JP3033102B2 - Exposure control device for electronic imager - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure control device for a movie or still video camera using an electronic imaging device.

2. Description of the Related Art FIG. 3 shows a configuration of a conventional video camera. Light of an image that has passed through the stop 10 and the optical system 12 is photoelectrically converted for each of a large number of pixels by the image pickup device 14, and is sequentially output as an electric signal. This output signal is amplified by the amplifier 16 and then
The size of the aperture of the diaphragm 10 is changed by the drive circuit 26 based on the detection output. That is, when the output of the image sensor is excessively large, the aperture of the diaphragm 10 is reduced, and when the output is excessively small, the aperture is increased, and feedback is performed so that the amount of incident light falls within the dynamic range of the image sensor 14. Control is performed.

The output of the amplifier 16 is further gain-adjusted by the variable gain amplifier 18 and subjected to predetermined processing such as gamma correction by the luminance signal processing circuit 30, and then the color difference generated by the color separation circuit 20 and the color signal processing circuit 22. Together with the signals (RY, BY), the composite video signal is prepared by the encoder 24. The luminance signal Y is detected by another detection circuit 32, and the gain of the amplifier 18 is controlled so that the magnitude of the detection signal is constant.

Among the above circuits, it is the variable gain amplifier 18 or the aperture 10 and the aperture drive circuit 26 that determine the final luminance signal level, but the detection circuits 28 and 32 that output the gains. The detection method of, that is, the exposure determination method, the average detection method,
There is a peak detection method and the like.

The average detection method controls the average luminance level of the entire screen to be constant. However, there is a disadvantage in that a highlight portion is overexposed and jumps on a screen having contrast. On the other hand, in the peak detection method, since the peak value of the highlight portion is set to a constant value, there is a disadvantage that the screen immediately becomes dark when the highlight portion enters a part of the screen.

In any case, when photographing a person, there is the following problem. When the white level of the screen is 100 IRE (here, IRE is a unit of a composite video signal level, and its rated pp output voltage 1 V is 140 IRE. However, since the upper limit 40 IRE corresponds to a synchronization signal, , 1
00IRE corresponds to the maximum video signal level. ), The appropriate exposure value of the skin part of the person (the exposure value that makes the skin part look most natural. It is called face tone) is slightly higher than the median value 50 IRE of the exposure range of 0 to 100 IRE (50 to 100 IRE). (About 80 IRE, center value about 65 IRE). Although there are very many opportunities for humans to be photographed in ordinary video shooting, none of the conventional methods take this point into consideration. For example, when a person is set as the central subject, the exposure is controlled so that the face tone becomes 50 IRE in the above-described average detection method, so that the human skin tends to appear slightly dark. Further, when a person is captured close-up by the peak detection method, there is a disadvantage that the human skin becomes too bright.
The above problem is not limited to the case where the variable gain amplifier 18 is feedback-controlled at the output luminance signal level, but also the case where the gain of the amplifier 18 is constant and the adjustment is performed by the aperture of the diaphragm 10.

An object of the present invention is to solve such a problem, and to provide an exposure control apparatus for an imaging apparatus that can perform exposure control so that human skin is naturally captured when a person is used as a subject.

Means for Solving the Problems In order to achieve the above object, an exposure control device of the present invention comprises:
An imaging means (14) for photoelectrically converting and outputting incident light from a subject; and extracting a luminance signal of a flesh color portion in a screen based on an output from the imaging means (34, 46). Detecting means (33) for obtaining a first parameter (S _HL ) proportional to the area of a portion showing high brightness (80 IRE or more) and a second parameter (Sd) proportional to the area of a portion showing low brightness (50 IRE or less) And exposure control means (18, 28) for performing exposure control based on parameters obtained by the detection means. However, in the above description, reference numerals in parentheses are reference numerals relating to embodiments described later, and the present invention is not limited to these. Although the parameters are described as voltages in the embodiment, it goes without saying that parameters other than the voltages may be used.

Embodiment FIG. 1 shows a configuration of an exposure control device of a video camera embodying the present invention. The aperture aperture feedback control from the image sensor 14 to the aperture drive circuit 28 is performed by the above-described conventional apparatus (third embodiment).
This is the same as FIG.
In addition to the conventional loop (amplifier 18-brightness signal processing circuit 26-detection circuit 32-amplifier 18), a face tone exposure control circuit 33 subsequent to the skin color detection circuit 34 is added to the exposure control in. Hereinafter, the configuration and operation of the face tone exposure control circuit 33 will be described.

The color difference signals RY, B- output from the color signal processing circuit 22.
Y is input to the skin color detection circuit 34. This skin color detection circuit 34
Then, a flesh-colored portion in the screen is detected based on the following criteria, and a signal of H level in the flesh-colored portion and L level in other portions is output.

The skin color varies depending on the race and the like, but generally, for the above-described mutually orthogonal color difference signals RY and BY, φ = tan ⁻¹ [1.78 × (RY) / (B− Y)] = 122 °, and is considered to have a hue of about ± 20 ° before and after the center. The color saturation is Is considered to be within a range of ± 0.2 above and below. These conditions [102 ° <φ <142 °] and [0.08 <E
The ranges of the values of RY and BY to satisfy <0.48] are individually set by Va, Vb, Vc, and Vd in the following equations. The skin color detection circuit 34 a color difference signal R-Y, B-Y level is within a predetermined range _{v a <R-Y <v} b, when _{v c <B-Y <v} d, the portion thereof is a skin color Judge and output an H level signal.

The H / L level signal of the skin color detection circuit 34 is
And gates the output of the luminance signal Y from the luminance signal processing circuit 26 to the two comparators 44a and 44b. That is, the gate circuit 46 allows the luminance signal Y to pass when the skin color detection circuit 34 outputs the H level signal, and blocks the passage when the L level signal is output. Note that the luminance signal Y from the luminance signal processing circuit 26 is also output to another comparator 44c, but no gate is interposed in this route. The luminance signal Y passed through only the skin color portion by the gate circuit 46 is
Comparators 44a and 44b respectively compare with predetermined potentials V ₁ and V ₂ and binarize. Here, V ₁ and V ₂ are respectively set to the upper limit and the lower limit of the optimum face tone exposure range, and specifically, V ₁ = 80 IRE and V ₂ = 50 IRE. First comparator 44a
In the luminance signal Y becomes H level output when the V ₁ or more,
Luminance signal Y in the second comparator 44b becomes the H level output when the V ₂ below. Each comparator 44a, both low-pass filter 42a outputs the 44b, is smoothed by 42b, respectively, there voltage S _HL, and flesh color part luminance signal level a flesh color part is proportional to the area of more parts 80IRE as the voltage S _d where the luminance signal level is proportional to the area of the following parts 50IRE Te, a / D
The data is input to the microcomputer 38 through the converters 40a and 40b. The luminance signal Y inputted to the comparator 44c without passing through the gate is binarized is compared with a reference potential of V ₃ corresponding to the white level 100IRE, by being passed through a low pass filter 42c, the total It is input to the microcomputer 38 through the a / D converter 40c as a voltage Y _HL proportional to the area of 100IRE or more portions of the screen.

In the microcomputer 38, based on these signals,
A gain control signal to the variable gain amplifier 18 is generated according to a predetermined program. This program will be described with reference to the flowchart of FIG.

After inputting the three parameter signals S _HL , S _d , and Y _HL in step # 10, it is first determined whether or not S _HL is equal to or greater than a predetermined value X (step # 12). S _HL
In the case of ≤X, it means that the area of the skin color portion whose exposure exceeds the appropriate range of 50 to 80 IRE in the screen is equal to or smaller than a predetermined value. In this case, further in step # 20, S _d is equal to or different value X ₁ or more. If the S _d ≦ X ₁ Again,
It is determined that the portion of the skin color portion where the luminance is inappropriate is very small on the screen, and the exposure control is performed based on the highlight portion only with the luminance without considering the hue. That, Y _HL predetermined value X ₂ corresponding to the area of the highlights in the step # 24
To determine at either or, when the Y _HL> X ₂ suppressed exposed by lowering the gain of the variable gain amplifier 18 in step # 26.
When Y _HL is less than a predetermined value X _2, gain as the exposure is appropriate without changing after waiting a reasonable time in step # 18 to repeat the routine returns to step # 10.

If S _HL > X in step # 12, it indicates that the area of the portion where the exposure in the flesh color portion exceeds the appropriate range of 50 to 80 IRE is large. In this case, in step # 14, S _d
> Determines X ₁ or not. Wherein if a S _d ≦ X _1, the area of underexposure (50 IRE or less) portion of the skin color portion indicates that small, in conjunction with the determination in step # 12, with respect to overall proper range skin color portion The microcomputer 38 outputs a control signal for decreasing the gain to the variable gain amplifier 18 via the D / A converter 36 in step # 16 because it is determined that the bias is applied to the overexposure side. Step #
If S _d > X ₁ at 14, it simply indicates that the contrast of the flesh-colored portion is strong, so the gain is not changed.

In step # 12, _SHL ≦ X, and step # 20
If S _d > X _1, it is determined that the exposure of the flesh-colored portion is biased in a direction below the appropriate range as a whole, and the gain is increased in step # 22.

Note that the time waiting in step # 18 is provided to avoid control instability due to frequent exposure change operations. Also, when the gain is changed in steps # 16, # 22, and # 26, the change rate is set to about 1% so that the exposure fluctuation on the screen does not look unnatural, and at the same time, hunting is avoided. I have.

As one specific example of X, X ₁ and X ₂ , X, X ₁ is set to a size corresponding to 1/20 area of the whole screen, and X ₂ is set to 1/20 of the whole screen.
The size should be equivalent to 10 areas.

As described above, in the present embodiment, the exposure control is performed not only by the simple luminance control but also by extracting the luminance signal of the flesh-colored portion, and when the area of the portion is equal to or larger than the predetermined value, the flesh-colored portion looks most natural. Exposure control is performed so as to fall within the proper exposure range. Therefore, when there are many opportunities to photograph a person with a video camera, a still electronic camera, or the like, particularly beautiful and natural images can be obtained.

In the above-described embodiment, the exposure control exclusively controls the amplification gain of the electric signal. However, as shown in FIG. 4, the amplification gain of the amplifier 18 'is fixed, and the aperture of the aperture 10 is increased and decreased to make the light incident. This can be performed by changing the amount of light.

Effect of the Invention As described above, according to the present invention, when the area occupied by the high luminance portion of the skin color is large, and when the area occupied by the low luminance portion of the skin color is large, the face tone is appropriately adjusted according to each state. Exposure can be adjusted so that a person can be photographed beautifully.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an exposure control device of a video camera according to an embodiment of the present invention. FIG. 2 is a flowchart of an exposure control process performed by the microcomputer.
FIG. 3 is a block diagram showing a configuration of a conventional exposure control device;
FIG. 4 is a block diagram showing another embodiment of the present invention. 10 ... Aperture, 12 ... Optical system 33 ... Face tone exposure control circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 9/64 H04N 5/235

Claims (4)

(57) [Claims] An image pickup means for photoelectrically converting incident light from a subject and outputting the same, and a luminance signal of a flesh color portion in a screen is extracted based on an output from the image pickup means, and the extracted luminance signal indicates high luminance. Detecting means for obtaining a first parameter proportional to the area of the portion indicating the brightness and a second parameter proportional to the area of the portion indicating the low brightness; and exposure control means for performing exposure control based on the parameter obtained by the detecting means. An exposure control device, comprising: 2. An exposure control means for decreasing an exposure level when the first parameter is larger than a first predetermined value and when the second parameter is smaller than a second predetermined value, and decreases the exposure level when the first parameter is smaller than the first predetermined value. The exposure control device according to claim 1, wherein the exposure level is increased when the two parameters are larger than a second predetermined value. 3. The exposure control apparatus according to claim 2, wherein said detecting means further obtains a third parameter corresponding to an area of a portion where the luminance signal is larger than a predetermined value in the entire screen. 4. The exposure control means decreases the exposure level when the first parameter and the second parameter are smaller than the first predetermined value and the second predetermined value, respectively, and when the third parameter is larger than the third predetermined value. The exposure control device according to claim 3, wherein: