Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1999-08-05
2003-12-23
Garber, Wendy R. (Department: 2712)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S362000
Reexamination Certificate
active
06667765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image pickup apparatus for photoelectrically transferring optical energy of an image to electric signals as image data and recording the image data into a recording medium after processing predetermined image processing.
2. Description of the Related Art
This type of equipment with image pickup apparatus is described below by taking a digital camera as an example.
A digital camera (hereinafter abbreviated as camera) generally has no mechanical shutter in order to downsize and to simplify the camera. Exposure of the camera is controlled by not only varying exposure time (charge storage time) of an image pickup device such as CCD (Charge Coupled Device), but also varying a size or an area of an aperture mechanism. The camera calculates a proper exposure time t and the size of the aperture by a predetermined program corresponding to a luminance of an object.
On the other hand, in the camera using the image pickup device, it is impossible to control the exposure control time t′ as an optional value, since the exposure time of the image pickup device is governed by a scanning time tr
0
for one horizontal line of the image pickup device. Thus, the camera uses the scanning time tr
0
for one horizontal line of the image pickup device as a standard time unit for calculating an exposure control time t′. Hereupon, tr
0
=1/(30×512)≈65 &mgr;s. The camera calculates the exposure control time t′ by integral multiply of the standard time unit tr
0
.
When an exposure value EV corresponding to the luminance of the object is 15 (EV=15) and an aperture value AV corresponding to the size of the aperture is 4 (AV=4), a time value TV corresponding to the proper exposure time t becomes 11 (TV=EV−AV=15−4=11). The proper exposure time t corresponding to the time value TV=11 becomes 1/2048 sec.
On the other hand, the camera selects a time of 7/(30×512)≈1/2194 sec which is the nearest time to the proper exposure time t as the exposure control time t′ of the image pickup device. When the exposure control time t′=1/2194 sec is converted to an exposure control time value TV′ of an APEX time value, the exposure control time value TV′ becomes 11.1 (TV′=11.1). Therefor, an error component &Dgr;TVe=TV′−TV=0.1 occurs.
When the error component &Dgr;TVe is smaller than an exposure control step &Dgr;EV which is, for example, ⅕(=0.2), there is no problem in the density of an image displayed on a monitor display. Thus, the photoelectric transferring operation of the image pickup device is controlled by using the exposure control time t′ or the exposure control time value TV′.
In view of further downsizing and simplifying the digital camera, it is proposed to use the monitor display such as LCD (Liquid Crystal Display) as a viewfinder. In such a camera, it is proposed to fix the size of the aperture immovably and to control the exposure by only varying the exposure control time t′ of the image pickup device when an image is taken for smoothly displaying on the monitor display serving as the viewfinder.
The camera, however, can select the exposure control time t′ calculated by multiplying an integer on the standard time unit tr
0
. Thus, when the exposure is controlled by varying the exposure control time t′ of the image pickup device without varying the size of thee aperture, the exposure cannot be controlled properly, especially in a highlight scene in which the exposure control time t′ calculated by the luminance of the object becomes shorter than the standard time unit tr
0
.
Alternatively, even when a plurality of the exposure control time t′ can be selected by using another time unit tr shorter than the standard time unit tr
0
for realizing a delicate exposure control, an error component &Dgr;t between the proper exposure time t and the exposure control time t′ becomes larger than the time unit tr in a highlight scene, so that the exposure cannot be controlled properly in the highlight scene.
Furthermore, it is assumed that the exposure control time t′ can be variable by 1/8 TV. When the exposure value EV is equal to or larger than 15 (EV=15) in the above-mentioned example, the error component &Dgr;TVe between the proper exposure time value TV and the exposure control time value TV′ becomes larger than 1/8. Thus, the exposure control time value TV′ cannot be varied substantially. For example, with respect to EV=15.625 to 15.875 in a table 1 shown below, values of the proper exposure time value TV correspond to 11.625 to 11.875. However, the exposure control time value TV′ which can be selected and smaller than the proper exposure time value TV is 11.907 (t′=4/(30×512) sec). Thus, the exposure control time value TV′ of the image pickup device is not varied in a region of the exposure value EV=15.625 to 15.875.
TABLE 1
EV
TV
Integer
TV′
&Dgr;TVe
15.500
11.500
5
11.585
0.085
15.625
11.625
4
11.907
0.282
15.750
11.750
4
11.907
0.157
15.875
11.875
4
11.907
0.032
16.000
12.000
3
12.322
0.322
Furthermore, when the time value TV=14 is converted to an actual exposure time, it becomes nearly equal to 0.94/(30×512) sec which is shorter than the standard time unit tr
0
=1/(30×512) sec. Thus, the exposure control time t′, which can be selected in the highlight scene equal to or higher than TV=14, becomes a constant value of 1/(30×512) sec, so that all images in the highlight scene will be over-exposed.
SUMMERY OF THE INVENTION
An object of this invention is to provide an image pickup apparatus by which an image with a proper density of colors can be taken even when an aperture is immovable and only an exposure time of an image pickup device is controlled.
An image pickup apparatus in accordance with this invention comprises an image sensor for photoelectrically converting optical energy of an image of an object to electric signals; a detector for sensing a luminance of the object; a first setter for setting a first exposure time which is calculated by integral multiply of a first time unit corresponding to the luminance sensed by the detector; a second setter for setting a second exposure time which is calculated by integral multiply of a second time unit shorter than the first time unit corresponding to the luminance sensed by the detector; a calculator for calculating a value of signal amplification due to a difference between the first exposure time and the second exposure time; and an amplifier for amplifying image signals obtained by exposing the image sensor by the first exposure time based on the value of the signal amplification calculated by the calculator.
By the above-mentioned configuration, an image having a proper density can be obtained without using adjustable aperture mechanism and shutter mechanism.
REFERENCES:
patent: 4635126 (1987-01-01), Kinoshita
patent: 5258848 (1993-11-01), Kondo et al.
patent: 5448293 (1995-09-01), Kogane et al.
patent: 5579049 (1996-11-01), Shimaya et al.
patent: 5745808 (1998-04-01), Tintera
Garber Wendy R.
Minolta Co. , Ltd.
Sidley Austin Brown & Wood LLP
Tillery Rashawn N.
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