JPH03104486A - Electronic still camera - Google Patents

Abstract

PURPOSE:To always obtain an image without generating visual unnaturalness and with appropriate contrast from every subject by performing the photometry of plural parts of the subject with a photometric means, and changing gradation conversion characteristic corresponding to a light quantity difference. CONSTITUTION:Gradation conversion parts 15e-15g are set so that respective gradation conversion characteristic can be set at gamma1, gamma2, and gamma3, respectively. For example, when the light quantity difference of each part of the subject is large, a release switch 19 is depressed by a user lightly, and when a contact 18a and a contact 18b are closed, a central arithmetic processing part 11 checks each output value of photometric elements 17a-17e converted via amplifiers 22a-22e and A/D converters 23a-23e. When the output value with the light quantity difference larger than the maximum value stored in the central arithmetic processing part 11 in advance exists in the output values, it is judged that the light quantity difference of the subject is large. And a switch 15d is closed so as to perform a gradation conversion processing with the third gradation conversion part 15g, and switches 15b and 15c are opened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electronic still camera that records still images.

[Prior Art] FIG. 2 is a block diagram showing the configuration of a conventional electronic still camera.

In FIG. 2, the amount of light of an object (not shown) is adjusted by a diaphragm member 2, and an image is formed on the imaging surface of an image sensor 3 by an optical lens 1, and the optical signal of the image is converted into an electrical signal. The image sensor 3 is a CCD (charge transfer device), a MOS
It consists of various solid-state image sensors such as devices and SITs. An output terminal of the image sensor 3 is connected to a sample and hold circuit 5. The drive pulse generator 4 generates a drive pulse for the image sensor 3, and causes the sample and hold circuit 5 to generate a sampling pulse for sample and hold. The sample and hold circuit 5 samples and holds the output signal from the image sensor 3 at the timing of the sampling pulse input from the drive pulse generator 4.
The analog video signal is output to the amplifier circuit 6. Next, the video signal amplified by the amplifier circuit 6 is input to the edge enhancement circuit 7, where processing is performed to emphasize the transition points of the video signal. The output signal of the edge enhancement circuit 7 is input to a gradation conversion circuit 8, and gamma correction is performed so that the image has a standard gradation. The output signal of the gradation conversion circuit 8 is input to a level adjustment circuit 9 that adjusts the white clip level and the setup level, and the output signal of the level adjustment circuit 9 is
It is input to the recording unit IO.

Reference numeral 13 denotes a photometric element that measures the amount of light on a subject before photographing, and is configured such that the image of the subject is formed on the photometric element 13 by a condenser lens l2. The image formed on the photometric element 13 is converted into an electrical signal by the photoelectric conversion action of the photometric element 13 and output to the amplifier 20 . The electrical signal amplified by the amplifier 20 and logarithmically compressed is sent to the A/D converter 2l.
The signal is converted into a digital signal and input to the central processing unit l1. Further, a strobe 14, which is a light emitting device, is provided to momentarily illuminate the subject when it is dark.

The release button l9 is a switch for the user to put the electronic still camera into the shooting state, and contacts 18a and 18b
, 18c. Contacts 18a, 18b, 18c
is connected to the central processing unit 11. When the release button 19 is pressed lightly, the contacts 18a and 18b are closed, and the central processing unit 1l performs photographing preparation operations such as photometry. When the release button l9 is further pressed and the contacts 18b and 18c close, the central processing unit l1 performs photographing operations such as accumulating charges in the image sensor 3 and recording video signals.

A central processing unit 11 connected to the recording unit 10 and the drive pulse generator 4 controls the operation of this device, and uses the output signal of the photometric element l3 converted by the amplifier 20 and the A/D converter 2l. The size of the aperture diameter of the aperture part shrine 2 and the charge accumulation time in the image sensor 3 are determined, and the strobe 14 is
It controls the light emission of the drive pulse generator 4, controls the generation of pulses for the drive pulse generator 4, and causes the recording section IO to record the output signal from the level adjustment circuit 9.

In the above structure, when taking a picture, the release button l9 is lightly pressed by the user, and the contacts l8a and 18b
When the aperture member 2 is closed, the amount of light from an object (not shown) is measured by the photometric element l3, and the size of the aperture diameter of the aperture member 2 and the charge accumulation time in the image sensor 3 are determined. If the central processing unit 11 determines that the subject is dark and sufficient exposure cannot be obtained, the strobe l4 is prepared to emit light. When the release button is pressed deeply, the contacts 18b and 18c close, and the light rays from the object (not shown) enter the image sensor 3 via the optical lens 1 and the aperture member 2, and the image sensor 3 , the video signal obtained by the sample and hold circuit 5 is input to the amplifier circuit 6.

The video signal is electrically amplified according to a predetermined amplification degree by an amplifier circuit 6, and a certain degree of edge emphasis is applied by an edge enhancement circuit 7. Next, the gradation conversion circuit 8 performs gradation conversion by gamma correction using a standard γ value set in advance, and then the white clip level and setup level are adjusted in the level adjustment circuit 9, and the recording section recorded in 10.

[Problems to be Solved by the Invention] The conventional techniques described above have the following problems.

In general photography, when the difference in light intensity between bright and dark areas of the subject is small, such as when photographing a scene on a cloudy day, the tone conversion circuit performs tone conversion using gamma correction using the standard γ value. , the contrast is weak, making it difficult to obtain a visually good image.

In addition, when there is a large difference in light intensity between bright and dark areas of the subject, such as when photographing a person on a sunny day or when using a strobe, the tone conversion circuit can perform tone conversion using gamma correction using the standard γ value. If this is done, a visually good image cannot be obtained due to the strong contrast.

As described above, in the conventional technology, the gradation conversion circuit always performs gradation conversion by gamma correction using the standard γ value, so the gradation conversion characteristics are fixed, and the gradation conversion is performed according to the subject. However, depending on the situation of the subject, it is not always possible to obtain a visually good image.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an electronic still camera that can always obtain visually good images regardless of the situation of the subject.

[Means for Solving the Problems] In order to solve the above problems, the electronic still camera of the present invention has the following features:
A photometry device that measures light at multiple locations on the subject within the shooting screen and outputs multiple signals corresponding to the amount of light at each location, an imaging device that converts the subject image into a video signal, and multiple selectable gradation conversion characteristics. , comprising a gradation conversion means for converting the gradation of the video signal, and a selection means for selecting one of the plurality of gradation conversion characteristics of the gradation conversion means, and the selection means selects one of the plurality of gradation conversion characteristics of the photometry means. Calculations are performed based on each output, and one of the plurality of gradation conversion characteristics is selected based on the calculation results. Further, it has a light emitting means for illuminating the subject, and the selection means selects one of the plurality of gradation conversion characteristics depending on whether or not the light emitting means emits light.

[Function] With the above configuration, when there is a large difference in the amount of light between different parts of the subject in the shooting screen, the contrast is reduced when the gradation conversion means converts the video signal, and conversely, the difference in the amount of light is reduced. If the contrast is small, the conversion is performed to increase the contrast, so that an image with good contrast can always be obtained from any subject. In addition, when the subject is illuminated by the light emitting means, the difference in the light amount of the subject becomes large, so by converting the contrast to weaken when converting the gradation of the video signal by the gradation converting means,
Images with good contrast can always be obtained.

[Example] An embodiment of the present invention will be described based on FIG.

FIG. 1 is a block diagram showing the configuration of an electronic still camera in an embodiment of the present invention. Optical members and circuits with the same reference numerals as in FIG. 1 and FIG. 2 are the same as those in FIG. 2, so their explanations will be omitted.

In FIG. 1, the output terminal l5a of the contour emphasizing circuit 7 is 3
The switches 15b-d are connected in parallel. These switches 15b-d are connected to the respective gradation converters 15e-
connected to g. The gradation conversion units l5e-g have gradation conversion characteristics of γl, γ2, and γ3 shown in FIG.
It is set so that

The gradation conversion characteristics in Figure 3 represent the input/output characteristics of gamma correction, with the horizontal axis representing the human power (output of the contour enhancement circuit 7) as Then, the following (
1) It is expressed by the formula.

y=x″' (1) The characteristic curves of γ1, γ2, and γ3 shown in Figure 3 show the cases of γ=1, γ=0.7, and γ=0.45 in equation (1), respectively. .

When gradation conversion is performed, the larger the γ value, the stronger the contrast, and the smaller the γ value, the weaker the contrast.

The first to third switches 15b-d and the first to third gradation converters 15e-g constitute a gradation conversion circuit 15, and the first to third switches 15b-d are located at the center. It is controlled by the arithmetic processing section 11 so that an arbitrary tone conversion characteristic can be selected.

The object image is formed on the photometric member 17 through the condensing lens l2. The photometric member 17 is composed of five photometric elements 17a to 17e for photometrically measuring a subject into five parts. The output of each photometric element is amplified and logarithmically compressed by amplifiers 22a to 22e, respectively, and then sent to an A/D converter 23.
It is converted into a digital signal at steps a-e and input to the central processing unit 11.

The operation of the electronic still camera configured as described above will first be described for the case where there is a large difference in the amount of light between different parts of the subject.

When the release switch l9 is lightly pressed by the user to close the contacts 18a and 18b, the central processing unit 11 converts the converted photometric elements 17a-e through the amplifiers 22a-e and A/D converters 23a-e. Check each output value, and if the difference between the maximum output and the minimum output, that is, the difference in light amount, is larger than the maximum value stored in advance in the central processing unit l1, it is determined that the difference in light amount of the subject is large. The third gradation converter 15 has the characteristic of γ3 having the smallest γ value.
switch 1 so that tone conversion processing is performed by g.
5d is closed, and the other switches 15b and 15c are open.

Also, amplifiers 22a-e and A,/D converters 23a-
The aperture diameter of the aperture member 2 and the image sensor 3 are checked to ensure that appropriate charge accumulation in the image sensor 3 is achieved by examining the outputs of the photometric elements 1.7a to 7e converted through
Determine the charge accumulation time.

When the release button 19 is pressed deeply and the contacts 18b and 1.8c close, the photographing operation begins. Then, the light that has passed through the optical lens 1 passes through the aperture member 2 having a predetermined aperture diameter, and forms an image on the image sensor 3.

Charge accumulation in the image sensor 3 is then performed for the charge accumulation time determined by the central processing unit 11.

The charges accumulated in the image sensor 3 pass through a sample and hold circuit 5 as a video signal, undergo a predetermined amplification in an amplifier circuit 6, and are contour-enhanced in an edge-enhancing circuit 7. Then, the signal passes through the switch 15d and is converted into gradation by the third gradation converter 15g using the characteristic of γ3 having the smallest γ value in FIG. This corrects the video signal, which makes it impossible to express gradation for so-called high-contrast subjects with large differences in light intensity, and results in an appropriate contrast, so the image will not become unnatural. do not have. Then, the white clip level and the setup level are adjusted in the level adjustment circuit 9, and recorded on a recording medium in the recording section 10.

Next, an explanation will be given of the operation when the difference in light amount between different parts of the subject is moderate.

When the release switch 19 is pressed by the user, the contact 18
When a and b are closed, the central processing unit 11
Each output value of the photometric elements 17a-e converted via ae and A/D converters 23a-e is examined.

If the difference between the maximum and minimum outputs is between the maximum and minimum values stored in advance in the central processing unit 11, it is determined that the difference in light intensity between each part of the subject is moderate. , in FIG. 3, the switch 15c is closed and the other switches 15b,
d is open. The subsequent operations until the video signal is recorded on the recording section 10 are as described above.

The operation when the light amount difference is small is similarly as follows. The central processing unit l1 includes amplifiers 22a-e and A/D.
Photometric elements 17a- converted via converters 23a-e
Check each output value of e, and if the difference between the maximum output and the minimum output is smaller than the minimum value stored in advance in the central processing unit 11, it is determined that the difference in light amount between each part of the subject is small. In FIG. 3, the switch 15b is closed and the other switch 15c is closed so that the first gradation converter 15e having the characteristic of γl with the largest γ value performs gradation conversion.
, d is open. The subsequent operations until the video signal is recorded on the recording section 10 are as described above.

In the case of a subject with a small difference in light intensity, gradation conversion is performed using the characteristic with the largest γ value so that the object is visually sharp, and finally an appropriate contrast is achieved.

Next, a case where the subject is dark and the strobe 14 is used will be explained.

When the release button 19 is pressed and the contacts 18a and 18b close, the central processing unit 11 activates the amplifiers 22a-e and A.
/D converter 23a-e converted photometric element 17
Check the outputs of a to e, and if it is determined that each output is small, that is, the subject is dark, and proper exposure cannot be achieved without firing the strobe 14, prepare for strobe light emission, for example, by charging a capacitor (not shown). . Then, when the release button 19 is pressed deeply and the contacts 1.8b and 8c close, a photographing operation is performed. In this case, the strobe 14 emits light while the image sensor 3 is storing charge. At this time, the central processing unit 1l includes amplifiers 22a-e and A/D converter 23a.
When the outputs of the photometric elements 17a-e converted through
, the switch 15d is closed and the other switches 15b . Let c be open. This happens when you take a photo using a strobe L4 that is close to a point light source.
The contrast between the shadows formed between the subject and the background of the subject is strong, and an image with a large difference in light intensity is output, so reducing the γ value in gradation conversion will ultimately result in an appropriate contrast and a visually good image. This is because. The subsequent operations are as described above.

In the case of strobe light emission, all photometric elements 17a
As described above, the case where the output of -e is small, but when only some of the multiple photometric elements, for example, the output of the photometric element 17c that measures the center part, is small, that is, the background is bright and the subject in the center part is dark. Even when it is determined that photography will be performed in a backlit condition, it is better to fire the strobe l4 at the central subject (main subject) so that the central subject does not become dark and a visually better image can be photographed. In this case, by emitting light from the strobe 14, the difference in light amount between the background and the main subject becomes relatively small, so the gradation conversion section 15f having an intermediate γ value is selected.

In this embodiment, a switching method using a switch was adopted so that the degree of gradation conversion characteristics could be changed in stages.
It may be possible to change it continuously. Furthermore, the use of a strobe may be determined not only by the central processing unit but also by the user's judgment. A selection switch may be provided to select whether or not to emit light, and the gradation conversion characteristics are switched in conjunction with this switch. Good too.

Furthermore, in this embodiment, the characteristics of gamma correction are used as the gradation conversion means, but for example, an arbitrary conversion table may be stored in memory and gradation conversion may be performed based on the conversion table. Any characteristics may be set and used.

Furthermore, in this embodiment, the gradation conversion characteristic is selected based on the difference between the maximum value and the minimum value of each output value from the photometric means, but the calculation method is not limited to this. A conversion table corresponding to each output value may be stored in the central processing unit, and the tone conversion characteristic may be selected based on this conversion table.

[Effects of the Invention] As described above, according to the present invention, by measuring the light at multiple locations on the subject using the photometer and changing the gradation conversion characteristics according to the difference in light intensity, it is possible to always make it visually invisible from any subject. It is possible to obtain a good image with moderate contrast without naturalness. Further, even when the subject is illuminated by the light emitting means and the difference in light amount becomes large, by changing the gradation conversion characteristic to weaken the contrast, it is possible to obtain a good image without any visual unnaturalness.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an electronic still camera according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a conventional electronic still camera, and FIG. 3 is a block diagram showing the configuration of an electronic still camera according to an embodiment of the present invention. It is a graph showing gradation conversion characteristics. [Description of symbols of main parts] 3...Image sensor 4...Drive pulse generator 5...Sample hold circuit 6...Amplification circuit 7...Contour enhancement circuit l1...Central processing unit 14... Strobe 15... Gradation conversion circuit 17... Photometric member 22... Amplifier 23... A/D converter

Claims (1)

[Claims] 1. A photometer that measures light at multiple locations on a subject and outputs multiple signals corresponding to the amount of light at each location; an imaging unit that converts the subject image into a video signal; A gradation converting means having gradation conversion characteristics and converting the gradation of the video signal; and a gradation converting means that performs calculations based on each output from the photometric means, and provides the gradation conversion means with a gradation conversion characteristic based on the results of the calculations. 1. An electronic still camera comprising: selection means for selecting one of a plurality of gradation conversion characteristics. 2. A light emitting means for illuminating a subject, an imaging means for converting the subject image into a video signal, a gradation conversion means having a plurality of selectable gradation conversion characteristics and converting the gradation of the video signal; an electronic still camera, further comprising a selection means for selecting one of a plurality of tone conversion characteristics provided in the tone conversion means based on whether or not the light emission means emits light at a certain time. 3. Selectable photometering means that measures light at multiple locations on the subject and outputs multiple signals corresponding to the amount of light at each location, light emitting means that illuminates the subject, and imaging means that converts the subject image into a video signal. a gradation converting means having a plurality of gradation conversion characteristics and converting the gradation of the video signal; and the gradation converting means based on each output from the photometric means and the presence or absence of light emission by the light emitting means at the time of shooting. 1. An electronic still camera comprising: selection means for selecting one of a plurality of gradation conversion characteristics provided in the electronic still camera.