Automatic exposure control apparatus

Details Automatic exposure control apparatus Automatic exposure control apparatus

1994-03-09

2001-06-19

Ho, Tuan (Department: 2712)

Television

Camera, system and detail

Optics

C348S349000

Reexamination Certificate

active

06249317

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic exposure control apparatus employed for a color video camera, etc.
2. Description of the Prior Art
In
FIG. 1
, portions other than the portions represented by the numerals
215
,
216
,
217
,
218
,
219
,
220
,
221
and
222
correspond to a prior art. The prior art will be described. Light having passed through a taking lens
201
is directed to an image sensor device
204
such as a CCD, etc. after its light quantity being settled by an iris
202
. After amplified by an amplifier
205
, a output signal of the image sensor device
204
is detected by a detecting circuit
212
. The iris
202
is driven by an iris driving portion
213
so that the level of the detecting output is constant, that is, so that the CCD (sensor device
204
) is at an optimal operating point.
After amplified by a variable gain amplifier
206
, a signal output from an image sensor device
204
is divided in two directions. One is directed to a color separating circuit
207
, where a color signal which is coated with a color filter attached to the image sensor device
204
is separated, and is color-signal-processed at a color signal processing circuit
208
to be converted into color difference signals R-Y and B-Y. The other is directed to a luminance signal processing circuit
210
, where a luminance signal component thereof is luminance-signal-processed, and is inputted to an encoder circuit
209
. The color difference signals of the former are balanced-modulated by the encoder circuit
209
and added with a luminance signal to be converted into a composite video signal
214
. The output of the luminance signal processing circuit is detected by a detecting circuit
211
and returned to the variable amplifier
206
to settle a gain of the variable gain amplifier
206
so that the level of the output of the detecting circuit
211
is constant.
Final level of the video signal is determined by the variable gain amplifier
206
. At lower illumination, since the level of a luminance signal is low even if an iris
202
is opened to its maximum value, a gain of the variable gain amplifier
206
is increased so that the level of the luminance signal becomes constant.
As described above, exposure has been conventionally controlled not according to a color signal but by controlling a luminance signal level so as to be constant.
Other than the above-described example, some conventional automatic exposure control apparatuses detect an object position by a difference among luminances or high-frequency components inside and outside of a photometry area within a shooting image plane to automatically follow the photometry area (see Japanese laid-open Patent Application No. H1-120178 and Japanese laid-open Patent Application No. H1-120181).
However, since none of the above-described control apparatuses sets exposure considering what is a main object, an exposure level is sometimes inappropriate particularly when a person is a main object.
When exposure of a video camera is manually set, it is well-known that a desirable reproduction is obtained if exposure is set: (1) so that a signal level of a highlighted portion in an image plane is 100 IRE (Institute of Radio Engineers); and (2) so that a signal level of a color of person's skin is between 55 IRE to 75 IRE.
As described above, an appropriate exposure level differs according to whether a person is a main object or not. Hence, with the conventional exposure controlling method, a signal level of a person's skin is not always appropriate even if a luminance signal level in an image plane is constant, particularly when a person is backlit or when the background is dark and a person is highlighted.
In order to obtain an appropriate exposure level when a person is a main object, it is considered that a skin-colored portion is extracted to make a signal level thereof constant.
However, even if there is a skin-colored portion, the skin-colored portion is not always a main object. Consequently, although the skin-colored portion is adequately exposed, the entire image plane is sometimes inadequately exposed, for example, when a person shot is located in a corner, when a person passes across an image plane, or when there are a plurality of persons.
Moreover, even if a skin color is detected in an image plane, an appropriate exposure level differs according to whether the person is a main object or not.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an automatic exposure control apparatus where in order to obtain an appropriate exposure level, a skin color is detected, and when the video camera is in focus on the skin-colored portion, exposure is controlled determining that a person is a main object and when the video camera is not in focus on the skin-colored portion or there is no skin-colored portion, exposure is controlled so that the landscape is adequately exposed.
To achieve the above-described object, the present invention is provided with: skin color extracting means for extracting a skin-colored portion from an input video signal; focus condition detecting means for detecting a focus condition of the skin-colored portion; exposure controlling means for controlling exposure so as to be appropriate with respect to the skin-colored portion based on outputs of said two means when a skin-colored portion is detected and it is detected that the skin-colored portion is in an in-focus condition.


REFERENCES:
patent: 4922279 (1990-05-01), Hamada et al.
patent: 4969045 (1990-11-01), Haruki et al.
patent: 4987482 (1991-01-01), Imai et al.
patent: 3-99585 (1991-04-01), None

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