JPH06292180A - Image compression encoder - Google Patents

Abstract

PURPOSE:To perform code quantity control with high accuracy in the code quantity control of a VTR which records by controlling code quantity after compression coding when digitized image data is encoded by compression, etc., so as to be controlled at quantity less than prescribed code quantity. CONSTITUTION:The control of an initial scale factor to set the code quantity of one field at prescribed code quantity and the feedback control of the scale factor are performed by predicting the code quantity when the initial scale factor is quantized in group unit divided in sequence of coded output with high accuracy and by an error between the code quantity coded actually by a Huffman encoder 6 by performing one time of pre-scan by a second quantizer 9 and a block code quantity calculation circuit 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention controls the recording so that the code amount after compression encoding becomes less than a predetermined code amount when the digitized image data is compression encoded and recorded.
The present invention relates to an image compression encoding device used for TR and the like.

[0002]

2. Description of the Related Art As a highly efficient compression coding technique for natural images, a system combining orthogonal transformation and variable length coding is effective, and this system is also adopted as an international standard for color natural image coding systems. Has been decided (reference:
"Journal of the Television Society" Vol.46 No.8 PP1021-1024).

In this method, the amount of code changes for each image because of variable-length coding. However, since it is necessary to record at a constant rate in a system such as a VTR, it is necessary to control the code amount for each image, and a code amount control method has been proposed (Reference: 1992 Television Society of Japan). Next competition 1
6-15 “Code amount control in JPEG-DCT encoding”).

FIG. 7 is a block diagram of a conventional image compression coding apparatus, and FIG. 2 is a diagram showing a zigzag scan sequence of DCT.
FIG. 3 is a diagram showing a quantization step of each coefficient of DCT, and FIG.
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 blocks and scale factors.

In FIG. 7, 1 is an input terminal for inputting image data, 2 is a blocking 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. ) Performing a DCT conversion 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,
Reference numeral 6 is a Huffman coding circuit for two-dimensionally Huffman coding the output of the first quantizer 5, reference numeral 7 is a buffer memory for buffering the coded data at a predetermined rate, 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-dimensionally Huffman coding the output of the second quantizer 9, and 13 is a first Is a code amount control circuit for determining the scale factor of the quantizer 5 and controlling the code amount.

The operation of the conventional image compression coding apparatus 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 into 64 DCT coefficients for each block by the DCT conversion circuit 3, output in the zigzag scan order shown in FIG. 2, and delayed by one field in the field memory 4.

The delayed DCT coefficient is transferred to the first quantizer 5
, The quantization step different for each coefficient shown in FIG. 3 and the scale factor αi determined by the code amount control circuit 13
Linearly quantized by the quantized value multiplied by, and the Huffman encoding circuit 6 outputs two-dimensional Huffman-encoded variable-length data. 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 prescan during the above delay time.

For all blocks of one field, as shown in FIG. 8, there are M different scale factors α1 for each block.
.. .alpha.M (.alpha.1 <.alpha.2 <... <.alpha.M) and a quantization value obtained by multiplying the quantization step shown in FIG. 3 to perform linear quantization and variable when the block code amount calculation circuit 10 performs two-dimensional Huffman coding. The code amount of long data per block is calculated. Here, the code amount control circuit 13 calculates the integrated values N1 to NM of the M code amounts for each scale factor. The relationship between the scale factors α1 to αM and the code amounts N1 to NM has the characteristics shown in FIG. Here, if the target code amount per field is Nt, the optimum scale factor αt can be predicted as shown in FIG.

[0009]

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

It is also conceivable to set the value slightly larger than the calculated value to reduce the probability of overflow when the scale factor αt is predicted. In this case, however, the code amount becomes smaller than necessary, so that the image quality is deteriorated due to compression. There may be a problem of getting bigger.

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

[0012]

To achieve this object, an image compression coding apparatus of the present invention comprises an orthogonal transformer for orthogonally transforming input image data block by block, and writing output data of the orthogonal transformer in advance. A memory for reading in a predetermined order, a first quantizer for quantizing output data of the memory, an encoder for variable-length coding an output of the first quantizer, and the encoder After writing the output data of, the buffer memory that outputs at a constant rate,
The code amount accumulator that accumulates 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 quantized with the quantized coefficient, and a block per block when the output of the second quantizer is variable length coded. A code amount calculator for calculating the code amount, and M screen code amounts when one screen is quantized by the M quantization coefficients from the block code amount output from the code amount calculator For a predetermined code amount, an initial quantization coefficient detector for determining a quantization coefficient (initial quantization coefficient), and a sum of block code amounts output from the code amount calculator for each of K groups. Is calculated, and the ratio is calculated by the initial quantization coefficient from the ratio. Group code amount calculator for predicting the target code amount for each group when converted, and the actual code amount accumulated by the code amount integrator each time the data of each group is output from the encoder and the It has a configuration including a quantization coefficient corrector for correcting the quantization coefficient of the first quantizer by correcting the initial quantization coefficient with a prediction error from the target code amount.

[0013]

According to the present invention, since the code amount prediction can be performed for each group divided in the order of data output and the feedback control with the actual code amount can be performed, the accuracy of the code amount control is improved and It is possible to improve the problems such as overflow of image data and deterioration of image quality.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram of an image compression encoding apparatus of the present invention, FIG. 4 is a diagram showing blocks on the screen and scale factors, FIG. 5 is a characteristic diagram showing scale factors and code amounts in one field, and FIG. 6 is an output. 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 after each group.

In FIG. 1, 1 is an input terminal for inputting image data, 2 is a blocking circuit for dividing the image data into 8 × 8 blocks, and 3 is an example of orthogonal transformation for each 8 × 8 block. DCT for cosine transform (DCT)
Transform 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, 6 is a Huffman code for two-dimensional Huffman coding the output of the first quantizer An encoding circuit, 7 is a buffer memory for buffering encoded data at a predetermined rate, and 8 is an output terminal.

Reference numeral 9 is a second quantizer for quantizing the DCT coefficient, 10 is a block code quantity calculating circuit for calculating the code quantity per block obtained by two-dimensionally Huffman coding the output of the second quantizer, 11 Is an initial scale factor calculation circuit that calculates the initial scale factor from the block code amount, 12 is a group target code amount calculation circuit that predicts the target code amount for each group, and 13 is the first quantum from the initial scale factor and the actual code amount. A scale factor correction circuit that determines the scale factor of the rectifier, and a code amount integration circuit 14 that integrates the code amount of the Huffman-encoded data.

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

The calculation of the scale factor αt is shown below. First, the DC of 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 classified into K groups corresponding to the output order of encoded data and M scale factors α1 as shown in FIG. ~ ΑM (α1 <α2 <... <αM) is assigned such that the number of blocks in one field is a multiple of M × K, and the number of blocks for assignment of scale factors in each group is the same. To be Although the scale factors are assigned in order in FIG. 4, they may be assigned in a random manner. The DCT coefficient of each block is linearly quantized by the quantized value obtained by multiplying the assigned scale factor and the quantizing step shown in FIG.

In the block code amount calculation circuit 10, the variable length data when the DCT coefficient quantized using the M scale factors is two-dimensionally Huffman coded,
The code amount per block is calculated. The code amount is calculated by outputting the code amount from a combination of 0 runs and non-zero coefficients 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 different scale factors is calculated for each group classification 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
Scale factor αi in (1 ≦ j ≦ K) (1 ≦ i
If the sum of the code amounts for ≦ M) is N (i, j), the code amount Ni when the data of one field is quantized by the scale factor αi is the code quantized by the scale factor αi for each group. It is predicted that the sum of the quantities is multiplied by the number M corresponding to the type of scale factor (Equation 1).

[0021]

[Equation 1]

The relationship between the scale factor αi and the code amount Ni has the characteristic shown in FIG. 5 in which Ni decreases as αi increases. Then, an initial scale factor α for encoding the code amount of one field into a predetermined target code amount
Calculate init. If 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)-(α3, N3) can be interpolated to calculate the initial scale factor αinit for setting the code amount of one field to Nt as shown in (Equation 2).

[0023]

[Equation 2]

The group target code amount calculation circuit 12 is supplied with the sum N (i, j) of code amounts in the scale factor αi in each group, and is quantized by the initial scale factor αinit for each of K groups. The integrated value of the code amount when is performed is predicted.

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

Therefore, the sum Nj of the code amounts in the case of the scale factor αinit in the group j is given by (Equation 3), where the target code amount Nt of one field is divided by the ratio of the sum of the code amounts 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 input. After being asked
The data amount actually encoded by the Huffman encoding circuit 6 is integrated by 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 used as a prediction error Δ, and the scale factor αt of the next group is corrected by the prediction error Δ each time the data output of each group is completed.

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

[0030]

[Equation 4]

For the calculation of αt, the scale factor αt for making the sum of the code amounts after the group j is (Equation 4) is set to (Equation 5) from the relationship between the scale factor and the code amount after each block (FIG. 9). 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 = α init.

From the prediction error, the scale factor αt
It is also possible to use the characteristic diagram FIG. 5 used to calculate α init, and α t 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 the present embodiment, the DCT blocks of one field are classified into K groups, and the initial scale factor calculation circuit 10 is calculated from the block code amount quantized with M different scale factors. The initial scale factor α init for quantizing to the target code amount of 1 field by
Since the group target code amount calculation circuit 12 calculates by predicting the code amount for each group in the encoding output order when quantized by init, the accuracy of the initial scale factor and the code amount prediction for each group is improved. . Then, since the scale factor correction circuit 13 controls the code amount based on the error between the actual code amount accumulated by the code amount integrating circuit 14 and the target code amount for each group, fine code of M times is performed in one field period. Quantity control can be performed.

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

For example, after the coding of the group (j-1) is completed, 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 (total coding error ΔK) at the end of one field is predicted as in (Equation 7).

[0039]

[Equation 7]

Therefore, the scale factor αt for making the error at the end of the 1-field encoding 0 is output to the first quantizer 5 and encoded by the Huffman encoding circuit 6 to obtain the prediction error ΔK. Are canceled out, and the code amount integrated value at the end of the one-field encoding can be corrected to a value near the target code amount integrated value. The calculation of αt calculates the scale factor αt for canceling ΔK from the code amount after the group j by the linear interpolation shown in (Equation 8) from the relationship between the scale factor after each block and the code amount (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 = α init.

From the prediction error, the scale factor αt
It is also possible to use the characteristics of FIG. 5 used to calculate α init, and α t 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, the scale factor can be corrected accurately so that the prediction error of the current code amount integrated value converges within a predetermined code amount at the end of encoding. .

Next, a third embodiment of the present invention will be described with reference to the drawings. 2 to 6 and FIG.
Since the configuration shown in 1 is the same, detailed description thereof will be omitted. In the present embodiment, the Huffman encoding circuit 6 is added with a code amount limitation to 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 coding 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 is the block code amount allocation. It is a figure.

In FIG. 11, 1 to 14 have the same structure as the first embodiment. Reference numeral 16 is a first control code amount setting circuit for setting a first control code amount corresponding to the number of uncoded blocks, and 17 is a first control code amount setting circuit for setting a second control code amount corresponding 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 integrating circuit 14 with the first control code amount, and 19 is the code amount integrated by the code amount integrating circuit 14 and the second control code A second comparison circuit for comparing the amount of code, a code amount limiting circuit 20 for limiting the code amount per block based on these comparison results, 2
Reference numeral 1 is a block power calculation circuit for obtaining the power sum for each block from the DCT coefficient.

In the first control code amount setting circuit 17 and the second control code amount setting circuit 18, when the K-th final group is reached, the control code amount corresponding to the number of uncoded blocks is shown in FIG.
Is set like the characteristics of. Here, each control code amount is
It shows the prediction of the code amount that is a fixed amount per block because it becomes 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 encoded (code amount per block). L1) and the second control code amount represent the case where the code amount per block is L2 (L1 <L2).

The block power calculation circuit 21 calculates the power sum for each block from the DCT coefficient. 1 block 8x
In the case of the DCT transform of 8, there are 64 DCT coefficients, and D
Assuming that the CT coefficient is D (i) (i = 0 to 63), the power sum PW is calculated by (Equation 10).

[0051]

[Equation 10]

In the code amount limiting circuit 20, the first comparing circuit 1
When the integrated code amount exceeds the first control code amount in 8, the second comparison circuit 19 encodes only DC so that the integrated code amount exceeds the second control code amount. The Huffman coding 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 code amount assigned to each block will be described. The total number of blocks per field is B
And the block power in the nth block is PW
Assuming that (n), the code amount allocation LG (n) is obtained by (Equation 11) as the 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 assigned to each block. Since LG (n) is proportional to the block power PW (n), it can be obtained by approximation as 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 the present embodiment, while the average code amount per block is set to a predetermined amount, the amount of code given to each block is finely limited according to the power of each block, so that the image local It is possible to reduce the deterioration of the image quality by controlling the predetermined amount of code, and it is possible to minimize the deterioration of the image quality by limiting the code amount only at the end of encoding. .

By coding the end of the screen last, it is possible to make the deterioration of the code amount limitation visually inconspicuous. Further, in this embodiment, the average code amount is set to two types 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.
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 above-mentioned third
The present embodiment is different from the embodiment described above in the allocation of the code amount in the code amount limiting circuit 20, and this point will be described in detail with reference to the drawings.

In FIG. 14, 1 to 14 have the same structure as the first embodiment, and 16 to 20 have the same structure as the third embodiment. Reference numeral 22 denotes a code amount allocation circuit that determines the code amount allocation from the code amount of 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
When the integrated code amount exceeds the first control code amount in 8, the second comparison circuit 19 encodes only DC so that the integrated code amount exceeds the second control code amount. To the Huffman coding circuit 6 by allocating the code amount calculated by the code amount allocating circuit 22.

The code amount allocating circuit 22 selects one of M scale factors calculated by the block code amount calculating circuit 10 and quantizes the code amount per block, and calculates the initial scale factor. The relationship between the scale factor and the code amount predicted by the circuit 11 is input,
The code amount of each block in the current scale factor is predicted.

For example, one block is the second quantizer 9
When the scale factor α1 is assigned at, and the code amount output from the block code amount calculation circuit 10 is s, and the current scale factor is α init, the code from the scale factor and code amount characteristic diagram of FIG. The amount TG is (Equation 1
3) is predicted.

[0065]

[Equation 13]

Here, assuming that the code amount prediction in the 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 prediction 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 of 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, the code amount is finely limited in block units, and the predicted code amount can be calculated using the parameters used to calculate the initial scale factor. The accuracy of the code amount control is improved without increasing

As in the third embodiment, the end of the screen is coded last so that the deterioration of the code amount limitation can be made 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.

In this embodiment, a code amount control system in multi-channel is shown. FIG. 15 is a block diagram of the image compression apparatus of this 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 2 channels, and 31 is Ach image data.
Ach blocking circuit for dividing into × 8 blocks, 32
Is an AchDCT transform circuit that performs discrete cosine transform (DCT), which is an example of orthogonal transform for each 8 × 8 block, 33
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, and 35 is Ach Huffman coding for two-dimensional Huffman coding the output of the first quantizer. A circuit, 36 is an Ach buffer memory for buffering encoded data at a predetermined rate, and 37 is an Ach output terminal.

38 is an Ach second quantizer for quantizing the DCT coefficient, and 39 is an Ach for calculating the code amount per block obtained by two-dimensionally Huffman coding the output of the second quantizer.
A block code amount calculation circuit, 40 is an Ach target code amount calculation circuit that predicts the target code amount for each group, and 41 is an Ach scale factor that determines the scale factor of the first quantizer from the initial scale factor and the actual code amount. The correction circuit 42 is an Ach code amount integration circuit that integrates the code amount of the Huffman-encoded data.

Reference numerals 51 to 62 are Bch processing circuits corresponding to Ach's 31 to 42, and 70 is an initial scale factor calculating circuit for calculating an initial scale factor from the block code amount.

The operation of the image compression coding apparatus 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. The divided data is divided into block circuits 31.
And 51 divide it into 8 × 8 DCT blocks. The data is converted into 64 DCT coefficients for each block by the DCT conversion circuits 32 and 52, output in the order of the zigzag scan shown in FIG. 2, and delayed by one field in the field memories 33 and 53.

The delayed DCT coefficient is transferred to the first quantizer 3
4 and 54 are linearly quantized by a quantization value obtained by multiplying the quantization step different for each coefficient shown in FIG. 3 by the scale factor αt determined by the scale factor correction circuits 41 and 61, and the Huffman encoding circuit. 35 and 5
At 5, variable-length data that has been two-dimensionally Huffman encoded is output. The encoded variable-length data is converted into a predetermined rate in 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 those in the first embodiment, and only the points concerning the channel division will be shown below.

First, the DCT coefficients for each block output from the DCT transform circuits 32 and 52 are calculated by the second quantizer 38.
And 58, each block of one field is classified into K groups corresponding to the output order of 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 quantized value obtained by multiplying the assigned scale factor and the quantizing step shown in FIG.

In the block code amount calculation circuits 39 and 59, D quantized using the M scale factors is used.
The code amount per block when the CT coefficient is two-dimensional Huffman coded 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 selected from the code amount for two channels.
init is required.

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

Scale factor correction circuits 41 and 61
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 are input to the correction target of the scale factor αt of the next group by the prediction error Δ. Is performed for each channel.

As described above, according to the present embodiment, when the image data of one field is divided into two channels and each channel is encoded within a predetermined code amount, the initial scale factor calculation circuit uses two channels. Since the initial scale factor α init can be obtained by using the relationship between the code amount and scale factor of, the prediction accuracy of the initial scale factor can be improved, and the scale factor can be corrected for each channel for fine code amount control. Is.

In this embodiment, the coding of two channels is shown, but it is clear that the same effect can be obtained with any number of channels. Further, when dividing channels, it is apparent that shuffling is performed so that one channel is not concentrated on the screen, the difference in the code amount between the channels is reduced, and the precision of the code amount control is improved.

It should be noted that although compression is performed in field units in all the embodiments, it is clear that the same effect can be obtained in compression in frame units or in macroblock units composed of a plurality of blocks. .

Further, in all the embodiments, the prediction of the code amount by the prescan is performed in all the blocks, but the same effect can be obtained when the sampling is performed in a part of the blocks.

Further, although the orthogonal transform by the DCT transform is shown in all the embodiments, it is obvious 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 for each group obtained by dividing the data of one screen into K groups can be accurately predicted only by performing the pre-scan once, The accuracy of the code amount control is improved by correcting the initial scale factor by comparing

Further, by providing a code amount limitation in block units, it is possible to prevent data overflow and perform fine code amount control, and also in multi-channel encoding, an image compression encoding device for improving the image quality of compressed images. Can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing 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 quantization steps of DCT coefficients.

FIG. 4 is a diagram showing blocks on the 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 code amount integrated values according to the first embodiment of this invention.

FIG. 7 is a block diagram showing a configuration of a conventional image compression encoding device.

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

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

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

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

FIG. 12 is a characteristic diagram showing the relationship between the coding time and the control code amount.

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

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

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

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

[Explanation of symbols]

 2 block forming circuit 3 DCT converting circuit 4 field memory 5 first quantizer 6 Huffman encoder 7 buffer memory 9 second quantizer 10 block code amount calculating circuit 11 initial scale factor calculating circuit 12 group target code amount Calculation circuit 13 Scale factor correction circuit 14 Code amount integration circuit

Claims (10)

[Claims] 1. An apparatus for dividing input image data into a plurality of blocks, and compressing each divided block into a predetermined code amount by an encoding method in which orthogonal transformation and variable length encoding are combined. An orthogonal transformer that orthogonally transforms the input image data block by block, a memory that writes the output data of the orthogonal transformer and reads it in a predetermined order, and a first quantizer that quantizes the output data of the memory. , An encoder for variable-length encoding the output of the first quantizer, a buffer memory for writing output data of the encoder at a constant rate after writing the output data of the encoder, and an output of the encoder The code amount accumulator that accumulates 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 are divided into blocks included in each group. 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 variable-length coded, and a block code amount output from the code amount calculator, one screen of the M number of screens. An initial quantized coefficient detector for predicting M different code amounts when quantized with the quantized coefficient and determining a quantized coefficient (initial quantized coefficient) for making one screen a predetermined code amount; Group code amount calculation for obtaining the total sum of the block code amounts output from the code amount calculator for each of the K groups and predicting the target code amount for each group when encoded with the initial quantization coefficient from the ratio And a prediction error between the actual code amount accumulated by the code amount integrator and the target code amount each time data of each group is output from the encoder, and the initial quantization coefficient is corrected. By the amount of the first quantizer Image compression encoding apparatus characterized by having a quantization coefficient corrector that corrects the coefficient. 2. The M and K are defined so that the number of blocks in one screen is a multiple of M × K, and allocation is performed so that the number of blocks corresponding to each scale factor of each group is the same. Item 1. The image compression encoding device according to Item 1. 3. The quantization coefficient corrector calculates a prediction error between the actual code amount accumulated by the code amount integrator and the target code amount each time the data of each group is output from the encoder, 2. The image compression coding according to claim 1, wherein the quantization coefficient of the next group is determined with the code amount obtained by subtracting the prediction error from the sum of the target code amounts of the next group and thereafter as the target code amount of the next group and thereafter. apparatus. 4. The quantization coefficient corrector calculates a prediction error between the actual code amount accumulated by the code amount integrator and the target code amount each time the data of each group is output from the encoder, Predicting the prediction error and the error (total coding error) when the entire screen is coded with the current quantization coefficient from the ratio of the coded data code amount and the uncoded data code amount prediction,
2. The image compression code according to claim 1, wherein the quantization coefficient of the next group is determined with the code amount obtained by subtracting all coding errors from the sum of the target code amounts of the next group and subsequent groups as the target code amount of the next group and subsequent groups. Device. 5. A code for setting a code amount (control code amount) when an uncoded block for making the code amount of one field a predetermined amount is encoded with a fixed length per block for each block. 2. A quantity setting device and a code amount controller for controlling the code amount for each block when the code amount accumulated by the code amount accumulator exceeds the control code amount. Image compression encoding device. 6. The image compression system according to claim 5, wherein two or more sets of code amount setters and code amount controllers are provided, and the control code amount and the code amount per block are set by a plurality of different combinations. Encoding device. 7. A block power calculator for obtaining a power sum for each block from output data of an orthogonal transformer, wherein a code amount controller gives a code amount proportional to the block power sum of uncoded blocks for each block. The image compression encoding apparatus according to claim 5, wherein the encoder is defined in 1. 8. A quantized coefficient and code amount assigned to each block encoded by a second quantizer calculated by a code amount calculator, and an initial quantized coefficient calculator. A block code amount predictor for predicting the code amount for each block when quantization is performed with the initial quantization coefficient from the relationship between the predicted quantized coefficient and the code amount, and the code amount controller is the block 6. The image compression coding apparatus according to claim 5, wherein a code amount proportional to a predicted code amount per hit is determined for each block to control the encoder. 9. A device for dividing one screen into a plurality of channels according to a predetermined rule and compressing the code into a predetermined code amount for each channel, wherein the input image data is orthogonally transformed for each block for each channel. An orthogonal transformer, a memory for delaying the output data of the orthogonal transformer, and a quantizer for quantizing the output data of the memory,
An encoder for variable-length encoding the output of the quantizer, and a buffer memory for outputting the output data of the encoder at a constant rate after writing the output data of the encoder are provided. An image compression encoding device, characterized in that a quantized coefficient (initial quantized coefficient) for obtaining a predetermined code amount for one screen is obtained. 10. A code amount accumulator for accumulating the code amount of output data of the encoder for each channel, and accumulating by the code amount accumulator each time data of each group is output from the encoder. 10. The quantizing coefficient corrector for determining the quantizing coefficient of the quantizer by correcting the initial quantizing coefficient with the prediction error between the actual code amount and the target code amount. Image compression encoding device.