GB2355879A

GB2355879A - Telecine systems

Info

Publication number: GB2355879A
Application number: GB9921332A
Authority: GB
Inventors: Stuart William Arundell Hunt
Original assignee: Innovation TK Ltd
Current assignee: Innovation TK Ltd
Priority date: 1999-09-09
Filing date: 1999-09-09
Publication date: 2001-05-02
Also published as: GB9921332D0

Abstract

A telecine system for the conversion of images stored on cinematographic film 2 to corresponding electrical signals, such as television signals (produced by a photodetector 3) comprises a light source 1 (e.g. a CRT) and focussing lenses 4 and 5. In order to reduce defects in the outputted electrical signals caused for example by inconsistent burning across the whole of the CRT phosphor screen, the whole light source assembly is moved in various directions in relation to the film. Further, by moving the light source towards and away from the film, zooming effects can be carried out without degradation in the outputted signals due to the phosphor particle grain size in the CRT screen.

Description

2355879 Telecine Systems The present invention relates to the conversion

of images stored on film, in particular cinematographic film, to corresponding electrical signals.

Systems for the conversion of images stored on cinematographic motion picture film into electrical signals, for example television signals, are well known.

Machines which perform this conversion in real time, i.e.

at the rate that television frames are broadcast are commonly referred to as "Telecinell machines. Examples of these machines include the "URSA Diamond" telecine from Cintel International Ltd of Ware, United Kingdom and the "Spirit Datacine" Telecine from Phillips Digital Video of Darmstadt, Germany. These telecine machines need to "scan" the cinematographic film. This is accomplished in the "Spirit" system by the use of a CCD (Charge Coupled Device) and in the "URSA Diamond" system, by the use of a CRT (Cathode Ray Tube).

The use of CRT (Cathode Ray Tubes) f or the use of film scanning has been known at least as long ago as 1975, where it was used in the 11Mk III Telecine" produced by Rank Cintel. In this system, the film is scanned by the imaging of a scanned "raster" patch on the front face of the CRT being imaged onto the film, and the collected light transmitted through the film being collected by photosensitive devices.

It is sometimes required to image only part of a film frame into video signals. For example, it may be desirable to zoom in on a part of a f ilm frame so as to produce a different artistic interpretation on the video or it may be necessary to scan only part of the film frame because of the different aspect ratio shapes between cinema film screens and television screens. This is quite common in the origination of f ilm material for television 2 advertisements.

It is known to zoom in on a part of a film frame using a CRT scanning telecine system by reducing the size of the raster patch on the front face of the CRT. One such system motorises the coils on a CRT neck, and by the movement of these coils, induces rotational and geometric distortions in the scan patch. Such a system is disclosed in US Patent 5, 355, 057 (Edgar et. al). In such a system, if for example the operator wishes to increase the zoom by a factor of two (i.e. to scan only half of the film frame), this means having a raster patch of half the linear size of the patch required to scan the entire film frame. However, the grain size of the phosphor particles in the deposited layer of phosphor on the inside of the CRT face is a limiting factor on the quality of reproduction of the image produced by the raster scan. Thus, where the size of the raster patch is reduced, this will reduce the quality of the reproduced image.

Another problem that is encountered in CRT telecine systems is the phenomenon of burn. This is caused by a differential heat related aging of the phosphor on the inside of the CRT face between heavily used areas of the CRT phosphor and relatively infrequently used areas. Because the telecine is used commonly for a given aspect ratio area, this makes a burn patch corresponding to the size of the most commonly used raster patch appear on the CRT face. This is of no consequence when the raster patch occupies just this area, because then all of the phosphor in this area has the same sensitivity. However, if a different raster patch size is in use, due to either a different aspect ratio, different film speed, or editorial effect such as blanking, cropping, or zoom, the edges of the burn patch will be visible in the scanned image.

Several solutions to the problem of burn have been suggested. One of these is the use of burn correction circuitry, such as the system disclosed in Patent application DE-OS 2525 073 from Rank Cintel Ltd. Further improvements to burn correction include the Iscantrack, system, which is included on a range of Cintel telecine systems. In the Scantrack system, the raster patch on the face of the CRT is modulated vertically via a small cyclical deflection of typically up to about 100-o of the height of the raster patch, with the film motion control servo driven by the same deflection in the alternate direction. This results in the scanning patch and the film area being both modulated vertically in synchronism, to avoid burn edges being formed on the CRT face corresponding to the top and bottom of the film frame being scanned.

A further problem encountered in Telecine systems relates to the different film frame formats within a given film stock. For example, 35mm film stock can be shot in the film camera as 1135mm Academy" format or "Super 35mm" format. The choice of format is controlled within the camera by the shape and position of the aperture that the film is exposed through. The differences between 1135mm Academy" format and "Super 35mm" format are that the frame centre line for the 1135mm Academy" format is in a different position to that of the "Super 35mm" format.

Thus, the problem exists that known telecine systems cannot be centred, so as to have the centre of the scanning patch in alignment with the centre of the optical assembly, which is then in line with the film frame centre for different film formats. Whilst it is possible to design and manufacture optical systems that will produce passable results despite not being centred for all film formats, the design of these systems is considerably more complex so that they are more expensive to manufacture than "on axis" optical systems. In addition, such systems cannot ever achieve the quality of electrical image that a simpler "on axis" optical system can produce.

Thus, from a first aspect, the present invention provides a system for the conversion of images stored on cinematographic film to corresponding electrical signals, the system comprising a cathode ray tube for scanning at least a part of the images on the film, photosensitive means for detecting the light transmitted by the film, and means for moving the cathode ray tube relative to the f ilm.

with the invention as described above, the cathode ray tube (CRT) may be moved backwards and forwards relative to the film to be scanned so as to produce a zoom effect. Thus, the present invention avoids the need to alter the size of the raster patch on the face of a CRT to produce a zoom effect such that the quality of the image produced is not limited by the granularity of the phosphor coating on the CRT face.

Further, the CRT may be moved in a lateral direction is relative to the longitudinal feeding direction of the film so as to align the centre of a film frame to be scanned with the centre of the CRT f ace. Thus, scanned images of a high quality can be obtained for different film formats using the system of the present invention.

In addition, using the system of the invention, the CRT may be moved laterally relative to the longitudinal feeding direction of the film before scanning each frame of the film, the CRT having a scan patch provided on the front face thereof which is moved by a corresponding amount in the opposite direction before scanning each frame of the film such that the position of the scan patch relative to the film remains constant while reducing the formation of longitudinally extending burn edges on the f ace of the CRT.

Alternatively, the scanning means may be a CRT which is moved longitudinally relative to the longitudinal feeding direction of the film before scanning each frame of the f ilm, the CRT having a scan patch provided on the f ront f ace thereof which is moved by a corresponding amount in the opposite direction before scanning each frame of the film such that the position of the scan patch relative to the film remains constant while reducing the formation of laterally extending burn edges on the face of the CRT.

Thus from a further aspect, the present invention comprises a system for the conversion of images stored on -5 cinematographic film to corresponding electrical signals, the system comprising a cathode ray tube for scanning at least a part of the images on the film, photosensitive means for detecting the light transmitted by the film, and means f or moving the cathode ray tube relative to the film in any of three orthogonal planes.

From a further aspect, the present invention provides a method of converting images stored on cinematographic film to corresponding electrical signals, the method comprising scanning at least a part of the images on the is film with a cathode ray tube, detecting the light transmitted by the film, and controlling the area of the film to be scanned by moving the cathode ray tube relative to the f ilm.

From a yet further aspect, the present invention provides a method of converting images stored on cinematographic f ilm to corresponding electrical signals, the method comprising scanning at least a part of the images on the f ilm with a cathode ray tube, detecting the light transmitted by the f ilm, and moving the cathode ray tube in a lateral or longitudinal direction relative to the longitudinal direction of travel of the film and moving a scan patch on the cathode ray tube by a corresponding amount in the opposite direction.

From a yet further aspect, the present invention provides a method of converting images stored on cinematographic film to corresponding electrical signals, the method comprising scanning at least a part of the images on the film with a cathode ray tube, detecting the light transmitted by the film, and moving the cathode ray tube in a lateral or longitudinal direction relative to the longitudinal direction of travel of the film so as to align the centre of the cathode ray tube with the f rame of 6 film to be scanned.

The zoom ef f ect provided by moving the cathode ray tube backwards and forwards relative to the film to be scanned could also be used in systems comprising a 1 t e r n a t i v e s c a n n i n g m e a n s.

Thus, from a further aspect, the present invention provides a system for the conversion of images stored on cinematographic film to corresponding electrical signals, the system comprising a light source for illuminating at least a part of the images on the film, means for detecting the light transmitted by the film, and means for moving the light source towards and/or away from the plane of the f ilm so as to determine the size of the image on the film which is to be converted.

The present invention further provides a method for converting images stored on cinematographic film to corresponding electrical signals, the method comprising illuminating at least a part of the images on the film with light from a light source, and detecting at least some of the light transmitted by the film, wherein the light source is moved towards and/or away from the plane of the f ilm so as to determine the size of the image on the f ilm which is to be converted.

Similarly, the possibility of aligning the centre of the cathode ray tube with the centre of the image to be scanned by moving the cathode ray tube laterally relative to the longitudinal direction of travel of the film to bg, scanned could also be used in systems comprising a 1 t e r n a t i v e s c a n n i n g m e a n s Thus, from a further aspect, the present invention provides a system for the conversion of images stored on cinematographic film to corresponding electrical signals, the system comprising a light source for illuminating at least a part of the images on the film, means for detecting the light transmitted by the film, and means for moving the light source laterally relative to the longitudinal direction of travel of the f ilm so as to align the centre of the image on the f ilm which is to be converted with the light source.

The present invention further provides a method for converting images stored on cinematographic film to corresponding electrical signals, the method comprising illuminating at least a part of the images on the f ilm with light from a light source, and detecting at least some of the light transmitted by the film, wherein the light source is moved laterally relative to the longitudinal direction of travel of the film so as to align the centre of the image on the f ilm which is to be converted with the light source.

Preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figures la to 1c show the general layout and operation of a telecine machine; Figure 2 shows a burn patch formed on the face of a CRT; Figures 3a to 3c show the operation of the prior art

Scantrack system described above; Figure 4 shows the differences between 1135mm Academy" format and "Super 35mm" format; and Figure 5 shows schematically a system according to an embodiment of the invention.

The use of the terms "horizontal" and vertical" iia the following description will be relative to the direction of travel of film in a telecine machine, which direction is defined as being vertical although it need not be so in a physical arrangement.

Figure la shows the arrangement of a system according to a first embodiment of the invention in which a cathode ray tube (CRT) 1 is provided on one side of film 2 to be scanned. A photodetector 3 is provided to collect the light from the CRT transmitted by the film. Imaging lenses 4, 5 are also provided to focus the light from the 8 CRT onto the part of the film to be scanned and to collect the transmitted light respectively.

Figure lb shows a typical raster patch 6 on the f ace 7 of the CRT 1 of Figure la. Figure ic then shows the projection of the raster patch 6 onto a film frame 9.

Figure 2 shows the f ace of a CRT 1 with a burn patch on it caused by a raster patch of a constant size and position being used for a prolonged period.

The prior art Scantrack system for correcting for burn in a telecine machine as described above operates in a system as described in relation to Figure 1. As shown in Figure 3, the raster patch 6 on the face of the cathode ray tube 1 is moved vertically in one direction while the portion 11 of the film to be scanned is moved vertically by a corresponding amount in the opposite direction.

Typical optical magnification in a telecine system for 35 mm film is a factor of 4. Using the scantrack system, the area scanned should be modulated by about 10'-. of the picture area. Thus, for 35mm format film, a modulation of between about 2 to 3mm is required on the f ilm which corresponds to a movement of the raster patch 6 on the CRT face of about 8 to 12mm.

Figure 4 shows the difference in alignment of the frame centres for 1135mm Academy" format and "Super 35mm" format. As can be seen, Academy format 35mm film has holes 13 provided at either side of the film and a soundtrack 14 located between the film frames 15 and the holes on the right hand side of the f ilm. Thus, the centerline 16 of the film frames is offset relative to the centre 17 of the film strip. In contrast, super 35mm film format does not include any soundtrack and so the centre line 18 of the film frames 15 corresponds to the centerline of the film strip. Thus, the centerlines 16 and 18 of the film frames of the different formats are offset by an amount x which is about 2mm.

Figure 5 is a schematic representation of a system according to an embodiment of the present invention. The Telecine CRT is mounted on a motorised stage, the movement of which is controlled in response to electrical signals to move the CRT assembly in any one (or more than one) of three mutually orthogonal directions X, Y and Z where the Y direction corresponds to the direction of transport of the film in the telecine machine.

In an alternative embodiment (not shown), the CRT is mounted on three leadscrews oriented in the three mutually orthogonal directions X, Y and Z. Thus a motor turns the lead screws to move the CRT in the X Y and Z directions respectively. Radial optical gratings are mounted to the ends of the respective lead screws and photodetectors are provided to count the grating rules of rotation such that the amount that the CRT moves in any one direction is known. Further, the movement of the CRT can be controlled by a feedback system if required.

Various examples of the use of the system described above in which the CRT is movable in any one of three mutually orthogonal directions are described below.

The first example to consider is the motion of the CRT in the Z direction, i.e. towards and away from the film. This will affect the size of the imaged scan patch on the f ilm. Moving the CRT away f rom the f ilm means that the CRT patch will illuminate a smaller patch of f ilm, providing the effect of an optical zoom in.

It is necessary to refocus the optical assembly after the CRT has been moved to ensure that the patch is still in focus at the film plane. This is accomplished by a motorised focus track fitted to the lens. This motorised focus track is driven by the same control signals as are used to drive the motorised stage that moves the CRT assembly in the Z direction. It should be noted here that the CRT and coil assembly on the CRT are held f ixed relative to each other, and the CRT and coil assembly are moved together. The effect of moving the CRT nearer to the film is that zoom effects can be accomplished without the quality of image achieved being grain limited as happens with the prior art f ixed CRT systems described above. In practice, it is hard to allow the movement of the CRT beyond certain bounds, due to the physical mounting constraints of the telecine chassis. Typically, the CRT would not be able to move by more than about + or - Smm in the Z direction. Thus, where a zoom of more than about 5mm is required, this is accomplished by a combination of some CRT movement, and some scan patch size reduction. It will be appreciated that any movement of the tube, combined with scan patch reduction will produce less grain defects in the image obtained than would be produced by scan patch reduction alone.

In another embodiment, it may be desirable to use the CRT movement in conjunction with a zoom lens. A typical good quality zoom lens has a zoom ratio of about 1:3. Generally the design of such zoom lenses (lenses that have a user variable focal length) are compromise designs. Thus these lenses have less resolution and contrast than comparable fixed focal length lenses. However, it may be found that with a good quality zoom lens, the defects produced are less significant than those produced by the grain limitation defects of the scan patch size reduction system. As for the previous embodiment, the focus of the lens may require alteration with the movement of the CRT in the Z direction.

It is also possible to utilise any combination of the above described embodiments with the movable CRT. Thu$ zoom can be accomplished by CRT movement alone, CRT movement together with scan patch size changing, CRT movement together with a zoom lens, and finally CRT movement together with both scan patch size changing and a zoom lens alteration.

A second example of the use of the system according to the invention is for the reduction or correction of burn on the CRT face. As described earlier, burn is noticed by seeing the differentially aged parts of the CRT face. This is noticed when the scan patch is changed in size. It is necessary to change the scan patch size to illuminate different film formats. However, by moving the CRT in the Z direction, it is possible to keep the same size scan patch and accommodate different film formats by CRT movement. Thus it is now possible to get an increased CRT life, thereby making a more economical telecine system. This is because the with the prior art systems it is quite common to have to install a new CRT when burn becomes apparent.

It will be noted that it is difficult to move the CRT to get the new format illuminated with the old scan patch if the new film format is a different aspect ratio to the old one. It will be noted in this case that either the horizontal or the vertical dimension can be accommodated is for, but not both. In this case, it has been found that the most noticeable burn edges of the scan patch are the horizontal edges. This is because the Iscantrack' system has some effect in reducing burn of the vertical edges, but not of the horizontal edges.

Thus in a further embodiment of the invention, the CRT is moved in the Z direction until the existing scan patch exactly fits the width of the new film format, and the vertical alignment is then accomplished by adjustment to the scan system control parameters. Since these adjustments are all made available to the operator, this can be adjusted as found best by the operator.

In an alternative embodiment of the invention for minimising burn effects on the face of the CRT, the CRT is slowly moved from side to side, i.e. in the Y direction whilst scanning film. Corrections can be applied to the scanning system parameters to counteract the physical movement of the CRT. Thus it is possible to move the tube with a horizontal sinusoidal motion, whilst keeping the scanning patch constant relative to the film. This provides two advantages. Firstly, it will be seen that burn edges horizontally will not be caused, as effectively there will be no sharp delineation of tube wear, as there would be in a fixed CRT situation. Secondly, the CRT grain pattern will be moving with respect to the film image. It is well known that fixed pattern noise is far more objectionable to the human observer than a moving pattern.

Thus as well as decreasing the running costs of telecine machines, the images produced by the system according to the embodiment of the invention are more pleasing.

In a further extension to the above system, it is also possible to accomplish the benefits of the prior art

Iscantrack' system in the vertical (X) direction by a slow sinusoidal movement of the CRT in the vertical direction. This is accomplished by the physical movement of the CRT in a vertical direction, together with applying inverse motion signals to the CRT scan generation system. This does not necessitate the modulation of the servo system as described in the Rank Cintel patent application and so provides a simpler solution to the problem identified by the scantrack system.

A further example of the use of the system of the present invention is that the scanning patch can always be optically centred with respect to the lens, thus ensuring that optimal optical performance is always achiever.

Further, it is also possible to physically centre the CRT such that the centre of the faceplate corresponds to the centre of the f ilm area. This again ensures the optimum optical quality of the scanning system.

Claims

1. A system for the conversion of images stored on cinematographic film to corresponding electrical signals, the system comprising a cathode ray tube for scanning at least a part of the images on the film, photosensitive means for detecting the light transmitted by the film, and means for moving the cathode ray tube relative to the f ilm.

2. A system as claimed in claim 1, wherein the means for moving the cathode ray tube relative to the f ilm are adapted to move the cathode ray tube backwards and forwards relative to the film in use.

3. A system as claimed in claim 1 or 2, wherein the means for moving the cathode ray tube relative to the film are adapted to move the cathode ray tube in a lateral direction relative to the longitudinal feeding direction of the film.

4. A system as claimed in claim 3, wherein in use, the cathode ray tube is moved in a lateral direction relative to the longitudunal feeding direction of the film before 25. scanning each frame of the film, the cathode ray tube having a scan patch provided on the front face thereof which is moved by a corresponding amount in the opposit( direction before scanning each frame of the film such that the position of the scan patch relative to the film remains constant while reducing the formation of longitudinally extending burn edges on the face of the CRT.

5. A system as claimed in claim 1, wherein the means f or moving the cathode ray tube relative to the f ilm. are adapted to move the cathode ray tube longitudinally relative to the longitudinal feeding direction of the f ilm and, in use, the cathode ray tube is moved before scanning each f rame of the f ilm, the cathode ray tube having a scan patch provided on the front face thereof which is moved by a corresponding amount in the opposite direction before scanning each frame of the film such that the position of the scan patch relative to the film remains constant while reducing the formation of laterally extending burn edges on the face of the CRT.

6. A system for the conversion of images stored on cinematographic film to corresponding electrical signals, the system comprising a cathode ray tube for scanning at least a part of the images on the film, photosensitive means for detecting the light transmitted by the film, and means for moving the cathode ray tube relative to the film in any of three orthogonal planes.

7. A system as claimed in any preceding claim, wherein the means for moving the cathode ray tube relative to the film comprise a motorised stage on which the cathode ray tube is mounted.

8. A system as claimed in any of claims 1 to 6, wherein the means for moving the cathode ray tube relative to the film comprise one or more leadscrews orientated in the respective directions of motion of the cathode ray tube, the cathode ray tube being mounted to the lead screws.

9. A method of converting images stored on cinematographic film to corresponding electrical signals, the method comprising scanning at least a part of the images on the f ilm with a cathode ray tube, detecting the light transmitted by the film, and controlling the area of the film to be scanned by moving the cathode ray tube relative to the film.

10. A method of converting images stored on cinematographic f ilm to corresponding electrical signals, the method comprising scanning at least a part of the images on the film with a cathode ray tube, detecting the light transmitted by the f ilm, and moving the cathode ray tube in a lateral or longitudinal direction relative to the longitudinal direction of travel of the f ilm and moving a scan patch on the cathode ray tube by a corresponding amount in the opposite direction.

11. A method of converting images stored on cinematographic film to corresponding electrical signals, the method comprising scanning at least a part of the images on the film with a cathode ray tube, is detecting the light transmitted by the film, and moving the cathode ray tube in a lateral or longitudinal direction relative to the longitudinal direction of travel of the f ilm so as to align the centre of the cathode ray tube with the f rame of f ilm to be scanned.

12. A system for the conversion of images stored on cinematocrralDhic film to corresponding electrical signals, the system comprising a light source for illuminating at least a part of the images on the film, means for detecting the light transmitted by the film, and means for moving the light source towards and/or away from the plane of the f ilm so as to determine the size of the image on the film which is to be converted.

13. A method for converting images stored on cinematographic film to corresponding electrical signals, the method comprising illuminating at least a part of the images on the film with light from a light source, and detecting at least some of the light transmitted by the film, wherein the light source is moved towards and/or away from the plane of the film so as to determine the size of the image on the film which 16 is to be converted.

14. A system for the conversion of images stored on cinematographic film to corresponding electrical signals, the system comprising a light source for illuminating at least a part of the images on the film, means for detecting the light transmitted by the film, and means for moving the light source laterally relative to the longitudinal direction of travel of the film so as to align the centre of the image on the f ilm which is to be converted with the light source.

15. A method for converting images stored on cinematographic film to corresponding electrical signals, the method comprising illuminating at least a part of the images on the film with light from a light source, and detecting at least some of the light transmitted by the film, wherein the light source is moved laterally relative to the longitudinal direction of travel of the film so as to align the centre of the image on the f ilm which is to be converted with the light source.

16. A system for the conversion of images stored on cinematographic film to corresponding electrical signals substantially as herein described with reference to the accompanying drawings.

17. A method of converting images stored on cinematographic film to corresponding electrical signals substantially as herein described with reference to the accompanying drawings - I s I I