KR20070021886A - Imaging apparatus - Google Patents

Abstract

Even an imaging device comprising a plurality of pixels capable of performing an exposure operation and a read operation at different timings, there is provided an imaging device that can accurately obtain the amount of light of the main emission based on preliminary light emission of a flash.

Before the pre-emission of the flash 21 and at the time of pre-emission, the exposure operation of all the pixels of the imaging element 13 is started at the same time, the image is taken before the pre-emission and pre-emission, and the detection circuit 17 By using this method, detection values before and during preliminary light emission are obtained. The calculation circuit 18 subtracts the detection value before the preliminary light emission from the detection value at the time of preliminary light emission, calculates the differential detection value of the preliminary light emission exclusive of the influence of external light, and calculates the amount of light of the present light emission amount based on the difference detection value. do.

Imaging device

Description

Imaging device {IMAGING APPARATUS}

The present invention relates to an image capturing apparatus in which photographing is performed by emitting a flash.

Background Art [0002] An imaging apparatus is known that preliminarily emits flash when performing flash photography, detects reflected light from a subject, and obtains the amount of light emitted by the main light for flash photography. As the imaging device of the imaging device, a charge coupled device (CCD) image sensor is mainly used. In recent years, as the pixel size of the imaging device is further advanced, a CMOS image sensor is attracting attention as a new imaging device. CMOS image sensors have advantages such as random access of pixel signals, high speed reading, high sensitivity, low power consumption, and the like.

However, in the conventional imaging device using the CMOS image sensor, since the exposure operation and the reading operation are different for each pixel, during the preliminary flash emission, only a part of the area of the imaging device can affect the preliminary light emission. There is a problem that it is difficult to accurately calculate the amount of light. In order to solve this problem, it is provided to lengthen the exposure time of the preliminary light emission of a flash (for example, refer patent document 1 (Unexamined-Japanese-Patent No. 2000-196951)).

However, in an imaging device in which the exposure time of preliminary light emission is sufficiently long, when preliminary light emission is performed when there is external light, the amount of input light in a certain region of the CMOS image sensor may exceed the dynamic range of the CMOS image sensor. Since the image signal does not become the original signal level, it leaves a problem that it is difficult to accurately obtain the amount of light of the present light emission.

This invention is made | formed in view of such a situation, The objective is an imaging element which consists of several pixel which can perform exposure operation and reading operation by different timing, like XY address type image sensor represented by CMOS image sensor. Even if it is, it is providing the imaging device which can obtain the light quantity of this light emission based on the preliminary light emission of a flash with high precision.

In order to achieve the above object, the imaging device of the present invention comprises an image pickup device comprising a flash for irradiating light onto a subject, a plurality of pixels capable of exposure operation and read operation at different timings, and the image pickup device. A detection circuit for detecting the brightness of the captured image information, and a control circuit for controlling operations of the flash, the imaging element, and the detection circuit, wherein the control circuit reserves the flash before the operation of the main light emission of the flash. Light emission is performed, the image at the time of preliminary light emission is picked up by the imaging element, and the brightness of the image information at the time of preliminary light emission picked up is detected by the detection circuit, and based on the brightness of the image information at the time of preliminary light emission detected. Wherein the control circuit calculates the light amount of the main light emission of the flash, wherein the control circuit The exposure operation of all the pixels of the imaging device is started at the same time so as to capture an image at the time of preliminary light emission.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a schematic configuration of an imaging device according to a first embodiment.

2 is a schematic configuration diagram of a CCD image sensor.

3 is a schematic configuration diagram of a CMOS image sensor.

4 is a time chart illustrating the operation of a CCD image sensor.

5 is a time chart illustrating the operation of a CMOS image sensor.

6 is a diagram illustrating a control flow of flash photography.

7 illustrates an example of an image of a subject;

8 is a diagram showing an example of calculation of the difference detection value in the absence of external light;

9 is a diagram showing an example of calculation of the difference detection value when there is external light;

10 is a diagram showing a flash photography still image sequence of a conventional CCD sensor.

Fig. 11 is a diagram showing a flash photography still image sequence of a conventional CMOS sensor.

Fig. 12 is a diagram showing an image at the time of preliminary light emission obtained by a conventional CCD sensor.

Fig. 13 is a diagram showing an image at the time of preliminary light emission obtained by a conventional CMOS sensor.

Fig. 14 is a diagram showing a flash photography still image sequence of the CMOS sensor of Example 1;

FIG. 15 is a diagram showing an example of calculation of the difference detection value according to the first embodiment; FIG.

In order to achieve the purpose of accurately obtaining the amount of light emitted by the flash based on the preliminary light emission of the flash, at the time of preliminary flash light operation, the exposure operation of all the pixels of the image pickup device is started simultaneously, and the image at the time of preliminary light emission is performed. The imaging device is configured to image.

(Example 1)

EMBODIMENT OF THE INVENTION Hereinafter, the imaging device of Example 1 of this invention is demonstrated with reference to drawings.

1 is a diagram showing a schematic configuration of an imaging device of Example 1. FIG.

As shown in FIG. 1, the imaging device of Embodiment 1 includes a lens 11, an aperture 12, an imaging device 13, an AGC (auto gain controller) 14, and an A / D converter 15. The camera signal processing circuit 16, the detection circuit 17, the arithmetic unit 18, the memory 19, the light emitting circuit 20, the flash 21, the lens driver 22 and the memory 23. Equipped.

The lens 11 passes the light from the subject when shooting, and focuses on the imaging element 13. The aperture 12 changes its aperture so that the amount of input light obtained through the lens 11 is appropriate for the sensitivity of the imaging element 13. In addition, the aperture 12 has a function of a shutter. The imaging element 13 is composed of a plurality of pixels in which color filters of R, G, and B are arranged, and photoelectrically converts each input light of each pixel input through the lens 11 into an analog image signal (charge). . Moreover, the imaging element 13 consists of an XY address type image sensor, for example, a CMOS image sensor, and is comprised so that each exposure operation and reading operation of a some pixel may be performed by a different timing. CMOS image sensors are advantageous in terms of low power consumption and high speed reading.

The AGC 14 amplifies the video signal generated by the imaging element 13. The A / D converter 15 converts the analog video signal amplified by the AGC 14 into a digital video signal. The camera signal processing circuit 16 performs various signal processings well known to the digital video signal converted by the A / D converter 15, for example, a white balance circuit and a YC separation circuit (not shown). , A filter circuit, an aperture controller, and a gamma correction circuit. The detection circuit 17 detects a distribution of brightness and color in the screen included in the video signal processed by the camera signal processing circuit 16. The detected value indicating the brightness is, for example, an integrated value of luminance signals of each pixel in the screen.

The computing device 18 is configured by, for example, a microcomputer, and is based on the distribution of brightness and color detected by the detection circuit 17 and the video signal processed by the camera signal processing circuit 16. To control each part of it. The calculation device 18 is, for example, an exposure timing control signal for controlling the exposure operation and the read operation of each pixel of the imaging element 13, a gain control signal for controlling the gain of the AGC 14, and the lens 11. The lens control signal for controlling the focal point and the aperture of the aperture 12 through the lens driver 22 and the flash control signal for controlling the light emission operation of the flash 21 are calculated and output. The storage device 19 stores the control data calculated by the calculation device 18.

The light emitting circuit 20 drives the flash 21 according to the flash control signal calculated by the arithmetic unit 18 at the time of flash photography. The flash 21 emits light in accordance with a drive signal from the light emitting circuit 20. The lens driver 22 drives the lens 11 and the aperture 12 in accordance with the lens control signal calculated by the computing device 18. The storage device 23 temporarily stores a video signal (for example, image information of a moving picture) processed by the camera signal processing circuit 16.

2 is a schematic configuration diagram of a CCD image sensor, and FIG. 3 is a schematic configuration diagram of a CMOS image sensor.

As shown in Fig. 2, the CCD image sensor includes a plurality of pixels 31 arranged in a two-dimensional matrix, a V transfer register 32 equal to the number of columns of the plurality of pixels 31, and an H transfer. The register 33 is provided. Each pixel 31 photoelectrically converts each input light into an analog video signal (charge). The plurality of V transfer registers 32 transmits each image signal of each photoelectrically converted pixel every pixel (one line) in the vertical direction. The V transfer register 32 transfers the video signal of each pixel 31 for one line transmitted by the plurality of V transfer registers 32 for each pixel in the horizontal direction.

When light is irradiated to the CCD image sensor, each light of each pixel 31 is photoelectrically converted into a charge (image signal). In each pixel 31, charges corresponding to the respective input light amounts are accumulated. Given a signal for transferring charge to the CCD image sensor, the charge accumulated in each of all the pixels 31 is simultaneously transferred to each of the V transfer registers 32. The charge of each pixel 31 (each line) of the V transfer register 32 is transferred in the vertical direction for each pixel (one line), and is transferred to the H transfer register 33. The video signal of one line of pixels transferred to the H transfer register 33 is transmitted and output in the horizontal direction every pixel. The plurality of V transfer registers 32 and H transfer registers 33 are shielded from light. For this reason, the electric charge of the pixel 31 once transmitted to them does not receive light from the exterior, and is kept constant.

As shown in FIG. 3, in the CMOS image sensor, a plurality of pixels 41 arranged in a two-dimensional matrix form and a plurality of pixels 41 in the same row are commonly connected and electrically connected to each other. A column 42 is provided for transferring each charge (video signal) transferred from the pixel 41 in a horizontal direction every pixel. The CMOS image sensor does not have the equivalent of the V transfer register 32 of the CCD image sensor. For this reason, each pixel 41 of a CMOS image sensor can enlarge the area compared with each pixel 31 of a CCD image sensor. Therefore, the sensitivity can be improved by extending the dynamic range. The CMOS image sensor can be configured to freely select and read the pixel 41 at the address. On the other hand, since the pixels 41 in the same row cannot be read simultaneously, the exposure operation and the read operation become complicated.

4 is a time chart showing the operation of the CCD image sensor, and FIG. 5 is a time chart showing the operation of the CMOS image sensor.

As shown in Fig. 4, the exposure operation of the CCD image sensor is performed on all the pixels 31 at the same time. Since the CMOS image sensor has no equivalent to the V transfer register 32 of the CCD image sensor, when one pixel 41 is read, the other pixel 41 is influenced by external light and charges are accumulated. As shown in FIG. 5, the exposure operation of each pixel 41 of the CMOS image sensor needs to match the read operation of each pixel 41. In this example, in order to make the exposure time of all the pixels 41 the same, the exposure start timing of each pixel (each line) 41 is shifted every line.

6 is a diagram illustrating a control flow of flash photography.

As shown in Fig. 6, when the still image pick-up mode is selected, the integral value of the luminance signal included in the image signal picked up by the imaging element 13 is detected by the detection circuit 17, and the arithmetic circuit 18 By this, it is judged whether the external light is bright or dark based on the integral value of the luminance signal (step S1). When it is judged that the external light is bright, the process proceeds to step S2 where normal photography is performed in which the flash 21 does not emit light. On the other hand, when it is judged that external light is dark in step S1, it progresses to step S3 and flash photography is performed. In addition, when there is an operation mode in which flash photography is forcibly performed irrespective of the contrast of external light, the process proceeds to step S3 regardless of the result of step S1, and flash photography is performed.

In flash photography, first, the aperture diameter of the diaphragm 12, the exposure time (shutter) of the imaging element 13, and the gain of the AGC 14 are set (step S3). It is preferable that the aperture of the diaphragm 12 is set so that the input light of the near subject does not exceed the dynamic range of the imaging element 13 at the time of preliminary light emission of the flash 21. The preliminary light emission is a process for calculating the light amount of the main light emission. When input light exceeding the dynamic range is input to the imaging device 13, a distorted (searched) image signal is obtained, and the light amount of the main light emission. Cannot be calculated with precision. In addition, it is preferable to shorten the exposure time of the imaging element 13 as much as possible. If the exposure time is long, the influence of external light is increased, the dynamic range for detecting the light amount of preliminary light emission is narrowed, and the calculation accuracy of the light amount of the main light emission is reduced. The gain of the AGC 14 is preferably set slightly lower so as to reduce the influence of noise of the video signal.

Next, while the flash aperture 21 does not emit light while fixing the set aperture, exposure time, and gain, the exposure operation and the read operation before preliminary light emission are performed by the imaging element 13, and the detection circuit 17 The pre-lighting detection value a, which is an integral value included in the luminance signal of the video signal, is detected and stored in the storage device 23. The detection value (a) before preliminary light emission means the detection value of only external light without preliminary light emission (step S4).

Next, preliminary light emission is performed by the flash 21 at a predetermined amount of light while fixing the set aperture, exposure time and gain (step S5), and the exposure operation and the read operation at the time of preliminary light emission by the imaging element 13. The detection circuit 17 detects the preliminary light emission value b, which is an integral value included in the luminance signal of the video signal, and is stored in the storage device 23 by the detection circuit 17. The detection value b at the time of preliminary light emission means the detection value containing preliminary light emission and external light (step S6).

Next, the preliminary light detection value b and the preliminary light emission detection value a stored in the storage device 23 are read out by the calculation circuit 18, and the preliminary light emission from the detection value b during preliminary light emission. The difference detection value obtained by subtracting the previous detection value a is calculated. The differential detection means a detection value that excludes external light and includes only preliminary light emission (step S7). Next, the light emission amount of the main light emission of the flash 21 is determined by the calculation circuit 18 based on the difference detection value (step S8), and the light emission of the flash 21 is performed according to the obtained light emission amount, and the flash photography is performed. This is performed (step S9).

It is preferable that the exposure operation before the preliminary light emission by the imaging element 13 in step S4 and the exposure operation during the preliminary light emission by the imaging element 13 in step S6 be performed in a shorter time. Flash photography is generally performed under low light conditions, but rarely does not have external light. In addition, for example, flash photography is also performed at the time of highlighting portrait photography in which backlight is darkly locked. When there is such external light, the correct detection value, in particular, the detection value (b) at the time of preliminary emission cannot be obtained due to the influence of the external light, and the correct differential detection value may not be obtained.

7 is a diagram illustrating an example of an image of a subject. 8 shows an example of calculation of the difference detection value when there is no external light, and FIG. 9 is a view showing an example of calculation of the difference detection value when there is external light.

The flash photographing of the image with a round image A in the center of the screen shown in FIG. 7 is performed, and the output of the image pickup device at the screen center position shown by the dotted line in the vertical direction in FIG. The calculation result of the differential detection value based on the following will be described.

As shown in Fig. 8, in the absence of external light, the output of the image pickup device before preliminary light emission is zero, and the detection value a before preliminary light emission also becomes zero. At the time of preliminary light emission, the detection value b at the time of preliminary light emission with a large output of the part corresponded to phase A is obtained. As a result, the difference detection value coincides with the detection value b at the time of preliminary light emission.

As shown in Fig. 9, when there is external light, before the preliminary light emission, the detection value (a) before preliminary light emission corresponding to the external light is obtained. At the time of preliminary light emission, preliminary light emission is added to external light and input into an imaging element. At this time, the luminance signal whose output of the imaging element exceeds 100%, that is, the luminance signal which exceeds the dynamic range of the imaging element, is clipped. As a result, the differential detection value is excluded from the clipped portion, and is slightly distorted. Therefore, it is not possible to calculate the correct amount of emitted light. As described above, flash photography when there is little external light is rare. For this reason, by making the exposure operation before preliminary light emission and preliminary light emission as short as possible, it is necessary to make the influence of external light small and to allow sufficient allowance for the dynamic range of the imaging element at the time of preliminary light emission.

Fig. 10 is a diagram showing a flash photography still image sequence of a conventional CCD sensor, and Fig. 11 is a diagram showing a flash photography still image sequence of a conventional CMOS sensor. 12 is a figure which shows the image at the time of preliminary light emission obtained by the conventional CCD sensor, and FIG. 13 is a figure which shows the image at the time of preliminary light emission obtained by the conventional CMOS sensor.

As shown in Fig. 10, when a conventional CCD sensor is used for the imaging device, the exposure before preliminary light is started at time T1 in the moving picture photographing mode, the exposure at preliminary light is started at time T2, and each detection is detected. The value is obtained and the difference detection value is calculated. Then, the camera enters the still image shooting mode and flash photography according to the present light emission is performed. As shown in Fig. 12, the influence of preliminary light emission in the exposure operation at the time of preliminary light emission is given to all regions within the screen.

As shown in Fig. 11, even when a conventional CMOS sensor is used for the imaging device, similarly, exposure before preliminary light is started at time T1 in the moving picture photographing mode, and exposure at preliminary light is started at time T2. Each detection value is obtained and a differential detection value is calculated. However, as shown in FIG. 13, since the time of preliminary light emission is short as a few 10 microseconds, the influence of preliminary light in the exposure operation at the time of preliminary light emission is limited to a part area (upper screen) in the screen. For this reason, only the detected value of the external light without the influence of preliminary light emission can be obtained from the remaining areas of the screen (the screen center part and the screen lower part). Therefore, since the detection value at the time of preliminary light emission cannot be obtained with high precision, the light quantity of this light emission cannot be calculated with high precision.

Fig. 14 is a diagram showing a flash photography still image sequence of the CMOS sensor of the first embodiment.

As shown in Fig. 14, the imaging device of Embodiment 1 of the present invention, when starting exposure before preliminary light emission and starting exposure when preliminary light emission, starts to charge the electric charges of all the pixels of the imaging element 13. Sweep and start the exposure operation of all the pixels in the screen at the same time. The influence of preliminary light emission in the exposure operation at the time of preliminary light emission is obtained all the way from the top to the bottom in the screen. Therefore, the detection value at the time of preliminary emission can be obtained with high precision. On the other hand, since it is not possible to read all the pixels in the screen at the same time, the reading of each pixel in the screen is performed sequentially by shifting for each line. The exposure time before the preliminary light emission and at the time of preliminary light emission becomes longer as the pixel of a lower line becomes long, the pixel of a 1st line is the shortest (for example 1 / 4000sec), and the pixel of the last line is the longest (for example, 1 / 100 sec).

The exposure time before the preliminary light emission and at the time of preliminary light emission varies depending on the top and bottom of the screen. However, by shortening the exposure time, the influence of external light given to the detection value during preliminary light emission can be reduced. Originally, preliminary light emission is an operation performed to calculate the light quantity of the main light emission. Therefore, it is only necessary to accurately detect the amount of reflected light from the subject during preliminary light emission. In addition, the imaging device of Example 1 subtracts the pre-luminescence detection value from the pre-luminescence detection value by detecting the pre-luminescence detection value in addition to the detection value during the preliminary light emission, and differential detection including only the preliminary light emission from which external light is excluded. Get chi. Thereby, the difference of the exposure time of the upper and lower screens in each exposure before and during preliminary light emission is canceled, and the differential detection value containing only the preliminary light emission from which external light was excluded can be obtained. Therefore, a high precision differential detection value can be obtained, and therefore, the light quantity of the main light emission with high precision can be obtained.

FIG. 15 is a diagram showing an example of calculation of the difference detection value according to the first embodiment. FIG.

Similar to the differential detection shown in Figs. 8 and 9, flash photography of the image having a round image A in the center of the screen shown in Fig. 7 is performed, and the screen center position shown by the dotted line in the vertical direction in Fig. 7 is shown. The calculation result of the differential detection value based on the output of the image pickup device, that is, the detection value, will be described.

As shown in Fig. 15, before the preliminary light emission, since the pixel at the top of the screen has an extremely short exposure time of 1/4000 sec, the image output is almost zero. And since the exposure time becomes longer for the pixel of the line located below the inside of a screen, the influence of external light also increases gradually. At the time of preliminary light emission, the output of the part corresponded to the image A becomes large, and also influenced by external light. However, in both before and after preliminary light emission, since the amount of external light included in each input light is small compared to the amount of preliminary light emission, the output of the imaging element does not exceed 100%, that is, imaging Image output that does not exceed the dynamic range of the device can be obtained.

As described above, according to the imaging device of the first embodiment, at the time of preliminary light emission of the flash, the exposure operation of all the pixels of the imaging element 13 is simultaneously started to capture an image at the time of preliminary light emission. For this reason, the effect of preliminary light emission can be given to all the areas of an imaging element, shortening the exposure time of an imaging element. Therefore, it is advantageous to obtain an accurate amount of light of the present light emission. The light emission time of the preliminary light emission of the flash 21 is set in a short time so that the input light amount of the imaging element 13 does not exceed the dynamic range of the imaging element 13. For this reason, since the image pick-up element 13 can image | capture the image without distortion faithfully reproduced, the input light amount is advantageous in obtaining the light quantity of this light emission more accurately.

Further, in addition to the detection value during preliminary light emission, the pre-light emission detection value is subtracted from the preliminary light emission detection value by detecting the pre-light emission detection value to obtain a differential detection value including only preliminary light emission in which external light is excluded. This makes it possible to obtain a differential detection value including only preliminary luminescence excluding external light, which is advantageous in determining the amount of light of the main luminescence with high accuracy.

In FIG. 14, the output of the imaging device 13 is one circuit at 2V (for two cycles of the vertical synchronization signal) during the period before the preliminary light emission and the preliminary light emission are performed by the imaging device 13. As a result, a sparse video signal (movie) is obtained. In addition, the difference in the exposure time in the screen also affects, during which the disturbed image is output from the image pickup device. Therefore, when the video signal before several V has been stored in the storage device 23 in advance, and the exposure operation before the preliminary exposure is started by the imaging device 13, instead of the image captured by the imaging device 13, What is necessary is just to be comprised so that the video signal of several V before memorize | stored in the memory | storage device 23 is read out, and it outputs to the image recorder or image output system of a later stage. Thereby, it is possible to prevent the user from recognizing the disturbance of the video.

According to the imaging device of the present invention, at the time of preliminary flash operation, the exposure operation of all the pixels of the imaging device starts at the same time, so that the input light amount of all the regions of the imaging device does not exceed the dynamic range of the imaging device as much as possible. Since it is possible to influence preliminary light emission in all areas of the image pickup device while shortening the exposure time, it is advantageous to obtain a high amount of light of the main light emission with high accuracy.

Claims (6)

An imaging element comprising a flash for irradiating light onto a subject, a plurality of pixels capable of exposure and reading operations at different timings, a detection circuit for detecting the brightness of image information captured by the imaging element, and the flash And a control circuit for controlling the operation of the imaging device and the detection circuit, The control circuit causes pre-emission of the flash before the operation of the main light emission of the flash, images the image at the time of pre-emission by the imaging element, and detects the brightness of the image information at the time of the imaged pre-emission. An imaging device that detects by a circuit and calculates the amount of light emitted by the flash based on the brightness of the detected image information at the time of preliminary light emission. And the control circuit starts an exposure operation of all the pixels of the imaging element at the time of preliminary light emission of the flash to image an image at preliminary light emission. The method of claim 1, And a storage device for storing image information picked up by the imaging device before the preliminary light emission operation of the flash, The control circuit reads the image information stored in the storage device, instead of the image at the time of preliminary light picked up by the imaging element, when the imaging of the image at the time of preliminary light is started by the imaging element. And an output to an image recording apparatus or an image output apparatus. An imaging element comprising a flash for irradiating light onto a subject, a plurality of pixels capable of exposure and reading operations at different timings, a detection circuit for detecting the brightness of image information captured by the imaging element, and the flash And a control circuit for controlling the operation of the imaging device and the detection circuit, The control circuit causes pre-emission of the flash before the operation of the main light emission of the flash, images the image at the time of pre-emission by the imaging element, and detects the brightness of the image information at the time of the imaged pre-emission. Detected by the circuitry, and before the operation of preliminary flashing of the flash, the image before preliminary light not emitted by the flash is picked up by the imaging device, and the brightness of the image information before the preliminary preliminarily photographed is detected by the detecting circuit. Imaging to calculate the difference between the brightness of the image information before pre-emission detected by the detection circuit and the brightness of the image information at the time of pre-emission, and calculate the light emission amount of the main light of the flash based on the calculated difference value As a device, The control circuit starts the exposure operation of all the pixels of the imaging device at the same time before the preliminary light emission operation of the flash and at the preliminary light emission operation of the flash to capture an image before preliminary light emission and preliminary light emission. An imaging device characterized by the above-mentioned. The method of claim 3, And a storage device for storing image information picked up by the imaging device before the image before preliminary light is picked up by the imaging device, The control circuit reads the image information stored in the storage device, instead of the image before preliminary light emission and preliminary light emission captured by the imaging device, when imaging of the image before preliminary light emission is started by the imaging device. And an output to an image recording apparatus or an image output apparatus of a subsequent stage. The method according to claim 1 or 3, The imaging device is an imaging device comprising an XY address type image sensor. The method of claim 5, The XY address type image sensor comprises a CMOS image sensor.

Images