Classifications

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  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
  • H04N19/174—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a slice, e.g. a line of blocks or a group of blocks
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  • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
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  • H04N21/234—Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs
  • H04N21/2347—Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs involving video stream encryption
  • H04N21/23476—Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs involving video stream encryption by partially encrypting, e.g. encrypting the ending portion of a movie
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  • H04N21/8451—Structuring of content, e.g. decomposing content into time segments using Advanced Video Coding [AVC]
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  • H04N21/845—Structuring of content, e.g. decomposing content into time segments
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  • H04L2209/30—Compression, e.g. Merkle-Damgard construction
• • H—ELECTRICITY
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• • H—ELECTRICITY
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  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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  • H04L2209/60—Digital content management, e.g. content distribution
  • H04L2209/601—Broadcast encryption

Definitions

• the invention relates to a method and a system for transmitting an at least partially compressed video stream by ensuring the security of the information to be transmitted.
• the method includes a step of encrypting selected areas in a given image of the stream.
• the invention applies to transmit compressed video streams in a transmission context that can be monitored and to prevent access to the content of certain protected areas of the image. Thus, any malicious visualization of the flow can be avoided. It allows to protect the privacy of people for example in places equipped with video surveillance.
• the term "foreground” designates the mobile object or objects in a video sequence, for example, a pedestrian, a vehicle, a molecule in medical imaging.
• the designation "background” is used with reference to the environment as well as to fixed objects. This includes, for example, soil, buildings, trees that are not perfectly immobile or parked cars.
• the invention can, inter alia, be applied in applications implementing the standard defined jointly by the ISO MPEG and the video coding group of the ITU-T called H.264 or MPEG-4 AVC (advanced video coding) which is a video standard providing more efficient compression than previous video standards while having a reasonable implementation complexity and directed towards network applications.
• H.264 or MPEG-4 AVC advanced video coding
• the Applicant uses the expression stream during compression or video sequence being compressed to designate the same object, namely: during compression means that the current image has not been compressed when we execute the steps leading to the encryption of the objects to be protected but that the previous images have already been compressed.
• the words encryption or encryption are used to designate the same transformation.
• the expression slice or portion more known in the field under the Anglo-Saxon "slice" corresponds to a sub-part of the image consisting of macroblocks that belong to the same set defined by the user.
• One of the objects of the present invention is to provide a method for protecting the image content or certain areas of an image in order to preserve the confidentiality of the data. This is, in this implementation example, executed during the step of compressing a data stream.
• the invention relates to a method for protecting at least part of a video stream or video sequence at least partially compressed against a violation of the information contained in said stream, said stream being able to be decomposed into several types of objects, the process applying on each of the images contained in a video sequence characterized in that it comprises at least the following steps: a) analyzing the video sequence in the compressed domain in order to define for a given image N at least one or more groups of objects to be protected by encryption, designated first group of objects, a second group of objects then being associated with the rest of the image, the transformed coefficients and the motion estimation vectors being directly transmitted to the compression step d), b ) predicting from the data obtained from the analysis in step a) of the compressed image N, the position of the objects for a next image N + 1, c) determining the division into portions or groups of portions of the image N + 1, d) compressing the parts of the image comprising the group or groups of portions of the image N + 1 related to the first group and encrypting at least a portion of the
• the method can add to the flows from steps d) and e), information identifying groups of encrypted objects or not.
• an undefined "NAL” network transport unit (described in H.264 as "undefined NAL") will be added. , which will convey information indicating which portions (slices) have been encrypted.
• the step of predicting the position of an object comprises, for example, the following steps:
• the appahement step may be based on a Munkres algorithm, and that of tracking on a Kalman filter.
• the method implements for the encryption step a selection of bits allowing decoding with a standard decoder, for example, according to the aforementioned article authored by Cyril Bergeron and Catherine Lamy. Since the video sequence is produced, for example, via the MPEG-4 part 10 / H.264 standard, the method for defining the portions or "slices groups" uses, for example, the flexible macroblock or FMO (Flexible) scheduling technique. Macrocbloc Ordering) authorizing the definition of macroblock portion groups or macroblock "slice groups". The method can associate either a group of portions or "slices group” by object to protect or moving object, or a group slices to all moving objects (a second then being assigned to the background). The "image update" of the slices group is accompanied, for example, by the transmission of a parameter PPS (Picture Parameters Set) which indicates to the decoder the new division of the image.
• PPS Picture Parameters Set
• the invention also relates to a system for visually encrypting at least part of a video stream or video sequence at least partially compressed against unauthorized viewing of information contained in said stream, characterized in that comprises at least: a video portion for transmitting an image stream during compression, a video encoder, a stream selection module to be encrypted or encrypted and a suitable encryption or encryption module) implementing the steps the method comprising the aforementioned characteristics and a transmission module of the stream at least partially encrypted or encrypted.
• FIGS. 1 to 4 the results obtained by an analysis in the compressed domain
• FIG. 5 an exemplary method according to the invention applied to a video stream during compression
• FIG. 6 is an exemplary diagram for a video encoder adapted to implement the encryption method according to the invention.
• the image is first divided into blocks of pixels (of 4x4 or 8x8 according to the MPEG-1/2/4 standards), which are then subjected to a transform allowing a passage in the frequency domain, then a quantization allows you to approximate or suppress the high frequencies to which the eye is less sensitive. Finally, the quantified data are entropically encoded. For this purpose, it allows to suppress or attenuate the high frequencies less sensitive to the eye and thus reduce the amount of information.
• the second step is to reduce time redundancy. For this purpose, it makes it possible to predict an image from one or several other image (s) previously decoded (s) within the same sequence (motion prediction). For this, the process searches in these reference images the block that best corresponds to the desired prediction.
• Vector Motion Estimation also known as motion vector
• a vector Vector Motion Estimation, also known as motion vector
• These vectors do not necessarily correspond to a real movement of an object in the video sequence but can be similar to noise. Different steps are needed to use this information to identify mobile objects.
• the work described in the aforementioned Leny et al publication, "Motion Estimation for Real-Time Analysis of Videos in the Compressed Domain", and in the aforementioned US patent application have delineated five functions making the analysis in the compressed domain possible, these functions and the modules implementing them are represented in FIG.
• a low-resolution decoder allows to reconstruct the entirety of a sequence at the resolution of the block, removing on this scale the motion prediction;
• a motion estimation vector generator (MEG - Motion Estimation Generator) determines vectors for all the blocks encoded by the encoder in "Intra" mode (within Intra or predicted images); 3) a Low-Res Object Segmentation (LROS) module relies on an estimation of the background in the compressed domain thanks to the sequences reconstructed by the LRD and thus gives a first estimate of the objects mobile; 4) a motion-based object filter (OMF) uses MEG output vectors to determine moving areas from motion estimation; 5) finally a module allowing to establish a cooperative decision (CD - Cooperative Decision) starting from these two segmentations, takes into account the specificities of each module according to the type of analyzed image (Intra or predicted).
• MEG Motion estimation vector generator
• LROS Low-Res Object Segmentation
• the main interest of the analysis in the compressed domain relates to computation times and memory requirements which are considerably reduced compared to conventional analysis tools.
• the analysis times are currently 10 to 20 times the real time (250 to 500 images processed per second) for 720x576 4: 2: 0 images.
• FIG. 2 show the identification of zones containing moving objects.
• Figure 3 schematizes the extraction of specific data such as motion estimation vectors and Figure 4 low resolution confidence cards obtained corresponding to the contours of the image.
• FIG. 5 schematizes an example of implementation of the method according to the invention in which zones of an image being compressed, that is to say during the compression step, will be encrypted or encrypted
• This encryption step will be executed during the compression step implemented within a video transmitter comprising at least one video encoder and a processing unit as shown schematically in FIG. 6.
• Some areas of the image having more importance, in the flow in the sense of confidentiality will be chosen to be protected against undesired uses.
• the example given for illustrative purposes includes two zones, but nothing prevents a user from applying the method to several zones, each of which will have an associated degree of confidentiality, therefore different encryption keys and adapted to the level of confidentiality.
• the method and the system according to the invention implement the analysis in the compressed domain coupled to a tracking of objects better known under the name Anglo-Saxon "tracking". This includes linking the independently segmented objects on each image to obtain a single, single object tracked during the sequence. For example, without "object tracking", if an object is present and segmented on 25 images, then the process will have to process 25 objects independently, which can bring multiple problems of merging tracks or indexing for example.
• the analysis of video sequences in the compressed domain presents, for its part, the advantage of using part of the work done by the video coder by exploiting the information available in the compressed domain.
• the method according to the invention will consider the images one after the other. It will select areas in an image that must be protected by encryption and apply the process to these areas.
• the stream 1 being compressed within an encoder is transmitted to a first analysis step 2.
• This step is executed frame by frame, whereas, just like the method, it can be implemented only on certain images. which will, for example, be determined and selected upstream of the process (output frequency less than that of the stream before compression, selection of certain images according to their type, etc.).
• the first step implemented during the method has the particular function of extracting data representative of an image that has been compressed. For a compressed image, the method has at the end of the first step, for example, a sequence of masks comprising blobs (regions having received the same label) related to the moving objects 3 or foreground in some cases.
• the purpose of the mask is to separate in a compressed image the zones corresponding to the moving objects of the other zones which are quasi-immobile, or background.
• the mask used can be a binary mask. By convention in this case, it is assigned the number "1" to designate foreground objects and the number "0" to designate the background. Any other convention may be used without departing from the scope of the invention.
• the "image update" of the slices group is accompanied, for example, by the transmission of a parameter PPS (Picture Parameters Set) which indicates to the decoder the new division of the image.
• PPS Picture Parameters Set
• compression used immediately by the analysis in the compressed domain does not lead directly to the video stream as it will be stored or transmitted.
• the transforms in the frequency domain are calculated, as well as the motion compensation, but the entropy coding and the encapsulation of the flow will take place only after analysis and encryption.
• the information resulting from the compression can be used directly by the analysis module without going through an unnecessary step of formatting the data (or parsing).
• the transformed coefficients and the motion estimation vectors are directly transmitted from the first to the second module.
• the analysis module that defines the slicing of the next image returns these parameters to the compression brick.
• the invention thus allows more than a simple juxtaposition of functions processing a video stream in series: feedback loops are possible and all the redundant steps between the intervening modules are only present once.
• the method according to the invention can also consider the enclosing boxes of moving objects.
• the bounding box coordinates correspond to the moving objects and are calculated using the mask. These boxes can be defined by two extreme points or by a central point associated with the dimensions of the box. In this case it is possible to have a set of image coordinates or a set for the whole of a sequence with the trajectory information (date and entry point, described curve, date and exit point). This method known to those skilled in the art will not be explained.
• the analysis in the compressed domain can be carried out by implementing the method described in the aforementioned US patent application.
• any method for obtaining an output of the analysis step in the form of masks per image may also be implemented for the analysis step in the compressed domain.
• a tracking or tracking step will be implemented. This tracking step can be performed from these blobs identified by pairing, for example by applying the Munkres algorithm and then by position prediction, for example by Kalman filter, using the history of the position of the objects on the N previous images from the data resulting from the analysis of the compressed image N, as well as the results obtained equivalently on the previous x images; N - x to N. It is then possible to predict the position foreground objects in the next image 4a. This next image N + 1 has not yet been compressed, so it is still possible to determine the division into groups of slices, better known by the English name "slice group", adapted, which corresponds to the step 4b.
• the analysis followed by the tracking step made it possible to predict for the image to be compressed zones containing mobile objects and others belonging to the background.
• the process will then define two types of "groups of portions" 5, 7 for the image.
• the first 5 will correspond to the background areas, which do not require visual cryptography.
• the second 7 will be dedicated to mobile objects, which the encryption or encryption step will target.
• the motion estimation vectors will not point to blocks of another group of portions or "slices group", which allows two independent reconstructions of the first and the background.
• the current result is therefore, in this example implementation, a video sequence comprising for each image at least two slices groups, one containing the background and the other the set of moving objects, with independent predictions between each group slices.
• the protection of the accessibility of the information contained in the image can then be achieved by targeting the "slice groups” comprising the foreground.
• the "slices group” comprising the background will be directly transmitted to a compression step 6.
• the “slices group (s)" including the moving objects will be compressed for the first time 8b and then encrypted 8a. It is also possible to associate different security levels with independent mobile objects, and depending on these levels to adapt the encryption step (number of modified bits, different keys, etc.).
• steps 6 and 8a then form a single compressed and partially encrypted stream Fc to which a NAL of undefined type or undefined type 30 and 31, within which it is possible to transmit any type of information, has been added to indicate the "slices" that have been encrypted.
• NALs 30 and 31 are not reserved for the flow itself or for RTP-RTSP type network protocols.
• a standard decoder will simply set aside this information whereas a specific decoder, developed to take into account these NAL, may choose to use this information to decrypt the portions ("slices”) encrypted.
• the use of a standard decoder will produce a sequence in which the first plan will be visually encrypted with a normal background, whereas, in the case of a decoder using the encryption or encryption key and the information identifying the portions of the encrypted stream, the images will be fully intelligible, readable.
• FIG. 6 is a block diagram of an exemplary system according to the invention comprising a video encoder adapted to execute the steps described in FIG. 5.
• the transmitter comprises a video coder 1 1 adapted to analyze, according to the steps described in FIG. 5, the different zones belonging to the foreground and other areas belonging to the background of a video image, to define the slices groups for the next image and compress it.
• the module 13 determines within the stream the "slice groups" that one or more modules
• This visual encryption operation can also be performed in parallel with a target bit rate order of the moving objects in the sequence. It will then be possible to add robustness to errors (which increases the bit rates) coupled to an adaptation to a target bit rate by optimization during compression or on the fly on the already compressed stream. This coupling will for example maintain a fixed rate while protecting the content related to the foreground.
• the method and the system according to the invention have the following advantages in particular: the fact of using the analysis in the compressed domain makes it possible to determine the areas that a user wishes to protect by visual cryptography.
• the proposed parameterization of "slice groups” makes it possible to closely observe the shape of moving objects at a block resolution. This allows in the context of video surveillance to transmit the encrypted stream, for example, to a guard post where security guards can identify the presence of a person, a car, a truck, etc. distinctly through a silhouette without being able to directly identify the face of the person or the license plate of the vehicle. This feature allows for wider dissemination of surveillance flows while respecting the constraints of respect for privacy.

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• Multimedia (AREA)
• Computer Security & Cryptography (AREA)
• Computer Networks & Wireless Communication (AREA)
• Compression Or Coding Systems Of Tv Signals (AREA)
• Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)

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• 2008
  • 2008-06-03 FR FR0803061A patent/FR2932045B1/fr active Active
• 2009
  • 2009-06-03 EP EP09757565A patent/EP2297952A1/de not_active Ceased
  • 2009-06-03 BR BRPI0913388A patent/BRPI0913388A2/pt not_active Application Discontinuation
  • 2009-06-03 WO PCT/EP2009/056831 patent/WO2009147184A1/fr not_active Ceased
  • 2009-06-03 US US12/996,347 patent/US8447034B2/en not_active Expired - Fee Related
  • 2009-06-03 MX MX2010013318A patent/MX2010013318A/es active IP Right Grant
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