JPH03252284A - Data compressor - Google Patents

Abstract

PURPOSE:To attain a simple and high speed processing by applying filter processing to a data, predicting data quantity through the calculation including addition and adjusting a quantized step number corresponding to the result of prediction. CONSTITUTION:An inputted picture data is inputted to a code quantity prediction device 1 directly or via a movement compensation and differential data generator 6. The code quantity prediction device 1 predicts the code quantity from an inputted data, sets the band limit and the quantization stop corresponding to the predicted value and outputs the result to a pre-filter (band limit means) 2 and a quantizer (quantization means) 4. The pre-filter 2 applies band limit corresponding to the band limit set by the code quantity prediction device 1 and outputs the value to a DCT circuit 3. The data processed by the DCT circuit 3 is inputted to a quantizer 4, in which the data is quantized by the quantization step number set by the code quantity prediction device 1. The quantized data is inputted to a coder 6, where the data is coded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data compression device suitable for use, for example, when compressing a color still image and recording it on a predetermined recording medium.

[Prior Art] When recording image data on a recording medium such as a magnetic disk, the data is compressed for efficient recording. For this compression, for example, image data is divided into blocks each having NXN (or NXM) pixels, and each block is orthogonally transformed. The orthogonally transformed data is further quantized by a predetermined quantization step and then zero-run length encoded or Huffman encoded. Compressing data in this way effectively compresses the data, but the amount of code varies depending on the image.

Therefore, conventionally, the following control has been performed to keep the code amount constant.

The first method is to calculate the amount of data actually quantized at a predetermined quantization step, and then adjust the number of quantization steps according to the calculation result so that the amount of data reaches the desired value. The method is to change it and redo the quantization.

The second method focuses on the fact that the coefficients of the data after orthogonal transformation have a predetermined relationship with the code amount, and calculates the sum of squares of the coefficients for each block. Each block is divided into, for example, four classes according to its size, and more bits are allocated to blocks in classes with larger amounts of data, and fewer bits are allocated to blocks in smaller classes. It is.

[Problems to be Solved by the Invention] However, in the first method described above, the process of actually calculating the code amount of quantized data must be repeated at least twice, so high-speed processing is not possible. Have difficulty.

Furthermore, in the second method described above, not only it is necessary to perform orthogonal transformation processing, but also information indicating the class must be added, which increases the amount of code and requires complicated processing.

The present invention was made in view of this situation, and enables simple and high-speed processing.

[Means for Solving the Problem] A data compression device according to claim 1 is a data compression device that divides input data into blocks of predetermined pixels, performs orthogonal transformation, quantizes, and further encodes the data. , a processing means for filtering input data, a calculation means for performing an operation including at least addition on the data processed by the filter processing means, and a code amount value for converting the output of the calculation means into a corresponding code amount value. A conversion means, a target value setting means for setting a target value of data amount, and a target value set by the target value setting means and a code amount value outputted from the code amount value conversion means are compared, and the difference is dealt with. and a quantization means that quantizes the orthogonally transformed data in accordance with the quantization step value outputted by the quantization step transformation means. The data compression device according to claim 2 is a data compression device that divides input data into blocks each having a predetermined number of pixels, performs orthogonal transformation, quantizes, and further encodes the input data, and filters the input data. a processing means for processing, a calculation means for performing an operation including at least addition on the data processed by the filter processing means, a code amount value conversion means for converting the output of the calculation means into a corresponding code amount value, and a code amount value converting means for converting the output of the calculation means into a corresponding code amount value; A target value setting means for setting a target value, compares the target value set by the target value setting means and the code amount value outputted from the code amount value converting means, and outputs a band limit value corresponding to the difference. and a band limiter that limits the band of the data prior to orthogonal transformation in accordance with the band limit value output from the band limit value converter.

[Operation] In the data compression device according to the first aspect, the data amount is predicted by filtering the data and further adding, for example, absolute values.

Then, the number of quantization steps is adjusted according to the prediction result.

Furthermore, in the data compression apparatus according to the second aspect of the present invention, the amount of data is similarly exceeded in advance, and the band limit value is adjusted in accordance with the prediction result.

Therefore, in either case, simple and high-speed processing becomes possible.

[Embodiment] FIG. 1 is a block diagram showing the configuration of an embodiment of a data compression device of the present invention.

The input image data is input to the code quantum θ11 unit 1 directly or via the motion compensation and difference data generator 6. The code quantum θ-reducer 1 predetermines the code amount from the input data, sets the band limit value and the number of quantization steps corresponding to the predicted value, and converts the code amount to the input data. 4 (quantization means).

The filter 2 band-limits the data supplied from the code amount predictor 1 in accordance with the band limit value set by the code amount predictor 1, and performs DCT (Discrete C
(osine transfer) circuit 3. D
The data processed by the CT circuit 3 is input to the quantizer 4 and is quantized by the number of quantization steps set by the code amount predictor 1. The quantized data is sent to the encoder 5
is input and encoded.

The code amount predictor l is configured as shown in FIG. 2, for example.

The input image data is temporarily stored in the frame memory 11. The data read from the frame memory 11 is filtered by the operator processor 12 (processing means), and then input to the absolute value sum calculation circuit 13 (calculation means), where it is calculated. The output of the absolute value sum calculation circuit 13 is
is input to the code amount value converter 14 (code amount value converting means),
It can be converted to a code amount value using a standard quantization step and a standard band limit value. This code amount value is output to the quantization step converter 15 (quantization step conversion means) and the band limit value converter 16 (band limit value conversion means).

A target value for the amount of data to be set is input to the quantization step converter 15 and the band limit value converter 16 from a control data transmission circuit (target value setting means). The quantization step converter 15 and the band limit value converter 16 compare the code amount value inputted from the code amount value converter 14 with the target value, and convert the quantization step value and band limit value corresponding to the error. , are output to the quantizer 4 and the Buri filter 2, respectively.

Next, its operation will be explained.

Input image data is input to the frame memory 11, and image data for one frame is temporarily stored therein. The data stored in frame memory 11 is read out, provided to operator processor 12, and filtered.

This filter processing will be explained with reference to FIG. 3.

FIGS. 3 ra) to 3 (C) each represent nine (3×3) coefficients of a bypass filter, a low-pass filter, or a Laplacian when each process is performed.

3×3 pixel data of a predetermined area is read out from the frame memory 11, and these data and 3×3 pixel data shown in FIG.
A factor of 3 is multiplied between the corresponding positions. The nine pieces of data obtained as a result of this multiplication are further added.

Next, the area read out from the frame memory 11 is shifted, for example, by one pixel to the right, and the 3X
Similar processing can be executed for the pixel data of No. 3. Thereafter, similar processing is performed on all data for one frame.

At this time, the amount by which the area is sequentially shifted is not 1 pixel but 2 pixels.
It can also be a pixel, three pixels, etc.

The data thus filtered is input to the absolute value sum calculation circuit 13. The absolute value sum calculation circuit 13 receives the 3X data from the operator processor 12 as described above.
Each time 3 pixel data are filtered, the absolute value of one piece of data is calculated, and the absolute value is added for one frame. This added value (sum of absolute values) is input to the code amount value converter 14.

The absolute value sum outputted by the absolute value sum calculation circuit 13 approximately corresponds to the code amount, as shown in FIG.

That is, when a predetermined sum of absolute values is given, the code amount of the image data is represented by the hatched area in FIG. The code amount value converter 14 is, for example, RO
As shown by the solid line in FIG. 4, the average value of the amount of codes corresponding to a predetermined sum of absolute values is stored.

Therefore, the code amount value change J! i! ! The unit 14 converts the absolute value sum input from the absolute value sum calculation circuit 13 into a corresponding code i value, and outputs it to the quantization step converter 15 and the band limit value converter 16.

The control data value transmitting circuit 17 outputs a preset target value of data amount to the quantization step converter 15 and the band limit value converter 16. The quantization step converter 15 and the band limit value converter 16 are also configured by, for example, a ROM, and each stores a corresponding number of quantization steps and a band limit value appropriate for obtaining a predetermined amount of code. . Following,
The quantization step converter 15 and the band limit value converter 16 are
Compare the code amount value input from the code amount value converter 14 and the target value input from the control data value transmitting circuit 7,
Corresponding to the error, the number of quantization steps and band limit value appropriate for obtaining the set target value are read out and output to the quantizer 4 and the Buri filter 2.

For example, as shown in FIG. 5, the Buri filter 2 is a filter with a characteristic of 15 scales in which the band limit value (cutoff frequency) sequentially changes by 1 in the range from 5/16 to 1/16 of the reference value. , and selects a filter with characteristics corresponding to the band limit value input from the band limit value converter 16. The data band-limited by this selected filter is
It is supplied to the T circuit 3.

Alternatively, the brifilter 2 can also be configured as shown in FIG.

In this embodiment, the Brifilter 2 includes a filter 21, multipliers 22, 23, and an adder 24. For two filters, as shown in Figure 7, the reference value is 1.
It has a band limit value of /2.

After the input data is band-limited by the filter 21, it is input to the multiplier
6 are multiplied by each coefficient.

Furthermore, the input data that has not passed through the filter 21 is sent to the multiplier 23.
You can enter from 16/16 to O according to the level.
/16 are multiplied by each coefficient. The outputs of multipliers 22 and 23 are added by adder 24 and output to OCT circuit 3.

Even in this case, the same operation as shown in FIG. 5 can be executed.

The DCT circuit 3 in Table 1 divides the input data into blocks and orthogonally transforms them. The orthogonally transformed data can be input to the quantizer 4.

The quantizer 4 quantizes the input data by the number of quantization steps set by the quantization step converter 15 and outputs it to the encoder 5. The encoder 5 performs run-length encoding or Huffman encoding on the quantized data.

Alternatively, both run-length encoding and Huffman encoding are performed.

In the above, the input image data is input as is to the code amount predictor 1 and processed.
After motion compensation is performed in the motion compensation and difference data generator 6, a difference between the reference image data and the interframe predicted image data may be generated, and this difference data may be input to the code amount predictor 1. can.

Furthermore, although the sum of absolute values of the outputs of the operator processor 12 is calculated, the sum of the square values of each output (sum of squares) or the average value of the sum of square values (mean square value) may be calculated.

Further, in the above description, both the band limit value and the number of quantization steps are controlled, but either one may be controlled.

[Effects of the Invention] As described above, according to the data compression device according to claim 1, data is filtered, and further, absolute value addition, 2
By performing arithmetic processing including addition of multiplication and addition, root mean square, etc.,
According to the data compression device according to claim 2, the data amount is similarly predicted and the number of quantization steps is adjusted according to the prediction result. Since the band limit value is adjusted in accordance with the results of ``11'', simple and high-speed processing becomes possible in any case.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a data compression device of the present invention, FIG. 2 is a block diagram showing the configuration of an embodiment of the code amount predictor in the embodiment of FIG. 1, and FIG. (a
) to (c) are diagrams explaining the operation of filter processing in the embodiment of FIG. 2, FIG. 4 is a diagram explaining the characteristics of the code amount value converter in the embodiment of FIG. 2, and FIGS. 7 is a diagram illustrating the characteristics of the BRI filter shown in FIG. 1, and FIG. 6 is a block diagram showing the configuration of one embodiment of the BRI filter shown in FIG. 1. 1... Code quantum θ11 unit, 2... Buri filter, 3...
...DCT circuit, 4...quantizer, 5...encoder,
6...Motion compensation and difference data generator, 11...Frame memory, 12...Operator processor, 13...
・Absolute value sum calculation circuit, 14"... code amount value converter, 15
...Quantization step converter, 1.6...Band limit value converter, 17...Control data value transmission circuit, 21...
Filter, 22.23... Multiplier, 24... Adder.

Claims (2)

[Claims] (1) A data compression device that divides input data into blocks of predetermined pixels, performs orthogonal transformation, quantizes, and further encodes the data, comprising: processing means for filtering the input data; and the filter processing means. a calculation means for performing an operation including at least addition on the data processed by the calculation means; a code amount value conversion means for converting the output of the calculation means into a corresponding code amount value; and a target value setting for setting a target value of the data amount. and a quantization step of comparing the target value set by the target value setting means and the code amount value outputted from the code amount value converting means and outputting a quantization step value corresponding to the difference. A data compression device comprising: a transformer; and a quantizer that quantizes orthogonally transformed data in accordance with the quantization step value output by the quantization step transformer. (2) A data compression device that divides input data into blocks of predetermined pixels, performs orthogonal transformation, quantizes, and further encodes the data, comprising: processing means for filtering the input data; and the filter processing means. a calculation means for performing an operation including at least addition on the data processed by the calculation means; a code amount value conversion means for converting the output of the calculation means into a corresponding code amount value; and a target value setting for setting a target value of the data amount. means, and a band limit value conversion for comparing the target value set by the target value setting means and the code amount value outputted from the code amount value converting means and outputting a band limit value corresponding to the difference. A data compression device comprising: means for band limiting data before orthogonal transformation in accordance with the band limit value outputted from the band limit value converting means.