Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1985-11-15
1987-10-27
Chin, Tommy P.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358160, 358105, 358174, H04N 521
Patent
active
047033584
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus for processing a television signal including a movement detector.
A major improvement in the television picture quality may be achieved by upconverting the line interlace format of the transmission system to a sequential format prior to display. The frame rate or number of pictures displayed every second may also be increased. The choice of interpolation scheme used to fill in the missing lines or frames will depend on the presence or absence of movement in the local area. Consider only upconversion to a sequential or double line rate non-interlace format. In a static scene temporal interpolation would be used to fill in the missing lines but if there was movement present this scheme would cause blurring and edge "fringing". For significant movement on interpolation scheme taking account of only vertically adjacent samples must be employed. If vertical interpolation were to be used for a static scene it would negate the main advantage of upconversion, that is, the removal of edge flicker.
SUMMARY OF THE INVENTION
The present invention provides apparatus for processing a television signal comprising a movement detector and an interpolator whose operation is responsive to an output from the movement detector, said movement detector including means for delaying a television signal, and means for comparing a current television signal (A) which a delayed television signal (B) and producing an output signal K indicative of the comparison, said output signal being fed to the interpolator whereby to control its operation.
One approach would be to use the absolute frame difference: samples. A small value for K would indicate a static scene and a large value a moving scene. Under certain circumstances this approach will give an incorrect indication of movement due to interlace. This may be compensated for elsewhere in the receiver.
Noise in the received video will be reflected in the value `K`. This may be a serious problem in the upconverter since ideally we would wish to signal low amplitude movement which generates only small values for `K`. These may be hidden in noise, so resulting in a random selection of the interpolation scheme. The subjective effect of this is to considerably increase the "noise" in the picture.
The dominant source of noise in the receiver will be from the FM satellite transmission channel. This is so because the video source will typically be a studio RGB camera, telecine, or in the near future components VTR's. The carrier to noise power ratio, (C/N), of the extended definition MAC Link, (Bandwidth 11 MHz) in a typical receiver will be of the order of 18-20 dB. This subjectively corresponds to a C/N figure of 16-18 dB in a standard MAC channel which is equivalent to an unweighted luminance to noise ratio of 31.6-33.6 dB.
One way of preventing much of the nosie on movement signal `K` effecting the interpolation is to apply a coring threshold to `K`. Any frame differences below this threshold would be assumed to be noise and consequently ignored. The problem here is that for the relatively high levels of noise introduced by the satellite link a high threshold would be necessary. In the instance of a received carrier to noise power ratio of 20 dB, it is found necessary to set the coring level to about 5% of peak video amplitude. The change from the temporal to vertical only interpolation must be gradual; abrupt changes will add visible noise, so that in this example vertical only interpolation is not implemented with a frame difference of less than about 10% of peak video amplitude. Coring of this order overcomes the problem of "interpolation added noise", but the process has severely degraded the performance of the upconverter with movement in the scene. A 10% change in luminance level between successive pictures would be typical of moving sharp edge of low contrast or a soft edge of higher contrast. Thus such moving edges within the scene may be "ignored" by the movement signal, or with sim
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IEEE Trans Communications, vol. COM-26, No. 10, Oct. 1978 (New York, U.S.) Kouji Kinuhata et al; "Digital Standards Converter by Adaptive Intra-Frame Line Interpolation", pp. 1413-1419, see p. 1415, paragraphs 2,3; p. 1417, paragraph 3,3.
Chin Tommy P.
Independent Broadcasting Authority
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