GB2320831A - Telecine system - Google Patents

Abstract

A flying spot telecine system uses an elongate scanning light beam 1. The cross-section of the light beam is preferably elliptical and its orientation or shape can be varied in response to the position of the flying spot on the scanned film frame.

Description

IMAGE PROCESSING The present invention relates to the processing of cinematographic film to produce electrical signals and, in particular, to a scanning light beam for use in such processing.

Conventionally cinematographic film (hereinafter referred to as "film") is scanned by a circular focused light beam which passes through a small circular region of the film. The amount of light transmitted by the film at that region is detected by one or more optoelectrical sensors to produce an electrical signal or electric signals (hereinafter referred to as "video signals??) corresponding to the exposure of the film in that region. In the case of a plurality of optoelectrical sensors, each sensor may detect only a single colour, for example red, green or blue, such that the combination of video signals from the sensors provides a full description of the colour transmission of the film.

The light beam is generally arranged to scan each frame of the film in a raster pattern, whereby the circular spot of light formed by the beam at the film surface traces a horizontal line from one edge of a film frame across the frame to the other edge. The spot then returns to the starting edge of the frame while moving down the frame a small distance to trace the next horizontal line in the same direction. This corresponds generally to the type of raster scanning that produces television pictures on a television screen and usually an equivalent number of lines are used, for example 576 in the European Television Standard. By means of this scanning process it is generally expected that the whole of a film frame will be covered by the scanning beam.

Of course, the terms "horizontal" and "vertical" as used herein, with reference to scanning directions merely indicate the two perpendicular directions of the scan and no limitation as to orientation of the film or scanning arrangement is implied.

The light beam is generally produced by a cathode ray tube in which an electron beam is generated which hits a phosphor screen to produce the light beam. The light beam may be further focused or directed towards the film by a system of lenses and/or mirrors.

Examples of commercially available machines, known as telecine machines, for the conversion of film into video signals are manufactured by Cintel International Limited of Ware, England under the names URSA and URSA Gold. Such machines incorporate a film transport mechanism passing the film through the scanning apparatus at the required speed. In general the technology of telecine machines is well known and is described in numerous publications, for example GB-A2231234.

To achieve the optimum quality of video signals it is desirable to scan the film at the highest possible resolution, and thus, in general, the scanning spot is made as small as possible. However, once the diameter of the spot is reduced below a certain limit, there are horizontal bands of the film frame which are not scanned by the circular spot when using a standard number, for example 576, of horizontal scanning lines. This is because the lines will no longer overlap or abut and unscanned space will be left between consecutive lines.

In order to ensure that all of a film frame is scanned, one solution, for example as used in the CLEARVIEW system manufactured by DAV Inc. of California USA, is to increase the number of horizontal scanning lines to above the number required for the appropriate television standard so that all lines either abut or overlap. The resultant video signals are then sampled down to a standard number of lines for the required television standard.

It is apparent that the CLEARVIEW system has the disadvantage that the number of horizontal scans required to cover the whole film frame is larger than the number of television raster lines required, such that this method of scanning will take longer than a standard scan. Furthermore the information obtained by these extra scanning operations will be wasted, at least partially, during the sampling down of the lines to television standard.

According to a first aspect of the present invention there is provided apparatus for the scanning of cinematographic film to produce electrical signals representative of the images stored on the film, wherein the film is scanned with a light beam having a crosssection of greater extent in a first direction than in a second direction perpendicular thereto.

Thus, the light beam according to the invention will form an elongate spot corresponding to the crosssection of the beam on the surface of the film. This spot may be aligned so that its longest dimension is perpendicular to the scanning line direction. In this way, a whole frame of film can be scanned with a high resolution in the scanning line direction whilst ensuring that the consecutive scanning lines overlap or at least abut to effect a scan of the entire frame of film.

Furthermore, the elongate spot has a larger area than a circular spot of equivalent extent in the direction of the scanning lines, such that more light will be incident on the film frame. For this reason, the signal to noise ratio of the resultant video signals will be improved.

Moreover, the elongation of the spot results in a spot that is not as sharply focused as a known circular spot. The diffuse, elongate spot does not therefore engrave the phosphor of the cathode ray tube to the same extent as prior art circular spots.

The spot may be, for example, oblong, oval, substantially rectangular, rhomboidal, or in the form of a rectangle having semi-circular ends. However, preferably the spot is elliptical with, most preferably, its major axis parallel to the direction of the vertical scan, i.e. parallel to a line between equivalent scanning positions, or pixels, of adjacent horizontal scan lines.

Preferably, the height of the spot is at least 10% greater than its width, although it is expected that the most suitable ratios of height to width will be greater, for example 1.5, 2, between 3 or 4 or even larger.

The height of the spot must be controlled such that adjacent horizontal scan lines abut. Thus, for example, for the scanning of a whole frame of Open Gate 35mm film, which has a usable frame area of 24 x 18mm, at 576 horizontal lines the height of the spot must be at least 18mum 576 = 31cm. Similarly, to obtain an equivalent horizontal resolution to that of the 2000 line circular spot scan described previously, the width of the elliptical spot must be equal to the diameter of the conventional circular spot, i.e. 18mm . 576 = 9ym.

The non-circular cross-section of the beam may be formed optically by one or more suitable lenses.

Preferably, however, the non-circular cross-section is formed electromagnetically in a cathode ray tube of the apparatus by applying a distorting electromagnetic field to the electron beam in the tube. An available device capable of applying such distortions to an electron beam is known as a stigmator coil. Using such a device, or other suitable apparatus, the orientation, as well as the shape, of the cross-section of the beam may be set and/or varied.

Thus from a second aspect, the present invention provides apparatus for generating a light beam for scanning cinematographic film to produce electrical signals corresponding to the images stored on the film, comprising means for shaping the cross-section of the light beam such that its extent in a first direction is greater than in a second direction perpendicular thereto.

Preferably, the above apparatus also comprises means for altering the orientation of the cross-section of the light beam. In a preferred embodiment, the shaping and/or orientation of the light beam is effected by applying an electromagnetic field to the electron beam in a cathode ray tube of the apparatus.

The orientation and/or shape of the spot may be altered at any point on the film frame, which is particularly useful in the case when the "horizontal" scan lines are not actually horizontal but may be curved in order to warp the resultant video image. In this case, in order to ensure that the "horizontal" scan lines abut, the height of the spot must be increased to match the instantaneous line spacing, or scan amplitude.

This is possible using the means for shaping the beam cross-section according to the present invention.

However, this feature may be applied to scanning spots of circular cross-section and thus from a third aspect, the present invention provides apparatus for scanning cinematographic film to produce electrical signals corresponding to the images stored on the film, wherein the film is scanned with a light beam and the apparatus comprises means for varying the size of the cross-section of the light beam in response to the location at which the beam is incident on a frame of the film. The invention also extends to a corresponding method of scanning cinematographic film.

The invention further extends to a method of scanning cinematographic film with a light beam to produce electrical signals corresponding to the images stored on the film, wherein the light beam has a crosssection of greater extent in a first direction than in a second direction perpendicular thereto.

An embodiment of the invention will now be described by way of example only and with reference to the figures, in which: Figure 1 is a schematic representation of the scanning operation in a conventional telecine machine; Figure 2 is a schematic representation of a highresolution scan in a conventional telecine machine; Figure 3 is a schematic representation of a scanning operation according to the present invention; Figure 4 is a schematic representation of a rotated scanning operation in a conventional telecine machine; Figure 5 is a schematic representation of a rotated scanning operation according to the present invention; Figure 6 is a schematic representation of the line distribution of a telecine scan effect in a conventional telecine machine; Figure 7 is a schematic representation of a scan effect operation according to the present invention; Figure 8 is a schematic representation of an octopole stigmator coil for use with the present invention; Figure 9A-9G are diagrams showing the effect of settings of the octopole stigmator on the beam crosssection according to the invention; Figure 10 is a block diagram illustrating a control system according to the invention; and Figure 11 is a block diagram of part of an alternative control system according to the invention.

Figure 1 shows schematically a conventional scan path for a light spot la of a telecine system such as the URSA or URSA Gold. The spot la scans along a line of a single frame of film in a horizontal direction (assuming the frame of film is supported in an upright orientation). The scanning spot la travels from one edge of the film to the opposite edge and then return quickly. As it returns to the front edge of the film the scanning spot drops down to the next line and repeats the horizontal scan on the next line.

As shown, the complete frame of film is scanned in 576 horizontal lines, each of which corresponds to a single line of a standard European television picture.

The circular spot is sized such that the 576 horizontal lines traced by the spot each abut their neighbouring lines and the scanning spot thereby covers the whole area of the film frame.

The control and generation of the scanning spot by means of a cathode ray tube are well known to those skilled in the art and will not be described herein for reasons of simplicity. Likewise the conversion of the light transmitted by the film into electrical video signals is also a well known technique which will not be further described herein.

Figure 2 shows a conventional film scanning pattern adapted from that of Figure 1. In this case the circular scanning spot la traces 2000 horizontal lines and may therefore be of a smaller size than the scanning spot of Figure 1, whilst still maintaining abutment of adjacent lines of the scan. The smaller size of the scanning spot lb improves the resolution of the scan, but in order to obtain a standard 576 line television picture, the 2000 lines must be sampled down, i.e.

averaged, in a known way.

The scanning system of Figure 2 exhibits improved resolution over that of Figure 1, but requires a larger number of horizontal movements which results in an increased scanning time.

Figure 3 shows a scanning pattern in accordance with the present invention. In this case, the scanning spot 1 is elliptical in shape, with its minor axis A aligned with the direction of the scanning lines of the telecine system and its major axis B, therefore, perpendicular to this direction, i.e. aligned with the direction of the vertical scan. The elliptical spot is formed by the cathode ray tube in a manner described hereinafter. Because the spot is elliptical its scanning resolution in the horizontal direction is roughly equivalent to that of the scanning spot of Figure 2, whereas its resolution in the vertical direction is equivalent to that of the scanning spot of Figure 1. Thus, the spot of Figure 3 has the advantage of the high resolution of the scan of Figure 2, but can scan a whole frame of film in 576 lines of a standard television picture. The need to downsample from 2000 lines to 576 is thereby obviated which removes one step from the telecine process.

Modern telecine machines are not only capable of converting film images into video signals. By varying the scanning pattern of the spot over the film frame various visual effects can be produced in the resultant video images.

Figure 4 shows the scan pattern of a conventional telecine spot when operating in a rotate mode. This mode may be used to correct, for example, for poor camera positioning during shooting of the film which has resulted in a non-horizontal horizon appearing in the image. By angling the scanning pattern relative to the film frame (shown in dotted lines in Figure 4), the "horizontal" scan lines of the telecine can be aligned with the perceived horizontal of the image to compensate for such defects or even for aesthetic effect.

Figure 5 shows the scanning pattern of the elliptical spot according to the present invention in a rotated orientation. Because the elliptical spot does not have total rotational symmetry, it is necessary not only to alter the orientation of the scanning pattern, so that the "horizontal" scanning lines correspond to the perceived horizontal of the image, but also to alter the orientation of the elliptical spot itself so that the major axis of the spot remains parallel to the vertical scan direction. The method of altering the orientation of the spot is described hereinafter.

Figure 6 shows the scan pattern for a further warping effect possible with modern telecine machines.

In this effect, the "horizontal" scan lines diverge towards one edge of the film, such that the resultant video image will be distorted when compared to the original film image.

In this case, as can be seen from Figure 6, the distance between adjacent "horizontal" scan lines, the scan amplitude, increases from left to right of the frame. Thus, even if the conventional circular scanning spot la is arranged such that adjacent scan lines abut at the left of the scan, on the right gaps will form between consecutive scan lines.

In order to understand how the present invention may be applied to this scan pattern, it is important to realise that the "horizontal" and "vertical" lines of this scan are not mutually perpendicular. Of course, in the resultant video images, these "horizontal" and "vertical" lines will be perpendicular.

Figure 7 shows three positions of the elliptical scanning spot 1 along one "horizontal" line of the scanning pattern of Figure 6. As can be seen, the orientation of the spot 1 is gradually changed across the film frame to ensure that the major axis of the ellipse remains parallel to the instantaneous vertical direction of the scan, i.e. the line, or in this case the tangent to the curve, joining all pixels at corresponding locations along each "horizontal" scan line. Because the scan lines diverge, the length of the major axis of the elliptical spot is also adjusted to ensure that the spot covers the whole of the scanning path as it travels across the film frame.

The method of generating the elliptical spot will now be described with reference to Figures 8 to 11.

Figure 8 shows a typical octopole stigmator coil 2 of the type suitable for controlling the orientation and shape of the elliptical scanning spot according to the present invention. The stigmator coil comprises a toroidal core 4 having formed on its inner periphery a number of poles 6. In this case, an octopole stigmator is shown which comprises eight poles, although this is only an example and any number of, preferably symmetrically distributed, poles may be used, for example four or sixteen.

The stigmator coil has two channels X and Y connected to windings 8 of the coils. Each channel has associated with it four poles 6 distributed evenly around the inner circumference of the core 4. The poles 6 associated with channel X are located pairwise opposite each other and with 900 between adjacent poles.

The poles 6 of channel Y are each located half way between two of the poles of channel X.

The windings 8 of channel X are wound around consecutive poles of that channel in opposite directions such that when channel X is energised, adjacent poles of channel X produce magnetic fields of opposing sign, whereas opposite poles of channel X produce magnetic fields of the same sign. The windings 8 of channel Y are correspondingly arranged.

The stigmator coil is positioned within or around the cathode ray tube of a standard telecine machine such that the electron beam passes through the centre of the core 4.

By selectively varying the current to the channels X and Y of the stigmator coil, the extent and orientation of the cross-section of the electron beam, and thus that of the scanning spot, can be varied.

Figures 9A to 9G show the effects of applying various combinations of positive and negative currents to the channels X and Y of the stigmator coil. Any orientation of the elliptical spot may be achieved by applying an appropriate combination of positive and negative currents to channels X and Y. By decreasing or increasing these currents while maintaining the same relative magnitudes, the extent of the spot can also be varied.

The relationship between the current value applied to each channel for orientation of the spot at an angle from the vertical is X = I cos 2 Y = I sin 2 where I is an arbitrary value of current.

Figure 10 shows, as a block diagram, a system for controlling the electron beam of a device according to the invention, to produce a suitable scanning light beam with optional scan effects. A digital scan effects generator 10 is provided, at its inputs, with standard television horizontal and vertical synchronisation signals H,V. These signals are processed to provide a cartesian coordinate position x,y on the film frame for each instantaneous value of the H and V parameters. The x and y values are moderated relative to the H and V parameters to include the effect of any selected scan effect, such as zoom, rotate or warp.

The x coordinate is delayed by one scan line at a delay 12, and this delayed signal is fed off as signal xO/p to the coil of the cathode ray tube that control the current x position of the scanning spot on the film frame. Similarly, the y coordinate is also delayed by one scan line at a delay 14, but the delayed y signal is fed to an adder 16, the output of which is a signal yO/p that has been corrected to allow for the speed of the film passing the scanning area. The signal yO/p is passed to the coil of the cathode ray tube that controls the current y position of the scanning spot on the film frame. Correction of the yO/p signal is carried out by multiplier 18 which multiplies the vertical synchronisation signal V by a signal corresponding to the position of the bottom (or top) of a film frame as it travels through the telecine film transport mechanism at constant velocity. Thus, the result of this multiplication is a sawtooth signal which is added to the y coordinate of the adder 16 to provide yO/p corrected for the continuous movement of the film through the telecine film transport.

The delayed x and y coordinates are each delayed by a further line at respective delays 20,22 and the delayed signals are differenced with the x or y value at the output of the effects generator 10 by respective differences 24,26 to provide a vector (AxF,AyF).

The position xO/p,yo/p represents the location on the film which is currently being scanned, i.e. the current position of the scanning spot; the x and y signals at the negative inputs of the adders 24,26 represent the corresponding position of the scanning spot on the last line to be scanned; and the x and y signals at the outputs of the effects generator 10 represent the corresponding position of the scanning spot on the next line to be scanned. The vector (AxF,OyF), therefore, represents the difference between the positions on the previous and the next line which correspond to the present spot position xO/p,yo/p i.e. the instantaneous vertical scan direction at (xO/p,yO/p).

The result of the first section 28 of circuitry of Figure 10 is to provide a vector (AxF,AyF) from the position corresponding to (Xo/p,Yo/p) on the previous scan line to the equivalent position on the following line.

This vector will be parallel to the instantaneous vertical scan direction at (xo/p,yo/p) and, as previously mentioned, the major axis of the elliptical spot must be aligned with this direction. Thus, the angle between this vector and the y-axis gives the rotation of the elliptical spot required, and the amplitude of the vector is proportional to the major axis of the ellipse required to ensure that adjacent scan lines abut.

Rotation of the elliptical spot is carried out by converting the (ExF,OyF) vector into polar coordinates using a standard convertor chip 28, such as the Ratheon TMC2330 CMOS coordinate transformer. After conversion, the angle is doubled to give 2 by a multiplier, or conveniently by performing a logical shift left, at doubler 30. Subsequently, the polar coordinates are converted back to Cartesian coordinates by a second converter chip 32, which may also be a Ratheon TMC2330 CMOS Coordinate Transformer operated in a reverse configuration. This operation preserves the value R, the length of the vector (OxF,OyF), which is proportional to the required height of the ellipse. The resultant digital coordinate parameters Ax,Ay are converted to analogue voltages by respective digital to analogue convertors 34,36. The analogue voltages are fed to respective amplifiers 38,40 and then to respective channels X,Y of the stigmator coil 2.

In this way the ellipse is rotated by an angle corresponding to the angle between the negative y- axis and the angle of the vector (AxF,ayF) between the scan position corresponding to Xo/p,Yo/p on the previous and subsequent lines. The ellipse is also lengthened to correspond to the value of R.

Figure 11 shows an alternative arrangement for converting the instantaneous scan vector (AxF,AyF) into a digital value to be fed as an equivalent analogue voltage to the stigmator coil 2. In Figure 11, the convertors 28,32 and doubler 30 of Figure 10 are replaced by dedicated look-up tables 42,44. Each lookup table 42,44 has at its input both AxF and AyF. These values are used to address a memory location containing the corresponding value of Ax or Ay for the values of AxF and AyF. The values of Ax and Ay are then processed as in Figure 10.

The look-up tables 42,44 may advantageously contain values of Ax and Ay corresponding to a non-linear relationship between AxF,AyF and Ax,Ay such that at small scan amplitudes, i.e. when the scan lines are close together it is possible to form a circular spot.

This is necessary as there is a finite limit to the minimum dimensions of the spot. In general, the elliptical spot is of greatest advantage when the scan amplitude is sufficiently large that a circular spot would leave gaps between adjacent scans. The non-linear relationship may be determined empirically.

Advantageously, a further look-up table may also be included to adjust the overall focus of the spot as a function of AxF and AyF. The output of this look-up table may be fed to the focus driving circuit of the cathode ray tube.

Claims (18)

Claims

1. Apparatus for the scanning of cinematographic film to produce electrical signals representative of the images stored on the film, wherein the film is scanned with a light beam having a cross-section of greater extent in a first direction than in a second direction perpendicular thereto.

2. Apparatus as claimed in claim 1, wherein said second direction is aligned with the scanning direction of the light beam.

3. Apparatus as claimed in claim 1 or 2, wherein the cross-section of the light beam is elliptical.

4. Apparatus as claimed in any preceding claim, wherein the extent of the cross-section of the light beam in the first direction is at least 10% greater than its extent in the second direction.

5. Apparatus as claimed in any preceding claim, wherein the cross-section of the light beam is controlled by optical means.

6. Apparatus as claimed in any of claims 1 to 4, wherein the light beam is produced by a cathode ray tube and the cross-section of the beam is controlled in the cathode ray tube by electromagnetic means.

7. Apparatus as claimed in claim 6, wherein the electromagnetic means is a stigmator coil.

8. Apparatus for generating a light beam for scanning cinematographic film to produce electrical signals corresponding to the images stored on the film, comprising means for shaping the cross-section of the light beam such that its extent in a first direction is greater than in a second direction perpendicular thereto.

9. Apparatus as claimed in any preceding claim further comprising orientating means arranged to control the orientation of the light beam.

10. Apparatus as claimed in claim 9, wherein the light beam is produced in a cathode ray tube and the orientating means comprises electromagnetic means.

11. Apparatus for scanning cinematographic film to produce electrical signals corresponding to the images stored on the film, wherein the film is scanned with a light beam and the apparatus comprises means for varying the size of the cross-section of the light beam in response to the location at which the beam is incident on a frame of the film.

12. A method of scanning cinematographic film with a light beam to produce electrical signals corresponding to the images stored on the film, wherein the light beam has a cross-section of greater extent in a first direction than in a second direction perpendicular thereto.

13. A method of generating a light beam for scanning cinematographic film to produce electrical signals corresponding to the images stored on the film, comprising shaping the cross-section of the light beam such that its extent in a first direction is greater than in a second direction perpendicular thereto.

14. A method of scanning cinematographic film to produce electrical signals corresponding to the images stored on the film, wherein the film is scanned with a light beam and the size of the cross-section of the light beam in response to the location at which the beam is incident on a frame of the film.

15. Apparatus for scanning cinematographic film to produce electrical signals corresponding to the images stored on the film, substantially as hereinbefore described with reference to the accompanying drawings.

16. Apparatus for generating a scanning light beam substantially as hereinbefore described with reference to the accompanying drawings.

17. A method of scanning cinematographic film to produce electrical signals corresponding to the images stored on the film, substantially as hereinbefore described with reference to the accompanying drawings.

18. A method of generating a scanning light beam substantially as hereinbefore described with reference to the accompanying drawings.