Television – Image signal processing circuitry specific to television – Transition or edge sharpeners
Patent
1993-12-06
1995-08-29
Groody, James J.
Television
Image signal processing circuitry specific to television
Transition or edge sharpeners
348607, 348618, 348622, H04N 5208, H04N 514
Patent
active
054465028
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is directed to a method for filtering signals, whereby signal amplitudes can be allocated to a quantized, two-dimensional reference plane, and whereby a filtered signal can be added to an unfiltered input signal for the amplification of a useful signal part after constant parts as well as high-frequency parts have been filtered out.
Over and above this, the invention is directed to an apparatus for filtering signals, whereby signal amplitudes can be allocated to a quantized, two-dimensional reference plane, and whereby a separating filter that branches the input signal as well as a frequency-dependent filter arranged in a filter branch are provided.
Such devices are particularly employed in electronic imaging processing apparatus in order to improve the image quality of images. Such image graduations particularly occur in the field of digital image processing and are improved with respect to their confidence capability with the assistance of the filter means. For example, EP-B-0 051 068 discloses a filter means of the prior art. It turns out, however, that the known filtering methods and filter devices do not supply satisfactory results particularly when the amplitude of the useful signal is not clearly higher than the amplitude of superimposed disturbances. The result of this is that signals having a low signal-to-noise ratio can only be inadequately filtered. Given, for example, image signals that are only weakly formed, such as comparatively regular textures on a surface, then, even given comparatively slight disturbances, it is not possible with the traditional methods to undertake an adequately sharp demarcation of the contours that limit the texture elements.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to improve a method of the species initially cited such that a qualitatively high-grade filtering of signals having low signal-to-noise ratio is enabled.
This object is inventively achieved in that, following a frequency filtering of the signal part to be filtered, components of the signal part to be filtered which have an amplitude above a prescribable threshold are eliminated in at least one contour filter unit. The threshold is adaptively adjusted dependent on an amplitude of the input signal. Before offering an overall filter signal, the output signal of the contour filter unit is subtracted from the output signal of the frequency filter in order to generate the overall filter signal.
A further object of the present invention is to improve an apparatus of the type initially cited such that it is suitable for the implementation of the method of the invention.
This object is inventively achieved in that the frequency-dependent filter is provided with at least one lower limit frequency. The output signal of the filter is branched in the region of a separating filter and is supplied both to at least one contour filter that eliminates contour signal parts as well as to a subtraction unit in whose region the output signal of the contour filter is subtracted from the output signal of the filter in order to eliminate noise.
It becomes possible with the assistance of the method of the invention to implement a nearly arbitrarily precise detection of a noise part on the basis of a cascading of contour filter units. By contrast to the methods known from the prior art, it is not exclusively a reduction of noise parts that is implemented here in a filter branch; rather, conversely, an elimination of contour parts from a signal part to be filtered is implemented first in a lower-ranking filter level. The goal of this lower-ranking filter level is to offer a signal that, insofar as possible, contains no contour information and as a result whereof no diminishment of the contour information occurs in a subtraction of the output signal of the filter preferably designed as a high-pass filter. This filtering method makes it possible to intensify even extremely weak contours in an input signal provided with considerable disturbances. In partic
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IEEE Transactions on Circuits and Systems, vol. CAS-34, No. 11, Nov., 1987, Reinhard Bernstein "Adaptive Nonlinear Filters for Simultaneous Removal of Different Kinds of Noise in Images".
Electronics and Communications in Japan, Part 1, vol. 71, No. 10, 1988, Yasuhiro Kawazoe, "Edge Extraction and Restoration of Noisy Image by Innovation Process in Kalman Filter".
Burgess Glenton B.
Groody James J.
Linotype-Hell AG
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