JP3087864B2 - HDTV signal subband encoding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoding system used for digital transmission of an HDTV (high definition image) signal while maintaining compatibility and compatibility with a conventional TV (television) signal. The present invention relates to a sub-band encoding method for an HDTV signal that realizes high-efficiency transmission by reducing the encoding bit rate.

[0002]

2. Description of the Related Art Hitherto, various HDTV signal encoding methods have been announced. For example, a DPCM (differential pulse code modulation) method for quantizing a difference signal between an input signal and a previous line, and an input signal in a frequency domain. A DCT (discrete cosine transform) method of converting a signal into a signal and encoding the signal is well known.
In particular, since the DCT method can obtain relatively high quality characteristics at a low bit rate, various types using the DCT method have been studied.

However, the DCT method requires a large amount of computation,
Also, it has been difficult to obtain compatibility with conventional TV signals. Therefore, conventionally, an input signal is divided into a plurality of band signals including a TV signal component in a low band by a band dividing filter, and only a low band signal having the highest power and having a component important in visual characteristics is encoded by a DCT method. In addition, a sub-band coding scheme has been proposed in which high-frequency signals are coded by a simple PCM method to improve consistency with a TV signal, and to improve quality and reduce the amount of calculation (for example,
DLGall, et al., "Transmission of HDTV signals u
sing SubbandDecomposition and Discrete Transform
Coding ", International Work-shop onSignal Processin
g of HDTV 1988, or Irie, et al., "Variable Rate Characteristics of Adaptive Subband DCT Coding for HDTV", SSE88-176, February 1989).

[0004] The following is a description of the sub-band coding scheme shown in FIG.
This will be described with reference to FIGS. FIG. 3 is a block diagram illustrating a configuration example of an encoder and a decoder according to a subband encoding scheme.

In FIG. 1, an HDTV signal 31 is input to a band division filter 32, where band division and downsampling are performed. Band division filter 32
Is composed of a low-pass filter LP and a high-pass filter HP. Here, the HDTV signal 31 is first divided into two bands in the horizontal (line) direction and further divided into two bands in the vertical direction. The HH signal is high in both the horizontal and vertical directions, and the horizontal is high and the vertical is high. Are converted into low band HL signals, horizontal is low band and vertical is high band LH signals, and horizontal and vertical are low band LL signals. The downsampling is performed simultaneously with the filtering. Further, as this filter configuration, QMF (Quadrature Mirror Fi
lter) or a non-recursive digital filter with several taps is used.

[0006] The LL signal is encoded through an adaptive DCT encoder 33 and a variable length encoding circuit (VLC) 34,
The other LH to HH signals are converted into quantized codes by a quantizer (Q) 35 by a simple PCM method, and then converted to variable length codes via a variable length coding circuit (VLC) 36. The variable length coding circuits 34 and 36
Is configured to assign a variable length code corresponding to each quantization code, and usually takes into account the amplitude distribution of the image signal, a short code is used for small quantization levels that occur frequently, and a small code is used for large ones. Corresponds to long codes.
Each variable length code output from the variable length coding circuits 34 and 36 is time-multiplexed by a multiplexing circuit (MUX) 37 and transmitted to a transmission line 38.

[0007] The adaptive DCT encoder 33 converts an adaptive prediction difference signal to be described later into a DCT coefficient in the frequency domain.
Transformer (DCT) 41, quantizer (Q) 4 that converts the DCT coefficient into a quantized code and provides it to variable length coding circuit 34
2, an inverse quantizer (Q ^-1 ) 43 for restoring DCT coefficients from a quantized code, an inverse DCT transformer (DCT ^-1 ) 44 for restoring an original signal value from DCT coefficients, or a prediction mode in adaptive prediction. , And a mode control circuit 45 for determining a motion vector, an adaptive predictor 46, a subtractor 47, and an adder 48.

In such an adaptive DCT encoder 33, L
The adaptive predictor 46 performs prediction by mode switching on the L signal based on information obtained by the mode control circuit 45, and the predicted signal is subtracted from the LL signal by the subtractor 47 to obtain an adaptive prediction difference signal. Next, the adaptive prediction difference signal is DCT-transformed by the DCT converter 41, and the obtained DCT
The coefficients are quantized by the quantizer 42 and output. In addition,
This quantized code is converted into a variable length code by the variable length coding circuit 34, and is time-multiplexed with the variable length codes of other band signals and transmitted.

[0009] The LL signal has been passed through a low-pass filter in the horizontal and vertical directions, and the image is similar to the original screen, and includes a correlation in the time direction. That is, like the original video signal, the same scene has the property that the pixel value is similar to the video signal one field before or one frame before, and the adaptive prediction method uses this.

Here, the configuration of the adaptive predictor 46 will be described with reference to FIG. 4 and the operating principle of the adaptive prediction system using inter-field / motion-compensated inter-frame prediction will be described with reference to FIG.

In FIG. 4, an adaptive predictor 46 has a frame memory 51 for storing an image signal of one frame before, and a field memory 5 for storing an image signal of one field before.
2, a motion compensation circuit 53 that shifts (moves) the image signal of one frame before by several pixels in the horizontal and vertical directions and outputs the result. A prediction mode output from the mode control circuit 45 indicates zero in an intra-field mode, The switching circuit 54 selects and outputs a signal from the field memory 52 in the mode and a signal from the motion compensation circuit 53 in the inter-frame mode.

In FIG. 5, “５, ●, ☆, ★” indicates a pixel (image sample). Note that here, frame n
A case will be described in which the pixel 71 marked with a star is encoded on the (n + 1) th line in the field 1 of FIG.

In the intra-field mode, pixel values are directly encoded. In the inter-field mode, the pixel at the same position one field before, that is, the TV signal is a pixel that is an interpolation (average value) of two pixels on the n and n + 1 lines in field 2 because the lines alternate in continuous fields. ) 72 is encoded. In the inter-frame mode, a difference signal from a pixel (☆) 73 shifted to a position where a motion component is compensated for a pixel one frame before, that is, a position of a motion vector is encoded. Here, the signals one field before and one frame before are recorded in the frame memory 51 and the field memory 52 in the adaptive predictor 46 in FIG. The processing of shifting the position of the pixel according to the motion vector is performed by the motion compensation circuit 53.
In practice, this is realized only by changing the access position (address) from the frame memory 51. A signal according to the prediction mode is selected from the switching circuit 54 as the prediction signal.

Next, a method of determining the prediction (difference) mode in the mode control circuit 45 will be described. The mode is usually a block unit (for example, 8 pixels × 8 lines)
Can be changed to First, the power (sum of squares of pixel values) in a block to be encoded is calculated, and this is set as P1. Next, the power of the inter-field difference signal is obtained, and this is set as P2. Furthermore, for the motion vectors V1 to Vn within the preset motion compensation range, the power P of the inter-frame difference signal at the position shifted by each vector amount is calculated.
V1 to PVn are obtained. Here, P1, P2 and PV
The minimum value is selected from 1 to PVn, and the mode at that time is used. At this time, the mode information and the motion vector information are transmitted to the decoder as side information together with the quantization code.

In the above, three types of prediction modes have been described, that is, within a field, between fields, or between motion compensation frames. However, only two of these modes (for example, within a field or between fields) or motion compensation are used. Can be easily changed as necessary, such as using an inter-frame difference signal at the same position without using, or adding a mode for further increasing the frame memory and performing bidirectional prediction from the previous and next frames.

The DCT output from the quantizer 42
The coefficient quantization code is calculated by the inverse quantizer 43 and the inverse DCT.
After being restored to the original signal value (adaptive prediction difference signal) via the converter 44, the signal value is added to the prediction signal according to the mode and recorded in the frame memory 51 and the field memory 52 in the adaptive predictor 46. As described above, by removing the correlation between fields or between frames, the coding efficiency of the LL signal can be improved.

By the way, since the above-mentioned method uses a variable length code, the amount of encoded information (bit rate) varies depending on the characteristics of an input image. Therefore, when transmitting at a fixed rate, the amount of output information from the variable length coding circuits 34 and 36 is stored in a buffer provided at the output point of the variable length coding circuit or the output point of the multiplexing circuit (not shown in FIG. 3).
In general, a method is used in which the bit rate is kept constant by increasing the quantization step size in the quantizers 35 and 42 when the bit rate is larger than a predetermined rate, and decreasing the step size when the bit rate is smaller. It is commonly used.

Having described the configuration and operation of the encoder, the configuration and operation of the decoder will now be described with reference to FIG. 3 again. In the decoder, the demultiplexing circuit (DM
UX) 61 to separate the transmission code into each band signal.
Each variable length code of H signal, HL signal and LH signal is
Variable length decoding circuit (VLD) 62, inverse quantizer (Q ^-1 )
The signal is converted from a variable length code to a quantized code via 63 and further into a signal value of each band. The variable length code of the LL signal is restored to a quantized code and a DCT coefficient via a variable length decoding circuit (VLD) 64 and an inverse quantizer (Q ^-1 ) 65. Then, for the DCT coefficient, the inverse D
The DCT inverse transform is performed by the CT transformer (DCT ^-1 ) 66, and the adaptive predictor 67 selectively outputs the signal according to the mode information and the motion vector information transmitted as side information, and the output signal of the inverse DCT transformer 66. Are added by an adder 68 to obtain a decoded signal. The signal of each band is input to the band synthesis filter 69, and in the reverse order of the encoder,
The HDTV signal is restored by first performing synthesis and upsampling (interpolation) in the vertical direction and then performing synthesis and upsampling (interpolation) in the horizontal direction.

[0019]

Since the band of the LL signal is close to (slightly larger than) the band of the conventional TV signal, it is easy to reproduce the TV signal from the LL signal in the conventional system. As the simplest method, if pixels corresponding to the number of TV signal pixels are extracted from the decoded LL signal, the TV image can be reproduced although the screen edge is partially deleted.

However, in the conventional coding method, the allocation of coding information to each sub-band signal is usually variable in accordance with the input signal. More information is allocated than the sub-band signal. Therefore, L
If the L signal information is limited to the encoding rate used for encoding a conventional TV signal, deterioration of HDTV playback video quality is inevitable. Also, it has been difficult to realize an encoding configuration that extracts TV signal information from a part of the transmission encoding information at the same rate as a conventional TV signal. That is,
Complete compatibility between the HDTV signal and the TV signal could not be ensured.

The present invention reduces the encoding bit rate while maintaining high quality characteristics, and further reduces the HDTV signal and TV
HDTV that can achieve full compatibility with signals
It is an object of the present invention to provide a signal subband coding scheme.

[0022]

According to the first aspect of the present invention, an HDTV signal is divided horizontally into low band and high band signals, and both horizontal band signals are vertically divided into low band and high band signals, respectively. Band signals are generated by dividing the band signals into four band signals, of which signals in both the horizontal and vertical directions are low by adaptive predictive orthogonal transform, and the encoded horizontal and vertical directions are both low. In the sub-band encoding method for HDTV signal, which decodes the signal of the band by the adaptive prediction orthogonal inverse transform and combines the band signal with another band signal to reproduce the HDTV signal, the adaptive prediction difference signal in the adaptive prediction orthogonal transform is converted into a TV signal. The information encoded at the encoding rate for use and the difference signal component obtained by subtracting the TV signal component from the adaptive prediction difference signal into encoded information, and performing variable length encoding, The TV signal is restored from the information encoded at the encoding rate for the TV signal, and the horizontal and vertical directions are used by using the information obtained by encoding the difference signal component, the TV signal component, and the prediction signal of the adaptive prediction orthogonal transform. Are characterized by decoding low-frequency signals.

According to a second aspect of the present invention, in the HDTV signal sub-band encoding method according to the first aspect, an orthogonal transform coefficient is used as a difference signal component.

[0024]

According to the first aspect of the present invention, when encoding a signal having a low band in both the horizontal and vertical directions by adaptive prediction orthogonal transform, an adaptive prediction difference signal (prediction residual signal) is converted to a TV signal.
Encoding is performed at the encoding rate for the signal, and further encoding is performed on the difference signal obtained by subtracting the TV signal component from the adaptive prediction difference signal, and the decoder separately restores the TV signal and the signals in both the horizontal and vertical directions. By doing
The compatibility between the HDTV signal and the TV signal can be realized.

According to the second aspect of the present invention, high coding efficiency can be obtained by using orthogonal transform coefficients as difference signal components.

[0026]

1 is a block diagram showing an embodiment of an encoder and a decoder based on the sub-band encoding method for HDTV signals according to the first aspect of the present invention.

It should be noted that components constituting the conventional encoder and decoder shown in FIG. 3 which can be used as they are are denoted by the same reference numerals. In the figure, the feature of the encoder of this embodiment is that the adaptive LL which encodes the LL signal divided by the band division filter 32 by adaptive prediction DCT is used.
CT encoder 10 encodes an adaptive prediction difference signal (prediction residual signal) in adaptive prediction DCT at a coding rate for a TV signal, and further encodes a difference signal obtained by subtracting a TV signal component from the adaptive prediction difference signal. In a separate encoding configuration.

That is, the quantizer (Q) 11 uses the DCT
The DCT coefficient of the adaptive prediction difference signal output from the converter 41 is coded with an information amount corresponding to a conventional TV signal coding rate, and is supplied to a variable length coding circuit (VLC) 12 to provide a variable length code of the TV signal. Convert to The inverse quantizer 13 and the inverse DCT transformer 44 restore the DCT coefficient from the quantized code quantized by the quantizer 11, and further restore and subtract the TV signal component from the original adaptive prediction difference signal. To the vessel 14. The subtractor 14 subtracts the TV signal component from the adaptive prediction difference signal, and converts the difference signal into a quantizer (Q _E ) 15 and a variable length coding circuit (VLC) 16.
Through the encoding.

The other functions and operations of the adaptive DCT encoder 10 are the same as those of the conventional adaptive DCT encoder 33. Here, the amount of information generated from the variable length coding circuit 12 is monitored by a buffer (omitted in FIG. 1) provided at the output point of the variable length coding circuit or the output point of the multiplexing circuit, as in the conventional example. When the encoding rate of the TV signal increases, the quantization step size in the quantizer 11 is increased, and when the encoding rate is small, the step size is decreased, thereby maintaining the information amount at the encoding rate of the TV signal. I do.

In parallel with this, a difference signal from the output signal of the inverse DCT converter 44 (TV signal component of the adaptive prediction difference signal) is obtained from the adaptive prediction difference signal, and the difference signal is obtained by the quantizer 15 and the variable length. Encoding is performed via the encoding circuit 16.
These variable length codes are time-multiplexed by the multiplexing circuit 37 with the variable length codes of other band signals and transmitted. In addition,
At this time, the step size of the quantizer 15 can be arbitrarily controlled by monitoring the buffer.

In the decoder, a demultiplexing circuit (DMUX) 6
1, the transmission code is separated into each band signal, and the HH signal,
Each variable length code of the HL signal and the LH signal is converted from the variable length code to a quantized code via a variable length decoding circuit (VLD) 62 and an inverse quantizer (Q ^-1 ) 63, and further, the signal value of each band Is converted to

The information coded at the TV signal coding rate is restored from a variable length code to a quantized code by a variable length decoding circuit (VLD) 17 and further dequantized (Q ^-1 ) 18 Restores the DCT coefficient of the adaptive prediction difference signal. The DCT coefficient is calculated by the inverse DCT converter 66 as D
The signal which is inversely transformed by CT and selectively output according to the mode information and the motion vector information transmitted as side information by the adaptive predictor 67 and the output signal of the inverse DCT converter 66 are added by an adder 68 to thereby obtain a TV. Obtain a decoded signal at the signal rate.

On the other hand, for the difference signal component, the variable length decoding circuit (VLD) 19 restores the variable length code to a quantized code, and further, the inverse quantizer (Q _E ^-1 ) 20 restores the difference signal. . The restored difference signal and the inverse quantizer 18
And the predicted signal output from the adaptive predictor 67 is added by the adder 22 to restore the LL signal.

The signals in the respective bands are input to a band synthesis filter 69, and are first synthesized and up-sampled (interpolated) in the vertical direction in the reverse order of the encoder, and then synthesized and up-sampled (interpolated) in the horizontal direction. ) To restore the HDTV signal.

As described above, in the decoder according to the present invention, the HDTV signal can be reproduced by the above-described procedure, and the TV signal can be decoded by using the TV signal decoder 23 enclosed by a dashed line. Signal compatibility can be achieved. For the LL signal, the TV signal
Since information encoded at a signal rate and information obtained by encoding a difference signal from the original LL signal are added and transmitted, the decoder can restore high quality. Therefore,
High quality characteristics can also be realized for the synthesized HDTV signal.

FIG. 2 shows an HDTV according to the first aspect of the present invention.
It is a block diagram which shows the structure of Example of the encoder and decoder by a signal sub-band encoding system. Note that the components that constitute the encoder and decoder of the embodiment shown in FIG. 1 that can be used as they are are given the same reference numerals and will not be described.

In the figure, the feature of the encoder of this embodiment is that the adaptive DCT encoder 10 that encodes the LL signal divided by the band division filter 32 by the adaptive prediction DCT is adapted to the adaptive prediction in the adaptive prediction DCT. In a separate encoding configuration, the difference signal (prediction residual signal) is encoded at a coding rate for a TV signal, and the difference signal obtained by subtracting the TV signal component from the DCT coefficient of the adaptive prediction difference signal is encoded.

That is, the quantizer (Q) 11 uses the DCT
DCT section of adaptive prediction difference signal output from converter 41
Information about the number corresponding to the conventional TV signal coding rate.
The information is coded by the information and given to the variable length coding circuit (VLC) 12.
Then, it is converted into a variable length code of the TV signal. Also, inverse quantum
The quantizer 13 is a quantization code quantized by the quantizer 11.
And restores the DCT coefficient to the subtractor 24. Subtractor
In 24, the TV signal is calculated from the DCT coefficient of the adaptive prediction difference signal.
Component is subtracted, and the difference signal is quantized (Q _E) 25
And encoding through a variable length encoding circuit (VLC) 26
I do.

In the decoder, a demultiplexing circuit (DMUX) 6
1, the transmission code is separated into each band signal, and the information coded at the TV signal coding rate is similarly processed by the variable length decoding circuit 17, the inverse quantizer 18, the inverse DCT converter 66, the adaptive prediction The decoder 67 and the adder 68 obtain a decoded signal of the TV signal rate.

On the other hand, with respect to the difference signal component, the variable length decoding circuit (VLD) 27 restores the variable length code to a quantized code, and the inverse quantizer (Q _E ^-1 ) 28 restores the difference signal. . The restored difference signal and the inverse quantizer 18
Are added by an adder 21 to obtain an inverse DCT converter 2
The DCL inverse transform is performed at 9 and the predicted signal output from the adaptive predictor 67 is added by the adder 22 to restore the LL signal. The signal of each band is input to the band synthesis filter 69, and firstly performs vertical synthesis and upsampling (interpolation) in the reverse order of the encoder.
Next, synthesis and upsampling (interpolation) in the horizontal direction
To restore the HDTV signal.

As described above, in the decoder according to the present invention, the HDTV signal can be reproduced by the above-described procedure, and the TV signal can be decoded by using the TV signal decoder 23 surrounded by a dashed line. Signal compatibility can be achieved. For the LL signal, the TV signal
Since the information encoded at the signal rate and the information obtained by encoding the difference signal from the original LL signal are added and transmitted, the decoder side can restore high quality, and as a result, the synthesized HDTV High quality characteristics can also be realized for signals. In this embodiment, since the difference signal is encoded in the DCT coefficient area, the encoding efficiency is high, and the encoding rate of the entire LL signal and the encoding rate of the entire HDTV signal can be reduced.

[0042]

As described above, according to the present invention, the encoding bit rate can be reduced while maintaining the high quality characteristic which is a characteristic of the subband encoding method.
Full compatibility between HDTV signals and TV signals can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment configuration of an encoder and a decoder based on the sub-band encoding method for HDTV signals according to the first embodiment of the present invention.

FIG. 2 is a block diagram showing an embodiment configuration of an encoder and a decoder based on the sub-band encoding method for HDTV signals according to the present invention.

FIG. 3 is a block diagram illustrating a configuration example of an encoder and a decoder according to a subband encoding scheme.

FIG. 4 is a block diagram showing a configuration of an adaptive predictor 46.

FIG. 5 is a diagram illustrating an operation principle of an adaptive prediction method using inter-field / motion-compensated inter-frame prediction.

[Explanation of symbols]

Reference Signs List 10 adaptive DCT encoder 11 quantizer (Q) 12, 16 variable length coding circuit (VLC) 13, 18 inverse quantizer (Q ^-1 ) 14 subtractor 15 quantizer (Q _E ) 17, 19 variable Long decoding circuit (VLD) 20 Inverse quantizer (Q _E ^-1 ) 21,22 Adder 23 TV signal decoder 24 Subtractor 25 Quantizer (Q _E ) 26 Variable length coding circuit (VLC) 27 Variable Long decoding circuit (VLD) 28 Inverse quantizer (Q _E ^-1 ) 29 Inverse DCT converter (DCT ^-1 ) 31 HDTV signal 32 Band division filter 33 Adaptive DCT encoder 34, 36 Variable length encoding circuit (VLC ) 35 Quantizer (Q) 37 Multiplexer (MUX) 38 Transmission line 41 DCT converter (DCT) 42 Quantizer (Q) 43 Inverse quantizer (Q ^-1 ) 44 Inverse DCT converter (DCT ^{− 1)} 45 mode control times 46 adaptive predictor 47 subtractor 48 adder 51 frame memory 52 field memory 53 the motion compensation circuit 54 switching circuit 61 demultiplexer (DMUX) 62, 64 variable-length decoding circuit (VLD) 63, 65 inverse quantizer (Q ^-1 ) 66 Inverse DCT converter (DCT ^-1 ) 67 Adaptive predictor 68 Adder 69 Band synthesis filter

Continuation of the front page (56) References JP-A-62-203496 (JP, A) 1991 Image Coding Symposium (PC SJ91) 173-175 (7-3 Study of hierarchical video coding method using sub-band division) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N ^7/ 24-7/68 H04N 11/00 -11/22

Claims (2)

(57) [Claims] 1. An HDTV signal is divided horizontally into low band and high band signals, and both horizontal band signals are vertically divided into low band and high band signals, respectively. Generating and encoding the low-band signals in both the horizontal and vertical directions by adaptive prediction orthogonal transform, decoding the encoded low-band signals in both the horizontal and vertical directions by adaptive prediction orthogonal inverse transform, In an HDTV signal sub-band encoding method for reproducing the HDTV signal by combining with another band signal, an adaptive prediction difference signal in the adaptive prediction orthogonal transform is represented by TV
Separating the information coded at the signal coding rate and the difference signal component obtained by subtracting the TV signal component from the adaptive prediction difference signal into coded information and performing variable length coding; From the information encoded at the rate
Reconstructing a V signal, and decoding signals in both the horizontal and vertical directions using the information obtained by encoding the difference signal component, the TV signal component, and a prediction signal of adaptive prediction orthogonal transform. HDTV signal sub-band encoding method. 2. The HDTV signal sub-band encoding method according to claim 1, wherein an orthogonal transform coefficient is used as a difference signal component.