Facsimile and static presentation processing – Facsimile – Recording apparatus
Patent
1983-11-30
1986-12-16
Lev, Robert G.
Facsimile and static presentation processing
Facsimile
Recording apparatus
358 54, H04N 911
Patent
active
046301208
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This application concerns various improvements in the field of telecine machines, and relates to various inventions concerned with improved operation of the machines. A telecine machine, often simply termed `a telecine`, is operative to generate a television signal or at least a video signal from cinematographic film.
There are now available two principal types of telecine machines which are of interest, namely the linear array type and the flying spot type. A linear array telecine has a linear array of light-sensitive elements, namely in the form of a charge coupled device (CCD), which provides a serial output representing a line of television signal at a time. The film is driven at a constant rate between the linear array and a light source in a direction substantially perpendicular to a plane containing the sensor array, and an optical system images an illuminated section of film on the sensor array. Such a telecine machine is described in U.S. Pat. No. 4,275,422.
The flying spot telecine has been available for many years and comprises an imaging CRT tube on which a spot is illuminated to provide a scanning light source for the film. A single sensor device is located on the other side of the film and an optical system collects the light which passes through the film and images it onto the sensor device.
With linear-array telecines, it has been proposed to include a digital store at the output of the telecine to convert non-standard signals from the sensor array into standard format. It has also been proposed to use digital stores with flying-spot scanning telecines.
The following description will initially be made with reference to a linear-array telecine. However the application of the principles described is not so limited and they can also be used with flying spot telecine machines, as is discussed in more detail below in the detailed description of a preferred embodiment.
DESCRIPTION OF THE PRIOR ART
The way in which a line-array telecine operates is, by now, well known. Vertical scanning of the film image is accomplishd by the physical movement of the film. There are several consequences of this. The first is that the signals emerge from the sensor in a sequential order, so conversion to standard interlaced form is thus necessary and this implies the use of digital storage at the output of the telecine. A second consequence is that the height of the final television picture can only be adjusted (for a given film speed) by varying the scan rate of the line-array sensor, and that this scan rate will also vary between the different film gauges, because of the different size of the frame bars. Another consequence is that the nominal scan rate of the sensor should be related to the nominal film speed, in other words, if the film is replayed at 18 frames per second, the sensor scan rate will be 0.72 times that at 25 frames per second.
It is thus apparent that the sensor only rarely scans at the same rate as the television line standard and that a second function of the digital output store is to provide a buffer between the incoming scan rate from the sensor and the outgoing scan rate locked to station syncs. Low sensor scan rates can be accommodated relatively easily; one convenient approach is to use a fixed clock frequency and and insert "gaps" of variable numbers of clock pulses between successive scans. The maximum scan rate of which a sensor is capable is fixed, however, and so there is a maximum speed at which a film can be run if the sensor is to scan every line. For example, the sensor scan rate required by normal aspect ratio 35 mm film running at 25 frames per second and producing an output intended for the 625/50 standard is 18.075 kHz (i.e. 1 line every 55.3 microseconds). If a telecine were to be designed with this as a limit, then 16 mm film could be run at speeds up to 28.9 frames per second; any increase over these speeds, or any increase in the displayed picture height, would mean that the sensor could not scan every line. Thus an alternative must be used
REFERENCES:
patent: 4264922 (1981-04-01), Hoffman et al.
patent: 4329715 (1982-05-01), Attridge
patent: 4331979 (1982-05-01), Bendell
"Novel Uses of Digital Processing in a Modern Telecine", I. Childs & M. J. Griffiths, International Broadcasting Convention, Brighton, U.K., Sep. 18-21, 1982, pp. 46-50.
"FDL 60-Progress in Film Scanning Using CCD Sensors and Digital Processing", D. Poetsch et al., `International Broadcast Engineer`, Jan. 1981, pp. 47-49.
British Broadcasting Corporation
Lev Robert G.
O'Connell Robert F.
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