Television – Format conversion
Reexamination Certificate
1997-02-21
2001-08-21
Garber, Wendy R. (Department: 2612)
Television
Format conversion
C348S262000
Reexamination Certificate
active
06278492
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for transmitting digital video signals obtained on imaging by a CCD imaging device.
2. Description of the Related Art
Up to now, there has been known a system in which, as a system for digitally transmitting digital color video signals obtained on imaging by a CCD imaging device, a portable television camera (camera head), and a camera control unit provided in a relaying car, editing room or an imaging room, are interconnected by a cable, such as a coaxial cable for digitally transmitting color image signals imaged by the camera head to the camera control unit.
In such digital transmission system for transmitting digital color video signals between the camera head and the camera control unit, the sampling rate is set so as to be the same as that for digital imaging signals outputted by the camera control unit, or as the sampling frequency (sampling rate) of a charge coupled device (CCD).
FIG. 1
shows an example for transmitting digital color imaging signals from the camera head to the camera control unit. The arrangement shown in
FIG. 1
uses a so-called multiple CCD type CCD camera head for a camera head in which the CCDs are offset relative to one another for suppressing pseudo signals and improving the resolution. This technique is known as a pixel offsetting technique. While the imaging signals of the frequency not less than one-half the sampling frequency represent pseudo signals in the single CCD type CCD camera head, even the imaging signals of a frequency not less than one-half the sampling frequency cease to be pseudo signals in the multiple CCD type CCD camera head employing the pixel offsetting technique, thus realizing high resolution.
Referring to
FIG. 1
, the light from an object, incident on a lens system
201
of a camera head
200
, is separated by a color separation prism
202
into light beams of three colors, namely red (R), green (G) and blue (B). The light beams of R, G and B are incident on solid-state imaging devices (CCDs)
203
a,
203
b
and
203
c
for conversion into electrical signals corresponding to the R, G and B colors, respectively. For exploiting the technique of the pixel offsetting technique, the CCDs
203
R,
203
G and
203
B are arranged so that the CCD
203
R and the CCD
203
B are horizontally offset relative to the CCD
203
G by one-half the pixel pitch. Consequently, the image incident on the CCDs
203
R,
203
G and
203
B has imaging signals for G complementally sampled with respect to the imaging signals for R and B.
The imaging signals for R, G and B from the CCDs
203
R,
203
G and
203
B are amplified by associated pre-amplifiers
204
R,
204
G and
204
B, respectively, so as to be then converted by analog/digital (A/D) converters
205
R,
205
G and
205
B, respectively, into digital imaging signals. It is noted that the A/D converters
205
R,
205
G and
205
B convert analog imaging signals into digital signals using clocks of the same frequency as the sampling clocks used in the CCDs
203
R,
203
G and
203
B, while the A/D converter
205
G for G perform digital conversion with clocks delayed in phase by 180° from those used in the A/D converters
205
R and
205
B for R and B, respectively, for realizing the pixel offsetting effect. In the example of
FIG. 1
, the frequency of the digital imaging signals outputted by the (A/D) converters
205
R,
205
G and
205
B is 18 MHz.
The digital imaging signals outputted by the (A/D) converters
205
R,
205
G and
205
B are sent to a digital processing circuit
206
which then performs so-called contour enhancement or gamma (&ggr;) processing on the digital imaging signals supplied thereto. The present digital processing circuit
206
performs processing with the frequency twice the frequency of the CCD sampling clocks for maintaining the pixel offsetting effect. Thus the frequency of the digital imaging signals obtained on processing by the digital processing circuit
206
is twice the frequency of the input digital imaging signals (18 MHz), or 36 MHz.
If a format of so-called SMPTE (Society of Motion Picture and Television Engineers) 295M composite signals, for example, is used as a format for digital video signals handled between the camera head
200
and a control unit
210
, the frequency of the digital imaging signals obtained by the digital processing circuit
206
(36 MHz) is converted into a rate of, for example, 13.5 MHz. To this end, the digital imaging signals obtained by the digital processing circuit
206
are sent to a frequency conversion circuit
207
for converting the signal with the rate of 36 MHz into a signals with a rate of 13.5 MHz. In the above example, the rate of 13.5 MHz is used, however, if the rate of 18 MHz which is the same as the sampling frequency of the imaging signal output of the CCD is used, the frequency of the digital imaging signals from the digital processing circuit
206
(36 MHz) is converted by the frequency conversion circuit
207
into the frequency of 18 MHz. Meanwhile, the SMPTE is the digital standard for composite signals, and the SMPTE 295M provides the digital encoding standard for the NTSC signals and the bit-serial interfacing standard. The SMPTE provides for two sorts of the sampling frequency, that is 13.5 MHz and 18 MHz, according to Recommendations
601
. The latter frequency of 18 MHz is a frequency raised from 13.5 MHz in proportion to the increased aspect ratio (13.5 4/3).
The R, G and B component signals, rate-converted by the frequency conversion circuit
207
, are converted by a parallel/serial conversion circuit (P/S conversion circuit)
208
into composite signals of the above-mentioned SMPTE 295M standard so as to be outputted along with various other sorts of the information at an output terminal
209
.
The composite digital imaging signals, outputted at the output terminal
209
, are supplied to an input terminal
211
of the camera control unit
210
via a cable along with the other information.
The composite digital imaging signals, supplied to the camera control unit
210
, are converted by a serial/parallel conversion circuit (S/P conversion circuit)
212
into component digital imaging signals of R, G and B. These component digital imaging signals of R, G and B are converted into analog imaging signals by digital/analog (D/A) converting circuits
213
R,
213
G and
213
B associated with R, G and B, respectively, so as to be outputted at output terminals
214
R,
214
G and
214
B, similarly associated with R, G and B, respectively.
If the composite digital video signals of the above-mentioned SMPTE 295M standard are outputted by the camera control unit
210
, the R, G and B component digital video signals from the S/P conversion circuit
212
are converted by the P/S conversion circuit
216
into composite signals of the above-mentioned SMPTE 295M standard which are outputted at an output terminal
217
. Meanwhile, if the rate of the component digital video signals of R, G and B from the S/P conversion circuit
212
S, for example, 18 MHz, it is converted by a frequency converter
215
into the rate of 13.5 MHz and thence supplied to the P/S conversion circuit
216
.
However, in the above-described system, there is raised no particular problem if the camera control unit
210
outputs only the above-mentioned digital video signals. However, if the camera control unit
210
outputs an analog video signal, the effect of pixel offsetting by the camera head
200
is annulled as concerns the resolution. Stated differently, if the sampling frequency of transmission from the camera head
200
to the camera control unit
210
is the above-mentioned frequency, the pixel offsetting in raising the resolution of the analog video signals obtained by the camera control unit
210
is not effective for the analog video signals obtained from the camera control unit
210
. More specifically, the limit resolution obtained from the 36 MHz rate digital video signals obtained with the digital processing circuit
206
of the camera h
Chang Dexter T.
Frommer William S.
Frommer Lawrence & Haug LLP.
Garber Wendy R.
Sony Corporation
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