JP2558963B2 - Recording and playback device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing apparatus for digital signals, and more particularly to a recording / reproducing apparatus for image data compressed and encoded in variable length.

[0002]

2. Description of the Related Art When an image signal is recorded and reproduced as digital data on a storage medium, it is very difficult to record and reproduce the moving image signal in real time because the amount of information is very large. For example, when an NTSC composite signal is quantized with a sampling frequency of 4 fsc (fsc is a color subcarrier frequency) of 8 bits, a transfer rate of about 120 Mbps is required. However, it is technically very difficult to create a recording / reproducing system capable of realizing a transfer rate of 120 Mbps. Therefore, when recording / reproducing on a storage medium, real-time processing is possible by using a plurality of recording / reproducing means and reducing the transfer rate per recording / reproducing means.

However, even if real-time processing is possible in this way, recording and reproducing all moving image signal information as it is on a storage medium having a limited storage capacity limits the recording and reproduction time. It will be. Therefore, in a recording / reproducing apparatus for a digitized moving image signal, compression encoding is performed to such an extent that deterioration of information of an original signal is not noticeable, recording is performed, and decoding processing is performed at the time of reproduction to facilitate real-time processing of recording / reproduction. At the same time, the recording and reproducing time is prolonged. As an example of the compression algorithm, data of several frames or fields are grouped into one group, and at least one frame or one field of data is compressed within a frame or field with a relatively low compression rate. Other data is compressed between frames or fields with a relatively high compression rate. By combining the intra-frame and inter-frame compression or the intra-field compression and the inter-field compression in this way, the overall compression rate is improved and the image deterioration is relatively suppressed.

Further, the compression rate is further increased by performing variable length coding such as Huffman coding. When this compression-encoded data is digitally recorded / reproduced on a storage medium, data conventionally compression-encoded within a frame or field and data compression-encoded between frames or fields are arranged in a time series. Recording / reproducing was performed by the recording / reproducing means. However, in the variable length compression coding method as described above, the amount of coded data generally changes remarkably depending on the difference in the correlation of the input image signals, and the transfer rate may change greatly.

On the other hand, since the transfer rate of information between the conventional storage medium and the recording / reproducing means is generally determined by the performance of the storage medium, the compression rate of encoded data is low, that is, the amount of information after compression is small. If there is a large amount, the encoded data amount exceeds the maximum transfer speed between the storage medium and the recording / reproducing head, and it may not be possible to process in real time, which may make it difficult to record / reproduce data in real time. There was a nature. Also,
When the amount of information after compression is small, there are problems such as a waiting time for recording / reproducing operation and an empty area in the storage medium.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks and enables recording / reproduction of a compression-coded digital video signal of variable length in real time without depending on the degree of correlation of the input video signal. It is an object of the present invention to provide a recording / reproducing apparatus capable of continuously recording / reproducing information without waiting time.

[0007]

In order to achieve this object, the present invention predetermines a maximum value of the amount of information after compression of an image digital signal in a specified time unit (at least 2 fields or 2 frames or more). The maximum data transfer rate is predetermined and the data transfer rate between the storage medium and the recording / reproducing apparatus is adaptively changed for each specific time unit.

[0008]

Operation: Specific time (at least 2 fields or 2
The maximum value of the total amount of information after compression is defined by averaging the information amount more than the maximum value of the information amount after compression for one field or one frame. It is possible to reduce the data transfer rate at the moment between the recording / reproducing device and the storage medium. Since the transfer speed of the recording / reproducing means and the storage medium is adaptively changed in a specific time unit to record / reproduce, a continuously compressed moving image digital signal can be recorded / reproduced in real time. Further, since the information recording density of the storage medium can be lowered when the compression rate is low, inter-code interference due to adjacent codes which occurs when the recording density is high can be reduced, and the error rate of the reproduced signal can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the outline of a recording / reproducing apparatus. An image signal analog-input by Y, U, V (Y is a luminance signal, U, V is a color signal) from an external device is used by the A / D converter 1 to sample the Y signal at a sampling frequency of 13.5 MHz.
The z, U, and V signals are each quantized with 8 bits at a sampling frequency of 6.75 Hz, and the quantized data is loaded into the frame memory 2. At this time, the total amount of data in one second is 216 Mbits. The frame memory 2 may directly input the digitized image signal. The image signal captured in the frame memory 2 is sent to the compression encoder 3 at least faster than the data transfer rate at the time of capturing, and the compression encoding process is performed.

At this time, the compression encoder 3 is encoded in advance so as to regulate the total amount of data within a specific time. For example, the average compression rate is about 1/43 when compression encoding is performed so that the total amount of data for 30 frames per second is limited to 5 Mbits or less. Here, assuming that only one frame out of 30 frames contains a very high frequency component, the deterioration of the image becomes conspicuous unless the compression rate of the one frame is kept low.

Therefore, when the compression rate is suppressed to about 1/20, the data amount after compression is 0.36 for that frame.
Since it is M bits, a transfer rate of 10.8 Mbps is required when only looking at this frame. However, if the other frames do not contain such a high frequency component and can be compressed at a high compression rate, the corresponding data can be distributed to the frames having a high frequency component to reduce the average transfer rate.

That is, the maximum transfer rate is 10.8 Mbp by collectively processing the image signals for 30 frames.
It is possible to reduce from s to 5 Mbps. At this time, the compression rate of the other frames excluding one frame containing the high frequency component is 1/45, which is not so high as compared with the original 1/43, so that the deterioration of information can be minimized.

The data encoded as described above is sent to the transmission buffer 4. The data transfer rate between the compression encoder 3 and the transmission buffer 4 is at least higher than the data transfer rate between the transmission buffer 4 and the recording processor 5. The data sent to the transmission buffer 4 is read at a read speed determined according to the total amount of encoded data.

For example, in the case of 5M bits, 5Mbp
In the case of s and 4 Mbits, the data is read at a speed proportional to the data amount, such as 4 Mbps. The read data is sent to the recording processor 5. The recording processor 5 divides the sent data into data of a certain fixed amount, for example, every 1 Kbyte, and collects the data as one unit.

If the data amount is 5 Mbits, it is divided into 625 units. The data collected for each unit is sent to the optical pickup 6 after adding a code indicating the head of the unit or data indicating the attribute of the unit, for example, a code indicating the transfer rate of the unit. The transfer rate at this time is also sent at a rate proportional to the amount of data, and 625 units can be processed in one second. The recording frequency changes in accordance with the sent data, the laser light is modulated at that frequency, and recorded on the optical disc 13 as digital data.

Regarding reproduction, the data reproduced from the optical disk 13 is binarized by the optical pickup 7 through the reproduction processor 8 and sent to the reception buffer 9 as reproduction data together with the reproduction clock. When passing through the reproduction processor 8, the information is read while recognizing the beginning of the unit. Also,
The additional information data added by the recording processor 5 is removed. Data is read from the reception buffer 9 at a transfer rate that is at least higher than the transfer rate between the reproduction processor 8 and the reception buffer 9, and the data is sent to the compression decoder 10 to be decoded. After the decoded image signal data is sent to the frame memory 11, it is read from the frame memory 11 at a constant transfer rate, and the D / A converter 1
It is output to the outside as an analog image signal after passing through 2. Alternatively, the data read from the frame memory 11 is directly output as digital data to the outside.

Although the recording / reproducing apparatus has been described in the embodiment, the recording apparatus or the reproducing apparatus may be independent. Further, the optical pickups 6 and 7 may be common.

[0019]

As described above, according to the present invention, since the maximum amount of data and the transfer rate after compression and encoding to variable length are determined in advance, the encoded data of a certain specific time unit is recorded and reproduced in real time. It has become possible. Further, when the amount of information after compression is small, the data transfer rate is slowed down to reduce the information recording density, so that it is possible to obtain a reproduced signal of good quality with little inter-code interference.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a recording / reproducing apparatus of an embodiment of the present invention.

[Explanation of symbols]

 1 A / D converter 2, 11 frame memory 3 compression encoder 4 transmission buffer 5 recording processor 6, 7 optical pickup 8 reproduction processor 9 reception buffer 10 compression decoder 12 D / A converter 13 optical disk

Claims (1)

(57) [Claims] 1. A device for recording / reproducing an image digital signal compression-encoded in a variable length, wherein a maximum value of the information amount after compression of the image digital signal for a specified time of at least two fields is a predetermined value. means for compression encoding the following, means for dividing a variable length digital data compressed and encoded by said compressing encoding means in units of a fixed length, and means for recording and reproducing the divided data in the specified time , The relative speed between the recording / reproducing means and the recording medium
A unit that is divided as the fixed-length unit while keeping it constant
Depending on the number of
Recording / reproducing control for controlling the recording / reproducing means to change the
Recording and reproducing apparatus characterized in that it comprises a means.