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EP0372774A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Method for the conversion of a video signal display frequency

Assignee: Nokia Consumer Electronics Ltd
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Filing: 1989-11-27
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Granted: —
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Expires: 2009-11-27
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Abstract

Abstract The invention relates to a method wherein it is possible, by digital signal processing taking place in the receiver, to reduce errors caused in a television picture by an in­terlaced transmission standard and a low field frequency. The transmitted interlaced (50 Hz/2:1) signal is converted in the receiver either to a non-interlaced (50 Hz/1:1) signal or to an interlaced (100 Hz/2:1) signal. The higher display frequency transfers the errors to higher frequen­cies, whereupon they no longer disturb the viewer. The conversion takes place by means of a weighted median filter operating in a 3*3 window. In the window, the first line is from the preceding field in the memory and the two others are from the latest received field. The filter interpolates a new dot according to these data. The structure of the filter selects implicitly temporal interpolation in a sta­tionary picture and spatial interpolation for moving ob­jects. By altering the coefficients of the weighted median filter it is possible to optimize the filter to operate either in a moving picture or in a stationary picture. The method can be carried out using a VLSI circuit.

Inventors

  • 👤 Janne Juhola
  • 👤 Ari Nieminen
  • 👤 Yrjo Neuvo
  • 👤 Juha Salo

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-11-08 16:33
CPC Classifications
H; H04; H04N; H04N7/00; H04N7/01; H04N7/0127; H04N7/0132; H04N19/00; H04N19/50; H04N19/503; H04N19/51; H04N19/577; H04N19/80; H04N7/0117; H04N7/012

Claims Analysis

Total Claims: 7
Claim 1
Independent Claim 120 words
A method for processing a digital signal in order to convert a video signal according to an interlaced transmis­sion standard and a low field frequency (50 Hz/2:1) to a non-interlaced (50 Hz/1:1) video signal, characterized in that in the field frequency conversion, in order to inter­polate the required fields which are lacking, a weighted median filter is used which operates in a 3*3 window and can be expressed by means of the formula y(n,m,t) = MED [x(n-1,m-1,t), x(n,m-1,t), x(n+1,m-1,t) x(n-1,m+1,t), x(n,m+1,t), x(n+1,m+1,t), a* x(n,m,t-1), b* X (n,m,t)] X (n,m,t) = 1/2[x(n,m-1,t) + x(n,m+1,t)] where a and b are coefficients indicating the weighting, * an operator expressing the weighting, and X(n,m,t) a preli­minary estimate for a new dot x(n,m,t) (line averaging).
Claim 2
Independent Claim 120 words
A method for processing a digital signal in order to convert a video signal according to an interlaced transmis­sion standard and a low field frequency (50 Hz/2:1) to a non-interlaced (50 Hz/1:1) video signal, characterized in that in the field frequency conversion, in order to inter­polate the required fields which are lacking, a weighted median filter is used which operates in a 3*3 window and can be expressed by means of the formula y(n,m,t) = MED [x(n-1,m-1,t), x(n,m-1,t), x(n+1,m-1,t) x(n-1,m+1,t), x(n,m+1,t), x(n+1,m+1,t), a* x(n,m,t-1), b* X (n,m,t)] X (n,m,t) = 1/2[x(n,m-1,t) + x(n,m+1,t)] where a and b are coefficients indicating the weighting, * an operator expressing the weighting, and X(n,m,t) a preli­minary estimate for a new dot x(n,m,t) (line averaging).
Claim 3
Dependent Claim 29 words
A method according to Claim 1, characterized in that the field frequency of a video signal having a frequency of 50 Hz is doubled (50 Hz/2:1 - 100 Hz/2:1).
Claim 4
Dependent Claim 29 words
A method according to Claim 1, characterized in that a video signal having a frequency of 60 Hz is converted to a non-interlaced signal (60 Hz/2:1 - 60 Hz/1:1).
Claim 5
Dependent Claim 29 words
A method according to Claim 1, characterized in that the field frequency of a video signal having a frequency of 60 Hz is doubled (60 Hz/2:1 - 120 Hz/2:1).
Claim 6
Dependent Claim 35 words
A method according to Claim 1 or 2, characterized in that by using a movement detector the suitable weighted median filter for interpolation is selected on the basis of the movement appearing in the picture.
Claim 7
Dependent Claim 26 words
A method for forming a still picture of an interlaced video signal, characterized in that the method according to Claim 1 is used for the interpolation.

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