The present invention relates generally to systems for recording the picture image content of a cinematographic film in a form of a video signal on a rotating recording medium and for subsequently reproducing therefrom the video signal. More particularly, the invention relates to a system which records the picture content of a cinematographic film traveling at a speed of 24 film frames or scenes per second in a form of a television video signal of 60 fields (namely, 30 frames) per second on a rotating recording medium rotating at a speed of 900 revolutions per second in a manner such that still picture reproduction can also be carried out, and which subsequently reproduces the video signal thus recorded from the recording medium.
In general, in a system for recording a television video single on a rotating recording medium, the fewer the field of the video signal to be recorded per revolution of the rotating recording medium, the higher is the rotational speed at which the rotating recording medium must be rotated. In this case, the system is subjected, mechanically, to unreasonably and excessively severe conditions, whereby vibration occurs, or automatic control becomes difficult. Moreover, the recording capacity of the recording medium is reduced.
On the other hand, the greater the number of fields of the video signal to be recorded per revolution of the rotating recording medium, the lower is the required rotational speed of the rotating recording medium. For this reason, the system is not subjected mechanically to excessively severe conditions, and furthermore, the recording capacity of the recording medium becomes large. On the other hand, however, since the wavelength of recording on the recording medium becomes short, in the case where the signal is recorded on the recording medium as a variation of geometrical shape and is thereafter reproduced as capacitance variation or optical variation, the reproducing element becomes unable to reproduce satisfactorily.
In this connection, a novel "Information signal recording and reproducing system" assigned to the same assignee of the present application was proposed by U.S. patent application Ser. No. 785,095, filed Apr. 6, 1977, now U.S. Pat. No. 4,331,976, and is now being reduced to practice. In accordance with this system, a video signal is recorded along a track of spiral form as a geometrical shape variation, without a reproducing stylus guide groove, on a rotating recording medium having a flat surface. Since there is no guide groove in the rotating recording medium, the reproducing stylus can move smoothly from one track turn to another at the time of still-picture, slow-motion, or quick-motion reproduction. Accordingly, in spite of the use of a reproducing stylus in this system, special reproducing modes such as the still-picture reproduction can be smoothly carried out.
However, in the case where still-picture reproduction is carried out by repeatedly reproducing the same track turn, if an information content signal of a larger number of fields is recorded along the same track turn, the reproduced still picture will not be one which is perfectly still but will appear unnatural and unsightly or indistinct. More specifically, particularly in the case where the information content is one of rapid motion, the position of each moving object at the starting point of the same track turn differs from that at the terminal point of the same track turn in the reproduced picture. For this reason, when the same track turn is repeatedly reproduced, each moving object repeatedly undergoes reciprocation been these two different positions, and the reproduced image appears to flicker or vibrate. Also at the time of slow-motion reproduction when the same track turn is reproduced a plurality of times and then the reproducing element (stylus) shifts to the succeeding track turn, the reproduced picture will move unnaturally.
In view of the various above described circumstances, we have decided that it is most desirable to record a video signal at a rate of four fields, that is, two frames, per revolution of the rotating recording medium.
The procedure of converting the picture image content of a cinematographic film of 24 film frames per second into a video signal of 60 fields (30 frames) per second and using this video signal for either television broadcasting or recording on a recording medium such as a magnetic tape has been practiced in the prior art. For this conversion of the picture of 24 film frames per second into a video signal of 60 fields per second, in general, a so-called 3-2 pull-down method is being used. This 3-2 pull-down method is carried out by controlling the cinematographic film feed and the shutter operation of the projector so that the first film frame is transcribed for 3 fields, the second film frame for 2 fields, the third film frame for 3 fields, the fourth film frame for 2 fields, the succeeding film frames similarly being transcribed alternately for 3 fields and 2 fields. The light image thus projected by this projector is picked up by a camera tube and thereby converted into a television video signal.
However, when the video signal converted by this 3-2 pull-down method is recorded directly as it is on a rotating recording medium at the above described rate of 4 fields per revolution (corresponding to one track turn), the information of the first film frame of 3 fields and the information of the second film frame of 1 field are recorded along the first track turn; the information of the remaining fields of the second film frame and the information of 3 fields of the third film frame are recorded along the second track turn; and so forth. In this manner, the information of a plurality of film frames are recorded over and with respect to all track turns.
For this reason, in the case of obtaining a still picture by reproducing only the same track turn a plurality of times, the information of two different film frames are repeatedly reproduced. Consequently, in the case where the movements of the image of the information contents are rapid, the resulting still picture flickers and becomes indistinct.