JP4296034B2 - Information embedding method and information processing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an information embedding method and information processing apparatus for embedding information in an MPEG stream.
[0002]
[Prior art]
As digital content distribution infrastructure is improved, how to realize copyright protection has become an important issue. One answer is given by embedding confidential information such as digital watermarks in the content. With the distribution of moving image content, embedding digital watermarks into MPEG, which is an international standard for moving image compression, has become important.
[0003]
Depending on the detection method, the method of embedding a digital watermark in MPEG can be classified into two methods: a method of directly extracting a digital watermark from an MPEG stream and a method of extracting a digital watermark from an image after MPEG stream decoding. In the latter method, watermark information can be extracted from the decoded image. Such digital watermarks are disclosed in Patent Documents 1 to 3.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-341450
[Patent Document 2]
Japanese Patent Laid-Open No. 2000-244881
[Patent Document 3]
Japanese Patent Laid-Open No. 2002-125115
[Problems to be solved by the invention]
However, the former method is advantageous in terms of detection cost, but watermark information cannot be extracted from the decoded result image. The latter method of embedding a digital watermark includes a method of embedding watermark information in an original image before MPEG compression and a method of processing DCT coefficients during MPEG compression. In order to process the frequency component and the like, a large amount of calculation is required.
[0008]
In view of the above problems, the present invention provides an information embedding method and information processing capable of embedding confidential information in an MPEG stream and extracting the confidential information from the decoding result of the MPEG stream by a simple method with a low processing load. An object is to provide an apparatus.
[0009]
[Means for Solving the Problems]
The present invention is an information embedding method for embedding confidential information in the MPEG stream by inserting an information picture, which is a picture in which difference information is embedded, into the MPEG stream, and a picture generating step for generating the information picture; and the insertion position determining step of determining the position for inserting the information picture to the MPEG stream, in the order of the picture obtained by decoding the MPEG stream, the difference information for the picture which is positioned in front of the information picture as the confidential information, A picture insertion step of inserting the information picture into the MPEG stream.
[0010]
According to the present invention, an information embedding method capable of embedding information in an MPEG stream and extracting confidential information from the decoding result of the stream by a simple method with low processing load without decoding the MPEG stream to the image level. Can provide.
[0011]
The present invention is an information processing apparatus for embedding confidential information in an MPEG stream by inserting an information picture, which is a picture in which difference information is embedded, into an MPEG stream, and a picture generating means for generating the information picture; an insertion position determining means for determining the position for inserting the information picture to the MPEG stream, in the order of the picture obtained by decoding the MPEG stream, the difference information for the picture which is positioned in front of the information picture as the confidential information, Picture insertion means for inserting the information picture into the MPEG stream.
[0012]
According to the present invention, an information processing apparatus capable of embedding information in an MPEG stream and extracting confidential information from the decoding result of the stream by a simple method with a low processing load without decoding the MPEG stream to the image level. Can provide.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
First, a method for embedding difference information in the embodiment of the present invention will be described. FIG. 1 shows an example in which a secret information picture in which difference information is embedded is inserted between other pictures. FIG. 1 shows an MPEG stream 10, a picture group 11 obtained by decoding the MPEG stream 10, an MPEG stream 12 into which the confidential information picture 13 is inserted, and a picture group 14 obtained by decoding the MPEG stream 12. .
[0015]
Also, “I0” shown in FIG. 1 represents an I picture, and “P0 / 1”, “P1”, “P2”, and “P3” represent P pictures. Hereinafter, each picture is expressed as “picture P2” or the like.
[0016]
The MPEG stream 12 shown in FIG. 1 is an example in which a secret information picture having no difference information from the previous picture I0 is inserted. The secret information picture 13 is assumed to have a picture I0 as a reference image, all macroblocks have a motion vector 0, and DCT coefficients are also 0. In this case, the picture P0 / 1 obtained by decoding the confidential information picture 13 is the same image as the picture obtained by decoding the picture I0.
[0017]
At this time, the picture P1 refers to the picture P0 / 1. However, since the picture P0 / 1 matches the picture I0, there is no influence on the decoding of the picture P1. Therefore, when the picture group 14 that is the decoded picture is displayed as a moving image, a moving image that is not different from the moving image before insertion can be seen by human eyes.
[0018]
FIG. 2 shows an example in which a B picture is inserted as a secret information picture. FIG. 2 shows an MPEG stream 20, a picture group 21 obtained by decoding the MPEG stream 20, an MPEG stream 22 in which the confidential information picture 23 is inserted, and a picture group 24 obtained by decoding the MPEG stream 22.
[0019]
“I2” represents an I picture, “B0”, “B0 / 1”, “B1”, “B3”, “B4”, “B5” represent B pictures, and “P5” represents P Represents a picture.
[0020]
The insertion of the secret information picture 23 by the method shown in FIG. 2 does not require decoding processing of the preceding and succeeding pictures, and therefore can be inserted very easily. Also, with this insertion method, even when difference information with respect to the previous picture is not embedded in a picture, it is possible to embed information by providing a pattern at intervals at which pictures are inserted.
[0021]
When the secret information picture 23 embedded in this way is extracted, information can be extracted by taking the difference between the decoded pictures and finding matching pictures before and after. However, in the method in which the difference information is not embedded, it is possible to extract and delete this information relatively easily on the extraction side. Therefore, it is effective to embed difference information in order to prevent this information. When the difference information is embedded, the information cannot be erased by a simple method of detecting matching pictures before and after.
[0022]
Next, a picture inserted when difference information is embedded will be described with reference to FIG. FIG. 3 shows a secret information picture 31 that is a picture to be inserted and a reference picture 30 to which the secret information picture 31 refers. Further, the reference picture 30 shows a block 32 having a pixel value of A in units of macroblocks (16 × 16 pixels) or blocks (8 × 8 pixels) having a point (x, y) as a vertex. . Similarly, the secret information picture 31 is a block 33 having a point (x, y) at the vertex and a pixel value of A ′. This pixel value A ′ is obtained by adding a minute difference value ΔA obtained from the DCT coefficient to the pixel value A of the block 32.
[0023]
As described above, the secret information is embedded by giving a minute difference value of the DCT coefficient to a specific luminance block or color difference block. In the method shown in FIG. 3, since secret information is given as a difference value, a relatively large amount of information can be embedded. In this case, it is necessary to consider the amount to be embedded and the image quality degradation caused by the amount.
[0024]
The embedded confidential information can be extracted by taking a difference between an image obtained by decoding the embedded picture and an image obtained by decoding the previous picture after decoding. If it is not known in which picture the confidential information is embedded, such as not having the pre-embedded data, it is difficult to extract the confidential information.
[0025]
Further, since the picture in which the confidential information is embedded is used as the next reference image, the information is propagated to the subsequent decoding results. This is a trade-off because the embedded confidential information spreads over many pictures and makes it difficult to extract illegally, but there is also an effect of image quality deterioration.
[0026]
As a method for preventing the influence of image quality deterioration on subsequent pictures, there is a method of inserting a confidential information picture immediately before an I picture, or a method of using the inserted confidential information picture as a B picture.
[0027]
Another method for embedding the difference information is shown in FIG. FIG. 4 shows a method for giving a minute motion vector in units of macroblocks or blocks in a secret information picture to be inserted.
[0028]
FIG. 4 shows a secret information picture 35 that is a picture to be inserted and a reference picture 34 to which the secret information picture 35 refers. Further, the reference picture 34 shows a block 36 having a DCT coefficient A, which is a macroblock or block having a point (x, y) as a vertex. Similarly, a block 37 having a point (x + Δx, y + Δy) at the vertex and a pixel value of A ′ is shown.
[0029]
For example, for a specific macroblock or block, a motion vector of 0.5 pixels is given as a minute motion vector, and information can be embedded depending on the direction in which the motion is given. In FIG. 4, information can be embedded by referring to the block 37 of the reference picture 34 with respect to the block having the point (x, y) of the secret information picture 35 at the vertex.
[0030]
Extraction of embedded information is performed by performing block matching processing in units of macroblocks or blocks between an image obtained by decoding an embedded picture and an image obtained by decoding a previous picture after decoding, and obtaining a motion direction by It is possible to take it out. Also in this method, when it is not known in which picture the information is embedded, it is difficult to extract the information.
[0031]
As described above, the difference information is embedded using the DCT coefficient and the motion vector, but a method of indicating information not by the value itself but by the macroblock or the position of the block in which the difference information is embedded will be described with reference to FIG. To do.
[0032]
FIG. 5 shows 26 pictures indicating in which position the macroblock is embedded in the difference information corresponding to the 26 letters of the alphabet. For example, the picture corresponding to “A” indicates that difference information is embedded at the upper end of the left end.
[0033]
Next, a picture in which difference information is actually embedded will be described with reference to FIG. FIG. 6 shows a reference picture 40 and a secret information picture 41 in which difference information “MPEG” is embedded.
[0034]
Difference information “MPEG” is embedded by dividing the secret information picture 41 into 3 × 4 blocks 42, 43, 44, and 45. In the block 42, two pieces of difference information are embedded from the left end of the upper end, and referring to FIG. Similarly, block 43 represents “P”, block 45 represents “E”, and block 44 represents “G”.
[0035]
Extraction of embedded information is realized by taking a difference between an image obtained by decoding an embedded picture and an image obtained by decoding a previous picture after decoding. As a result, it is possible to reproduce the original information if there is a code table when the pattern is embedded after determining which block has the difference.
[0036]
Next, a digital broadcast storage / playback apparatus that performs the above-described processing will be described with reference to FIG. FIG. 7 is a block diagram showing the configuration of the digital broadcast storage / playback apparatus. As shown in FIG. 7, the digital broadcast storage / playback apparatus includes a storage block 50, a playback block 54, a display device 57, and a VTR 58.
[0037]
The accumulation block 50 further includes an index generation unit 52, a secret information picture insertion unit 53, and a stream accumulation unit 51. The reproduction block 54 includes a TS Demux unit 55 and an MPEG decoder unit 56.
[0038]
The index generation unit 52 creates index information regarding a picture. This index information will be described later. The stream storage unit 51 stores the broadcast MPEG stream. The secret information picture insertion unit 53 embeds the difference information in the picture and inserts the picture. The secret information picture insertion unit 53 corresponds to a picture generation unit, an insertion position determination unit, and a picture insertion unit.
[0039]
The TS Demux unit 55 is a transport stream demultiplexer. The MPEG decoder unit 56 performs MPEG decoding processing. The display device 57 displays an image. The VTR 58 records an image.
[0040]
Next, the index information will be described with reference to FIG. As shown in FIG. 8, the index information is information having items of “Index Number”, “Picture Type”, “start packet No”, “end packet No”, and “Vop_time_increment”.
[0041]
“Index Number” is a number assigned from 0 for each picture. “Picture Type” indicates whether the picture is an I picture, a P picture, or a B picture. “Start packet No” is the number of the packet at which the corresponding picture starts. “End packet No” is the number of the packet at which the corresponding picture ends. “Vop_time_increment” is time information in MPEG4 and is “temporal_reference” in MPEG1 and MPEG2.
[0042]
If this index information is used, the secret information picture insertion unit 53 can easily determine a TS packet serving as a picture delimiter and insert a packet containing the secret information at an appropriate position during reproduction. . Even in an MPEG stream without index information, this method can embed confidential information at an appropriate position with a small amount of processing such as picture header analysis.
[0043]
FIG. 9 shows the MPEG stream 60 input to the storage block 50 and the confidential information insertion stream 61 into which the confidential information is inserted and output from the storage block unit 50. As shown in FIG. 9, it can be seen that the picture 62 is inserted into the MPEG stream 60 in the confidential information insertion stream 61. Thereby, confidential information is embedded in the image recorded by the VTR 58.
[0044]
Note that when a picture is inserted, a picture that did not originally exist is decoded, so there may be a case where the time information, vop_time_increment (hereinafter referred to as VTI) or temporal_reference, becomes a syntax problem.
[0045]
In MPEG4, since time information can be set relatively freely, it is often necessary to consider only the time information of the inserted picture itself. For example, in an MPEG stream in which VTI is increased by 66 with vop_time_increment_resolution (hereinafter referred to as VTIR) = 1000, for example, if 99 pictures are inserted between 66 and 128, an MPEG stream conforming to the syntax Can be generated.
[0046]
On the other hand, in an MPEG stream in which VTI increases by 1, the syntax can be protected by rewriting and inserting VTIR and VTI of other pictures. For example, when VTIR = 15, VTIR = 30 is set so that the VTI of another picture is incremented by 2 and the value is increased by 1 when a picture is inserted.
[0047]
For example, even if there is an abnormality in the syntax of the VTI value, for example, VTIs with the same value continue, such processing is not necessary if the decoder that receives the MPEG stream operates normally. .
[0048]
Next, the process of the confidential information picture insertion unit 53 will be described using the flowchart of FIG. In step S101 corresponding to the picture generation stage, a secret information picture is generated in advance. The time information is embedded in the generated secret information picture later. The next step S102 corresponding to the insertion position determination stage determines the embedded position of the confidential information picture. In step S103, the entry contents before and after the position where the picture in which the difference information is embedded are inserted are read from the index information.
[0049]
In step S104, time information T1 of the previous picture and time information T2 of the subsequent picture are acquired. In the next step S105, the time information T of the secret information picture to be inserted is set so that T1 <T <T2. For example, when T1 = 0 and T2 = 66, T = 33 and 33 is written in the header portion of the secret information picture generated in step S101.
[0050]
In step S106, the end packet No (N1) of the previous picture and the start packet No (N2) of the next picture are acquired. In step S107 corresponding to the picture insertion stage, a secret information picture packet is inserted between N1 and N2, and the process ends.
[0051]
Next, a modification of the digital broadcast storage / playback apparatus described with reference to FIG. 7 will be described with reference to FIG. The digital broadcast storage / playback apparatus shown in FIG. 11 inserts confidential information into an encrypted MPEG stream.
[0052]
Accordingly, a descrambling unit 80 and a local scramble unit 78 are newly added to the storage block 70 shown in FIG. 11, and a local scramble unit 79 is added to the playback block 74.
[0053]
The index generation unit 72, the secret information picture insertion unit 73, the stream storage unit 71, the TS Demux unit 75, the MPEG decoder unit 76, the display device 77, and the VTR 59 are the same as those in FIG.
[0054]
The accumulation block 70 in FIG. 11 descrambles the input encrypted stream. Next, the storage block 70 scrambles the descrambled MPEG stream again, inserts secret information, and outputs it to the playback block.
[0055]
In this processing, the descrambling unit 80 descrambles the encrypted MPEG stream, and the local scrambler 78 performs local scrambling.
[0056]
In this way, the MPEG stream that is scrambled locally and into which the confidential information is inserted is input to the reproduction block 74. The MPEG stream input to the playback block 74 is input from the TS Demux unit 75 to the local descrambling unit 79. The local descrambling unit 79 descrambles the locally scrambled MPEG stream and outputs the descrambled MPEG stream to the MPEG decoder unit 76. The image decoded by the MPEG decoder unit 76 is displayed on the display device 77. Also, confidential information is embedded in the image recorded by the VTR 59.
[0057]
In the modification described above, the MPEG stream from the storage block 70 to the reproduction block 74 is scrambled. Therefore, only the scrambled MPEG stream flows on the data bus.
[0058]
In the conventional secret information embedding method that simply scrambles, it is difficult to embed secret information unless some mechanism is provided in the decoding apparatus. However, in the embodiment of the present invention, it is possible to embed confidential information in the MPEG stream based on the index information generated at the time of recording by the same method as the digital broadcast storage / playback apparatus shown in FIG.
[0059]
Further, in the embodiment of the present invention, as described above, the picture with the embedded confidential information is inserted, but it is also possible to avoid the increase in the number of pictures due to the insertion of the confidential information picture. .
[0060]
For example, it is possible to avoid an increase in the number of pictures by deleting a picture that originally existed instead of the inserted picture. In addition, if the B picture that is not used for reference or the P picture immediately before the I picture is deleted instead of the inserted picture, it is possible to avoid an increase in the number of pictures and display it as a moving picture. If so, the degradation of the moving image quality can be minimized.
[0061]
Finally, some of the gist of the present invention are listed below.
[0062]
(Supplementary Note 1) An information embedding method for embedding information in an MPEG stream by inserting an information picture, which is a picture in which predetermined information is embedded, into the MPEG stream,
Generating the information picture;
Determining a position to insert the information picture into the MPEG stream;
And a step of inserting the information picture into the MPEG stream as a picture of difference information with respect to a picture located before the information picture in the order of pictures decoded from the MPEG stream.
[0063]
(Supplementary note 2) The information embedding method according to supplementary note 1, wherein the difference information is a DCT coefficient corresponding to a predetermined block in the information picture.
[0064]
(Supplementary note 3) The information embedding method according to supplementary note 1 or 2, wherein the difference information is a motion vector.
[0065]
(Supplementary note 4) The information embedding method according to any one of supplementary notes 1 to 3, wherein the information picture represents information by a position where the difference information is embedded.
[0066]
(Supplementary note 5) The information according to any one of supplementary notes 1 to 4, further comprising a step of writing time information included in a header of the information picture according to a position where the information picture is inserted. Embed method.
[0067]
(Supplementary note 6) The information embedding method according to any one of supplementary notes 1 to 5, further comprising a step of rewriting time information of a picture including pictures before and after the position where the information picture is inserted.
[0068]
(Supplementary note 7) An information processing apparatus for embedding information in an MPEG stream by inserting an information picture, which is a picture in which predetermined information is embedded, into the MPEG stream,
Means for generating the information picture;
Means for determining a position to insert the information picture into the MPEG stream;
An information processing apparatus comprising: means for inserting the information picture into the MPEG stream as a picture of difference information with respect to a picture located before the information picture in the order of pictures decoded from the MPEG stream.
[0069]
【The invention's effect】
As described above, according to the present invention, it is possible to embed information in an MPEG stream and extract confidential information from the decoding result of the stream by a simple method with a low processing load without decoding the MPEG stream to the image level. A possible information embedding method and an information processing apparatus can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing how a P picture is inserted.
FIG. 2 is a diagram illustrating a state in which a B picture is inserted.
FIG. 3 is a diagram illustrating a picture in which difference information is embedded.
FIG. 4 is a diagram illustrating a picture in which difference information is embedded.
FIG. 5 is a diagram illustrating difference information corresponding to 26 alphabetic characters.
FIG. 6 is a diagram illustrating a picture in which difference information is embedded.
FIG. 7 is a diagram showing a configuration of a digital broadcast storage / playback apparatus.
FIG. 8 is a diagram showing index information.
FIG. 9 is a diagram illustrating a state in which a picture is inserted into a broadcast stream.
FIG. 10 is a flowchart showing processing of a secret information picture insertion unit.
FIG. 11 is a diagram showing a configuration of a digital broadcast storage / playback apparatus having a scramble function.
[Explanation of symbols]
10, 12, 20, 22, 60 ... MPEG streams 11, 14, 21, 24 ... picture groups 13, 23 ... confidential information 30, 34, 40 ... reference pictures 31, 35, 41 ... confidential information pictures 32, 33, 36 , 37, 42, 43, 44, 45 ... block 62 ... picture 50 ... accumulation block 51, 71 ... stream accumulation unit 52, 72 ... index generation unit 53, 73 ... confidential information picture insertion unit 54, 74 ... reproduction block 55, 75 ... TS Demux section 56, 76 ... MPEG decoder section 57, 77 ... Display device 58, 59 ... VTR
61 ... Secret information insertion stream 78 ... Local scrambler 79 ... Local descrambler 80 ... Descrambler

Claims (5)

An information embedding method for embedding confidential information in an MPEG stream by inserting an information picture, which is a picture in which difference information is embedded, into the MPEG stream,
A picture generating step for generating the information picture;
An insertion position determining step for determining a position at which the information picture is inserted into the MPEG stream;
In order of pictures obtained by decoding the MPEG stream, and characterized in that as the confidential information the difference information for the picture which is positioned in front of the information picture, and a picture inserting step of inserting the information picture to the MPEG stream How to embed information.   2. The information embedding method according to claim 1, wherein the difference information is a DCT coefficient corresponding to a predetermined block in the information picture.   3. The information embedding method according to claim 1, wherein the difference information is a motion vector. 4. The information embedding method according to claim 1, wherein the information picture represents the confidential information by a position where the difference information is embedded. 5. An information processing apparatus for embedding confidential information in an MPEG stream by inserting an information picture, which is a picture in which difference information is embedded, into the MPEG stream,
Picture generating means for generating the information picture;
Insertion position determining means for determining a position at which the information picture is inserted into the MPEG stream;
In order of pictures obtained by decoding the MPEG stream, and characterized in that as the confidential information the difference information for the picture which is positioned in front of the information picture, and a picture inserting unit for inserting the information picture to the MPEG stream Information processing apparatus.

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