Television – Image signal processing circuitry specific to television – Transition or edge sharpeners
Reexamination Certificate
1999-07-06
2001-04-10
Peng, John K. (Department: 2714)
Television
Image signal processing circuitry specific to television
Transition or edge sharpeners
C348S606000, C382S266000
Reexamination Certificate
active
06215527
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to signal processing of video signals reproduced from a television receiver or a VTR, and more particularly relates to a video signal contour correcting circuit for enhancing the contour of video signals.
2. Description of the Related Art
The video signal reproduced by a recording/reproducing apparatus, the video signal transmitted by a cable, or the video signal imaged by a television camera loses its high frequency component depending on the general transmission band generally, and the sharp rising waveform or the sharp falling waveform of the video signal loses the sharpness of the contour to form a rounded waveform, as the result, the sharpness of an image on a monitor screen is rounded.
An contour correcting circuit for correcting the signal contour by use of a circuit is used.
FIG. 5A
is an exemplary correcting circuit for contour correction of the video signal,
21
and
22
denote differential circuit, and
23
denotes a subtraction circuit for subtracting an contour-corrected signal from an original video signal.
FIG. 5B
shows the signal waveforms at respective positions on the above-mentioned circuits, (A) is the video signal waveform having the contour which forms a inflection point of the video signal rounded due to the circuit characteristics, (B) is the harmonic signal component (first order differential) of an edge formed by passing the video signal waveform (A) through the first differential circuit
21
, and (C) is a quadratic differential waveform signal formed by passing further the signal of (B) through the second differential circuit
22
, which (C) is resultantly the signal waveform obtained by differentiating the harmonic component twice.
The signal waveform which has been differentiated twice is provided to the subtraction circuit
23
, and subtraction circuit
23
subtracts the provided signal waveform from the original video signal to form a signal having the contour with the inflection point of the video signal which rises steeply and is enhanced as shown in (D).
As described herein above, the signal which has been differentiated twice to correct the contour of the video signal has a waveform contour which rises sharply and falls sharply, however, the high level overshoot Q and preshoot P are added to the original video signal when the contour correction is enhanced, and a needless frame is resultantly added to the original video signal to form an image which seems different from the original image.
On the other hand, if the video signal is subjected to mild differentiation, the sharp contour is not obtained.
SUMMARY OF THE INVENTION
The present invention has been accomplished to mitigate the above-mentioned problem, and is a video signal contour correcting circuit, which is is provided with the first differential circuit for extracting the high frequency component of the video signal, the second differential circuit for differentiating the output of the first differential circuit, and a correlator to which the output of the first differential circuit, the inverted output of the first differential circuit, and the output of the second differential circuit are supplied, wherein, for example, the first order differential output is obtained for the rising portion of the emphasizing signal, the inverted first differential output is obtained for the falling portion of the signal, and the second order differential output is obtained for the middle portion of the signal respectively from the correlator, and the emphasizing signal is overlapped to the input signal.
The first and second filter means may comprise a high frequency band passing filter or sine filter, and otherwise may comprise a delay circuit and a subtracter for subtracting the input/output signal of the circuit.
Particularly in the case that a delay circuit is used, all the circuit elements may easily comprise video signal processor for performing digital signal processing.
REFERENCES:
patent: 4360830 (1982-11-01), Poetsch et al.
patent: 4393407 (1983-07-01), Yokomizo
patent: 4541014 (1985-09-01), Yagi
patent: 5243427 (1993-09-01), Yu
patent: 5491520 (1996-02-01), Nozawa et al.
patent: 5561473 (1996-10-01), Saionji et al.
patent: 6088065 (2000-07-01), Uchida
Miyamoto Masaru
Okamoto Hiroshige
Takahashi Yoko
Tsukimura Atsuko
Frommer William S.
Frommer Lawrence & Haug LLP.
Peng John K.
Sony Corporation
Tran Trang U.
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