JP2012095214A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device which enables global-shutter photographing having no contrast within a screen, without using a mechanical shutter.SOLUTION: The imaging device comprising an imaging element capable of reading image signals for one frame obtained by photoelectric conversion is provided with: light emission means capable of varying light distribution characteristics; and light distribution control means which controls light distribution by the light emission means in accordance with the contrast within the screen occurring when reading the image signals.

Description

  The present invention relates to an imaging apparatus and a control method thereof, and more particularly to an imaging apparatus including a light emitting device that illuminates a subject and a control method thereof.

In recent years, many digital still cameras and digital video cameras using solid-state imaging devices such as CCD and CMOS have been developed. In particular, CMOS sensors are attracting attention because of their high performance of reading out pixels at high speed.
In a general CMOS sensor, pixel signals are read out sequentially for each line when reading out pixel signals. However, since this sequential readout causes a difference in readout time within the screen, various problems exist.

  Hereinafter, problems caused by this sequential reading will be described.

  There are two types of electronic shutter (pixel charge reset) methods for determining the exposure time: a rolling shutter method and a global shutter method.

  First, the rolling shutter method will be described.

  The rolling shutter system is a system in which an electronic shutter is sequentially applied to each line in the same way as reading so as not to cause a difference in exposure time due to sequential reading, and the exposure time is designed to be the same at all positions in the screen. Is possible. Therefore, if this method is adopted, there will be no difference in exposure time within the screen.

  FIG. 11 is a schematic diagram showing the horizontal axis time t when the rolling shutter is driven and the exposure time in each of the upper to lower rows in the screen. Thus, in the rolling shutter system, as shown in FIG. 11, the exposure time differs depending on the position in the screen (upper screen: t0 to t2, lower screen: t1 to t3). This causes a problem of distortion when a moving subject is photographed. To solve this problem, it is necessary to use a global shutter method described later.

  In the present invention, for simplification of description, pixel signals are sequentially read out line by line from the line on the screen to the line below.

  In the case of the rolling shutter system, when the exposure time is sufficiently short as shown in FIG. 11, the exposure times at the top and bottom of the screen may not overlap at all. This causes a problem that when the auxiliary light is irradiated to the subject with a light emitting device such as a strobe, light is not uniformly applied to the entire screen. Therefore, in general, this is dealt with by not shortening the exposure time. However, Patent Document 1 attempts to solve this problem by changing the irradiation range of the auxiliary light with time.

  Next, the global shutter method will be described.

  In the global shutter method, since all the pixels in the screen are reset at once, the exposure start time is the same for all the pixels. However, since reading is sequentially performed when reading, the exposure end time is shifted between the upper part and the lower part of the screen. FIG. 12 is a schematic diagram showing the horizontal axis time t when the global shutter is driven and the exposure time in each of the upper to lower rows in the screen. As can be seen from FIG. 12, when shooting is performed by the global shutter method, the exposure time at the lower part of the screen is longer than that at the upper part of the screen, and the image becomes brighter toward the lower part of the screen.

  To solve this problem, a method of making the exposure end time the same for all pixels by providing a mechanical shutter mechanism is conceivable. With this method, there is no problem of exposure time shift and exposure time shift.

JP 2005-236513 A

  In the conventional technique disclosed in Patent Document 1 described above, the problem of deviation of the exposure time in the screen, which is a harmful effect of the rolling shutter system, remains. Therefore, the global shutter system is useful for avoiding this problem.

  As an example of the global shutter exposure difference problem, there is a solution that provides a mechanical shutter mechanism. However, the provision of the mechanical shutter mechanism is accompanied by an increase in cost, and there is a significant problem that the response speed of the mechanical shutter becomes a bottleneck when performing high-speed reading, which is a feature of the CMOS sensor.

  Therefore, in recent years, it is desirable to shoot with a global shutter system without using a mechanical shutter. For this reason, the remaining problem is that the exposure start time is the same for all the pixels, but the exposure end time is shifted due to sequential readout, resulting in an exposure time difference in the screen.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an imaging apparatus that can perform global shutter photography without a contrast difference in a screen without using a mechanical shutter.

  In order to achieve the above object, the present invention provides a light emitting means capable of changing a light distribution characteristic in an image pickup apparatus having an image pickup device capable of reading an image signal for one frame obtained by photoelectric conversion. And a light distribution control means for controlling the light distribution of the light emitting means in accordance with a difference in brightness in the screen that occurs when the image signal is read out.

  According to the present invention, it is possible to provide an imaging apparatus that can perform global shutter photography without a contrast difference in a screen without using a mechanical shutter.

1 is a block diagram illustrating a configuration of an imaging apparatus according to an embodiment of the present invention. It is the schematic showing the structure of the light-emitting device 100 which concerns on one Embodiment of this invention. It is the schematic showing the light distribution parameter table of an example of the light distribution pattern which concerns on one Embodiment of this invention, and its result. It is the schematic showing the light distribution parameter table of the example of the light distribution pattern which concerns on one Embodiment of this invention, the light distribution coefficient table, and its result. It is a flowchart which shows the operation | movement at the time of imaging | photography of the imaging device which concerns on 1st embodiment of this invention. It is the schematic showing the light distribution parameter table which concerns on 1st embodiment of this invention. It is the schematic showing the light distribution pattern selection table which concerns on 1st embodiment of this invention. It is a flowchart which shows the operation | movement at the time of imaging | photography of the imaging device which concerns on 2nd embodiment of this invention. It is the schematic showing the light distribution parameter table which concerns on 2nd embodiment of this invention. It is the schematic showing the light distribution pattern selection table which concerns on 2nd embodiment of this invention. It is a schematic diagram for demonstrating the drive of a rolling shutter system. It is a schematic diagram for demonstrating the drive of a global shutter system.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Example 1]
Hereinafter, global shutter imaging according to the first embodiment of the present invention will be described with reference to FIGS.

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

  In FIG. 1, reference numeral 100 denotes a light emitting device that emits LED auxiliary light toward a subject, 101 denotes a light distribution control unit of the light emitting device, and 180 denotes a system control circuit that controls the entire imaging device. The light distribution control unit 101 controls the light amount and light distribution of the light emitting device based on the control by the system control circuit 180.

  Reference numeral 110 denotes a photographing lens. In FIG. 1, the photographing lens 110 is shown as a single lens, but actually includes a plurality of lenses such as a focus lens and a zoom lens. A diaphragm mechanism is also included here. A lens control unit 111 controls the focus, zoom, and aperture of the photographing lens 110 based on control by the system control circuit 180.

  The image sensor 120 is a CMOS sensor that generates and outputs charges corresponding to the amount of incident light by photoelectric conversion. In addition to reading out signals of all pixels, the image sensor 120 adds charges of specific pixels and thins out charges every specific row or column. Can also be read.

  Reference numeral 121 denotes an image sensor driving circuit that drives the image sensor 120 based on control by the system control circuit 180.

  The image signal output from the image sensor 120 is digitized and taken into the digital process circuit 130. The digital process circuit 130 performs various digital signal processing such as gamma processing and color signal processing. At this time, the image signal is written to / read from the memory 140. The output of the digital process circuit 130 can also be displayed on the LCD display 150.

  The image data that has been subjected to image processing by the digital process circuit 130 is compressed via the image conversion circuit 160, written to the memory card 170, and recorded. The image conversion circuit 160 has a function of compressing the image data from the digital process circuit 130 and outputting it to the memory card 170, and a function of expanding the image data read from the memory card 170 and outputting it to the digital process circuit 130. It is a device.

  Further, the system control circuit 180 uses a signal processed by the digital process circuit 130 to perform a TTL (through-the-lens) type autofocus (AF) process, automatic exposure (AE) process, flash pre-flash ( EF) process.

  The operation unit 190 is an operation unit for a photographer to input an instruction to the imaging apparatus, such as a shutter button or a mode switching dial, and the input content is notified to the system control circuit 180.

  FIG. 2 is a schematic diagram illustrating the configuration of the light emitting device 100.

  The light emitting device 100 is an LED array arranged on a matrix horizontally and vertically. In the present embodiment, as shown in FIG. 2, a total of 100 LEDs 200 of 10 horizontal × 10 vertical are combined. At this time, each LED 200 can be expressed by 100 addresses (1, 1) to (10, 10).

  Each LED 200 incorporated in the LED array can individually control the irradiation intensity, and can be lit at an intensity specified by the light distribution control unit 101.

  The light distribution control unit 101 has a table of light distribution patterns, and various light distribution patterns can be realized as an LED array by lighting each LED 200 with a specified intensity.

  As an example, one light distribution parameter table is shown in FIG. This specifies the intensity corresponding to the X and Y addresses of each LED 200. 3B and 3C, the horizontal axis indicates the X direction and the Y direction, respectively, and the vertical axis indicates the light emission intensity.

  For example, when the light distribution parameter table shown in FIG. 3A is followed, as shown in FIGS. 3B and 3C, the distribution in which the irradiation intensity gradually decreases from the top to the bottom of the LED array. It becomes a light pattern. As a result, it is possible to irradiate auxiliary light that brightens the top of the screen and darkens the bottom.

  As a next example, FIGS. 4A and 4B show a light distribution parameter table and a light distribution coefficient table. The light distribution coefficient table is obtained by multiplying each intensity determined by the light distribution parameter table corresponding to the X and Y addresses of each LED 200 by a coefficient.

  When FIGS. 4A and 4B are followed, as shown in FIGS. 4C and 4D, the light distribution pattern is such that the irradiation intensity gradually decreases from the center of the LED array to the outside. . This makes it possible to perform irradiation with the irradiation range narrowed down from the center. This is an operation equivalent to narrowing the radiation directivity.

  Thus, the light distribution control unit 101 can control the light emitting device 100 to irradiate an arbitrary light distribution pattern by having a plurality of light distribution parameter tables and light distribution coefficient tables.

  The system control circuit 180 multiplies the irradiation intensity according to each of the object distance information obtained from the focus adjustment result and the zoom lens position information, and selects a light distribution coefficient table that widens or narrows the irradiation directivity. I can do it. This is because, for example, when the zoom is positioned on the telephoto side, the intensity is increased so as to irradiate farther than when the zoom is positioned on the wide-angle side, and the irradiation directivity is reduced according to the shooting angle of view. A light distribution coefficient table is selected.

  FIG. 5 is a flowchart showing an operation at the time of shooting by the imaging apparatus according to the present embodiment. Hereinafter, the photographing method according to the present embodiment will be described with reference to FIG.

  First, in step S501, it waits for the switch SW1 to be turned on by, for example, halfway operation (for example, half-pressing) of the shutter button included in the operation unit 190, and when it is turned on, the process proceeds to step S502 to perform exposure control. I do. In exposure control, the system control circuit 180 determines exposure conditions (aperture, exposure time, sensitivity) used for shooting.

  Next, in step S503, focus adjustment control is performed. In the focus adjustment control, the system control circuit 180 controls the focus lens of the photographic lens 110 via the lens control unit 111 to focus on the subject. In step S504, it is determined whether or not the switch SW2 that is turned on by, for example, a full-pressing operation of the shutter button is turned on. If the switch SW2 is turned off, the process returns to step S501 and the above processing is repeated. .

  In step S505, the system control circuit 180 determines whether to turn on the LED auxiliary light according to the sensitivity, exposure time, and information from the operation unit 190 determined in step S502. If not, the process proceeds to step S507 as normal shooting processing.

  If it is set to turn on the LED auxiliary light, the process proceeds to step S506.

  In step S506, the system control circuit 180 determines the light emission condition of the LED auxiliary light based on the exposure condition obtained in step S502, and transmits to the light distribution control unit 101 which light distribution parameter table is used.

  In step S507, the subject is photographed by controlling the light distribution control unit 101, the lens control unit 111, and the image sensor control circuit 121 under the conditions determined above. Since the processing of the photographed image has been described above, it is omitted here.

Finally, a specific method for determining the light distribution pattern in step S506 will be described.
In the present embodiment, tables as shown in FIGS. 6A to 6C are prepared as light distribution parameter tables.

In step S506, first, an exposure time parameter is extracted from the exposure conditions obtained in step S502. This is SS (shutter speed).
By the way, the exposure time difference between the top and bottom of the screen caused by the global shutter shooting is always the same amount if the driving method is the same. Therefore, the amount that appears as the difference in brightness between the top and bottom of the screen becomes significant when the overall exposure time is short, and becomes a level that is relatively unnoticeable when the exposure time is sufficiently long.

  In the present embodiment, in order to obtain a light distribution pattern that cancels the contrast between the top and bottom of the screen caused by global shutter photography, the light distribution pattern is determined based on the SS value.

  Specifically, it follows the light distribution pattern selection table shown in FIG. (For example, when SS is 50 ms, the light distribution pattern (b) is used.) When SS is short, the light distribution pattern also has a large difference in the vertical direction, and when SS is long, it is flatter. It is close to a light distribution.

  In this embodiment, only three types of light distribution patterns are described for the sake of simplicity of explanation. However, by setting a subdivided light distribution parameter table, a setting that cancels the brightness difference between the top and bottom of the screen with higher accuracy. Needless to say, you can.

  As described above, according to the present embodiment, it is possible to provide an imaging apparatus that can perform global shutter photography without a contrast difference in a screen without using a mechanical shutter.

[Example 2]
Next, Example 2 will be described.

  In this embodiment, in order to cancel the brightness difference between the upper and lower portions of the screen due to the global shutter shooting, in addition to the contents of the first embodiment, a light distribution pattern having further optimum directivity can be obtained.

FIG. 8 is a flowchart illustrating an operation at the time of shooting of the imaging apparatus according to the present embodiment.
The difference from the global shutter shooting according to the first embodiment is the position of determining the light distribution coefficient in step S807 in FIG. Therefore, this part will be described.

  Referring to the flowchart of FIG. 8, in step S807, a light distribution coefficient table is determined according to focal length information and zoom lens position information, and multiplied by the light distribution parameter table determined in step S806 to distribute light distribution parameters. To decide. Using this parameter, shooting is performed in step S808.

  Other configurations and the shooting flow are the same as those in the first embodiment.

  Hereinafter, a specific method for determining the light distribution coefficient pattern in step S807 in the present embodiment will be described.

  In the present embodiment, it is assumed that the light distribution coefficient table has tables as shown in FIGS.

  In step S807, information on whether the focal length is the close side or the telephoto side is acquired from the result of the focus adjustment control in step S803, and a distinction is made. Similarly, the zoom lens position information Z obtained in a step (not shown) is acquired, and Wide, Middle, and Tele are distinguished.

  In this embodiment, in order to cancel the brightness difference between the top and bottom of the screen due to global shutter shooting, in addition to the contents of the first embodiment, in order to obtain a light distribution pattern having an optimum directivity, the above focal length information and zoom position are used. The light distribution coefficient pattern is determined by the information.

  Specifically, it follows the light distribution pattern selection table shown in FIG. (For example, if the position of the zoom lens is Wide and the focal length information is on the telephoto side, the light distribution coefficient pattern (b) is used.) This is a light distribution pattern when the distance to the subject is small and the angle of view is narrow. However, when the distance to the subject is short and the angle of view is wide, the light distribution becomes closer to a flat light distribution.

  In this embodiment, the focal length information and zoom lens position information patterns are reduced for the sake of simplicity of explanation, but it goes without saying that the effect is further increased by further subdividing the pattern.

  As described above, according to the present embodiment, it is possible to provide an imaging apparatus that can perform global shutter photography without a contrast difference in a screen without using a mechanical shutter.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined. Also, when a software program that realizes the functions of the above-described embodiments is supplied from a recording medium directly to a system or apparatus having a computer that can execute the program using wired / wireless communication, and the program is executed Are also included in the present invention. Accordingly, the program code itself supplied and installed in the computer in order to implement the functional processing of the present invention by the computer also realizes the present invention. That is, the computer program itself for realizing the functional processing of the present invention is also included in the present invention. In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS. As a recording medium for supplying the program, for example, a magnetic recording medium such as a hard disk or a magnetic tape, an optical / magneto-optical storage medium, or a nonvolatile semiconductor memory may be used. As a program supply method, a computer program that forms the present invention is stored in a server on a computer network, and a connected client computer downloads and programs the computer program.

100 light emitting device,
101 Light distribution controller

Claims (7)

In an imaging apparatus having an imaging device capable of reading out an image signal for one frame obtained by photoelectric conversion,
A light emitting means capable of changing the light distribution characteristics;
An image pickup apparatus comprising: a light distribution control unit that controls light distribution of the light emitting unit in accordance with a light / dark difference in a screen generated when the image signal is read.   The control of the light distribution control means controls the light distribution of the light emitting device in a direction that cancels out according to the exposure time difference in the screen caused by sequentially reading out the image signal from the image sensor. The imaging apparatus according to claim 1.   The imaging apparatus according to claim 1, wherein the control of the light distribution control unit is changed according to distance information to a subject.   The imaging apparatus according to claim 1, wherein the control of the light distribution control unit is changed according to zoom position information of a lens in the imaging apparatus.   The imaging apparatus according to claim 1 or 2, wherein the light distribution control means is selected from parameters of a light distribution characteristic selection table set in advance.   The imaging apparatus according to claim 1, wherein the light emitting unit is an LED array in which a plurality of LEDs are arranged.   The imaging device according to claim 6, wherein the light emitting unit can control light distribution characteristics by making a difference in light emission intensity or light emission time for each LED of the LED array.