FR2734921A1 - TRAINING DEVICE FOR A CINEMATOGRAPHIC FILM, IN PARTICULAR FOR THE DIGITIZATION OR PRINTING OF FILM IMAGES - Google Patents

Abstract

A device for continuously driving a motion picture film, particularly for digitising frames of said film or printing images thereon, includes motor-driven reels (10, 12) for spooling and unspooling the film (14), movable rollers (18) for maintaining the film (14) under constant tension, and means (20) for driving and guiding the film past frame digitising or image printing means (22) which are controlled synchronously with the instantaneous movement of the film. The invention enables the rate of digitising frames of a photographic film or printing images thereon to be increased while improving the digitising or printing resolution.

Description

DEVICE FOR DRIVING A CINEMATOGRAPHIC FILM,
ESPECIALLY FOR DIGITIZATION OR
PRINTING FILM IMAGES
The invention relates to a device for driving a cinematographic film, in particular for digitizing images of the film or printing images on the film at a high rate.

 Known devices for reading and digitizing images from a cinematographic film or printing images on a cinematographic film do not allow high scanning or printing rates, for example of the order of several images per second.

 These devices are often of the advance-by-frame type of film and therefore operate according to successive phases of advancing the film over a distance corresponding to an image, stopping the film, scanning or printing, advancing on a distance corresponding to an image, etc.

 There are, however, devices for the continuous movement of the film at constant speed (case of tele-cinema devices) which are associated with reading means constituted either by a video camera associated with a rotating prism, or by a strip of photo-detectors. , these devices being capable of operating at a relatively high rate, but with relatively low positioning accuracy and a relatively low resolution, which makes it possible to use them for making a video copy of a cinematographic film, but does not allow processing precise digital images of a film.

 The known means of printing images on a photo-sensitive film which are currently used to transfer to a cinematographic film sequences of images produced or processed digitally, such as computer generated images or special effects, generally comprise a monochrome cathode-ray tube associated with a color filter system, and a cinema camera ensuring the images are taken on the cathode screen in view-by-view mode with three shots per image, one per color, in synchronism with the permutation of the colored filters. These printing devices have a relatively limited operating rate and a low resolution (that of the cathode-ray tube).

 There are also printing devices using the projection onto a photosensitive film of a laser beam modulated in brightness and in color, which scans the surface of the film along parallel lines. The film is held in position on a mobile support with controlled micrometric displacement.

The movement of the film is discontinuous and is done image by image.

 I1 therefore does not currently exist devices which would make it possible to ensure the continuous running of a cinematographic film at constant speed for the digitization of images or the printing of images at high rate (of at least one image per second ) and with a good resolution, compatible with that required for the images of a cinematographic film.

 The subject of the invention is a device which enables this gap to be remedied.

 To this end, it provides a device for continuously driving a cinematographic film, in particular for digitizing images of the film or printing images on the film at a high rate, this device comprising winding reels and for film unwinding, motor means for driving the reels in rotation, film tensioning means and film guiding means in front of image scanning or printing means, characterized in that the guiding means of the film comprise a drive roller making it possible to scroll the film at constant speed in front of the digitization or printing means and a roller driven by the film and associated with a digital encoder making it possible to measure the instantaneous movement of the film, means being provided between the digital encoder and the means for digitizing or printing images to synchronize the operation of the latter with the measured displacement of the film.

 By using an appropriate digital encoder, it is thus possible to read cinematographic film images, for example with a linear array of photodetectors, according to parallel scanning lines whose pitch is of the order of 5 to 10 Cun, with a rate of scanning which is limited only by the performance of the scanning or printing means and which, with current means, easily reaches values of the order of 1000 to 5000 lines per second or more, which makes it possible to digitize several images per second (for example from 5 to 10 images per second or more) and with excellent resolution, typically of the order of a pin.

 This makes it possible in particular to digitize images of a cinematographic film, to modify the digitized images by means of an information processing system, then to print the modified images on a paper medium or on a photosensitive film.

 Synthetic images can also be transferred to a film (created by an information processing system).

 According to another characteristic of the invention, the device comprises movable rollers exerting a constant tension on the film, arranged between the reels for winding and unwinding the film and the aforementioned rollers of the film guide means, measuring means position deviations of these movable rollers with respect to a predetermined average position, and servo means for determining the rotational speeds of the winding and unwinding coils as a function of the measured values of the position deviations of the movable rollers.

 The movement of the film at constant speed in front of the means for digitizing or printing images makes it possible to reduce the mechanical stresses exerted on the film, which is particularly advantageous in the case of the digitization of old films which are often quite fragile. The displacement of the film at constant tension makes it possible to avoid any elongation of the film and to guarantee a constant dimension of images. This also makes it possible to reduce the risks of accidental tearing of the film and therefore to increase the reliability of the device.

 According to another characteristic of the invention, the aforementioned means for guiding the film comprise a portion of cylinder of which a generator is located opposite the means for digitizing or printing images.

 Advantageously, this cylinder portion is defined by curved tracks in the cylinder portion and / or by ball bearings or the like, on which the edges of the film are applied, means for transversely guiding the film, exerting an elastic thrust on a lateral edge of the film, also being provided.

 These guide means make it possible to ensure perfect flatness of the film opposite the means for digitizing or printing images, and this without it being necessary to press the film on a solid surface, which limits friction and the risk of deterioration of the film.

 When the means for digitizing or printing images of the device according to the invention are of the prism or rotating mirror type for scanning the images or the film along parallel lines, means are provided to compensate for position differences of the film with respect to the desired theoretical positions for the beginnings of the scanning lines, these means comprising a movable mirror with piezoelectric control or the like interposed between the film and the prism or rotating mirror.

 This makes it possible to compensate for differences in the position of the film at the start of each scanning line, which may be of the order of a micrometer.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the appended drawings in which
FIG. 1 schematically represents a device according to the invention
Figures 2 and 3 schematically show film guide means
FIG. 4 schematically represents the means of constant tension of the film
FIG. 5 schematically represents an alternative embodiment of a part of the device according to the invention;
FIG. 6 schematically represents another variant embodiment of the device according to the invention.

 Reference is first made to FIG. 1, which schematically represents a device according to the invention essentially comprising two reels 10 for unwinding and 12 for winding the film 14, rollers 16 for guiding the film, rollers 18 for tensioning the film. film and specific means 20 for guiding the film in front of means 22 for digitizing the images of the film or for printing images on the film.

 The invention essentially consists in moving the wire continuously at a constant speed and under constant tension, at least at the level of the digitizing or printing means 22, to accurately measure the movement of the film in front of the means 22 and to synchronize the operation of the means 22 with the measured displacement of the film.

 For this, the means 20 for guiding the film comprise a guiding surface 24 in the form of a cylinder allowing a cylindrical shaping of the film 14 in line with the axis 26 of the means 22 so that the part of the film which is located on the axis 26 forms a generatrix of the cylinder portion 24 and is therefore perfectly straight.

 The guide means 20 also comprise a drive roller 28 arranged at the outlet of the surface 24 in the portion of a cylinder and associated with a guide roller 16 so that the film 14 passes over the roller 28 over approximately 180 o so as to be able to be driven without sliding by the roller 28. A driven roller 30 on the axis of which is mounted a digital encoder 32, is provided at the other end of the guide surface 24, that is to say at the entrance to that -ci and is also associated with a guide roller 16 so that the film 14 passes over about 180 o on the roller 30 to drive the latter without sliding.

 The output of the digital encoder 32 is connected by processing and synchronization means 34 to a control input of the means 22 for digitizing or printing images.

 Means, not shown, are provided for regulating the speed of rotation of the drive roller 28, these means comprising for example a tachometric dynamo driven by the axis of the roller 28 and producing a signal which is compared with a set speed to control the roller drive motor 28.

 As shown diagrammatically in FIG. 2, the surface 24 in the portion of the film guiding cylinder 14 may consist of cylindrical tracks 36 on which the lateral edges 38 of the film 14 are applied and by annular tracks 40 of transverse film guiding, one of these tracks 40 being carried by a ring 42 subjected to the action of a pressure spring 44 to push the film 14 in abutment on the other annular track 40.

 The cylindrical 36 and annular 40 guide tracks of a lateral edge of the film and the guide tracks of the other lateral edge of the film can be mounted independently and adjustable on the same support 46, for adaptation of the device according to the invention to films of different widths.

 Alternatively, as shown in Figure 3, the guide tracks of the lateral edges of the film 14 can be replaced by ball bearing rings or the like, some 48 of which correspond to cylindrical tracks 36 and the other of which 50 correspond to annular tracks 40 of the embodiment of FIG. 2.

 The means enabling the film 14 to be placed under constant tension at the level of the digitization or printing means 22, comprise two movable rollers 18 for guiding the film, which are placed on either side of the guide means 20, upstream and downstream respectively of the aforementioned rollers 32 and 28, and which are subjected to identical and parallel tensile forces T, as shown in FIG. 1. The movable rollers 18 are movable in one direction and in the other parallel to the aforementioned forces T , and are each arranged between two guide rollers 16 which define a film path substantially parallel to the tensile forces T exerted on the movable rollers 18. Means 52 are provided for detecting the positions of the movable rollers 18 along their movement path, compare the detected positions with predetermined average positions and control the rotational speeds of the unwinding and rewinding coils 10, resp ectively, as a function of the detected deviations, so as to keep the movable rollers 18 as much as possible in their predetermined average position or in the immediate vicinity thereof.

 The aforementioned means 52 are equipped with position sensors such as potentiometers or contactless sensors, for example with Hall effect.

 An embodiment of the means making it possible to apply tensile forces T identical to the two movable rollers 18 is shown diagrammatically in FIG. 4.

 In this embodiment, each roller 18 is carried by an arm 54 mounted pivoting about an axis 56 parallel to the axis of the roller 18, the two arms 54 being identical and mounted symmetrically with respect to the same spring of tension 58 to which they are connected by a common beam 60 and by inextensible links 62, the tension spring 58 being hooked on the one hand in the middle of the beam 60 and on the other hand on a support 64, optionally adjustable.

 The tension spring 58 is chosen so as to exert approximately constant restoring forces on the rollers 18 regardless of their position on either side of their predetermined average position, so that the tension exerted on the film 14 by the rollers 18 does not vary appreciably as a function of the position deviations of these rollers with respect to their predetermined average position.

The operation of the device which has just been described is as follows
The speeds of rotation of the unwinding reels 10 and of the film winding 12 are determined by the means 52 so as to maintain the movable rollers 18 in their predetermined average position where they exert a constant predetermined tension on the film 14, on the one hand and other guide means 20. This tension is for example of the order of 1 N per cm of width of the film 14.

 The speed of movement of the film on the guide means 20, opposite the scanning or printing means 22, is controlled by the drive roller 28 and is kept constant by the servo loop of the drive motor of this roller , this speed being for example of the order of a few cm per second.

 The instantaneous movement of the film is precisely measured by the digital encoder 32 associated with the driven roller 30 and is used to synchronize the operation of the digitizing or printing means 22.

 For example, when the digitization means are constituted by a linear array of photodetectors arranged along the aforementioned generatrix of the surface 24 in the portion of a cylinder, the operation of the photodetectors is controlled to produce transverse scanning lines on the film with a steps of the order of 5 to 10 pins at a rate of the order of 1000 to 5000 scans per second, for example, or more. For this, the digital encoder 32 can be of the type providing 40,000 points per revolution, which corresponds to approximately one hundredth of a degree per point, and the output signal of the digital encoder can be processed (for example divided by a constant factor) to provide the film scan line step signal.

 Resolutions are thus obtained whose order of magnitude is the pin, for example resolutions which are between 1 and 3 pin, while the resolution of a conventional tele-cinema device is approximately 30 pin.

 The start and end of each image can be signaled to the digitizing means 22 by counting the perforations formed in the lateral edges of the film, this counting being carried out by a counter associated with a photoelectric cell or with a conventional toothed wheel.

 When the means 22 are of the rotating prism or faceted rotating mirror type, the speed of rotation of the prism or the mirror can be determined globally by the output signal from the digital encoder 32. However, due to the inertia of the prism or of the rotating mirror, small variations in the speed of movement of the film 14 cannot be taken into account in order to instantly modify the rotation of the prism or of the rotating mirror, and the device shown schematically in FIG will be used for this purpose. 5.

 In this figure, a laser beam 66, which can be modulated in brightness and in color for printing images on the film 14, is projected by a rotating mirror 68 with facets on a small mirror 70 orientable around an axis 72 to return the laser beam to the film 14 perpendicular thereto.

 The angular position of the small mirror 70 around the axis 72 is controlled by displacement means 74 of the piezoelectric type or the like as a function of the instantaneous displacement of the film 14 measured by the digital encoder 32 of the device of FIG. 1.

Thus, small variations in this displacement, which are for example of the order of 1 pin, can be compensated for by very small displacements of the mirror 70 around the axis 72, in one direction or the other, so that the scanning of the film 14 by the laser beam 66, resulting from the rotation of the mirror 68, begins each time at the desired point without having to modify the instantaneous speed of rotation of the mirror 68.

 As a variant, the mirror 70 can be moved in translation by the means 74 in the direction of the incident laser beam 66, which makes it possible to move the position of the point of impact of the laser beam on the film 14 in a corresponding manner.

 6 shows an alternative embodiment of the device of Figure 1, this variant comprising the same means as those already described, namely coils 10 and 12 for unwinding and winding the film 14, tension rollers 18, means 20 for guiding the film in line with the digitization or printing means (not shown), these guide means 20 comprising at their ends a drive roller 28 and a driven roller 30 associated with a digital encoder, the embodiment of FIG. 6 differing from FIG. 1 in that the guide rollers 16 placed on either side of a movable tension roller 18, are themselves movable between a service position where they are shown in solid lines and a rest position shown in dotted lines where they exert no action on the film 14 which then takes a relaxed position shown in dotted lines between the coils 10 and 12.

 Thus, when the guide rollers 16 are in their rest position shown in dotted lines, it is easy to mount the film on the device by simply making it occupy the position shown in dotted lines between the two coils 10 and 12.

Then, the rollers 16 are brought back to their service position shown in solid lines, which has the effect of applying the film to the guide means 20 and putting it under tension on the rollers 18.

 To facilitate the movement of the rollers 16 between their two positions, they can be mounted two by two on arms movable in translation and / or in rotation by operating a common lever.

 In general, the invention allows the digitization of the images of a photographic film or the printing of images on a photographic film at a high rate of several images per second with excellent resolution, or even with a very high rate of several tens of images per second if we accept a slightly worse resolution.

Claims (10)

 1. Device for continuously driving a cinematographic film, in particular for digitizing images of the film or printing images on the film at a high rate, comprising reels (10, 12) for unwinding and winding of the film (14), motor means for driving the film in rotation, means (18) for tensioning the film and means (20) for guiding the film in front of means (22) for scanning or printing images, characterized in that the means (20) for guiding the film comprise a drive roller (28) making it possible to run the film (14) at constant speed in front of the means (22) for scanning or printing and a roller (30) driven by the film and associated with a digital coder (32) making it possible to measure the instantaneous displacement of the film, means (34) being provided between the digital coder (32) and the means (22) for digitizing or printing to synchronize the operation of the latter on the measured displacement of the film (14).  2. Device according to claim 1, characterized in that it comprises movable rollers (18) exerting a constant tension on the film (14), arranged between the unwinding and winding coils (10, 12) and the rollers aforementioned (28, 30) guide means (20), means (52) for measuring the position deviations of the movable rollers (18) relative to a predetermined average position, and servo means for determining the speeds of rotation of the unwinding and winding coils (10, 12) as a function of the measured values of the position deviations of the movable rollers (18).  3. Device according to claim 2, characterized in that the movable rollers (18) of film tension, which are arranged on either side of the guide means (20) above, are subjected to the restoring force of a common spring (58).  4. Device according to claim 2 or 3, characterized in that the mobile tension rollers (18) are carried by pivoting arms (54) connected to the same tension spring (58) by a beam (60).  5. Device according to claim 3 or 4, characterized in that the spring (58) for returning the movable rollers (18) exerts a substantially constant tensile force on these rollers for their entire displacement travel.  6. Device according to one of claims 2 to 5, characterized in that rollers (16) for guiding the film are mounted on either side of each movable tension roller (18) to define a path for the passage of film substantially parallel to the direction of movement of the movable roller.  7. Device according to claim 6, characterized in that the aforementioned guide rollers (16) are carried by movable supports movable between a service position and a rest position.  8. Device according to one of the preceding claims, characterized in that the means (20) for guiding the film comprise a surface (24) in the portion of a cylinder of which a generator is located opposite the means (22) for scanning or printing images.  9. Device according to one of the preceding claims, characterized in that the means (20) for guiding the film include curved tracks (36, 40) and / or bearings (48, 50) for guiding the edges of the film. (14), as well as means (42, 44) of transverse guide with elastic action on a lateral edge of the film.  10. Device according to one of the preceding claims, characterized in that the digitization or printing means are of the prism or rotating mirror type (68) for scanning images or film along parallel lines and in that means are provided to compensate for deviations in the position of the film relative to the desired theoretical positions of the film for the start of each scanning line, these means comprising a movable mirror (70) with piezoelectric control (74) or the like, interposed between the film (14) and the prism or rotating mirror (68).