JP3265696B2 - Image compression coding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for compressing and recording digitized image data and recording the image data by controlling the code amount after the compression and encoding to be equal to or less than a predetermined code amount.
The present invention relates to an image compression encoding device used for a TR or the like.

[0002]

2. Description of the Related Art As a high-efficiency compression coding technique for natural images, a method in which orthogonal transform is combined with variable-length coding is effective, and this method is also adopted as an international standard for color natural image coding. Has been determined (literature:
"The Journal of the Institute of Television Engineers of Japan" Vol.46 No.8 PP1021-1024).

In this method, the code amount changes for each image because of variable length coding. However, in a system such as a VTR, it is necessary to record at a constant rate, so that it is necessary to control the code amount for each image, and a code amount control method has been proposed. Next tournament 1
6-15 "Code amount control in JPEG-DCT coding").

FIG. 7 is a block diagram of a conventional image compression encoding apparatus, FIG. 2 is a diagram showing the order of zigzag scanning of DCT,
FIG. 3 shows a quantization step of each coefficient of DCT.
FIG. 8 is a characteristic diagram for calculating a target scale factor from the scale factor and the code amount, and FIG. 8 is a diagram showing a relationship between the block and the scale factor.

In FIG. 7, 1 is an input terminal for inputting image data, 2 is a block circuit for dividing the image data into 8 × 8 blocks, and 3 is a discrete cosine transform (hereinafter referred to as DCT) for each 8 × 8 block. DCT conversion circuit that performs
4 is a field memory for delaying the DCT coefficient by one field time, 5 is a first quantizer for quantizing the DCT coefficient,
Reference numeral 6 denotes a Huffman encoding circuit that performs two-dimensional Huffman encoding on the output of the first quantizer 5, reference numeral 7 denotes a buffer memory that buffers encoded data at a predetermined rate, reference numeral 8 denotes an output terminal, and reference numeral 9 denotes an output terminal. Is a second quantizer for quantizing DCT coefficients, 10 is a block code amount calculation circuit for calculating the code amount per block obtained by two-dimensional Huffman coding of the output of the second quantizer 9, and 13 is a first code amount calculation circuit. Is a code amount control circuit that determines the scale factor of the quantizer 5 and controls the code amount.

The operation of the conventional image compression / encoding device configured as described above will be described below.
The data input from the input terminal 1 is divided by the blocking circuit 2 into 8 × 8 DCT blocks. The data is converted by the DCT conversion circuit 3 into 64 DCT coefficients for each block, output in the order of zigzag scan shown in FIG. 2, and delayed by one field in the field memory 4.

[0007] The delayed DCT coefficient is supplied to the first quantizer 5.
, A different quantization step for each coefficient shown in FIG. 3 and a scale factor αi determined by the code amount control circuit 13.
The variable-length data is linearly quantized by the quantized value multiplied by .times. And subjected to two-dimensional Huffman encoding by the Huffman encoding circuit 6. The encoded variable-length data is converted into a predetermined rate in the buffer memory 7 and then output together with the scale factor αt. Scale factor αt
Is calculated by the following pre-scan during the delay time.

As shown in FIG. 8, M blocks of different scale factors α1 differing from block to block in one field.
ΑαM (α1 <α2 <... <ΑM) and a quantized value obtained by multiplying the quantization step shown in FIG. 3 by a linear quantization, and a variable when the block code amount calculation circuit 10 performs two-dimensional Huffman coding. The code amount per block of the long data is calculated. Here, the code amount control circuit 13 calculates M kinds of integrated values N1 to NM of the code amount for each scale factor. The relationship between the scale factors α1 to αM and the code amounts N1 to NM has characteristics as shown in FIG. Here, assuming that the target code amount per field is Nt, an optimum scale factor αt can be predicted as shown in FIG.

[0009]

However, in the above-mentioned conventional configuration, the prediction of the scale factor αt is performed once per field, and when a prediction error is large, a predetermined code amount may overflow. In this case, for example, the VTR has a problem that the last image data cannot be recorded.

It is conceivable to reduce the probability of overflow by setting the value slightly larger than the calculated value when predicting the scale factor αt. However, in this case, since the code amount becomes smaller than necessary, the image quality degradation due to compression is reduced. There is also a problem that it becomes larger.

An object of the present invention is to solve the above-mentioned conventional problems and to provide an image compression encoding apparatus which improves the accuracy of code amount control.

[0012]

In order to achieve this object, an image compression encoding apparatus according to the present invention comprises: an orthogonal transformer for orthogonally transforming input image data for each block; A memory for reading in a determined order, a first quantizer for quantizing output data of the memory, an encoder for variable-length encoding the output of the first quantizer, and the encoder A buffer memory that outputs at a constant rate after writing the output data of
A code amount integrator for integrating the code amount of the output data of the encoder, and the output data of the orthogonal transformer are classified into K groups corresponding to the output order of the memory, and blocks included in each group. A second quantizer for allocating one of M quantized coefficients to the quantized coefficients, and a block per block when the output of the second quantizer is subjected to variable-length encoding. A code amount calculator for calculating the code amount, and predicting M kinds of code amounts when one screen is quantized with the M kinds of quantization coefficients from the block code amount outputted from the code amount calculator, and And an initial quantization coefficient detector for determining a quantization coefficient (initial quantization coefficient) for obtaining a predetermined code amount, and a total sum of the block code amounts output from the code amount calculator for each of K groups From the ratio and use the initial quantization coefficient A group code amount calculator that predicts a target code amount for each group when the coding is performed, and an actual code amount integrated by the code amount integrator each time data of each group is output from the encoder. It has a configuration including a quantization coefficient corrector that corrects the quantization coefficient of the first quantizer by correcting the initial quantization coefficient with a prediction error from a target code amount.

[0013]

According to the present invention, since the code amount prediction is performed for each group divided in the order of data output and the feedback control with the actual code amount can be performed by the above configuration, the accuracy of the code amount control is improved and the data amount is improved. Can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an image compression encoding apparatus according to the present invention, FIG. 4 is a diagram showing blocks on a screen and a scale factor, FIG. 5 is a characteristic diagram showing a scale factor and a code amount in one field, and FIG. FIG. 9 is a characteristic diagram showing the integrated value of the code amount and the target code amount, and FIG. 9 is a characteristic diagram showing the scale factor and the code amount for each group and thereafter.

In FIG. 1, 1 is an input terminal for inputting image data, 2 is a block circuit for dividing the image data into 8 × 8 blocks, and 3 is a discrete circuit which is an example of orthogonal transform for each 8 × 8 block. DCT that performs cosine transform (DCT)
A transformation circuit, 4 is a field memory for delaying the DCT coefficient by one field time, 5 is a first quantizer for quantizing the DCT coefficient, and 6 is a Huffman code for two-dimensional Huffman encoding the output of the first quantizer. An encoding circuit, 7 is a buffer memory for buffering the encoded data at a predetermined rate, and 8 is an output terminal.

9 is a second quantizer for quantizing DCT coefficients, 10 is a block code amount calculation circuit for calculating the code amount per block obtained by two-dimensional Huffman coding the output of the second quantizer, 11 Is an initial scale factor calculation circuit for calculating an initial scale factor from the block code amount, 12 is a group target code amount calculation circuit for predicting a target code amount for each group, and 13 is a first quantum factor based on the initial scale factor and the actual code amount. A scale factor correction circuit 14 for determining the scale factor of the converter is a code amount integrating circuit for integrating the code amount of the Huffman encoded data.

The operation of the image compression / encoding device configured as described above will be described below. First, the data input from the input terminal 1 is converted into 8 data by the blocking circuit 2.
It is divided into × 8 DCT blocks. The data is converted by the DCT conversion circuit 3 into 64 DCT coefficients for each block, output in the order of zigzag scan shown in FIG. 2, and delayed by one field in the field memory 4. The delayed DCT coefficient is linearly converted by the first quantizer 5 by a quantization value obtained by multiplying a different quantization step for each coefficient shown in FIG. 3 and a scale factor αt determined by the scale factor correction circuit 13. The variable-length data that has been quantized and two-dimensionally Huffman-coded by the Huffman coding circuit 6 is output. The encoded variable-length data is converted into a predetermined rate in the buffer memory 7 and then scale factor αt
Is output with.

The calculation of the scale factor αt will be described below. First, the DC for each block output by the DCT conversion circuit 3
The T coefficient is input to the second quantizer 9, and each block of one field is divided into K groups corresponding to the output order of encoded data and M scale factors α1 as shown in FIG. To αM (α1 <α2 <... <ΑM), so that the number of blocks in one field is a multiple of M × K, and the number of blocks of the scale factor of each group is the same. Can be In FIG. 4, the scale factors are assigned in order, but they may be assigned in a random manner. The DCT coefficient of each block is linearly quantized by the assigned scale factor and a quantization value obtained by multiplying the quantization step shown in FIG.

In the block code amount calculation circuit 10, the DCT coefficients quantized by using the M kinds of scale factors are converted into two-dimensional Huffman codes.
Calculate the code amount per block. The code amount is calculated by outputting the code amount from a combination of 0 run and non-zero coefficient using a ROM or the like, and integrating the value for each block.

The initial scale factor calculation circuit 11 includes:
The code amount for each block is sequentially input, and the integrated value of the code amount for M scale factors is calculated for each of the group classifications assigned in advance. Next, the relationship between the scale factor and the code amount of one field is derived from the relationship between the scale factor and the code amount for each group. Group j
The scale factor αi (1 ≦ i) in (1 ≦ j ≦ K)
Assuming that the total sum of the code amounts under .ltoreq.M) is N (i, j), the code amount Ni when one-field data is quantized by the scale factor αi is the code quantized by the scale factor αi for each group. The sum of the quantities is multiplied by the number M corresponding to the type of the scale factor, and is predicted as (Equation 1).

[0021]

(Equation 1)

The relationship between the scale factor αi and the code amount Ni has a characteristic as shown in FIG. 5 in which Ni decreases as αi increases. And an initial scale factor α for encoding the code amount of one field to a predetermined target code amount.
Calculate init. Assuming that the target code amount of one field is Nt, as shown in FIG. 5, for example, if the target code amount Nt is between the predicted code amounts N2 and N3, a straight line (α2, N
2) By the interpolation of-(α3, N3), the initial scale factor αinit for setting the code amount of one field to Nt can be calculated as shown in (Equation 2).

[0023]

(Equation 2)

The total target code amount N (i, j) at the scale factor αi in each group is input to the group target code amount calculation circuit 12, and quantization is performed at the initial scale factor αinit for each of the K groups. Of the code amount at the time of is performed.

Here, since the number of blocks assigned to the scale factors in each group is the same, the ratio of the sum of the code amounts quantized at M different scale factors to the ratio of the code amounts at the same scale factor Are the same.

Accordingly, the total code amount Nj when the scale factor αinit is set in the group j is expressed by (Equation 3) assuming that the target code amount Nt of one field is divided by the ratio of the code amount sum of each group. Predicted as shown.

[0027]

(Equation 3)

The predicted code amount Nj for each group calculated by the group target code amount calculation circuit 12 is input to the scale factor correction circuit 13, and the target code amount integrated value for each group obtained by integrating the predicted code amount Nj is calculated. After being asked,
The data amount actually encoded by the Huffman encoding circuit 6 is integrated in the code amount integrating circuit 14 and input as a code amount integrated value. The relationship between the target code amount integrated value and the code amount integrated value is shown in the characteristic diagram of FIG. The difference between the target code amount integrated value and the code amount integrated value is set as a prediction error Δ, and each time the data output of each group is completed, the scale factor αt of the next group is corrected using the prediction error Δ.

For example, the encoding of the group (j-1) is completed, and the prediction error between the predicted code amount integrated value in the group (j-1) and the actual code amount integrated value is represented by Δ (j-1). Then
By outputting the scale factor αt for setting the target code amount from the group j to the end of one-field encoding to (Equation 4) to the first quantizer 5 and encoding the scale factor αt by the Huffman encoding circuit 6, The prediction error Δ (j−1) is canceled, and the code amount integrated value at the end of the next group coding can be corrected to a value near the target code amount integrated value.

[0030]

(Equation 4)

The calculation of αt is based on the relationship between the scale factor and the code amount after each block (FIG. 9), and the scale factor αt for making the sum of the code amounts after group j into (Equation 4) is expressed by (Equation 5). It is calculated by the linear interpolation shown.

[0032]

(Equation 5)

When the prediction error Δ is 0, or in the first group 1 of the field, quantization is performed with αt = αinit.

Note that the scale factor αt is calculated from the prediction error.
Can be calculated using the characteristic diagram FIG. 5 used for calculating αinit, and αt is calculated by linear interpolation shown in (Equation 6). In this case, the circuit scale can be reduced.

[0035]

(Equation 6)

As described above, according to this embodiment, the DCT blocks of one field are classified into K groups, and the initial scale factor calculating circuit 10 uses the block code amounts quantized with M different scale factors. To obtain an initial scale factor αinit for quantizing to a target code amount of one field,
By predicting the code amount for each group in the encoding output order when quantized by init, and calculating by the group target code amount calculation circuit 12, the accuracy of the initial scale factor and the code amount prediction for each group is improved. . Then, since the code amount control is performed by the scale factor correction circuit 13 based on the error between the actual code amount integrated by the code amount integration circuit 14 and the target code amount for each group, M fine codes are performed in one field period. Volume control can be performed.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. Note that the configurations shown in FIGS. 1 to 6 have the same configuration, and a detailed description thereof will be omitted. In this embodiment, the calculation of αt in the scale factor correction circuit 13 is different from that of the first embodiment described above. This will be described in detail with reference to the characteristic diagram of FIG.

For example, the encoding of the group (j-1) is completed, and the prediction error between the predicted code amount integrated value in the group (j-1) and the actual code amount integrated value is Δ (j-1). Then
The error at the end of one field (the total coding error ΔK) is predicted as in (Equation 7).

[0039]

(Equation 7)

Therefore, the scale factor αt for setting the error at the end of one-field encoding to 0 is output to the first quantizer 5 and encoded by the Huffman encoding circuit 6 to obtain the prediction error ΔK Are canceled, and the code amount integrated value at the end of the one-field encoding can be corrected to be close to the target code amount integrated value. In calculating αt, the scale factor αt for canceling ΔK from the code amount after group j is calculated by linear interpolation shown in (Equation 8) from the relationship between the scale factor and the code amount after each block (FIG. 10).

[0041]

(Equation 8)

When the prediction error Δ is 0 or in the first group 1 of the field, quantization is performed with αt = αinit.

Note that the scale factor αt is calculated from the prediction error.
Can be calculated using the characteristic of FIG. 5 used for calculating αinit, and αt is calculated by linear interpolation shown in (Equation 9). In this case, the circuit scale can be reduced.

[0044]

(Equation 9)

As described above, according to the present embodiment, it is possible to accurately correct the scale factor so as to converge within a predetermined code amount at the end of coding from the prediction error of the current code amount integrated value. .

Next, a third embodiment of the present invention will be described with reference to the drawings. 2 to 6 and FIG.
Are the same as those described above, and therefore detailed description thereof is omitted. In this embodiment, a code amount restriction is added to the Huffman encoding circuit 6 in the first embodiment.
This point will be described in detail with reference to the drawings.

FIG. 11 is a block diagram showing the configuration of the image compression encoding apparatus of this embodiment, FIG. 12 is a characteristic diagram showing the relationship between the number of uncoded blocks and the control code amount, and FIG. 13 shows the block code amount allocation. FIG.

In FIG. 11, 1 to 14 have the same configuration as the first embodiment. 16 is a first control code amount setting circuit for setting a first control code amount according to the number of uncoded blocks, and 17 is a first control code amount setting circuit for setting a second control code amount according to the number of uncoded blocks. Second control code amount setting circuit, 18
Is a first comparison circuit for comparing the code amount integrated by the code amount integration circuit 14 with the first control code amount, and 19 is a code amount integrated by the code amount integration circuit 14 and the second control code. A second comparing circuit 20 for comparing the amount with the code amount limiting circuit 20 for limiting the amount of code per block based on these comparison results.
Reference numeral 1 denotes a block power calculation circuit for calculating the power sum for each block from the DCT coefficient.

When the first control code amount setting circuit 17 and the second control code amount setting circuit 18 are in the K-th final group, the control code amount corresponding to the number of uncoded blocks is changed as shown in FIG.
It is set like the characteristic of Here, each control code amount is
This shows prediction of a code amount that is a fixed amount per block so as to become a predetermined amount at the end of one field, and the first control code amount is a case where only DC of DCT coefficients is coded (code amount per block). L1), the second control code amount indicates a case where encoding is performed with a code amount L2 per block (L1 <L2).

The block power calculation circuit 21 calculates the power sum for each block from the DCT coefficients. 8 × per block
8, the number of DCT coefficients is 64, and
Assuming that the CT coefficient is D (i) (i = 0 to 63), the power sum PW is obtained by (Equation 10).

[0051]

(Equation 10)

In the code amount limiting circuit 20, the first comparing circuit 1
8, when the integrated code amount exceeds the second control code amount in the second comparison circuit 19 so that only DC is encoded when the integrated code amount exceeds the first control code amount. The Huffman encoding circuit 6 is controlled by assigning a code amount to each block based on the block power calculated by the block power calculation circuit 21.

Next, the amount of code allocated to each block will be described. B is the total number of blocks per field
And the block power in the n-th block is PW
Assuming that (n), the code amount allocation LG (n) is obtained by (Equation 11) as a code amount proportional to the block power.

[0054]

[Equation 11]

Therefore, as shown in FIG. 13, a code amount corresponding to each block power is allocated to each block. Since LG (n) is proportional to the block power PW (n), it can be obtained by approximation as shown in (Equation 12).

[0056]

(Equation 12)

Here, K (α) is a proportional constant between the block power and the code amount when the scale factor is α, and can be statistically obtained.

As described above, according to this embodiment, while the average code amount per block is a predetermined amount, the code amount given to each block is finely limited in accordance with the power of each block, so that the local amount of the image can be reduced. It is possible to control the code amount to a predetermined amount by reducing the deterioration of the image quality, and to limit the code amount only at the end of the encoding, thereby minimizing the deterioration of the image quality. .

By coding the end of the screen last, it is possible to make the degradation of the code amount limit visually inconspicuous. Further, in this embodiment, the average code amount is set to two types of L1 and L2, but a larger code amount may be set, and the unit for limiting the code amount may be a plurality of block units. .

Next, a fourth embodiment of the present invention will be described with reference to FIG.
This will be described with reference to the block diagram of FIG. Since the configurations shown in FIGS. 2 to 6 and 9 are the same, detailed description thereof will be omitted. In the present embodiment, the third
This embodiment differs from the embodiment in that the code amount is assigned by the code amount limiting circuit 20. This will be described in detail with reference to the drawings.

In FIG. 14, 1 to 14 have the same configuration as in the first embodiment, and 16 to 20 have the same configuration as in the third embodiment. A code amount assignment circuit 22 determines the code amount assignment from the code amount for each block at the time of prescan output from the block code amount calculation circuit 10.

In the code amount limiting circuit 20, the first comparing circuit 1
8, when the integrated code amount exceeds the second control code amount in the second comparison circuit 19 so that only DC is encoded when the integrated code amount exceeds the first control code amount. The Huffman coding circuit 6 is controlled by allocating the code amount calculated by the code amount allocation circuit 22 to.

In the code amount allocating circuit 22, one of the M scale factors calculated by the block code amount calculating circuit 10 is selected and quantized, and the code amount per block and the initial scale factor calculation are calculated. The relationship between the scale factor and the code amount predicted by the circuit 11 is input,
The code amount for each block in the current scale factor is predicted.

For example, if a certain block is the second quantizer 9
When the code amount output from the block code amount calculation circuit 10 is s and the current scale factor is αinit, the code is obtained from the characteristic diagram of the scale factor and the code amount in FIG. The quantity TG is (Equation 1)
Predicted as in 3).

[0065]

(Equation 13)

Here, assuming that the code amount prediction in block n is TG (n), the code amount allocation LG (n) is (Equation 14)
Required by

[0067]

[Equation 14]

Since LG (n) is proportional to the predicted code amount TG (n), it can be obtained by approximation as shown in (Equation 15).

[0069]

(Equation 15)

Here, L (α) is a proportional constant between the block power and the code amount when the scale factor is α, and can be statistically obtained.

As described above, according to the present embodiment, the code amount can be finely limited in block units, and the prediction code amount can be calculated using the parameters used for calculating the initial scale factor. The accuracy of the code amount control is improved without increasing.

As in the third embodiment, by encoding the end of the screen last, it is possible to make the deterioration of the code amount limit visually inconspicuous.

Next, a fifth embodiment of the present invention will be described with reference to the drawings. Since the configurations shown in FIGS. 2 to 6 and 9 are the same, detailed description thereof will be omitted.

This embodiment shows a code amount control method in a multi-channel. FIG. 15 is a block diagram of the image compression device of the present embodiment, and FIG. 16 is a diagram showing channel division.

In FIG. 15, 1 is an input terminal for inputting image data, 30 is a channel dividing circuit for dividing the image data into two channels, and 31 is the Ach image data.
Ach blocking circuit for dividing into × 8 blocks, 32
Is an AchDCT transform circuit that performs a discrete cosine transform (DCT) as an example of an orthogonal transform for each 8 × 8 block;
Is an Ach field memory for delaying the DCT coefficient by one field time, 34 is an Ach first quantizer for quantizing the DCT coefficient, 35 is Ach Huffman coding for two-dimensional Huffman encoding the output of the first quantizer. A circuit 36 is an Ach buffer memory for buffering the encoded data at a predetermined rate, and 37 is an Ach output terminal.

Reference numeral 38 denotes an Ach second quantizer for quantizing DCT coefficients, and reference numeral 39 denotes an Ach for calculating a code amount per block obtained by two-dimensional Huffman encoding the output of the second quantizer.
A block code amount calculation circuit; 40, an Ach target code amount calculation circuit for predicting a target code amount for each group; 41, an Ach scale factor for determining a scale factor of a first quantizer from an initial scale factor and an actual code amount The correction circuit 42 is an Ach code amount integrating circuit that integrates the code amount of the Huffman encoded data.

Reference numerals 51 to 62 denote processing circuits of Bch corresponding to 31 to 42 of Ach, and reference numeral 70 denotes an initial scale factor calculating circuit for calculating an initial scale factor from the block code amount.

The operation of the image compression / encoding device configured as described above will be described below. First, the data inputted from the input terminal 1 is divided into two channels A and B by the channel dividing circuit 30 as shown in FIG. Each of the divided data is divided into block circuits 31.
And 51 split into 8 × 8 DCT blocks. The data is converted into 64 DCT coefficients for each block by DCT conversion circuits 32 and 52, output in zigzag scan order shown in FIG. 2, and delayed by one field in field memories 33 and 53.

The delayed DCT coefficient is supplied to the first quantizer 3
At 4 and 54, a Huffman encoding circuit is linearly quantized by a quantization value obtained by multiplying a different quantization step for each coefficient shown in FIG. 3 and a scale factor αt determined by the scale factor correction circuits 41 and 61. 35 and 5
In step 5, variable-length data subjected to two-dimensional Huffman encoding is output. The encoded variable-length data is converted into a predetermined rate by the buffer memories 36 and 56, and then output together with the scale factor αt.

The details of the method of predicting the group target code amount and the method of correcting the scale factor αt are the same as in the first embodiment, and only points relating to channel division will be described below.

First, the DCT coefficients for each block output from the DCT transform circuits 32 and 52 are converted by the second quantizer 38.
And 58, and each block of one field is divided into K groups corresponding to the output order of the encoded data and M scale factors α1 to α as shown in FIG.
One of M (α1 <α2 <... <ΑM) is assigned. The DCT coefficient of each block is linearly quantized by the assigned scale factor and a quantization value obtained by multiplying the quantization step shown in FIG.

The block code amount calculation circuits 39 and 59 use the M scale factors to quantize D
The code amount per block when the CT coefficient is subjected to the two-dimensional Huffman coding is calculated.

The initial scale factor calculation circuit 70 includes:
The code amount for each block for two channels is input, and one type of initial scale factor α is calculated from the code amount for two channels.
init is required.

Group target code amount calculation circuits 40 and 6
At 0, the integrated value of the code amount when quantization is performed with the initial scale factor αinit for each of the K groups independently for two channels is calculated.

Scale factor correction circuits 41 and 61
Is input with the predicted code amount for each group calculated by the group target code amount calculation circuits 40 and 60 and the code amount actually Huffman-coded, and corrects the scale factor αt of the next group by the prediction error Δ. Is performed for each channel.

As described above, according to this embodiment, when one field of image data is divided into two channels and each channel is encoded within a predetermined code amount, the initial scale factor calculating circuit uses two channels. The initial scale factor αinit can be obtained by using the relationship between the code amount and the scale factor, so that the prediction accuracy of the initial scale factor can be improved, and the scale factor can be corrected for each channel to enable fine code amount control. It is.

In this embodiment, two-channel encoding is described, but it is clear that the same effect can be obtained with any number of channels. In addition, when channel division is performed, it is apparent that shuffling such that one channel is not concentrated on the screen reduces the difference in code amount between channels and improves the accuracy of code amount control.

In all the embodiments, the compression is shown in units of fields. However, it is apparent that the same effect can be obtained in the case of compression in units of frames or in units of macroblocks composed of a plurality of blocks. .

In all the embodiments, the prediction of the code amount by the pre-scan is performed for all the blocks. However, the same effect can be obtained when a part of the blocks is sampled and operated.

Further, in all the embodiments, the orthogonal transform by the DCT transform has been described. However, it is apparent that the same effect can be obtained by any orthogonal transform such as LOT and Hadamard transform.

[0091]

As described above, according to the present invention, 1
Since the initial quantized coefficient and the integrated value of the code amount of each group obtained by dividing the data of one screen into K groups can be accurately predicted only by the prescanning times, the actual integrated code amount and the actual code amount integrated value can be predicted. The accuracy of the code amount control is improved by correcting the initial scale factor by comparing.

Further, by setting a code amount restriction on a block basis, it is possible to prevent data overflow and to perform fine code amount control, and to improve the image quality of a compressed image even in multi-channel coding. Can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image compression encoding apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a zigzag scan of DCT coefficients.

FIG. 3 is a diagram showing a quantization step of DCT coefficients;

FIG. 4 is a diagram showing blocks on a screen according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a scale factor and a code amount in one field.

FIG. 6 is a characteristic diagram showing a time history of a code amount integrated value according to the first embodiment of the present invention.

FIG. 7 is a block diagram illustrating a configuration of a conventional image compression encoding apparatus.

FIG. 8 is a diagram showing blocks on a screen in a conventional example.

FIG. 9 is a diagram illustrating a relationship between a scale factor and a code amount after j group in the first embodiment of the present invention.

FIG. 10 is a characteristic diagram showing a time history of a code amount integrated value according to the second embodiment of the present invention.

FIG. 11 is a block diagram illustrating a configuration of an image compression encoding apparatus according to a third embodiment of the present invention.

FIG. 12 is a characteristic diagram showing a relationship between an encoding time and a control code amount.

FIG. 13 is a diagram showing code amount allocation to blocks.

FIG. 14 is a block diagram illustrating a configuration of an image compression encoding apparatus according to a fourth embodiment of the present invention.

FIG. 15 is a block diagram illustrating a configuration of an image compression encoding apparatus according to a fifth embodiment of the present invention.

FIG. 16 is a diagram showing channel division on a screen according to a fifth embodiment of the present invention.

[Explanation of symbols]

 2 Blocking circuit 3 DCT transformation circuit 4 Field memory 5 First quantizer 6 Huffman encoder 7 Buffer memory 9 Second quantizer 10 Block code amount calculation circuit 11 Initial scale factor calculation circuit 12 Group target code amount Calculation circuit 13 Scale factor correction circuit 14 Code amount integration circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N ^7/ 24-7/68

Claims (7)

(57) [Claims] 1. An apparatus for dividing input image data into a plurality of blocks, and compressing each of the divided blocks to a predetermined code amount by a coding method combining orthogonal transform and variable length coding, An orthogonal transformer for orthogonally transforming the input image data for each block, a memory for writing output data of the orthogonal transformer and reading in a predetermined order, and a first quantization for quantizing output data of the memory Encoder, an encoder for performing variable length encoding on the output of the first quantizer, a buffer memory for writing the output data of the encoder, and outputting the data at a constant rate, and an output of the encoder. A code amount integrator for integrating the code amount of data, and the output data of the orthogonal transformer are classified into K groups corresponding to the output order of the memory, and the blocks included in each group are divided into K groups. A second quantizer for quantizing the assignment the quantization coefficient of one of the quantized coefficients are M and,
A code amount calculator for calculating the code amount per block when the output of the second quantizer is subjected to variable length coding; and M screens of one screen from the block code amount output from the code amount calculator. An initial quantized coefficient detector for predicting M kinds of code amounts when quantized with the quantized coefficients and determining a quantized coefficient (initial quantized coefficient) for setting one screen to a predetermined code amount; Group code amount calculation for obtaining the total sum of the block code amount output from the code amount calculator for each of the K groups and predicting the target code amount for each group when encoding is performed using the initial quantization coefficient from the ratio. And correcting the initial quantization coefficient by a prediction error between an actual code amount integrated by the code amount integrator and the target code amount each time data of each group is output from the encoder. By the quantity of the first quantizer Image compression encoding apparatus characterized by having a quantization coefficient corrector that corrects the coefficient. 2. The method according to claim 1, wherein M and K are determined so that the number of blocks in one screen is a multiple of M × K, and the blocks are allocated so that the number of blocks corresponding to each scale factor of each group is the same. Item 3. An image compression encoding apparatus according to Item 1. 3. A quantizing coefficient corrector calculates a prediction error between an actual code amount integrated by a code amount integrator and a target code amount each time data of each group is output from the encoder, 2. The image compression coding according to claim 1, wherein a code amount obtained by subtracting the prediction error from a total sum of target code amounts of the next and subsequent groups is used as a target code amount of the next and subsequent groups to determine a quantization coefficient of the next group. apparatus. 4. A quantization coefficient corrector calculates a prediction error between an actual code amount integrated by a code amount integrator and a target code amount each time data of each group is output from the encoder, The prediction error and the error (all coding errors) when the entire screen is coded by the current quantization coefficient is predicted from the ratio between the already coded data code amount and the uncoded data code amount prediction,
2. The image compression code according to claim 1, wherein a code amount obtained by subtracting all coding errors from a total sum of target code amounts of the next and subsequent groups is determined as a target code amount of the next and subsequent groups, and a quantized coefficient of the next group is determined. Device. 5. A code for setting a code amount (control code amount) in a case where an uncoded block is coded at a fixed length per block for setting a code amount of one field to a predetermined amount for each block. 2. The apparatus according to claim 1, further comprising an amount setting device, and a code amount controller for controlling the code amount for each block when the code amount integrated by the code amount integrator exceeds the control code amount. Image compression encoding apparatus. 6. A block power calculator for calculating a power sum for each block from output data of an orthogonal transformer, wherein a code amount controller calculates a code amount proportional to the block power sum of an uncoded block for each block. 6. An image compression encoding apparatus according to claim 5, wherein the encoder is controlled according to the following. 7. An assigned quantization coefficient and code amount for each block encoded by a second quantizer calculated by a code amount calculator and an initial quantization coefficient calculator. From the relationship between the predicted quantization coefficient and the code amount, a block code amount predictor for predicting the code amount for each block when quantization is performed with the initial quantization coefficient, and the code amount controller 6. The image compression encoding apparatus according to claim 5, wherein a code amount proportional to a predicted code amount per block is determined for each block and the encoder is controlled.