A picture type identifier, indicating one of intra-picture coding (an I-picture), forward or backward predictive coding (a P-picture) and bi-directionally predictive coding (a B-picture), is included with a picture signal when the signal is encoded and when the signal is decoded. Each of initial and subsequent encoding and decoding is a function of the included picture type.
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0. 53. A method of encoding a video signal obtained by decoding a previously encoded video signal, comprising the steps of:
receiving said video signal and structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
presently encoding by an encoding device the received video signal utilizing the received structure information to generate a re-encoded video signal; and
controlling the present encoding to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said previously encoded video signal.
0. 54. encoding apparatus for encoding a video signal obtained by decoding a previously encoded video signal, comprising:
a receiver for receiving said video signal and structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
an encoder for presently encoding the received video signal utilizing the structure information received by said receiver to generate a re-encoded video signal; and
a controller for controlling the encoding by said encoder to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said previously encoded video signal.
0. 43. encoding apparatus for encoding a video signal obtained by decoding a previously encoded video signal, comprising:
receiving means for receiving said video signal and structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
encoding means for presently encoding the received video signal utilizing the structure information received by said receiving means to generate a re-encoded video signal; and
controlling means for controlling the encoding by said encoding means to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said previously encoded video signal.
0. 41. A method of re-encoding a decoded video signal obtained by decoding a previously encoded video signal, comprising the steps of:
generating structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
decoding by a decoding device the received encoded video signal on the basis of said structure information to generate a decoded video signal;
transferring the decoded video signal and said structure information;
receiving means for receiving the transferred decoded video signal and structure information;
using the received structure information to re-encode the received decoded video signal and generate a re-encoded video signal; and
controlling said re-encoding to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said previously encoded video signal.
0. 38. A method for re-encoding a decoded video signal obtained by decoding a previously encoded video signal, comprising the steps of:
receiving an encoded video signal and structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
decoding by a decoding device the received encoded video signal on the basis of said structure information to generate a decoded video signal;
transferring the decoded video signal and said structure information;
receiving the transferred decoded video signal and structure information;
using the received structure information to re-encode the decoded video signal and thereby generate a re-encoded video signal; and
controlling said re-encoding to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said received encoded video signal.
0. 42. Re-encoding apparatus for re-encoding a decoded video signal obtained by decoding a previously encoded video signal, comprising:
a generator for generating structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
a decoder for decoding the received encoded video signal on the basis of said structure information to generate a decoded video signal;
a transfer unit for transferring the decoded video signal and said structure information;
a receiver for receiving the transferred decoded video signal and structure information;
an encoder utilizing the structure information received by said receiver to re-encode the received decoded video signal and generate a re-encoded video signal; and
a controller for controlling said re-encoding by said encoder to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said previously encoded video signal.
0. 40. Re-encoding apparatus for re-encoding a decoded video signal obtained by decoding a previously encoded video signal, comprising:
generating means for generating structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
decoding means for decoding the received encoded video signal on the basis of said structure information to generate a decoded video signal;
transferring means for transferring the decoded video signal and said structure information;
receiving means for receiving the transferred decoded video signal and structure information;
encoding means utilizing the structure information received by said receiving means to re-encode the received decoded video signal and generate a re-encoded video signal; and
controlling means for controlling said re-encoding by said encoding means to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said previously encoded video signal.
0. 39. Re-encoding apparatus for re-encoding a decoded video signal obtained by decoding a previously encoded video signal, comprising:
a first receiver for receiving an encoded video signal and structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
a decoder for decoding the received encoded video signal on the basis of said structure information to generate a decoded video signal;
a transfer unit for transferring the decoded video signal and said structure information;
a second receiver for receiving the transferred decoded video signal and structure information;
an encoder utilizing the structure information received by said second receiver to re-encode the decoded video signal received by said second receiver and generate a re-encoded video signal; and
a controller for controlling said re-encoding by said encoder to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said received encoded video signal.
0. 28. Re-encoding apparatus for re-encoding a decoded video signal obtained by decoding a previously encoded video signal, comprising:
first receiving means for receiving an encoded video signal and structure information indicating the location within a group of pictures of a respective picture or a first picture resulting from the previous encoding of said video signal, said group of pictures containing a number of pictures of different picture types, the number of pictures in said group of pictures and the picture type of said first picture in the group not being fixed;
decoding means for decoding the received encoded video signal on the basis of said structure information to generate a decoded video signal;
transferring means for transferring the decoded video signal and said structure information;
second receiving means for receiving the transferred decoded video signal and structure information;
encoding means utilizing the structure information received by said second receiving means to re-encode the decoded video signal received by said second receiving means and generate a re-encoded video signal; and
controlling means for controlling said re-encoding by said encoding means to match the location and picture type of said respective picture or first picture in said re-encoded video signal with the location and picture type of said respective picture or first picture in said received encoded video signal.
0. 1. An apparatus for processing a digital picture signal, comprising:
means for receiving a digital picture signal having picture type data included in a data identification area of said digital picture signal indicating one of intrapicture coding, predictive coding and bidirectionally predictive coding for respective pictures represented by said digital picture signal, said picture type data identifying an encoding structure of a group of pictures represented by said digital picture signal and further identifying each respective picture within said group of pictures so as to identify the type of encoding of said digital picture signal for each said picture; and
coding means for encoding said digital picture signal as a function of said picture type data to produce an encoded digital picture signal.
0. 2. The apparatus of
0. 3. The apparatus of
0. 4. The apparatus of
0. 5. The apparatus of
0. 6. The apparatus of
0. 7. The apparatus of
0. 8. The apparatus of
0. 9. An apparatus for processing an encoded digital picture signal, comprising:
means for decoding said encoded digital picture signal to produce picture type data representing a type of encoding of said encoded digital picture signal and to produce a decoded digital picture signal, said picture type data identifying a previous encoding structure of a group of pictures represented by said encoded digital picture signal and further identifying each respective picture within said group of pictures represented by said decoded digital picture signal so as to identify the previous type of encoding for each picture represented by said decoded digital picture signal; and
means for including said picture type data in a data identification area of said decoded digital picture signal to produce an output signal.
0. 10. The apparatus of
0. 11. The apparatus of
0. 12. The apparatus of
0. 13. The apparatus of
0. 14. The apparatus of
0. 15. A method of processing a digital picture signal, comprising the steps of:
receiving a digital picture signal having picture type data included in a data identification area of said digital picture signal indicating one of intrapicture coding, predictive coding and bidirectionally predictive coding for respective pictures represented by said digital picture signal, said picture type data identifying an encoding structure of a group of pictures represented by said digital picture signal and further identifying each respective picture within said group of pictures so as to identify the type of encoding of said digital picture signal for each said picture; and
encoding said digital picture signal as a function of said picture type data to produce an encoded digital picture signal.
0. 16. The method of
0. 17. The method of
0. 18. The method of
0. 19. The method of
0. 20. The method of
0. 21. The method of
0. 22. The method of
0. 23. A method of processing an encoded digital picture signal, comprising the steps of:
decoding said encoded digital picture signal to produce picture type data representing a type of encoding of said encoded digital picture signal and to produce a decoded digital picture signal, said picture type data identifying a previous encoding structure of a group of pictures represented by said encoded digital picture signal and further identifying each respective picture within said group of pictures represented by said decoded digital picture signal so as to identify the previous type of encoding for each picture represented by said decoded digital picture signal; and
including said picture type data in a data identification area of said decoded digital picture signal to produce an output signal.
0. 24. The apparatus of
0. 25. The method of
0. 26. The method of
0. 27. The method of
0. 29. The re-encoding apparatus according to claim 28, wherein
said transferring means multiplexes the structure information into the decoded video signal.
0. 30. The re-encoding apparatus according to claim 29, wherein
said transferring means multiplexes the structure information in the vertical blanking interval of the decoded video signal.
0. 31. The re-encoding apparatus according to claim 28, wherein the encoded video signal is encoded in accordance with an MPEG standard.
0. 32. The re-encoding apparatus according to claim 28, further comprising
output means for outputting the generated re-encoded video signal and the structure information utilized by said encoding means.
0. 33. The encoding apparatus according to claim 28, wherein
said encoding means re-encodes the decoded video signal in accordance with an MPEG standard.
0. 34. The re-encoding apparatus according to claim 28, wherein the respective picture or first picture in the group of pictures is an I picture; and
the structure information identifies the minimum number of frames between succeeding I pictures.
0. 35. The re-encoding apparatus according to claim 28, wherein said group of pictures includes I and P pictures; and
the structure information identifies the minimum number of frames between an I picture and a succeeding P picture.
0. 36. The re-encoding apparatus according to claim 28, wherein the group of pictures includes P pictures; and
the structure information identifies the minimum number of frames between P picture and P picture.
0. 37. The re-encoding apparatus according to claim 28, wherein
the structure information identifies the total number of frames in a group of pictures.
0. 44. The encoding apparatus according to claim 43, further comprising
output means for outputting the re-encoded video signal generated by said encoding means and the structure information utilized by said encoding means.
0. 45. The encoding apparatus according to claim 43, wherein
said encoding means encodes the received video signal in accordance with an MPEG standard.
0. 46. The encoding apparatus according to claim 43, wherein
the previously encoded video signal was previously encoded in accordance with an MPEG standard.
0. 47. The encoding apparatus according to claim 43, wherein the respective picture or first picture in the group of pictures is an I picture; and
the structure information identifies the minimum number of frames between succeeding I pictures.
0. 48. The encoding apparatus according to claim 43 wherein said group of pictures includes I and P pictures; and
the structure information identifies the minimum number of frames between an I picture and a succeeding P picture.
0. 49. The encoding apparatus according to claim 43, wherein the group of pictures includes P pictures; and
the structure information identifies the minimum number of frames between P picture and P picture.
0. 50. The encoding apparatus according to claim 43, wherein
the structure information identifies the total number of frames in a group of pictures.
0. 51. The encoding apparatus according to claim 43, wherein
the structure information is multiplexed in the received video signal, and
said receiving means acquires the structure information from said video signal.
0. 52. The encoding apparatus according to claim 51, wherein
the structure information is multiplexed in the vertical blanking interval of said received video signal.
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Notice: More than one reissue application has been filed for the reissue of U.S. Pat. No. 5,715,009. The reissue applications are Ser. No. 10/497,026, the instant continuation application and three applications filed concurrently herewith.
This is a continuation-in-part of U.S. patent application Ser. No. 08/219,472, filed Mar. 29, 1994, now U.S. Pat. No. 5,473,380.
The present invention relates to coding and decoding of a picture signal for transmission, and, more particularly, is directed to matching the type of predictive coding applied to pictures of the picture signal.
In, for example, a teleconferencing system or a video telephone system, moving picture signals are compressed and encoded by taking advantage of intra-frame and inter-frame correlation so that they can be more efficiently transmitted over a communication channel to a remote location.
Intra-frame correlation can be utilized by an orthogonal transformation, such as a discrete cosine transformation (DCT).
Inter-frame correlation can be utilized by predictive encoding between successive pictures. As used herein, a picture generally refers to an image represented by a frame. When the fields of a frame are coded in a non-interlaced manner, that is, separately, each field may be referred to as a picture.
As shown in
However, if only the difference signals are transmitted, the original picture cannot be restored. It is advantageous to occasionally transmit a picture which is not predictively encoded as a reference for difference picture data, and because it is sometimes more efficient than transmitting the picture as a predictively encoded picture.
Pictures which are encoded utilizing only intra-frame correlation and not inter-frame correlation, are referred to herein as intra-pictures or I-pictures.
Pictures which are encoded with predictive encoding relative to one previously encoded picture are referred to herein as predictive pictures or P-pictures. The previously encoded picture may be an I-picture or a P-picture, and temporally succeeds the P-picture.
Pictures which are encoded with predictive encoding relative to at most two pictures, a temporally preceding and a temporally succeeding picture, are referred to herein as bi-directionally predictive coded pictures or B-pictures. The two pictures may each be an I-picture or a P-picture. When both are used, the mean value of the two pictures is obtained and used as a reference picture for the picture to be encoded.
A series of pictures may be considered as groups of pictures having a predetermined number of frames such as F1 . . . F17. The luminance and chrominance picture signals of the leading frame F1 are encoded as an I-picture, the picture signals of the second frame F2 are encoded as a B-picture, and the picture signals of the third frame F3 are encoded as a P-picture. The fourth and the following frames F4 to F17 are encoded alternately as B-pictures and P-pictures.
As shown in
The first method, shown as SP1, is to not use predictive encoding, that is, to use only intra-frame correlation. This is suitable for any macro-blocks of an I-picture, a P-picture and a B-picture. In other words, if less encoded data is produced without predictive encoding, then this method is selected.
The second method, shown as SP2, is to predictively encode relative to a picture which temporally succeeds the current picture, referred to as backward predictive encoding. The third method, shown as SP3, is to predictively encode relative to a picture which temporally precedes the current picture, referred to as forward predictive encoding. The second method is suitable for macro-blocks of only B-pictures. The third method is suitable for macro-blocks of P-pictures and B-pictures.
The fourth method, shown as SP4, is to predictively encode relative to the mean value of two pictures, one temporally preceding and one temporally succeeding the current picture. This method is suitable for macro-blocks of only B-pictures.
The encoding sequence will now be described.
The first frame F1 is encoded as an I-picture using the first method SP1 so that it is directly transmitted over a transmission channel as encoded data F1X.
The third frame F3 is encoded as a P-picture. When the third method SP3, forward predictive coding, is used for a macro-block, difference signals from the temporally preceding frame F1 used as the reference picture, as indicated by a broken-line arrow SP3, and a motion vector x3 between the reference picture F1 and the current picture F3, are calculated and encoded as data F3X for that macro-block. Alternatively, in this or another macro-block of the P picture, if a smaller amount of encoded data is produced for a macro-block of the P picture being encoded, the first method SP1 can be used wherein the data of the original frame F3 are directly utilized as the transmission data F3X for that macro-block.
The second frame F2 is encoded as a B-picture.
When the fourth method SP4 is used to encode a macro-block of the frame F2, a difference between the mean value of the temporally preceding frame F1 and the temporally succeeding frame F3 is calculated, on a pixel by pixel basis. The difference data and the motion vectors x1 and x2 are encoded as data F2X.
When the first processing method SP1 is used to encode a macro-block of the frame F2, the data of the original frame F2 forms the encoded data F2X.
When one of the second or third methods SP2, SP3 is used to encode a macro-block of the frame F2, one of the difference between the temporally succeeding frame F3 and the current frame F2, and the difference between the temporally preceding frame F1 and the current frame F2 is calculated. The difference data and one of the motion vectors x1, x2 are encoded as the data F2X.
The frame F4 for the B-picture and the frame F5 for the P-picture are processed in a similar manner as described above to generate transmitted data F4X and F5X.
The encoding device 1 includes an input terminal 10, a pre-processing circuit 11, A/D converters 12 and 13, a frame memory 14 including a luminance signal frame memory 15 and a color difference signal frame memory 16, a format converting circuit 17 and an encoder 18.
Input terminal 10 is adapted to receive a video signal VD and to supply the signal VD to pre-processing circuit 11 which functions to separate the video signal VD into luminance signals and color signals, herein chrominance or color difference signals, that are applied to analog-to-digital (A/D) converters 12 and 13, respectively. The video signals, digitized by analog-to-digital conversion by the A/D converters 12 and 13, are supplied to frame memory 14 having memories 15, 16 which function to store the luminance signals and the color difference signals, respectively, and to read out the signals stored therein to format converting circuit 17.
The converter 17 is operative to convert frame format signals stored in the frame memory section 14 into block format signals. As shown in
The encoder 18 operates to encode the block format signals and to supply the encoded signals as a bitstream over a transmission channel for recording on the recording medium 3.
The decoding device 2 includes a decoder 31, a format converting circuit 32, a frame memory section 33 including a luminance signal frame memory 34 and a color difference signal frame memory 35, digital-to-analog converters 36 and 37, a post-processing circuit 38 and an output terminal 30.
The decoder 31 is operative to reproduce encoded data from the recording medium 3 and to decode the encoded data, as described in detail below with reference to
Generally, the encoder 18 stores three pictures, the current picture and the pictures temporally preceding and succeeding the current picture. Based on the sequential position of the current picture in the group of pictures, the picture coding type (I, P or B) is selected for each picture. The picture type sequence is determined by a user using picture type input device 65, independent of the pictures applied to an input terminal 49.
The encoder 18 also chooses one of frame-based and field-based predictive encoding as will be explained with reference to
At the encoder 18, the quantized data are dequantized, inverse orthogonally transformed, and stored as the reference pictures. The predictive encoding applies the motion vector(s) obtained for the current picture to the reference picture(s) to produce a prediction picture which is subtracted from the current picture to yield the difference data.
The elements of the encoder 18 will now be explained in detail.
Picture data for encoding is supplied macro-block by macro-block to the input terminal 49 and thence to a motion vector detection circuit 50 which is operative to process the picture data of respective frames as I-pictures. P-pictures or as B-pictures, in accordance with a predetermined sequence for each group of pictures, as shown for example, in
More specifically, the frames F1, F2, F3 are stored in the memories 51a, 51b, 51c, respectively. Then the picture stored in memory 51c is transferred to memory 51a. The frames F4, F5 are stored in the memories 51b, 51c, respectively. The operations of transferring the picture in memory 51c to memory 51a and storing the next two pictures in memories 51b, 51c are repeated for the remaining pictures in the group of pictures.
After the pictures are read into the memory and temporarily stored, they are read out and supplied to a prediction mode changeover circuit 52 which is adapted to process the current picture for one of frame based and field based predictive encoding. After processing the first frame picture data in a group of pictures as an I-picture and before processing the second frame picture as a B-picture, the motion vector detection circuit 50 processes the third frame P-picture. The processing sequence is different from the sequence in which the pictures are supplied because the B-picture may involve backward prediction, so subsequent decoding may require that the P-picture temporally succeeding the B-picture have been previously decoded.
The motion vector detection circuit 50 calculates as an estimated value for intra-coding for each macro-block, the sum of absolute values of prediction errors for the frame prediction mode for each macro-block and the sum of absolute values of prediction errors for the field prediction mode for each macro-block and supplies these sums to the prediction decision circuit 54 which compares these sums and selects frame prediction mode or field prediction mode in accordance with the smallest of these values and provides the selected mode to the prediction mode changeover circuit 52.
If the frame prediction mode is selected, the prediction mode changeover circuit 52 outputs the four luminance blocks Y1 to Y4 and the two chrominance or color difference blocks Cb, Cr of each macro-block received from the motion vector detection circuit 50 without processing. As shown in
If the field prediction mode is selected, the prediction mode changeover circuit 52 processes the signals received from the motion vector detection circuit 50 so that each of the four luminance blocks comprises data from a single field and the two color difference blocks have non-interlaced odd and even field data. Specifically, as shown in
The prediction mode changeover circuit 52 supplies the current picture, as processed for frame based or field based predictive encoding, to arithmetic unit 53 of
The motion vector detection circuit 50 calculates, for the current picture, the sum of absolute values of the differences between each Aij and the average value of the Aij in each macro-block Σ|Aij−(average of Aij)| and supplies the sum as an estimated value for intra-coding to the prediction decision circuit 54.
The motion vector detection circuit 50 calculates the sum of absolute values (or sum of squares) of the difference (Aij−Bij) between signals Aij of the macro-blocks of the current picture, and signals Bij of the macro-blocks of the prediction picture Σ|Aij−Bij| in each of frame prediction mode and field prediction mode. As explained above, the motion vector(s) for the current picture are applied to the reference picture(s) to generate the prediction picture. When the reference picture temporally precedes the current picture, the quantity Σ|Aij−Bij| is referred to as a forward prediction error signal, and when the reference picture temporally succeeds the current picture, the quantity Σ|Aij−Bij| is referred to as a backward prediction error signal. When the prediction picture is the mean of a temporally preceding and a temporally succeeding reference picture, as motion-compensated, the quantity Σ|Aij−Bij| is referred to as a bi-directional prediction error signal.
The circuit 50 supplies the forward frame prediction, the forward field prediction, the backward frame prediction, the backward field prediction, the bi-directional frame prediction and the bi-directional field prediction error signals to the prediction decision circuit 54.
The prediction decision circuit 54 selects one of intra-coding, forward inter-picture prediction, backward inter-picture prediction or bi-directional inter-picture prediction and one of frame and field prediction mode in accordance with the smallest of the estimated value for intra-coding and the forward frame, the forward field, the backward frame, the backward field, the bi-directional frame and the bi-directional field prediction error signals. The arithmetic unit 53 predictively encodes the current picture, as processed by the frame or field changeover circuit 52, in accordance with the prediction mode selected by the prediction decision circuit 54.
The motion vector detection circuit 50 serves to calculate and supply the motion vector(s) associated with the selected prediction mode to a variable length encoding circuit 58 and a motion compensation circuit 64, explained later.
The sums of the absolute values of the inter-frame differences (prediction errors) on the macro-block basis are supplied from the motion vector detection circuit 50 to the prediction mode changeover circuit 52 and to the prediction decision circuit 54, in the manner as described above.
The arithmetic unit 53 supplies predictively encoded data, also referred to as difference data, for the current picture to a DCT mode changeover circuit 55 which is adapted to process the current picture for one of frame based and field based orthogonal transformation.
The DCT changeover circuit 55 functions to compare the encoding efficiency when the DCT operations for the macro-blocks in a picture are performed with the odd field data alternating with the even field data, that is, for frame based orthogonal transformation, as shown in
To evaluate the encoding efficiency for frame based orthogonal transformation, the DCT mode changeover circuit 55 places the luminance macro-block data into interlaced form, as shown in
To evaluate the encoding efficiency for field based orthogonal transformation, the DCT mode changeover circuit 55 places the luminance macro-block data into non-interlaced form, as shown in
The DCT changeover circuit 55 compares the difference between the frame based and field based sums of the absolute values with a predetermined threshold and selects frame based DCT transformation if the difference EFM−EFD is less than the predetermined threshold.
If the frame prediction mode is selected in the prediction mode changeover circuit 52, the probability is high that the frame DCT mode will be selected in the DCT mode changeover circuit 55. If the field prediction mode is selected in the prediction mode changeover circuit 52, the probability is high that the field DCT mode will be selected in the DCT mode changeover circuit 55. However, since this is not necessarily the case, the prediction mode changeover circuit 52 sets the mode which will give the least value of the sum of the absolute values of prediction errors, while the DCT mode changeover circuit 55 sets the mode which will give the optimum orthogonal transformation encoding efficiency.
If frame based orthogonal transformation mode, also referred to as frame DCT mode, is selected, the DCT mode changeover circuit 55 functions to ensure that the four luminance blocks Y1 to Y4 and two color difference blocks Cb, Cr represent alternating or interlaced odd and even field lines, as shown in
If field based orthogonal transformation mode, also referred to as field DCT mode, is selected, the DCT mode changeover circuit 55 functions to ensure that each of the luminance blocks represents only one field, and that each of the color difference blocks has segregated or non-interlaced odd and even field lines, as shown in
The DCT mode changeover circuit 55 functions to output the data having the configuration associated with the selected DCT mode, and to output a DCT flag indicating the selected DCT mode to the variable length encoding circuit 58 and the motion compensation circuit 64.
The DCT mode changeover circuit 55 supplies appropriately configured difference picture data to a DCT circuit 56 shown in
The variable length encoding circuit 58 is also supplied with the quantization step or scale data from the quantization circuit 57, prediction mode data from the prediction decision circuit 54, that is data indicating which of the intra-picture prediction, forward prediction, backward prediction or bi-directional prediction is used, and motion vector data from the motion vector detection circuit 50. The encoding circuit 58 also receives prediction flag data from the prediction decision circuit 54 comprising a flag indicating which of the frame prediction mode or the field prediction mode is used, and prediction flag data from the DCT mode changeover circuit 55 comprising a flag indicating which of the frame DCT mode or the field DCT mode is used. This information is placed into the header portion of the encoded data stream.
The variable length encoding circuit 58 serves to encode the quantized data and the header information using a variable length code such as a Huffman code, in accordance with the quantization step data supplied from the quantization circuit 57, and to output the resulting data to a transmission buffer 59.
The quantized data and quantization step are also supplied to a dequantization circuit 60 which serves to dequantize the quantized data using the quantization step, and to supply the recovered DCT coefficient data to an inverse DCT circuit 61 that functions to inverse transform the DCT coefficient data to produce recovered difference data and to supply the recovered difference data to an arithmetic unit 62.
The arithmetic unit 62 combines the recovered difference data with a previously encoded and decoded reference picture, as motion compensated, to produce decoded data for a reconstructed picture which will be used as a reference picture and which is read into one of two frame memories 63a, 63b. The memories 63a, 63b are adapted to read out the reference picture data stored therein to a motion compensation circuit 64 that uses the motion vectors from the motion vector detection circuit 50 to produce a prediction picture from the reference picture. Specifically, the circuit 50 uses the motion vector to alter the readout address of the reference picture from the memory 63a or 63b.
For a group of pictures, after the first frame I-picture data and the third frame P-picture data are stored in the forward and backward prediction picture memories or units 63a, 63b, respectively, the second frame B-picture data is processed by the motion vector detection circuit 50. The prediction decision circuit 54 selects the frame or field prediction mode, while setting the prediction mode to one of intra-frame prediction mode, forward prediction mode, backward prediction mode and bi-directional prediction mode in correspondence with the sum of absolute values of predictive errors by macro-block.
Since a reconstructed B-picture is not used as a reference picture for other pictures, it is not stored in the frame memory 63.
It will be appreciated that the frame memory 63 has its forward and backward prediction picture units 63a, 63b bank-exchanged as needed so that a picture stored in one of the units 63a or 63b can be outputted as either a forward or a backward prediction picture.
The motion compensation circuit 64 functions to supply the motion compensated data as a prediction picture to the arithmetic unit 62 and to the arithmetic unit 53 which subtracts the prediction picture from the P-picture or the B-picture currently being predictively encoded.
More specifically, when the motion vector detection circuit 50 receives picture data for an I-picture from the forward original picture unit 51a, the prediction decision circuit 54 selects the intra-frame prediction mode and sets a switch 53d of the arithmetic unit 53 to an input contact a. This causes the I-picture data to be inputted directly to the DCT mode changeover circuit 55. In this case, no prediction picture is expected from the motion compensation circuit 64. The I-picture data is also supplied to the forward prediction picture unit 63a.
When the forward prediction mode is selected by the prediction decision circuit 54, the circuit 54 also sets the switch 53d to an input contact b which causes the arithmetic unit 53a to subtract the prediction picture, produced by the motion compensation circuit 64, from the picture read out from the memory 51, for each macro-block on a pixel by pixel basis, to produce difference data. The P-picture, after encoding and local decoding, is supplied to one of the units 63a, 63b. For example, if the P-picture immediately follows an I-picture, then the P-picture is stored in the backward prediction picture unit 63b.
For forward predictive encoding, the prediction picture is a reference I-picture or P-picture read out from the forward prediction picture unit 63a of the frame memory 63 and motion-compensated by the motion compensation circuit 64 in accordance with the motion vector outputted from the motion vector detection circuit 50. More specifically, for each macro-block, the motion compensation circuit 64 shifts the readout address of the forward prediction picture unit 63a in an amount corresponding to the motion vector currently output by the motion vector detection circuit 50.
When the backward prediction mode is selected by the prediction decision circuit 54, the circuit 54 also sets the switch 53d to an input contact c which causes the arithmetic unit 53b to subtract the prediction picture, produced by the motion compensation circuit 64, from the picture read out from the memory 51, on a pixel by pixel basis, to produce difference data.
For backward predictive encoding, the prediction picture is a P-picture read out from the backward prediction picture unit 63b of the frame memory 63 and motion-compensated by the motion compensation circuit 64 in accordance with the motion vector outputted from the motion vector detection circuit 50. More specifically, for each macro-block, the motion compensation circuit 64 shifts the readout address of the backward prediction picture unit 63b in an amount corresponding to the motion vector currently output by the motion vector detection circuit 50.
When the bi-directional prediction mode is selected by the prediction decision circuit 54, the circuit 54 sets the switch 53d to an input contact d which causes the arithmetic unit 53c to subtract a prediction picture from the picture read out from the memory 51, on a pixel by pixel basis, to produce difference data. The prediction picture is the mean value of a forward prediction picture and a backward prediction picture.
In the case of bi-directional prediction, the picture stored in the forward prediction picture unit 63a, and the picture stored in the backward prediction picture unit 63b, are read out and motion-compensated by the motion compensation circuit 64 in dependence upon the motion vectors outputted from the motion vector detection circuit 50. More specifically, for each macro-block, the motion compensation circuit 64 shifts the readout address of the forward and backward prediction picture units 63a, 63b in an amount corresponding to the appropriate one of the motion vectors currently output by the motion vector detection circuit 50.
The transmission buffer 59 temporarily stores the data supplied thereto, generates control data indicating the volume of data stored therein and supplies the control data to the quantization circuit 57. When the volume of data stored in the transmission buffer 59 reaches a predetermined upper limit value, the control data from the transmission buffer 59 causes the quantization scale of the quantization circuit 57 to increase so as to decrease the volume of the quantized data. Similarly, when the volume of data stored in the transmission buffer 59 reaches a predetermined lower limit value, the control data from the transmission buffer 59 causes the quantization scale of the quantization circuit 57 to decrease so as to increase the volume of the quantized data. In this manner, the transmission buffer 59 prevents the data supplied thereto from overflowing or underflowing its capacity. The data stored in the transmission buffer 59 are read out at a predetermined timing to an output terminal 69 and thence to a transmission channel for recording on, for example, the recording medium 3.
Although the foregoing description has been made with reference mainly to the luminance blocks, the color difference blocks are similarly processed and transmitted using the motion vector which corresponds to the motion vector of the luminance block halved in both the vertical and horizontal directions.
The reproduced encoded picture data transmitted from the recording medium 3 is applied to a reception circuit, not shown, or to an input terminal 80 which applies the encoded picture data to a reception buffer 81 that serves to temporarily store the encoded picture data and to supply this data to a variable length decoding circuit 82 of a decoding circuit 90.
The variable length decoding circuit 82 functions to variable length decode the encoded data, to output the recovered motion vector, prediction mode data, prediction flags and DCT flags to the motion compensation circuit 87, and to output the quantization step data and variable length decoded picture-data, including the predictive mode, the motion vector, the predictive flag, the DCT flag and the quantized picture data for each macro-block, to an inverse quantization circuit 83.
The inverse quantization circuit 83 is adapted to dequantize the picture data supplied from the variable length decoding circuit 82 in accordance with the quantization step data supplied from the variable length decoding circuit 82 and to output the thus recovered coefficient data to an inverse transformation IDCT circuit 84.
The IDCT circuit 84 is adapted to perform an inverse transformation on the recovered coefficient data to produce recovered difference data, and to supply the recovered difference data to an arithmetic unit 85.
If the recovered difference data supplied from the IDCT circuit 84 represents an I-picture, the arithmetic unit 85 does not process the data and simply supplies it through an output terminal 91 to the format converting circuit 32 shown in
If the recovered difference data supplied from the IDCT circuit 84 represents a macro-block of a P-picture produced in the forward prediction mode, then the reference picture data of the preceding frame, as stored in the forward prediction picture memory 86a of the frame memory 86, is read and motion-compensated by a motion compensation circuit 87 in dependence upon the motion vector outputted from the variable length decoding circuit 82 to generate a prediction picture. Specifically, the motion compensation circuit 87 uses the motion vector to alter the read out address supplied to the memory 86a. The arithmetic unit 85 adds the prediction picture to the recovered difference data to produce a decoded or reconstructed picture which is stored in a backward prediction picture memory 86b of the frame memory 86. The decoded P-picture is retained in the decoder 31, and output after the next B-picture is decoded and output, so as to restore the pictures to the order in which they were supplied to the encoder 18 of
Even if the macro-block of the P-picture was encoded as intra-coded mode data, the decoded P-picture is directly stored in the backward prediction picture unit 86b, without being output to the output terminal 91 by the arithmetic unit 85.
If the recovered difference data supplied from the IDCT circuit 84 represents a macro-block of a B-picture encoded in the intra-coding mode, as determined from the prediction mode supplied from the variable length decoding circuit 82 to the motion compensation circuit 87, a prediction picture is not generated.
If the recovered difference data supplied from the IDCT circuit 84 represents a macro-block of a B-picture encoded in the forward prediction mode, as determined from the prediction mode supplied from the variable length decoding circuit 82 to the motion compensation circuit 87, the data stored in the forward prediction picture unit 86a of the frame memory 86 is read out and motion compensated by the motion compensation circuit 87 using the motion vector supplied from the variable length decoding circuit 82 to form the prediction picture. The arithmetic unit 85 sums the recovered difference data with the prediction picture to form the recovered B-picture.
If the recovered difference data supplied from the IDCT circuit 84 represents a macro-block of a B-picture encoded in the backward prediction mode, as determined from the prediction mode supplied from the variable length decoding circuit 82 to the motion compensation circuit 87, the data stored in the backward prediction picture unit 86b is read out and motion compensated by the motion compensation circuit 87 using the motion vector supplied from the variable length decoding circuit 82 to form the prediction picture. The arithmetic unit 85 sums the recovered difference data with the prediction picture to form the recovered B-picture.
If the recovered difference data supplied from the IDCT circuit 84 represents a macro-block of a B-picture encoded in the bi-directional prediction mode, as determined from the prediction mode supplied from the variable length decoding circuit 82 to the motion compensation circuit 87, the data stored in both the forward and backward prediction picture memories 86a, 86b are read out and respectively motion compensated by the motion compensation circuit 87 using the motion vectors supplied from the variable length decoding circuit 82, then averaged to form the prediction picture. The arithmetic unit 85 sums the recovered difference data with the prediction picture to form the recovered B-picture.
The recovered B-picture is supplied via the output terminal 91 to the format converting circuit 32. However, since the B-picture is not utilized for generating a prediction picture for other pictures, it is not stored in the frame memory 86.
After outputting of the B-picture, picture data of the P-picture stored in the backward prediction picture unit 86b is read and supplied via the motion compensation circuit 87 to the arithmetic unit 85. Motion compensation is not performed at this time.
The counterpart circuits to the prediction mode changeover circuit 52 and the DCT mode changeover circuit 55 in the encoder 18 of
The processing of the luminance signals has been explained in the foregoing. As will be appreciated by one of ordinary skill in the art, the processing of the color difference signals is carried out in a similar manner. However, the motion vector employed in such case is the motion vector for luminance signals which is halved in both the vertical and horizontal directions.
If all pictures cannot be transmitted as I-pictures, it is better to transmit a series of pictures as shown in
Accordingly, in the configuration of
To dub pictures, two coder-decoder (codec) units are used in series. However, the picture quality obtained from the second codec is substantially worse than the picture quality obtained from the first codec, as explained below.
In
The coded digital video signal from coding circuit 212 of coder 201 is supplied to a decoding circuit 213 of decoder 202 which is adapted to decode the coded digital video signal and to apply the decoded video signal to D/A converter 214.
The analog video signal produced by D/A converter of decoder 202 is supplied as an output signal b to the coder 203, which functions in a similar manner as the coder 201.
The digital video signal produced by the coder 203 is supplied to decoder 204 which functions in a similar manner as the decoder 202. The decoder 204 delivers an analog video signal as an output signal c to a terminal 205, which may transmit the signal c to another coder (not shown) and so on.
The deterioration in picture quality results from a mismatch between the picture type applied in the first codec and the picture type applied in the second codec. Namely, if a picture coded as a B picture in the first coder/decoder pair is coded as, e.g., P picture in the second coder/decoder pair, a great deterioration of picture quality results because the picture quality changes as a function of the picture type.
Since the deterioration in picture quality results from the mismatch between picture types of respective stages of codecs, such deterioration similarly takes place when digital connections are used between respective codecs.
An analog video signal is supplied to terminal 300, which supplies the analog video signal as an input signal a to A/D converter 301 that serves to digitize the signal a, and to apply the digital signal to a digital interface 311 of coder 302. The digital interface 311 applies the signal supplied thereto to a coding circuit 312 which encodes or compresses the digital video data to an encoded digital video bit stream.
The encoded digital video signal from the coding circuit 312 is supplied to decoding circuit 313 of decoder 303 that decodes the signal supplied thereto, and applies the decoded signal to digital interface 314. The interface 314 functions to output the decoded signal as an output signal b.
The output signal b is supplied to coder 304 which functions in a similar manner as coder 302 to produce a coded signal that is applied to decoder 305 which functions in a similar manner as decoder 303. The digital signal output from the decoder 303 is supplied to a D/A converter that serves to convert the signal supplied thereto to an analog video signal and to supply the analog video signal as an output signal c to output terminal 307.
Therefore, an object of the present invention is to provide a method and apparatus for encoding and decoding picture signals which avoid the aforementioned disadvantages of the prior art.
Another object of the present invention is to provide a method and apparatus for transmitting and receiving picture signals in serial stages which minimizes the deterioration in picture quality at each stage.
Yet another object of the present invention is to match the type of coding applied to pictures of a picture signal in serial processing stages, each stage comprising coding and decoding.
In accordance with one embodiment of the present invention, apparatus and method for processing a digital picture signal operate by receiving a digital picture signal which has picture type data included in a data identification area of the digital picture signal and which indicates one of intrapicture coding, predictive coding and bidirectionally predictive coding for respective pictures represented by the digital picture signal. The picture signal is encoded as a function of the picture type data to produce an encoded picture signal.
In accordance with another embodiment of the present invention, apparatus and method for processing an encoded digital picture signal operate by decoding the encoded digital picture signal so as to produce picture type data which represents the type of encoding of the encoded digital picture signal and to produce a decoded digital picture signal. The picture type data is added to a data identification area of the decoded digital picture signal to produce an output signal.
The above, and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the present invention when read in conjunction with the accompanying drawings in which corresponding parts are identified by the same reference numeral.
The present invention comprises a picture type identifier which is included with the picture signal at all times, namely, when the signal is encoded and when the signal is decoded. The picture type indicates one of intra-picture coding (an I-picture), predictive coding (a P-picture) and bi-directionally predictive coding (a B-picture). An I-picture includes macro-blocks encoded by only intra-coding. A P-picture includes macro-blocks encoded by intra-coding and/or macroblocks encoded by forward predictive coding. A B-picture includes macro-blocks encoded by intra-coding and/or macroblocks encoded by forward predictive coding and/or macroblocks encoded by backward predictive coding and/or macroblocks encoded by bi-directionally predictive coding.
Initially, each picture of a picture signal is encoded as a function of a respective picture type, then appropriately decoded. The decoded picture signal includes the respective picture types, preferably in the vertical blanking interval of each decoded picture. The decoded picture signal may be further processed by, for example, dubbing.
When the pictures of the decoded picture signal are again encoded, the re-encoding is a function of the picture type included in the decoded picture signal. The re-encoded signal includes the picture type. Subsequent decoding of the re-encoded picture is a function of the picture type. Each picture of the re-decoded picture signal includes its respective picture type.
Thus, the present invention matches the type of predictive coding applied to pictures in a picture signal by serially arranged coders which process the picture signal.
The present invention promotes optimum picture quality. A picture, previously encoded as an I-picture, P-picture or B-picture is again encoded as an I-picture, P-picture or B-picture, respectively. Also, encoding of a picture, previously encoded as a B-picture, as an I-picture or a P-picture is prevented. Thus, deterioration in signal quality after plural coding and decoding operations is minimized.
Referring now to the drawings, and in particular to
In
The input terminals 100, 108 function to apply the analog video signal and the picture type signal, respectively, to an A/D converter 101 and a coding circuit 102, respectively, of coder 120. The converter 101 is adapted to convert the analog video signal to a digital video signal, and to apply the digital video signal to the coding circuit 102.
The coding circuit 102 serves to encode the digital video signal as a function of the picture type signal to produce a coded digital video signal which includes, for each encoded picture, its picture type as identified by the picture type signal. More specifically, if the picture type for a picture indicates intra-picture coding, then the coding circuit 102 codes the picture as an I-picture. If the picture type for a picture indicates predictive coding, then the coding circuit 102 codes the picture as a P-picture. If the picture type for a picture indicates bi-directionally predictive coding, then the coding circuit 102 codes the picture as a B-picture.
The coding unit 120 may alternatively have the structure shown in
The coded digital video signal from coding circuit 102 of
The multiplexer 105 is operative to multiplex the picture type information with the decoded video signal to produce a multiplexed analog video signal as an output signal b in which the picture type information is contained in the decoded video signal. Preferably, the multiplexer 105 inserts the picture type for a picture of the decoded video signal into the vertical blanking interval of the picture. As mentioned, a picture may be either a frame or a field of the video signal.
The output signal b is supplied from the multiplexer 105 to a separating circuit 106 of the coder 122. The separating circuit is operative to separate or demultiplex the analog video signal and the picture type information from the output signal b, to supply the separated analog video signal to an A/D converter 107, and to supply the separated picture type information to a coding circuit 108. The converter 107 is adapted to convert the separated analog video signal to a digital video signal, and to apply the digital video signal to the coding circuit 108.
The coding circuit 108 serves to encode the digital video signal as a function of the separated picture type to produce a re-coded digital video signal which includes, for each re-encoded picture, its picture type as identified by the separated picture type signal.
The re-coded digital video signal from the coding circuit 108 is supplied to the decoder 123, which operates in a similar manner as the decoder 121.
Decoding circuit 110 of decoder 123 decodes the re-coded digital video signal to produce a re-decoded digital video signal and a corresponding picture type signal. The re-decoded digital video signal is converted to an analog signal by D/A converter 109, and applied to a multiplexer 111 which multiplexes the analog video signal with the picture type signal from decoding circuit 110 to produce a multiplexed analog video signal as an output signal c. Preferably, the multiplexer 111 inserts the picture type for a picture into the vertical blanking interval of the picture. The multiplexer 111 applies its output signal c to an output terminal 119.
Due to the inclusion of the picture type identifier in the signals b and c, the codecs of
That is, since the type of predictive coding applied to each picture is the same in each of the serially arranged codecs, the deterioration in picture quality at each codec is minimized even when the picture quality changes from picture to picture due to the type of predictive coding employed from picture to picture.
In
The coding circuit 152 serves to encode the digital video signal as a function of the picture type signal to produce a coded digital video signal which includes, for each encoded picture, its picture type as identified by the picture type signal. More specifically, if the picture type for a picture indicates intra-picture coding, then the coding circuit 152 codes the picture as an I-picture. If the picture type for a picture indicates predictive coding, then the coding circuit 152 codes the picture as a P-picture. If the picture type for a picture indicates bi-directionally predictive coding, then the coding circuit 152 codes the picture as a B-picture.
The coding unit 120 may alternatively have the structure shown in
The coded digital video signal from coding circuit 152 is supplied to a decoding circuit 153 of decoder 143 which is adapted to decode the coded digital video signal as a function of the picture type included in the encoded signal and to apply the decoded video signal to a digital interface 154. The decoding circuit 153 is further adapted to apply the picture type decoded from the coded digital video signal to a multiplexer 155.
The multiplexer 155 is operative to multiplex the picture type information with the decoded video signal to produce a multiplexed digital video signal as an output signal b in which the picture type information is contained in the decoded video signal. Preferably, multiplexer 155 multiplexes the picture type for a picture of the decoded video signal as a flag in the respective picture.
In a preferred embodiment of the present invention, the picture type information is inserted (or multiplexed) into the decoded video signal at a location therein which precedes the actual video data that represents the video field or frame.
In accordance with the present invention, the picture type information is inserted into the DID area of the ANC area of each of the horizontal scanning lines in the first and second vertical blanking areas. However, the picture type information also may be inserted into the DID area of the ANC area of other horizontal scanning lines of the decoded video signal, although these DID areas may be used for transmitting other types of data. For example, the DID areas in horizontal lines of non-vertical blanking areas may include other formatting information.
The picture type information (or picture type data) may identify the type of encoding of the picture (e.g., intra-picture coding, predictive coding, and bi-directionally predictive coding) in various ways.
When the picture type data identifies the “M” and “N” numbers, the type of encoding for each picture can be determined by the location of a respective picture within the group of pictures, and the location of a respective picture may be identified in the picture type data either by identifying each picture's location within the group of pictures or by identifying only the first picture within the group of pictures. For example, when M=3 and N=9 for a group of frames in the decoded video signal (
Returning to
The coding circuit 158 serves to encode the separated digital video signal as a function of the separated picture type to produce a re-coded digital video signal which includes, for each re-encoded picture, its picture type as identified by the separated picture type signal.
The re-coded digital video signal from the coding circuit 158 is supplied to the decoder 145, which operates in a similar manner as the decoder 143.
Decoding circuit 160 of decoder 145 decodes the re-coded digital video signal to produce a re-decoded digital video signal and a corresponding picture type signal. The re-decoded digital video signal is supplied to a digital interface 159 and thence to a multiplexer 161 which multiplexes the re-decoded digital video signal with the picture type signal from decoding circuit 160 to produce a multiplexed digital video signal. The multiplexer 161 multiplexes the picture type signal as a flag (e.g., in the DID area of the ANC area) in the re-decoded digital video signal.
The multiplexer 161 supplies the multiplexed digital video signal to an A/D converter 146 which serves to convert the multiplexed digital video signal to an analog video signal also referred to as output signal c. The converter 146 applies the output signal c to an output terminal 147.
Due to the inclusion of the picture type identifier in the signals b and c, the codecs of
In
Variable length decoding circuit 482 of
Although an illustrative embodiment of the present invention, and various modifications thereof, have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to this precise embodiment and the described modifications, and that various changes and further modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.
Tahara, Katsumi, Yoshinari, Hiromi
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