Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
2000-06-06
2004-06-08
Vu, Ngoc-Yen (Department: 2615)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S223100, C348S235000, C348S280000, C348S672000, C348S678000, C382S172000
Reexamination Certificate
active
06747694
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a television signal processor for generating a video signal in wide dynamic range, a television camera using the same, and a method for television signal processing. The wide dynamic range television camera is designed to properly reproduce any images even though different-brightness images are mixed in an object being shot.
The conventional, general television camera has a limit of about fourfold dynamic range because of limited charge storage capacity of the imaging device. Therefore, as when shooting an objet including both a dark indoor image and a bright outdoor image, or a scene including a mixture of an extremely bright (high-brightness) object (outdoor) and a relatively dark (low-brightness) object (indoor), we cannot help controlling exposure time or the like so that only one of the high-brightness objet and low-brightness object can be obtained to have a correct level. Making the low-brightness portion have a correct level will cause the high-brightness portion white saturation, while making the high-brightness portion have a correct level will cause the low-brightness portion black level cut-off.
Recently, a wide dynamic range imaging device has been developed so as to solve the above problems. As shown in
FIG. 7
, charge accumulating operation is performed for the normal exposure time during the vertical video period, and for a short exposure time during the vertical blanking period to produce a standard luminance video signal (long-time exposure video signal) V
1
by which a standard-brightness object can be reproduced to have a correct level according to the normal exposure and a high-brightness video signal (short-time exposure video signal) V
2
by which an extremely bright object can be reproduced to have a correct level according to the short exposure. In addition, a dual amplification system has been developed. As shown in
FIG. 8
, a video signal C from an imager
22
is supplied to amplifiers
23
,
24
having different amplification factors so that the standard-brightness video signal V
1
and high-brightness video signal V
2
can be produced from the amplifiers.
These standard-brightness video signal V
1
and high-brightness video signal V
2
produced by the wide dynamic range imager or dual amplification system are, as shown in
FIG. 9
, supplied to multipliers
26
,
27
of which the multiplication factors L, S are calculated by a multiplication factor calculator
25
according to a combining ratio R which will be described later. The multiplied signals are supplied to a combiner
28
where they are combined to produce a wide dynamic range video signal W about 64 times wider than the normal one.
The video signal produced from the imagers of the television camera are subjected to nonlinear processing such as white balance, gamma correction and knee characteristic correction, and then supplied to the outside. The wide dynamic range television camera generates two or more different video signals for one object, and adequately combines that plurality of signals to produce a wide dynamic range video signal. Those plurality of video signals can be produced by changing the exposure condition or gain at the time of shooting as will be described later.
The present invention tries to provide a high-quality video signal by solving the problems that, as described below, are caused by the video signal processing in the wide dynamic range television camera, such as in the white balance process, nonlinear process or signal combining process.
The above television camera that produces a wide dynamic range video signal generates, from its one solid-state imager, two video signals: a long-time exposure video signal with the exposure condition meeting the low-brightness region of an object, and a short-time exposure video signal with the exposure condition meeting the high-brightness region of the object. These long-time exposure and short-time exposure signals are subjected to a certain combining process, and then to white balance process in a video signal processor.
The construction of this conventional television camera will be described with reference to FIG.
5
. Referring to
FIG. 5
, there is shown a charge coupled device (CCD)
11
as a solid state imager for generating a video signal by transducing the light image from an object into a charge image. The imager
11
generates the short-time exposure video signal by, for example, exposure to light for {fraction (1/2000)} second, and the long-time exposure video signal by exposure to light for a longer time than the short-time exposure video signal, for example, exposure to light for {fraction (1/60)} second, with their time base compressed during one horizontal scanning period of the video signal produced from the television camera
10
. There are also shown a sample and hold/automatic gain controller (CDS & AGC)
12
that samples and holds the video signal from the CCD
11
and amplifies it to a necessary level, and an A/D converter
13
for converting the analog video signal from the CDS & AGC
12
to a digital video signal. Shown at
14
is a synchronizer for separating the long-time exposure and short-time exposure video signals of digital video signals in each horizontal scanning period from the A/D converter
13
, expands the their time base to one horizontal period and synchronizes those separated and expanded video signals so that they can be produced at a time. Shown at
17
is a combiner that receives the long-time exposure and short-time exposure video signals from the synchronizer
14
, and combines those signals by a predetermined way. In this method for combining, the two input signals are combined to produce such a combined video signal as to have a video signal level corresponding to, for example, the level of a more appropriate-exposure one of the two video signals. As a result of such combining process, for example, the region in which the details are not clear because the long-time exposure video signal shows white saturation on the screen is made appropriate by the correct signal level of the short-time exposure video signal, and the region in which the details are not clear because the short-time exposure video signal shows black level cut-off is made appropriate by the correct signal level of the long-time exposure video signal. The combined video signal from the combiner
17
is supplied to a digital signal processor (DSP)
15
. In this DSP
15
, the combined video signal is subjected to a certain video treatment for gamma correction and white balance. The processed video signal is supplied from the DSP
15
to the subsequent stage (not shown).
FIG. 6
is a block diagram of one example of the white balance adjuster. This white balance adjuster can be constructed by a DSP or a combination of circuits having the functions of the blocks shown. An RGB gain processor
30
adjusts individually the gains of the amplitude levels of the color signals R (red), G (green) and B (blue). A color difference conversion processor
31
generates color difference signals R-Y, B-Y from the R, G, B signals and Y (luminance) signal. A white signal component detector
32
detects and produces the white signal component included in a certain white detection level frame range from the color difference signals R-Y, B-Y and Y signal. A white balance controller
33
detects in what color direction and how much the white balance is deviated by comparing the white signal components of R-Y and B-Y, and produces a signal WB (corresponding to the color temperature) indicating the deviation of the white balance. A gain controller
34
adjusts the gains of the R signal and B signal in the RGB gain processor
30
in such a direction that the WB becomes zero according to the deviation signal WB.
The object to be shot includes, as shown in
FIG. 2
, both a human
FIG. 20
in a room under fluorescent lighting, and a sunny outdoor scene
21
seen through a window. The room is a dark region (low brightness) as hatched, and the outdoor scene
21
is a much brighter region
Fukushima Akira
Nishikawa Hiroyuki
Antonelli Terry Stout & Kraus LLP
Hitachi Denshi Kabushiki Kaisha
Long Heather R.
Vu Ngoc-Yen
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