JP4285668B2 - Imaging apparatus, exposure control method thereof, and recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus suitable for use in a so-called digital camera, an exposure control method thereof, and a recording medium on which a program is recorded.
[0002]
[Prior art]
Conventionally, in exposure control in camera devices such as silver halide cameras and digital cameras, photometry is performed using various metering methods such as full surface average metering, center-weighted metering, multi-segment metering, spot metering, etc. to determine the appropriate exposure during shooting It has been. For example, in the multi-division metering method, we devise a method for dividing the shooting screen, and shoot forward light, backlight, people, landscapes, etc. based on the photometric value pattern of each divided area and thousands of patterns of shooting data prepared in advance Appropriate exposure is determined according to the conditions (in the simplest case, it is determined that the backlight is bright when the area above is bright). As a result, an appropriate exposure according to the photographing screen can be obtained.
[0003]
[Problems to be solved by the invention]
However, in conventional camera device exposure control, even if exposure control using the multi-division metering method described above is performed, the basis is the average photometric value in each divided range of the shooting screen, so it is prepared in advance. Even if the number of shooting data to be increased is increased, there is a limit to finely controlling the exposure according to the subject.
[0004]
In addition, there are the following problems in recording an image using a fixed image pickup device such as a CCD like a digital camera. That is, the latitude of the CCD is narrow. For example, as shown in FIG. 10, the human latitude when the subject is a landscape is 13 to 14 EV, whereas the CCD has a narrow sensitivity range of about 4 EV. For this reason, if exposure control is simply performed based on the exposure value calculated from the photometric result, an image in which a bright part is overexposed or a dark part is crushed is likely to be obtained. For this reason, exposure control based on a reference exposure value that makes the screen gray with a reflectance of 18% (a general value used as a reflectance when a natural landscape is taken as an object) is compelled during shooting. Even in this case, there is a limit to fine exposure control according to the subject.
[0005]
The present invention has been made in view of such conventional problems, and provides an imaging apparatus capable of finer exposure control according to a subject, an exposure control method thereof, and a recording medium on which a program is recorded. With the goal.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problem, in the invention of claim 1, in an imaging apparatus including an imaging unit that converts a subject image into image information, an image is captured by the imaging unit along with prior imaging prior to regular imaging. Distribution information acquisition means for evaluating the brightness of each pixel constituting a reference image as a reference divided into a plurality of brightness areas and acquiring distribution information indicating the brightness distribution of each pixel, and the distribution information In the distribution information acquired by the acquisition means, it is determined whether there is a distribution non-existing side on either the brightest side or the darkest side. presence brightness distribution indicated by the distribution information acquired by the distribution acquisition unit, in the range of recognizable brightness by the image pickup means, the distribution comprising one of a bright side or the dark side A calculating means for calculating a correction value required to move the city side, it was that a exposure control means for correcting the exposure at the time of imaging of the normal based on the calculated correction value by the calculating means.
[0007]
In such a configuration, the exposure control means is based on the distribution information indicating the brightness distribution of the image represented by the reference image captured by the distribution information acquisition means in accordance with the pre-imaging prior to the regular imaging. Control exposure. That is, exposure control is performed based on distribution information in which brightness information of each pixel unit is reflected as it is. In addition, exposure control is performed that enables imaging that makes the most of the light / dark recognition ability of the imaging means.
[0008]
According to a second aspect of the present invention, the calculation means calculates the correction value based on an imaging condition determined based on the distribution information, and corrects exposure during normal imaging based on the calculated correction value. To do. In such a configuration, since the imaging condition is determined based on the distribution information in which the brightness information of each pixel unit constituting the image to be captured is reflected as it is, the imaging condition can be determined more accurately. And exposure control according to it becomes possible.
[0010]
Further, in the invention of claim 3 , the distribution information acquisition means evaluates the brightness of each pixel constituting a predetermined emphasis area of the reference image divided into a plurality of brightness areas, and the emphasis It is assumed that distribution information indicating the brightness distribution of the area is acquired. In such a configuration, exposure control based on more brightness information can be performed for a predetermined priority area of the imaging screen.
[0011]
In the invention of claim 4, in the exposure control method of an imaging apparatus including an imaging unit that converts a subject image into image information, a reference image serving as a reference is captured by prior imaging prior to regular imaging, A process of evaluating the brightness of each pixel constituting the captured reference image by dividing it into a plurality of brightness areas and obtaining distribution information indicating the brightness distribution of each pixel, and the brightest in the acquired distribution information A step of determining whether there is a non-distributed side on either the dark side or the darkest side, and the distribution information acquired when it is determined by the determining step that the presence exists. the brightness distribution, calculating a correction value required to move within a range of recognizable brightness, a one of a bright side or the dark side to the side where there is no distribution by said image pickup means And that step was the method including the step of correcting the exposure at the time of imaging of the normal based on the calculated correction value.
[0012]
According to such a method, the brightness information of each pixel constituting the captured image, that is, based on more brightness information than obtained from the average value of the brightness of each divided portion by dividing the imaging screen into a plurality of parts. Exposure control is performed. In addition, exposure control is performed that enables imaging that makes the most of the light / dark recognition ability of the imaging means.
[0013]
Further, in the recording medium according to claim 5, a computer having an imaging apparatus including an imaging unit that converts a subject image into image information is a reference imaged by the imaging unit in association with prior imaging prior to normal imaging. Distribution information acquisition means for evaluating the brightness of each pixel constituting the reference image to be divided into a plurality of brightness areas and acquiring distribution information indicating the brightness distribution of each pixel; and the distribution information acquisition In the distribution information acquired by the means, it is determined whether or not the brightest side or the darkest side has a distribution non-existing side, and if this exists, the distribution information acquisition means the brightness distribution indicated by the acquired distribution information, within the scope of recognizable brightness by the image pickup means, a one of a bright side or the dark side and the side where there is no distribution A calculating means for calculating a correction value required to motion, the exposure at the time of imaging of the normal based on the calculated correction value and a recording of a program to function in an exposure control means for correcting this calculation means.
[0014]
By using a program recorded on such a recording medium, the image capturing apparatus performs exposure control based on more brightness information than is obtained from the average value of the brightness of each divided part by dividing the image capturing screen into a plurality of parts. Can be made. In addition, exposure control can be performed that enables imaging that makes full use of the light / dark recognition ability of the imaging means.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block configuration diagram showing an outline of an electrical configuration of a digital camera 1 provided with an imaging apparatus of the present invention.
[0016]
That is, the digital camera 1 has a CCD 2 that is a solid-state imaging device that captures a subject image formed by an optical system (not shown) and outputs it as an imaging signal, and converts the captured image into a JPEG format. The MPU 3 is mainly configured with a processing function. Although not shown, the CCD 2 is disposed on the optical axis behind the lens group and the diaphragm, and forms a subject image on the surface thereof. The MPU 3 is connected with a timing generator (TG) 4 that generates a timing signal. A V driver 5 (vertical driver) drives the CCD 2 on the basis of the timing signal generated by the TG 4, and the CCD 2 generates a subject image accordingly. An analog imaging signal corresponding to the luminance is output and sent to the unit circuit 6. The unit circuit 6 includes a CDS that holds an imaging signal output from the CCD 2, a gain adjustment amplifier (AGC) that is an analog amplifier that is supplied with the imaging signal from the CDS, and an imaging signal that is amplified and adjusted by the gain adjustment amplifier. It comprises an A / D converter (AD) that converts it into image data, and the output signal of the CCD 2 is sampled with the black level matched and sent to the MPU 3 as a digital signal. The sent digital signal (imaging signal) is temporarily stored in the DRAM 7, subjected to various image processing by the MPU 3, and finally stored in the flash memory (FLASH) 8 as a compressed video signal. . The stored video signal is read to the MPU 3 as necessary, and is generated into a digital video signal or an analog video signal through processing such as expansion processing, addition of a luminance signal and a color signal.
[0017]
Further, the MPU 3 is connected with an MROM 9, a power supply circuit 10, an operation key unit 11, a TFT liquid crystal monitor 12, and a strobe 13. The MROM 9 is a program ROM in which an operation program of the MPU 3 is recorded, that is, a recording medium of the present invention. The MROM 9 stores program AE data constituting a program diagram showing a combination of an aperture value (F) corresponding to an appropriate exposure value (EV) at the time of shooting and a shutter speed. The MPU 3 functions as a distribution information acquisition unit and an exposure control unit of the present invention by operating the built-in RAM as a working memory according to the operation program, and according to the program diagram, the charge accumulation time of the CCD 2 and the aperture (see FIG. (Not shown), the gain of the gain adjustment amplifier (AGC) of the unit circuit 6 is set. The charge accumulation time set by the MPU 3 is supplied as a shutter pulse to the V driver 5 via the TG 4, and the charge accumulation time, that is, the shutter speed is controlled by the V driver 5 driving the CCD 2 according to this. That is, the CCD 2 functions as an electronic shutter.
[0018]
The operation key unit 11 includes a power key that is operated when the power is turned on / off, a mode switching key that switches between a recording mode (REC mode) and a reproduction mode (PLAY mode), and an image captured in the recording mode in a flash memory. Various keys such as a video capture key (shutter) that are operated when storing the image in the memory 8 are provided. The TFT liquid crystal monitor 12 displays sequentially captured images as a through image in the recording mode, and displays an image based on an analog video signal generated from the image data recorded in the flash memory 8 in the reproduction mode. The strobe 13 is driven as necessary to operate the video capture key (when shooting) and emits auxiliary light. The program data and the like stored in the MROM 9 described above can be stored on another recording medium such as an IC card that is separately provided or detachably mounted as long as the recorded contents can be retained. The program data may be recorded, and the program data may be supplied from another device such as a personal computer.
[0019]
Next, the operation of the digital camera 1 having the above configuration will be described with reference to the flowchart of FIG. This flowchart relates to exposure control of the MPU 3 in a state where the recording mode is set after the power is turned on.
[0020]
That is, when the recording mode is set, the digital camera 1 displays an image captured by the CCD 2, that is, a through image on the TFT liquid crystal monitor 12. At this time, the MPU 3 performs exposure control so that the display image is always gray with a reflectance of 18% (step SA1). Next, the MPU 3 determines the brightness of each pixel constituting an image captured as a through image, that is, a reference image as a reference, and the light and dark sensitivity range width (1 to 255) of the CCD 2 in a plurality of brightness areas. Evaluation is performed for each brightness area divided into AP, and the number of pixels (number of pixels) corresponding to each brightness area is totaled to generate distribution data constituting a histogram as shown in FIG. Step SA2). The distribution data generated here is the distribution information of the present invention indicating the brightness distribution of the reference image. In the example shown in FIG. 3, the brightness area where no distribution exists from the A area to the D area, and the brightest area where the distribution begins to exist when viewed from the A area side is the E area.
[0021]
Subsequently, based on the distribution data, the MPU 3 determines whether or not the image at that time is an image having no atmosphere (a so-called sleep image or the like) (step SA3). Such a determination is made, for example, based on whether or not the number of areas having no distribution is greater than or equal to a predetermined number from the brightest E area where the distribution exists to the A area which is the maximum brightness area. In other words, it is based on whether or not the image requires positive exposure correction. If it is determined that the image has no atmosphere, the exposure time correction magnification (exposure magnification) is further calculated (step SA4), and then the process proceeds to step SA5. Conversely, if it is determined that the exposure correction is unnecessary (step SA3). NO), it proceeds to step SA5 as it is. Here, the correction magnification calculated in step SA4 is a correction magnification necessary for lifting the brightness area where the above-described distribution exists to a predetermined area, and the gamma curve at the time of the through image is a solid line shown in FIG. If it is linear,
Exposure magnification = lifting level / obtained from the level where distribution exists. That is, if the E area (119/255 level) is raised to the C area (223/255 level) in the example of FIG. 3, the exposure is calculated to be 223/191 times plus with respect to the 119/255 level. When a gamma curve having a curve as shown by a dotted line in FIG. 4 is used for a through image, the exposure magnification is calculated in consideration of a change along the curve.
[0022]
On the other hand, in step SA5, it is determined whether or not the shutter has been pressed, and the process returns to step SA1 and repeats the above-described processing until it is pressed. If the shutter is eventually pushed during that time, the exposure time for regular shooting is set using the exposure magnification obtained in the process of step SA4 performed immediately before.
Shooting exposure time = Through image exposure time × Exposure magnification is obtained, and the exposure time set immediately before is changed to the shooting exposure time without changing the aperture value set at the time of the previous exposure control (however, If the determination result of step SA3 performed immediately before is NO, no change is made), and exposure is performed (step SA6). Then, the exposure control process for one shooting is completed.
[0023]
Thus, in the above example, the brightest brightness area is lifted from the E area to the C area as shown in FIG. 5 in the above example, and the brightness distribution described above reaches the brighter area. A histogram with a wide distribution width is obtained. In other words, the latitude of the CCD 2 can be fully utilized by changing (correcting) the exposure time, and a more natural image with a wide range of light and darkness can be taken. Moreover, even when shooting a subject (high key) that is an image that is bright and has no atmosphere, especially a flat landscape such as a blue sky or a white bright building wall, the above-mentioned “smooth image” does not occur, and the whiteout You can shoot images with no atmosphere. Note that imaging of a through image displayed on the TFT liquid crystal monitor 12 by the CCD 2 performed in step SA1 immediately before regular imaging in step SA6 is performed is the preliminary imaging of the present invention.
[0024]
Further, in the above description, as an example in which it is determined that the image has no atmosphere in step SA3, the case where the brightness distribution in the image at the time of the above-described pre-imaging does not reach the bright side (A area side) is given. As described above, when the brightness distribution does not reach the dark side (P area side), it can be moved (shifted) so that the distribution width reaches the darker area. Therefore, an image having an atmosphere can be taken without causing dark portions to rise. When the brightness distribution is widened to the A area side, the degree of spread is large when there is a distribution on the darkest side (P area side), and conversely small when there is no distribution on the dark side (N area side). Similarly, when the brightness distribution is widened to the P area side, the degree of spreading is large when there is a distribution on the brightest side (A area side) and distributed on the bright side (A area side) When there is no, it is better to make it smaller. In such a case, the balance between light and dark is improved and a more natural image can be taken.
[0025]
Further, in the present embodiment, the case where the exposure time (shutter speed) set at the time of the previous exposure control is changed at the time of regular photographing has been described, but instead of this, the gain adjustment of the unit circuit 6 is performed. The gain of the amplifier (AGC) may be corrected. However, in step SA4 described above, calculation of the correction magnification corresponding to it is necessary. Furthermore, if the configuration is such that the aperture value can be set finely or the amount of light of the optical image reaching the CCD 2 can be finely adjusted by other methods, those exposure times can be changed without changing the exposure time. Only the setting may be changed, or both settings may be changed. Even in such a case, the same effect as the present embodiment can be obtained. That is, one or a plurality of setting contents of various exposure amount adjusting means for determining the exposure amount at the time of photographing may be corrected based on the correction value such as the above-described exposure magnification obtained from the distribution data.
[0026]
In the present embodiment, the distribution data generated in step SA2 described above is distribution data indicating the brightness distribution of the entire screen of the reference image at the time of preliminary imaging prior to normal imaging, and normal imaging is performed based on this. The case of performing exposure control at the time has been described. For example, as shown in FIG. 6, the reference image a is divided into a plurality of parts, and the distribution data is generated for the emphasis area b of the reference image a. You may make it perform exposure control at the time of photography. In that case, it is possible to shoot an image in which the emphasis area b has no overexposure or underexposure. In addition, it is better if the photographer can select the priority area b as desired.
[0027]
Further, in the above description, it is determined whether or not the brightness distribution of the reference image at the time of preliminary imaging prior to regular imaging mainly exists on the bright side (A area side) or the dark side (N area side). Although the case where exposure control is performed to widen the brightness distribution during normal shooting according to the result has been described, the exposure control shown in FIG. 7 may be performed separately.
[0028]
That is, FIG. 7 is a flowchart showing another embodiment of the present invention and relates to another exposure control of the MPU 3 in a state where the recording mode is set after the power is turned on. As will be described below, when the recording mode is set, the digital camera 1 displays an image captured by the CCD 2, that is, a through image on the TFT liquid crystal monitor 12. At this time, the MPU 3 performs exposure control so that the display image is always gray with a reflectance of 18% (step SB1). Next, the MPU 3 generates distribution data constituting the histogram described in the above-described embodiment for each divided area when the image captured as a through image, that is, the reference image is divided into a plurality of parts (step SB2). . Subsequently, the MPU 3 indicates that the distribution data in the priority area (see FIG. 6) in each divided area is the number of pixels in the brightest brightness area, as shown in FIG. It is determined whether or not it indicates a histogram with a large amount (for example, a predetermined number or more), that is, whether or not a distribution that causes overexposure in an important part is displayed (step SB3). If the determination result is YES, a negative value is set as a correction value for the appropriate exposure value (step SB4), and the process proceeds to step SB7.
[0029]
If the determination result in step SB3 is NO, the distribution data acquired in step SB2 further shows a histogram in which the distribution state of the reference image at that time is biased toward both ends of light and dark as shown in FIG. It is determined whether or not the image is an object, that is, whether or not the photographing condition indicates backlighting (step SB5). If the determination result is YES, a positive value is set as the correction value for the appropriate exposure value (step SB6). If NO, on the other hand, nothing is done and the process proceeds to step SB7. In step SB7, it is determined whether or not the shutter has been pressed, and the process returns to step SB1 and repeats the above-described processing until it is pressed. When the shutter is pressed eventually therebetween, step SB4 was performed immediately before, or correct for proper exposure value by the correction value that has been set in the processing at step SB6 (however, met the judgment result of step SB5 is NO If not, no correction is performed.) Regular photographing exposure is performed (step SB8). Then, the exposure control process for one shooting is completed.
[0030]
In other words, by correcting the appropriate exposure value according to the brightness distribution state indicated by the distribution data indicating the brightness distribution in the reference image at the time of pre-shooting, an image in which no overexposure occurs in an important part or backlighting Even so, it is possible to capture an image in which the subject does not become dark. Here, in the distribution data indicating the brightness distribution in the reference image at the time of pre-shooting, the brightness information of each pixel constituting the entire reference image or the priority area is reflected as it is. For this reason, compared to the case of using a photometric value in which the brightness information of each pixel unit is averaged, such as the average value of the brightness of the entire reference image or a specific portion used in the conventional exposure control. More appropriate exposure control based on detailed brightness information is possible. As a result, it is possible to focus the area of the whole or Jo Tokoro imaging screen, obtaining image information representing fewer natural image is affected by the difference of imaging conditions. It is also possible to more accurately determine the shooting conditions such as the backlight described above.
[0031]
In the present embodiment, the case where the present invention is mainly used for a digital camera has been described. However, the present invention may be used for other imaging devices such as a video camera and a scanner.
[0032]
【The invention's effect】
As described above, in the present invention, exposure control is performed based on distribution information in which brightness information of each pixel unit constituting the entire imaging screen and a predetermined predetermined emphasis area is reflected as it is. Therefore, compared to the conventional exposure control based on the average photometric value in each divided range of the shooting screen, that is, the brightness information of each pixel constituting the imaging screen is averaged, the brightness information is finer. More appropriate exposure control based on this is possible. In addition, exposure control is performed so that imaging using the light / dark recognition performance by the imaging means to the maximum is possible. Therefore, it is possible to obtain image information representing a more natural image with a wide expression range of light and dark.
[0033]
Furthermore, in the imaging apparatus of the present invention, the imaging condition is determined based on the brightness information of each pixel constituting the image to be captured, so that the imaging condition can be determined more accurately and accordingly I was able to control the exposure. Therefore, highly accurate exposure control is possible.
[0035]
[Brief description of the drawings]
FIG. 1 is a block diagram of a digital camera showing an embodiment of the present invention.
FIG. 2 is a flowchart showing an exposure control process in the same embodiment.
FIG. 3 is a histogram showing an example of a brightness distribution in an image at the time of preliminary shooting.
FIG. 4 is a diagram illustrating a gamma curve during a through image.
FIG. 5 is a histogram showing an example of a brightness distribution in an image at normal photographing.
FIG. 6 is a diagram showing divided areas and priority areas of a screen.
FIG. 7 is a flowchart showing another exposure control process according to another embodiment of the present invention.
FIG. 8 is a diagram illustrating a brightness distribution state in which overexposure occurs in a priority area of a reference image.
FIG. 9 is a diagram illustrating a brightness distribution state indicating backlight in a reference image.
FIG. 10 is a diagram showing the latitude of a human eye and a CCD.
[Explanation of symbols]
1 Digital camera 2 CCD
3 MPU
9 MROM

Claims (5)

In an imaging apparatus provided with imaging means for converting a subject image into image information,
The brightness distribution of each pixel is evaluated by dividing the brightness of each pixel constituting a reference image, which is a reference image taken by the imaging means, prior to regular imaging into a plurality of brightness areas. Distribution information acquisition means for acquiring distribution information indicating
When the distribution information acquired by this distribution information acquisition means determines whether there is a distribution nonexistent side on either the brightest side or the darkest side, and it is determined that this exists Further, the brightness distribution indicated by the distribution information acquired by the distribution information acquisition means is either the bright side or the dark side within the brightness range recognizable by the imaging means and A calculation means for calculating a correction value necessary for moving to the non-existent side;
An image pickup apparatus comprising: an exposure control unit that corrects exposure during normal imaging based on the correction value calculated by the calculation unit.   2. The imaging according to claim 1, wherein the calculation unit calculates the correction value based on an imaging condition determined based on the distribution information, and corrects exposure during normal imaging based on the calculated correction value. apparatus.   The distribution information acquisition means evaluates the brightness of each pixel constituting the predetermined emphasis area of the reference image by dividing it into a plurality of brightness areas, and acquires distribution information indicating the brightness distribution of the emphasis area. The imaging apparatus according to claim 1, wherein: In an exposure control method for an imaging apparatus including an imaging means for converting a subject image into image information,
A reference image serving as a reference is captured by prior imaging prior to normal imaging, and the brightness of each pixel constituting the captured reference image is evaluated by dividing it into a plurality of brightness areas, and the brightness distribution of each pixel a step of acquiring distribution information indicating a
Determining whether there is a non-distributed side on one of the brightest side or the darkest side in the acquired distribution information; and
In this determining step, the brightness distribution indicated by the distribution information acquired when it is determined that there exists is either the bright side or the dark side within the brightness range recognizable by the imaging means. A step of calculating a correction value necessary to move to one side where the distribution does not exist;
And a step of correcting exposure at the time of normal imaging based on the calculated correction value. The brightness of each pixel that constitutes a reference image that serves as a reference, which is captured by the image capturing unit in accordance with prior image capturing prior to normal image capturing, is included in a computer included in an image capturing device that includes an image capturing unit that converts a subject image into image information. The distribution information acquisition means for obtaining the distribution information indicating the brightness distribution of each pixel and evaluating the distribution in a plurality of brightness areas, and the distribution information acquired by the distribution information acquisition means, the brightest side or It is determined whether or not there is a non-distributed side on one of the darkest sides, and if this exists, the brightness distribution indicated by the distribution information acquired by the distribution information acquiring means is determined. An operation for calculating a correction value necessary for moving to either the bright side or the dark side within the brightness range recognizable by the imaging means and to the side where no distribution exists. It means a recording medium characterized by recording a program to function in an exposure control means for correcting the exposure at the time of imaging of the normal based on the calculated correction value by the calculating means.

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