GB2247801A

GB2247801A - Video post-production of material acquired on film

Info

Publication number: GB2247801A
Application number: GB9018805A
Authority: GB
Inventors: John William Richards; Milan Krsljanin; Yoshio Ozaki
Original assignee: Sony Broadcast and Communications Ltd
Current assignee: Sony Broadcast and Communications Ltd
Priority date: 1990-08-29
Filing date: 1990-08-29
Publication date: 1992-03-11
Also published as: GB9112077D0; GB2247588A; GB2247588B; GB9018805D0

Abstract

Apparatus for converting, for example, 24Hz 1:1 format film to, for example, a 60Hz 2:1 interlace format video signal comprises a converter 12 for transferring 24Hz 1:1 format film material to a 60Hz 2:1 interlace format video signal using 3 2 3 2 pull down, and a coder 13 associated with the converter 12 for associating a 10-field sequence identifier with the video signal. The 10-field sequence identifier is used to maintain identification of the phantom fields i.e. the third video fields produced from every other film frame due to the 3 2 3 2 pull down system, through subsequent processing, and in particular to control motion processing in post production equipment 3 such as special effects generators. The 10-field sequence identifier eg. a modulo-10 coding of a time code in the video signal, is also used to ensure that the phantom fields are dropped in converting the video signal into a 24Hz 1:1 format for an electron beam film recorder 4. <IMAGE>

Description

1 VIDEO POST-PRODUCTION OF MATERIAL ACQUIRED ON FILM This invention

relates to video post-production of material acquired on film, and,more particularly to the use of high-definition video equipment for the post-production of material acquired on movie f i 1m.

60Hz, that is 60 fields per second, 2:1 interlace format highdefinition video equipment is now well known and in widespread use. Despite this, movie film remains a very good way of acquiring material, even where the material is subsequently to be distributed in the form of high-definition video. This is not only because of the favourable rendition of material on film, but also due to the relative portability of film, cameras comparec with the current generation of high-ciefinition video cameras, and also the ability of film cameras to produce good is slow motion by acquisition at high frame rates.

Nevertheless, it is desirable to enable material acquired on film, normally at 24Hz, but possibly at 25Hz or 30Hz, to be postproduced using 60Hz 2:1 interlace format high-definition video equipment, even in cases where the material may subsequently be transferred back to film for distribution. This is because there are many processes and effects which can readily be carried out on a video signal, for example, digital multi-effects, the integration into the film material of live video material, manipulation of the image, or even mere'. -,, tne simple addition of captions or tlit-les which is very expensive ts do optically.

Figure 1 snows in block form a possible system for video postproduction of material which has been acquired on film and is to be distributed on film or video. 24Hz 1:1 format film material 1 is read by a telecine 2 to derive a 60Hz 2:1 interlace format video signal.

This may be done, for example, using 3 2 3 2 pull down, referred to in more detail below, and as currently used, for example in Japan and USA, for converting film material to a video signal. The video signal is supplied to a post-production unit 3 from which the modified video signal is supplied to an electron beam recorder 4 for recording as film material 5 in a 24Hz 1:1 format, for example using a drop field technique. The modified video signal may also be supplied to a video recorder 6 for recording in 60Hz 2:1 interlace format.

It might be considered that the initial transfer from film to 2 video could be done directly, in the sense that each frame of the film became a frame of video. Then, following post-production, each frame of video could be transferred directly back to a film frame. However, if this method were used then the video signal in the post-production unit 3 could not be viewed at real time speeds, because all action would be speeded up by a factor of 30/24. This would make it difficult to evaluate the aesthetic aspects of the programme material during the post- production process. Moreover, the modified video signal could not be directly transferred to the video recorder 6 for distribution in video form. This possibility is not, therefore, a practical option.

The alternative is as indicated above in connection with Figure 1, in which there is field repetition in the transfer from film to video. Figure 2 illustrates the 3 2 3 2 pull down system, and shows the correspondence between film frames and video fields. This is shown for 24Hz 1: 1 format film transfer to 60Hz (30 frames per second) 2:1 interlace format video. It will be seen that film frame 1 is used to form video fields 1, 2 and 3, video field 3 being a so-called phantom field. Film frame 2 is then used to form video fields 4 and 5. This gives an oddeven-odd-even-odd sequence of five video fields derived from the two film frames. To maintain the required odd/even alternation in the video fields, the 5-field sequence obtained then has to be repeated starting with an even field. Thus, film frame 3 is used to form video fields 6, 7 and 8, and film frame 4 is used to form video fields 9 and 10. In this case, video field 8 is the phantom field. Repetition of this 10-field sequence gives the required ocid/even alternation.

This method produces correct speed of action during video postproduction, although motion characteristics will be slightly jerky due to the phantom fields, that is the repeated video fields in each 5- field sequence. Although, as mentioned above, this 3 2 3 2 pull down method is commonly used for film to video transfer in USA and Japan, the motion portrayal is not strictly correct, although it is acceptable to viewers.

All video post-production equipment currently available is intended to operate on a video signal which is interlaced, that is a signal in which the two fields which compose a frame are equally separated in time from adjacent fields. Any post-production equipment that produces motion, such as special effects generators, or equipment

3 which generates wipes or moving captions, therefore operate in such a way as to produce a regular motion across video fields. An example of this is shown for a switcher wipe in Figure 3, where a wiping edge moves regularly across the picture from side to side. Fields 1 to 6 shown on the left correspond to fields 1 to 6 from Figure 2; field 3 being one of the phantom fields in the 10-field sequence. The arrows in the centre of the figure indicate the fields selected for transfer to film, the image on which is indicated on the right of the figure. The areas within the concentric circles indicate a magnified view of the line structure derived from the video signal. The hatched area in the images show the smear region, and it will be noted that in particular due to dropping the phantom field, there is a sharp jump in the motion due to the dropped field. What has happened, is that there is now an incorrect temporal sequence as a result of dropping the phantom field.

According to the present invention there is provided a method of film to to video signal transfer involving the creation of phantom video fields, wherein a field sequence identifier is associated with said video signalL to identify said phantom fields.

According to the present invention there is also provided a methc.c of 24Hz 1:1 format film to 60Hz 2:1 interlace format video signal transfer using 3) 2 3 2 pull down, wherein a 10field sequence identifier is associated with said video signal.

Acecr,ding to tne present invention there is also provided a method of 24Hz 1:1 format film to 60Hz 2:1 interlace video signal to 24Hz 1:1 format film transfer comprises the steps of: converting 24Hz 1:1 format film material to a 60Hz 2:1 interlace format video signal using 3 2 3 2 pull down; associating a 10-field sequence identifier with said video signal, said

10-field sequence identifier indicating the phantom fields added during said pull down; effecting motion processing of said video signal in dependence on said 10-field sequence indentifier; modifying said 10-field sequence identifier in dependence on processing delays occuring during motion processing of said video signal, to maintain correct indication of said phantom fields added during said pull down; converting said video signal to 24Hz 1:1 format, including dropping 4 said phantom fields added during said pull down and indicated by said modified 10-field sequence identifier; and recording said converted video signal on film.

According to the present invention there is also provided apparatus for film to video signal transfer involving the creation of phantom video fields, the apparatus comprising means to associate a field sequence identifier with said video signal to identify said phantom fields.

According to the present invention there is also provided apparatus for converting 24Hz 1:1 format film to a 60Hz 2:1 interlace format video signal, the apparatus comprising: conversion means for transferring 24Hz 1:1 formal., film material to a 60Hz 2:1 interlace format video signal using 3 2 3 2 pull down; and coding means associated with said conversion means for associating a 10-field sequence identifier. with said video signal.

According to the present invention there is also provided apparatus for 24Hz 1:1 format film to 60Hz 2:1 interlace format video signal to 24Hz 1:1 format film conversion, the apparatus comprising: means for transferring 24Hz 1:1 format film material to a 60Hz 2:1 interlace format video signal using 3 2 3 2 pull down; coding means for associating a 10-field sequence identifier with said video signal, said 10-field sequence identifier indicating the phantom fields added during said pull down; a motion processor for effecting motion processing of said video signal in dependence on said 10-field sequence indentifier; means for modifying said 10-field sequence identifier in dependence on processing delays occuring during processing of said video signal, to maintain correct indication of said phantom fields added during said pull down; conversion means for converting said processed video signal to 24Hz 1: 1 format, said conversion means dropping said phantom fields added during said pull down and indicated by said modified 10-field sequence identifier; and recording means for recording said converted video signal on film.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows in block diagrammatic form equipment for post production of material acquired on film; 1 Figure 2 shows a 10-field video sequence produced by 2 3 2 pull

2 5-, down; Figure 3 shows video fields in a smooth horizontal switcher wipe and the resulting film image produced by dropping fields;

Figure 4 shows the motion sequence required in an embodiment of the present invention; and Figure 5 shows an embodiment of apparatus according to the present invention.

Before describing the embodiment, some further consideration of the matters discussed above may be helpful for a fuller understanding of the invention.

Where material acquirec, for example, as a 24Hz 1:1 format film has been transferred to 60Hz 2:1 interlace format video, it needs to be understooc that the video material derived is not identical as regards motion characteristics to material which is derived directly as 60Hz 2:1 interlace format video. So far as the motion characteristics are concerned, they are dependent on the way in which the material was acquired initially, and hence in characteristics are those of 24Hz 1:1 format.

If then one considers, for example, this example the motion the case where some additional motion has been put into the material, for example the switcher wipe illustrated in Figure 3, then it needs to be understood that the resulting picture in fact incorporates two motions. Firstly, there is the motion derived from the original material, which in effect will. have been. pre-filtered and will not be too badly aliased. Secondly, there is any motion introduced electronically by manipulation of the video signal, and this may be very badly aliased. It could be said, therefore, that what is required is to give these two motions the same movement characteristics, in order to avoid unnatural effects in the final material. When manipulating the video signal, therefore, any motion introduced must be modified to take account of the temporal positions of the input and output sequences of fields of frames.

Put very simply, this is done by relating the video fields to the film frames. In more detail, what this means is that in the case described above where film frames are converted to video fields by a 3 2 3 2 pull down which creates a 10-field sequence containing two phantom fields, these phantom fields must tracked, and also account must be taken of their temporal positions all through the post-

6 production equipment, so that correct motion is introduced, and, when the material is converted back to 24Hz, it is the phantom fields which are dropped.

This identification can be done in a variety of different ways.

For example, the 10-field sequence can be identified by modulo-10 coding the video time code, by auxiliary data inserted into the video signal itself, for example by marking a specific line or inserting data in a specific line in the blanking interval of each field, or by using some other auxiliary signal, such as audio user bits. This marking of the 10-field sequence is done at the time that the film material is transferred to video and is maintained thereafter up to the point where the phantom fields are dropped.

All circuitry in the post-production unit which introduces motion into the video signal, such as switchers, digital multi-effects equipment, rolling caption generators, special effects generators and so on, incorporate means to decode the 10-field video sequence identifier, so as to control their own operation. Other circuitry carries forward the 10-field video sequence identifier, and all circuits effect any necessary compensating delay in the 10-field video sequence identifier.

The motion characteristics produced by circuits in the postproduction equipment are modified so as to form the correct motion sequence in the output after dropping the phantom fields. This is illustrated in Figure 5 which shows the motion sequence from the 10- field video sequence to the final sequence of four film frames. The 10- field sequence is the same as that shown in Figure 2, fields 3 and 8 being the phantom fields. The motion in fields 1, 2 and 3, all of which are derived from frame 1, is the same, and is referred to as motion 1. This must carry forward to motion 1 in the output frame 1.

Likewise, motion 2 in fields 4 and 5 derived from input frame 2 must carry forward to output frame 2, motion 3 in fields 6 and 7 derived from input frame 3 must carry forward to output frame 3, and motion 3 in fields 8, 9 and 10 derived from input frame 4 must carry forward to output frame 4.

At the stage of 60Hz 2: 1 interlace format video to 24Hz 1: 1 format film transfer, the phantom frames must be recognized and dropped from the video sequence. It is particularly to be noted that equipment processing delays must be taken into account when using or passing on -1 7 the 10-field video sequence identifier, and this is preferably done by having each circuit in the post-production equipment modify the 10field video sequence identifier according to its own processing delay.

The overall result is that post-produced video is seen at the correct speed with adequate motion rendition; adequate here meaning that the motion rendition is similar to that achieved now by 3 2 3 2 pull down in a telecine. An important point so far as the producer is concerned, is that the video can be seen at the correct speed. More importantly, the correct motion portrayal is produced on the resulting 24Hz 1:1 format film, whereas without the measures outlined above, the motion portrayal would have become very unnatural.

The above results can be achieved merely by modification of those circuits of the post-production equipment which introduce motion of - into the picture. Circuits which do not introduce motion do some sort not need any modification except to effect the necessary compensating delay in the 10-field video sequence indentifier.

fic embodiment will now be described with reference to A spec.

Figure 5. The system is intended for video post-production of material which has been acquired on film and is to be distributed on film or video. 24Hz 1:1 format film material 1 is read by a film to video converter 12, such as an image scanner, to derive a 60Hz 2:1 interlace forma: video signal. The converter 12 will generally not be a tel.ecine, as these ususally operate at high speed and do not result in a hign quality video signal due to the difficulty of registering the film frame by frame at the necessary high speed. It is therefore preferred that the converter 12 is a device which operates at lower speed so that the film frames are accurately aligned and unwanted motion is not introduced into the video signal. The converter 12 operates using 3 2 3 2 pull down as described above, although alternatives, such as 3 2 2 3 pull down are possible.

The video signal is supplied to a post-production unit 3 from which the modified video signal is supplied to an electron beam recorder 4 for recording as film material 5 in a 24Hz 1:1 format, using a drop field technique. The modified video signal may also be supplied to a video recorder 6 for recording in 60Hz 2:1 interlace format.

Associated with the converter 12 is a sequencer 13, which creates the 10-field video sequence identifier, for example, by modulo-10 coding a time code associated with the video signal, in order to 8 sequence are indicate the 10-field sequence, and in particular which fields in the the phantom fields. The 10-field video sequence identifier is in this case incorporated in the time code associated with the video signal supplied to the post-production unit 3, but in other cases it may be supplied separately to a modify sequencer 14 associated with the post-production unit 3. The modify sequencer 14 modifies the 10-field video sequence identifier as necessary to maintain the clear identification of the sequence, and in particular of the phantom fields, to take account of any changes introduced by the post-production unit 3. The modified 10-field video sequence identifier is then supplied in the video signal or separately as shown to the electron beam recorder 4 where it is used to ensure that the phantom fields are dropped, so achieving the required result.

Various modifications are of course possible without departing from the invention as defined by the appended claims.

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Claims

1. A method of film to to video signal transfer involving the creation of phantom video fields, wherein a field sequence identifier 5 is associated with said video signal to identify said phantom fields.

2. A method according to claim 1 further comprising motion processing of said video signal in dependence on said field sequence identifier.

3. A method of 24Hz 1:1 format film to 60Hz 2:1 interlace format video signal transfer using 3 2 3 2 pull down, wherein a 10-field sequence identifier is associated with said video signal.

4. A method of 24Hz 1:1 format film to 60Hz 2:1 interlace video signal to 24Hz 1:1 format film transfer comprises the steps of: converting 24Hz 1:1 format film material to a 60Hz 2:1 interlace format video signal using 3 2 3 2 pull down; associating a 10-field sequence identifier with said video signal, said 10-field sequence identlfier indicating the phantom fields added during said pull down; effecting motion processing of said video signal in dependence on said 10-field sequence indenrifier; modifying Said 10-field sequence identifier in dependence on processing delays occuring during motion processing of said video signal, to maintain correct indication of said phantom fields added during said pull down; converting said video signal to 24Hz 1:1 format, including dropping said phantom fields added during said pull down and indicated by said modified 10-field sequence identifier; and recording said converted video signal on film.

5. A method according to claim 3 or claim 4 wherein said 10-field sequence identifier comprises modulo-10 coding of a time code in said video signal.

6. A method according to claim 3 or claim 4 wherein said 10-field sequence identifier comprises marked lines or data incorporated in lines of the blanking intervals of said video signal.

7. A method according to claim 3 or claim 4 wherein said 10-field sequence identifier comprises audio user bits in a time code.

8. Apparatus for film to video signal transfer involving the creation of phantom video fields, the apparatus comprising means to associate a field sequence identifier with said video signal to identify said phantom fields.

9. Apparatus according to claim 1 further comprising means to motion process said video signal, the motion processing being effected in dependence on said field sequence indentifier.

10. Apparatus for converting 24Hz 1:1 format film to a 60Hz 2:1 interlace format video signal, the apparatus comprising: conversion means for transferring 24Hz 1:1 format film material to a 20 60Hz 2:1 interlace format video signal using 3 2 3 2 pull down; and coding means associated with said conversion means for associating a 10-field sequence identifier with said video signal.

11. Apparatus for 24Hz- 1:1 format film to 60Hz 2:1 interlace format video signal to 24Hz 1:1 format film conversion, the apparatus comprising: means for transferring 24Hz 1:1 format film material to a 60Hz 2:1 interlace format video signal using 3 2 3 2 pull down; coding means for associating a 10-field sequence identifier with said video signal, said 10-field sequence identifier indicating the phantom fields added during said pull down; a motion processor for effecting motion processing of said video signal in dependence on said 10-field sequence indentifier; means for modifying said 10-field sequence identifier in dependence on processing delays occuring during processing of said video signal, to maintain correct indication of said phantom fields added during said pull down; conversion means for converting said processed video signal to 24Hz 1: 1 j 11 format, said conversion means dropping said phantom fields added during said pull down and indicated by said modified 10field sequence identifier; and recording means for recording said converted video signal on film.

12. Apparatus according to claim 10 or claim 11 wherein said 10-field sequence identifier comprises modulo-10 coding of a time code in said video signal.

13. Apparatus according to claim 10 or claim 11 wherein said 10-field sequence identifier comprises marked lines or data incorporated in lines of the blanking intervals of said video signal.

14. Apparatus according to claim 10 or claim 11 wherein said 10-field 15 sequence identifier comprises user bits in a time code.

15. A method of 24Hz 1:1 format film to 60Hz 2:1 interlace format video signal transfer substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.

16. Apparatus for converting 24Hz 1:1 format film to a 60Hz 2:1 interlace format video signal, the apparatus being substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.

Published 1992 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 IRH. Further copies may be obtained from Sales Branch, Unit 6. Nine Mile Point, Cwinfelinfach. Cross Keys, Newport. NPI 7RZ. Printed by Multiplex techniques lid. St Mary Cray, Kent.