JP2011114442A - Electronic camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic camera for appropriately determining a blacklight state. <P>SOLUTION: The electronic camera includes: an imaging element 2; a luminance detecting means 2 for respectively detecting luminance information in different areas of an image obtained by the imaging element 2; a light emission-instructing means 12 for instructing light emission to a light-emitting device 17 for illuminating an object; and a determining means 12 for calculating a first luminance difference between a bright area and a dark area of a first image obtained by the imaging element 2 when a light emission instruction is not made on the basis of the luminance information detected by the luminance detecting means 12, calculating a second luminance difference between the dark area of the first image and an area corresponding to the dark area of the first image in a second image obtained by the imaging element 2 when the light emission instruction is made, and determining whether to be a backlight state on the basis of the first luminance difference and the second luminance difference. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electronic camera.

  A technique is known in which a photographing screen is divided into a plurality of areas, and whether or not the backlight is backlit is determined based on the luminance state of each divided area (see Patent Document 1).

JP 2004-4449 A

  In the prior art, there is a case where a low-luminance subject is erroneously determined as a backlight state.

  An electronic camera according to the present invention includes an imaging device, luminance detection means for detecting luminance information in different regions of an image obtained by the imaging device, light emission instruction means for instructing light emission to a light emitting device that illuminates the subject, and luminance detection Based on the luminance information detected by the means, a first luminance difference is calculated between the bright area and the dark area of the first image obtained by the imaging device when no light emission instruction is given, and the dark area of the first image When a light emission instruction is given, a second luminance difference is calculated between the second image obtained by the imaging device and a region corresponding to the dark region of the first image, and based on the first luminance difference and the second luminance difference. And determining means for determining whether or not the backlight is in the backlit state.

  With the electronic camera according to the present invention, the backlight condition can be appropriately determined.

It is a block diagram explaining the principal part structure of the electronic camera by one embodiment of this invention. It is a flowchart explaining the flow of imaging | photography process. It is a flowchart explaining the flow of a backlight determination process.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram for explaining a main configuration of an electronic camera according to an embodiment of the present invention. In FIG. 1, an electronic camera includes a lens unit 1, an image sensor 2, an A / D converter 3, a memory 4, an image processing circuit 5, a control circuit 8, a CPU 12, a motor 13, and focus control. The mechanism 14, the LCD monitor 15, the operation member 16, and the light emitting device 17 are included, and the external storage circuit 6 is configured to be detachable.

  The lens unit 1 includes a focusing lens (not shown). The focusing lens is a lens that adjusts the focal position so that a subject image formed by the light beam that has passed through the lens unit 1 is formed on the imaging surface of the imaging device 2. When the motor 13 drives the focus control mechanism 14, the focus control mechanism 14 moves the focusing lens forward and backward in the optical axis direction. The motor 13 is driven by a lens driving signal output from the CPU 12.

  The image sensor 2 is configured by, for example, a CMOS image sensor. The image sensor 2 captures a subject image on the imaging surface and outputs a photoelectric conversion signal corresponding to each pixel. The signal level of the photoelectric conversion signal output from the image sensor 2 varies depending on the intensity of light incident on each pixel. The control circuit 8 generates a timing signal necessary for driving the image sensor 2 and supplies the timing signal to the image sensor 2.

  A color filter 2A is provided on the image pickup surface of the image pickup device 2, and the image pickup device 2 outputs a photoelectric conversion signal received through the color filter 2A. For example, by arranging R, G, B color filters at the pixel positions of the image sensor 2, photoelectric conversion signals corresponding to light of R color components are output from the pixels received through the R color filters, A photoelectric conversion signal corresponding to light of the G color component is output from the pixel received through the G color filter, and a photoelectric conversion signal corresponding to light of the B color component is output from the pixel received through the B color filter. .

  The electronic camera of the present embodiment uses the photoelectric conversion signal from the image sensor 2 for shooting image recording, photometric calculation (including backlight determination described later), and focus evaluation value calculation. The photoelectric conversion signal output from the image sensor 2 is converted into a digital signal by the A / D converter 3. The converted digital data is stored in the buffer memory 4. The image processing circuit 5 performs compression processing on the image data stored in the memory 4 by a predetermined method (for example, JPEG), and stores the compressed image data in the external storage circuit 6. The image processing circuit 5 also performs decompression processing when the compressed data recorded in the external storage circuit 6 is read and decompressed. The external storage circuit 6 is configured by a data storage member such as a memory card, for example. The LCD monitor 15 is disposed on the back surface of the camera body. The LCD monitor 15 reproduces and displays captured images and through images.

  The CPU 12 includes an AE / AWB circuit 7, a detection filter 9, an integration circuit 10, and an AF circuit 11. The CPU 12 is connected to the control circuit 8 and the memory 4 and performs various calculations such as automatic focus detection (AF), automatic exposure (AE), and white balance adjustment (AWB) of the electronic camera, and sequence control of camera operation. In the AE calculation, for example, using the photoelectric conversion signal from the image sensor 2, the luminance information is calculated for each divided area of the shooting screen, and it is determined whether or not the backlight is in the backlight state. The CPU 12 further performs a known exposure calculation using the calculated luminance information, the control imaging sensitivity Sv, the control aperture Av and the control shutter time Tv, the necessity of illumination by the light emitting device 17, and the light emission amount when illumination is necessary. To decide.

  The light emitting device 17 is configured with a xenon tube or LED as a light source, and emits light with a light amount and timing according to an instruction from the CPU 12 to illuminate a subject.

  Various operation signals are input from the operation member 16 to the CPU 12. The CPU 12 performs camera control such as AF control, AE control, and AWB control of the electronic camera in accordance with an operation signal input from the operation member 16.

  The AE / AWB circuit 7 performs known exposure calculation and white balance adjustment processing. The white balance adjustment process is performed on the image data stored in the memory 4.

  The detection filter 9 is a filter that extracts a high frequency component from image data corresponding to a focus detection area (focus area) in the image data before image processing stored in the memory 4. The image data after the filter processing by the detection filter 9 has a frequency component in a predetermined band, specifically, a low frequency component, particularly a direct current component, removed compared to the image data before the filter processing.

  The integration circuit 10 integrates the image data corresponding to the pixels included in the focus area and filtered by the detection filter 9. Note that the absolute values of the image data are integrated in order to integrate the differences due to the high frequency components.

  The AF circuit 11 obtains a focus evaluation value using the integrated value obtained by the integrating circuit 10. The calculation of the focus evaluation value is performed, for example, while moving the focusing lens from one of the movable ends (for example, the closest end) toward the other (the infinite end). The AF circuit 11 calculates a focal point corresponding to the maximum point of the focus evaluation value curve thus obtained. The focal point is a lens position that eliminates blurring of the edge of the subject image captured by the image sensor 2 and maximizes the contrast of the image. The position of the focal point varies depending on the distance from the camera to the main subject.

  The focus evaluation value calculation process described above is performed in correspondence with the focus area provided in the shooting screen. In general, where the focus area is set on the screen is determined by a method in which the photographer operates the operation member 16 to indicate a focus area position, or a method in which the CPU 12 automatically sets a focus area corresponding to a predetermined subject. and so on.

  In the present embodiment, the operation when the electronic camera switched to the method of automatically setting the focus area sets the focus area corresponding to a predetermined subject will be mainly described. In this case, the CPU 12 detects a position where a main subject (for example, a person's face) exists based on the through image acquired by the image sensor 2. A predetermined range corresponding to the detection position is set as a focus area. A known detection method is used to detect the “face region” in the image. In addition, you may comprise so that another object (for example, a flower etc.) can be selected instead of a "face" as a main subject.

  The through image refers to a monitor image captured at a predetermined time interval (for example, 30 frames / second) before shooting. The image data for the through image is stored in the memory 4 in units of frames every predetermined time. The image processing circuit 5 sequentially reads the image data stored in the memory 4 to generate display data, and the LCD monitor 15 sequentially displays the reproduced image based on the display data (through image display).

<Shooting process>
A flow of photographing processing performed by the electronic camera will be described with reference to a flowchart illustrated in FIG. The CPU 12 activates the processing shown in FIG. 2 when a release button (not shown) constituting the operation member 16 is pressed halfway. In step S1 of FIG. 2, the CPU 12 starts displaying a through image and proceeds to step S2. In step S2, the CPU 12 calculates a luminance difference between the high luminance region and the low luminance region based on the through image. Specifically, the through screen is divided into a plurality of areas, and the luminance representing each area is calculated for each of the plurality of areas. Then, the difference between the maximum value and the minimum value of the representative luminance is set as the luminance difference between the high luminance region and the low luminance region.

  In step S3, the CPU 12 determines whether or not the luminance difference calculated in step S2 is greater than or equal to a predetermined determination threshold value. If the luminance difference is equal to or greater than the determination threshold, the CPU 12 makes a positive determination in step S3 and proceeds to step S5. When the luminance difference is less than the determination threshold, the CPU 12 makes a negative determination in step S3 and proceeds to step S4. When the negative determination is made in step S3, the backlight correction is not performed without determining the backlight.

  In step S5, the CPU 12 performs a backlight determination process and proceeds to step S6. Details of the backlight determination process will be described later. In step S6, the CPU 12 determines whether or not backlight correction is possible. The CPU 12 makes an affirmative decision in step S6 and proceeds to step S7 when the light emitting device 17 can emit light (for example, ready to emit light). If the CPU 12 cannot emit light due to insufficient battery power, the CPU 12 makes a negative determination in step S6 and proceeds to step S4.

  In step S7, the CPU 12 performs backlight correction setting and proceeds to step S4. When the backlight correction setting is made, the CPU 12 causes the light emitting device 17 to emit light in the shooting process of the next step.

  In step S4, the CPU 12 performs a photographing process. Specifically, photographing is performed at the control imaging sensitivity Sv, the control aperture Av, and the control shutter time Tv obtained by performing focusing (AF processing) and performing exposure calculation based on the latest through image. If the backlight compensation setting is set, and if it is determined that the photographing auxiliary light is necessary in the exposure calculation even if the backlight compensation setting is not set, the light emitting device 17 is caused to emit light with the light emission amount determined in the exposure calculation ( Main flash). When the CPU 12 stores the acquired image data in the external storage circuit 6, the processing in FIG.

<Backlight determination processing>
The details of the backlight determination process will be described with reference to the flowchart illustrated in FIG. In step S51 of FIG. 3, the CPU 12 stores (holds) the information of the low luminance area in the memory and proceeds to step S52. The information includes the representative luminance value of the low luminance region, the color information of the pixel signal included in the low luminance region (for example, the signal ratio (G / B) of the G color component and the B color component, and the G color component and the R color). Component signal ratio (G / R)). In step S52, the CPU 12 causes the light emitting device 17 to emit light with a small light amount (for example, guide number = 2) for backlight determination, and proceeds to step S53 (preliminary light emission).

  In step S53, the CPU 12 compares the through image acquired (captured) at the time of light emission for backlight determination with the information of the low luminance area held in the memory 4 in step S51, and proceeds to step S54.

  In step S <b> 54, the CPU 12 determines whether or not a change in luminance or color has occurred in the through image acquired (captured) at the time of light emission for backlight determination compared to the through image acquired at the time of non-light emission. If the comparison result in step S53 corresponds to at least one of the predetermined luminance change amount and the predetermined color change amount, the CPU 12 makes an affirmative decision in step S54 and proceeds to step S56. If none of the above applies, the CPU 12 makes a negative determination in step S54 and proceeds to step S55. The color change amount is determined by the above-described changes in (G / B) and (G / R).

  When the process proceeds to step S55, there is a high possibility that the backlight is not in the backlight state, or even if the subject is in the backlight state, it is difficult to correct (improve) the backlight state because the subject in the low brightness area is at a distance that the illumination light does not reach. Corresponds to the case. Therefore, in step S55, the CPU 12 determines that there is no backlight correction and ends the processing in FIG.

  The case of proceeding to step S56 corresponds to a case where the backlight state can be corrected (improved) because the luminance of the low-luminance region is increased by the small amount of illumination light, although it is highly possible that the backlight state is in the backlight state. Therefore, in step S56, the CPU 12 determines whether or not a face region can be detected from a through image acquired (captured) at the time of light emission for backlight determination. If the CPU 12 detects a face area, the CPU 12 makes a positive determination in step S56 and proceeds to step S59. If the face area is not detected, the CPU 12 makes a negative determination in step S56 and proceeds to step S57.

  The process proceeds to step S57 when no face area is found. In this case, the CPU 12 determines in step S57 that the backlight state can be corrected, and proceeds to step S58. In step S <b> 58, the CPU 12 determines to perform backlight correction and ends the process of FIG. 3. In this case, backlight correction is performed so that the area determined to have a change in luminance or color in step S54 is appropriately exposed, and the closest subject included in the area is focused (AF processing). ).

  The process proceeds to step S59 when a face area is found. In this case, in step S59, the CPU 12 determines to perform focusing (AF processing) on the face area and proceeds to step S60. In step S60, it is determined that the backlight correction is performed so that the face area is properly exposed, and the process of FIG.

According to the embodiment described above, the following operational effects can be obtained.
(1) The electronic camera detects luminance information in each of the image sensor 2 and different regions of the image obtained by the image sensor 2, instructs the light emitting device 17 that illuminates the subject to emit light for backlight determination, and detects the detected luminance. Based on the information, when the light emission instruction is not issued, a first luminance difference is calculated between the bright area and the dark area of the first image obtained by the image sensor 2, and the light emission instruction is issued with the dark area of the first image. A second luminance difference is calculated between the second image obtained by the image sensor 2 and the region corresponding to the dark region of the first image, and the backlight state is calculated based on the first luminance difference and the second luminance difference. Since the CPU 12 for determining whether or not is provided, the backlight state can be appropriately determined. Further, it can be distinguished from a low-luminance subject that is not backlit and a case where illumination light from the light emitting device 17 does not reach the subject in the dark area even in the backlit state.

(2) Further, the CPU 12 detects color information in different areas of the image obtained by the image sensor 2 and between the dark area of the first image and the area corresponding to the dark area of the first image in the second image. The color information difference is calculated, and it is determined based on the color information difference whether the backlight is in the backlight state. Thereby, even when it cannot be determined only by the second luminance difference, it can be determined based on the color information difference.

(3) A light emission instruction for determining backlighting is given to the light emitting device 17 before photographing, and when the backlight state is determined by the CPU 12, the main light emitting instruction is controlled to be performed at the time of photographing. By performing the light emission for backlight determination used for determining whether or not the backlight is in the state before photographing, the influence of the light emission on the photographed image can be suppressed. Moreover, the dark part area | region of a backlight condition can be correct | amended appropriately by this light emission.

(4) When determining the backlight state, the CPU 12 sets an area corresponding to the dark area of the first image in the image obtained by the image sensor 2 as a target for the exposure calculation or the focus detection calculation for the lens unit 1. Therefore, it is possible to obtain appropriate exposure and focus on the dark area to be corrected for backlight.

(Modification 1)
In step S54 described above, an affirmative determination is made when the comparison result in step S53 corresponds to at least one of a predetermined luminance change amount and a predetermined color change amount. Instead, the determination may be made based only on the luminance change. That is, an affirmative determination is made when a through image acquired (captured) at the time of preliminary light emission for backlight determination has a luminance difference greater than or equal to a predetermined value compared to a through image acquired at the time of non-light emission (that is, the amount of change is greater than or equal to a predetermined value). I do.

(Modification 2)
In the above embodiment, it is determined to focus on the face area (AF processing) in step S59, but instead, it is determined to move the focus lens so that the subject whose shooting distance is 2 m is in focus. May be. The fact that the luminance of the low luminance region is increased by the light of the guide number 2 for determining the backlight is likely to cause the main subject to be within 2 m from the electronic camera. By using a so-called “placement pin”, it is possible to omit the process of calculating the focal point corresponding to the maximum point of the focus evaluation value curve.

(Modification 3)
A plurality of images having different ISO sensitivities may be calculated by applying different gains to the data of through images acquired (captured) during preliminary light emission for backlight determination. By determining by changing the ISO sensitivity stepwise, it is possible to improve the determination accuracy when the subject exists near the boundary (2 m in this example) where the light for backlight determination reaches / does not reach. Specifically, in the initially set ISO sensitivity, there is no change in brightness or color of the through image acquired (captured) at the time of preliminary light emission for backlight determination compared to the through image acquired at the time of non-light emission. Even if it is determined that the signal level increases as the ISO sensitivity is increased, it may be determined that a change in luminance or color has occurred.

(Modification 4)
When a plurality of images with different ISO sensitivities are calculated in stages, the distance to the main subject is estimated according to which ISO sensitivity corresponds to the boundary where the light for backlight determination reaches / does not reach It may be. For example, even if it is determined that a change in luminance or color occurs due to the presence or absence of backlight determination light in the initially set ISO sensitivity, if the ISO sensitivity is lowered, the signal level is lowered. A state in which no change in brightness or color occurs can be obtained. In this case, the distance to the main subject is estimated using the rate of decrease from the initial ISO sensitivity, and the focus lens is determined to move so that the subject at this estimated distance is in focus.

(Modification 5)
The example in which the light emitting device 17 emits light with a small amount of light (for example, guide number 2) and is used as a light source for backlight determination has been described. However, in the case of having an AF auxiliary light source that illuminates the main subject during AF processing, AF auxiliary light Can also be used as a light source for backlight determination.

  The above description is merely an example, and is not limited to the configuration of the above embodiment. For example, the light emitting device 17 may be configured by an external light emitting device different from the electronic camera.

DESCRIPTION OF SYMBOLS 1 ... Lens unit 2 ... Image pick-up element 5 ... Image processing circuit 12 ... CPU
16 ... Operation member 17 ... Light emitting device

Claims (4)

An image sensor;
Brightness detection means for detecting brightness information in different regions of the image obtained by the image sensor;
A light emission instruction means for instructing light emission to a light emitting device that illuminates the subject;
Based on the luminance information detected by the luminance detection means, a first luminance difference is calculated between the bright area and the dark area of the first image obtained by the imaging device when the light emission instruction is not given, Calculating a second luminance difference between the dark area of one image and the area corresponding to the dark area of the first image in the second image obtained by the imaging element when the light emission instruction is given; Determining means for determining whether or not the backlight is in a backlight state based on the first luminance difference and the second luminance difference;
An electronic camera comprising: The electronic camera according to claim 1,
Further comprising color information detection means for detecting color information in different regions of the image obtained by the imaging device,
The determination means further calculates a color information difference between the dark area of the first image and an area corresponding to the dark area of the first image in the second image, and based on the color information difference An electronic camera characterized by determining whether or not the backlight is in the backlit state. The electronic camera according to claim 1 or 2,
The apparatus further includes a control unit that performs a light emission instruction to the light emitting device before photographing, and controls the light emission instruction unit so that the main light emission instruction is performed at the time of photographing when the determination unit determines a backlight state. And an electronic camera. In the electronic camera by the invention as described in any one of Claims 1-3,
The control means performs exposure calculation or focus detection calculation of the photographing optical system for an area corresponding to the dark area of the first image in the image obtained by the imaging element when the determination means determines the backlight state. An electronic camera characterized by being targeted.

Images