Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1999-04-12
2003-09-02
Moe, Aung S. (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
Reexamination Certificate
active
06614475
ABSTRACT:
DESCRIPTION
Correction Apparatus and Method for Imaging Signals and Video Camera
TECHNICAL FIELD
This invention relates to a correction method and apparatus for imaging signals for flare correction and a video camera having the flare correcting finction.
BACKGROUND ART
Heretofore, in a video camera in which an image of an object formed on an imaging surface of an image pickup device by the imaging light incident thereon via an image pickup optical system is converted into electrical signals, which electrical signals are outputted as image pickup signals, a phenomenon termed flare is sometimes produced. This flare is a phenomenon in which the incident light is reflected by an image pickup surface or plural lenses of a zoom lens unit to fall on an image pickup device to raise (or float) the signal level of dark portions of the image (the signal level of the entire image) than an actual level. In particular, a lead oxide (PbO) layer forming a photoelectric conducting surface of a photoelectrically conductive image pickup tube used in a conventional video camera, absorbs the red light to a lesser extent and reflects it, this reflected light being reflected by a surface plate glass to be reincident on the PbO layer to raise the signal level of the dark portion or to cause flare responsible for color distortion, all in a well-known manner.
For this reason, it is practiced in the video camera to correct the above flare. The correction level necessary for flare correction, that is the 0 flare correction level, is said to be proportionate to the average value of the incident light volume, that is proportionate to the average picture level APL. Therefore, the flare correction circuit loaded on the video camera integrates picture signals obtained from an image pickup device to detect the APL and subtracts the APL multiplied by a preset coefficient as the flare correction level from the original image to prevent the signal level of the dark portion from being increased.
In a video camera used in, for example, a broadcasting station, camera adjustment is made using a gray scale chart
10
as shown in FIG.
1
. This gray scale chart is prepared by bonding a paper sheet with a prescribed reflectance on a 4:3 picture frame. A 11-stage or a 9-stage gray scale chart is commonly used. The gray scale chart
10
shown in
FIG. 1
is a 11-stage gray scale and has a reflectance of a white area
10
W with the maximum reflectance of 89.9% and has a reflectance of a black area
10
B with the maximum reflectance of 2%.
Using the gray scale chart
10
, the white portion is matched to 100% of the picture signal level (
100
IRE (Institute for Radio Engineers)). A video engineer (VE) of a broadcasting station performs gamma correction, knee point adjustment or flare correction required for video camera setup, before starting the program recording or relaying.
The signal waveform of image signals, obtained on imaging with a routine video camera, and observed by a measurement equipment, termed a waveform monitor, is shown in FIG.
2
.
In the image signals of the signal waveform, shown in
FIG. 2
, the white portion corresponding to the white area
10
W, has the maximum signal level. If this signal level is adjusted to
100
IRE, the signal level of the black portion corresponding to the black area
10
B is 100×2/89.9=2.2 IRE.
However, in an actual video camera, the vicinity of the black level is amplified by a factor of approximately four by gamma correction. There is also a function termed a pedestal in which the complete black level is not set to 0 IRE but the signal level is raised to prevent collapsing of the black and its vicinity, such that, in the total absence of the incident light, pedestal level of the order of approximately 51 RE is added. There is also produced a phenomenon, termed flare, in which he black level is slightly floated by the flare effect caused by the random scattering of the incident light in the inside of the lens or on the imaging surface. Thus, the black level in the signal waveform of the imaging signals is approximately 2.2×4+5+ flare effect or 15 IRE.
Since the flare inherently ins proportionate to the average value of the incident light volume, that is the average picture level (APL), the APL is detected by integrating the picture signals obtained from the image pickup device and the APL thus detected is multiplied with the flare correction coefficient to give a flare correction level which is then subtracted from the original picture signals to correct the flare.
Specifically, with the signal waveform of the imaging signals, shown in
FIG. 2
, the black level is of the order of 15 IRE due to the flare effect of approximately 1.2%. In the incident light volume which gives the signal waveform of the image pickup signals shown in
FIG. 2
, the flare correction level of 1.2 IRE obtained on multiplying the APL of the imaging signal with the flare correction coefficient is subtracted from 15 IRE to give the black level of 13.8 IRE. With a video camera having the flare correction function, the flare correction level is doubled in a manner corresponding to the doubled flare effect, even if the iris is opened by one throttle level to give an excess incident light volume. Thus, the flare effect can be canceled to maintain the black level at 2×(2.2×4)+5=22.6 IRE.
The structure of a video camera having a conventional flare correction function is shown in FIG.
5
.
In a color video camera
30
shown in
FIG. 5
, the light from an object, incident via an image pickup lens optical system
11
on an image pickup unit
12
, is separated by a color separation prism, not shown, in the image pickup unit
2
, to give three color beams, that is red (R), green (G) and blue (B) beams, which are incident on associated image pickup devices, not shown. The image pickup devices, associated with R, G and B, convert the incident light beams R, G and B into electrical signals (imaging signals of the respective color components). The imaging signals of the respective color components from the image pickup devices are amplified by amplifiers in the image pickup unit
12
to output signals of a require signal level which are outputted.
The output imaging signals of the image pickup unit
12
are sent to associated variable gain amplifiers
13
R,
13
G and
13
B where the imaging signals are adjusted for white balance so that the white portion of the object will be of the correct white color, that is so that, for imaging signals of the respective colors obtained from the white portion of the object, correct white color picture signals will be obtained on subsequent conversion of the imaging signals into picture signals. The imaging signals outputted from these variable gain amplifiers
13
R,
13
G and
13
B are entered to subtractors
14
R,
14
G and
14
B.
The output signals from the subtractors
14
R,
14
G and
14
B are sent via associated amplifiers
15
R,
15
G and
15
b
to an APL detection circuit
16
and to an image enhancer
19
.
This APL detection circuit
16
integrates the imaging signals of the respective color components R, G and B over several frames to detect an average signal level APL of the imaging signals associated with the respective color components. The APL signals associated with the respective color componentsas detected by the APL detection circuit
16
are sent to a coefficient multiplication circuit
17
.
This coefficient multiplication circuit
17
multiplies the APL signals as found from one color component to another with the flare correction coefficients associated with the respective color components supplied from a system control micro-computer
18
. The product values resulting from multiplication by the coefficient multiplication circuit
17
represent the flare correction levels associated with the respective color components. The relation between the APL signals, the flare coefficients multiplied with the APL signals and the flare correction level is shown in
FIG. 6
, in which the ordinate and the abscissa stand fo
Ito Keiichi
Sato Seiji
Yamaga Satoshi
Frommer William S.
Frommer & Lawrence & Haug LLP
Kessler Gordon
Moe Aung S.
Sony Corporation
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