JP4314968B2 - Camera device and light amount control method - Google Patents

Description

  The present invention relates to a camera device and a light amount control method in which a light amount is controlled using a physical element capable of controlling light transmittance.

  Conventionally, a mechanical diaphragm has been used as a means for controlling the amount of incident light in a camera or the like. In an imaging optical system, light from a subject is incident on an imaging element that performs light source conversion such as a CCD (Charge Coupled Device) through the optical system. In such a configuration, a mechanical aperture is provided for the optical system to control the amount of light incident on the image sensor, thereby performing exposure control.

  On the other hand, there has been proposed a camera device that performs exposure supplementation by controlling the amount of light incident on an image sensor using a physical element such as a liquid crystal capable of controlling light transmittance in an image pickup optical system. By performing light amount control using a physical element, the mechanical aperture mechanism can be omitted, and the camera module can be reduced in size.

  In recent years, products in which cameras are incorporated in mobile phone terminals have become widespread, but physical properties that can control light transmittance can be used when mechanical apertures cannot be used due to size restrictions. , Suitable for use.

In the physical property element capable of controlling the light transmittance, the light transmittance can be continuously changed from the highest state to the lowest state. Therefore, a camera device using such a physical property element is operated so as to continuously control the light transmittance of the physical property element, as described in Patent Document 1.
JP-A-5-34763

  By the way, there is a problem that many physical property elements used for the light amount control of the camera device have a long response time of the light transmittance change with respect to the control signal. For example, in view of the frame frequency of the camera device, there are many physical property elements that require several frames to several tens of frames or more for the response of light transmittance to the control signal. There is also a problem that a large difference occurs in response time between when the light transmittance is changed greatly and when it is changed small.

  Also, some physical property elements such as liquid crystal may not have a uniform change in the light transmittance over the entire surface of the physical property element when the light transmittance is largely changed. When such a physical property element is used, there is a problem that when the light transmittance is changed, the resolution of the transmitted light transmitted through the physical property element is deteriorated.

  In addition, the relationship between the light transmittance of the physical property element and the control signal for changing the light transmittance often varies with each physical property element. In this case, in the manufacturing process of the camera device or the like, correction values are individually given to absorb variations. However, when the light transmittance is continuously changed, the correction value based on the light transmittance density is not always a constant value. In order to perform the correction, the control signal corresponds to the resolution of the control signal or the control signal. It is necessary to have a correction value that is coarser than the resolution of the above, but does not affect continuous control. Therefore, there has been a problem that the amount of correction value becomes enormous.

  In addition, it is necessary to obtain an enormous amount of correction values for each apparatus, and it takes a long time to obtain correction values, resulting in an increase in manufacturing cost.

  Accordingly, an object of the present invention is to provide a camera capable of obtaining a quick response speed and good image quality with a simple configuration by using a physical element capable of controlling light transmittance, such as liquid crystal, for light amount control. It is in providing an apparatus and the light quantity control method.

In order to solve the above-described problems, the present invention provides a camera device in which the amount of incident light on an image sensor is controlled using a physical element that can control the light transmittance, and the change ratio of the light transmittance is constant. Based on the ratio of the change in light transmittance that can be completed within a predetermined period, with a multi-stage state, the physical element that can control the light transmittance and the light transmittance of the physical element are incident A physical element control unit that sequentially switches and controls in multiple steps according to the amount of light, an image sensor that picks up incident light incident through the physical element, and a shutter speed of the image sensor continuously according to the amount of incident light possess a controllable shutter control means, the control by the properties element control means controls the amount of incident light to the imaging device in combination with the control of the shutter speed by the shutter control unit, in accordance with the amount of incident light Shi When the shutter speed reaches a predetermined threshold, a plurality of stages are switched by one step by the physical property element control means, and the amount of incident light controlled by the shutter control means by switching the shutter speed by one stage. In this camera apparatus, the shutter speed is controlled within a range corresponding to the control amount after the speed corresponding to the speed is returned .

Further, the present invention provides a light quantity control method in which the light quantity is controlled by using a physical property element capable of controlling the light transmittance , and has a plurality of states in which the ratio of change in the light transmittance is constant , changes based on the ratio of the change completion possible light transmission within a predetermined time period, the light transmittance of the controllable physical element the light transmittance, the first controlling sequentially switching a plurality of steps in accordance with the amount of incident light Controlling the amount of incident light on the image sensor by combining the control step and a second control step for continuously controlling the shutter speed of the image sensor that captures incident light incident through the physical property element according to the amount of incident light. When the shutter speed reaches a predetermined threshold according to the amount of incident light, the first control step switches a plurality of steps to one step, and the second control step switches the shutter speed to one step. After returning only the speed corresponding to the control amount of the incident light amount is controlled by being a light quantity control method to control the shutter speed range corresponding to the control amount.

  As described above, according to the present invention, since the light transmittance of the physical property element capable of controlling the light transmittance is controlled by sequentially switching to a plurality of stages in accordance with the amount of incident light, the physical property element has a limited range. It is only necessary to perform control at the same time, and the control at each stage can be stably performed, and a high-speed and stable response to the control can be obtained.

  According to this invention, the physical property element capable of controlling the light transmittance is controlled step by step for each control level such that the reaction to the control is completed within a predetermined period. Therefore, there is an effect that it is possible to realize a control characteristic capable of responding at high speed even when a physical property element having a characteristic that requires a long time to respond when controlled within the controllable range is used.

  Therefore, when the present invention is applied to the exposure correction of the camera device, there is an effect that a stable output image can be provided particularly for dynamic subject photography.

  Further, by applying the present invention to a camera device, it is possible to appropriately control the output of the image sensor in a camera device that does not have a mechanical aperture mechanism for miniaturization, and the range of the incident light quantity from the subject can be widened. Therefore, there is an effect that a high-performance camera device capable of controlling exposure in an illuminance range that could not be controlled due to whiteout of an image, occurrence of smear, and the like can be configured in a small size.

  Furthermore, according to the embodiment of the present invention, an effect of realizing an exposure correction system capable of obtaining an image having a better SN ratio and gradation resolution than when exposure control is performed by the amplification factor of the amplifier of the circuit. There is.

  Furthermore, when the amount of incident light on the image sensor is controlled by the mechanical aperture, the depth of field changes due to the change in the aperture diameter, but the amount of incident light can be reduced using a physical property element capable of controlling the light transmittance. By performing the control, the amount of incident light can be controlled without changing the aperture diameter. Therefore, by using the present invention, there is an effect that it is possible to realize an exposure correction system that can keep the depth of field constant.

  Further, when shooting under a fluorescent lamp or the like, shooting is performed with a shutter speed of about 1/100 second in order to prevent flickering that causes a beat between the commercial power supply frequency and the frame or field frequency. In one embodiment of the present invention, by setting the light blocking threshold and / or the open threshold to be close to 1/100 second, a wide illuminance range in which flicker does not occur can be obtained, and control by AGC can be reduced. Therefore, according to the embodiment of the present invention, there is an effect that it is possible to realize an exposure correction system that obtains an image with a small SN ratio and good gradation resolution.

  Furthermore, in the embodiment of the present invention, since only the shutter speed is used as the determination threshold value, there is an effect that the mounting is easy.

  Furthermore, according to the present invention, by controlling the light transmittance of the physical property element stepwise, it is possible to easily control even non-linear transmission characteristics, and to solve the problem of the reaction speed. .

  Further, according to the present invention, since the light transmittance of the physical property element is controlled within a limited range for each stage, the response time of the physical property element is varied depending on whether the light transmittance is largely changed or smallly changed. There is an effect that a large difference is hardly generated.

  Furthermore, by controlling the physical element within a limited range, there is an effect that a relatively uniform light transmittance can be obtained over the entire surface of the physical element. Further, since the physical property elements are controlled within a limited range, stable characteristics can be obtained, and a large correction value is not required.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a configuration of an example of a camera device to which an embodiment of the present invention is applied. The physical property element 1 is made of, for example, liquid crystal and can control light transmittance. The physical element 1 is configured, for example, by sandwiching a liquid crystal between two opposing transparent electrodes that have been subjected to a predetermined alignment treatment, and the light transmittance is close to 100% by controlling the voltage applied to the electrodes. It is possible to change from the transmission state to the shielding state where the light transmittance is close to 0%. The light transmittance of the physical element 1 is variably controlled based on the drive signal supplied from the physical element drive signal generation circuit 8.

  The image pickup device 2 is composed of, for example, a CCD (Charge Coupled Device), converts incident light into an electric signal by photoelectric conversion, and outputs the signal as an image pickup signal. The photoelectric conversion accumulation time in the image sensor 2 is controlled based on the drive signal supplied from the image sensor drive signal generation circuit 3. The charge accumulation time during photoelectric conversion in the image sensor 2 is the shutter speed of the image sensor 2. That is, in the image pickup device 2, an electronic shutter is configured by controlling the charge accumulation time during photoelectric conversion.

  In FIG. 1, the image pickup optical system of the camera such as the zoom mechanism and the focus mechanism is not directly related to the gist of the present invention, and is omitted to avoid complexity.

  Light from the subject enters the image sensor 2 via the physical element 1. The imaging signal output from the imaging device 2 is supplied to an AGC (Auto Gain Control) circuit 4. The AGC circuit 4 provides an automatic control amplification function that keeps the camera output signal within a certain range. For example, the control unit 7 generates a control signal that keeps the level of the output signal within a certain range and supplies it to the AGC circuit 4. The AGC circuit 4 adjusts the gain based on the control signal supplied from the control unit 7 and amplifies the input imaging signal. The imaging signal output from the AGC circuit 4 is supplied to the control signal extraction circuit 6 and the signal processing circuit 5. The signal processing circuit 5 outputs the supplied imaging signal to the output terminal 9 as an image signal by a predetermined process.

  The control signal extraction circuit 6 detects, for example, the imaging signal supplied from the AGC circuit 4 and extracts a signal necessary for control by the control unit 7. The signal extracted by the control signal extraction circuit 6 is supplied to the control unit 7. The control unit 7 is, for example, a microcomputer, which generates various control signals based on signals supplied from the control signal extraction circuit 6 and controls each unit of the camera apparatus using the various control signals. To do. Various control signals output from the control unit 7 are supplied to the AGC circuit 4, the signal processing circuit 5, the image sensor driving signal generation circuit 3, and the physical element driving signal generation circuit 8, respectively.

  In the camera having the configuration as shown in FIG. 1, one image is continuously output per predetermined time. Hereinafter, this single image is referred to as one frame, and the number of frames output per second is referred to as a frame frequency. For example, when 30 images are output per second, the frame frequency is 30 Hz. Many of the processes for generating a camera image are controlled in units of frames. Therefore, in the configuration of FIG. 1, it is required that the control for appropriately maintaining the level of the output signal with respect to the amount of incident light is appropriately performed for each frame.

  Here, both the accumulation time control of the image pickup device 2 and the gain control of the AGC circuit 4 are set within one frame time for the control value (control signal) from the control unit 7. Can have the property of being changed. On the other hand, the physical property element 1 does not necessarily end the change of the light transmittance within one frame time with respect to the control value from the control unit 7. That is, the response speed of the light transmittance change with respect to the control signal of the physical property element 1 requires a long time to complete the change when the light transmittance is largely changed. On the other hand, when the light transmittance is changed small, it has a characteristic that the change can be completed in a shorter time.

  FIG. 2 shows a configuration of a more specific example of the camera apparatus of FIG. In FIG. 2, the same reference numerals are given to portions common to FIG. 1, and detailed description thereof is omitted. The physical element 1 has liquid crystal as a main component and changes the light transmittance according to a duty ratio of a PWM (Pulse Width Modulation) signal. The physical element 1 is used in close contact with a lens (not shown), for example.

  The PWM signal is generated by the PWM output circuit 23 by phase-modulating two PWM signals based on the control of the microcomputer 22. By phase-modulating the two PWM signals based on the control of the microcomputer 22, the duty ratio of the PWM signal can be controlled. The phase-modulated PWM signal is supplied to the driver 15, amplified to an amplitude (for example, 12 V) necessary for driving the physical element 1, and supplied to the physical element 1.

  The CCD 11 corresponds to the image sensor 2 of FIG. 1, and an electronic shutter is controlled based on a shutter pulse generated by a TG (Timing Generator) 21 based on the control of the microcomputer 22. For example, the CCD 11 performs charge accumulation and signal charge readout every frame. The accumulated charge is once discharged in the middle of one frame, and the shutter control is performed by reading out the accumulated charge in the remaining period of one frame. The remaining period of one frame in which charges for reading are accumulated is used as the shutter speed. That is, an electronic shutter operation can be performed by generating a shutter pulse at a predetermined timing within the frame period and discharging the charge in the CCD 11 in accordance with the shutter pulse.

  Light from the subject is incident on the CCD 11 via a lens system (not shown) and the physical property element 1 and converted into an imaging signal by photoelectric conversion. The imaging signal output from the CCD 11 is supplied to an AFE (Analog Front End) circuit 12. The AFE circuit 12 is an amplifier that amplifies an input analog signal, and an amplification factor is adjusted according to an AGC (Auto Gain Control) control signal supplied from the microcomputer 22. The imaging signal amplified by the AFE circuit 12 is supplied to the image signal processing circuit 30 in the camera signal processing circuit 13.

  The image signal processing circuit 30 performs a predetermined process on the supplied imaging signal based on the control signal of the microcomputer 22 and outputs it as an image signal composed of a luminance signal Y and a color signal C. For example, the image signal processing circuit 30 performs primary color separation processing on the supplied imaging signal to generate an RGB signal including an R (red) signal, a G (green) signal, and a B (blue) signal. White balance processing and gamma correction processing are performed on the RGB signals. The RGB signal subjected to the white balance process and the gamma correction process is converted into an image signal composed of a luminance signal Y and a color signal C, and is output from the image signal processing circuit 30. The image signal output from the image signal processing circuit 30 is led to the output terminal 32.

  In the image signal processing circuit 30, the luminance signal Y is extracted and supplied to the detection circuit 31. The detection circuit 31 calculates an integral value for one frame of the luminance signal Y and supplies it to the microcomputer 22.

  The microcomputer 22 controls the entire camera device by generating various control signals in advance and supplying the control signals to the respective units constituting the camera device. A ROM (Read Only Memory) 24 stores various data and programs in advance. An exposure control program for causing the microcomputer 22 to execute the exposure control method according to the present invention is also stored in the ROM 24 in advance. The microcomputer 22 reads data and programs stored in the ROM 24 and controls the operation of the camera device based on the read data and programs.

  For example, the microcomputer 22 determines the amount of incident light with respect to the CCD 11 based on the integrated value for one frame of the luminance signal Y received from the detection circuit 31 so that the amount of incident light and the image signal level output from the CCD 11 are appropriate. In addition, control signals for performing shutter speed control, control of the physical element 1 and AGC control using the AFE circuit 12 are generated. Each generated control signal is supplied to the AFE circuit 12, the TG 21 and the PWM output circuit 23, respectively.

  The nonvolatile memory 14 stores a shutter speed value that is a threshold value for light transmittance control, a step control gain amount of light transmittance, and the like. Details of the shutter speed value and the step control gain amount will be described later.

  The TG 21 generates various timing signals such as a frame pulse for designating the frame timing in addition to the shutter pulse described above based on the control of the microcomputer 22 and supplies the timing signal to each part of the camera device (not shown). .

  FIG. 3 shows an example of light transmittance characteristics with respect to the duty ratio of the physical property element 1. FIG. 3 shows the light transmittance as a dimming gain amount (dB) based on the maximum light transmittance of the physical property element 1 as a base point. As shown in FIG. 3, the light transmittance characteristic of the physical property element 1 does not have a linear relationship with the duty ratio of the PWM signal, but has a value with a duty ratio (about 5% in the example of FIG. 3). ), The light transmittance suddenly decreases, and changes gently when the duty ratio is about 50%. The physical property element 1 shown in the example of FIG. 3 can change the light transmittance by about 11 dB at maximum by controlling the duty ratio.

  FIG. 4 shows an example of the relationship between the dimming gain amount and time when the light transmittance of the physical property element 1 is changed. FIG. 4 also shows the light transmittance as a light attenuation gain amount based on the maximum light transmittance of the physical element 1 as in FIG. Here, the frame frequency is 15 Hz, the duty ratio is changed from 0% to 100% in the 11th frame, the duty ratio is maintained at 100% from the 12th frame to the 44th frame, and the duty ratio is set in the 45th frame. Is changed from 100% to 0%. The system is fixed at 15 FPS (Frame Per Second) and the shutter speed is fixed at 1/100 second.

  The reaction speed of the physical property element 1 when the duty ratio is changed is generally about 20 ms. Therefore, in the system of FIG. 4, a predetermined dimming gain should be obtained within one frame. However, in practice, as shown in FIG. 4, it takes about 35 frames (approximately 2.3 seconds) until the change in the amount of dimming gain with respect to time becomes gentle and stabilizes to some extent. This is due to the performance of the physical property element 1 itself, and occurs when the duty ratio is controlled so that the dimming gain amount is increased at once, for example, 6 dB or more.

  That is, in the case where the light transmittance of the physical property element 1 is continuously controlled with respect to the incident light amount, the duty ratio is changed so that the light transmittance of the physical property element 1 is greatly changed when the incident light amount changes greatly. As a result, as shown in FIG. 4, a phenomenon that takes a long time for the light transmittance to actually change to a predetermined value occurs.

  In order to solve this problem, in the present invention, the light transmittance of the physical property element 1 is controlled only at a limited level. In this embodiment using the physical property element 1 having the characteristics shown in FIG. 3, as shown in an example in FIG. 5, the minimum value of the dimming gain is set to 0 dB, and the maximum value is set to 10 dB. Six control levels are set by dividing the dimming gain amount into 5 equal parts every 2 dB. That is, according to the present invention, the physical property element 1 is provided with several stages such that the ratio of change in light transmittance (attenuation gain amount) is constant (2 dB in the example of FIG. 5). The light transmittance of 1 is controlled while sequentially switching a plurality of stages according to the amount of incident light.

  In the example of FIG. 5, in the physical property element 1, when the dimming gain amount is switched from 0 dB to 2 dB, the duty ratio is switched from 0% to 7.0%. When the dimming gain amount is switched from 2 dB to 4 dB, the duty ratio is switched from 7.9% to 9.2%. When the dimming gain amount is switched from 4 dB to 6 dB, the duty ratio is switched from 9.2% to 12.1%. When the dimming gain amount is switched from 6 dB to 8 dB, the duty ratio is switched from 12.1 dB to 18.7%. Further, when the dimming gain amount is switched from 8 dB to 10 dB, the duty ratio is switched from 18.7% to 47.5%.

  In the control of the physical element 1, a limiter is provided in a controllable amount so that the control level is the same level between consecutive frames or the light transmittance (attenuation gain amount) is only one level different. This level interval is set within a range in which the reaction of the physical element is completed within one frame. For example, if the reaction of the physical property element 1 can be completed within one frame with respect to the attenuation level of 2 dB, the control level interval is set within 2 dB as the attenuation level.

  As an example, let us consider a case where the amount of incident light changes greatly and brightly, and the attenuation gain amount by the physical property element 1 is increased correspondingly. In the embodiment of the present invention, when the dimming gain amount is greatly changed as described above, the physical property element 1 is controlled step by step so that the dimming gain amount changes every frame.

  For example, when it is desired to change the dimming gain amount from 0 dB to 10 dB, the physical property element 1 is controlled step by step so that the dimming gain amount changes by 2 dB every frame. More specifically, the dimming gain amount is switched from 0 dB to 2 dB in the first frame, switched from 2 dB to 4 dB in the second frame, switched from 4 dB to 6 dB in the third frame, and 6 dB in the fourth frame. The physical property element 1 is controlled so that 10 dB is changed stepwise over 5 frames. Similarly, when it is desired to change the attenuation gain by 8 dB, the physical property element 1 is controlled so as to change stepwise over 4 frames, and when it is desired to change 6 dB, the physical property changes so as to change stepwise over 3 frames. The element 1 is controlled.

  As described with reference to FIG. 4, when the amount of attenuation gain of the physical property element 1 is changed by 10 dB at a time, it takes 35 frames or more to complete the reaction of the physical property element 1. Although illustration is omitted, when the amount of attenuation gain of the physical element 1 is changed to 6 dB and 8 dB at a time, similarly, it takes 35 frames or more to complete the reaction of the physical element 1. On the other hand, when the attenuation gain of the physical property element 1 is changed by 6 dB by performing the control according to the embodiment of the present invention, the reaction of the physical property element 1 is completed in 3 frames at 6 dB = 2 dB × 3. Similarly, when changing 8 dB, the reaction of the physical property element 1 is completed in 5 frames even when changing 10 dB.

  As described above, by controlling the light transmittance (attenuation gain amount) of the physical property element 1 in a stepwise manner, the problem of the reaction speed can be solved, and the non-linear transmission characteristic can be easily controlled.

  When the attenuation gain of the physical property element 1 is changed by 4 dB, even when the control according to the embodiment of the present invention is not performed, the reaction of the physical property element 1 is completed in one frame, and the control according to the embodiment is performed. The number of reaction completion frames (4 dB = 2 dB × 2) takes more time, but considering the entire light transmittance control range of the physical property element 1, it takes a maximum of 35 frames or more. However, the control is completed in 5 frames, and it can be said that higher speed control is realized as a whole.

  Next, an example in which the control of the physical property element 1 described above is applied to a camera device will be described. First, the basic concept of exposure control will be described with reference to FIG. FIG. 6 shows an example in which the light amount control is performed using the shutter and the AGC, and shows a relationship of an example of the dynamic range, the shutter speed, and the AGC (Auto Gain Control) operation in the exposure control of the camera device. In FIG. 6, it is assumed that NdB exposure control can be performed by controlling the shutter speed, and MdB exposure control can be performed by controlling AGC. In FIG. 6, the left side is the low illuminance side of the incident light from the subject, the right side is the high luminance side, and the incident light from the subject changes from low illuminance to high luminance.

  Here, the exposure control is control that appropriately maintains the output level with respect to the incident light amount, and the dynamic range is a range of incident light amount that can appropriately maintain the camera output. The shutter speed is the charge accumulation time of the image sensor 2 (CCD 11). The AGC is an amplifier whose amplification factor is controlled in accordance with a control signal. For example, the output can be stabilized by using the control signal as a signal based on the output of the entire system.

  Operations in the range (a) and the range (b) in FIG. 6A will be described respectively.

(A) AGC Control Range AGC control is performed mainly on the low illumination area side, and when the light amount is further required when the shutter speed is the longest, the AGC gain is increased to amplify the signal. The gain value of AGC is controlled in the range from the minimum value AGCMIN to the maximum value AGCMAX.

(B) Shutter speed control range Control based on the shutter speed is performed mainly on the high-luminance region side, and the signal level is increased by increasing the shutter speed (shortening the time during which the shutter is open) when the amount of light is excessive. Suppress. The shutter speed ranges from the maximum value SHTMAX (the shutter speed is the slowest, that is, the state in which the shutter is opened for the longest time) to the minimum value SHTMIN (the shutter speed is the fastest, that is, the time for which the shutter is opened is the shortest). It is controlled in the range.

  A value obtained by summing the exposure control level MdB in the above-described (a) AGC control range and (b) the exposure control level NdB in the shutter speed control range is the dynamic range according to the conventional method. That is, by using the exposure control by the shutter and the exposure control by the AGC in combination, a dynamic range of (N + M) dB can be obtained as shown in FIG. 6B.

  An exposure control method according to an embodiment of the present invention will be described with reference to FIGS. As described above, the control with only the physical property element 1 cannot perform fine control within the attenuation gain amount of 2 dB. Therefore, in this embodiment, fine control within 2 dB is realized by appropriately controlling both the shutter speed and the AGC control in addition to the control of the physical property element 1.

  In the system shown in FIG. 7 and FIG. 8, the dimming gain amount of the light transmittance of the physical element 1 is divided into five stages for each K dB, and the total (5 × K) dB dimming gain amount is controlled by the physical element 1. Is possible. Further, as described with reference to FIG. 6, it is assumed that exposure control can be performed for N dB by controlling the shutter speed and by M dB by controlling AGC.

  FIG. 7 shows an example where the incident light from the subject changes from the low illuminance side to the high luminance side. That is, in FIG. 7, the left side is the low illuminance side and the right side is the high luminance side, and the state changes from the left side to the right side in FIG. In FIG. 7, range (a) and range (b) are an AGC control range and a shutter control range, respectively, as in FIG. 6, and range (c) is a combination of shutter control and physical element control 1. It is the range to do. The range (c) is provided in a range sandwiched between the shutter control range (b) on the low illuminance side and the shutter control range (b) on the higher luminance side.

  The operations of range (a), range (b), and range (c) will be described. Range (a) and range (b) are the same as in the case of FIG. 6 described above. That is, control by AGC is performed mainly by controlling the AGC gain value in the range from the minimum value AGCMIN to the maximum value AGCMAX on the low illuminance region side (range (a)), and the shutter control is mainly performed with high brightness. This is done by controlling the shutter speed in the range from the maximum value SHTMAX to the minimum value SHTMIN on the region side (range (b)).

  The range (c) will be described. After shifting from the AGC control range (a) to the shutter control range (b), when the amount of incident light from the subject increases, exposure control is performed by shortening the shutter speed in accordance with the amount of incident light. At this time, when the shutter speed value reaches a predetermined light shielding threshold and becomes smaller than that, the control level of the physical element 1 is decreased by one step, that is, K dB (see FIG. 7B), and the shutter speed value is controlled from the light shielding threshold to K dB. The shutter speed is set to a value that is longer by that amount (see FIG. 7A).

  According to such control, when the shutter speed value becomes smaller than the light shielding threshold, the amount of incident light on the image sensor 2 decreases by KdB due to the change in the light transmittance of the physical element 1, but the shutter speed is increased by KdB. Since this is set, the decrease in the amount of incident light is canceled out, and there is no change in the amount of the image signal output from the image sensor 2 (CCD 11).

  Thereafter, as the amount of incident light from the subject increases, the control level of the physical element 1 is decreased by one step, and the shutter speed value is decreased according to the amount of incident light. When the shutter speed value becomes smaller than the light shielding threshold, the control level of the physical property element 1 is further lowered by one step. This process is repeated according to the amount of incident light, and the control level of the physical element 1 is lowered to the maximum control level (light transmittance MIN). If the amount of incident light is still large, the range (b) on the right end side of FIG. As shown, the shutter speed value is controlled below the light-shielding threshold value while controlling the physical property element 1 at the maximum control level.

  FIG. 8 shows an example where incident light from a subject changes from a high luminance side to a low illuminance side. That is, in FIG. 8, it is assumed that the state changes from the right side to the left side in FIG. Even in this case, the control of the range (a) and the range (b) is the same as in the case of FIG.

  The range (c) will be described. When the amount of incident light from the subject decreases with the control level of the physical element 1 lowered by one or more steps, the shutter speed is set longer. At this time, when the shutter speed value reaches the predetermined opening threshold value and becomes larger than that, the control level of the physical property element 1 is increased by one step, that is, KdB (see FIG. 8B), and the shutter speed value is increased from the opening threshold value to the KdB control amount. (See FIG. 8A).

  By controlling in this way, as in the example of FIG. 7, when the shutter speed value becomes larger than the open threshold, the amount of incident light on the image sensor 2 (CCD 11) becomes K dB due to the change in light transmittance of the physical element 1. However, since the shutter speed is set shorter by K dB, the increase in the incident light amount is canceled out, and the amount of the image signal output from the image sensor 2 does not change.

  Thereafter, the control level of the physical property element 1 is increased by one step as the amount of incident light from the subject decreases, and the shutter speed value is increased in accordance with the amount of incident light. When the shutter speed value becomes larger than the open threshold, the control level of the physical property element 1 is further increased by one step. This process is repeated according to the amount of incident light, and the control level of the physical element 1 is increased to the minimum control level (light transmittance MAX). If the amount of incident light is still small, the range (b) on the left side of FIG. As described above, while controlling the physical property element 1 at the minimum control level, the shutter speed value from the shutter speed value smaller by KdB than the open threshold to the maximum value SHTMAX is controlled.

According to the control as described above, the total of the control ranges of the light transmittance (attenuation gain amount) in the ranges (a), (b), and (c) is the dynamic range. In the example of FIGS. 7 and 8, the dynamic range is as follows (see FIGS. 7C and 8C).
NdB + MdB + (5 × K) dB = (N + M + (5 × K)) dB

  If the shutter speed value changed by KdB exceeds the open threshold value (or the light shielding threshold value) when the light shielding threshold value (or the open threshold value) is reached, the control level and shutter speed value of the physical property element 1 are set. It will oscillate. Therefore, the light shielding threshold value and the opening threshold value are set so that the gain difference between the light shielding threshold value and the opening threshold value is larger than the gain amount for one step (KdB in this example) of the control level.

  As described above, in the embodiment of the present invention, since a wide dynamic range is obtained by controlling the amount of incident light to the image sensor 2 (CCD 11), the SN is better than the method of controlling the amplification factor of the amplifier of the circuit. An image with a high ratio and high gradation resolution can be obtained. In addition, since a wide dynamic range can be obtained, it is possible to control exposure even in an illuminance range that cannot be controlled due to the occurrence of whiteout or smearing of the image due to the characteristics of the image sensor 2 (CCD 11). In addition, since only the shutter speed is used as the determination threshold (the light shielding threshold and the open threshold), it can be mounted relatively easily.

  Also, when shooting under a fluorescent lamp or the like, in order to prevent flicker caused by a beat between the commercial power supply frequency and the frame or field frequency, it is common to shoot with a shutter speed of about 1/100 second. Has been done. In one embodiment of the present invention, by setting the light blocking threshold and / or the open threshold to be close to 1/100 second, a wide illuminance range in which flicker does not occur can be obtained, and control by AGC can be reduced. Therefore, according to the embodiment of the present invention, it is possible to realize an exposure correction system that obtains an image with a small SN ratio and good gradation resolution.

  The light shielding threshold value, the opening threshold value, the control levels of the physical property element 1 and the duty ratio information corresponding to the control levels set in this way are stored in advance in the nonvolatile memory 14. The microcomputer 22 reads these pieces of information from the nonvolatile memory 14 and performs the control as shown in FIGS. 7 and 8 based on the read information.

  In the embodiment of the present invention, since the amount of attenuation gain by the physical property element 1 is changed only in one step per frame, it takes time for the response of the physical property element 1 by the number of (number of set levels−1) frames. . However, when the physical property element 1 has such a characteristic that the response time is short enough to switch between a plurality of steps within one frame time, the control level of the physical property device 1 is switched in a plurality of steps one by one within one frame. By controlling, it becomes possible to realize a higher speed control characteristic.

  If the difference in light transmittance for each control level of the physical property element 1 is within the allowable range as the output signal level of the camera, the control of only the control level of the physical property element 1 can be performed without changing the shutter speed and AGC. Exposure control can be performed, and a simple exposure correction system can be realized.

  Furthermore, when the amount of light incident on the image sensor 2 is increased or decreased by the aperture mechanism, the depth of field changes because the aperture diameter changes. In the camera device to which the embodiment of the present invention is applied, the incident light amount is controlled by changing the light transmittance with the physical property element 1, and exposure control can be performed without changing the aperture ratio. An exposure correction system that can increase or decrease the amount of light without changing the depth of field can be realized.

  In the above description, the camera device according to the embodiment of the present invention has been described as not using a diaphragm mechanism using mechanical means or the like. Of course, a diaphragm mechanism may be provided for the imaging optical system.

It is a block diagram which shows roughly the structure of an example of the camera apparatus which can apply one Embodiment of this invention. It is a block diagram which shows the structure of a more specific example of the camera apparatus which can apply one Embodiment of this invention. It is a basic diagram which shows the light transmittance characteristic of an example with respect to the duty ratio of a physical property element. It is a basic diagram which shows the example of the relationship between the amount of light attenuation gain, and time at the time of changing the light transmittance of a physical property element. It is a basic diagram which shows the setting of an example of the control level according to the dimming gain amount of a physical property element. It is a figure for demonstrating the basic view of exposure control. It is a figure for demonstrating the exposure control method by one Embodiment of this invention. It is a figure for demonstrating the exposure control method by one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Physical element 2 Image pick-up element 3 Image pick-up element drive signal generation circuit 4 AGC circuit 6 Control signal extraction circuit 7 Control part 8 Physical element drive signal generation circuit 11 CCD
12 AFE circuit 14 Non-volatile memory 15 Driver 21 TG (timing generator)
22 microcomputer 23 PWM output circuit 31 detection circuit

Claims (6)

In the camera device configured to control the amount of incident light on the image sensor using a physical element capable of controlling the light transmittance,
The light transmittance can be controlled based on the ratio of the light transmittance change that can be completed within a predetermined period of time and has a plurality of states where the light transmittance change ratio is constant. A physical element;
The light transmittance of the properties element, an imaging element for imaging an incident light entered through the physical element control means and the physical properties element so as to control sequentially switched to the several stages in accordance with the amount of incident light,
The shutter speed of the imaging device have a <br/> continuously controllable shutter control means in accordance with the amount of incident light,
Controlling the amount of incident light on the image sensor in combination with the control by the physical element control means and the control of the shutter speed by the shutter control means,
When the shutter speed reaches a predetermined threshold in accordance with the amount of incident light, the physical element control unit switches the plurality of steps to one step, and the shutter control unit switches the shutter speed to the one step. A camera device in which the shutter speed is controlled within a range corresponding to the control amount after being returned by a speed corresponding to the control amount of the incident light quantity controlled by being performed . Upper Symbol predetermined period, a camera apparatus according to claim 1 corresponding to the unit time for processing the output signal of the image pickup device. Upper SL is input the output signal of the image pickup device further comprises a controllable amplification means the amplification factor for the output signal of the imaging device in accordance with the amount of incident light,
2. The amount of incident light on the image pickup device is controlled by combining the control by the physical element control unit, the control of the shutter speed by the shutter control unit, and the control of the amplification factor by the amplification unit . Camera device. Upper Symbol amplifying means, the shutter speed of the shutter control means is controlled to maximum, further when the amount of incident light is required, the camera apparatus according to claim 3 which is adapted to control the amplification factor. The camera device according to claim 1,
A camera apparatus, further comprising a diaphragm unit that controls the amount of light incident on the imaging element by changing an aperture ratio. In the light amount control method in which the light amount is controlled using a physical property element capable of controlling the light transmittance,
The light transmittance can be controlled based on the ratio of the light transmittance change that can be completed within a predetermined period of time and has a plurality of states where the light transmittance change ratio is constant. A first control step of controlling the light transmittance of the physical property element by sequentially switching the plurality of stages according to the amount of incident light ;
A second control step of continuously controlling the shutter speed of the image pickup device that picks up incident light incident through the physical property element according to the amount of incident light;
To control the amount of incident light to the image sensor,
When the shutter speed reaches a predetermined threshold according to the amount of incident light, the plurality of stages are switched by one stage by the first control step, and the shutter speed is changed by 1 by the second control step. It said after returning only the speed corresponding to the control amount of the incident light amount, the light amount control method in <br/> so to control the shutter speed range corresponding to the control amount is controlled by being switched out.

Images