JP2001238179A - Image recording and reproducing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image recording and reproducing apparatus which can reduce variation of the compressed file sizes. SOLUTION: This image recording and reproducing apparatus has a storage means which stores plural types of equalization tables for attaining all target file sizes and also stores the range of application of quantization tables decided previously for each target file size, a means which selects a quantization table within its application range that is decided to its target file size when the quantization tables are selected so that the compressed file sizes are equal to the target ones in a recording mode and a means which carries out the image compression processing via an image compressor by using the selected quantization table.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital VTR.
And the like.

[0002]

2. Description of the Related Art Images captured by a surveillance camera are
For example, a video recording / reproducing device that compresses data using a JPEG image compression / decompression device, records the data on a video tape, reads data recorded on the video tape, decompresses the data, and outputs the data is already developed. Have been.

In this type of video recording / reproducing apparatus, a target file size after compression is determined based on a recording time and a recording interval. The compression ratio is controlled so that the compressed file size becomes the target file size. Specifically, a quantization table (Q table) corresponding to a plurality of predetermined compression rates is prepared.
Then, the Q table is selected so that the compressed file size becomes the target file size.

The Q table is selected based on the compressed file size of the previous image. That is, if the file size of the previous image after compression is larger than the target file size, the Q table is selected so as to increase the compression ratio, and conversely, the file size of the previous image after compression is the target file size. If smaller than the file size,
The Q table is selected so as to lower the compression ratio.

Conventionally, the applicable range of the Q table has not been determined for each target file size. For this reason,
Depending on the image to be recorded, there is a problem that the variation in the file size after compression is large and the image quality is reduced.

For example, it is assumed that an image with a large amount of information is input after an image with a small amount of information is continuously input. When images with a small amount of information are successively input, the compression ratio is gradually lowered, so that a Q table having a considerably low compression ratio is selected. In this state, if an image with a large amount of information is input, the compressed file size of the image becomes considerably larger than the target file size. As a result, the quality of the images recorded on the video tape varies greatly, even though the recording mode is the same.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a video recording / reproducing apparatus which can reduce the variation in the file size after compression.

[0008]

According to a video recording / reproducing apparatus according to the present invention, at the time of recording, in a video recording / reproducing apparatus for compressing input image data by an image compression apparatus and then recording the compressed data on a recording medium, all target file sizes are set. A storage unit in which a plurality of types of quantization tables for realization are stored and an application range of a quantization table predetermined for each target file size are stored. When selecting the quantization table so that is the target file size,
A means for selecting a quantization table within an applicable range of a quantization table determined for a target file size, and means for causing an image compression device to perform compression processing using the selected quantization table. It is characterized by.

The upper limit of the application range of the quantization table is set to the lower compression side as the target file size increases, and the lower limit of the application range of the quantization table is set to the higher compression side as the target file size decreases. Is done.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a digital VTR that records and reproduces a video image captured by a surveillance camera will be described below with reference to the drawings.

FIG. 1 shows the configuration of a digital VTR. In FIG. 1, the audio signal processing circuit is omitted.

The digital VTR includes a video signal processing circuit 1,
A servo system (drum servo system and capstan servo system) 2, a system control circuit 3, a mechanical system 4, an operation panel 5, and the like are provided.

The video signal processing circuit 1 includes a decoder (A / D
Converter) 11, first FPGA (field programmable gate array) 12, field memory 13, JP
EG type image compression / expansion circuit 14, memory 16, formatter 18, signal recording / reproducing unit 19, second FPGA 2
0, an encoder (D / A converter) 21 and a microcomputer (hereinafter referred to as a microcomputer) 22.

The signal recording / reproducing unit 19 includes a recording amplifier, a reproducing amplifier, and a video head. The image compression / decompression circuit 14, the memory 16, and the formatter 18 are controlled by the second FPGA 20. First FPGA
The 12 and the second FPGA 20 are controlled by the microcomputer 22.

The operation at the time of recording will be described. Here, the case where the recording unit is one field unit will be described, but the present invention can also be applied when the recording unit is one frame unit.

At the time of recording, a surveillance camera (video camera)
The analog video signal sent from the
Is converted into digital image data. The image data obtained by the decoder 11 is stored in the first FPGA 1
Sent to 2.

The first FPGA 12 stores the input image data in the field memory 13 at an image capture period according to the recording time mode set by the user.
The image data stored in the field memory 13 is sent to an image compression / expansion circuit 14. Image compression / decompression circuit 14
Compresses the sent image data for one field using a Q table such that the file size after compression becomes the target file size. The target file size refers to a target size of a compressed file size of an image for one field.

A Q table whose compressed file size becomes the target file size is selected by the microcomputer 22, and the Q table data selected from the microcomputer 22 is transferred to the image compression / expansion circuit 14 via the second FPGA 20.
Sent to In other words, when the file size of the previous image after compression is larger than the target file size, the microcomputer 22 selects the Q table so as to increase the compression ratio, and conversely, selects the Q table after the compression of the previous image. If the file size is smaller than the target file size, the Q table is selected so as to lower the compression ratio.

The second FPGA 20 adds, to the encoded data obtained by the image compression / decompression circuit 14, Q table data used for compression together with additional information such as recording time information. Then, the encoded data to which the additional information and the Q table data are added is written to the memory 16.

Every time the amount of data written in the memory 16 becomes equal to the unit of one block (the amount of data for a predetermined number of tracks), data is read from the memory 16 and sent to the formatter 18. Is converted into data having a data structure that can be recorded on a video tape by the formatter 18.

The data obtained by the formatter 18 is recorded on a video tape (recording medium) 23 via a recording amplifier and a video head in a signal recording / reproducing unit 19.

As the Q table, a Q table for the luminance signal and a Q table for the color difference signal are separately prepared. A Q table control method for the luminance signal;
Since the control method of the Q table for the color difference signal is the same, only the Q table for the luminance signal will be described here.

As the Q table for the luminance signal, when an image with a small expected amount of information and an image with a large expected amount of information are input, the file size after compression is set to all the assumed target file sizes. A plurality of types of Q tables are prepared in advance in order to make it possible. In this example, as shown in FIG. 2, 60 types of Q tables Q1 to Q60 are prepared. Q30
Are the basic Q tables, and the other Q tables Q1
Q29, Q31 to Q60 are the basic Q table Q3
It is created by multiplying 0 by a coefficient N shown in FIG.

In this embodiment, the applicable range of the Q table is determined for each target file size. In the example of FIG. 2, two types of target file sizes (50 KBYT
E, 30 KBYTE) are shown.

The applicable range of the Q table includes an upper limit value (a Q table corresponding to the lowest compression rate in the applicable range), a lower limit value (a Q table corresponding to the highest compression rate in the applicable range), and an initial value. The value is defined. The upper limit of the applicable range is set to the lower compression side as the target file size increases. Conversely, the lower limit of the applicable range is set to a higher compression side as the target file size becomes smaller. In this example, the initial value is set to the upper limit of the applicable range.

The upper limit value and the lower limit value for each target file size are obtained by compressing each of the input images predicted by the digital VTR after compression of the images having a small amount of information and an image having a large amount of information as sample images. Is determined by selecting a value such that the file size of the file is controlled to the target file size.

The application range (upper limit value, lower limit value, and initial value) of a plurality of types of Q tables Q1 to Q60 for realizing all target file sizes and a Q table predetermined for each target file size are determined by a microcomputer. It is stored in the memory 22a on the 22 side.

At the time of compression by the image compression / expansion circuit 14,
The microcomputer 22 determines the Q determined for each target file size.
Select a Q table within the table's scope. As described above, since the applicable range of the Q table is limited for each target file size, the variation in the file size after compression can be reduced.

The operation at the time of reproduction will be described. At the time of reproduction, data read from the video tape 23 by the video head in the signal recording / reproducing unit 19 is temporarily stored in the memory 16 via the reproducing amplifier and formatter 18 in the signal recording / reproducing unit 19. Second FPGA
20 acquires additional information such as recording time information from the data stored in the memory 16. The additional information obtained by the second FPGA 20 is sent to the microcomputer 22.

The second FPGA 20 reads out data (encoded data and Q table data) other than the additional information from the data stored in the memory 16 for each field. The encoded data and Q table data read from the memory 16 are sent to the image compression / decompression circuit 14.

The image compression / decompression circuit 14 decompresses the coded data read from the memory 16 using the Q table data read from the memory 16 together with the coded data. Digital image data obtained by the image compression / expansion circuit 14 is stored in the field memory 13. The image data for one field stored in the field memory 13 is repeatedly read by the first FPGA 12 and sent to the encoder 21. The encoder 21 converts the sent image data into an analog video signal, and then sends it to a monitor (not shown).

[0032]

According to the present invention, it is possible to reduce the variation in the file size after compression.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a digital VTR.

FIG. 2 is a schematic diagram showing types of all Q tables prepared in advance and a Q table application range for each target file size.

[Explanation of symbols]

 Reference Signs List 1 video signal processing circuit 2 servo system 3 system control circuit 4 mechanism system 5 operation panel 11 decoder 12 first FPGA 13 field memory 14 image compression / decompression circuit 16 memory 18 formatter 19 signal recording / reproducing unit 20 second FPGA 21 encoder 22 Microcomputer 22a memory

Continuing on the front page F-term (reference) 5C053 FA11 FA22 GA11 GA14 GB06 GB21 GB28 GB34 GB36 JA22 JA30 KA03 KA08 KA24 LA01 LA06 5C054 EB05 EB07 EG06 EH07 FF03 GA01 GA04 GD09 HA18 5C059 KK22 LA01 MA00 MC14 PP04 RC16 RC32 SS04 RC32 SS TC18 TC38 TD15 UA02 UA33 5C078 BA21 CA02 DA01 DB07 9A001 BB02 BB03 BB04 DD09 EE02 EE04 EE05 HH27 HH31 JJ36 KK42 KK43 KZ60 LZ09

Claims (2)

[Claims] 1. A video recording / reproducing apparatus which records input image data on a recording medium after compressing the input image data by an image compressing apparatus during recording, stores a plurality of types of quantization tables for realizing all target file sizes. And storage means for storing a predetermined application range of the quantization table for each target file size. At the time of recording, the quantization table is stored so that the compressed file size becomes the target file size. Means for selecting a quantization table, when selecting, within an applicable range of the quantization table defined for the target file size;
Means for causing the image compression apparatus to perform compression processing using the selected quantization table. 2. The upper limit of the applicable range of the quantization table is:
2. The method according to claim 1, wherein the larger the target file size, the lower the compression level is set, and the lower limit of the applicable range of the quantization table is set to a higher compression side as the target file size decreases. Video recording and playback device.