EP0408620A1 - Drift correction in telecine - Google Patents

Drift correction in telecine

Info

Publication number
EP0408620A1
EP0408620A1 EP19890903785 EP89903785A EP0408620A1 EP 0408620 A1 EP0408620 A1 EP 0408620A1 EP 19890903785 EP19890903785 EP 19890903785 EP 89903785 A EP89903785 A EP 89903785A EP 0408620 A1 EP0408620 A1 EP 0408620A1
Authority
EP
European Patent Office
Prior art keywords
photodetector
correction signal
film strip
signal
scanning means
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP19890903785
Other languages
German (de)
French (fr)
Inventor
William Mead Terence
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rank Cintel Ltd
Original Assignee
Rank Cintel Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rank Cintel Ltd filed Critical Rank Cintel Ltd
Publication of EP0408620A1 publication Critical patent/EP0408620A1/en
Ceased legal-status Critical Current

Links

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)
  • Details Of Television Scanning (AREA)

Abstract

Dans un télécinéma à point d'exploration comprenant un moyen de balayage à tube à rayons cathodiques servant à générer un point d'exploration, ainsi qu'un photodétecteur recevant la lumière transmise par une bande de film balayée par le télécinéma, on a prévu un dispositif de commande provoquant le balayage, par le moyen de balayage à TRC, d'une région (8, 18) correspondant à la position d'une ou de plusieurs perforations (16) dans la bande de film (10) balayée. Le signal de sortie provenant du photodétecteur pendant un balayage de la région (18) fournit un signal de correction servant à régler le niveau des signaux vidé. On procède au balayage de la région (18), de préférence pendant les périodes de suppression de ligne ou de suppression de la trame.In an exploration point telecine comprising a cathode ray tube scanning means for generating an exploration point, as well as a photodetector receiving the light transmitted by a film strip scanned by the telecine, provision has been made for control device causing the scanning, by the CRT scanning means, of a region (8, 18) corresponding to the position of one or more perforations (16) in the film strip (10) scanned. The output signal from the photodetector during a region scan (18) provides a correction signal for adjusting the level of the emptied signals. The region (18) is scanned, preferably during the line blanking or frame blanking periods.

Description

DRIFT CORRECTION IN TELECINE
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.
For example, 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.
Attempts have been made to reduce signal drift due to variations in the sensitivity of photomultiplier tubes by fitting heating elements adjacent the tubes to inaintain them at a constant temperature. Whilst this does to an extent reduce signal drift, the elevated temperatures which result increase the noise contributions to the output signal from the photomultiplier tubes and adjacent amplifiers. Furthermore, the fitting of heating elements has no effect on drift due to factors other than temperature.
The method and apparatus of the invention are characterised in that cathode ray tube ("CRT") scanning means used to generate the flying spot is caused to scan an area σorrespcinding 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.
Thus, by collecting light which passes through the film perforations, equivalent to a 'no-film' condition, a direct measure can be obtained of the composite effect of all the errors outlined above. The video signal level can then be corrected by adjusting the gain of the amplifier or of the photomultiplier tube or by altering the brightness of the CRT scanning means.
Preferably, scanning of the film perforations to correct video signal drift is performed during line or frame blanking periods.
An embodiment of the invention will now be described, by way of example, with reference to the drawings, in which:
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; and
Figure 3 is a block diagram of control circuitry in accordance with the invention.
In conventional flying spot telecine equipment a typical example of which is showsn schematically in Figure 1, 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. At the film gate 112 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. In the telecine equipment of the invention 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.
Light from the auxiliary scan passes through the film perforation 16 and the perforation aperture 18 of the skid plate 14 to be collected by the photomultiplier tubes 118 in the usual way. The 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. When the photomultiplier tube gain is just sufficient to compensate for the error, 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. However, in telecines using programmable colour correction techniques it may be necessary to change the system gain very quickly. This can be achieved by temporarily increasing the speed of the gain control circuitry whenever a change to the gain control voltage is required.
Where dense film or negative film is used, 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.
To overcome this difficulty, 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. Alternatively, 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.
Preferably, the method is applied to each colour independently so as to maintain the correct colour balance as well as the overall video signal level.

Claims

1. A method for correcting drift in the level of a video signal provided by a flying spot telecine characterised in that cathode ray tube ("CRT") scanning means used to generate the flying spot is caused to scan an area (12) corresponding to the position of one or more perforations (16) in a film strip (10) being scanned by the telecine; the output from a photodetector receiving light transmitted during a scan of the said area (15) providing a correction signal for adjusting the video signal level.
2. A method according to claim 1 in which the correction signal is obtained by comparing the output from the photodetector with a reference signal to provide a signal representing the difference therebetween, the difference signal being applied as the correction signal.
3. A method according to claim 1 or 2 in which the CRT scanning means is caused to scan the area corresponding to perforations in the film strip during line blanking or frame blanking periods.
4. A method according to any preceding claim in which the correction signal is applied to the CRT scanning means to adjust the brightness of the flying spot.
5. A method according to any of claims 1 to 3 in which the correction signal is applied to an amplifier used to amplify the photodetector output to adjust the gain of the amplifier.
6. A method according to any of claims 1 to 3 in which the correction signal is applied to the photodetector to adjust the gain thereof.
7. A method according to any preceding claim in which the light transmitted by the film strip is split into a plurality of beams containing different wavelength ranges respectively, there being provided a plurality of photodetectors, each arranged to receive a respective one of the said beams so that each photodetector provides a correction signal for one of the wavelength ranges.
8. A method according to any preceding claim in which an attenuating filter is provided over said area corresponding to the position of one or more perforations in the film strip.
9. A flying spot telecine including cathode ray tube ("CRT") scanning means for generating the flying spot, a photodetector for receiving light transmitted by a film strip (10) being scanned by the telecine characterised in that it comprises control means for causing the CRT scanning means to scan an area (15) corresponding to the position of one or more perforations (16) in a film strip (10) being scanned, the output from the photodetector during a scan of the said area (18) providing a rorrection signal for adjusting the video signal level.
10. Apparatus according to claim 9 including a comparator (20) for comparing the output of the photodetector with a reference signal to provide a signal representing the difference therebetween, the difference signal being applied as the correction signal.
11. Apparatus according to claim 9 or 10 in which the CRT scanning means is caused to scan the area (18) corresponding to perforations (16) in the film strip (10) during a line blanking or frame blanking period.
12. Apparatus according to any of claims 9 to 11 in which the correction signal is applied to the CRT scanning means to adjust the brightness of the flying spot.
13. Apparatus according to any of claims 9 to 11 including an amplifier (22) used to amplify the photodetector output, the correction signal being applied to the amplifier (22) to adjust the gain thereof.
14. Apparatus according to any of claims 9 to 11 in which the correction signal is applied to the photodetector to adjust the gain thereof.
15. Apparatus according to any of claims 9 to 14 including means for splitting light transmitted by the film strip into a plurality of beams containing different wavelength ranges respectively, there being provided a plurality of photodetectors, each arranged to receive a respective one of the said beams so that each photodetector provides a correction signal for one of the wavelength ranges.
16. Apparatus according to any of claims 9 to 15 in which an attenuating filter overlies the said area (18) corresponding to the position of one or more perforations (16) in the film strip (10).
EP19890903785 1988-03-04 1989-03-03 Drift correction in telecine Ceased EP0408620A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8805219A GB2215551B (en) 1988-03-04 1988-03-04 Drift correction in telecine
GB8805219 1988-03-04

Publications (1)

Publication Number Publication Date
EP0408620A1 true EP0408620A1 (en) 1991-01-23

Family

ID=10632863

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19890903785 Ceased EP0408620A1 (en) 1988-03-04 1989-03-03 Drift correction in telecine

Country Status (4)

Country Link
EP (1) EP0408620A1 (en)
JP (1) JPH03504305A (en)
GB (1) GB2215551B (en)
WO (1) WO1989008365A1 (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2241625B (en) * 1990-02-02 1994-01-19 Rank Cintel Ltd Automatic photo-multiplier tracking
US5680172A (en) * 1992-01-21 1997-10-21 Video Post & Transfer, Inc. Consecutive frame scanning of cinematographic film
US5565912A (en) * 1994-02-16 1996-10-15 Eastman Kodak Company Film positioning system using dual perforation sensors
GB2304932A (en) * 1995-09-06 1997-03-26 Kodak Ltd Determining correct exposure of film for telecines
GB2325367A (en) * 1997-04-25 1998-11-18 Cintel Int Ltd Stabilisation of photoelectric cells
GB2355355A (en) * 1999-10-11 2001-04-18 Cintel Internat Ltd Afterglow correction in flying spot scanners

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8908365A1 *

Also Published As

Publication number Publication date
JPH03504305A (en) 1991-09-19
WO1989008365A1 (en) 1989-09-08
GB8805219D0 (en) 1988-04-07
GB2215551A (en) 1989-09-20
GB2215551B (en) 1992-07-08

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