Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1989-02-17
1990-04-17
Shepperd, John W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358 37, 358 96, 358166, H04N 5208
Patent
active
049185284
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a contour control device for improving sharpness or fineness of image signals used in color television receivers, video tape recorders and so forth.
BACKGROUND ART
FIG. 3 illustrates the manner in which the state of rise of a stepped waveform is improved by a known edge stressing method, disclosed in an article entitled as "A Method of Computing Sharpness of Television Image" appearing in the Gazette of Society of Electro-Communication Engineering" (July 1983, Vol. J66-B No. 7).
It is well known that the sharpness of a television image can be improved by enhancing contour portions of the image, and this method is widely applied to luminance signals which determine the shape of an object.
A typical known correction means capable of enhancing contour portions of an image is arranged, as shown in FIG. 3, such that a signal obtained by quadratic differentiation of an original signal waveform is multiplied with a certain coefficient and the product of the multiplication is added to the original signal waveform.
Referring to this Figure, more specifically, a stepped waveform I.sub.2 (=Q(x)), which is an original signal obtained through a band restriction in a transmission path, is subjected to a quadratic differentiation so that a quadratic-differentiated waveform Q"(x) is obtained. Then, the quadratic-differentiated waveform Q"(x) is multiplied with a coefficient -a so that a waveform Id is obtained. The signal Id thus obtained is added to the original signal waveform I.sub.2, whereby a contour correction signal waveform I.sub.2 +Id is obtained.
The amount of improvement in the rise time achieved by this contour correction means is expressed in terms of time relative to the amount of change in the amplitude. In the case of the original waveform I.sub.2, the amount of improvement is expressed as V.sub.1 /X.sub.1, whereas, in the case of the contour correction signal waveform I.sub.2 +Id, the amount of improvement is V.sub.2 /X.sub.2. It will be seen that the rise time is improved appreciably.
The improvement in the rise of signals corresponding to the contour portions of a television image, i.e., enhancing of contour portions, provides a higher sharpness of the image.
In the known contour correction means, the correction signal is obtained by determining the quadratic-differentiated value of the original waveform, multiplying this value with a coefficient, and adding the product of the multiplication to the original waveform. Thus, as represented by hatched portions in FIG. 3, the level of the correction signal waveform exceeds the level of the original signal waveform so that saturation of the waveform may take place when the amplitude of the original waveform coincides with the maximum amplitude of the dynamic range of the transmission path.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to overcome the above-described problems of the prior art, by providing a contour correction device which is capable of improving the sharpness of an image by enhancing the contour portion of the image without causing any saturation of an original signal waveform.
To this end, according to the present invention, there is provided a contour correction device comprising: first delay means for delaying an input signal by a predetermined time; second delaying means for delaying the input signal by a time which is longer than the delay time provided by the first delaying means; means for computing the absolute value A of the difference in the amplitude between the output signal from the first delay means and the input signal; means for computing the absolute value B of the difference in the amplitude between the output signal from the first delay means and the output signal from the second delay means; and means for comparing the absolute values A and B and for producing an output signal representative of the result of the comparison. The device further comprises means for computing the absolute value C=/A-B/ of the difference between the absolute valu
REFERENCES:
patent: 4677461 (1987-06-01), Mizutani et al.
patent: 4698673 (1987-10-01), Johnson
patent: 4706113 (1987-11-01), Ito et al.
patent: 4758891 (1988-07-01), Hitchcock et al.
patent: 4839725 (1989-06-01), Ueda
Mitsubishi Denki & Kabushiki Kaisha
Parker Michael D.
Shepperd John W.
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