GB2025731A

GB2025731A - Electronic film scanning apparatus

Info

Publication number: GB2025731A
Application number: GB7924904A
Authority: GB
Original assignee: Agfa Gevaert AG
Current assignee: Agfa Gevaert AG
Priority date: 1978-07-17
Filing date: 1979-07-17
Publication date: 1980-01-23
Also published as: JPS5514400U; FR2431810B1; GB2025731B; FR2431810A1; JPS6336768Y2

Abstract

An apparatus for the electronic scanning of colour films for projection onto a TV screen. The apparatus comprises a film illumination and drive system 1 and an oscillatory mirror system 2 including an oscillatory coil S for deflecting the image in the direction of film transport. A picture sensor 3 is arranged in the image plane and includes a charge coupled device having a line of photosensitive diodes and an analog register responsive to the diodes. For each picture point, there are three diodes sensitive respectively to red, green and blue. The output of the sensor 3 is connected through decoding logic 8 to an encoding unit 13 which produces a conventional FBAS video signal. The coil S is driven by a saw- tooth voltage onto which is superimposed a large positive pulse for providing flyback acceleration and a large negative pulse for subsequent retardation. <IMAGE>

Description

SPECIFICATION Electronic film scanning apparatus The present invention relates to an apparatus for the electronic scanning of films for projection onto a TV screen comprising a continuously operated film projector, a picture sensor having a line of photo-sensitive elements arranged transversely of the direction of film transport in the projection plane of the projector, and a signal processor responsive to the output of the picture sensor for producing a video signal.

In an existing apparatus for electronically scanning "super-eight" films for projection onto a colour TV screen with a continuously operated film projector (Funkschau 1974, Volume 9, pages 292 to 298) the film is scanned by a pick-up tube. For producing the red, green and blue selector signals required for a colour television tube there is provided a reflector box with two dichroic mirrors and three colour filters which co-operate with three photo-multiplier tubes. This apparatus is mechanically complex and expensive.

It is further basically possible for producing a video signal for a black and white TV receiver set to arrange in the projection plane of the projector lens a charge coupled device (CCD) having a scanning line of photo-diodes extending transversely of the direction of film transport, the photo-diodes acting as picture sensor elements. However, up to now it has not been possible to use such an arrangement with a colour television set.

According to the present invention there is provided an apparatus for the electronic scanning of films for projection onto a TV screen comprising a continuously operated film projector, a picture sensor having a line of photo-sensitive elements arranged transversely of the direction of film transport in the direction plane of the projector and a register means responsive to each element, and a signal processor responsive to the output of the picture sensor for producing a video signal, the line of photo-sensitive elements comprising a set of three photo-sensitive elements for each picture point, the three elements of each set being arranged in the longitudinal direction of the line and being sensitive respectively to the three different colours.

Usually, the three different colours are red, green and blue.

Preferably, the picture sensor comprises a charge coupled device, the photo-sensitive elements being photo-diodes.

With this arrangement only a single line of photo-diodes is required in the CCD for producing a colour television signal which, by comparison with a black and white system, comprises three times the number of picture sensor elements. The colour splitting of each scanned picture point by means of the red, green and blue sensitive sensor elements arranged in the longitudinal direction of the diode line is particularly suitable for modern "in-line" television tubes wherein the three colours of any one picture point are also reproduced in one line.

The output charges provided by the individual sensor elements of the photo-diode line to the register means produces the electronic signal of one video line. Successive video lines are obtained by moving the projected film image over the photo-diode line in synchronism with the vertical scan frequency of a television picture.

Preferably, the register means is an analog shift register having storage capacitors connected in parallel with the photo-sensitive elements, the output of the shift register being fed to a time division demultiplexer.

The individual colour signals are then available at the output of the demultiplexer. This arrangement has the advantage of using only a simple analog shift register but requires a comparatively high shift frequency.

Alternatively, the register means may comprise a set of three analog shift registers, each individual shift register being associated with one of the three colours and responsive to the photo-sensitive elements which are sensitive to said colour. Such an arrangement makes higher demand on IC technology since three analog shift registers are required on the CCD-chip, but the required shift frequency is reduced to about one third.

Advantageously, the photo-sensitive elements are rendered sensitive to the three different colours by being coated by vapour-deposition with interference layers. This may be achieved by conventional integrated circuit masking techniques.

As a convenient alternative, the photo-sensitive elements may be rendered sensitive to the three different colours by a filter having bands of the three colours.

Conveniently, a transfer gate is provided between the line of photo-sensitive elements and the register means.

Preferably, the film projector includes an oscillatory mirror system for deflecting the image of the film picture in the direction of film movement at a frequency corresponding to the frame scan frequency of the video signal.

Preferably, during each oscillation of the oscillatory mirror system the image of the film pictures is deflected by an amount corresponding to two thirds of the height of an individual picture.

The oscillatory mirror system may be of a kind provided in galvanometer technology, subject to a minor modification to the magnet. A modified galvanometer mirror system of this kind will satisfy the high frequency requirements of the apparatus of the present invention.

Preferably, the oscillatory mirror system includes an oscillatory coil of the kind used in galvanometer technology. The coil oscillator is preferably controlled by means of a summing circuit.

In order to use the apparatus of the present invention with a galvanometer mirror having a large surface area and a critical frequency in the vicinity of the required deflection frequency, the mirror system prefereably further includes a saw tooth pulse generator, a first pulse forming stage controlled by the sawtooth pulse generator for providing a short flyback acceleration pulse during the flyback of the sawtooth pulse, and a second pulse forming stage controlled by the sawtooth pulse generator for providing a short braking and acceleration pulse, the sum of the pulse duration of said two short pulses not exceeding the standard T.V. flybacktime, the summing circuit being responsive to the outputs of the sawtooth pulse generator and the two pulse forming stages and including adjustable elements whereby the amplitude of the sawtooth pulse and that of the two short pulses can be independently regulated. The sum of the pulse durations of said two short pulses should preferably not exceed 1 .2msecs.

With this arrangement, it is possible to use an oscillatory mirror having a comparatively large surface area whilst ensuring that the flyback time will be terminated within a maximum period of 1.2ms. The oscillatory mirror system displaces the image of the film pictures or frames in the vertical direction at the standard T.V.

scanning frequency of 50Hz. Consequently the flyback time between each frame must not exceed the standard T.V. vertical flyback time of 1 .2ms. The upper frequency limit of the oscillatory mirror system should be selected such that the transient oscillations during flyback are terminated within 1 .2ms. In critically damped systems this is achieved after a time of 1/fox where f0 is the characteristic resonance frequency of the oscillatory mirror system.However, since most galvanometer systems are designed with a damping factor of 0.7, that is to say with a small amount of overshoot, the transient oscillations will be terminated only at the end of time t = approximately 1 .5/fro. In this case, therefore, the characteristic resonance frequency fmin of the oscillatory mirror system must be at least: fmin 1.5/1.2ms. = 1.25 kHz.

In a further development, the first pulse forming stage for providing the flyback acceleration pulse comprises a monostable, the second pulse forming stage for providing the flyback braking and acceleration pulse comprises two monostables, and the moment in time and the duration of the output pulses are independently adjustable.

By virtue of these provisions a very simple control circuit for the oscillatory mirror system is created which does not require a complex and expensive feedback circuit of the kind provided in a conventional arrangement and in which the oscillatory mirror is associated with a position indicator which executes the same movements as the mirror and has a voltage output which is proportional to this movement. The actual mirror position is compared constantly with a potential which is proportional to the desired mirror position and the difference between the actual and desired potentials is fed via an amplifier as a control potential to the oscillatory mirror system. With the arrangement of the present invention there is no need for providing such a feedback control circuit with its well known drawbacks regarding synchronization of the time base.

The present invention will now be described in more detail by way of example with reference to the accompanying drawings in which: Figure 1 is a diagram of an electronic film scanning apparatus embodying the present invention, Figure 2 is a voltage/time graph for the oscillatory mirror sysystem forming part of the apparatus shown in Figure 1, Figure 3 is a diagrammatic representation of the picture scanning process of the oscillatory mirror system, Figure 4 is a block circuit diagram of a charge coupled device and associated decoding logic forming part of the apparatus of Figure 1 together with a truth table for the decoding logic, Figure 5 is a graph of the signals appearing in the circuit of Figure 4 plotted against time, Figure 6 is a block circuit diagram of another example of a charge couple device forming part of the apparatus of Figure 1, Figure 7 is a graph of the movement plotted against time of an oscillatory mirror forming part of the oscillatory mirror system, Figure 8 is a graph of the voltage plotted against time used to drive the oscillatory mirror, and Figure 9 is a block circuit ciagram of the control circuit for the oscillatory mirror.

Figure 1 shows an electronic scanning apparatus for scanning "super-eight" films for their projection onto a colour television screen. The apparatus comprises a film projector in the form of an illumination and drive system 1 with a projection lens for the "super-eight" film and an oscillatory mirror system 2, a picture sensor 3 comprising a charge coupled device (CCD) having a scan line of photodiodes providing colour splitting of each scanned picture point, and a signal processor for producing a video signal.

The illumination and drive system 1 is controlled by a phase comparator 4. The oscillatory mirror system 2 includes an oscillatory coil S which is controlled by a summing circuit 5 and an amplifier 6. The output of the picture sensor 3 includes an amplifier 7 which feeds decoding logic 8. The decoding logic 8 has three outputs which are respectively for red, green and blue signals which are conducted via amplifiers 10, 11 and 12 to an encoding unit 13. The encoding unit 13 comprises an FBAS encoder E, a high frequency modulator H, and a high frequency generator C. The output of the encoding unit 13 is fed to the colour T.V. set.

A central timing circuit 9 is provided for controlling the phase comparator 4, the summing circuit 5, the picture sensor 3, the decoding logic 8 and the encoding unit 13.

The illumination and drive system 1 is similar to that provided in a conventional "super-eight" film projector but has certain special features compared with the latter. The super-eight film is continuously advanced or transported by a capstan or toothed wheel engaging the film perforations. The phase position of the individual super-eight pictures or frames relative to the phase of the oscillatory mirror system 2 is measured and adjusted by the circuitry of the phase comparator 4, and preferably the film perforations are scanned by a small light cell Lfor measuring the relative phase position of the super-eight frames.

The frame or picture frequency is not 18 or 24 frames per second but a whole number fraction of the standard T.V. vertical vertical scan frequency of 50 Hz, i.e. 16 2/3 or 25 frames per second. The slight acceleration or retardation effect in the projection of the film does not impair reproduction quality and is perfectly acceptable.

The oscillatory mirror system 2 defects the -images of the film pictures in the vertical direction at the required TV standard vertical scan frequency of 50Hz. Flyback time between said picture or frame must not exceed the prescribed vertical flyback standard time of 1 .2ms. A suitable oscillatory mirror system for this apparatus is an oscillatory mirror system of the kind used in galvanometer technology. The upper frequency limit of the system must be selected so that transient oscillations during flyback are terminated within a maximum period of 1 .2ms. This would be achieved in a critically damped system after a time of 1/fox f0 being the characteristic resonance frequency of the oscillatory system.However, since most galvanometer oscillatory systems are designed with a damping factor of 0.7, that is to say with a small amount of overshoot, the transitory oscillations are terminated only after t = 1.5 (1/fro) This means that the characteristic resonance frequency fmin of the oscillatory system must be at least: fmin = 1.5/1.2 ms. = 1.25kHZ.

It should be mentioned that oscillatory coils having a characteristic frequency f0 = 15kHz are commercially available.

The oscillatory coil S is controlled by the summing circuit 5 and the amplifier 6. The composite sawtooth signal which is needed for scanning a super-eight film, taken at the rate of 18 frames per second, is shown in Figure 2. The signal form for the sweep voltage thereshown can easily be produced by adding a simple sawtooth voltage to a square wave voltage. Concurrent with this addition a pre-distortion voltage may be applied to the sawtooth voltage, e.g. for compensation of the tangent fault in the scan.

The movement of the oscillatory mirror is shown more clearly in Figure 3 where the instantaneous film positions at 20 ms. intervals are drawn side by side, that is to say the positions after each scan (for a TV half picture).

At time t = 0 the mirror is at such a position where the first line of one of the frames (frame 1 in Figure 3) projected on to the line of photodiodes in the picture sensor 3. After 20 ms. the film has descended by a distance corresponding to one third of the height of a picture frame and the movement of the oscillatory mirror ensures that after 20 ms. precisely the last line of the picture is projected on to the line of photodiodes.

In other words, the mirror movement corresponds to only two thirds of the height of the frame, the remaining third being provided by the film transport.

Mirror flyback corresponds to the length of a whole frame as indicated by the dotted sawtooth line, which represents the control voltage applied to the oscillatory coil. At the end of each third scan, that is to say when t = 60 ms. there is no flyback because the position of the last line of the first frame corresponds approximately to the position of the first line of the second frame. The small difference in the position between these two lines may be compensated by the addition of an appropriate square wave voltage. The actual form of the oscillatory mirror movement includes the flyback movement as shown by the dashed lines in Figure 2. In Figure 3 the frame or image window of the illumination system is designated F.

Turning now to the rest of the apparatus, it is sufficient to described the picture sensor 3 together with the associated decoding logic 8 as the processing of signals to provide an output FBAS signal modulated on an HF carrier is well known in television technology.

Turning now to Figure 4, there is shown a first example of the picture sensor 3 in which the three colour signals are produced by a time demultiplexor. The CCD comprises a line of photodiodes 14 connected by a transfer gate 15 to an analog shift register 16. Timing is provided by a clock circuit U which produces timing signals T. The output line of the analog shift register 16 includes a charge amplifier 17 at the output of which appears a colour signal A containing in series the colour components of each scanned picture point. The colour signal A is fed into a three channel demultiplexer 18 at the output of which appear the colour signals R, G and B. The demultiplexer 18 is controlled via an associated decoding logic 19 which includes a two bit counter Z and associated gates as shown in Figure 4. The signals appearing in Figure 4 are shown plotted against time in Figure 5.

The photosensitive part of the CCD consists of a line photodiodes 14 which, for example, comprises 1200 silicon photodiodes spaced at intervals of 13 micrometers thereby providing a total width to the line of 15.6 millimeters. The objective lens of the illumination and drive system 1 is arranged so that one line of super-eight film is enlarged to the width of the photodiode line. The oscillatory mirror is spaced from the photo-diode line 14 by a distance which provides the maximum required deflection of the projective image, which is 1 1/3 times the height of the frame, without exceeding the permitted angle of deflection of the mirror. This distance should also be as large as possible so as to minimize the tangent error occurring during projection.

When t = 0 in the example shown in Figure 3 and the first line of frame 1 is projected onto the photodiode line 14 (Figure 4), the transfer gate 15 will be briefly rendered conductive in the forward direction by means of a pulse edge and the brightness signal stored in each photosensitive element (each photosensitive element of the photodiode line is connected with a storage capacitor) will be transferred to the analog shift register 16.

After this, the pulses Twill push the signal which is stored in the analog shift register 16 out so that it is available via charge amplifier 17 at the output of the CCD.

The frequency of the pulses T is selected so that the content of the analog shift register 16 are pushed out precisely within the horizontal sweep time (52.5 microseconds) of the associated TV line. For black and white reproduction this signal corresponds directly to the actual video signal and is processed in the usual way into a BAS signal. In this case, it is sufficient for the photodiode line to have approximately 400 photo-sensitive elements. For colour reproduction, the three colour components of each picture point could be obtained by means of the familar colour television process of beam splitting by dichroic mirrors, colour filters and three photodiode lines.

In the illustrated example, however, only a single photodiode line 14 is provided having three times this number of elements. Also, the photosensitive elements are arranged sequentially to be red, green, and blue sensitive, either by vapour deposition of interference layers during their manufacture, masking of this kind is common practice in the making of integrated circuits - or by means of a filter having bands of these three colours. In other words, each picture point is defined by a set of three photosensitive elements which are sensitive respectively to the three colour components. This is particularly advantageous for modern "in line" television tubes because these likewise reproduce each picture point by three laterally adjacent colour points: red, green and blue.

At the output of the CCD the sequential colour signal A is available which contains in three successive time periods the red, green and blue components of each picture point. This signal is converted with the aid of the three channel demultiplexer 18 and associated decoding logic 19 into the parallel colour signals R, G and B.

The demultiplexer 18 produces the signal A sequentially at its three outputs, R, G, and B where it is stored, for example, by small capacitors, until the arrival of the next picture point information. As already mentioned, the output frequency of the clock circuit must be chosen so that the contents of the analog shift register 16 are pushed out within the horizontal sweep duration (52.5 microseconds) of each television line.

In the present example where there are 1200 photodiodes in the photodiode line, the output frequency fT of the clock circuit U must be: fT= Hz = 1200 52.5.10-6 CCD components capable of working at clock frequencies of this order are commerically available.

Figure 6 illustrates anothe form of the picture sensor 3 which operates at a substantially lower clock frequency but makes higher demands on IC technology in as much as three analog shift registers are required on the CCD chip.

The photodiode line 20 of this CCD corresponds exactly to the photodiode line 14 of the example shown in Figure 4. However, in the example shown in Figure 6, each of the analog shift registers 22,2324 is responsive only to the photodiodes which are sensitive to an associated colour. This means that there is a separate shift register for each of the red, green, and blue sensitive photodiodes. The transfer gate 21 connects the photodiodes in parallel to the three shift registers.

The charges are driven out of the three shift registers 22, 23 and 24 and are amplified respectively by three charge amplifiers 26, 27 and 28, the three colour signals R, G and B appearing respectively at the output of the three amplifiers. These output signals may be fed directly to a conventional television signal processor for producing an FBAS signal. The required clock frequency is now reduced by precisely a factor of three in comparison with the system described with reference to Figure 4 since each clock pulse T produces a picture point with complete colour information from the three analog shift registers.For 1200 photodiodes the clock frequency fT of the clock circuit U is calculated as follows: fT= ~ 400 Hz 7.5 MHz 52.5. 106 Figure 7 shows the oscillatory mirror movement 5 required for vertical deflection of the film projection onto the photodiode line, one TV half frame being scanned during each interval between minimum and maximum deflection. As will be seen from Figure 7, with the arrangement described above the transient oscillations occurring during flyback are terminated within 1.2 milliseconds so that the linear rise of deflection follows directly from each minimum deflection.In contrast, the dashed curve a illustrates mirror deflection which occures with excessive retardation, curve b shows mirror deflection occurring with insufficient retardation and curve c shows the deflection which occurs with insufficientflyback acceleration.

Referring now to Figure 8, on completion of each forward sweep of the mirror, a large negative pulse is initially required for strongly accelerating the mirror in the flyback direction. The energy which may be supplied by this pulse is limited only by the electromechanical load bearing capacity of the oscillatory mirror system. This negative pulse causes the mirror to have a very high speed at the end of flyback. This must be quickly retarded and the mirror must then be accelerated in the opposite direction up to the speed required for the next forward sweep. This retardation and acceleration to the forward speed is obtained by a positive pulse 110 following shortly after the negative pulse 109.By precise adjustment of the positive pulse with regard to its amplitude, duration and time, it is possible to accelerate the mirror very rapidly without overshoot to the required forward sweep speed, that is to say, that it executes the required sawtooth movement with very different forward sweep and flyback speeds.

Referring now to Figure 9, there is shown the circuit for providing the control voltage Us as shown in Figure 8 for the oscillatory coil of the oscillatory mirror system. The circuit comprises a sawtooth generator 101 which provides the linear forward sweep and the rapid flyback voltages and which is of conventional design and so is not here specifically described. The sawtooth generation 101 also provides during flyback a short pulse which is fed to a first pulse forming stage 102, which produces the flyback acceleration pulse, and also to a second pulse forming stage 103 which provides the retardation and forward sweep acceleration purse. In the present example, the pulse forming stage 102 comprises a monostable in which the duration of the output pulse can be easily adjusted. The pulse forming stage 102 comprises two monostables which have two adjustable potentiometers for independently adjusting in known manner the time and duration of the output pulses. The sawtooth voltage and the two pulses provided by the pulse forming stages 102 and 103 are fed into a circuit in the form of a summing amplifier 104 and the amplitude of the voltages can be adjusted by means of potentiometers 105, 106 and 107. The output of the summing amplifier 104 is fed into the oscillatory coil indicated at 112. Conveniently, the summing amplifier 104 is provided with a current limitor for protecting the oscillatory mirror system.

Claims

1. An apparatus for the electronic scanning of films for projection onto a TV screen comprising a continuously operated film projector, a picture sensor having a line of photosensitive elements arranged transversely of the direction of film transport in the projection plane of the projector and a register means responsive to each element, and a signal processor responsive to the output of the picture sensor for producing a video signal, the line of photosensitive elements comprising a set of three photosensitive elements for each picture point, the three elements of each set being arranged in the longitudinal direction of the line and being sensitive respectively to three different colours.

2. An apparatus according to claim 1 in which the three different colours are red, green and blue.

3. An apparatus according to claim 1 or claim 2 in which the picture sensor comprises a charge-coupled device, the photosensitive elements being photodiodes.

4. An apparatus according to any one of the preceding claims in which the register means is an analog shift register having storage capacitors connected in parallel with the photosensitive elements, and in which the output of the shift register is fed to a time-division demultiplexer.

5. An apparatus according to any one of claims 1 to 3 in which the register means comprises a set of three analog shift registers, each individual shift register being associated with one of the three colours and responsive to the photosensitive elements which are sensitive to said colour.

6. An apparatus according to any of the preceding claims in which the photosensitive elements are rendered sensitive to the three different colours by being coated by vapour disposition with interference layers.

7. An apparatus according to any one of claims 1 to 5 in which the photosensitive elements are rendered sensitive to the three different colours by a filter having band of the three colours.

8. An apparatus according to any one of the preceding claims in which a transfer gate is provided between the line of photosensitive elements and the register means.

9. An apparatus according to any one of the preceding claims in which the film projector includes an oscillatory mirror system for deflecting the image of the film pictures in the direction of film movement at a frequency corresponding to the frame scan frequency of the video signal.

10. An apparatus according to claim 9 in which during each oscillation of the oscillatory mirror system the image of the film pictures is deflected by an amount corresponding to two thirds of the height of each individual picture.

11. An apparatus according to claim 9 or claim 10 in which the oscillatory mirror system includes an oscillatory coil of the kind used in galvanometer technology.

12. An apparatus according to claim 11 in which the oscillatory coil is controlled by means of a summing circuit.

,

13. An apparatus according to claim 12 in which the oscillatory mirror system further includes a sawtooth pulse generator, a first pulse forming stage controlled by the sawtooth pulse generator for providing a short fly-back acceleration pulse during the flyback of the saw-tooth pulse, and a second pulse forming stage controlled by the sawtooth pulse generator for providing a short braking and acceleration pulse, the sum of the pulse durations of said two short pulses not exceeding the standard TV flyback time, the summing circuit being responsive to the outputs of the sawtooth pulse generator and the two pulse forming stages and including adjustable elements whereby the amplitude of the sawtooth pulses and that of the two short pulses can be independently regulated.

14. An apparatus according to claim 13 in which the sum of the pulse durations of said two short pulses does not exceed 1.2 milliseconds.

15. An apparatus according to claim 13 or claim 14 in which the first pulse forming stage for providing the flyback acceleration pulse comprises a monostable, the second pulse forming stage for providing the flyback braking and acceleration pulse comprises two monostables, and the moment in time and duration of the output pulses are independently adjustable.

16. An apparatus for the electronic scanning of films for projection onto a TV screen substantially as hereinbefore described with reference to and as shown in Figures 1,3,4 and 9 of the accompanying drawings.

17. An apparatus for the electronic scanning of films for projection onto a TV screen substantially as hereinbefore described with reference to and as shown in Figures 1,3,6 and 9 of the accompanying drawings.