JP2860016B2 - Interframe coding of image signal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inter-frame encoding method for an image signal, and more particularly to an inter-frame encoding method for an image signal capable of realizing good information compression characteristics with a small amount of hardware. .

[0002]

2. Description of the Related Art There are known two typical methods for compressing information of an image signal: an intra-frame coding method and an inter-frame coding method.

[0003] The intra-frame encoding method can be realized with a small amount of hardware because a frame memory for reference is not required. However, compared to the inter-frame encoding method,
It is difficult to increase the information compression ratio.

[0004] The inter-frame coding method requires a reference frame memory, which increases the amount of hardware. However, since the code can be compressed by utilizing the correlation between frames, the information compression degree is generally high. In particular, in the case of an image with little "movement", it can be said that the coding method is effective.

[0005] As a typical inter-frame coding system, "motion compensation, inter-frame difference, orthogonal transform, variable length coding system" is known. In this method, while compensating for motion between two consecutive frames, an inter-frame difference is obtained, the difference value is subjected to discrete cosine transform, and the result is quantized, variable-length coded, and transmitted. Yes, CC
H.ITT Recommendation International Standard Coding System Recommendation Number 261.

FIG. 3 is a block diagram showing the configuration of the above-mentioned conventional information source encoder. In FIG. 3, CC is a controller, T is an orthogonal transformation circuit, T- ¹ is an inverse orthogonal transformation circuit, Q is a quantization circuit, Q- ¹ is an inverse quantization circuit, and F is a frame memory.

The information source coder according to the prior art shown in FIG. 3 performs inter-frame coding of a video input signal and sends it to a video signal multiplexing unit. The description is omitted.

[0008]

The prior art includes an encoding loop, which includes a reference frame memory F for reference, a difference circuit, an orthogonal transformation circuit T, and an inverse orthogonal transformation circuit T- ^1. , Quantization circuit Q,
It is composed of an inverse quantization circuit Q- ^{1 and the} like. In addition, the above-described prior art has a problem that it is difficult to realize a compact circuit because all of these circuit elements except for the differential circuit have a large amount of hardware.

In other words, in the above-mentioned prior art, since the inter-frame difference is executed in the image domain, the input image for removing the correlation between the frames and the encoded / decoded image restored by the local decoder are compared. It is necessary to perform a difference operation between them, and therefore, a conversion circuit, an inverse transformation circuit, a quantization circuit, an inverse quantization circuit, and the like must be provided in the encoding loop.

An object of the present invention is to solve the problems of the prior art and realize an inter-frame differential encoding system by using a small number of circuit elements and a small amount of hardware.
An object of the present invention is to provide an inter-frame coding method for an image signal having the same capability as that of the conventional technique.

[0011]

According to the present invention, the object is to realize an inter-frame differential encoding method, in which the above-mentioned components of the encoding loop in the prior art are indispensable. Are considered to be not necessarily essential elements, so that the difference encoding is performed in the coefficient domain obtained by converting the inter-frame difference and in the coefficient domain after the quantization is performed. This is achieved by storing the converted and quantized coefficient values, not the amplitude values of the image information, in the memory.

That is, the above object is achieved by the following configuration and operation of the present invention. The present invention performs inter-frame encoding of an image signal. First, intra-frame encoding is performed. This intra-frame encoding is performed by a circuit including orthogonal transform and quantization of transform coefficients.
As a result, a quantized coefficient domain is obtained. Even in the case of the quantized coefficient domain, since a correlation is naturally preserved between frames, a difference operation from the previous frame is performed in this domain. . According to the difference result, whether the unit of conversion (block) is significant, if it is significant, it is better to transmit the inter-frame difference, or
It is determined whether it is better to transmit the in-frame signal itself, and the result is variable-length coded and transmitted to the receiving side.

[0013]

The input image signal is divided into blocks, and the blocks are orthogonally transformed in accordance with (Equation 1).

[0014]

(Equation 1)

In _equation (1), _Yt is a matrix representing the input image signal divided into blocks at time t, D
Is a matrix for performing orthogonal transformation, and D ^T is its transposed matrix. _Xt is the converted time t
Is a coefficient matrix in. In the conversion itself according to (Equation 1), the information amounts of Y _t and X _t do not change at all,
By the processing according to (Equation 1), preparations (part 1) for the entropy encoding are made.

Next, quantization of the transform coefficients is performed according to (Equation 2).

[0017]

(Equation 2)

In equation (2), Q [•] indicates a quantization operation performed on each element of the matrix. Quantization is performed with different characteristics for each transform coefficient. By this quantization operation, QX _{t obtained} by quantizing X _t becomes X _t
, There is some reduction in entropy (which is a trade-off with image degradation), and preparations are made to improve the efficiency of the subsequent inter-frame difference and variable-length coding (part 2). Will be.

Next, a process for obtaining a difference from the reference frame is performed based on (Equation 3) in the transform quantization coefficient domain.

[0020]

(Equation 3)

In (Equation 3), QX _t _ ₁ is a reference signal that has been stored in the reference frame memory and has been subjected to encoding at a previous point in time, and is a transformed quantization coefficient matrix of a corresponding block position. .

Next, ΔQ obtained from X _t and (Equation 3)
Using _Xt , a comparative evaluation is performed using (Equation 4).

[0023]

(Equation 4)

[0024] This comparative evaluation was the block and invalid blocks when the ΔQX _t = 0, it is determined that block effective block in the case of ΔQX _t ≠ 0, further, QX _t
Comparison of the result, in which DerutaQX _t, determining whether to transmit by selecting any of the QX _t is the amount of information to less advantageous.

[0025] between the former ΔQX _t frame (INTE
R), will be referred to as latter QX _t frame as (INTRA). When the value of J in (Equation 4) is specified by a variable length code using a code tree, it can be expressed as (Equation 5).

[0026]

(Equation 5)

Based on the result of (Equation 5), J = “0”
For (disabled), and transmits only the J itself, in the case of J = "10", and transmits those to the sign and DerutaQX _t and variable length coding. When J = “11”, this code and X
Transmits variable-length encoded data of _t itself.

The present invention can achieve a large amount of information compression by the entropy coding described in the last step described above.

The procedure of image restoration on the receiving side is performed by executing the reverse process.

First, the received variable length code is decoded, and the value of J for each block is known.

In the case of J = "0", the contents of the reference frame memory on the receiving side are used again.

[0032] J = "10" if the (INTER block) received with DerutaQX _t obtained by variable length decoding,
The block signal is reproduced using (Equation 6).

[0033]

(Equation 6)

In this (Equation 6), ΔQX _t _ ₁ is a quantized transform coefficient signal reproduced at the previous encoding time,
It is stored in the receiving side reference frame memory.

[0035] J = "11" if the (INTRA block) received using the QX _t itself was obtained by variable-length decoding.

[0036] Then, these QX _t, according to simultaneously rewrite the reference frame memory (7), inverse quantizes the coefficients.

[0037]

(Equation 7)

In (Equation 7), Q ~ ¹ [·] is an inverse transformation of (Equation 2), and a representative value for each element is reproduced.

Further, the inverse transformation of (Equation 1) is executed using (Equation 8) to reproduce the image signal.

[0040]

(Equation 8)

As described above, in the inter-frame coding method according to the present invention, first, after performing intra-frame coding by the intra-frame coding method, entropy coding is performed in consideration of inter-frame coding. Therefore, in the encoding method of the present invention, the image quality is entirely determined by the orthogonal exchange in the intraframe code and the quantization thereof. The amount of coded data decreases in consideration of the characteristics of inter-frame coding.

[0042]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an interframe coding method for an image signal according to the present invention.

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention, and FIG. 2 is a diagram for explaining a peripheral situation to which the present invention is applied. 1 and 2, reference numeral 52 denotes an orthogonal transformation circuit;
53 is a quantization circuit, 54 is a subtraction circuit, 55 and 75 are reference frame memories, 56 is a block determination circuit,
7 is a variable length coding circuit, 60 is a transmission line, 72 is an inverse orthogonal transform circuit, 73 is an inverse quantization circuit, 74 is an addition circuit, 76 is a block control circuit, 77 is a variable length decoding circuit, and 20 analog-to-digital conversion. Device, 30 is a pre-processing circuit, 40 is an encoding frame memory, 50 is an encoding circuit, 70 is a decoding circuit, 80 is a decoding frame memory, 90 is a post-processing circuit,
100 is a digital-to-analog converter.

First, with reference to FIG. 2, a description will be given of the situation around the present invention, which performs compression encoding, transmission, and decoding of a video signal.

In FIG. 2, an input video signal applied to an input terminal 10 is digitized by an analog-to-digital converter 20 and then converted by a pre-processing circuit 30 into an image format in which conversion coding can be easily performed. Specifically, this conversion is to perform processing for separating a video signal into component components such as a luminance signal and a color difference signal, and each component is written to the encoding frame memory 40.

The contents of the frame memory 40 are image domain information, and this information is input to the encoding circuit 50 according to the present invention. The compressed encoded information encoded by the encoding circuit 50 is transmitted to the ground via the transmission path 60, and the image domain is restored in the decoded frame memory 80 by the decoding circuit 70 on the ground side. The restored image component is output to the output terminal 110 as an original video signal by the post-processing circuit 90 and the digital-to-analog converter 100.

The present invention relates to an inter-picture coding method including the coding circuit 50 and the decoding circuit 70 in such a surrounding situation, and the structure of one embodiment thereof is shown in FIG.
Is shown in

In the embodiment of the present invention shown in FIG. 1, an input terminal 51 of an image component component, an orthogonal transformation circuit 52, a quantization circuit 53,
It includes a difference circuit 54, a reference frame memory 55, a block determination circuit 56, and a variable length encoding circuit 57, and includes a variable length decoding circuit 7 as a component on the decoding (receiving) side.
7, a block control circuit 76, a reference frame memory 75, an adder circuit 74, an inverse quantization circuit 73, an inverse orthogonal transform circuit 72, and an image component component output terminal 71.

[0049] In FIG. 1, the input image signal Y _t applied to the input terminal 51, the pre-processing described above, are converted to the component ingredients already suitable for conversion, the frequency domain X from the image domain by orthogonal transform circuit 52 Converted to _t . This transform is a well-known discrete cosine transform. Normal conversion is performed block-wise, and the size of the block is 8 × 8 (two-dimensional).

The 64 transform coefficients X _t of this block are:
Are quantized by the quantization circuit 53, it is QX _t.
The image quality of the restored image is determined by the degree of quantization. Transformed and quantized coefficient QX of previous coded screen
Since _t _ ₁ is stored in the frame memory 55, retrieves the coefficients of the same block position, the difference DerutaQX _t is calculated for each coefficient corresponding the subtractor 54.

The block decision circuit 56 calculates ΔQX _t , QX _t
Is analyzed, and if ΔQX _t = 0, the block is determined to be an invalid block, and that fact is transmitted only with J = "0".

If the block is a valid block,
The block determination circuit 56 compares both QX _t and ΔQX _t , determines which of ΔQX _t (INTER) and QX _t (INTRA) is more advantageous to transmit, and determines J =
"10" and J = "11" are determined. The variable length coding circuit 57 sends out the compressed code data on which the entropy coding has been performed to the transmission line 60 based on the result.

On the receiving side, first, the variable length decoding circuit 77
Decodes the compressed code data and restores information such as the value of J, ΔQX _t and QX _t . The block control circuit 76 controls the adder 74 based on the value of J.

That is, the block control circuit 76 applies the output QX _t _ ₁ of the reference frame memory 75 to
Nothing added together not if J = "0", if J = "10", by adding the ΔQX _t, the QX _t by disenable the QX _t _ ₁ if J = "11" Regenerate. Then, QX _t is written into the reference frame memory 75.

A representative value of QX _t is reconstructed by an inverse quantization circuit 73 to be RX _t, and is further converted back to an image domain signal RY _t by an inverse discrete cosine transform circuit 72. Is output. The output signal RY _t, as described in FIG. 2, the post-processing circuit 90, is outputted as a video signal via a digital-to-analog converter 100.

As described above, in the configuration of one embodiment of the present invention, after the intra-frame encoding (transformation and quantization) is performed first, the difference from the reference frame is determined, and entropy encoding is performed. . For this reason, in the embodiment of the present invention, the conversion circuit and its inverse conversion circuit, and the quantization circuit and its inverse quantization circuit, which are conventionally required for interframe coding, are not present in the coding loop.

According to one embodiment of the present invention,
It is possible to greatly simplify the hardware configuration and economically achieve the inter-frame coding scheme, and furthermore, the configuration of the coding loop can be extremely simplified, so that high-speed signal processing can be performed. It is possible to perform wideband television signal processing.

That is, the embodiment of the present invention is suitable for use in high-speed processing of full-band NTSC signals, high-definition television signals, and the like.

Also, in one embodiment of the present invention, the coding image quality depends only on the quantization in intra-frame coding.
High quality "still image quality" can be obtained. on the other hand,
In the embodiment of the present invention, since the feature of inter-frame coding, that is, frame correlation, can be used as the amount of compressed data, the “data amount of still image” is replaced with the “data amount of inter-frame coding”. Can be reduced.

[0060]

As described above, according to the present invention, it is possible to maintain the image quality equivalent to the conventional one while greatly reducing the amount of hardware, and to make the inter-frame encoding of the image extremely simple and clear. , Can be implemented with few circuit elements,
An economical device configuration can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a peripheral situation to which the present invention is applied.

FIG. 3 is a block diagram showing a configuration of an information source encoder which is an example of an inter-frame encoding method according to the related art.

[Explanation of symbols]

 Reference Signs List 20 analog-to-digital converter 30 pre-processing circuit 40 encoding frame memory 50 encoding circuit 52 orthogonal transformation circuit 53 quantization circuit 54 subtraction circuit 55, 75 reference frame memory 56 block determination circuit 57 variable-length encoding circuit 60 transmission path 70 decoding Circuit 72 inverse orthogonal transformation circuit 73 inverse quantization circuit 74 addition circuit 76 block control circuit 77 variable length decoding circuit 80 decoding frame memory 90 post-processing circuit 100 digital-to-analog converter

Claims (1)

(57) [Claims] An image signal inter-frame encoding circuit having an encoding frame memory and a reference frame memory divides an input image signal in the encoding frame memory into blocks, performs orthogonal transformation, and quantizes the orthogonal transformation coefficients. Calculate the inter-frame difference between the quantized coefficient domain obtained by the quantization and the intra-frame conversion information in the reference frame memory as the intra-frame conversion information, and compare the inter-frame difference information with the intra-frame conversion information. By doing, whether the block is valid or invalid, further, if it is valid to determine whether it is better to select the intra-frame conversion information or to select the inter-frame difference information, A method for inter-frame encoding of an image signal, wherein the determination result and the selected conversion information are entropy-encoded. formula.