KR20080007086A - A method and apparatus for decoding/encoding a video signal - Google Patents

Abstract

A method and an apparatus for decoding/encoding video signals are provided to perform coding more efficiently when separately coding an anchor picture and a non-anchor picture according to anchor picture identification information because inter-view dependency between the anchor picture and the non-anchor picture is different from each other. A video signal decoding method comprises the following steps of: obtaining flag information indicating whether a video signal is a multi-view video coded bit stream; if so, obtaining identification information indicating whether a coded picture of a current NAL(Network Abstraction Layer) is an anchor picture or not; and decoding information about a multi-view video according to the identification information.

Description

A method and apparatus for decoding / encoding a video signal

1 is a schematic block diagram of a video signal decoding apparatus to which the present invention is applied.

FIG. 2 illustrates a structure of an NAL unit including anchor picture identification information according to an embodiment to which the present invention is applied.

3 is an embodiment to which the present invention is applied and shows a prediction structure for explaining the concept of an anchor picture.

FIG. 4 is an embodiment to which the present invention is applied and shows a structure of an NAL unit including anchor picture identification information in a bitstream compatible with H.264 / AVC.

FIG. 5 is a schematic block diagram of an apparatus for decoding a multiview image using anchor picture identification information according to an embodiment to which the present invention is applied.

6 is an embodiment to which the present invention is applied and shows a prediction structure for explaining the concept of a newly defined anchor picture.

The present invention relates to a method and apparatus for decoding / encoding a video signal.

The mainstream video broadcasting image is a single view image acquired with one camera. Multi-view video, on the other hand, is a three-dimensional (3D) image processing method that geometrically corrects images taken by more than one camera and provides users with various viewpoints in various directions through spatial synthesis. It is a field. Multi-view video can increase the freedom of view for the user, and has a feature that includes a larger area than the image area that can be acquired using a single camera.

When a multi-view video image is randomly accessed according to an overall coding structure, the structure is complicated and a long time delay becomes a problem. Therefore, in order to solve this problem, it is necessary to efficiently use a new picture type called an anchor picture.

An object of the present invention is to provide a method and apparatus for efficiently decoding multi-view image data.

Another object of the present invention is to efficiently perform random access of a multiview video image by adding anchor picture identification information in a standardized manner.

Still another object of the present invention is to more efficiently perform inter-view prediction by using anchor picture identification information.

Another object of the present invention is to more efficiently manage reference pictures for inter-view prediction by using anchor picture identification information.

In order to achieve the above object, the present invention provides a method for obtaining flag information indicating whether a video stream is a multiview video coded bit stream from a video signal and when the video signal is a multiview video coded bitstream according to the flag information. And acquiring identification information indicating whether the coded picture of the NAL is an anchor picture and decoding the information on the multi-view image according to the identification information.

In addition, the present invention provides a video signal encoding method based on multiple viewpoints, the method comprising: generating view dependency information indicating an prediction structure between views and whether the current NAL coded picture is an anchor picture according to the view dependency information. A method of encoding a video signal, the method comprising generating identification information indicating the identification information.

The present invention also provides a bitstream determination unit for obtaining flag information indicating whether a multiview video coded bitstream is a video stream and a current NAL when the video signal is a multiview video coded bitstream according to the flag information. A video signal decoding comprising: an anchor picture identification information acquisition unit for obtaining identification information indicating whether a coded picture of an anchor picture is an anchor picture and a multiview image decoding unit for decoding information about a multiview image according to the identification information Provide the device.

The above objects and features of the construction will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In addition, the terms used in the present invention was selected as a general term widely used as possible now, but in some cases, the term is arbitrarily selected by the applicant, in which case the meaning is described in detail in the description of the invention, It is to be understood that the present invention is to be understood as the meaning of terms rather than the names of terms.

1 is a schematic block diagram of a video signal decoding apparatus to which the present invention is applied.

The decoding apparatus includes a parsing unit 100, an entropy decoding unit 200, an inverse quantization / inverse transform unit 300, an intra prediction unit 400, a deblocking filter unit 500, a decoded picture buffer unit 600, Inter prediction unit 700 and the like. The decoded picture buffer unit 600 includes a reference picture list generator 610, a reference picture manager 620, and the like.

 The parsing unit 100 performs parsing on a NAL basis to decode the received video image. In general, one or more sequence parameter sets and picture parameter sets are transmitted to the decoder before the slice header and slice data are decoded. In this case, various attribute information may be included in the NAL header area or the extension area of the NAL header. For example, temporal level information, view level information, anchor picture identification information, view identifier information, and the like may be included.

Here, the anchor picture identification information refers to information for identifying whether the coded picture of the current NAL unit is an anchor picture (3). An anchor picture refers to an encoded picture in which all slices refer only to slices in frames of the same time zone. For example, an encoded picture refers to only a slice at another viewpoint and no slice at the current viewpoint. In the decoding process of a multiview image, random access between viewpoints is essential. Therefore, access to arbitrary time points should be made possible while minimizing decryption effort. Here, anchor picture identification information may be needed to realize efficient random access.

In addition, according to the overall coding structure of the multiview video image, since the dependency between the viewpoints of the anchor picture and the non-anchor picture is different, it is necessary to distinguish the anchor picture from the non-anchor picture according to the anchor picture identification information. Therefore, the anchor picture identification information may be used to add reference pictures for inter-view prediction when generating a reference picture list. It may also be used to manage the added reference pictures for the inter-view prediction. For example, the reference pictures may be divided into an anchor picture and a non-anchor picture, and the reference pictures that are not used when performing inter-view prediction may be marked not to be used. The anchor picture identification information may also be applied to a hypothetical reference decoder.

Also, temporal level information refers to information on a hierarchical structure for providing temporal scalability from a video signal. Through such temporal level information, it is possible to provide a user with images of various time zones. In addition, the view level information refers to information about a hierarchical structure for providing view expandability from a video signal. In a multi-view video image, it is necessary to define the levels of time and view in order to provide a user with images of various times and views. The viewpoint identification information refers to information for distinguishing a picture at a current view from a picture at a different view. When a video image signal is coded, a picture order count (POC) and frame_num are used to identify each picture. In the case of a multiview video image, since prediction is performed between views, identification information for distinguishing a picture at a current view from a picture at a different view is required.

The parsed bitstream is entropy decoded by the entropy decoding unit 200, and coefficients, motion vectors, and the like of each macroblock are extracted. The inverse quantization / inverse transform unit 300 multiplies the received quantized value by a constant constant to obtain a transformed coefficient value, and inversely transforms the coefficient value to restore the pixel value. The intra prediction unit 400 performs intra prediction from the decoded samples in the current picture by using the reconstructed pixel value. Meanwhile, the deblocking filter unit 500 is applied to each coded macroblock in order to reduce block distortion. The filter smoothes the edges of the block to improve the quality of the decoded frame. The choice of filtering process depends on the boundary strength and the gradient of the image samples around the boundary. The filtered pictures are output or stored in the decoded picture buffer unit 600 for use as a reference picture.

The decoded picture buffer unit 600 stores or opens previously coded pictures in order to perform inter prediction. In this case, in order to store or open the decoded picture buffer unit 600, frame_num and POC (Picture Order Count) of each picture are used. Therefore, some of the previously coded pictures in MVC have pictures that are different from the current picture. Therefore, in order to utilize these pictures as reference pictures, not only the frame_num and the POC but also the view information for identifying the view point of the picture are included. It is available. The decoded picture buffer unit 600 includes a reference picture list generator 610 and a reference picture manager 620.

The reference picture list generator 610 generates a list of reference pictures for inter prediction. In this case, the reference picture list may be generated by distinguishing the anchor picture from the non-anchor picture. In multi-view video coding, since inter-view prediction may be performed, it may be necessary to generate a reference picture list for inter-view prediction when the current picture refers to a picture at a different view. In this case, the reference picture list generator 610 may use information about a viewpoint to generate a reference picture list for inter-view prediction.

The reference picture manager 620 manages the reference picture in order to more flexibly implement inter prediction. In this case, the reference picture may be managed by distinguishing an anchor picture from a non-anchor picture. For example, an adaptive memory management control method and a sliding window method may be used. This is to manage the memory of the reference picture and the non-reference picture into one memory and manage them efficiently with less memory. In multi-view video coding, since pictures in a view direction have the same picture order count, information for identifying the view point of each picture may be used for their marking. Reference pictures managed through this process may be used in the inter predictor 700.

The inter prediction unit 700 performs inter prediction using a reference picture stored in the decoded picture buffer unit 600. Inter-coded macroblocks can be divided into macroblock partitions, where each macroblock partition can be predicted from one or two reference pictures.

FIG. 2 illustrates a structure of an NAL unit including anchor picture identification information according to an embodiment to which the present invention is applied.

Looking at the structure of the bit stream in H.264 / AVC, the network abstraction between the video coding layer (VCL) that deals with the video encoding process itself and the subsystem that transmits and stores the encoded information Layer, which is defined as a separate hierarchical structure. The output of the encoding process is VCL data and is mapped in units of NAL before transmission or storage. Each NAL unit includes raw video sequence payload (RBSP), which is data corresponding to compressed video data or header information.

The NAL unit basically consists of two parts: the NAL header and the RBSP. The NAL header includes flag information (nal_ref_idc) indicating whether a slice serving as a reference picture of the NAL unit is included and an identifier (nal_unit_type) indicating the type of the NAL unit. The RBSP stores the compressed original data and adds an RBSP trailing bit at the end of the RBSP to represent the length of the RBSP in multiples of 8 bits. These NAL unit types include Instantaneous Decoding Refresh (IDR) pictures, Sequence Parameter Set (SPS), Picture Parameter Set (PPS), and Supplemental Enhancement Information (SEI). Etc.

In such a NAL unit structure, the anchor picture identification information may be obtained from a header area. The header area may include, for example, an NAL header, an extended area of the NAL header, or a slice header. In addition, for example, the case where the anchor picture identification information is obtained from the extension region of the NAL header may be applied when the NAL type is a picture for a multiview video image. For example, nal_unit_type = 20 or 21.

3 is an embodiment to which the present invention is applied and shows an overall prediction structure of a multiview image signal for explaining the concept of an anchor picture.

As shown in FIG. 3, T0 to T100 on the horizontal axis represent frames according to time, and S0 to S100 on the vertical axis represent frames according to viewpoints, respectively. For example, pictures in T0 refer to images taken by different cameras in the same time zone (T0), and pictures in S0 refer to images in different time zones taken by one camera. In addition, the arrows in the drawings indicate the prediction direction and the order of each picture. For example, a P0 picture at S2 time point in the T0 time zone is a picture predicted from I0, which refers to a P0 picture at S4 time point in the TO time zone. It becomes a picture. It is also a reference picture of the B1 and B2 pictures in the T4 and T2 time zones at the time of S2.

In the decoding process of a multiview image, random access between viewpoints is essential. Therefore, access to arbitrary time points should be made possible while minimizing decryption effort. Herein, the concept of an anchor picture may be necessary to realize efficient random access. An anchor picture refers to an encoded picture in which all slices refer only to slices in frames of the same time zone. For example, an encoded picture refers to only a slice at another viewpoint and no slice at the current viewpoint. 3, if the I0 picture at the time S0 of the time zone T0 is an anchor picture, all pictures in the same time zone, that is, at another time point in the time zone T0, are also anchor pictures. As another example, if an I0 picture at time S0 in the T8 time zone is an anchor picture, all pictures in the same time zone, that is, at other times in the T8 time zone, are also anchor pictures. Similarly, T16,... All pictures in, T96, T100 are examples of anchor pictures. After the anchor picture is decoded, all pictures coded in turn are decoded without inter-prediction from the decoded picture prior to the anchor picture.

Therefore, according to the overall coding structure of the multi-view video image of FIG. 3, the anchor picture and the non-anchor picture need to be distinguished according to the anchor picture identification information because the dependency between the viewpoints of the anchor picture and the non-anchor picture is different. There is.

FIG. 4 is an embodiment to which the present invention is applied and shows a structure of an NAL unit including anchor picture identification information in a bitstream compatible with H.264 / AVC.

We need at least one view sequence to be compatible with the H.264 / AVC decoder. Therefore, it is necessary to define viewpoints that can be independently decoded for fast random access, which is called a base view. This base view serves as a reference for encoding among multi views, which corresponds to a reference view. In MVC (Multiview Video Coding), an image corresponding to a reference time point is encoded by a conventional general video encoding method (MPEG-2, MPEG-4, H.263, H.264, etc.) to form an independent bitstream.

For example, when information having nal_unit_type = 1 or 5 is obtained from a NAL header of NAL unit 1, the RBSP information of the NAL may be regarded as NAL compatible with H.264 / AVC. Therefore, even when the anchor picture identification information comes in, it cannot be coded, so that the anchor picture identification information value of the preceding NAL can be known from the following NAL. In this case, the following NAL (NAL unit 2) is called a suffix NAL, and the suffix NAL may include only description information of the preceding NAL. Accordingly, nal_unit_type = 20 or 21 of the NAL unit 2 is obtained, and anchor picture identification information can be obtained from the extended region of the NAL header. Here, "svc_mvc_flag = 1" means a multiview video coded bitstream, and "view_level = 0" means that the NAL corresponds to a reference time point.

FIG. 5 is a schematic block diagram of an apparatus for decoding a multiview image using anchor picture identification information according to an embodiment to which the present invention is applied.

The decoding apparatus in this embodiment includes a bitstream determination unit 510, an anchor picture identification information acquisition unit 520, and a multiview image decoding unit 530. When the bitstream is input, the bitstream determination unit 510 determines whether the bitstream is a scalable video coded bitstream or a multiview video coded bitstream. This may be determined by flag information flying into the bitstream.

The anchor picture identification information acquisition unit 520 may acquire anchor picture identification information when the multiview video coded bitstream is a result of the determination. If the obtained anchor picture identification information is true, this means that the coded slice in the current NAL is an anchor picture, and if it is false, it may mean a non-anchor picture. Such anchor picture identification information may be obtained from an extended region of the NAL header, or may be obtained from a slice layer region.

The multiview image decoding unit 530 decodes a multiview image according to the anchor picture identification information. Depending on the overall coding structure of a multiview video image, since the anchor picture and the non-anchor picture have different inter-view dependencies, for example, when generating a reference picture list, the reference pictures for inter-view prediction are added to the anchor picture. Picture identification information may be used. It may also be used to manage the added reference pictures for the inter-view prediction. The anchor picture identification information may also be applied to a hypothetical reference decoder.

6 is an embodiment to which the present invention is applied and shows a prediction structure for explaining the concept of a newly defined anchor picture.

An anchor picture refers to an encoded picture in which all slices refer only to slices in frames of the same time zone. For example, this refers to an encoded picture that refers only to slices at different views and does not refer to slices at the current view. In the overall prediction structure of MVC, a GOP can be started from an I picture, and the I picture is compatible with H.264 / AVC. Thus, all anchor pictures compatible with H.264 / AVC can always be I pictures. However, if we replace the I pictures with P pictures, we can enable more efficient coding. In other words, more efficient coding will be enabled if the GOP starts with a P picture that is compatible with H.264 / AVC.

At this time, if the anchor picture is redefined, all the slices become encoded pictures that can refer not only to slices in frames of the same time zone but also slices in different time zones of the same viewpoint. However, when referring to slices in different time zones at the same time, it may be limited to anchor pictures compatible with H.264 / AVC. For example, in FIG. 6, the P picture at time T8 at the time S0 may be a newly defined anchor picture, similarly the P picture at time T96 at the time S0 and the P picture at time T100 at the time S0. It can be a newly defined anchor picture. Alternatively, the anchor picture may be defined only at the reference time point.

As described above, according to the overall coding structure of the multi-view video image, since the dependency between the anchor picture and the non-anchor picture is different from each other, the anchor picture and the non-anchor picture are distinguished according to the anchor picture identification information. In this case, more efficient coding may be possible. In addition, more efficient coding may be possible by newly defining an anchor picture to be possible from an existing I picture to a P picture.

Claims (12)

Obtaining flag information indicating whether a multiview image coded bitstream is from a video signal; Acquiring identification information indicating whether a coded picture of a current NAL is an anchor picture when the video signal is a multiview image coded bitstream according to the flag information; And Decoding information on a multiview image according to the identification information; Video signal decoding method comprising a. The method of claim 1, And the information on the multi-view image includes information on view dependency between views. The method of claim 1, And the information about the multi-view image includes information for generating a reference picture list. The method of claim 1, And the information on the multi-view image includes information for reference picture marking process. The method of claim 1, The identification information is obtained from a header region of the video signal. The method of claim 5, And the header area is an extension area of a NAL header. The method of claim 5, And the header area is an extended area of a slice layer. The method of claim 1, wherein the video signal decoding method comprises: Obtaining view level information (view_level) indicating view scalability from the video signal, And if the current NAL corresponds to a reference time according to the view level information, the anchor picture identification information obtained from the current NAL header indicates the anchor picture identification information of the preceding NAL. The method of claim 1, The anchor picture is a video signal decoding method of claim 1, wherein the reference picture is a picture that can be temporally predicted from pictures in different time zones of the same view. The method of claim 9, And when a current picture corresponds to the anchor picture, all pictures at different time points in the same time zone as the current picture also correspond to the anchor picture. In the video signal encoding method based on multiple views, Generating viewpoint dependency information indicating an predictive structure between viewpoints; Generating identification information indicating whether a coded picture of a current NAL is an anchor picture according to the view dependency information. A bitstream determination unit for obtaining flag information indicating whether the bitstream is a multiview image coded bitstream from the video signal; An anchor picture identification information obtaining unit for obtaining identification information (anchor_pic_flag) indicating whether the current NAL coded picture is an anchor picture when the video signal is a multiview video coded bitstream according to the flag information; And A multiview image decoding unit to decode information on a multiview image according to the identification information; Video signal decoding apparatus comprising a.

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