Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Reexamination Certificate
1999-03-30
2001-05-01
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
C382S261000
Reexamination Certificate
active
06226051
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the filtering of digital video signals and has particular application to the filtering of noise from video signals.
Digital video signals often include noise. The noise can either be intrinsic to the process by means of which the signal has been generated or it may have been introduced by later processing of the signal during storage or transmission of the signal.
2. Description of the Related Art
Noisy video signals are difficult to compress and it is a common step to filter out the noise prior to compression. At the data rates used for video signals it is important that the filter used is computationally simple and efficient. It is also important the filter should be able to adapt to changes in the underlying scene statistics.
The recursive filters that have been employed in the past to filter digital video signals often produce visible artifacts and are generally of relatively low performance. It is the aim of the present invention to provide filtering of digital video signals in a manner that is computationally simple and efficient.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of filtering an input digital video raster signal to produce a double sided impulse response in the time domain, the method comprising the steps of; applying the input video signal to a filter apparatus having one adaptive filter producing an impulse response on one side of the time domain and another adaptive filter producing an impulse response on the other side of the time domain, comparing each pixel of the video signal to adjacent pixel samples in the video raster to generate gain coefficient values for the pixels of the video signal, and adapting the impulse response of each filter by means of the generated gain coefficient values.
Further according to the present invention there is provided apparatus for filtering an input digital video raster signal to produce a double sided impulse response in the time domain, the apparatus comprising; an adaptive filter producing an impulse response on one side of the time domain and another adaptive filter producing an impulse response on the other side of the time domain, and a gain coefficient generator to compare each pixel of the video signal to adjacent pixel samples in the video raster and to generate therefrom gain coefficient values for the pixels of the video signal, each filter being connected to vary its impulse response to gain coefficient values generated by means of the gain coefficient generator. The invention has the advantage that a cascade of stages of filtering can be employed to filter a video signal in a vertical, a horizontal and a temporal dimension. The filtering may be made non-linear so that, in the spatial dimensions, sharp edges are preserved and, so that in the temporal dimension, no trails are left behind objects seen in moving scenes. At least some of the cascaded stages may include a forward filter path in addition to a recursive filter path to provide a double-sided impulse response.
REFERENCES:
patent: 5159442 (1992-10-01), Mizuta
patent: 0778707 (1997-06-01), None
patent: 2575879 (1986-07-01), None
patent: 2287153 (1999-09-01), None
Patent Abstracts of Japan vol. 012, No. 265 (E-637), Jul. 23, 1988 & JP 63 048970A (NEC Home Electronics Ltd.) Mar. 1, 1988.
Beattie Robert
Funnell John Stuart
Hsia Sherrie
Ladas & Parry
Tandberg Television ASA
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