Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1982-08-24
1985-12-17
Chin, Tommy P.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358166, H04N 514
Patent
active
045595585
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a picture quality adjusting circuit, in which an input video signal is added with a correcting signal for sharpness improving formed by the secondary-differentiation or the like of the input video signal to prevent the picture quality from being deteriorated mainly by the spot size of an electron beam being enlarged.
BACKGROUND ART
There has been well known such a picture quality adjusting circuit that upon transmitting a video signal, a correcting signal provided by secondary-differentiating an input video signal was superimposed upon the input video signal so as to improve the sharpness of a picture. However, when such a video signal in which a video signal with a large amplitude is superimposed thereon with a correcting signal having a relatively large level is produced from the conventional picture quality adjusting circuit, and a Braun-tube is driven by this signal, such a problem is brought about that the spot size of the electron beam is enlarged by a white peak with a value larger than a specified value and fine portions of the picture are damaged to cause white blurs thus resulting in picture degradation.
In order to prevent the picture quality from being deteriorated by the spot size of the electron beam enlarged, there may be considered two methods. One method is such that the white peak of the video signal applied to the Braun-tube can be detected and when the white peak is detected, the amplitude of the video signal is made low. Such circuit is called a peak ABL (automatic beam current limiter), in which a video signal S.sub.0 shown in FIG. 1A is converted into a video signal S.sub.0 ' shown in FIG. 1B. The other method is such that the white peak of a video signal can be similarly detected and when the white peak of the video signal shown in FIG. 2A is detected, the white side thereof is clipped or compressed thereby converted into a video signal S.sub.0 ' shown in FIG. 2B.
But, the former method has such problems that the circuit arrangement thereof is made complex, and when the white peak is detected, the contrast of the picture is lost suddenly. Whereas, the latter method inherits such a defect that as will be clear from FIG. 2B, the information on the white portion is likely to be lost.
An object of the present invention is to provide a picture quality adjusting circuit which can avoid white blurs caused by the spot size of the electron beam being enlarged.
DISCLOSURE OF INVENTION
Based upon the fact that since a video signal component with a large amplitude per se has sufficient contrast, it requires not so much improvements of sharpness of picture, the present invention is to provide such a picture quality adjusting circuit that the correcting amount of the white side for the video signal component with large amplitude is suppressed more as compared with the correcting amount of the black side, whereby the white blur is not caused, and the video signal with small amplitude or medium amplitude can be corrected sufficiently. In addition, the picture quality adjusting circuit according to the present invention has an advantage that its circuit arrangement is simplified.
Moreover, in accordance with the present invention, by a simple arrangement with a provision of a large amplitude white side suppressing circuit, it is possible to prevent the white peak from being protruded by the correcting signal component thus the white blur being avoided. Furthermore, the correcting signal for the white peak portion is suppressed so that the picture quality on the black side can be prevented from being deteriorated. In other words, in the case of the video signal which rises from the black level to the white side, the correcting signal on the black side becomes less than the cut-off level so that effect of the improvement of sharpness is not achieved. But, in the case of the video signal with large amplitude which rises from a background of a level on a somewhat white side rather than the black level (dark grey), the sharpness of the black portion
REFERENCES:
patent: 3838598 (1974-10-01), Okada
patent: 3946153 (1976-03-01), Peth
patent: 3984865 (1976-10-01), Avins
patent: 4263616 (1981-04-01), Lee
patent: 4410912 (1983-10-01), Hess
patent: 4414564 (1983-11-01), Hitchcock
Hosoya Mitsuru
Toyoda Naokuni
Tsuchiya Takao
Chin Tommy P.
Eslinger Lewis H.
Sinderbrand Alvin
Sony Corporation
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