Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1991-08-19
1993-10-19
Groody, James J.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358 11, 358 54, 358214, H04N 701, H04N 911
Patent
active
052550915
DESCRIPTION:
BRIEF SUMMARY
This invention relates to digital television standards conversion and is concerned, for example, with apparatus and processes for converting an NTSC 525 line/60 fields per second video signal to the PAL 625 line/50 fields per second standard.
Techniques exist for conducting the necessary field and line interpolation to convert from one standard to the other and these techniques operate well with "true" video signals. A difficulty arises, however, with video signals that derive from film material.
It is common practice, particularly in the United States of America, to transfer film shot at 24 frames per second to video tapes on the NTSC standard. Each film frame is scanned twice to produce two interlaced fields and a system known as "3/2 pull down" is used to produce the necessary 30 video frames from the available 24 film frames. The system operates by duplicating selected film fields to produce the necessary additional frames in the video signal. If material produced in this way is passed through a known standards converter to produce a 625/50 signal, the output is degraded as a result of temporal distortions of the duplicated fields. The degree of perceptible degradation will vary according to the visual subject matter of the film and will in many cases be significant.
It is one object of this invention to provide a television standards conversion process for use with a film-originating video signal which overcomes or considerably reduces the importance of this difficulty.
Accordingly, the present invention consists in one aspect in a television standards conversion process for use with film originating video signals, comprising the steps of comparing successive corresponding fields to detect pairs of duplicate fields deriving from the same film frame and eliminating one field of each of said pairs from the video signal.
In another aspect, the present invention consists in a digital television standards converter for use with film-originating video signals, comprising means for comparing fields in successive frames; means for detecting through said comparison duplicate fields deriving from the same film field and means for generating a video output from said video signals with the deletion of said duplicate fields.
Advantageously said means for comparing fields comprises a comparator receiving input video signals mutually delayed by one frame and means for integrating the comparator output over one field.
In one form of the invention, 12 duplicated fields per second are detected and eliminated from a 30 frame per second video signal originating from a 24 frame per second film. Line interpolation is conducted as necessary, in accordance with known line interpolation techniques. It will be understood that a 24 frame video signal produced in this manner and converted, for example, to 625 lines, has fields corresponding one to one with the original film material. In one approach contemplated by this invention, a 625 lines/48 fields video tape produced in this way is reproduced directly on a 625/50 television set using an adapted VTR. In circumstances where the use of an adapted VTR is impractical, this invention contemplates the addition of fields to produce a conventional 625/50 signal.
The ability to produce high quality PAL (for example) video from film originating NTSC video is of considerable commercial importance.
Up until the mid eighties, film was the universal medium for television programme makers wishing to reach an international market. Both 16 mm and 35 mm formats were accepted worldwide as readily transmittable on any television standard. The high cost of film stock and film processing has more recently led to an increased use of video tape for post-production work and editing. It is still usual for programmes and features to be shot on film, but this is transferred immediately to NTSC video tape. When a television programme produced in this way is eventually broadcast under the NTSC standard, there is no difference in picture quality. If, however, the video tape is required to undergo standard
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Caplin Guy R.
Lyon David
Groody James J.
Ingerman Jeffrey H.
Lee Michael H.
Snell & Wilcox Limited
Wildes Morey B.
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