Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
  • H04N3/36—Scanning of motion picture films, e.g. for telecine
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/222—Studio circuitry; Studio devices; Studio equipment
  • H04N5/257—Picture signal generators using flying-spot scanners

Definitions

• the present invention relates to a method and apparatus for the correction of drift in the level of a video signal provided by a flying spot telecine, in particular, drift arising from instability or progressive drift in the preliminary stages of telecine equipment.
• Such errors may be caused by variations in the intensity of the output of the cathode ray tube (“CRT") scanning means used in flying spot telecine equipment or by variations in photomultiplier tube sensitivity or amplifier gain. These variations are usually of a relatively long term nature. That is to say they cause the video signal level or the colour balance to drift over a period of minutes or longer.
• CTR cathode ray tube
• cathode ray tube used to generate the flying spot is caused to scan an area ⁇ orrespcinding to the position of one or more perforations in a film strip being scanned by the telecine; the output from a photodetector receiving light transmitted during a scan of the said area providing a correction signal for adjusting the video signal level.
• CTR cathode ray tube
• scanning of the film perforations to correct video signal drift is performed during line or frame blanking periods.
• Figure 1 is a schematic diagram of a flying spot telecine
• Figure 2 is a fragmentary schematic view of the film skid plate region of flying spot telecine equipment.
• FIG. 3 is a block diagram of control circuitry in accordance with the invention.
• the film 110 to be scanned passes through a film gate 112 where it is scanned by a flying spot generated by CRT scanning means 114.
• Light transmitted by the film in its transparent and translucent areas is collected by one or more photomultiplier tubes 118 after being split at a beam splitter 116 into three or more colour components and otherwise processed.
• the output signals from the photomultiplier tubes 118 form the basis for the video signal.
• the area of the film strip 10 actually scanned by the flying spot is defined by a viewing aperture 12 formed in a skid plate 14 over which the film strip 10 passes, as shown in Figure 2.
• the film strip 10 is transported through the telecine film gate 112 by means of a capstan or other drive means. Picture synchronisation is achieved by pulses from a suitable sprocket which engages in rows of perforations 16 formed along the longitudinal edges of the film strip 10.
• a second aperture 18, the perforation aperture is formed in the skid plate 14 and the CRT scanning means 114 is caused to perform an auxiliary scan of the film strip perforations 16 through the perforation aperture 18 during the frame blanking period.
• This is achieved by providing scanning amplifiers 120 which drive the CRT scanning means 114 with a suitable waveform which produces a small auxiliary scan at a location equivalent to a film perforation 16.
• the waveform includes a component to track the motion of the continuously moving film strip 10.
• auxiliary scan thus gives rise to a video signal which corresponds to a 'no-film' condition, that is, a signal the level of which is dependent only on the conditions of the telecine equipment itself.
• the signal resulting from the auxiliary scan is then compared by means of a comparator circuit 20, to an adjustable gain voltage and the result applied to a control circuit 22.
• the control circuit 22 increments or documents the photomultiplier control output which controls the voltage applied to the photomuItiplier tubes and, hence, their gains.
• the comparator circuit 20 will reach its threshhold and the photomultiplier control output be maintained constant until a further error occurs.
• the rate of incrementing or decrementing the photomultiplier control output must be slow enough to avoid the possibility of translating video noise into frame-by-frame flicker which would be visible to the viewer.
• one or more colour signals may need a greater system gain than is usual; during the scan of the perforations 16 the whole of the light beam produced by the CRT scanning means is transmitted to the photomultiplier tube. With the greater system gain, there is a risk that overloading of the video signal during the scan of the perforations may occur which would preventt correct operation.
• an attenuating filter may be placed over the perforation aperture 18 in the skid plates 14. This results in an overall reduction in the video signal level, leading to a lower auxiliary scan signal level during normal operation but avoiding overload problems when a higher gain is required.
• the output of the CRT scanning means may be reduced by turning the beam current down during the auxiliary scan of the film perforations 16.
• the above method can be applied using either digital or analogue techniques as appropriate to the particular telecine equipment being used. It will be appreciated that, although the method described above applies a correction signal to the photomultiplier gain, it might equally well be applied to the CRT scanning means to control the brightness or to the amplifier to adjust the gain.
• the method is applied to each colour independently so as to maintain the correct colour balance as well as the overall video signal level.

Landscapes

• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Color Television Image Signal Generators (AREA)
• Studio Devices (AREA)
• Facsimile Image Signal Circuits (AREA)
• Details Of Television Scanning (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10632863

Family Applications (1)

Country Status (4)

Families Citing this family (6)

• 1988
  • 1988-03-04 GB GB8805219A patent/GB2215551B/en not_active Expired - Fee Related
• 1989
  • 1989-03-03 WO PCT/GB1989/000240 patent/WO1989008365A1/en not_active Ceased
  • 1989-03-03 EP EP19890903785 patent/EP0408620A1/de not_active Ceased
  • 1989-03-03 JP JP1503476A patent/JPH03504305A/ja active Pending

Non-Patent Citations (1)

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