Photography – With object illumination for exposure – Exposure control circuit with illumination mode
Reexamination Certificate
2000-02-29
2001-10-09
Perkey, W. B. (Department: 2851)
Photography
With object illumination for exposure
Exposure control circuit with illumination mode
C396S176000, C396S225000
Reexamination Certificate
active
06301442
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical instrument and an image photographing method. More particularly, the present invention relates to an optical instrument and an image photographing method for photographing an object image with appropriate color balance in indoor photography in particular.
2. Description Related to the Prior Art
Optical instruments, such as a photographic camera and a digital still camera, are widely used for photographing an object image. The photographic camera is used with silver halide photo film. The digital still camera incorporates a CCD image sensor. Any of such optical instruments is generally provided with an electronic flash device, which makes it possible to photograph an object indoors with insufficient illumination.
A photographic camera is used with a daylight type of color negative photo film which is the most suitable for outdoor photography under daylight. The flash device incorporated in the camera has color balance (color temperature) of flash light corresponding to color balance of daylight. Recently, there have been color negative photo films having high speed without lowering the image quality. As cameras of types with the flash device have been widely used, users takes indoor photographs the more frequently.
It is likely indoors that the use of flash light creates a high contrast frame in which an image of a principal object is over-exposed and recorded in a whitened manner, and/or an image of a background scene is under-exposed and darkened. To avoid such unwanted exposures, various suggestions have been made, including heightening speed of the photo film, lowering a shutter speed, and lowering the f-number of a photographic optical system. Also the principal object is illuminated with flash light being weakened, and the background scene is illuminated suitably by indoor illumination of an indoor light source.
However it is impossible to obtain a photographic print with sufficiently high color reproduction or color balance. When the principal object is effectively illuminated by flash light, the principal object is photographed on the photo film with coloration or tint near to that of its image which would be photographed while illuminated by daylight. The background scene behind the principal object is not illuminated by flash light, and thus photographed with the coloration of the indoor illumination. In general, the indoor illumination has color different from the daylight color, to cause a problem in the color reproduction. When the principal object is reproduced from the photo film on the photographic print neutrally or with the coloration or chromaticity very near to color of the photographic object, the color of the indoor illumination strongly remains in the background scene. In contrast, when the background scene is reproduced on the photographic print with neutral coloration, the color complementary to that of the indoor illumination strongly remains in the principal object. In any case, color failure occurs.
Let the indoor illumination be light of a tungsten lamp, the photo film of a daylight type be used under the indoor illumination, and the principal object be photographed while illuminated with flash light of the daylight color. When the photographic print is produced, the background scene has deep orange color while the principal object has its neutral coloration on the photographic print. If a printer of a type capable of correcting the colors effectively is used to produce the photographic print, the whole of the frame is finished with the coloration near to the neutral coloration. In such a frame, the background scene only has light orange color. But the cyan color is conspicuously added to the portion of the principal object, the cyan color being complementary to the orange color. An image of a person's face will be finished with very unnatural color reproduction.
If the indoor illumination is light of fluorescent lamps, pale green is added to an image of the background scene of the photographic print. Or the magenta color is conspicuously added to the image of the principal object for example a flesh-color portion of a person, the magenta color being complementary to the green color. A portrait of a person results in very unnatural color reproduction.
In order to prevent such problems, professional photographers selectively use photo films of a daylight type and a tungsten light source type. Also they use selectively lens filters suitable for the types of light sources for the purpose of obtaining optimized color balance. Those methods of indoor photography are well-known in the field of photography, but very difficult for amateur photographers to use. In addition, similar problems occurs with the digital still camera as optical instrument which uses the CCD image sensor instead of the silver halide photo film.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present invention is to provide an optical instrument and an image photographing method for photographing an object image with acceptable color balance in indoor photography in particular.
In order to achieve the above and other objects and advantages of this invention, an optical instrument for photographing an object comprises an electronic flash unit for applying flash light to the object. An exposure station forms a color image by object light from the object. The optical instrument satisfies a condition of:
0≦&Dgr;E≦0.08
where &Dgr;E is a light source color difference amount between the flash unit and a white fluorescent lamp of F6 type, and obtained from conditions of:
&Dgr;E={square root over ( )}[(X
1
−X
2
)
2
+(Y
1
−Y
2
)
2
]
X
1
=[(RF−R0)−(GF−G0)]−[(BF−B0)−(GF−G0)]/2
Y
1
=[(BF−B0)−(GF−G0)]×sin (&pgr;/3)
X
2
=[(RS−R0)−(GS−G0)]−[(BS−B0)−(GS−G0)]/2
Y
2
=[(BS−B0)−(GS−G0)]×sin (&pgr;/3)
where RF, GF and BF are Status-M converted density of red, green and blue colors of a gray reference reflector plate having a reflectance factor of 18%, the Status-M converted density being obtained by illuminating the gray reflector plate with the white fluorescent lamp of the F6type, by photographing an image of the gray reflector plate in the exposure station, and by detection of the image.
RS, GS and BS are Status-M converted density of the red, green and blue colors of the gray reflector plate, the Status-M converted density being obtained by illuminating the gray reflector plate with the flash unit, by photographing an image of the gray reflector plate in the exposure station, and by detection of the image.
R0, G0 and B0 are Status-M converted density of the red, green and blue colors of the gray reflector plate, the Status-M converted density being obtained by illuminating the gray reflector plate with a standard light source C, by photographing an image of the gray reflector plate in the exposure station, and by detection of the image.
Preferably, the optical instrument satisfies a condition of:
0≦&Dgr;E≦0.06.
More preferably, the optical instrument satisfies a condition of:
0≦&Dgr;E≦0.04.
Furthermore, a mode selector designates a selected one of first and second predetermined photographing modes, wherein if the first and second photographing modes are designated, the image is recorded with respectively first and second color balance in the exposure station. A color balance adjustor subjects the flash light or the object light to correction if the first photographing mode is designated, to satisfy the condition of:
0≦&Dgr;E≦0.08
so as to set the first and second color balance substantially equal to one another.
By the construction of the present invention, an object image can be photographed with acceptable color balance in indoor photography in particular, because flash light or object light is s
Kume Yuji
Nozawa Yasushi
Uchida Mitsuhiro
Fuji Photo Film Co. , Ltd.
Perkey W. B.
Young & Thompson
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