Television – Image signal processing circuitry specific to television – Including nonstandard signal detection controlling processing
Reexamination Certificate
2000-04-20
2003-04-08
Miller, John (Department: 2614)
Television
Image signal processing circuitry specific to television
Including nonstandard signal detection controlling processing
C348S449000, C348S554000, C348S558000
Reexamination Certificate
active
06545725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a standard and non-standard video signal identifying apparatus for determining whether a composite video signal input to a television receiver or the like is a standard signal or a non-standard signal.
The above-mentioned standard signal refers to a television signal in which the frequency of the color subcarrier signal is strictly managed so as to be exactly an integral multiple of the frequency of the vertical synchronizing signal like a broadcast wave (composite video signal) from a broadcasting station. The non-standard signal refers to a television signal in which the frequency of the color subcarrier signal is a non-integral multiple of the frequencies of the vertical synchronizing signal and the horizontal synchronizing signal like a playback video signal (composite video signal) output from a digital video tape recorder, a digital video camera, a digital still camera or other video apparatuses.
2. Description of the Prior Art
In television broadcast signals, the frequency of the color subcarrier signal is strictly managed so as to be exactly an integral multiple of the frequency of the vertical synchronizing signal. Therefore, television receivers are configured as described below in order to effectively use the relationship between the color subcarrier frequency and the vertical frequency and that the vertical synchronizing signal can be precisely played back even when the electric field is weak or when a disturbance occurs due to ghosts. That is, one burst signal is extracted from an input video signal, a clock of a frequency of a×f
SC
(a is an integer not less than 1, and f
SC
is the color subcarrier frequency) is generated based on a color burst signal, and the clock is divided, thereby playing back the vertical synchronizing signal.
In the above-mentioned dividing operation, when a standard signal such as a broadcast wave is handled, vertical playback can be normally performed because standard signals satisfy.
V
count=(
a×f
SC
/f
H
)×(
N
/2).
Here, Vcount is the number of clocks of one field section, f
H
is the horizontal frequency, and N is the number of scanning lines of one frame.
However, when a non-standard signal like a signal obtained in special playback of a VTR (video tape recorder) is handled, the dividing operation cannot be normally performed because the following relationship holds for non-standard signals:
V
count≠(
a×f
SC
/f
H
)×(
N
/2).
Therefore, in the case of a non-standard signal, vertical playback is performed by separating the vertical synchronizing signal from the video signal by a synchronizing separator circuit.
Moreover, in television receivers, a processing such as Y/C separation using a frame comb filter or inter-field interpolation is used to enhance the image quality. When the Y/C separation is used, in the case of standard signals in which the color subcarrier frequency is exactly an integral multiple of the vertical frequency, the luminance signal and the color signal can be precisely separated by the frame comb filter, so that the effect of enhancing the image quality is expected.
However, in the case of non-standard signals in which the color subcarrier frequency is a non-integral multiple of the vertical frequency, the luminance signal and the color signal cannot be separated precisely, so that the above-mentioned image quality enhancing processing rather degrades the image quality. Therefore, it is desirable that the image quality enhancing processing be performed only in the case of standard signals and be not performed in the case of non-standard signals.
In order that vertical synchronization playback is not performed by the synchronizing separator circuit or the image quality enhancing processing is not performed when the input video signal is a non-standard signal, it is necessary to detect that the video signal is a non-standard signal.
Now, the configuration and operation of a conventional apparatus for identifying standard and non-standard video signals will be described.
FIG. 7
is a block diagram showing a concrete example of the conventional standard and non-standard video signal identifying apparatus in the case of generation of the vertical synchronizing signal of an NTSC television receiver.
A reset circuit comprising an AND gate
401
outputs a reset signal when an external reset signal supplied from a microcomputer comes in or when an external vertical synchronizing signal separated by a synchronizing separator circuit (not shown) comes in. The reset signal is input to a reset terminal R of a vertical counter
402
. Moreover, to the vertical counter
402
, a clock of a frequency of a×f
SC
generated by a clock generating circuit
403
is input to a clock terminal CLK. The clock generating circuit
403
generates the clock of a frequency of a×f
SC
based on a color burst signal extracted from the video signal.
The vertical counter
402
counts the number of clocks of one field section after the reset signal is input. A load hold flip-flop
404
, which receives the output of the vertical counter
402
as the input signal and uses the external vertical synchronizing signal as the load hold pulse, latches the value that the vertical counter
402
indicates when the external vertical synchronizing signal comes in, and outputs the latched value. That is, the output of the load hold flip-flop
404
represents the clock count of one field section defined by the external vertical synchronizing signal.
In a field clock count setting register
405
, a value corresponding to the clock count of one field section of a standard signal is set. A subtracter
406
subtracts the value set in the field clock count setting register
405
from the output of the load hold flip-flop
404
. The output value of the subtracter
406
corresponds to the shift of the clock count value of one field section defined by the external vertical synchronizing signal from the clock count value corresponding to the standard signal. Then, the output of the subtracter
406
is converted into an absolute value by an absolute value circuit
407
and the absolute value of the shift is output. In a threshold value setting register
408
, a threshold value for identifying standard and non-standard signals is set. A comparator
409
compares the output of the absolute value circuit
407
with the threshold value set in the threshold value setting register
408
. When the output of the absolute value circuit
407
is not more than the threshold value, the input video signal is determined to be a standard signal, and when the output exceeds the threshold value, the input video signal is determined to be a non-standard signal.
The basic idea of the above-described conventional apparatus for identifying standard and non-standard video signals is as follows: In the case of the NTSC system, the input video signal is determined to be a standard signal when the clock count Vcount of one field section satisfies the following relationship:
−
M≦{V
count−(
a×f
SC
/f
H
)×(
N
/2)}≦
M
(
M
>0)
where M is the threshold value for identifying standard and non-standard signals. In other cases, the input video signal is determined to be a non-standard signal.
However, in the conventional apparatus for identifying standard and non-standard video signals, the identification of standard and non-standard signals is performed based on the clock count of only one field section. Therefore, a non-standard signal such as the output of a digital still camera in which the clock count is shifted by one clock (clock frequency a×f
SC
) in n field sections although the shift of the clock count of one field section is smaller than one clock and Vcount satisfies the above-mentioned relationship in the unit of one field is erroneously determined to be a standard signal.
For this reason, although the output of a digital still camera is a non-standard signal, a playback vertical synchronizing signal obtai
Fujita Nobuko
Kageyama Atsuhisa
Matsushita Electric - Industrial Co., Ltd.
Miller John
Tran Trang U.
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