JPH02170779A - Imaging device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an imaging device such as an electronic camera or a VTR camera. This invention relates to circuit technology that enables photographing.

[Background Art] In recent years, video equipment including imaging devices has become more widespread, and the general public has come to take pictures using electronic cameras and VTR cameras.

However, except for some enthusiasts, general users do not have any special photographic techniques, and the photographing conditions vary widely.

Considering this background, it is desirable that the photographing device be designed so that general users can always take good photographs.

For example, when photographing a person as the main subject, if the sun is in the background, the person will be photographed darkly due to backlight.

On the other hand, in situations where the main subject is exposed to strong light, such as a person in the spotlight on a stage, a phenomenon known to those skilled in the art as highlight occurs, and the back of the main subject becomes dark. I end up being photographed.

Therefore, in the past, an exposure compensation circuit was installed in the photographic device, and the exposure was compensated according to the main subject even under the above-mentioned abnormal light, that is, the exposure was compensated to the positive side for backlighting, and to the negative side for highlights. , it was possible to take pictures at appropriate exposure values.

[Problems to be Solved by the Invention] However, although conventional photographing devices are equipped with an exposure compensation circuit, the amount of exposure compensation is fixed.

Therefore, when there is a scene with a large brightness difference, in other words, there is a large difference between the brightness of the main subject and the brightness of the background, or when the main subject is uneven in the brightness distribution, for example, the main subject is in a dark or bright area. In some cases, when the main subject is set to the appropriate exposure value using exposure compensation, the entire screen becomes brighter, resulting in a phenomenon in which the bright areas become completely white, a so-called broken state, while the entire dark areas become black, a so-called crushed state. Become.

Furthermore, since the imaging device cannot automatically determine the photographing situation and change the amount of gamma correction, the above-mentioned photographing mistake may be made at a good photo opportunity.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a photographing device that can perform good photographing by automatically determining the photographing situation and performing gamma correction.

[Means for Solving the Problems] In order to achieve such an object, the present invention divides a subject into a plurality of areas and collects photographic data of each area, for example, data corresponding to brightness, into photographic data that becomes an image, Or, obtain it based on photometric data, determine whether gamma correction is necessary, unnecessary, and the degree of correction for the photographed image based on the photographic data, and select a gamma curve from a plurality of gamma correction curves in accordance with the determination. Accordingly, the subject is configured to be photographed at an optimum exposure value.

[Function] In the present invention having such a configuration, a gamma correction curve for setting an optimum exposure value is automatically selected based on photographic data of a subject.

Therefore, even under abnormal light such as backlight, it is possible to always take good pictures.

Furthermore, since the gamma correction curve is automatically selected, excellent effects such as improved usability of the photographing device can be achieved.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

Note that FIG. 1 is a circuit diagram showing an example of an electronic still camera to which the present invention is applied, FIG. 2 is an explanatory diagram showing a photographing situation of a subject, and FIG. 3 is an explanatory diagram showing multi-division of a subject. FIG. 4 is a gamma correction curve and a characteristic diagram of gamma correction during reproduction.

First, the imaging optical system 1 will be explained. It consists of an autofocus lens 2, an aperture mechanism 3, a condenser lens 4, a half mirror 5-5, and an optical low-pass filter 6. A subject image is optically formed on -7.

Note that an optical color filter (not shown) is provided in front of the image sensor 7, that is, on the imaging plane of the subject image.

The photometric optical system 11 includes lenses 12 and 13 and a half mirror 14, and monitors the image being photographed and forms a subject image on the light receiving element 15, which becomes photometric data.

Next, the signal processing system will be explained. The image sensor 7 generates a color video signal Va corresponding to the brightness and color of the subject image by photoelectric conversion. The video signal Va
is a minute voltage level, and is amplified to a desired voltage level by the preamplifier 21.

The color separation circuit 22 obtains R (red), G (R), and B (blue) color signals.The color signals R, G, and B are supplied to the gamma correction circuit 23 and gamma corrected. However, this gamma correction operation will be explained in detail later with reference to FIG. 2 and the subsequent figures.

The matrix circuit 24 receives gamma-corrected color signals R, G.
, B, to obtain a luminance signal Y and a color difference signal R-YSB-Y.

The color encoder 25 also outputs a total color video signal (
NTSC color video signal), Y+S, R-Y
, B-Y, etc., and these are supplied to a display device (not shown) or a recording circuit, etc., and used for a desired purpose.

Next, to explain the photometry system, the subject image reflected by the half mirror 5 is projected onto the half mirror 14 via the lens 12, and this subject image is reflected by the finder F.
The image can be visually viewed as a monitor image through the lens 13.

In addition, the brightness of the subject image transmitted through the half mirror 14 is
It is detected by the light receiving element 15. The light receiving element 15 is constituted by a photoelectric conversion element, for example, an element with excellent photoelectric conversion efficiency such as a silicon photocell.

The present embodiment is configured not only to obtain a photometric signal corresponding to the brightness of the subject image, but also to divide the subject image into multiple parts and perform photoelectric conversion. That is, one frame of the subject is divided into a plurality of areas, and a photometric signal corresponding to the luminance of each divided area is obtained individually.

Here, to explain an example of a subject in abnormal light with reference to Fig. 2, the sun B is located behind the main subject, person A, so not only the face of person A but the entire person becomes dark and dark. This is a typical backlit situation.

On the other hand, if the light-receiving element 15 is divided into four areas Pi, P2, P3, and P4 as shown in FIG. 3, when photographing the subject shown in FIG. Person A, the main subject, is located in area P1, and the bright background is in areas P2, P3, and P4.
will be located in

Under such backlight conditions, in other words, under abnormal light conditions,
The brightness of area P1 corresponding to the position of person A, who is the main subject, is at a low level, and the brightness of areas P2 to P4, which are divided and formed around the area P1, is high level.

Therefore, from each of the areas P1 to P4 of the light receiving element 15, a photometric signal vb having a level difference corresponding to the difference in brightness of each area is obtained. Photometric signal v obtained in this way
b is supplied to the AE photometry section 16, and the AE photometry section 16 performs the following noteworthy actions.

That is, the photometric signals vb obtained from each of the areas P1 to P4 are designated as Pbl, Pb2, Pb3, and Pb4, respectively. Then, for example, a reference value k for determining backlight and highlight is determined from the Pb4/Pb1O value. The calculation for setting the reference value k is automatically performed by inputting the photometric signals Pbl to Pb4 of each area.

k is obtained by the above calculation, and following this calculation, for example, Pb
1-Pb4<k is calculated, and when k becomes IEV or more, it is determined that it is backlight, and a control signal Vc for controlling the gamma correction amount is supplied to the camera control circuit 31. In addition,
The photometry circuit 16 may be configured to perform various types of calculations in addition to those described above, and examples of other calculations will be described later.

On the other hand, as a result of calculating the discriminant value k, if it is determined that it is No. 1 light, then following this calculation, for example, Pb1-Pb4>
A control signal Vc that calculates k, determines it as a highlight when k is 28V or more, and controls the gamma correction amount.
is supplied to the camera control circuit 31.

Therefore, the control signal Vc has information for determining backlight and highlight by the series of calculations and for controlling the gamma correction amount.

The camera control circuit 31 is composed of a microprocessor, and controls the gamma correction circuit 23 in response to the control signal Vc.
) A large number of gamma correction curves are formed.

That is, in a normal gamma correction circuit, γ=0, denoted as C.
．． It is configured to perform gamma correction using a No. 45 gamma correction curve. However, in the gamma correction circuit 16 in this embodiment, a large number of gamma correction curves are formed as shown as a, b, d, and e, and these gamma correction curves are automatically selected by the camera control section 31. It is configured.

Assume now that the AE photometry section 16 determines that there is backlighting through the calculation, and supplies the camera control section 31 with a control signal Vc corresponding to the degree of backlighting.

The camera control unit 31 drives the gamma correction circuit 23 based on the control signal Vc, and selects gamma correction curves d and e in accordance with the degree of backlighting. As a result, the gamma correction circuit 23
R, G with gamma correction from.

A B color signal is obtained and supplied to the matrix circuit 24 at the next stage.

Further, suppose that the AE photometry section 16 determines that it is a highlight by the calculation, and the control signal V corresponding to the degree of highlight is
Suppose that c is supplied to the camera control section 31.

The camera control unit 31 drives the gamma correction circuit 23 based on the control signal Vc, and selects the gamma correction curve aSb corresponding to the degree of highlight. As a result, gamma-corrected R, G, and B color signals are obtained from the gamma correction circuit 23 and are supplied to the next-stage image processing circuit 24.

By performing the above-mentioned gamma correction, the brightness of parts that were dark due to backlighting is corrected to become brighter, and, using FIG. 2 as an example, the brightness of person A is increased, resulting in a very easy-to-see image. Further, contrary to the case illustrated in FIG. 2, if person A is a highlight, the brightness of that part will be corrected to be darker.

Note that when the exposure correction is performed as described above, the gamma characteristic diagram during reproduction is as shown in FIG. 4(B).

That is, when gamma correction curve C is selected, the input-to-output relationship becomes approximately 1:1 as shown in a'. Also, a gamma correction curve d corresponds to backlighting.

When e is selected, the input-to-output relationship is d/.

When the gamma correction curves a and b are selected corresponding to the highlight, the input-to-output relationship changes as shown in a' and b'.

Then, if the whole is shifted by exposure compensation, a'
The entire characteristic is shifted up, as shown.

Next, other control systems related to the camera control section 31 will be explained.

The camera control section 31 has a central function of the camera, and is configured to perform various types of control in addition to the gamma correction control described above. lens 32, light receiving element 33,
The AF distance measuring section 34 obtains distance data for autofocus, and supplies data Vd obtained by measuring the distance to the main subject to the camera control section 31. The camera control unit 31 controls the lens drive unit 35 based on the distance data Vd.
provides a control signal for focusing.

The lens drive unit 35 drives a lens drive mechanism 36 composed of a pinion, a rack, etc. in response to the control signal, moves the lens 2 in the left and right direction in FIG. 1, and performs automatic focus adjustment.

Furthermore, the camera control section 31 drives the aperture drive section 37 to control the aperture mechanism 3 and perform optimal exposure control.

Further, the camera control section 31 performs various operations such as driving the CCD drive section 38 to control the image sensor 7 and performing a predetermined photographing operation.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above, and various modifications are possible.

For example, in addition to the above calculations, the AE photometry section 16 calculates Pbl +Pb2-Pb4, Pbl +Pb2 +
Pb3-Pb4, further Pb2-Pb4, Pb3-P
It may be configured to perform a comparison operation between b4 and the above to obtain the control signal Vc for performing gamma correction as described above.

Further, in the embodiment described above, the light receiving element 15 is provided to obtain the photometric signal vb, but the light receiving element 15 is deleted,
It is also possible to obtain the photometric signal vb based on the video signal obtained from the image sensor 7. In this case, for example, the color signals R, G, and B obtained from the color separation circuit 22 are multi-divided as explained with reference to FIG. 3, and the resulting data is supplied to the photometry section 16.

That is, the control signal Vc for selecting the gamma correction curve can be obtained from the photographic data that becomes the photographed image.

According to this configuration, since the light receiving element 15 is not required, there is an advantage that not only the circuit configuration becomes simple but also the mechanical structure can be simplified.

Furthermore, the following modifications regarding gamma correction are possible.

That is, when changing the gamma correction curve as described above, it is necessary to adjust the white balance in accordance with the gamma curve.

Therefore, when a camera is provided with a large number of gamma correction curves, the circuit load of the camera increases, but it may be desirable to reduce the circuit load even if the number of gamma correction curves is reduced.

Since gamma correction is often required in backlight situations and rarely in highlight situations, it may be configured to obtain the control signal Vc from the AE photometry section 16 and perform the gamma correction in backlight situations. Even with this configuration, even if the main subject is on the high-brightness side, that is, in a position corresponding to area P4 according to the embodiment, it will fall within the latitude and can be photographed and reproduced well.

It should be noted that although the above-described embodiment shows an example of application to an analog electronic still camera, the present invention can be used in a wide range of applications.

That is, it can be used for gamma correction of digital electronic still cameras.

Some digital electronic still cameras are configured to perform gamma correction or the like on a video signal obtained from an image sensor in a preprocessing circuit, and are suitable for this preprocessing circuit.

Furthermore, it goes without saying that the present invention can be used in a gamma correction circuit for a VTR camera known as a video movie.

[Effects of the Invention] As explained above, according to the imaging device of the present invention, the amount of gamma correction is calculated based on the imaging data of the subject, and the negative gamma correction curve among the plurality of gamma correction curves is determined based on the calculation result. The camera is configured to automatically select the optimum exposure value to take pictures.

Therefore, even when photographing under abnormal light such as backlight or highlights, photographing errors such as the main subject becoming too dark or too bright are reduced, and good photographing can always be performed.

Furthermore, since the selection of the gamma correction curve is performed completely automatically, the usability of the photographing device is improved and the load value of the photographing device is further improved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an electronic still camera showing an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the photographing situation of a subject, Fig. 3 is an explanatory diagram showing multi-division of the subject, and Fig. 4 is an explanatory diagram showing the subject shooting situation. FIG. 4 is a characteristic diagram of a gamma correction curve and gamma correction during reproduction. Reference numeral 1 in Fig. 2 = photographing optical system 7: image sensor 15: light receiving element 16: AE photometry section 22: color separation circuit 23: gamma correction circuit 24: matrix circuit 25: encoder 31: camera control section Va: Color video signal Vb = Photometric signal A: Main subject

Claims (1)

[Claims] Either the photographic data or the photometric data, which is a photographed image of the subject, is divided into desired areas, and calculations are made based on the main subject data and data other than the main subject among the divided data. and a gamma correction unit that selects an optimal gamma correction curve from among a plurality of pre-prepared gamma correction curves based on the determination, and adjusts at least the photographed image of the main subject to an appropriate exposure value. An imaging device comprising means.