, - The camera is configured to interrupt the feeding of newly captured image frames to the image processing unit. - The camera is configured to feed a set of image frames from the pre-event buffer to the image processing unit. - The image processing unit is configured to perform image processing on a set of image frames. - The camera is configured to store a processed set of image frames in memory as a pre-event video sequence.

[0027] The features of the method according to the first embodiment described above also apply to this second embodiment, where applicable. References are made above to avoid unnecessary repetition.

[0028] Further scope of applicability of the present invention will become apparent from the detailed description below. However, since various changes and modifications within the scope of the present invention will become apparent to those skilled in the art from this detailed description, it should be understood that the detailed description and specific examples are provided for illustrative purposes only, while illustrating preferred embodiments of the present invention.

[0029] Therefore, it is understood that the present invention is not limited to specific component parts of the device described or specific actions of the method described, because such devices and methods may vary. It is also understood that the terms used herein are merely for describing specific embodiments and are not intended to be restrictive. It should be noted that, as used herein and in the appended claims, the articles “a,” “an,” “the,” and “said” are intended to mean that there is one or more elements unless the context explicitly indicates otherwise. For example, a reference to “a unit” or “the unit” could include several devices and similar. Furthermore, the phrases “comprising,” “including,” “containing,” and similar phrases do not exclude other elements or steps.

[0030] The present invention will be described more fully hereafter with reference to the accompanying drawings illustrating currently preferred embodiments of the invention. However, the invention can be embodied in many different forms and should not be construed as being limited to the embodiments described herein; rather, these embodiments are provided for thoroughness and completeness and to fully convey the scope of the invention to those skilled in the art. [Brief explanation of the drawing]

[0031] [Figure 1] This is a diagram of a camera. [Figure 2] This figure shows the situation in which the camera in Figure 1 is used. [Figure 3] The present invention presents a method according to an embodiment of the present invention. [Modes for carrying out the invention]

[0032] Figure 1 shows a camera such as a wearable or body-worn camera, BWC, 100. Camera 100 has optical components 102 and an image acquisition unit 104, as is generally known.

[0033] Referring to Figure 1, the camera 100 also includes an image processing unit 106 and a memory 108 for storing the processed images. The memory 108 can be provided in the form of an SD card or flash memory. In the context of this application, the term image processing can encompass a wide variety of operations, some examples of which are defective pixel correction, white balancing, demosaicing, matrixing, gamma correction, sharpening, noise filtering, scaling, and encoding.

[0034] The camera also includes a pre-event buffer 112 configured to store a set of pre-event image frames received from the image acquisition unit 104. The pre-event buffer may be provided in the form of memory adapted for primary storage, such as RAM, DRAM, or SRAM memory.

[0035] Generally, the pre-event buffer 112 is configured as a circular buffer or a first-in, first-out (FIFO) buffer, where newly acquired images supplied to the pre-event buffer 112 from the image acquisition unit 104 replace the oldest images already stored in the pre-event buffer 112. However, other configurations of the pre-event buffer 112 are also possible. Further improvements can be made in selecting which images should be discarded from the pre-event buffer. For example, in situations where HDR / WDR video is acquired, it may be possible to decide to discard all long exposures or all short exposures. When creating a pre-event video sequence, if, for example, a longer period with a lower frame rate is considered useful, it may be possible to discard all second images or all third images, etc.

[0036] The pre-event buffer 112 is located upstream of the image processing unit 106. Therefore, the set of pre-event image frames stored in the pre-event buffer 112 is not processed by the image processing unit 106, which means that the set is typically larger than it would be after being processed by the image processing unit 106, as is the case in prior art solutions for creating pre-event video sequences. However, as we have recognized, in situations where saving power is of paramount importance, adding more storage space to the pre-event buffer 112 to allow storage of a set of raw or nearly raw image frames from the image acquisition unit 104 is better than spending power unnecessarily processing image data that may be discarded later due to the absence of events requiring a pre-event video sequence.

[0037] Optionally, simple compression in the compression unit 114 can be performed on the image frames before storing them in the pre-event buffer 112. This can still be done without consuming excessive power and reducing the size of the captured image frames by approximately tenfold. For example, lossless run-length encoding using dedicated hardware blocks, or a form of JPEG compression using, for example, 4x4 or 8x8 blocks. The selected compression method is typically of a type that avoids time dependencies between images. A smaller pre-event buffer can be used to store the same amount of images.

[0038] Furthermore, or alternatively, it is possible to perform limited image processing using a very low-power processing step before storing the image frame in the pre-event buffer 112. This is shown as moving such a step from the image processing unit 106 to a separate initial image processing unit 116, allowing the pre-event image frame to be processed in the initial image processing unit 116 before being stored in the pre-event buffer 112. It should be noted that showing this as a separate unit is merely for illustrative purposes, and that it could also be shown as an image processing unit 106 having an output that feeds the image to the pre-event buffer 112 after performing only the processing steps illustrated below.

[0039] Examples of steps that can be performed by the initial image processing unit 116 before being stored in the pre-event buffer 112 include defective pixel correction and demozaising, the latter also known as color interpolation or reconstruction, i.e., the process of converting an image from Bayer values ​​to RGB values. The reason for performing these steps within the initial image processing unit 116 is that these steps consume a limited amount of power, and these steps are performed at the start of image processing.

[0040] Furthermore, the conversion from Bayer to RGB results in increased smoothness, which in turn makes the image more easily compressible, thereby allowing an optional compression unit 114 to further reduce the image size, which in turn allows the use of a smaller pre-event buffer 112 to store a set of pre-event image frames, or, if so desired, allows the storage of a large number of pre-event image frames within the pre-event buffer 112.

[0041] However, it is important to note that pre-event image frames are mostly stored in the pre-event buffer 112 in an unprocessed or raw format in order to consume as little power as possible for processing images that will likely become uninteresting and be discarded. It should be noted that although camera 100 is continuously capturing video of the scene, the images are not being fed to the image processing unit 106 and memory 108. The captured image frames are typically only temporarily stored in the pre-event buffer 112, as described above.

[0042] Therefore, image frames are not sent to the image processing unit 106 until an event occurs that requires video recording by the camera 100. However, as will be discussed in more detail below in this text, there may be cases where a subset of image data from the image acquisition unit 104 is supplied to the image processing unit 106 even during periods when no events are occurring.

[0043] Figure 2 shows a typical situation in which camera 100 is in use. Camera 100 is used to monitor scene 200 and is worn by person 202. Various activities may occur in scene 200, and at some point person 202 may determine that an event has occurred that requires video recording to begin.

[0044] Person 202 will then activate a switch on camera 100 or press button 204 to enable video recording to begin. When button 204 is pressed, a first signal 120 is sent to event unit 118 located inside camera 100. Pressing button 204 is just one example of how an external event detection unit signals camera 100, or more precisely, event unit 118, that an event requiring video recording has occurred, started, or is occurring.

[0045] Other examples of events that may be detected that could cause such an external event detection unit and a first signal 120 typically include a pressure sensor or motion sensor that signals that a weapon has been removed from its holster in a situation where the camera 100 is being held by a police officer, or a sensor with an accelerometer or gyroscope that signals that a certain type of movement is occurring that indicates that the person holding the camera 100 is moving in a certain manner. One example of this is a movement that indicates a fall has occurred, for example, that the camera (and person) has moved from a vertical position (standing) to a horizontal position (lying down). Another example is when the sensor detects a movement that indicates the person holding the camera is being pushed or shoved.

[0046] Another example of an external event detection unit that can be used to provide the first signal 120 to the event unit 118 is a motion detector that detects motion in a scene. The motion detector that detects motion in a scene can be a PIR sensor, a depth-of-field sensor, a laser, a radar, or any other type of device capable of detecting motion in a scene. More advanced analysis of the scene can also be performed, which may allow for ignoring motions smaller than a threshold, repetitive motions, or motions from certain scene areas that are known to contain, for example, a swaying tree. All of these are examples of how an external event detection unit can be made to send the first signal 120 to the event unit 118.

[0047] Another example of an external event detection unit that generates the first signal would be an audio analysis unit configured to capture and analyze sounds or voices in a scene, such as gunshots or screams, indicating that an event is occurring, and then transmit the first signal 120 in response.

[0048] Another example of an external event detection unit is a location determination unit that uses a GPS signal or some other location measurement signal to determine that the camera has reached a location or area where it should record video. In response to such determination, the external event detection unit transmits a first signal 120 to the event unit 118. A changed connection state to a GPS network or another type of location measurement network can also cause the first signal 120 to be transmitted.

[0049] Another example of an event that can be detected by an external event detection unit and cause the event unit 118 to send the first signal 120 is a change in connection to a communication network, such as a connection to a Wi-Fi network or a mobile phone network.

[0050] Another example of how the first signal can be achieved is by using an image analysis unit 122 that analyzes the captured image frames to find specific content in the scene, such as motion with certain features or objects that meet certain predetermined criteria.

[0051] When the event unit 118 receives the first signal 120, the image acquisition unit 104 stops feeding image frames to the pre-event buffer 112, and newly acquired image frames are instead fed from the image acquisition unit to the image processing unit 106, which performs image processing on the image frames. The processed image frames from the image processing unit 106 are stored in memory 108 as a post-event video sequence.

[0052] At some point after the first signal is received by the event unit 118, the event unit 118 will receive a second signal 124. The second signal 124 indicates that an event requiring video recording has stopped, or is likely to have stopped. The second signal can be generated by person 202 pressing button 204 again to indicate that video recording can be stopped. A second button may also be provided on camera 100 to generate the second signal.

[0053] Another option for generating the second signal 124 is from a timer, which starts when the first signal 120 is received and generates the second signal 124 after a predetermined time has elapsed or after input from a sensor included in an external event detection unit, or after the loss of that input. For example, the second signal 124 could be generated by a sensor indicating that the weapon has been reinserted into the holster or by a sensor indicating that the movement has stopped. Furthermore, just as when the first signal is generated, an image frame can be analyzed by the image analysis unit 122 to determine that the event that triggered the video recording has now stopped, and thus trigger the generation of the second signal.

[0054] Other types of inputs can also be used to generate a second signal. Such inputs may come from sensors indicating, for example, that the person holding the camera has left a certain area or position, that sound has stopped, or that movement in the scene has stopped or an object has left the scene.

[0055] As discussed above, there is often a need to understand what happened even before the first signal 120 is generated, i.e., a pre-event video sequence is required. Therefore, upon reception of the second signal 124, the feeding of image frames from the image acquisition unit 104 to the image processing unit 106 is stopped, and instead, the set of image frames that were waiting in the pre-event buffer 112 while the image processing unit 106 was receiving image frames from the image acquisition unit 104 is now fed to the image processing unit 106. The set of images is then processed, and the processed set of images is then appended to memory 108 as a pre-event video sequence to the post-event video sequence that has been stored in memory 108 beforehand. Furthermore, the image acquisition unit 104 will now resume feeding newly acquired images to the pre-event buffer 112, which is ready to start receiving images again.

[0056] It may be noted that a set of image frames from the pre-event buffer can be processed at a rate slower than the full frame rate, meaning that more time can be used to process each image frame than is permissible when processing live video. Thus, more advanced image processing can be used, or the image processing unit 106 can be configured to use less power to process each image frame, for example, by being configured to run at a lower clock frequency. Processing a set of image frames at a rate slower than the full frame rate, conveniently combined with the use of a larger pre-event buffer, allows for the storage of any new pre-event image frames that may be conceivable while the set of image frames is being processed.

[0057] Figure 3 shows a method 300 for recording an event video sequence. In step 302, an image frame is captured by an image acquisition unit 104. In an optional step 304, the image frame is compressed before being stored in a pre-event buffer 112 in step 306. At some point, a first signal 120 indicating that an event has occurred is received in step 308. The image acquisition unit 104 then stops sending the image frame to the pre-event buffer 112 for storage, and the image frame is instead sent to an image processing unit 106 for processing and to memory 108 for storage to create a post-event video sequence in step 310.

[0058] As an optional measure in this step, the processed image can also be streamed to a remote recipient in a form in which the server provides the logged-in operator with immediate access to the video captured by the camera 100 after receiving the first signal 120, and the operator determines whether it is necessary to perform actions such as sending help to the person 202 holding the camera 100.

[0059] In step 312, a second signal 124 indicating the end of the event is received. The pre-event video sequence is then created in step 314 by supplying the set of image frames stored in the pre-event buffer 112 to the image processing unit 106 for processing, and then supplying the processed set of images to the memory 108 for storage as the pre-event video sequence. If the image frames were compressed in connection with being stored in the pre-event buffer 112, appropriate decompression is performed prior to processing in the image processing unit 106. Both the post-event video sequence and the pre-event video sequence form the event video sequence in step 316, and the event video sequence is stored in the memory 108.

[0060] It should be noted that step 302 occurs sequentially during camera operation and is presented only as the first step for illustrative purposes. Similarly, upon reception of the second signal, when the contents of the pre-event buffer 112 are fed to the image processing unit, the image acquisition unit 104 will feed the image frames back to the pre-event buffer 112, which will then store the image frames as a new set of image frames in preparation for the next event to occur and for a new pre-event video sequence to be created, after any optional compression of the image.

[0061] As described above, in the variations of the solution presented in this text, a subset of image data can be fed from the image acquisition unit 104 to the image processing unit 106 during the period when image frames are fed to the pre-event buffer 112, i.e., during the period when no event is indicated to occur. This subset of image data can be used, for example, to stream from camera 100. The subset of image data is provided by spatially subsampling the acquired image frames to provide lower resolution image frames, or by temporally subsampling the acquired image frames to provide a reduced frame rate, or both. The processed subset of image data can also be stored in memory 108 and used when creating an event video sequence.

[0062] The storage of the processed subset of image data can be done in a manner similar to how images are stored in the pre-event buffer 112, i.e., how older images can be discarded after a certain period of time has elapsed or after a certain amount of new images have been added to memory. The camera can be set up to feed only image data that was not included in the temporally or spatially subsampled image data used for streaming distribution from the image acquisition unit 104 to the pre-event buffer 112. Once the pre-event video sequence is created, the image processing unit 106 then combines the set of image frames from the pre-event buffer 112 with the pre-processed subset of image data to provide the complete pre-event video sequence.

[0063] It should be noted that the different units presented in the above text, such as the image processing unit 106, the compression unit 114, the initial image processing unit 116, the event unit 118, and the image analysis unit 122, can each be implemented in hardware, software, or any combination thereof. One or more units may be provided in the form of dedicated circuit sections configured to perform the functions of their respective units, or as a set of software program instructions implemented to run on a standard processing unit and perform the functions of their respective units.

[0064] Finally, it should be stated that, based on the examination of the drawings, disclosures, and appended claims, a person skilled in the art can understand and implement other variations of the disclosed embodiments when carrying out the claimed invention.

[0065] An example of such a modification is that, although the present invention has been described in relation to a body-worn camera, it can also be used, for example, in a camera mounted on a building or inside a vehicle. When the camera has a limited amount of power available, or when it is possible to provide a larger amount of memory space in the pre-event buffer, and there are other reasons to want to conserve power in relation to event video recording, the solutions described herein can be used to enable lower power consumption during periods when no events are occurring.

[0066] In summary, a method is presented for providing an event-initiated video sequence that includes a pre-event sequence and a post-event sequence. Pre-event image frames are stored in their raw format until the event occurs. Power savings are achieved by deferring image processing of the pre-event video sequence.

Claims

1. A method (300) for recording an event video sequence, the event video sequence comprising: a pre-event video sequence showing the monitored scene (200) for a predetermined period of time before the event detection, and a post-event video sequence showing said monitored scene from the time of event detection; Including, The method comprises: - capturing (302) successive image frames; - storing (304) a newly captured image frame in a pre-event buffer (112) consecutively by appending the newly captured image frame to a set of pre-event image frames corresponding to the predetermined period, wherein the newly captured image frames stored in the pre-event buffer (112) have not yet been subjected to image processing in an image processing unit (106) consisting of one or more of the following: defective pixel correction, white balancing, demosaicing, matrixing, gamma correction, sharpening, noise filtering, scaling and encoding; receiving (308) a first signal (120) indicating that an event is detected; upon receiving said first signal, interrupting the storage of newly captured image frames in the pre-event buffer; feeding the newly captured image frame to said image processing unit (106); - performing image processing of said newly captured image frame in said image processing unit; storing (310) the processed image frames as the post-event video sequence in memory (108); receiving (312) a second signal (124) indicating that said event has ended; upon receiving said second signal, interrupting the feeding of newly captured image frames to the image processing unit; - feeding said set of image frames from said pre-event buffer to said image processing unit; performing image processing of said set of image frames in said image processing unit; o storing (314) the processed set of image frames in the memory as the pre-event video sequence; Including, A method (300), wherein said step of performing image processing comprises one or more of the following: defective pixel correction, white balancing, demosaicing, matrixing, gamma correction, sharpening, noise filtering, scaling, and encoding.

2. The method of claim 1 , further comprising the step of continuously discarding the oldest image frame from the pre-event buffer as a newly captured image frame is stored.

3. The method of claim 1 , further comprising: prior to receiving the first signal, sending a subset of image data of the newly captured image to the image processing unit.

4. 4. The method of claim 3, wherein the subset of image data is generated by spatially subsampling the newly captured image, whereby an image frame having a reduced resolution compared to the newly captured image is delivered to the image processing unit.

5. 5. The method of claim 3 or 4, wherein the subset of image data is generated by temporally subsampling the newly captured image frames, whereby a stream of image frames having a reduced frame rate compared to a frame rate of the newly captured images is fed to the image processing unit.

6. 6. The method of claim 1, further comprising resuming continuous storage of newly captured image frames in the pre-event buffer after delivering the set of image frames from the pre-event buffer to the image processing unit.

7. 7. The method according to claim 1, wherein the first signal is received from an image analysis unit (122) arranged to detect an event in the monitored scene based on the captured image frames.

8. The method according to claim 1 , wherein the first signal is received from an external event detection unit arranged to detect an event in the monitored scene.

9. 9. The method of claim 1, wherein the second signal is generated in response to the first signal being no longer received.

10. 10. A method according to claim 1, wherein the second signal is generated in response to a timer reaching a predetermined value, the timer being started when the first signal is received.

11. 11. The method of claim 1, further comprising the step of streaming the processed image frames of the post-event video sequence to a recipient upon receiving the first signal indicating that an event is detected.

12. A monitoring camera (100) configured to record an event video sequence, comprising: The event video sequence includes: a pre-event video sequence comprising a video showing the monitored scene (200) for a predetermined period of time before the event detection; and a post-event video sequence comprising video showing said monitored scene from the time of event detection; Including, The monitoring camera includes: an image capture unit (104) configured to capture image frames successively; an event unit (118) configured to receive a first signal indicating that an event is detected and a second signal indicating that said event has finished; an image processing unit (106) configured to process image frames; a pre-event buffer (112) arranged upstream of said image processing unit and configured to successively store newly captured image frames by appending said newly captured image frames to a set of pre-event image frames corresponding to said predetermined period, wherein said newly captured image frames stored in said pre-event buffer have not yet undergone image processing in an image processing unit consisting of one or more of the following: defective pixel correction, white balancing, demosaicing, matrixing, gamma correction, sharpening, noise filtering, scaling and encoding; a memory (108) adapted to store the processed image frames; Equipped with Upon receiving the first signal, the monitoring camera is adapted to interrupt the storage of newly captured image frames in the pre-event buffer and to feed newly captured images to the image processing unit; - said image processing unit is configured to perform image processing of said newly captured image frames and to store said processed images as said post-event video sequence in said memory; Upon receiving the second signal, the monitoring camera is adapted to interrupt the feeding of newly captured image frames to the image processing unit; the monitoring camera is configured to deliver the set of image frames from the pre-event buffer to the image processing unit; - said image processing unit is configured to perform image processing of said set of image frames; - said monitoring camera is configured to store said processed set of image frames as said pre-event video sequence in said memory; The image processing of the monitoring camera (100) includes one or more of the following: defective pixel correction, white balancing, demosaicing, matrixing, gamma correction, sharpening, noise filtering, scaling, and encoding.

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