Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1999-01-05
2003-02-04
Moe, Aung S. (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S645000
Reexamination Certificate
active
06515700
ABSTRACT:
TECHNICAL FIELD
This invention relates to a picture signal processing apparatus for level compressing high-luminance portions of picture signals, a color video camera carrying the apparatus and a picture signal processing method.
BACKGROUND ART
In picture signal standards of standard television systems, such as National Television System Committee (NTSC) or Phase Alternation by Line (PAL) systems, the black level and the maximum white level of luminance signals are fixed, such that a portion brighter than the maximum white level cannot be displayed. Thus, in video cameras, luminance compression is used in order for the high luminance portion to be accommodated in picture signals. That is, with the white level in the picture signal standard of 100%, the maximum white level is 105 to 110%, so that image pickup signals of the luminance signal level of 95 to 200% obtained from an imager are compressed in level so that the imaged signals with the luminance signal level of 90 to 200% obtained from the imager will be accommodated in the luminance signal level of from 95 to 110%.
An illustrative inner structure of a video camera
9
handling monochomatic picture signals is shown in FIG.
1
.
The video camera
9
shown in
FIG. 1
includes a CCD image sensor
2
on which falls an imaging light beam from an object via an imaging lens
1
. The CCD image sensor
2
images an object image formed by the imaging light for conversion to electrical signals. The electrical signals obtained by the CCD
2
, that is the imaging signals, are processed by a contour enhancement circuit
3
with contour enhancement in both the horizontal and vertical directions. The electrical signals are also processed by a luminance compression circuit
4
with luminance compression.
An output signal of the luminance compression circuit
4
is processed by a gamma correction circuit
5
with non-linear correction known as gamma correction and is further processed by a white clipping circuit
6
with white clipping for prohibiting outputting of a signal higher in luminance signal level than the video signal standard. The resulting signal then is amplified by an amplifier
7
so as to be used as an output video signal of the video camera
9
.
If the signal level of a luminance signal Y prior compression by the luminance compression circuit
4
is y, the signal level of the luminance signal after compression is y′ and a signal Y for which the signal level y exceeds the signal level Kp is compressed with a compression ratio Ks, the luminance compression by the luminance compression circuit
4
is given by the following equations:
y′=y
, if
y≦Kp
y′=Ks
(
y−Kp
)+
Kp
, if
y>Kp.
For example, if the 100% white level in the above image signal standard is 1, the luminance signal Y prior to compression, having the luminance signal level up to 200% (=2) is suppressed to the luminance signal level of 110% (=1.1), and the signal of Kp is 95% (=0.95),
Ks=
(1.1−0.95)/(2−0.95)
such that
y′=y
, if
y≦
0.95
and
y′={
(1.1−0.95)/(2−0.95)}×(
y−
0.95)+0.95, if
y>
0.95.
This luminance compression can be represented by a graph of FIG.
2
. If the white level in the image signal standard is 100%, the abscissa and the ordinate in
FIG. 2
represent the signal level of the luminance signal Y prior to compression, that is the input signal, in percentage (%), while the ordinate in
FIG. 2
represents the signal level of the luminance signal Y after compression, that is the output signal, similarly in percentage
The above-described luminance compression system is herein termed the first system.
Although
FIG. 1
shows the structure of the video camera
9
handling monochromatic signals, as an example, the inner structure of the color video camera handling color image signals, shown for example, in
FIG. 3
, is known.
As differences between the structure of a color video camera
10
shown in FIG.
3
and that of the video camera
9
shown in
FIG. 1
, a color separation prism
12
for separating the imaging light for forming an image of an object into color components of three prime colors of red, green and blue is arranged at back of an imaging lens
11
, while there are provided CCD image sensors
13
R,
13
G and
13
B for imaging each object image separated into respective color components, amplifiers
14
G,
14
R and
14
B for taking white balance of red, green and blue signals R, G and B obtained as imaging signals of respective colors by the CCD image sensors
13
R,
13
G and
13
B, contour enhancement circuits
15
R,
15
G and
15
B for executing contour enhancement or luminance compression for three channels, luminance compression circuits
16
R,
16
G and
16
B, gamma correction circuits
17
R,
17
G and
17
B and while clip circuits
18
R,
18
G and
18
B. In addition, there is added an encoder
19
for converting three prime colors R, G and B to color image signals of, for example, NTSC or PAL.
That is, in the color video camera
10
shown in
FIG. 3
, the imaging light from an object, incident via an objective lens
11
, is separated by a color separation prism
12
into three prime colors of red, green and blue. The light of the respective color components falls on the associated CCD image sensors
13
R,
13
G and
13
B so as to be thereby converted into imaging signals associated with the light of the respective color components, that is into three prime color signals R, G and B.
These three prime color signals R, G and B from the CCD image sensors
13
R,
13
G and
13
B are adjusted in signal levels by associated amplifiers
14
G,
14
R and
14
B in order to achieve the white balance. The resulting signals are sent to associated respective contour enhancement circuits
15
R,
15
G and
15
B for contour enhancement. Output signals of the luminance compression circuits
16
R,
16
G and
16
B are gamma-corrected by the respective gamma correction circuits
17
R,
17
G and
17
B and white-clipped by the associated while clip circuits
18
R,
18
G and
18
B so as to be thence supplied to an encoder
19
. The encoder
19
generates color video signals pursuant to the standard television system, such as NTSC or PAL. These color video signals are sent to an amplifier
20
. The color video signals, amplified by the amplifier, serve as output video signals of the color video camera
10
.
It is noted that luminance compression by the color video camera
10
shown in
FIG. 3
is performed by the above-mentioned first system independently for each of the three prime color signals R, G and B. The system for independently luminance-compressing the three prime color signals R, G and B by the above-mentioned first system is herein termed a second system.
However, with this second system, there is raised a problem that the color hue or saturation is changed in high luminance portions obtained on imaging a colored object.
Thus, the present Assignee proposed in Japanese patent application no. H-8-91575, which corresponds to WO98/51089 and U.S. Pat. No. 6,111,607, a level compressing method for color video signals in which luminance signals Y are generated from the three prime color signals R, G and B to perform luminance compression on the basis of the luminance signals Y instead of compressing the three prime color signals R, G and B by independent luminance compressing circuit.
In this level compressing method for color video signals, disclosed in Japanese Patent Application No. H-8-91575, the three prime color signals R, G and B are compressed in luminance using a luminance compressing circuit
150
shown for example in FIG.
4
.
In the luminance compressing circuit
50
, the three prime color signals R, G and B entering input terminals
51
R,
51
G and
51
B are sent to associated multipliers
56
R,
56
G and
56
B, respectively, while being also sent to a Y-matrix circuit
52
.
The Y matrix circuit
52
generates luminance signals Y from the supplied three prime color signals R, G and B.
Kawa Seiji
Nakamura Hitoshi
Sudo Fumihiko
Frommer Willliam S.
Frommer & Lawrence & Haug LLP
Moe Aung S.
Smid Dennis M.
Sony Corporation
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