JP2009290630A - Video coding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent images before and after scene change from being mixed due to a transmission error. <P>SOLUTION: A scene change detection device (16) detects the change of a video scene (scene change) from image data from an input terminal 10. Then, the scene change detection device (16) gives a reduced image generation device (30) a video timing as the reference image (I image or P image) of the first predicted coding after scene change. The reduced image generation device (30) creates the reduced image of an image instructed by the scene change detection device (16), and outputs it to a multiplex processor (26). The multiplex processor (26) multiplexes the reduced image with the encoded video data from an entropy coding device (24). The reduced image is used for error interpolation processing for a reference image in decoding. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a video encoding apparatus.

  MPEG-4 AVC (ISO / IEC 14496-10) is one of the moving image encoding systems, and is adopted in digital television broadcasting and video recording media. In MPEG-4 AVC, encoding efficiency is improved by adopting a context-adaptive entropy encoding method. Context-adaptive entropy coding methods include context-adaptive variable-length coding (CAVLC) and context-adaptive binary arithmetic coding (CABAC). There is.

  Such context adaptive entropy coding adaptively selects a coding scheme with good coding efficiency in accordance with the surrounding macroblock information of the macroblock to be coded. Therefore, peripheral macroblock information of the decoding target macroblock is necessary at the time of decoding. When an error occurs in the encoded data due to some factor, it is extremely difficult to perform subsequent decoding processing in the same slice.

  From this point of view, MPEG-4 AVC provides various error tolerance tool sets that enhance error tolerance. For example, ASO (Arbitrary Slice Order) enables encoding and transmission of slices in a screen in an arbitrary order. FMO (FlexibleMacroblockOrdering) makes it possible to select a macroblock order within a slice. RS (Redundant Slice) enables the same macroblock to be encoded a plurality of times. By adopting such an error tolerance tool, error tolerance can be improved (see Non-Patent Document 1).

Patent Document 1 describes a technique for changing a slice shape according to a transmission path error or an image motion.
JP 2005-124041 A ISO / IEC 14496-10 “Part-10 Advanced Video Coding”

  Although it is for error tolerance, excessive slice division is not a good idea from the viewpoint of coding efficiency.

  The error resilience tools described above can greatly sacrifice coding efficiency. In addition, the amount of calculation increases, the error interpolation process itself becomes complicated, and the correspondence is prescribed by the profile and level, so that it is often difficult to apply in practice.

  On the other hand, in general, it is possible to perform an effective error interpolation process by using a pixel in the immediately preceding reference image. However, when the pixel value of the immediately preceding reference image is used, if an error occurs at the switching point of the video scene, the influence on the subsequent inter-screen predictive encoded image is great. In particular, when an error occurs in an I picture that is an intra-picture coded picture, a reproduced video with a sense of incongruity in which pixels before and after a scene change are mixed in a GOP (Group Of Pictures) may be generated.

  Under such circumstances, an effective video coding technique that is easy to implement and is not affected by scene changes is desired.

  It is an object of the present invention to provide a video encoding device that satisfies such a demand.

  A video encoding apparatus according to the present invention is a video encoding apparatus that encodes a video signal using predictive encoding that encodes a difference between intra-picture encoding and a reference image. In the intra-picture encoding, Outputs a residual signal indicating a difference between the video signal and a predicted image generated from surrounding pixels encoded in advance, and in the predictive encoding, a residual signal indicating a difference between the video signal and a reference image Is decoded by the local decoding means, the encoding means for encoding the output of the prediction processing means, the local decoding means for decoding the intermediate code data by the encoding means, and the local decoding means A memory for storing the captured image as the reference image, a scene change detecting means for detecting a scene change of the video signal, and the scene change according to the detection of the scene change by the scene change detecting means. A reduced image generating means for generating a reduced image of an image that will be a reference image for the predictive encoding first after being changed, and a multiplexing processing means for multiplexing the reduced image on the output of the encoding means. Features.

  According to the present invention, since a reduced image of an image that is first encoded as a reference image is transmitted for interpolation after a scene change is detected, an error interpolation process that is not affected by a scene change can be performed with a simple process at the time of decoding. become.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an MPEG-4 AVC video encoding apparatus according to an embodiment of the present invention. In this embodiment, it is assumed that the video signal is encoded into a 4: 2: 0 component signal of 1920 × 1088 pixels.

  The video encoding apparatus according to the present exemplary embodiment encodes a video signal in units of macroblocks obtained by dividing an encoding target screen into 16 × 16 pixel blocks. Image data in units of 16 × 16 pixel blocks is input from the input terminal 10 to the prediction method determination device 12, the prediction processing device 14, and the scene change detection device 16.

  The prediction method determination device 12 determines a prediction method with the optimal encoding efficiency for each macroblock in the encoding target screen. Specifically, the prediction method determination device 12 determines a prediction method to be applied to the image data from the input terminal 10 from the image data from the input terminal 10 and the image data previously encoded and decoded. decide. The memory 18 stores previously encoded and decoded image data and image data obtained by applying a deblocking filter process to the image data.

  Specifically, when the encoding target macroblock is an I slice to be intra-coded, the prediction method determination device 12 uses the intra-frame prediction encoding parameters such as the intra-frame prediction pixel block size and the intra-frame prediction mode. Decide. When the encoding target macroblock is a P slice to be unidirectionally predicted encoded or a B slice to be unidirectionally predicted encoded, the prediction method determination device 12 encodes one of intra prediction and inter prediction. Choose the one with the highest efficiency. For intra prediction, parameters for intra prediction encoding such as intra prediction pixel block size and intra prediction mode are determined. For inter prediction, inter prediction encoding parameters such as a reference image frame, a macroblock division pattern, and a motion vector are determined. The prediction method determination device 12 supplies the prediction coding parameter determined in this way to the prediction processing device 14.

  The prediction processing device 14 generates a prediction image (or prediction image data) from the image data stored in the memory 18 in accordance with the prediction encoding parameter from the prediction method determination device 12, and the encoding target image from the input terminal 10 A prediction residual signal that is a difference between the data and the predicted image is generated. The prediction processing device 14 supplies the generated prediction residual signal to the orthogonal transform / quantization device 20 and supplies the generated predicted image data to the local decoding device 22. Specifically, in the intra-screen coding, the prediction processing device 14 calculates the difference between the encoding target block included in the image data from the input terminal 10 and the predicted image generated from the peripheral pixels encoded in advance. Is output as a residual signal. Further, in the predictive encoding between the screens using the reference image, a residual signal indicating a difference between the encoding target block included in the image data from the input terminal 10 and the reference image is output.

  The orthogonal transform / quantization apparatus 20 performs orthogonal transform processing on the prediction residual signal by integer precision discrete cosine transform in a designated pixel block unit (for example, 8 × 8 pixel or 4 × 4 pixel block unit). Discrete Hadamard transform is further performed on the DC component (DC component) of the discrete cosine transform coefficient of the luminance signal and color difference signal subjected to the intra-screen prediction processing in units of 16 × 16 pixel blocks. The orthogonal transform / quantization apparatus 20 quantizes the transform coefficient subjected to the orthogonal transform at a quantization step corresponding to the designated quantization parameter, and outputs the result to the entropy encoding apparatus 24.

  The entropy encoding device 24 performs entropy encoding on the quantized transform coefficient data from the orthogonal transform / quantization device 20 by CAVLC or CABAC. The entropy encoding device 24 outputs encoded data obtained by entropy encoding processing to the multiplexing processing device 26.

  The transform coefficient data quantized by the orthogonal transform / quantization device 20 is also supplied to the local decoding device 22 as intermediate code data. First, the local decoding device 22 performs inverse quantization and inverse orthogonal transform on the data from the orthogonal transform / quantization device 20 to restore the prediction residual signal. The local decoding device 22 adds the predicted image data from the prediction processing device 14 to the obtained prediction residual signal, and restores the image data. In this way, the image data encoded by the prediction processing device 14 and the orthogonal transform / quantization device 20 is locally decoded.

  The local decoding device 22 stores the decoded image data in the memory 18 and supplies it to the deblocking filter processing device 28. The deblocking filter processing device 28 performs deblocking filter processing on the image data from the local decoding device 22 and writes it in the memory 18. The output image data of the local decoding device 22 stored in the memory 18 is used for subsequent intra-screen prediction processing. The output image data of the deblocking filter processing device 28 stored in the memory 18 is used for the subsequent inter-screen prediction processing.

  The scene change detection device 16 detects a video scene change point (scene change) from the image data from the input terminal 10. Then, the scene change detection device 16 instructs the reduced image generation device 30 to determine the video timing of the reference image (I picture or P picture) of the first predictive encoding after the scene change. The scene change detection method in the scene change detection device 16 is not limited to a specific method. For example, a scene change may be detected using a motion vector calculated by the prediction method determination device 12, or a scene change may be detected using a histogram of pixel values in the screen.

  For example, assume that a scene change is detected at frame number 3 in the video as shown in FIG. In the order example of the picture types shown in FIG. 2, the frame having the frame number 4 first becomes the I picture or the P picture after the frame having the frame number 3. Accordingly, the scene change detection device 16 instructs the reduced image generating device 30 to generate a reduced image for the frame of frame number 4.

  In the order example of the coded picture type shown in FIG. 2, even if a scene change is detected in the frame with frame number 2, the first I picture or P picture after the scene change is detected is frame number 4. It is a frame. Accordingly, in this case as well, the scene change detection device 16 instructs the reduced image generating device 30 to generate a reduced image for the frame of frame number 4.

  The reduced image generation device 30 generates a reduced image according to the timing instructed from the scene change detection device 16 and outputs the reduced image to the multiplexing processing device 26. That is, the reduced image generating apparatus 30 generates a reduced image of a frame that first becomes an I picture or P picture after detecting a sea change.

  The reduced image generated by the reduced image generation apparatus 30 is an image generated for the purpose of error interpolation processing for a reference image in decoding, and the original image (or main image) is reduced in the horizontal direction, the vertical direction, or both. It is an image. For example, as shown in FIG. 3, with respect to the original image, the luminance signal is reduced to 1/16 in each of the horizontal and vertical directions, and the color difference signal is reduced to 1/8 in each of the horizontal and vertical directions. It is an image. The reduction processing itself may be sub-sampling or averaging filter processing. In addition, the pixel value of the predicted image generated by the prediction processing device 14 is used by unifying the intra-screen prediction process (intra-screen prediction mode) of the original image into an average value (DC) in units of 16 × 16 pixels. Is possible. In this case, the reduced image generating device 30 may receive data of one pixel for each macroblock of the predicted image from the prediction processing device 14 and output it as a reduced image. Thereby, a reduced image in which one pixel of the luminance signal and the color difference signal of the reduced image corresponds to one macro block of the original image is generated.

  In addition to the encoded video data from the entropy encoding device 24 and the reduced image data from the reduced image generating device 30, system data from a system control device (not shown) is input to the multiplexing processing device 26. The system data includes data for controlling the operation of the decoding apparatus, such as a quantization scale value and a motion compensation motion vector. The multiplexing processing device 26 multiplexes these data and outputs them as encoded data to a transmission path or a recording medium.

  In MPEG-4 AVC, utilization in various networks is considered. That is, a network abstraction layer (NAL) is defined between a video coding layer (VCL) that handles video coding processing and a transmission / storage system. As shown in FIG. 4, the NAL is packetized in units called NAL units composed of a NAL header and an RBSP (Row Byte Sequence Payload). The type of NAL unit and whether it is a reference image can be identified by the NAL header. The actual encoded data is stored in the RBSP following the NAL header.

  The type or type of NAL unit is defined as shown in FIG. A sequence parameter set (SPS) is information relating to a sequence of video encoded data. A picture parameter set PPS (Picture Parameter Set) is information relating to a picture of video encoded data. Supplemental enhancement information (SEI) is additional information that is not essential for decoding video-encoded data. Mainly, NAL units such as video encoded data (slice), SPS, PPS, or SEI are used.

  A unit in which these NAL units are grouped into pictures is called an access unit. As shown in FIG. 6, an NAL unit called an access unit delimiter is located at the head of the access unit. The access unit delimiter includes information identifying the picture type in the access unit. This NAL unit is followed by a group of NAL units necessary for the picture, such as SPS, PPS, and slice data.

  In SEI, user data SEI (user data SEI) that can use user-defined syntax is prepared. The user data SEI includes user data unregistered SEI, user data registered by ITU-T Recommendation T., and so on. 35 SEI is defined. Here, the reduced image is multiplexed using user data unregistered SEI (user data unregistered SEI).

  FIG. 7 shows the syntax of user data unregistered SEI. Of the syntax elements in FIG. 7, a reduced image can be stored in the user_data_payload_byte area. The fact that the reduced image is stored in the user data unregistered SEI can be identified by the UUID in the uuid_iso_iec_11578 area. Error interpolation data for storing a reduced image in the user_data_payload_byte area is called “esl_picture”, and the definition of the syntax is shown in FIG. In FIG. 8, num_slice indicates the number of slices of the stored reduced image. top_x and top_y indicate the coordinates of the first pixel of the reduced image corresponding to the slice of the main image, and correspond to the macroblock coordinates of the first slice of the main image. num_pix indicates the number of pixels of the reduced image, and similarly corresponds to the number of macroblocks for the main image. pix_y is a pixel value of the luminance signal Y of the reduced image, and pix_cb and pix_cr are pixel values of the color difference signals Cb and Cr of the reduced image, respectively. As can be seen from this syntax, even when one screen of the main image is divided into a plurality of slices and encoded, a reduced image corresponding to an arbitrary slice can be stored. In this way, when it is desired to reduce the data amount of the reduced image for error interpolation, it is also possible to store only the reduced image as the important slice.

  For example, as shown in FIG. 9, an image having a slice structure in which one screen is equally divided into four in the vertical direction is assumed. Considering the case where the reduced images of slice 1 and slice 2 located at the center of this image are stored, num_slice = 2. The coordinate position of the top pixel of the reduced image corresponding to slice 1 is (top_x [0], top_y [0]) = (0, 17), and the number of pixels is 120 × 17 = 2040. num_pix [0] = 2040 is stored, and subsequently the pixel data of the reduced image corresponding to slice 1 is stored in the order of the luminance signal Y and the color difference signals Cb and Cr. Next, the coordinate position of the top pixel of the reduced image corresponding to slice 2 is (top_x [1], top_y [1]) = (0, 34), and the number of pixels is 2040 similarly. num_pix [1] = 2040 is stored, and subsequently, pixel data of the reduced image corresponding to slice 2 is stored in the order of the luminance signal Y and the color difference signals Cb, Cr. In FIG. 9, the numerical values are shown in hexadecimal notation.

  As described above, a reduced image of an arbitrary slice can be stored in the user data unregistered SEI, and this is multiplexed in the success unit.

  The video decoding apparatus that receives the encoded data in which the reduced images are multiplexed in this way can perform error interpolation processing using esl_picture. When a video decoding apparatus and a corresponding video decoding apparatus are connected via a network, an error may occur in the encoded stream due to the reception environment on the video decoding apparatus side, particularly in wireless transmission. For example, as shown in FIG. 10, when the encoded data of the third macroblock of slice 1 is parsed, if the syntax element in the macroblock shows a non-standard value, decoding after this macroblock is almost complete. It becomes impossible. In such a case, a reduced image corresponding to slice 1 is extracted according to the esl_picture syntax from the SEI in which the user data is not registered and the SEI in which the UUID indicates esl_picture in the received SEI. The luminance signal Y is enlarged by 16 times in both the horizontal and vertical directions, and the color difference signals Cb and Cr are enlarged by 8 times in both the horizontal and vertical directions. As a result, it is possible to interpolate macro block data after the fourth macro block that cannot be decoded.

  With reference to FIG. 11 and FIG. 12, the state of a reproduced video by error interpolation processing when such an error occurs in an I picture at a scene change boundary will be described. FIG. 11 shows an example in which an errored I picture is interpolated by the previous P picture. FIG. 12 shows an example in which an I picture in which an error has occurred is interpolated with a reduced image according to this embodiment. As shown in FIG. 11, when the I picture is interpolated using the pixel of the immediately preceding P picture, the image before the scene change is affected in the frame having a reference relationship with the I picture, and the reproduced image is disturbed. there's a possibility that. However, as shown in FIG. 12, a reproduced image having a relatively uncomfortable feeling can be obtained by interpolating an I picture using a reduced image according to this embodiment.

  As can be easily understood from the above description, in this embodiment, a reduced image is generated at the first reference image encoding timing after the scene change is detected, and is multiplexed as encoded data of the main image as an SEI message. As a result, even when an error occurs in the reference image on the video decoding device side, it is possible to perform error interpolation processing with less discomfort by an easy method.

It is a schematic block diagram of one Example of this invention. It is a schematic diagram which shows the example of a reduced image generation timing of a present Example. It is a schematic diagram which shows the relationship between a main image and a reduced image. It is a figure which shows the structure of a NAL unit. It is a figure which shows a NAL unit type. It is a figure which shows the structure of an access unit. It is a figure which shows the syntax of user data unregistered SEI. It is a figure which shows the syntax of esl_picture. It is a figure which shows the example of application of esl_picture syntax. It is a figure which shows the example of an error interpolation process using esl_picture. It is a schematic diagram which shows the example which interpolates the I picture in which the error generate | occur | produced by the 1 previous P picture. It is a schematic diagram which shows the example which interpolates the I picture in which the error generate | occur | produced with the reduced image by a present Example.

Explanation of symbols

10: Video input terminal 12: Prediction method determination device 14: Prediction processing device 16: Scene change detection device 18: Memory 20: Orthogonal transformation / quantization device 22: Local decoding device 24: Entropy coding device 26: Multiplexing processing Device 28: Deblocking filter processing device 30: Reduced image generation device

Claims (4)

A video encoding device that encodes a video signal using predictive encoding that encodes a difference between in-screen encoding and a reference image,
In the intra-frame coding, a residual signal indicating a difference between the video signal and a predicted image generated from surrounding pixels encoded in advance is output. In the predictive coding, the video signal and a reference image are output. Prediction processing means for outputting a residual signal indicating the difference;
Encoding means for encoding the output of the prediction processing means;
Local decoding means for decoding intermediate code data by the encoding means;
A memory for storing the image decoded by the local decoding means as the reference image;
Scene change detecting means for detecting a scene change of the video signal;
In response to detection of the scene change by the scene change detection unit, a reduced image generation unit that generates a reduced image of an image that becomes a reference image of the predictive encoding first after the scene change;
A video encoding apparatus comprising: a multiplexing processing unit that multiplexes the reduced image on an output of the encoding unit. The intra coding and the predictive coding are determined in units of each slice of a plurality of slices constituting the screen,
The video encoding apparatus according to claim 1, wherein the reduced image generation unit generates the reduced image in units of the slices.   3. The video encoding apparatus according to claim 1, wherein the multiplexing processing unit multiplexes the reduced image as SEI (Supplemental Enhancement Information) in the MPEG-4 AVC system.   4. The video encoding apparatus according to claim 3, wherein the reduced image is generated from a prediction image having an intra-screen prediction mode in the MPEG-4 AVC system as an average value.

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