1. Field of the Invention
The present invention relates to an apparatus for recording a moving image and, more particularly, to an apparatus capable of compressing the amount of information by using a correlation between pictures or to an apparatus capable of effecting compression so that each picture has a different amount of information.
2. Description of the Related Art
A digital video tape recorder (VTR) is known as one type of image recording apparatus arranged to digitally compress moving-image information and record the digitally compressed moving-image information on a recording medium such as a magnetic tape. It is also known that there are two types of compression systems: a compression system using a fixed-length coding method and a compression system using a variable-length coding method.
FIG. 1 is a block diagram schematically showing the arrangement of a conventional example of an image recording and reproducing apparatus using the fixed-length coding method. An analog image signal indicative of a moving image to be recorded is inputted through an input terminal 10. An A/D converter 12 digitizes the analog image signal inputted through the input terminal 10, and a fixed-length coding circuit 14 encodes the output data of the A/D converter 12 by fixed-length coding. A modulating circuit 16 executes suppressed low-frequency modulation of the output of the fixed-length coding circuit 14. The output of the modulating circuit 16 is amplified to a predetermined level by a recording amplifier 18. A switch 20 is arranged to be selectively connected to contacts xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d during recording and reproduction, respectively. The output of the recording amplifier 18 is applied to a magnetic head 22 through the switch 20, whereby the output is recorded on a magnetic tape 24.
During reproduction, the signal recorded on the magnetic tape 24 is reproduced by the magnetic head 22 and the output of the magnetic head 22 is applied toga demodulating circuit 28 through the switch 20 and a reproducing amplifier 26. A fixed-length- decoding circuit 30 is a decoding circuit corresponding to the fixed-length coding circuit 14, and serves to decode the output of the demodulating circuit 28 and output a digital reproduced image signal. The output of the fixed-length decoding circuit 30 is converted into an analog signal by a D/A converter 32, and the analog signal an analog reproduced image signal, is outputted for external use through an output terminal 34.
The fixed-length coding circuit 14 normally adopts a coding method in which the amount of data after coding is kept constant for one picture (one field or one frame). The fixed-length coding method includes a pulse-code modulation (PCM) method accompanied by no compression as well as a method accompanied by digital compression, such as a so-called sub-sampling method and a differential coding (DPCM) method. Since the former method does not at all compress image information during processing, no substantial degradation occurs in image quality. However, a huge amount of data must be recorded and the rate of recording must be increased with the result that a large number of disadvantages occur in terms of hardware design and the recording density and time of a recording medium.
If digital compression is executed by using fixed-length coding, a compression ratio of approximately 1/4 to 1/6 can be achieved. However, if a high-definition television signal such as an HDTV signal is compressed at such a compression ratio, the amount of information to be recorded will still be excessively large. In addition, a considerable degradation in image quality is visually observed.
In contrast, the variable-length coding method using, for example, a Huffman code or an arithmetic code, can achieve a compression ratio of as high as approximately 1/10 to 1/20 without excessively degrading image quality.
However, the variable-length coding method also has a number of problems. In this coding method, the amount of information recorded per picture is basically inconstant and coding is executed by using a correlation between a plurality of pictures. Therefore, according to the variable-length coding method, it is difficult to realize various reproduction functions such as xe2x80x9ceditxe2x80x9d, xe2x80x9csearchxe2x80x9d and xe2x80x9cspecial reproductionxe2x80x9d. This problem is particularly outstanding in the field of a digital VTR using as a recording medium a magnetic tape which is a sequential access medium.
It is, therefore, an object of the present invention to provide a recording apparatus in which it is possible to easily realize various reproduction functions such as xe2x80x9ceditxe2x80x9d, xe2x80x9csearchxe2x80x9d and xe2x80x9cspecial reproductionxe2x80x9d and which is capable of effecting recording at a high compression ratio without degrading image quality.
To achieve the above-described object, according to one aspect of the present invention, there is provided a video signal recording apparatus which comprises inputting means for inputting a video signal sequentially containing a plurality of pictures correlated to one another, the video signal having an amount of information, compressing means for compressing the amount of information of the video signal, the compressing means being capable of selectively assuming an intrapicture coding mode for executing compression by using only a correlation within each of pictures of the video signal and an interpicture coding mode for executing compression by using a correlation between a plurality of pictures of the video signal, recording means for recording on a recording medium the video signal the amount of information of which is compressed by the compressing means, operating means for commanding the recording means to start a recording, and controlling means responsive to an operation of the operating means for controlling the compressing means so that a video signal for one picture recorded immediately after the recording means has started the recording becomes a video signal compressed in the intrapicture coding mode.
According to another aspect of the present invention, there is provided a video signal recording apparatus which comprises inputting means for inputting a video signal sequentially containing a plurality of pictures correlated to one another, the video signal having an amount of information, compressing means for compressing the amount of information of the video signal, the compressing means varying an amount by which information is to be outputted for each picture, operating means for commanding a start of recording of the video signal, and recording means for recording the video signal the amount of information of which is compressed by the compressing means, while sequentially forming a multiplicity of tracks on a recording medium, the recording means being responsive to an operation of the operating means to begin recording a video signal for one picture to be recorded immediately after the start of recording, at the forefront of the tracks.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.