KR0141192B1 - Data writing method and apparatus for trick play - Google Patents

Abstract

Disclosed are a method for creating a data for trick play of a digital video tape recorder capable of appropriately representing a moving image, and an apparatus suitable for the same.

A method for generating trick play data according to the present invention includes the steps of quantizing an AC coefficient excluding a DC coefficient among DCT conversion coefficients by a given quantization step; Runlength coding the quantized AC coefficient according to the frequency order according to the target bit quantity; An evaluation process of evaluating the result of run length coding and quantizing step by adaptively adjusting the quantization step to include a large number of AC coefficients having a large value, thereby repeating the quantization process and run length coding process; And generating a trick play data as a quantized AC coefficient and an applied quantization step in the DC coefficient and the run length coding process.

The method for creating trick play data according to the present invention has an effect of sufficiently reproducing a motion component of an image by including more AC coefficients having a larger value when creating trick play data.

Description

Method and device for creating data for trick play

1 is a block diagram showing a conventional compression protection device.

FIG. 2 is a diagram showing the conversion result of the DCT converter in FIG.

3 is a diagram showing a method for creating trick play data according to the present invention.

4 is a block diagram showing an embodiment of a trick play data generating apparatus according to the present invention.

TECHNICAL FIELD The present invention relates to a method for creating trick play data of a digital video tape recorder, and more particularly, to an improved method and apparatus for generating trick play data for enabling a proper reproduction of a large number of motion components.

Trick play refers to an operation in which the video tape recorder is moved forward or backward at a faster speed than the normal play mode PLAY.

In the analog video tape recorder, the signals are recorded in a certain pattern according to the scanning order, and there is some correlation between the frame video signals, so that a part of the recorded signals can be regularly sampled, and appropriately combined to reproduce the original image. However, in the digital video tape recorder, since the data blocks are not regularly recorded as in the analog video tape recorder, the original picture cannot be reproduced in this manner.

Therefore, in the digital video tape recorder, a technique of making separate data blocks for trick play during recording and mixing them appropriately into the data blocks for normal reproduction is used.

The data block for trick play has a relatively small amount of information compared to the data block for normal play, and can cope with high speed playback.

This is based on the logic that during trick play, the image quality may be lowered than during normal play.

Patent application 94-3495 (1994.2.25) filed by the present applicant discloses a technique for alternately recording data blocks for normal reproduction and data blocks for trick play.

In DCT (Discrete Cosine Transform) based image compression coding, a trick play that includes DC coefficients and AC coefficients of several low frequency components among transform coefficients in the frequency domain generated as a result of DCT transformation of a block having a size of 8x8 pixels. Create a datablock for the dragon.

As a result of the DCT conversion, a portion of the energy of the signal is concentrated in the low frequency region including the DC, so that only a few AC coefficients including the DC coefficient can reproduce the video signal having the image quality suitable for trick play.

However, in the case of an image signal with a large movement, the original image cannot be reproduced sufficiently. This is because a large-motion image signal contains a lot of high frequency components, and the DCT conversion coefficient included in the trickle-use data block excludes this high frequency coefficient.

Accordingly, an object of the present invention is to provide a method for creating a trick play data suitable for sufficiently reproducing a large motion image signal, which has been created to solve the above problems.

Another object of the present invention is to provide a trick play data generating apparatus suitable for sufficiently reproducing a large moving image signal.

According to the present invention, there is provided a method of generating trick play data, the method comprising: quantizing an AC coefficient excluding a DC coefficient among DCT conversion coefficients by a given quantization step; Runlength coding the quantized AC coefficient according to the frequency order according to the target bit quantity; Evaluating the results of the runlencoding and adaptively adjusting the quantization step to include a large number of AC coefficients to repeat the quantization process and the runlength coding process; And generating data for trick play as the quantized AC coefficient and the applied quantization step in the DC coefficient and the run length coding process.

According to another aspect of the present invention, there is provided a trick play data generating apparatus comprising: a quantizer for quantizing an AC coefficient excluding a DC coefficient among DCT conversion coefficients by a given quantization step; A run-length coder configured to run-length code the transform coefficients quantized in the quantizer by a given target bit amount; If there is an AC conversion coefficient having a value greater than 1 by checking the AC conversion coefficient not included in the run length coding in the run length coding unit 48, the quantization step applied by the quantization unit 46 is increased to quantize and run. A run length coding evaluation unit to perform length coding again, and to terminate quantization and run length coding when there is no AC conversion coefficient having a value greater than 1; When the end of the coding is recognized by the run length coding evaluation unit, it comprises a trick play data processing unit for outputting the DC coefficient, the output from the run length coding unit and the quantization step applied to the quantization unit.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

Fig. 1 shows a conventional trick play data generating apparatus, showing the contents disclosed in patent application 94-3459.

The apparatus shown in FIG. 1 has a structure for generating normal reproduction data and trick play data in parallel, multiplexing them, and outputting the same.

The block forming unit 11 converts the input frame image data into a DCT change block having a size of 8x8 pixels and outputs the converted image.

The first DCT converter 12 converts the DCT conversion blocks in the time domain into 64 DCT conversion coefficients in the frequency domain and outputs them.

The energy of the change result signal in the first DCT converter 12 is concentrated in the low frequency region including the DC coefficient.

The quantization unit 13 quantizes the DCT transform coefficient output from the first DCT change unit 12 by a predetermined quantization step.

The variable length encoder 14 compresses the data output from the quantization unit 13 and outputs the compressed data to the multiplexer 18.

The block reforming unit 15 sub-samples the pixels included in the DCT conversion block formed by the block forming unit 11 according to a predetermined rule, so that the trick play DCT conversion block is sampled between adjacent blocks. It may be taken, or it may be extracted between blocks separated to some extent.

The second DCT converter 16 operates in the same manner as the first DCT converter 12, and converts the DCT change blocks for trick play in the time domain into 64 DCT conversion coefficients in the frequency domain and outputs the converted DCT conversion coefficients.

The trick-blade data processor 17 forms the trick play data having only a few AC coefficients including DC from the conversion coefficient generated as the DCT conversion result and outputs the trick play data to the multiplexer 18.

The multiplexer 18 multiplexes the normal play data provided by the variable length encoding unit 14 or the trick play data provided by the trick play data processing unit 17 in a predetermined order.

The data output from the multiplexer 18 is recorded on the tape through a recording unit (not shown) after the error correction code is added through the error correction code unit 19.

2 is a diagram showing a conversion coefficient generated as a DCT conversion result.

The conversion coefficient generated as a result of the DCT conversion of the 8 × 8 pixel DCT conversion block includes one DC coefficient and 63 AC coefficients.

In FIG. 2, the upper left side is the DC coefficient, and the lower right side is the 63rd AC coefficient. Moreover, it arrange | positions so that a frequency component may become low toward the upper left side.

As a result of the DCT conversion, most of the signal's energy is concentrated at a few low frequencies, including DC, so that they can reproduce the original picture to some extent.

In order to use this, the data for trick play is to include only a DC coefficient and a few AC coefficients.

As a specific method, scanning is performed by a known zigzag scan method from a low frequency coefficient including a DC coefficient, and run-length coding is performed until the target bit amount is reached.

As a result of run length coding, the number of coefficients included in the data for trick play is unspecified.

Since run-length coding is performed in the order of the DC coefficients and the frequency, the index of the restored coefficients is also arranged in order from the DC coefficients.

However, when the motion component of the image signal is large, the energy of the signal is distributed to the high frequency side. In this case, since it is difficult to sufficiently reproduce the original image only by the low frequency component, it is necessary to include more high frequency components.

3 is a flowchart showing a method of forming a data for trick play according to the present invention.

In the present invention, when generating data for trick play, the AC coefficient is selected according to the order of the conversion coefficient, that is, the order from the low frequency to the high frequency, as in the conventional method, but the quantization step of the conversion coefficient is varied so that It is characterized by increasing the number of relatively large AC coefficients included.

First, the AC coefficient excluding the DC coefficient from the transform coefficient generated as a result of the DCT conversion is quantized by the given initial quantization step (step 300).

In operation 300, the quantized result is runlength-coded according to the target bit amount.

By checking the magnitude of the coefficient not included in the run coding, it is checked whether there is a coefficient having a value larger than the quantization step applied in the quantization (step 32).

If there is a coefficient having a value larger than the applied quantization step, the quantization step is increased in step 330 and the flow returns to step 300.

As a result of the quantization, values smaller than the quantization step are zero among AC coefficients, and only values larger than the quantization step have a nonzero value.

As the size of the quantization step increases, the probability of including a high frequency AC coefficient with a large value increases.

Since the larger the number of motion components, the higher the AC coefficient of the high frequency component is, the AC coefficient of the high frequency component having a larger value can be included by adaptively changing the quantization step. As a result of this operation, it is possible to sufficiently reproduce the motion component in the reproduced image.

In creating the trick-play data of a large motion component image, the resolution of the transform coefficient (resolution for expressing the transform coefficient) decreases due to the increase in the quantization step. It is in a relationship and cannot be avoided.

In order to prevent the resolution of the conversion coefficient from being excessively degraded by the large AC coefficient present in the unnecessary high frequency region, the range of the frequency component to be inspected may be limited in step 310. For example, by limiting the inspection object to only the tenth AC coefficient, the unnecessary high frequency region is limited.

If there is no coefficient having a larger value than the applied quantization step, the DC coefficient, the AC coefficient included in the run length coding in step 310, and the applied quantization step are run length coded and output as the trick play data (step 340).

4 is a block diagram showing a device suitable for a trick play data creation method according to the present invention, showing an example of a device for forming trick play data from a data string compressed and encoded by MPEG (Moving Picture Expert Group) standard. will be.

I picture (Intra picture) as a result of compression encoding according to MPEG standard as well known. P picture (Previous picture) and B picture (Bidirectional picture) are generated.

Among them, the I picture is a reference picture in trick play or the like and can be independently restored without regard to other pictures.

The trick play data is extracted from the data of the I picture.

In the apparatus shown in FIG. 4, reference numeral 40 denotes a buffer memory for extracting only the data string of the I image from the compressed coded image data, and 42 is compressed from the data string of the I image output from the buffer memory 40. A variable length decoder for restoring the quantized transform coefficients before encoding, and 44 is an inverse quantizer for dequantizing the quantized transform coefficients output from the variable length decoder 42 and restoring the original transform coefficients. to be.

46 is a quantizer which requantizes the AC coefficient excluding the DC coefficient among the transform coefficients output from the inverse quantizer 44 by a given quantization step, and 48 is a target bit amount of the given quantized transform coefficient by the quantizer 46. The run length coding unit performs run length coding, and 50 is a run length coding evaluation unit that evaluates the run length coded result and readjusts the quantization step. 52 is a trick to run-length code the DC coefficient, the output from the run length coding unit 48 and the quantization step applied by the quantization unit 46 when the end of coding is recognized by the run length coding evaluation unit 50. Play data processing section.

The data sequence of the image and the trick play data output from the trick play data processing unit 52 are provided to a recording unit (not shown) through the multiplexer 54 to be recorded on the tape.

In the initial operation, the quantization unit 46 performs quantization by a given initial quantization step, and then performs quantization by applying the quantization step adjusted by the run length coding evaluation unit 50.

The quantized result in the quantization unit 46 is run length coded in accordance with the target bit amount in the run length coding unit 48.

The number of AC conversion factors involved in run length coding is unspecified.

The run length coding evaluation unit 50 checks whether the AC conversion coefficient having a value greater than 1 by checking the AC conversion coefficient not included in the run length coding in the run length coding unit 48.

If there is an AC conversion coefficient having a value greater than 1, the quantization step applied by the quantization unit 46 is increased. If there is no AC conversion coefficient having a value greater than 1, the DC conversion coefficient and the quantization unit 46 included in the run length coding by the run coefficient coding unit 48 are controlled by controlling the data processing unit 52 for trick play. Run quantization of the quantization system applied in.

As described above, the method for creating a trick play data according to the present invention has an effect of sufficiently reproducing a motion component of an image by including more AC coefficients having a larger value when creating a trick play data.

In this specification, an example of adaptively adjusting the quantization step in the quantization unit is disclosed, but it should be noted that the quantization step may be fixed to a predetermined value and used non-adaptively. In this case, the quantization step may be determined according to the amount of motion of the image or may be determined according to the size of the motion component to be expressed.

Claims (3)

CLAIMS 1. A method for generating trick play data as a DC coefficient and some AC coefficients in a DCT conversion coefficient, the method comprising: quantizing an AC coefficient excluding a DC coefficient among the DCT change coefficients by a given quantization step; Runlength coding the quantized AC coefficient according to a frequency order according to a target bit amount; Evaluating the results of the sound run length coding and adaptively adjusting the quantization step to include a large number of AC coefficients to repeat the quantization process and run length coding process; And generating data for trick play as a quantized AC coefficient and an applied quantum hose step in a DC coefficient and run length coding process. The method of claim 1, wherein the evaluation process examines an AC coefficient not included in the run length coding and adjusts the quantization step until there is no AC coefficient having a value larger than the applied quantization step. A method of creating data for trick play, characterized by repeating the coding process. An apparatus for generating trick play data as a DC coefficient and some AC coefficients in a DCT conversion coefficient, comprising: a quantizer for quantizing an AC coefficient excluding a DC coefficient in a DCT conversion coefficient by a given quantization step; A run-length coder configured to run-length code the transform coefficients quantized by the quantizer by a given target bit amount; If there is an AC conversion coefficient having a value greater than 1 by checking the AC conversion coefficient not included in the run length coding in the run length coding unit, the quantization step applied in the quantization unit is increased to repeat the quantization and run length coding. A run length coding evaluation unit configured to perform quantization and run length coding when there is no AC conversion coefficient having a value greater than 1; And a trick play data processing unit for outputting a DC coefficient, an output from the run length coding unit, and a quantization step applied to the quantization unit when the end of coding is recognized by the run length coding evaluation unit.