JP2000307939A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record a higher quality image by discriminating a main object area and a background area from the entire image area to set areas on the basis of 1st image information and giving different gradation characteristics to the set main object area and background area. SOLUTION: A system controller 12 controls a digital process circuit 8 and performs all of area discrimination setting, gradation correction processing, the generation of a record image being a use object image by means of selection or synthesis of image, etc. The controller 12 also performs an exposure operation including stroboscopic light emission by controlling an exposure control driver 17. A digital camera has a normal mode as photographic mode and a unique gradation correction mode in a switchable way and can perform switching selection before photographing by a control switch 13. The main object area of a 1st image and the background area of a 2nd image are combined to be a final record image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an imaging device having an image processing function.

[0002]

2. Description of the Related Art An image pickup device such as an electronic still camera mainly constituted as a still image recording device, typically a digital camera using a memory card or the like as a recording medium, not to mention a so-called video camera. 2. Description of the Related Art An electronic image pickup apparatus that captures a subject image using an image and records the image in the form of an electric signal is widely known.

In an electronic image pickup apparatus, various signals are processed to improve the image quality when a recorded image is generated because the signal can be processed by an electric circuit. It only compensates for the image quality that is often still inferior to the image quality of film camera systems.

On the other hand, when performing image processing for improving image quality, various possibilities are widened if different processing is performed for each region. Several techniques have been tried from such a viewpoint. For example, JP-A-8-51
Japanese Unexamined Patent Publication No. 632 discloses an area-compatible white balance processing technique that performs white balance control of a strobe photographed image on a block basis based on a luminance comparison between a strobe photographed image and an image photographed only with external light. I have. Also, Japanese Patent Application Laid-Open No. 5-292524 discloses a method of detecting a skin color portion and lowering the degree of contour emphasis from other portions to smoothly express the skin. Also, JP-A-7-466.
Japanese Patent Laid-Open No. 21 discloses a tone correction means for detecting a flesh color portion and improving the brightness of the portion to reduce dullness. The technologies disclosed in these publications are for solving individual technical problems, and in solving the problems, an area correspondence type process is performed as needed.

[0005]

In general, when flash photography is performed, the illuminance of a subject due to illumination is inversely proportional to the square of the distance to the subject. The dynamic range of the distribution, that is, the required dynamic range of the image becomes extremely large. The fact that the required dynamic range of the image is large means that blackening of dark areas and overexposure of bright areas often occur, which is not preferable. This is improved when the gradation characteristic is lowered, but the contrast of the image is weakened, which is not preferable. It is also known to keep the gradation in the luminance region that is thought to include the main subject and leave only the gradation in the other luminance regions flat, but in any case, uniform gradation correction over the entire screen area , The image quality deterioration as described above cannot be essentially saved.

To solve this problem, if different image processing is allowed for each area of the screen, there is a possibility of correction, but no concrete proposal has been made. As a slightly related one, Japanese Patent Application Laid-Open No. Hei 7-46621 proposes a processing method for varying the gradation characteristics adaptively in a region.
The problem, the configuration, and the effect of the proposed technology are completely different from the problem at the time of flash photography, and the above-described problem cannot be solved by the technology disclosed in this publication.

As another technique for solving the above problem from another aspect, there is a so-called daylight synchro photography, that is, a flash photography using external light in combination. Exposure time must be increased (this is particularly noticeable when focusing is required to increase the depth of field, such as in macro photography), and image blur due to camera shake occurs. However, there is a problem that usable shooting conditions are limited.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem in the conventional image pickup apparatus. By performing appropriate gradation correction on both the main subject and the background in flash photography, higher image quality can be obtained. It is an object of the present invention to provide an imaging device capable of recording an image. An object of the present invention is to provide an imaging apparatus capable of discriminating a main subject area from a background area and performing different gradation correction for each area. I do. Another object of the present invention is to provide an image pickup apparatus capable of generating one image based on a main subject area and a background area that have been subjected to different gradation corrections. Another object of the present invention is to provide an imaging apparatus which does not require processing such as image synthesis when generating an image in the invention according to the second aspect. According to a fourth aspect of the present invention, there is provided the imaging apparatus according to the second or third aspect, wherein the main subject region and the background region can be distinguished from each other by taking into consideration the degree of the contribution of the external light and the irradiation by the illumination device. The purpose is to provide.

[0009]

According to a first aspect of the present invention, there is provided an exposure device including an object illumination device, an exposure control device for controlling the exposure device, and at least the illumination device. Area setting means for discriminating a main subject area and a background area from the entire image area based on information of a first image captured by performing irradiation, and setting the area;
The image pickup apparatus comprises an area-compatible tone correction means for giving different tone characteristics to the main subject area and the background area set by the area setting means.

With this configuration, the main subject area and the background area can be discriminated from each other to set each area, and different gradation correction can be performed for each area, so that a high quality image can be recorded. A possible imaging device can be realized.

According to a second aspect of the present invention, in the image pickup apparatus according to the first aspect, at least the first image and the first image are stored.
By selecting one of the two images with the second image captured under an exposure condition substantially including at least an exposure component caused by external light, and combining these two images. Recording image generating means for generating a third image which is an image to be used for recording or the like,
The area-based tone correction means is configured to give different tone characteristics to the main subject area and the background area in the process of generating the third image by the recorded image generation means. It is characterized by the following.

With this configuration, it is possible to generate one image by the main subject area and the background area that have been subjected to different gradation corrections. Therefore, even in the case of, for example, flash photography, both the main subject and the background can be generated. It is possible to obtain an image having sufficient contrast, and to realize an imaging device that enables advanced image expression that cannot be achieved with a conventional film camera that actively applies different gradation corrections depending on regions. .

According to a third aspect of the present invention, in the imaging apparatus according to the second aspect, the exposure control means sets the substantial exposure time in order to eliminate the influence of external light when capturing the first image. The recording image generation means is configured to generate the third image by selecting the second image by making the recording image smaller than when the second image was captured. . With such a configuration, processing such as image synthesis is not required when generating an image to be used, so that circuits, control, and the like can be simplified.

According to a fourth aspect of the present invention, in the image pickup apparatus according to the second or third aspect, the exposure control means is provided with the first
Controlling the exposure means so that the imaging of the image of the second image and the imaging of the second image have the same exposure value, and the area setting means images the first image and the illumination without the illumination by the illumination device. The apparatus is characterized in that the discrimination setting of the main subject area is performed based on a comparison with a second image. With this configuration, it is possible to discriminate the main subject region from the background region by specifically considering the degree of the contribution of the illumination device and the external light, and the background is relatively compared to the main subject. It is possible to cope with the case where the distance is close.

[0015]

Next, an embodiment will be described. FIG. 1 is a block diagram showing an embodiment of an imaging apparatus (digital camera) according to the present invention. In FIG. 1, 1 is a lens system, 2 is a lens driving mechanism, 3 is an exposure control mechanism, 4 is a filter system, 5 is a CCD image sensor, 6 is a CCD driver, 7 is a pre-processing circuit including an A / D converter, Reference numeral 8 denotes a digital process circuit which includes a memory as hardware and performs all digital process processing. 9 is a memory card interface, 10 is a memory card, 11 is an LCD image display system, 12 is a system controller including a microcomputer as a main configuration, 13 is an operation switch system, 14 is an operation display system including a display LCD and a sounding buzzer, 15 Is a flash, 16 is a lens driver, and 17 is an exposure control driver. In addition, the imaging device is provided with a release button (not shown) and the like.

In the digital camera configured as described above, the main operations such as discrimination setting of an area, gradation correction processing, generation of a recorded image to be used by selecting or synthesizing an image, and the like are all performed by a digital process. The circuit 8 is controlled by the system controller 12,
In addition, the system controller 12 controls the exposure control driver 17 as necessary to perform an exposure operation including flash emission. Further, the digital camera according to the present embodiment has a switching mode between a normal mode corresponding to conventional shooting and a gradation correction mode unique to the embodiment of the present invention as a shooting mode. Prior to photographing, this can be switched and selected. Further, the camera control in the following description is all executed by the system controller 12 appropriately controlling each unit.

Next, the operation of the embodiment configured as described above will be described. When the photographer operates the release button in the gradation correction mode, first, the first exposure is performed with strobe irradiation. At this time, the aperture and the shutter may be controlled in several ways depending on the method of the area discrimination processing. In the present embodiment, the aperture is opened regardless of the exposure value of the main photographing, and the exposure time is determined by the flash emission time. It is set to the shortest time within the range that does not fall below. The amount of light emitted from the strobe is appropriately adjusted by a known technique such as flashmatic or photometry. By opening the aperture, it is possible to extend the reaching limit of the strobe light, and to shorten the exposure time to reduce the influence of external light. The image obtained at this time is defined as a first image. In the following, it is assumed that the background is sufficiently far from the main subject. Therefore, the strobe light reaching the background is sufficiently smaller than the main subject.

The second exposure is performed immediately after the first exposure under the originally intended exposure conditions. However, no flash emission is performed at this time. The image obtained at this time is defined as a second image. In normal photographing, if the time difference between the two exposures is set to be sufficiently small, the change in the subject can be ignored. Therefore, in the following description, the first and second images will be images having exactly the same composition in practical use. It will be described as having been performed. In the gradation correction mode of the camera according to the present embodiment, the limit of the exposure time at the time of the main exposure is set so as to be a high speed (short time) higher than a so-called camera shake limit shutter speed. This prevents image blur caused by camera shake. For this reason, the background luminance level cannot be so high when photographing under normal room illumination.

Here, if the second image is an image as shown in FIG. 2A, the first image is an image in which the background portion is almost dark as shown in FIG. 2B. become that way.
Note that, in FIG. 2A, the hatched background represents that the level is low. That is, since the exposure time is set to the shortest in the first image as described above, the exposure by the external light can be almost ignored. Since the background is far away, the exposure level by the strobe is low. The first image is subjected to level comparison with respect to a predetermined level on a pixel-by-pixel basis, and a pixel position at or above the predetermined level is registered as a main subject area, and a pixel position at or below another predetermined level is registered as a background area. As mentioned earlier, external light exposure is almost negligible, but in reality there may be some exposure, and there is also background exposure using a strobe, so this level comparison process will definitely remove this effect. is there. If the strobe light control level at the time of the first exposure is set higher than that at the time of normal photographing, the possibility of erroneous determination of a low reflectance portion in the main subject can be reduced. Area setting in the processing can be made more reliable.

Next, image synthesis for generating a recorded image is performed. That is, the image of the main subject area of the first image and the image of the background area of the second image are combined to form one final recorded image. In the synthesis process, tone correction is independently performed on each area extracted image. The main subject area extracted image of the first image should have been given an appropriate exposure using only the strobe light (it is possible to control such that overexposure does not easily occur or does not occur because there is no external light fog). Therefore, correction is not necessary in principle, but processing similar to the second image described later may be performed as necessary.

Since the background area extracted image of the second image is exposed by the combined illumination of the outside light within a range permitted by other conditions and a relatively small amount of strobe light, the luminance histogram often has a low luminance side. And a low-brightness, low-contrast state. Therefore, for example, the distribution of the histogram has a distribution that is sufficiently widened with respect to the luminance range of the recording system.
1 such that the maximum value-minimum value is approximately equal to the luminance range
Subsequent correction: y = ax-b (x: input luminance signal level before correction, y: output luminance signal level after correction), etc.], and a well-known contrast enlargement correction is performed.

The resulting recorded image is one strobe photographed image in which both the main subject and the background have sufficient contrast. Finally, the generated recording image is subjected to processing such as compression as appropriate, and is recorded on the memory card 10. As described above, according to the present embodiment, it is possible to obtain an imaging device in which appropriate gradation correction is performed on both the main subject and the background in flash photography, and a higher quality image can be recorded.

Although the present invention has been described based on the above embodiment, various modifications can be considered in the above embodiment. As a first modified example, there is one related to exposure processing. In the above embodiment, the setting is made so as to exclude external light when exposing the first image. However, if the background is closer than assumed above, a malfunction may occur. To address this, the first
Equalizing the exposure level to external light in the exposure and the second exposure,
As a condition for setting an area, it is conceivable to perform level comparison of two images. This makes it possible to discriminate the main subject from the background by specifically considering the contribution of the strobe light and the external light. As a specific example, a case in which an area where the contribution of strobe light is greater than that of external light is set as a main subject will be described. In this case, the important thing is the exposure level,
The value of the individual exposure time itself is the exposure value EV (Exposure Value).
e) It can be set arbitrarily under certain conditions. From the viewpoint of suppressing the waste of strobe light emission and extending the reach distance, control for opening the aperture is a preferred example.

As a second modification, the first exposure and area setting processing are performed in the same manner as in the above-described embodiment, and a strobe is also emitted at the time of the second exposure, and the exposure is performed under the originally intended exposure condition of the main exposure. What you do. In this case, when generating the recorded image, the second image can be subjected to the same tone correction as in the above-described embodiment, which differs for each region between the main subject and the background, without using the first image. Because
No processing such as image synthesis is required.

As a third modification, exposure is performed only once,
There is a method in which a strobe light is emitted and the exposure is performed under the originally intended exposure condition of main exposure. In this case, the use of the camera is restricted, for example, by limiting the use of external light in the main exposure to a certain level or less. It is possible to perform the same tone correction as in the above-described embodiment on the one captured image as shown in FIG. This modification is particularly useful in a macro mode of a camera having a macro shooting function.

As a fourth modification, there is the following example which can be applied not only to the prevention of image quality deterioration at the time of flash photography but also to new video expression including general photography. . That is, the exposure processing is performed in the same manner as in the above embodiment or the first modified example, but the photographing target image as the main exposure is a case where the second image that does not use a strobe is selected. In other words, although an image obtained by shooting only with ordinary external light does not cause the “degradation of image quality due to flash shooting” as described above, the conventional image is obtained by performing tone correction for each set area. Can produce an effective image that could not be obtained.

That is, in the fourth modification shown here, gradation processing for reducing the contrast of the background is performed.
Correction of the main subject area extracted image of the second image should not be necessary because proper exposure to external light should have been given. However, if necessary, contrast expansion correction as in the above embodiment may be performed if necessary. Good. On the other hand, for the background region extracted image of the second image, a contrast state similar to that of the main subject region is obtained at the time of imaging, except for the pictorial elements. This is adjusted so that, for example, the distribution of the histogram is concentrated in a specific part of the luminance range of the recording system, specifically, in a part of medium luminance to slightly high luminance (for example, the maximum value is 3 of the maximum luminance level). /
5, a primary correction such that the minimum value is substantially equal to 4/5 of the maximum luminance level: y = ax + b is uniformly applied), and a known contrast reduction correction is performed. The recorded image generated as a result is an image suitable for, for example, a portrait or the like, such as a main subject clearly appearing in a bright and hazy background. Of course, it goes without saying that the processing method as in the fourth modified example is similarly effective for actual photographing using a strobe.

Next, as a fifth modified example, the following example is given. That is, the second embodiment in the above embodiment
If the tone correction processing for the background area extracted image of the image is performed with the tone processing as in the fourth modified example (for simplicity, a process of simply adding an appropriate offset can also be adopted), the fourth correction can be performed. The one having the same effect as that of the modified example can be obtained. At this time, an effect that cannot be overlooked that image quality does not deteriorate due to amplification of noise, which is a problem associated with the contrast enlarging process as in the above-described embodiment, can be obtained.

[0029]

As described above with reference to the embodiments, according to the present invention, it is possible to perform appropriate gradation correction for both a main subject and a background in photographing using a subject lighting device such as a strobe. Accordingly, it is possible to realize an imaging device capable of recording a higher quality image. In particular, according to the first aspect of the present invention, it is possible to set each area by discriminating the main subject area and the background area and perform different gradation corrections for each area, so that a high quality image can be recorded. It is possible to realize an imaging device capable of performing the above. According to the second aspect of the present invention, it is possible to generate one image based on the main subject area and the background area that have been subjected to different gradation corrections. This makes it possible to obtain a single image having a high contrast, and to achieve advanced image expression that cannot be achieved with a conventional film camera that actively applies different gradation corrections depending on regions. According to the third aspect of the present invention, since processing such as image synthesis is not required when generating an image, circuits, control, and the like can be simplified. According to the invention according to claim 4, it is possible to discriminate the main subject area from the background area by specifically considering the degree of the irradiation by the illumination device and the contribution of the external light. Even when the subject is close to the main subject, it is possible to appropriately cope with the situation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an imaging apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a second image by exposure without strobe irradiation (light emission) and a first image by exposure with strobe irradiation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens system 2 Lens drive mechanism 3 Exposure control mechanism 4 Filter system 5 CCD image sensor 6 CCD driver 7 Preprocess circuit 8 Digital process circuit 9 Memory card interface 10 Memory card 11 LCD image display system 12 System controller 13 Operation switch system 14 Operation Display system 15 Strobe 16 Lens driver 17 Exposure control driver

Claims (4)

[Claims] 1. An exposure device including a subject illumination device, an exposure control device for controlling the exposure device, and at least a first image captured by irradiating the illumination device. Area setting means for distinguishing between a main subject area and a background area to set an area, and area-corresponding tone correction means for giving different tone characteristics to the main subject area and the background area set by the area setting means An imaging device comprising: 2. At least two images of the first image and a second image taken under an exposure condition substantially different from the first image and including at least an exposure component caused by external light. Further comprising a recording image generating means for generating a third image which is an image to be used for recording or the like by selecting one of the above or by combining these two images. The means is configured to apply different gradation characteristics to the main subject area and the background area in the process of generating the third image by the recording image generating means. 1. The imaging device according to 1. 3. The exposure control means according to claim 1, wherein said exposure control means sets a substantial exposure time shorter than that of said second image in order to eliminate an influence of external light when said first image is taken. The imaging apparatus according to claim 2, wherein the generation unit is configured to generate the third image by selecting the second image. 4. The exposure control means controls the exposure means so that the imaging of the first image and the imaging of the second image have the same exposure value.
The discrimination setting of the main subject area is performed based on a comparison between the image of the main subject area and a second image captured without irradiation by the lighting device, wherein Such an imaging device.