Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1996-08-08
2003-04-08
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S228100
Reexamination Certificate
active
06545710
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an image pick-up apparatus including an image pick-up device such as a CCD and, particularly to adjustment of white balance of a picked up image.
In a color video camera or still video camera for reading a light image incident upon a lens by converting it into electrical signals, spectral sensitivity characteristic of an image sensor in use such as a CCD (Charge Coupled Device) is fixed. In the case that a color temperature of a light source of an object varies, a color deviation is caused in a picked up image and, accordingly, the white balance of the signal representing the picked up image is normally read in order to correct this color deviation.
The white balance can be adjusted by adjusting a ratio of levels of color components of red (R), green (G) and blue (B) of the picked up image based on an image data of a high luminance portion (white portion) of the picked up image where a color temperature information of the light source is included. However, since a CCD having a linear photoelectric conversion characteristic, i.e., a CCD which outputs a voltage in proportion to an amount of incident light is used in the conventional color video cameras and still video cameras, a dynamic range in relation to a luminance range of the object is insufficiently wide and the color temperature information of the light source cannot accurately be extracted from the high luminance portion of the picked up image. A white balance adjusting method using the image data of the high luminance portion is not adopted.
FIG. 13
shows a photoelectric conversion characteristic of a conventional CCD image sensor. In
FIG. 13
, abscissa is an amount of incident light and ordinate is an output voltage of the image sensor. Also, OJ
1
denotes people under a tree, OJ
2
denotes people under the sun light, OJ
3
denotes a distant object in clear day, OJ
4
denotes an object on a skiing slope, and OJ
5
denotes a mass of snow in a clear day.
As indicated,by a characteristic curve {circle around (1)} of
FIG. 13
, the image sensor used in the conventional video camera has a linear photoelectric conversion characteristic with which it outputs a voltage in proportion to the amount of incident light with the intensity of the light being a slope (inclination of the characteristic curve {circle around (1)}. The range of the amount of incident light in relation to the dynamic range (portion A
1
) is narrow. If an image is picked by controlling only an exposure time of the image sensor, the image of the high luminance portion (portion A
2
) including the color temperature information of the light source is subject to overflow. Particularly in the video camera using a CCD of complementary color and single plate type, color modulation carriers saturate, thereby changing colors. Accordingly, in view of color reproducibility, the dynamic range becomes even narrower.
Thus, if the white balance is adjusted based on the image data of the high luminance portion from which a precise color temperature information of the light source cannot be obtained, the color deviation gets worse.
The image in the high luminance portion can be read without causing an overflow by restricting the amount of incident light via an aperture to change the slope of the characteristic curve {circle around (1)} into that of a characteristic curve {circle around (2)} and by controlling the amount of incident light and the exposure time to expand the dynamic range of the image sensor. However, such an exposure control cannot be performed since it leads to a reduction in a signal-to-noise (S/N) ratio of a main object. Therefore, the white balance adjustment based on the image data of the high luminance portion is not adopted.
Since a reliable light source information cannot be obtained from the high luminance portion due to the photoelectric conversion characteristic of the image sensor, the white balance has conventionally been adjusted based on image signals from a portion having a relatively high brightness and a low saturation.
More specifically, the image signals of R-, G-, B-components are converted into a Y-signal (luminance signal) and a C-signal (chrominance signal). The white balance is adjusted based on the image signals from a portion where the C-signal is below a specified level and the Y-signal is above a specified level.
However, according to the above-mentioned conventional white balance adjusting method, the color temperature information of the light source is estimated based on the image data of the portion having a relatively high brightness and a low saturation. Accordingly, the accuracy and reliability of the white balance adjustment values are not satisfactory. It has been difficult to perform a suitable color correction for a variety of photographic scenes, such as an against-the-sun scene, a clear-day scene and a night scene, where the color temperature of the light source differs.
Further, data used to adjust the white balance are renewed in a specified cycle so that the color deviation can be corrected even when the color balance of the image changes due to a variation of the light source of the object and a variation of a screen construction.
In the case that the image changes as in an operation of photographing a moving object under the same light source, if the white balance is adjusted according to the change of the image, the color balance becomes unstable each time the moving object changes, making it uncomfortable to see images. Accordingly, it is not preferable to; frequently adjust the white balance.
However, in the case that the cycle in which the white balance adjustment data are renewed is set long, no white balance adjustment is made when the light source of the object changes, thereby making the color deviation likely to occur. For this reason, it is preferable to perform a white balance adjustment according to change in the light source of the object.
As mentioned above, however, the color temperature of the light source cannot be precisely estimated in the conventional method. Therefore, it has been very difficult to perform a white balance adjustment according to the change of the light source of the object.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image pick-up apparatus which has overcome the problems residing in the prior art.
It is another object of the present invention to provide an image pick-up apparatus which makes it possible to accurately detect a color temperature of a light source with use of an image sensor having a photoelectric conversion characteristic of logarithmic output type, and then perform an easy and accurate color correction based on a detected color temperature.
It is still another object of the present invention to provide an image pick-up apparatus which makes it possible to accurately detect a color temperature of a light source with use of an image sensor having a photoelectric conversion characteristic of logarithmic output type, and then assure a suitable color correction in accordance with a changed light source.
It is yet still another object of the present invention to provide an image pick-up apparatus which makes it possible to accurately detect a color temperature of a light source with use of an image sensor having a photoelectric conversion characteristic of logarithmic output type, and then assure a suitable color correction for each of a variety of photographic scenes.
The present invention is directed to an image pick-up apparatus comprising: an image sensing section which photoelectrically converts light from an object into an electrical output having a logarithmic function in relation to an amount of the light to produce image data regarding a light image of the object; a detecting section which detects a color temperature of a light source in connection with the object based on image data from the image sensing section; and a correcting section which corrects image data from the image sensing section based on a detected color temperature.
The detecting section may be m
Ishii Toru
Kubo Hiroaki
Ogoshi Takeshi
Sasaki Gen
Burns Doane , Swecker, Mathis LLP
Garber Wendy R.
Minolta Co. , Ltd.
Wilson Jacqueline
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