JPH07312756A - Circuit, device and method for conversion of information quantity of compressed animation image code signal - Google Patents

Abstract

PURPOSE:To simplify rate revision circuit and to reduce the processing delay by segmenting a variable code whose data length changes depending on a bit rate from a bit stream, applying bit rate revision processing thereto and replacing it with a variable code before revision processing in the stream. CONSTITUTION:A bit stream in 4Mbps of the MPEG-2 standards is given to the input terminal 10 of a bit rate revision circuit, a data demultiplexer circuit 12 separates data from the motion vector data C of processing type data (b) whose data content and data length are unchanged, and gives the result to a coupling circuit 26. Coefficient data (e) whose data content and data length are changed are fed to an inverse variable length coding circuit 14, subjected to variable length decoding and the result is fed to an inverse quantization circuit 16, in which inverse quantization is implemented. A quantization step width Qin is multiplied with coefficient data C'ij after inverse quantization, a specific constant Kij is multiplied with the coefficient C'ij, the constant Kijspecific to the coefficient C'ij is multiplied and each of quantized coefficient data C''ij is given to the quantization circuit 20, in which the signal is quantized and the step width is decided in a rate control circuit 32 so that the bit rate is 2Mbps.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit or an apparatus and a method for changing a bit rate of a bit stream obtained by compressing and encoding a moving picture signal. For example,
A circuit or a device for changing the bit rate of a bit stream conforming to the moving picture coding standard MPEG.
Regarding the method.

[0002]

2. Description of the Related Art In a method of compressing and encoding data obtained by digitizing a moving image signal, methods such as prediction with motion compensation, orthogonal transformation, quantization, and variable length coding are used.
For example, in MPEG, prediction with motion compensation, discrete cosine transform (DCT), adaptive quantization, and Huffman coding are adopted. MPEG is the name "Moving Picture Experts Gro" of the image compression standardization committee established under ISO (International Organization for Standardization).
Abbreviation for "up". The MPEG-1 standard is "ISO /
IEC 11172 ”and MPEG-2.
The draft standard is specified in "ISO / IEC 13818".

As a conventional technique in this field, USP49
85784 (JP-A 1-200793), USP52
31484 (JP-A-5-252507), USP52
93229 (JP-A-5-276502), USP53
25125 (JP-A-6-225284), JP-A-6-
There is a publication of 164408.

In the DCT, each block divided into 8 × 8 pixels is decomposed into frequency components of a low frequency term to a high frequency term and converted into an 8 × 8 coefficient matrix [Cij].

In the quantization, each coefficient Cij of the 8 × 8 coefficient matrix is divided by a certain divisor (quantization step width Q × corresponding coefficient C).
It is divided by a constant Kij) specific to ij, and the remainder is rounded. Here, the constant Kij unique to the coefficient Cij is given as a quantization table. In this quantization table, a large value is generally prepared for a high frequency component and a small value is prepared for a low frequency component in the intra block. In the adaptive quantization, the bit rate of the output bit stream is monitored, and the quantization step width Q is determined so that the value becomes a target value. That is, if the bit rate is smaller than the target value, the quantization step width Q is controlled to be small,
If it is larger than the target value, the quantization step width Q is controlled to be large.

In the Huffman coding, code words are assigned according to the appearance probability of each quantized coefficient value C'ij so that the higher the appearance probability is, the shorter the code word becomes.

The larger the quantization step width Q, the greater the degree of data compression and the lower the bit rate. That is, the amount of information is reduced. Further, as the bit rate becomes lower, the image quality of the reproduced image deteriorates, but the load on the system such as the transmission system becomes smaller. Therefore, in equipment for broadcasting stations, which is for material transmission, a high-quality bit stream with a high bit rate is desired. On the other hand, in a household device for distributed transmission, a bit stream with a low bit rate and low quality, but a low burden on the device, is desired. Therefore, there is a need for a device that changes the bit rate.

The bit rate may be fixed or variable. When the bit rate is variable, for example,
This is a case where the bit rate is in the range of 2 Mbps to 4 Mbps and the average is 3 Mbps. This is a scene where the deterioration of image quality is not noticeable even if the compression degree is increased,
Considering that there is a case where the image quality is significantly deteriorated when the compression degree is increased, the bit rate is increased in a case where the deterioration of the image quality is conspicuous, and the bit rate is decreased in a case where the deterioration of the image quality is not remarkable. In the coefficient matrix, an image with a large coefficient value in the high-frequency term has a quantization step width Q.
Even if the compression degree is increased and the compression degree is increased, the deterioration of the image quality is not conspicuous, but in the image in which the coefficient value of the high frequency range is small, if the quantization step width Q is increased and the compression degree is increased, the image quality is significantly deteriorated.

[0009]

In the conventional device for changing the bit rate, the bit stream is decoded, the moving image data is reproduced, and then the moving image data is re-encoded to obtain a bit having a desired bit rate. You are getting a stream. That is, the conventional device for changing the bit rate has an MPEG encoder arranged at the subsequent stage of the MPEG decoder. Further, the bit rate of the bit stream output by this MPEG encoder is monitored, and the quantization step width Q is adjusted so that the value becomes a target value (= value designated as the changed bit rate). Is to control.

In the MPEG decoder, well-known processes such as variable length decoding (= inverse variable length coding), inverse quantization, inverse DCT, prediction with motion compensation and the like are performed. In the prediction with motion compensation, a temporally preceding image and a temporally later image are added to the decoded moving image data. Therefore, a memory (frame memory) for storing an image that precedes in time and an image that follows in time is required. Also,
Since the images that are later in time are added, a corresponding delay occurs.

The MPEG encoder performs well-known processing such as prediction with motion compensation, DCT, quantization, and variable length coding. In motion-compensated prediction, a temporally preceding image and a temporally subsequent image are subtracted from the input moving image data. For this reason, a frame memory is required to store an image that precedes in time and an image that follows in time. In addition, a local inverse quantization circuit and a local inverse DCT circuit, which are circuits for reproducing the data of the image preceding in time and the image subsequent in time, are required. Further, since the image that is later in time is subtracted, a delay corresponding to that is generated.

The conventional bit rate changing device in which the MPEG decoder and the MPEG encoder are directly connected to each other naturally has a complicated circuit structure and a large size, resulting in a high cost. In addition, the degree of processing delay is large. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a circuit, a device, and a method for changing a bit rate, which has a relatively small and simple circuit configuration and a small degree of processing delay. .

Further, according to the present invention, an optimum image quality and an optimum image quality can be obtained depending on whether the bit stream after the bit rate change is a business equipment bit stream or a household equipment bit stream. An object of the present invention is to provide a circuit, a device, and a method that can change the bit rate so that the bit stream has a code amount. For this reason, not only is the fixed bit rate changed to another fixed bit rate, but the fixed bit rate is changed to a variable bit rate, the variable bit rate is changed to another variable bit rate, and the variable bit rate is changed. It is an object of the present invention to provide a circuit, a device, or a method that can change the bit rate to a fixed bit rate.

[0014]

The present invention is a circuit for changing the bit rate of a bit stream containing main data (e, d) whose data length changes according to the bit rate. Means (12) for cutting out the data (e, d) and means for converting the cut out main data (e, d) according to the target bit rate and outputting the converted main data (e ', d') And a means (26) for returning the converted main data (e ', d') to the bit stream in place of the unconverted main data (e, d).

The present invention further comprises means (12) for cutting out variable length coded data (e) of quantized orthogonal transform coefficients from a bit stream (A) of compressed moving image data compliant with the MPEG standard, The variable length coded data (e) cut out
Means to perform variable length decoding and inverse quantization on (14,16)
, And dequantized data is quantized with a new quantization step width and variable-length coded to generate new variable-length coded data.
means (20, 24) for outputting (e '), and new variable-length coded data (e') is replaced by the variable-length coded data (e) cut out from the bit stream (A). (26) for outputting a different bit stream (B), and an information amount conversion circuit having:

Further, the present invention transfers a bit stream data signal (A) compression-coded by subjecting moving image data to prediction processing with motion compensation, orthogonal transformation processing, quantization processing, and variable length coding processing. In the rate conversion circuit for changing the rate, means (12) for cutting out variable length coded data (e) of at least quantized orthogonal transform coefficients from the bit stream data signal (A), and the cut out A means (14) for variable-length decoding the variable-length encoded data (e) and a means (1) for performing inverse quantization on the variable-length decoded data
6), means (20) for quantizing the dequantized data with a new value, and variable length coding for the quantized data to obtain new data (e '). Output method (2
4) and the data (e) cut out by the cutting means (12)
And a means (26) for generating a new bit stream (B) by replacing and arranging with the new data (e ').

Further, according to the present invention, in an information amount conversion circuit for an image compression coded signal in which at least moving image data is adaptively quantized and compression coded, in the image compression coded signal, the A separation means (12) for cutting out the data (e) that has been adaptively quantized, and the data that has been adaptively quantized are quantized with a quantization step width (Qout) different from the original quantization step width (Qin). Adaptive quantization conversion means (16, 20) (360) for converting into the converted data, and the separation means (12) for the data (e ') from the adaptive quantization conversion means (16, 20) (360)
Replacement means (26) for replacing the data (e) cut out by
And an information amount conversion circuit for a moving image compression coded signal having:

Further, according to the present invention, a moving image compression coded signal having a first transfer rate, which is created by subjecting moving image data to at least orthogonal transform processing and adaptive quantization processing, to a moving image having a second transfer rate. In an information amount conversion circuit of a moving image compression code signal for converting into a compressed code signal, at least coefficient data (e) and quantization width step data are selected from the moving image compression code signal of the first transfer rate. Extracting means (12) for extracting a value (Qin), quantization width setting means (32) for setting a quantization step width value (Qout) adapted to the second transfer rate, the coefficient data (e), Adaptive quantization conversion means (16, 20) (34, 34) for outputting new coefficient data (e ') adapted to the second transfer rate based on the two quantization width data values (Qin, Qout). 36), and an information amount conversion circuit for a moving image compression code signal.

The present invention is also an information amount conversion circuit for converting a first bit rate into a second bit rate by converting a bit stream obtained by compressing a moving image signal and entropy-encoding it. Depending on the bit rate separated by the separation circuit (12) and the separation circuit (12) that separates the bit stream into a code whose data length changes according to the bit rate and a code whose data length does not change regardless of the bit rate. A decoder (14) for entropy-decoding a code whose data length changes, and a conversion means (16, 16) for converting the data decoded by the decoder (14) according to the value designated as the second bit rate. 20)
An encoder (24) for entropy coding the data converted by the conversion means (16, 20), and the encoder
(24) means for replacing the corresponding code in the bitstream on which the entropy coded code is based by the encoder (24) with the code entropy coded (26), and information of the compressed video code having It is a quantity conversion circuit.

Further, according to the present invention, the moving image signal is converted into DCT,
A code for converting a bit stream obtained by quantization and variable-length coding to change the bit rate from a first bit rate to a second bit rate, the code changing the data length when the bit rate changes. (e, d) and a separation circuit (12) for separating into a code whose data length does not change even if the bit rate changes, and a code whose data length changes according to the bit rate separated by the separation circuit (12) (e , d)
, A variable length decoder (14) for variable length decoding, an inverse quantizer (16) for inverse quantizing the data decoded by the variable length decoder (14), and a bit stream output from the circuit Of the new quantization step width (Qout) so that the bit rate of is equal to the value specified as the second bit rate.
A bit rate control circuit (32) that determines and outputs, and the new quantization step width (data) that is dequantized by the dequantizer (16) from the bit rate control circuit (32). Quantizer (20) for quantizing using Qout),
Variable length encoder for variable length coding the data quantized by the quantizer (20), and outputs as code (e ', d') (24)
And a means (26) for replacing the code (e, d) with the code (e ', d') and outputting a bit stream.

Further, according to the present invention, the moving image signal is converted into DCT,
A circuit for converting a bit stream obtained by quantization and variable-length coding to change from a first bit rate to a second bit rate, and a code whose data length changes when the bit rate changes from the bit stream ( A clipping circuit (12) for clipping e), and a variable length decoder (14) for variable length decoding the code (e) clipped by the clipping circuit (12),
An inverse quantizer (16) that inversely quantizes the data decoded by the variable length decoder (14), and a new quantization step width (Qout) for the data inversely quantized by the inverse quantizer (16). ), And a bit rate control circuit (32) for determining the new quantization step width (Qout) so that the output bit stream has the second bit rate. ), And a variable length encoder (24) for variable length coding the data quantized by the quantizer (20) and outputting it as a code (e ', d'), and the code (e, d). An information amount conversion circuit for a compressed moving image code, comprising: means (26) for substituting the code (e ', d') for outputting a bit stream.

In the above, the bit stream is
For example, it may be a code string conforming to the MPEG standard. Further, the bit rate control circuit may determine the quantization step width by referring to a transfer bit rate of an input bit stream. Also,
Instead of the inverse quantizer and the quantizer, the quantization step width given by the quantization step width data of the input bit stream is divided by the quantization step width determined by the bit rate control circuit. A division circuit for outputting to a requantization circuit, and the requantization unit for multiplying the value input from the division circuit by the data decoded by the variable length decoder and outputting to the variable length encoder. , May be configured. A requantizer that performs the functions of the division circuit and the requantizer may be provided. Further, the bit rate control circuit may be configured to adjust the determined value of the quantization step width in accordance with the value of the coefficient of the high frequency term of the coefficient matrix data output from the inverse quantizer. Further, when the bit rate control circuit outputs a coefficient value of a high-frequency term of coefficient matrix data output from the inverse quantizer exceeds a predetermined set value, the determined value of the quantization step width is further reduced. It may be configured to adjust. Further, the bit rate control circuit may be configured to detect the transfer bit rate based on the transfer bit rate data in the input bit stream. Further, a bit rate detection circuit for detecting the transfer bit rate of the input bit stream and outputting it to the bit rate control circuit may be provided.

Further, the present invention is an apparatus for converting the code amount of a bit stream by changing the bit rate of the bit stream obtained by compressing a moving image signal and encoding the moving image signal by a predetermined method. An information amount conversion device for a compressed moving image code, comprising any one of the information amount conversion circuits and an input means for designating a changed bit rate. Here, the input means may be configured to specify the changed bit rate range and the representative value.

Further, the present invention is a method for converting a bit stream containing a code (e) whose data length changes when the bit rate changes from a first bit rate to a second bit rate, wherein From the code (e)
And the code (e) is converted according to the second bit rate to obtain a code (e '), and the code (e') is converted into the code (e).
It is a method of converting a bitstream, which is returned to the bitstream instead of.

Further, according to the present invention, a bit stream obtained by subjecting moving image data to at least DCT, quantization, and variable length coding is converted to convert the first bit rate to the second bit rate.
Of the first DCT coefficient code (e) in which the bit stream is separated into a first DCT coefficient code (e) whose data length changes according to the bit rate and a residual code. ) Is variable-length decoded, the variable-length decoded data is dequantized, and the dequantized data is converted to the second
Quantized using the quantization step width (Qout) set so that the bit rate of becomes the target value, and the quantized data is variable length coded to the second DCT coefficient code (e '),
This is a bitstream conversion method in which the second DCT coefficient code (e ′) and the residual code are multiplexed and output.

[0026]

The bit stream of the compressed moving image code has a code whose value changes when the bit rate changes (hereinafter referred to as "variable code") and a code whose value does not change even if the bit rate changes (hereinafter referred to as "invariant code") Consists of. The variable code is
The code corresponding to the coefficient data Cij and the quantization step width Q
Is a code corresponding to. Hereinafter, in this specification, the subscripts “i” and “j]” represent the i-th row and the j-th column, and the invariant code is a code corresponding to header data, processing type data, motion vector data, etc. In the present invention, The variable code is cut out from the bitstream, the process for changing the bit rate is performed only on the variable code, and the variable code after the changing process is replaced with the variable code before the changing process.
The degree of compression is controlled according to the information amount of the high frequency component, whereby the bit rate is changed without significantly degrading the image quality, and the information amount of the bit stream is set to a desired amount.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The following description describes a bitstream conforming to the MPEG-2 standard for bitrates below 100 Mbps, but the invention is not limited to the MPEG-2 standard. That is, the present invention is applied to a bit stream whose bit rate can be changed by controlling the quantization step width of the compressed moving image code. For example, H.264, which is a moving image coding standard for videophones / conferences. 261 or
The same applies to a bit stream conforming to the MPEG-1 standard.

* Bitstream and Bitrate First, the relationship between the bitstream and the bitrate will be described. As shown in FIG. 1, MPEG-2 standard bit streams generated so as to have different bit rates based on the same moving image signal, for example, 4 Mbps and 2 Mbps, have different data lengths. In the figure, (A) is 4 Mbps and (B) is 2 Mbps. This difference in data length mainly occurs due to the coefficient data e in the bitstream. That is, the MPEG-2 standard bit stream includes header data a, processing type data (MP
EG Macro Block Type / MBT) b, motion vector data c, quantization step width data (MPEG Quantize
r Scale / QS) d, coefficient data e, etc., and the header data a includes picture type data a1,
Transfer bit rate data (MPEG Bit-Rate Value /
BRV) a2, image size data a3, and the like. Among these codes, the data length of the coefficient data e changes greatly when the bit rate changes. The reason is that the bit rate is changed by changing the quantization step width when quantizing the coefficient data e.

On the other hand, as shown in FIG. 2, the header data a, the processing type data b, the motion vector data c, and the picture type data a1 have substantially the same data content and data length regardless of the bit rate. Also,
Quantization step width data d and transfer bit rate data a
In 2, the data length is almost the same regardless of the bit rate, but the data content differs depending on the bit rate. According to the MPEG-2 standard, the quantization step width data d is "QSC (quantize scale code)" of the slice layer.
And the macroblock layer "QSC (quantize scale Cod
e) ”, the coefficient data e is block layer data, and the transfer bit rate data a2 is sequence layer“ B ”.
RV (Bit Rate Value) ”, and the picture type data a1 is“ PCT (Picture Coding Typ) of the picture layer.
e) ”.

As is apparent from the above circumstances, when changing the bit rate, it is not necessary to newly calculate the processing type data b and the motion vector data c, and the conventional code can be used as it is. Here, arithmetic means
This is a process in which an MPEG decoder temporarily decodes moving image data, and then an MPEG encoder encodes it into a compressed code again. To be precise, when the bit rate changes, the decoded image decoded by the local decoder incorporated in the MPEG encoder also changes, so the processing type data b and the motion vector data c may change slightly. However, this variation is small and can be ignored. Therefore, the coefficient data e, the quantization step width data d, and the transfer bit rate data a2 are substantially changed by the change of the bit rate, and the coefficient data e is substantially changed in the data length. is there. The present invention utilizes this fact.

First Embodiment Next, a first embodiment will be described with reference to FIG. The circuit shown in Fig. 3 uses a bitstream with a bit rate of 4 Mbps to 2 Mbps.
It is a circuit for changing to the bit stream of. The fact that the bit rate of the output bit stream should be changed to a bit stream of 2 Mbps may be designated by an input operation from an operation switch (not shown), or may be designated as a default. .

A 4 Mbps MPEG-2 standard bit stream is input to the input terminal 10 of the bit rate changing circuit shown in FIG. This bit stream is separated by the data separation circuit 12 according to the classification described above. That is,
Processing type data b whose data content and data length do not change
And the motion vector data c are sent to the combining circuit 26 as they are.

The coefficient data e whose data content and data length are changed is the inverse variable length coding circuit (= variable length decoding circuit) 14
To the inverse quantization circuit 16 and subjected to variable length decoding, and then inversely quantized. That is, each coefficient data C′ij after the variable length decoding is multiplied by the quantization step width Qin, and the coefficient C′ij is further multiplied by the unique constant Kij. The quantization step width Qin is given by the quantization step width data d separated by the data separation circuit 12 and sent. The constant Kij unique to each coefficient is given by the quantization matrix table 18.

Each dequantized coefficient data C "ij is then sent to the quantization circuit 20 to be quantized. That is, each dequantized coefficient data C" ij is quantized in a quantization step width. Qout
, And each further divided by a constant Kij unique to the coefficient C ″ ij. The quantization step width Qout is input from the rate control circuit 32. Further, the constant Kij unique to each coefficient is a quantum. Given by the quantization matrix table 22. Here, the quantization matrix table 22 has the same contents as the quantization matrix table 18 of the inverse quantization circuit 16.

Further, the rate control circuit 32 monitors the state of the buffer 28, and the bit rate of the bit stream output from the buffer 28 is designated as the bit rate 2
Determine the quantization step width Qout so that it becomes Mbps,
It is sent to the quantization circuit 20. For example, the occupancy rate or the occupancy change rate of the buffer 28 is monitored, and the quantization step width Qout is determined so that the value becomes a desired value. The quantization step width Qout may be controlled to be small when the average bit rate of the data input to the buffer 28 is lower than the specified bit rate of 2 Mbps, and may be controlled to be large when the bit rate is higher than 2 Mbps.

In order to determine the quantization step width Qout, the picture type is I picture, P picture, or
Information about which of the B pictures is required. This is because the target code amount is different for each picture type, and thus the quantization step width is also changed. This information is given by the picture type data a1 separated by the data separation circuit 12 and sent. Further, in the inverse quantum processing and the quantization processing, it is necessary to have information on whether the macro block to be processed is an intra macro block or an inter macro block. This is because the value of the quantization table is changed between the intra block and the inter block. This information is given by the processing type data b separated by the data separation circuit 12 and sent. The thus quantized coefficient data C ″ ′ ij is sent to the variable-length coding circuit 24 and variable-length coded to be coefficient data e ′, which is input to the combining circuit 26.

In the combining circuit 26, the processing type data b and the motion vector data c sent from the data separation circuit 12 and the header data a except the transfer bit rate data a2 also sent from the data separation circuit 12 are Transformed coefficient data e ′ sent from the variable length coding circuit 24
And the quantization step width data d'corresponding to the new quantization step width Qout sent from the rate control circuit 32.
And the transfer bit rate data a2 ′ corresponding to the new bit rate sent from the rate control circuit 32 are combined, and the combined 2 Mbps bit stream is output from the output terminal 30 via the buffer 28. To be done. In this way, the bit rate changing process is performed in the circuit of FIG. 3, and as a result, the bit stream (A) is converted to the bit stream (B) as shown in FIG.

Second Embodiment Next, a second embodiment will be described with reference to FIG. Figure 5
Paying attention to the fact that the contents of the quantization matrix table 18 and the quantization matrix table 22 in FIG.
This is an example in which the processing performed by the quantization circuit 20 and the quantization circuit 20 is simplified. Hereinafter, blocks common to those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

The output C "i of each coefficient of the inverse quantization circuit 16 of FIG.
j is given by C ″ ij = C′ij × Qin × Kij, where Kij is a constant specific to each coefficient given by the quantization matrix table 18, as described above.

The output C "'ij of each coefficient of the quantization circuit 20 in FIG. 3 is C"' ij = C "ij / Qout / Kij = C'ij * Qin * Kij / Qout / Kij = C '. ij × Qin ÷ Qout, which is used to provide a division circuit 34 for dividing Qin ÷ Qout in FIG.
Instead of 16 and the quantization circuit 20, a requantization circuit 36 for multiplying C′ij × Qin · out is provided. Here, Qin · out = Qin ÷ Qout. As described above, in the example of FIG. 5, the circuit equivalent to that of the circuit of FIG. 3 is realized by the circuit simpler than that of FIG.

* Modification of Second Embodiment Next, an example in which the function of changing the bit rate of the circuit of FIG. 5 is realized by software using a CPU will be described with reference to FIG. Each data cut out from the input bit stream is first determined whether or not it is the quantization step width data d, and if YES, it is changed to the quantization step width data d ′ and output. That is, the quantization step width Qin is changed to the quantization step width Qout.
The quantization step width Qout can be calculated as Qout = C1 + (MN) / C2 based on the target data amount N and the data amount count value M, for example. Here, C1 and C2 are constants.

On the other hand, if the result of the above determination is that it is not the quantization step width data d, it is further determined whether or not it is coefficient data e. If YES, it is changed to coefficient data e'and output. . That is, the coefficient C'ij is changed to the coefficient C "'ij. The coefficient C"' ij can be calculated as C "'ij = C'ij * Qin ÷ Qout, as described above. As a result of the above judgment,
Not the quantization step width data d, and the coefficient data e
If not, it is output as is.

Third Embodiment The circuit of FIG. 5 can also be modified as shown in FIG. That is, the division processing performed in the division circuit 34 in FIG. 5 may be performed in the requantization circuit 360. That is, the requantization circuit 360 may perform the multiplication and division of C "'ij = C'ij * Qin ÷ Qout. Further, in FIG. Each of the rates is a variable bit rate, but it may be a fixed bit rate, and the same blocks as those in FIG.

Fourth Embodiment Next, a fourth embodiment will be described with reference to FIG. In FIG. 8, the rate control circuit 32 shown in FIG.
In addition to setting 0, a high-frequency information amount check circuit 31 is added, and in addition to the monitoring result of the buffer 28 and picture type data a1 in FIG. The data from is added and adopted.

The high-frequency information amount check circuit 31 monitors the value of the coefficient of the high-frequency term in the coefficient C "ij output from the inverse quantization circuit 16 and the value exceeds the upper limit set value. In case of falling below the lower limit set value, the rate control circuit
Send to 320. When the data value of the high frequency coefficient exceeds the upper limit set value, the rate control circuit 320 determines the quantization step width Q
The out degree is further controlled to increase the compression degree, and when it is below the lower limit setting value, the quantization step width Qout is further reduced to reduce the compression degree.

Here, "larger" or "smaller" means "larger than the value of the third embodiment determined only by the monitoring result of the buffer 28 and the picture type data a1".
Alternatively, it is "smaller than the value of the third embodiment determined only by the monitoring result of the buffer 28 and the picture type data a1". By controlling in this way, the compression rate is not increased so much in the situation where the deterioration of the image quality is easily noticeable, and the compression rate is increased in the situation where the deterioration of the image quality is not noticeable so that the desired information amount can be obtained as a whole. The effect of reducing the value is achieved. That is, even if the amount of information is reduced, the effect of minimizing the deterioration of image quality is achieved.

The high-frequency information amount check circuit 31 does not compare the set values of the upper limit and the lower limit, but detects only the coefficient value of the high-frequency term, and sends the detection result to the rate control circuit 320. The rate control circuit 320 may be configured to compare with the upper and lower set values.

* Fifth Embodiment Next, a fifth embodiment will be described with reference to FIG. In FIG. 9, the monitoring result of the buffer 28 and the picture type data a in FIG. 7 are input to the rate control circuit 32 of FIG.
In addition to 1, the transfer bit rate data a2 from the data separation circuit 12 is additionally adopted. In addition, in FIG.
The bit rate of the input bit stream is a fixed bit rate for at least a certain period, and data indicating the bit rate for that period is included in the bit stream as transfer bit rate data a2. The transfer bit rate data a2 is data serving as an index of the compression degree of the scene managed by the transfer bit rate data a2. By thus incorporating the transfer bit rate data a2, it is possible to obtain the optimum quantization step width Qout according to the nature of each scene.

Sixth Embodiment Next, a sixth embodiment will be described with reference to FIG. Figure 10
In FIG. 9, the transfer bit rate detection circuit 11 is provided in the preceding stage of the data separation circuit 12, and the transfer bit rate data a2 detected by the transfer bit rate detection circuit 11 is input to the rate control circuit 32. That is, in the circuit of FIG. 10, a bit stream of variable bit rate having no transfer bit rate data a2 in the bit stream is input. For this reason, the transfer bit rate detection circuit 11 detects the transfer bit rate and sends the result to the rate control circuit 32, so that the optimum quantization step according to the nature of each scene can be obtained as in the case of FIG. The width Qout can be obtained. In FIGS. 9 and 10, the bit rate of the output bit stream being 1 to 3 Mbps means that a bit stream having a variable bit rate within this range is output.

In the above, if Qin is larger than Qout, there is no effect in this device. Therefore, the following may be performed. That is, Qin and Qout are compared, and if Qin <Qout, the same process as described above is performed. If Qin ≧ Qout, the value of Qout is rewritten to Qin, and then the same process as described above may be performed. . In this case, data conversion in that section is not performed.

[0051]

According to the present invention, the variable code whose data length changes according to the bit rate is cut out from the bit stream, the bit rate changing process is performed on the variable code, and the variable code before the changing process in the bit stream. (= Variable code before change processing corresponding to the variable code after change processing). Therefore, the configuration of the bit rate changing circuit is simplified, and the processing delay is reduced.

Also, in the case of an image with a large amount of high frequency component information, deterioration of the image quality is not noticeable even if the quantization step width is increased and the degree of compression is increased. A bitstream with a low bit rate but little deterioration in image quality is used because the compression ratio can be changed according to the amount of information in the high frequency range by utilizing the property that the image quality deteriorates significantly when the step width is increased and the compression ratio is increased. Can be obtained.

[Brief description of drawings]

FIG. 1 is a bit rate 4 generated from the same moving image.
Explanatory drawing which shows the bit stream of each compression code of Mbps and 2 Mbps.

2 is an explanatory diagram showing the difference between the data content and the data length for each data type of the two bit streams in FIG. 1. FIG.

FIG. 3 is a block diagram showing a circuit configuration of the device of the first embodiment.

FIG. 4 is an explanatory diagram of a bit stream whose bit rate is changed by the circuit of FIG.

FIG. 5 is a block diagram showing a circuit configuration of a device according to a second embodiment.

FIG. 6 is a flowchart when the second embodiment is implemented by software.

FIG. 7 is a block diagram showing a circuit configuration of an apparatus according to a third embodiment.

FIG. 8 is a block diagram showing a circuit configuration of a device of a fourth embodiment.

FIG. 9 is a block diagram showing a circuit configuration of a device of a fifth embodiment.

FIG. 10 is a block diagram showing a circuit configuration of a device of a sixth embodiment.

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Claims (21)

[Claims] 1. A circuit for changing the bit rate of a bit stream including main data (e, d) whose data length changes according to the bit rate, wherein the main data (e, d) is cut out from the bit stream. Means (12), means for converting the cut out main data (e, d) according to the target bit rate and outputting converted main data (e ', d'), and the main data before conversion An information amount conversion circuit having means (26) for returning the converted main data (e ', d') to a bit stream instead of (e, d). 2. Means (12) for cutting out variable length coded data (e) of quantized orthogonal transform coefficients from a bit stream (A) of compressed moving image data compliant with the MPEG standard.
A means (14, 16) for performing variable length decoding and dequantization on the cut out variable length encoded data (e), and quantizing the dequantized data with a new quantization step width, Further, means (20, 24) for performing variable-length coding and outputting new variable-length coded data (e ') and new variable-length coded data (e') from the bit stream (A). The variable length coded data (e) cut out
And an information amount conversion circuit having means (26) for outputting a new bit stream (B). 3. A bitstream data signal compression-coded by subjecting moving image data to prediction processing with motion compensation, orthogonal transformation processing, quantization processing, and variable-length coding processing.
In the rate conversion circuit for changing the transfer rate of (A), at least from the bit stream data signal (A), variable length coded data of quantized orthogonal transform coefficients
means (12) for cutting out (e), means (14) for variable-length decoding the cut-out variable-length coded data (e), and means for performing inverse quantization on the variable-length decoded data (16), means (20) for quantizing the dequantized data with a new value, and variable length coding for the quantized data to obtain a new data (e '). Means (24) for outputting the data (e) cut out by the cutting means (12) and replaced by the new data (e '), and means for generating a new bitstream (B) ( 26), and a bit rate conversion circuit having. 4. An information amount conversion circuit for an image compression coded signal in which at least moving image data is subjected to an adaptive quantization process for compression coding, and the adaptive quantization process is performed from the image compression coded signal. Separation means (12) for cutting out the extracted data (e), and data obtained by quantizing the adaptively quantized data with a quantization step width (Qout) different from the original quantization step width (Qin). Adaptive quantization conversion means (16,2
0) (360) and the data (e ') from this adaptive quantization conversion means (16, 20) (360)
An information amount conversion circuit for a moving image compression coded signal, comprising: a replacing means (26) for replacing the data (e) cut out by the separating means (12). 5. A moving image compression code signal having a first transfer rate, which is created by subjecting moving image data to at least orthogonal transform processing and adaptive quantization processing, to a moving image compression code signal having a second transfer rate. In a moving image compression code signal information amount conversion circuit for conversion, at least coefficient data (e) and a quantization width step data value (Qin) are selected from the moving image compression code signal of the first transfer rate. Extracting means (12) for extracting the data, a quantization width setting means (32) for setting a quantization step width value (Qout) adapted to the second transfer rate, the coefficient data (e) and the two quantum data. Width data value (Q
in, Qout) and adaptive quantization conversion means (16, 20) (34, 36) for outputting new coefficient data (e ') adapted to the second transfer rate, Information conversion circuit for compressed code signals. 6. An information amount conversion circuit for converting a bit stream obtained by compressing a moving image signal and performing entropy coding to change a first bit rate to a second bit rate, the bit stream comprising: A separation circuit (12) that separates a code whose data length changes according to the bit rate and a code whose data length does not change regardless of the bit rate, and a data length that depends on the bit rate separated by the separation circuit (12). A decoder (14) for entropy decoding the changing code, and a conversion means (16, 20) for converting the data decoded by the decoder (14) according to the value designated as the second bit rate. An encoder (24) for entropy coding the data converted by the conversion means (16, 20) and a code entropy coded by the encoder (24) And a means (26) for replacing a corresponding code in the following bit stream with a code entropy-encoded by the encoder (24). 7. A circuit for converting a bit stream obtained by subjecting a moving image signal to DCT, quantization, and variable length coding to change the bit stream from a first bit rate to a second bit rate. Are separated by a code (e, d) whose data length changes when the bit rate changes, a separation circuit (12) which separates the data length which does not change even if the bit rate changes, and the separation circuit (12). A variable length decoder (14) for variable length decoding a code (e, d) whose data length changes according to the bit rate, and dequantizing the data decoded by the variable length decoder (14). Dequantizer (16) and a new quantization step width (Qout) is determined and output so that the bit rate of the bit stream output from the circuit becomes the value specified as the second bit rate. Bit rate control circuit (3 2), and quantizing the data inversely quantized by the inverse quantizer (16) using the new quantization step width (Qout) input from the bit rate control circuit (32). Bowl (2
0), and the variable length encoder that quantizes the data quantized by the quantizer (20), and outputs it as a code (e ', d') (24)
And a means (26) for replacing the code (e, d) with the code (e ', d') and outputting a bitstream, and an information amount conversion circuit for a compressed moving image code. 8. A circuit for converting a bit stream obtained by subjecting a moving image signal to DCT, quantization, and variable length coding to change from a first bit rate to a second bit rate, wherein the bit stream From the cutout circuit (12) that cuts out the code (e) whose data length changes when the bit rate changes, and a variable length decoder that performs a variable length decoding of the code (e) cut out by the cutout circuit (12) ( 14), an inverse quantizer (16) which inversely quantizes the data decoded by the variable length decoder (14), and a new quantization of the inversely quantized data by the inverse quantizer (16) Quantizer for quantizing using step width (Qout)
(20), a bit rate control circuit (32) that determines the new quantization step width (Qout) so that the output bit stream has the second bit rate, and the quantizer (20) Variable-length encoder (24) that variable-length-encodes the data quantized by and outputs as code (e ', d')
And a means (26) for replacing the code (e, d) with the code (e ', d') and outputting a bitstream, and an information amount conversion circuit for a compressed moving image code. 9. The information amount conversion circuit according to claim 3, 6, or 7, wherein the bit stream is a code string complying with the MPEG standard. 10. The compressed moving image according to claim 7, wherein the bit rate control circuit determines the quantization step width with reference to a transfer bit rate of an input bit stream. Code information conversion circuit. 11. The moving image data includes at least DC.
A bit stream containing a code (e, d) that is obtained by performing T, quantization, and variable length coding, and whose data length changes when the bit rate changes, and converts the first bit rate to the second bit rate. A separation circuit (12) for separating the bit stream into the code (e, d) and a residual code whose data length does not change even if the bit rate changes, and the separation circuit (12 Variable length decoder (14) for variable length decoding the code (e, d) separated by), and the quantization step width (Qin) of the bit stream having the first bit rate to the second bit. A requantizer (360) for multiplying the variable-length decoded data output from the variable-length decoder (14) by a ratio divided by the quantization step width (Qout) of the bitstream having a rate; The second bit rate is set so as to reach the target value. Bit rate control circuit for determining quantization step width (Qout)
(32) and a variable length coder (2) for variable length coding the data output from the requantizer (360) and outputting it as a code (e ', d').
4), a means (26) for multiplexing and outputting the code (e ', d') and the residual code, and an information amount conversion circuit for a compressed video code. 12. The moving image data includes at least DC.
A bit stream containing a code (e, d) that is obtained by performing T, quantization, and variable length coding, and whose data length changes when the bit rate changes, and converts the first bit rate to the second bit rate. A cut-out circuit (12) for cutting out the code (e, d) from the bit stream, and variable-length decoding the code (e, d) cut out by the cut-out circuit (12). A variable length decoder (14), and a quantization step width (Qin) of the bit stream having the first bit rate is divided by a quantization step width (Qout) of the bit stream having the second bit rate. A requantizer (360) for multiplying the variable-length decoded data output from the variable-length decoder (14) by a ratio, and the quantizer so that the second bit rate becomes a target value. Bit rate control circuit that determines the step width (Qout)
(32) and a variable length coder (2) for variable length coding the data output from the requantizer (360) and outputting it as a code (e ', d').
4), and means (26) for replacing the code (e, d) with the code (e ', d')
And an information amount conversion circuit for a compressed moving image code including: 13. The quantizer according to claim 11 or 12, wherein the requantizer determines a quantization step width (Qin) of a bitstream having the first bit rate to the second bit rate. The division circuit (34) for dividing by the quantization step width (Qout) of the bit stream that it has, and the output of the division circuit (34) is the data after the variable length decoding output from the variable length decoder (14). Multiply circuit to multiply
An information amount conversion circuit composed of (36) and. 14. The bit rate control circuit (32) according to claim 7, claim 8, claim 11, claim 12, or claim 13, wherein the inverse quantizer (16)
An information amount conversion circuit for a compressed moving image code, which adjusts the determined value of the new quantization step width (Qout) according to the value of the high frequency coefficient of the coefficient matrix data (C ″ ij) output from 15. The bit rate control circuit (32) according to claim 14, wherein the inverse quantizer (16)
When the value of the high frequency coefficient of the coefficient matrix data (C "ij) output from the above exceeds a predetermined set value, the determined value of the new quantization step width (Qout) is adjusted to a smaller value. Image code information amount conversion circuit. 16. The compressed moving image according to claim 10, wherein the bit rate control circuit (32) detects the transfer bit rate based on transfer bit rate data (a2) in an input bit stream. Image code information amount conversion circuit. 17. The compressed moving image according to claim 10, further comprising a bit rate detection circuit (11) for detecting a transfer bit rate of an input bit stream and outputting it to the bit rate control circuit (32). Image code information amount conversion circuit. 18. A device for converting a bit stream obtained by compressing moving image data to change the bit rate from a first bit rate to a second bit rate, the information according to claim 1. A quantity conversion circuit, and an information quantity conversion apparatus for a compressed moving picture code, comprising: an input unit for designating the second bit rate. 19. The information amount conversion apparatus according to claim 18, wherein the input unit specifies a range and a representative value of the second bit rate. 20. A method for converting a bitstream containing a code (e), the data length of which changes when the bitrate changes, from a first bitrate to a second bitrate, wherein The code (e) is cut out, the code (e) is converted according to the second bit rate to obtain a code (e ′), and the code (e ′) is replaced with the code (e) in the bit stream. How to convert the bitstream back to. 21. At least DC for moving image data
A method of converting a bit stream obtained by performing T, quantization, and variable length coding to change from a first bit rate to a second bit rate, wherein the bit stream has a data length according to the bit rate. The first DCT coefficient code (e) to be changed is separated into the residual code, the first DCT coefficient code (e) is variable-length decoded, the variable-length decoded data is dequantized, and the dequantized data is dequantized. Data is quantized using a quantization step width (Qout) set so that the second bit rate becomes a target value, and the quantized data is variable-length coded to generate a second DCT coefficient code ( e ′), the second DCT coefficient code (e ′) and the residual code are multiplexed and output.