JP4426427B2 - Camera and exposure control method - Google Patents

Description

  The present invention relates to a camera and an exposure control method. The present invention also relates to a camera and an exposure control method that can shorten the startup time.

  2. Description of the Related Art Conventionally, there is a digital camera provided with a distance measuring sensor for automatic focus adjustment (AF) and a photometric sensor for automatic exposure adjustment (AE). In addition, a digital camera has been proposed in which an AE photometric sensor is also used as an AF range sensor and spot photometry data is obtained using the output of the range sensor. A camera that reduces the photometric error caused by the spectral sensitivity of the distance measuring sensor and obtains accurate spot photometric information from the output of the distance measuring sensor has also been proposed (see Patent Document 1).

  By the way, in a digital camera, it is common to continuously capture an image in advance and determine it on a display device in order to determine exposure and focus (focus position) before actual shooting (storage of subject image data). It has become. The photographer can determine the framing while viewing the display image, and can confirm the brightness level and the in-focus position of the captured image. Here, AE is performed by evaluating whether or not the luminance level of the captured image is a target level. If the target level is not reached, the exposure is brought close to appropriate exposure by feedback control that gradually changes the aperture and shutter speed based on the luminance level of the captured image.

On the other hand, immediately after turning on the power of the digital camera, there is no data in the digital camera for the image to be taken now. Therefore, immediately after the power is turned on, a predetermined reference value (fixed value) or data of the captured image recorded immediately before the power is turned off (a value when the power is turned off) is read, and this is the initial value in the feedback control. It is common to perform AE by resetting the aperture and shutter speed as values.
JP-A-9-203857

  However, when a conventional digital camera is turned on when the subject brightness is extremely bright or dark, it takes time to stabilize the exposure from a fixed value to an appropriate state. Even when reading values at the time when the power is turned off in the past, if the shooting environment differs greatly between the time when the power is turned off and the current time, it takes more time to stabilize the exposure than when using a fixed value. It becomes. Therefore, with conventional digital cameras, it takes time for the exposure to stabilize to an appropriate state from the time the power is turned on, preventing the reduction of the time (start-up time) from when the power is turned on until the first picture can be taken. There is a problem that. In addition, the camera described in Patent Document 1 does not have a technical idea that the exposure time is quickly brought close to an appropriate state when the power is turned on, and the activation time is shortened. In current digital cameras and the like, the length of startup time is a major factor in determining product value.

The present invention has been made to solve the above-described problems, and provides a camera and an exposure control method that can quickly bring the exposure close to an appropriate state at the time of startup and can shorten the startup time. With the goal.
It is another object of the present invention to provide a camera and an exposure control method that can quickly bring the exposure close to an appropriate state even when the luminance of the subject changes abruptly.

  In order to achieve the above object, a camera according to the present invention includes an imaging unit (lens, CCD, etc.) for imaging a subject, an aperture variable unit for changing an aperture, a shutter speed variable unit for changing a shutter speed, It comprises at least one of a gain variable section that varies the amplification degree of the output, the exposure changing means for changing the exposure state in the imaging means, and the exposure changing means based on the output of the imaging means Automatic exposure adjusting means for variably controlling the state of the camera, a distance measuring sensor for measuring the distance to the subject and having at least a photoelectric conversion function, and at least the automatic exposure adjusting means based on the output of the distance measuring sensor And high-speed exposure control means for setting an initial state or a reference state of the variable control.

According to the present invention, the initial value in the exposure control can be set by the high-speed exposure control means using the output of the distance measuring sensor used for AF or the like. Therefore, according to the present invention, the exposure state can be brought close to the optimum value at high speed by the high-speed exposure control means before or during the time-consuming conventional AE (AE using the output of the imaging means). . Therefore, the present invention can quickly bring the exposure close to an appropriate state at the time of start-up or when the luminance of the subject suddenly changes, and the start-up time and the shooting interval can be shortened.
That is, a distance measuring sensor used for AF or the like generally has a photoelectric conversion function, and thus can detect a rough value of the luminance of the subject. Therefore, the exposure (aperture, shutter speed, gain, etc.) can be directly controlled at high speed based on the luminance of the subject detected by the distance measuring sensor.
Here, in the AE of a conventional digital camera, an exposure period to the CCD that constitutes the imaging means, an image data transfer period from the CCD to the memory, an AE calculation period, and the like form one exposure control sequence. Since each period of this exposure control sequence is synchronized with a vertical synchronization signal (VD) which is a reference for capturing and transferring image data of one screen, one period (1 field = 1 frame) of the vertical synchronization signal is required. Become. In the conventional AE, since the luminance level of the object is detected from the output of the CCD, the exposure state is changed using the detection result, and further, the feedback control for repeatedly detecting the luminance level and changing the exposure state is performed. Compared with high-speed exposure control means that simply controls exposure based on a distance measuring sensor, AE requires a long time. On the other hand, according to the high-speed exposure control means of the present invention, the exposure state can be brought close to the optimum value in less than one field.
Moreover, in the conventional digital camera, the imaging state by the imaging means is displayed on the monitor. If the monitor display image suddenly becomes brighter or darker, the display quality is considered to be poor. Therefore, the exposure variable amount in one loop in the feedback control is reduced, and the exposure state is gradually shifted to the optimum state. Yes. As a result, the conventional AE takes a long time to control exposure because the loop is repeated many times to obtain an appropriate exposure state.
Also, since the brightness of the subject is not known at all when the camera is turned on, an exposure state is set for the time being based on a predetermined reference value (initial setting value), and exposure according to the subject brightness is performed from this state. Feedback control will be performed. As a result, when the brightness of the subject at power-on is very small or large, the conventional AE takes time for the feedback control, and it takes a long time to shoot the first image after power-on. According to the present invention, before performing such conventional AE, the high-speed exposure control means can bring the exposure state close to the optimum value at high speed. Thus, it is possible to quickly approach the desired state, and the activation time and the photographing interval can be shortened.

In the camera of the present invention, the automatic exposure adjustment unit detects a luminance level of an image captured by the imaging unit from an output of the imaging unit, and controls the exposure changing unit based on the luminance level. It is desirable to have a configuration including a feedback control unit that controls the exposure state so that the luminance level of the image becomes a desired level (target level).
According to the present invention, for example, after performing rough exposure control at high speed by the high-speed exposure control means, high-precision exposure control can be performed by the automatic exposure adjustment means. Therefore, the present invention can achieve both high speed and high precision in exposure control.

The camera according to the present invention further includes a startup setting unit in which the high-speed exposure control unit sets an initial state of the automatic exposure adjustment unit based on an output of the distance measuring sensor immediately after the camera is turned on. It is desirable to have a configuration.
According to the present invention, immediately after the camera is turned on, the high-speed exposure control means can perform exposure control at high speed. Therefore, the present invention can shorten the startup time that is regarded as important in digital cameras and the like.

Further, in the camera of the present invention, the exposure changing means is connected to the output of the distance measuring sensor after the camera is turned on and before the automatic exposure adjusting means sets the state of the exposure changing means. It is desirable to have a configuration having a startup setting unit for setting an initial state in the automatic exposure adjusting means.
According to the present invention, for example, at the time of turning on the camera, before setting various image capturing conditions such as the shutter speed to the image sensor driver, the approximate brightness range of the subject using the distance measuring sensor is set. Can be examined. Therefore, according to the present invention, it is possible to set various conditions for exposure earlier than the conventional AE when the power is turned on, and to shorten the startup time.

In the camera of the present invention, the high-speed exposure control means determines whether the change value of the luminance of the subject at a predetermined time interval is greater than a reference value based on the output of the imaging means or the output of the distance measuring sensor. It is desirable to have a configuration having a brightness sudden change setting unit that sets the state of variable control in the automatic exposure adjusting means based on the output of the distance measuring sensor when it is determined that the reference value is greater than or equal to the reference value.
According to the present invention, it is possible to detect that the subject luminance has changed extremely during framing after the camera is activated. When the subject brightness changes extremely, the exposure can be quickly brought close to an appropriate state based on the output of the distance measuring sensor. Therefore, the camera of the present invention can also photograph a subject whose luminance changes abruptly with higher quality than before.

In the camera of the present invention, the high-speed exposure control unit includes a high-speed feedback exposure control unit that feedback-controls the state of the exposure change unit based on the output of the distance measuring sensor, and the high-speed feedback exposure control unit It is desirable to have a configuration including a smooth display unit that reduces the feedback amount so that the exposure state does not vibrate across an appropriate value.
According to the present invention, exposure control can be performed in the vicinity of the optimum exposure state (AE target value) only by the high-speed exposure control means. Here, the high-speed exposure control means can avoid that the exposure state (that is, the monitor display) alternately repeats too bright and too dark. Therefore, the present invention naturally shifts the captured image to an optimal exposure state, for example, on the monitor display of the camera. Therefore, the present invention can always display a high-quality image on the monitor display while performing high-speed exposure control.

In the camera of the present invention, the high-speed exposure control means stores a plurality of exposure setting values in advance, and one exposure setting is selected from the plurality of exposure setting values based on the output of the distance measuring sensor. It is desirable to have a selection unit that selects a value and sets the initial state or the reference state based on the selected exposure setting value.
According to the present invention, for example, the exposure setting value close to the optimum exposure setting can be selected and controlled by the high-speed exposure control means. Thereafter, the exposure can be controlled with high accuracy by the automatic exposure adjusting means. Therefore, the present invention can increase the speed and accuracy of exposure control while simplifying the constituent elements.

In the camera of the present invention, the distance measuring sensor is a sensor used for automatic focus adjustment, and does not project auxiliary light for distance measurement onto the subject, but measures the light from the subject. Desirably, it is one of a passive AF sensor that measures distance, and an active AF sensor that projects auxiliary light for distance measurement onto the subject and measures the distance using light from the subject at the time of projection. .
According to the present invention, it is possible to perform high-speed AE using a passive AF sensor or an active AF sensor conventionally used for AF, and to shorten the start-up time, the shooting interval, and the like.
As a passive AF sensor, a separator lens or two lenses and a plurality of photoelectric conversion elements are linearly arranged, and light collected by the separator lens or the two lenses is any of the plurality of photoelectric conversion elements. It is desirable to use what is comprised with the line sensor arrange | positioned so that it may be irradiated.
Further, as an active AF sensor, there is a configuration that cancels the steady light component so that the light receiving unit extracts only infrared light, but a configuration that does not cancel the steady light component is preferable. In this way, it is possible to detect an approximate amount of light from the subject.

In the camera of the present invention, the high-speed exposure control means sets at least an initial state or a reference state of variable control in the automatic exposure adjustment means based on an integrated value of the output of the distance measuring sensor. Is desirable.
According to the present invention, for example, when the passive AF sensor is used as a distance measuring sensor, a rough value of the subject luminance level can be obtained simply by integrating the output of each photoelectric conversion element of the line sensor constituting the passive AF sensor. Can be detected.

  In order to achieve the above object, the camera of the present invention has an imaging means for imaging a subject, an aperture variable section for changing the aperture, a shutter speed variable section for changing the shutter speed, and an amplification degree for the output of the imaging means. It comprises at least one of variable gain variable sections, and controls the exposure change means for changing the exposure state in the image pickup means, and variably controls the state of the exposure change means based on the output of the image pickup means. Automatic exposure adjusting means, a flash that irradiates light toward the subject, a flash dimming sensor that detects the luminance of the subject when the flash irradiates light, and an output of the flash dimming sensor A high-speed exposure control means for setting at least an initial state or a reference state of variable control in the automatic exposure adjustment means, Characterized in that it.

  According to the present invention, the initial value in the exposure control can be set based on the output of the flash light control sensor by the high-speed exposure control means. Therefore, according to the present invention, the exposure state can be brought close to the optimum value at high speed by the high-speed exposure control means before or during the time-consuming conventional AE (AE using the output of the imaging means). . Therefore, the present invention can quickly bring the exposure close to an appropriate state at the time of start-up or when the luminance of the subject suddenly changes, and the start-up time and the shooting interval can be shortened.

In order to achieve the above object, the exposure control method of the present invention controls the exposure based on the output of the imaging means at least excluding the time immediately after the camera is turned on or when the brightness of the subject changes suddenly. Immediately after the power is turned on or when the luminance of the subject changes abruptly, exposure control is performed based on the output of the distance measuring sensor.
According to the present invention, the exposure control can be performed at high speed based on the output of the distance measuring sensor when the power is turned on or the subject brightness is abruptly changed. Therefore, according to the present invention, it is possible to shorten the start-up time and the photographing interval in the camera, and it is possible to greatly reduce missed photo opportunities.

  According to the present invention, the startup time can be shortened. That is, in the case of AE by feedback control with respect to the output of the image pickup means, each of “image pickup”, “transfer from image pickup device to memory”, “AE calculation”, etc. requires a period of one field or more. In the AE based on feedback control, the exposure control value is updated with these at least three fields as one unit. For this reason, if the initial setting is far from the luminance level of the subject, several tens of frames are required until the exposure is stabilized, which greatly affects the start-up time during which the first image can be taken. According to the present invention, the exposure state can be brought to a state close to the optimum value (the initial state or the reference state of the present invention) in less than one field based on the output from the distance measuring sensor or the like. Therefore, the present invention can shorten the start-up time and the shooting interval.

  Further, according to the present invention, even when the subject brightness changes suddenly during framing after the camera is activated, the exposure state is set to the optimum value in less than one field based on the output from the distance measuring sensor or the like. It can be in a state close to. Therefore, according to the present invention, it is possible to photograph a subject whose brightness changes rapidly with higher quality than before.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating an example of the overall configuration of a camera according to an embodiment of the present invention. In the present embodiment, a digital camera will be described as an example of the camera according to the present invention.

  The digital camera of this embodiment includes a zoom lens 1, an iris (aperture) 2, a focus lens 3, an image pickup device (CCD) 4, a zoom motor 5, an iris motor 6, a focus motor 7, a timing generator 8, and a CDS and AGC circuit. 9. Here, the zoom lens 1, the iris 2, the focus lens 3, and the imaging element 4 constitute imaging means for imaging a subject.

  The iris motor 6 forms a diaphragm variable unit that changes the opening degree of the iris 2. The timing generator 8 forms a shutter speed variable unit that changes the shutter speed. A CDS (Corelated Double Sampling) and AGC (Automatic Gain Control) circuit 9 constitutes a gain variable section that varies the degree of amplification with respect to the output of the image pickup device 4 that is the output of the image pickup means. The iris motor 6, the timing generator 8, and the CDS and AGC circuit 9 constitute an exposure changing unit that changes the exposure state in the imaging unit.

  The position of the zoom lens 1 can be moved by a zoom motor 5. The opening degree of the iris 2 can be controlled by the iris motor 6. The position of the focus lens 3 can be controlled by the focus motor 7. The subject image light that has passed through the zoom lens 1, the iris 2, and the focus lens 3 forms an image on the light receiving surface of the image sensor 4.

  The image sensor 4 photoelectrically converts subject image light imaged on its light receiving surface. As the image sensor 4, a CCD (Charge Coupled Device) image sensor, a CMOS (Complementary MOS) image sensor, or the like is used. Color filters are arranged on the front surface of the image sensor 4. The arrangement of the color filters includes R (red), G (green), and B (blue) primary color filters, and Cy (cyan), Mg (magenta), and Ye (yellow) complementary color filters. May be used. The image sensor 4 is driven by a timing signal from the timing generator 8.

  The digital camera of this embodiment includes an A / D converter 10, an image input controller 11, an image signal processing circuit 12, an image compression / decompression circuit 13, a video encoder 14, an image display device 15, and motor drivers 16, 17, and 18. CPU 19, AF detection circuit 20, AE and AWB detection circuit 21, memory 22, VRAM 23, media controller 24, recording medium 25, and passive AF sensor 26. In addition, the digital camera of this embodiment includes a shutter switch SW1, a recording / reproducing switch SW2, a zoom switch SW3, a strobe switch SW4, and a shooting mode selection switch SW5.

  The CPU 19 controls the entire digital camera. An AE (Automatic Exposure) and AWB (Automatic White Balance) detection circuit 21 detects an image signal level in order to perform exposure and white balance. Then, the CPU 19 and the AE and AWB detection circuit 21 perform automatic exposure for variably controlling the state of the exposure changing means (the iris motor 6, the timing generator 8, and the CDS and AGC circuit 9) based on the output of the image sensor 4. It constitutes the adjusting means.

  The passive AF sensor 26 is a sensor used for AF and measures the distance to a subject, and is a distance measuring sensor having a photoelectric conversion function. For example, the passive AF sensor 26 includes a separator lens (or two lenses arranged in parallel) and a plurality of photoelectric conversion elements arranged in a straight line, and the light condensed at two locations by the separator lens And a line sensor arranged to irradiate one of the plurality of photoelectric conversion elements. The distance to the subject is measured by detecting, with a line sensor, the interval between the two images formed by the separator lens. Further, the output of the passive AF sensor 26 is also an input of the high-speed exposure control means according to the present invention. Further, the digital camera will be described in detail.

  The output signal of the image sensor 4 is supplied to the A / D converter 10 via the CDS and AGC circuit 9. In the A / D converter 10, the image signal is digitized. The output signal of the A / D converter 10 is taken into the CPU 19 via the image input controller 11.

  The CPU 19 is supplied with input signals from a shutter switch SW1, a recording / reproducing switch SW2, a zoom switch SW3, a strobe switch SW4, a shooting mode selection switch SW5, and the like. The CPU 19 controls the zoom drive signal for moving the zoom lens 1, the focus drive signal for moving the focus lens 3, the iris drive signal for opening and closing the iris 2, and the gain of the CDS and AGC circuit 9. A gain control signal for output is output.

  Further, the CPU 19 inputs the output of the passive AF sensor 26. Then, the CPU 19 calculates the distance from the digital camera to the subject based on the output of the passive AF sensor 26, and performs focus control (AF) based on the calculated distance. That is, the CPU 19 gives a focus drive signal to the focus motor 7 via the motor driver 18 according to the calculated distance, and controls the focus lens 3 to the in-focus position.

  The AF (Automatic Focus) detection circuit 20 is for AF based on the output of the image sensor 4. In this digital camera, AF can be performed using a passive AF sensor, but in order to perform AF with higher accuracy, AF using the AF detection circuit 20 can also be performed. Therefore, in the present digital camera, the AF detection circuit 20 is not always necessary. Specifically, the AF detection circuit 20 detects the high frequency component level of the image signal in order to perform focus control. That is, at the focal point, the high-frequency component level of the image signal increases. Therefore, the in-focus state can be determined by detecting the high-frequency component level of the image signal. The high-frequency component level of the image signal is detected by the AF detection circuit 20, and the high-frequency component level of the image signal is integrated during a predetermined focus area to obtain an AF evaluation value. The obtained AF evaluation value is supplied to the CPU 19. The CPU 19 gives a focus drive signal to the focus motor 7 via the motor driver 18 in accordance with the AF evaluation value, and controls the focus lens 3 to the in-focus position.

  The AE and AWB detection circuit 21 detects an image signal level in order to perform exposure and white balance. The image signal level is detected by the AE and AWB detection circuit 21, and an exposure control signal and a white balance control signal are formed. The exposure control signal and the white balance control signal are supplied to the CPU 19.

  In normal times, an iris drive signal is output from the CPU 19 and a gain setting signal is output in accordance with the exposure control signal output from the AE and AWB detection circuit 21. Then, the iris drive signal from the CPU 19 is supplied to the iris motor 6 via the motor driver 17, and the opening degree of the iris 2 is controlled so as to reach a predetermined signal level. Further, the gain control from the CPU 19 is supplied to the CDS and AGC circuit 9, and the gain of the CDS and AGC circuit 9 is controlled so as to have a predetermined signal level. Further, the gain of the three primary color signals is controlled by the image signal processing circuit 12 in accordance with the white balance control signal from the AE and AWB detection circuit 21. The normal AE, that is, the AE basic operation, is described in detail later, but is a relatively time-consuming operation.

  At the time of start-up, that is, immediately after the digital camera is turned on, the CPU 19 becomes a high-speed exposure control unit that sets the initial state (or reference state) of the variable control in the automatic exposure adjustment unit based on the output of the passive AF sensor 26. Also, the CPU 19 becomes a high-speed exposure control means when the luminance of the subject changes extremely and rapidly. The AE operation (operation of the high-speed exposure control means) using the passive AF sensor 26 will be described later in detail.

  The zoom switch SW3 is a switch for moving the zoom lens 1. That is, when the zoom switch SW3 is operated, a zoom drive signal is output from the CPU 19 accordingly. This zoom drive signal is supplied to the zoom motor 5 via the motor driver 16, and the zoom lens 1 is moved.

  The recording / reproducing switch SW2 is a switch for setting the recording mode or the reproducing mode. When the recording mode is set, the output signal of the image sensor 4 is digitized by the A / D converter 10 via the CDS and AGC circuit 9 and then supplied to the image signal processing circuit 12. The image signal processing circuit 12 performs image processing such as gamma correction, edge enhancement, and white balance. This image signal is supplied to the video encoder 14. A component color video signal is formed by the video encoder 14, and this color video signal is developed in a VRAM (Video RAM) 23. This color video signal is supplied to an image display device 15 such as an LCD (Liquid Crystal Display), and a monitor image being shot is displayed on the image display device 15.

  The shutter switch SW1 is a switch that is pressed when taking an image. When the shutter switch SW1 is pressed, a shutter signal is sent to the timing generator 8, and the image at that time is taken into the image sensor 4. The image signal for one screen at this time is stored in the memory 22.

  The image signal for one screen captured in the memory 22 is supplied to the image compression / expansion circuit 13 after being subjected to image processing by the image signal processing circuit 12. The image compression / decompression circuit 13 compresses and encodes image data. For example, JPEG (Joint Photographic Experts Group) is used as the image data compression method. JPEG is a standard for compressing images using DCT (Discrete Cosine Transform). Note that the image data compression method is not limited to JPEG.

  The compressed and encoded image signal is supplied to the recording medium 25 via the media controller 24 and recorded on the recording medium 25. As the recording medium 25, for example, a card-type detachable memory using a flash memory is used. As the recording medium 25, a nonvolatile memory built in a digital camera, a magnetic tape, a magnetic disk, an optical disk, or the like may be applied.

  At the time of reproduction, the recording / reproduction switch SW2 is operated to the reproduction side. When the recording / reproduction switch SW2 is operated to the reproduction side, the reproduction mode is set. In the reproduction mode, an image file on the recording medium 25 is opened and image data is read out. The image data read from the recording medium 25 is supplied to the image compression / decompression circuit 13. The image compression / decompression circuit 13 performs image signal decompression processing. The output of the image compression / decompression circuit 13 is supplied to the video encoder 14. An output signal of the video encoder 14 is supplied to the image display device 15, and a reproduced image is displayed on the image display device 15.

  The shooting mode selection switch SW5 is a switch for selecting one shooting mode according to the shooting situation from the person shooting mode, the sport mode, the landscape mode, the night mode, and the like. The person shooting mode is a mode suitable for shooting a person. The sport mode is a mode suitable for photographing a moving subject. The landscape mode is a mode suitable for photographing a distant landscape with high quality. The night mode is a mode suitable for taking a night view clearly.

  Next, the operation of the digital camera after the power is turned on will be described. The main power of the digital camera is turned on / off by operating a power switch (not shown). When the power is turned on, the digital camera initializes memory, zooming, DSP, various drivers (16, 17, 18), and the like.

  In capturing an image, first, the exposure amount is determined by the charge accumulation time (electronic shutter time) in the image sensor 4, the opening (aperture) of the iris 2, and the mechanical shutter. Next, the image sensor 4 is exposed with the exposure amount, and an analog image signal is output from the image sensor 4. The analog image signal is gain-controlled by the CDS and AGC circuit 9 and converted into a digital image signal by the A / D converter 10. This digital image signal is taken into the CPU 19 or the memory 22 via the image input controller 11. Thereafter, the captured digital image signal is subjected to image processing such as gamma correction, edge enhancement, white balance, and YC conversion in the image signal processing circuit 12, and data compression is performed in the image compression / decompression circuit 13. To be recorded.

(AE basic operation)
FIG. 2 is a diagram showing an AE metering area in the AE basic operation (normal AE). With reference to FIG. 2, the AE basic operation of the digital camera will be described. The AE basic operation is an AE performed by the automatic exposure adjustment unit according to the present invention, and is an operation of performing exposure control based on the output of the image sensor 4. The AE metering area is obtained by dividing the screen formed by the image sensor 4 into 5 × 5 blocks and adding weight to the center of the screen. That is, the output value of each pixel of the image sensor 4 is weighted according to the position of the pixel. The CPU 19 evaluates the luminance level of the subject with respect to the output of one frame of the image sensor 4 based on the weighted average value using the AE metering area of FIG. 2, and sets this as the AE evaluation value. Equation 1 below is an example of a mathematical expression for obtaining an AE evaluation value. In the following equation 1, k (h, v) is a weighting coefficient for each block in the AE photometry area. Y (h, v) indicates the average input luminance value in each block.

  Then, the CPU 19 increases the shutter speed when the weighted average value (AE evaluation value) is larger than the target value (appropriate exposure value), that is, when the subject is bright and overexposed. The amount of light to the image sensor 4 is reduced by narrowing the opening or reducing the gain of the CDS and AGC circuit 9. Conversely, when the weighted average value is smaller than the target value, the light amount to the image sensor 4 is increased by slowing the shutter speed, widening the opening of the iris 2, or increasing the gain of the CDS and AGC circuit 9. Let In this way, controlling the shutter speed, aperture, CDS, gain of the AGC circuit 9 and the like based on the output of the image sensor 4 is the AE basic operation of this digital camera.

  FIG. 3 is a diagram illustrating an example of the AE basic operation. The AE evaluation value is represented by 12 bits, and is represented by an integer from 0 to 4095 in decimal. The target value is 640 decimal. For example, when the AE evaluation value is in the range of 660 to 4095, the shutter speed is increased, the opening of the iris 2 is decreased, or the gain of the CDS and AGC circuit 9 is decreased. As a result, the AE evaluation value is driven into the range of 621 to 659. On the other hand, when the AE evaluation value is in the range of 0 to 620, the shutter speed is decreased, the opening of the iris 2 is increased, or the gain of the CDS and AGC circuit 9 is increased. As a result, the AE evaluation value is driven into the range of 621 to 659.

  FIG. 4 is a diagram showing a specific sequence example of the AE basic operation. In the AE basic operation, the “exposure period”, “transfer period”, and “AE calculation period” form one exposure control sequence. Here, the exposure period is a period during which the image sensor 4 is exposed. The transfer period is a period required to transfer the output of the image sensor 4 to the memory 22. In the AE calculation period, an AE evaluation value is calculated for the data transferred to the memory 22 using Formula 1, and the shutter speed, the opening degree of the iris 2 and the gain of the CDS and AGC circuit 9 are calculated based on the calculation result. This is the period required to change.

  One exposure control sequence is repeated many times as one feedback loop, so that the AE evaluation value is within the range of 621 to 659. Further, the exposure period, the transfer period, and the AE calculation period are synchronized with the vertical synchronization signal VD. The vertical synchronizing signal VD is a reference signal when capturing or displaying an image of one screen, and is generally a pulse having an interval of 1/30 [second]. The pulse interval is one frame period. Even if the shutter speed is 1/250 [second], the exposure period needs 1/30 [second].

  As described above, in the sequence of the AE basic operation, the exposure state can be changed only every three frames or more. Therefore, it takes a calculation period (number of feedbacks) × 3 frame periods to drive the target value. Further, when the power is turned on, if the subject brightness is far from the reference state such as extremely bright or dark, it may take several tens of frames before the exposure (AE evaluation value) is driven to the target value. Therefore, only the AE basic operation may greatly affect the startup time.

(AE operation using passive AF sensor)
FIG. 5 is a diagram for explaining an AE operation using a passive AF sensor in the digital camera. With reference to FIG. 5, the AE operation using the passive AF sensor 26 will be described. The passive AF sensor 26 is a distance measuring sensor that obtains a distance (focus) from an image distance when an image is formed by a separator lens to a subject. Here, since the passive AF sensor 26 detects the inter-image distance by the line sensor, it can be used for measuring the light quantity although the accuracy is relatively low. That is, the luminance level of the subject can be roughly grasped from the output of the passive AF sensor 26.

  Here, since the passive AF sensor 26 includes a line sensor, the output of the passive AF sensor 26 is the output of each photoelectric conversion element forming the line sensor. Therefore, for example, the values sequentially output from the photoelectric conversion elements may be integrated, and the integrated value may be used as the output of the passive AF sensor 26 according to the present embodiment. Note that the maximum value in the output of each photoelectric conversion element forming the line sensor may be the output of the passive AF sensor 26 according to the present embodiment.

  The CPU 19 can control the exposure by controlling the shutter speed, the opening degree of the iris 2 or the gain of the CDS and the AGC circuit 9 based on the output of the passive AF sensor 26. This is an AE operation using the passive AF sensor 26 and forms the basis of the operation of the high-speed exposure control means according to the present invention, and the CPU 19 functions as the high-speed exposure control means.

  In particular, in the present digital camera, the AE operation using the passive AF sensor 26 is performed when the power is turned on (when the camera is activated). When the power is turned on, the reference value (fixed value) set in advance in the memory 22, etc., or the data of the captured image recorded just before the power is turned off in the past (the value when the power is turned off) is read and used as the initial value. A method of performing the above AE basic operation is conceivable. However, it takes a long time to control the exposure to the target value (621 to 659 in FIG. 3) regardless of whether a fixed value or a power-off value is used.

  Therefore, when the power is turned on, the CPU 19 first observes the rough luminance level of the subject using the output of the passive AF sensor 26. The CPU 19 determines an initial setting value of the AE basic operation from the observed value. That is, the CPU 19 functions as a startup setting unit according to the present invention. The operation of the startup setting unit is performed before setting various image capturing conditions such as setting the shutter speed to the timing generator 8. As a result, it is possible to significantly reduce the variation in the average time until the AE settles when the camera is activated.

  For example, as shown in FIG. 5, when the output of the passive AF sensor 26 is “0” and the luminance level of the subject is very low, the initial setting values of the AE basic operation are set (shutter speed 1/30 seconds, aperture F2). .8, gain 6 dB). With this initial setting value, the exposure state increases directly and approaches the target value directly. On the other hand, when the output of the passive AF sensor 26 is “1023” and the luminance level of the subject is very high, the initial setting values of the AE basic operation are (shutter speed 1/250 seconds, aperture F4.0, gain 6 dB). To do. With this initial setting value, the exposure state directly decreases and approaches the target value directly.

  As a result, the digital camera according to the present embodiment uses the passive AF sensor 26 at the time of camera startup to determine the initial setting value (initial state) of the AE basic operation. Therefore, the average time until the AE settles after the camera startup. Can be reduced. Therefore, this digital camera can shorten the activation time.

  In addition, the digital camera according to the present embodiment can perform AE with high accuracy by AE basic operation using the output of the image sensor 4 after AE using the passive AF sensor 26. Therefore, it is possible to achieve both high speed and high accuracy of AE.

  The digital camera according to the present embodiment may perform the “AE operation using the passive AF sensor” during framing after the camera is activated. That is, when the CPU 19 determines whether or not the change value of the luminance of the subject at a predetermined time interval is greater than or equal to the reference value based on the output of the image sensor 4 or the output of the passive AF sensor 26, It functions as a brightness sudden change setting unit that changes the setting value (reference state) of the AE basic operation based on the output of the passive AF sensor 26. With such a configuration, when the subject brightness changes drastically, for example, during framing after the camera is activated, the exposure can be quickly brought close to an appropriate state. Therefore, the present digital camera can shoot a subject whose luminance changes abruptly with higher quality than before, and can shorten the shooting interval.

  The digital camera according to the present embodiment is configured to determine whether or not to perform the “AE operation using the passive AF sensor” during framing after the camera is activated, based on the state of the shooting mode selection switch SW5. It is good. For example, when the shooting mode selection switch SW5 is “sport mode”, “AE operation using a passive AF sensor” is performed. Thereby, even if the brightness of a subject such as a sports player changes suddenly, it is possible to take a picture with higher quality than before. On the other hand, when the shooting mode selection switch SW5 is in the “landscape mode”, the “AE operation using the passive AF sensor” is not performed, and the exposure control is performed using only the “AE basic operation”. Thereby, while avoiding power consumption due to the “AE operation using the passive AF sensor”, it is possible to shoot a high-quality object such as a distant landscape where the subject luminance hardly changes.

  In the digital camera of the present embodiment, the CPU 19 may function as a high-speed feedback exposure control unit that performs feedback control of the exposure state based on the output of the passive AF sensor 26. Here, in the high-speed feedback exposure control, the CPU 19 desirably functions as a smooth display unit that reduces the feedback amount so that the exposure state does not vibrate across the appropriate value (target value). That is, when changing the exposure state based on the output of the passive AF sensor 26, the CPU 19 performs feedback control so that the exposure is changed before the target value so that the target value is not excessively exceeded due to the change.

  As a result, the digital camera can control the exposure in the vicinity of the optimal exposure state (AE target value) only by the output of the passive AF sensor 26, and the monitor display or the like is alternately bright or dark alternately by changing the exposure. Repeating things can be avoided. Therefore, the present digital camera can display the captured image so that it automatically moves to the optimum exposure state on a monitor display or the like while performing high-speed exposure control.

  The digital camera according to the present embodiment stores a plurality of exposure setting values (shutter speed, aperture, gain, etc.) in advance when performing the above-described “AE operation using the passive AF sensor 26”, and performs passive AF. A selection unit that selects one (or one set) from the plurality of exposure setting values based on the output of the sensor 26 may be used. For example, the CPU 19 functions as a selection unit. In this way, it is possible to increase the speed and accuracy of AE while simplifying the constituent elements.

(Modification)
Next, a digital camera according to a modification of the present embodiment will be described. In the digital camera of the above embodiment, instead of performing the AE operation using the passive AF sensor 26, the digital camera performs the AE operation using the output of a flash light control sensor (not shown). . Others are the same as the digital camera of the said embodiment. That is, the digital camera includes a flash (not shown), a flash dimming sensor for detecting the luminance of a subject when the flash is irradiated with light, and flash dimming. And high-speed exposure control means (CPU 19) for setting the initial state of the AE basic operation based on the output of the sensor.

  According to the digital camera of the present modification, the initial value of AE can be set based on the output of the flash light control sensor. Therefore, the exposure state can be brought close to the target value at high speed before or during the time-consuming AE basic operation. Therefore, the present digital camera can quickly bring the exposure close to an appropriate state at the time of start-up or when the luminance of the subject suddenly changes, and the start-up time and the photographing interval can be shortened.

  Although the embodiment of the present invention has been described above, the camera and the exposure control method of the present invention are not limited to the illustrated examples described above, and various modifications are made without departing from the gist of the present invention. Of course you get.

  For example, in the above-described embodiment, a passive AF sensor has been described as an example of a distance measuring sensor, but the present invention is not limited to this, and various AF sensors can be applied to the distance measuring sensor. For example, an active AF sensor may be applied to the distance measuring sensor instead of the passive AF sensor. The active AF sensor is a sensor used for automatic focus adjustment, and is a sensor that projects distance measuring auxiliary light onto a subject and measures the distance using light from the subject at the time of projection. Even if this active AF sensor is used, it is possible to detect a substantial amount of light from the subject and to quickly bring the exposure close to an appropriate state.

  The present invention is useful for various cameras. In particular, the present invention is suitable for exposure control of digital cameras and digital video cameras.

It is a block diagram which shows the camera which concerns on embodiment of this invention. It is a figure which shows the AE photometry area used for AE basic operation | movement of a camera same as the above. It is a figure which shows an example of AE basic operation | movement. It is a figure which shows the example of a specific sequence of AE basic operation | movement. It is a figure for demonstrating AE operation | movement using a passive AF sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Zoom lens, 2 ... Iris (aperture), 3 ... Focus lens, 4 ... Image sensor, 5 ... Zoom motor, 6 ... Iris motor, 7 ... Focus motor, 8 ... Timing generator, 9 ... CDS and AGC circuit, DESCRIPTION OF SYMBOLS 10 ... A / D converter, 11 ... Image input controller, 12 ... Image signal processing circuit, 13 ... Image compression / decompression circuit, 14 ... Video encoder, 15 ... Image display device, 16, 17, 18 ... Motor driver, 19 ... CPU, 20 ... AF detection circuit, 21 ... AE and AWB detection circuit, 22 ... Memory, 23 ... VRAM, 24 ... Media controller, 25 ... Recording medium, 26 ... Passive AF sensor, SW1 ... Shutter switch, SW2 ... Recording / playback Switch, SW3 ... Zoom switch, SW4 ... Strobe switch, SW5 ... Shooting mode selection switch

Claims (11)

Imaging means for imaging a subject;
It comprises at least one of an aperture variable unit that changes the aperture, a shutter speed variable unit that changes the shutter speed, and a gain variable unit that varies the amplification degree of the output of the imaging unit. Exposure changing means for changing the exposure state;
Automatic exposure adjusting means for variably controlling the state of the exposure changing means based on the output of the imaging means;
A distance measuring sensor for measuring a distance to a subject and having at least a photoelectric conversion function;
High-speed exposure control means for setting at least an initial state or a reference state of variable control in the automatic exposure adjustment means based on the output of the distance measuring sensor;
The high-speed exposure control means determines whether or not the change in luminance of the subject at a predetermined time interval is greater than or equal to a reference value based on the output of the imaging means or the output of the distance measuring sensor, and determines that it is greater than or equal to the reference value. And a sudden brightness change setting unit for setting a variable control state in the automatic exposure adjusting means based on the output of the distance measuring sensor.   The automatic exposure adjusting unit detects a luminance level of an image captured by the imaging unit from an output of the imaging unit, and controls the exposure changing unit based on the luminance level so that the luminance level of the image is desired. The camera according to claim 1, further comprising a feedback control unit configured to control the exposure state so as to reach a level.   The high-speed exposure control means includes a startup setting unit that sets an initial state of the automatic exposure adjustment means based on the output of the distance measuring sensor immediately after the camera is turned on. Or the camera of 2.   The exposure changing means is after the power of the camera is turned on, and before the automatic exposure adjusting means sets the state of the exposure changing means, based on the output of the distance measuring sensor in the automatic exposure adjusting means. The camera according to claim 1, further comprising a startup setting unit that sets an initial state. The high-speed exposure control means includes a high-speed feedback exposure control unit that feedback-controls the state of the exposure change means based on the output of the distance measuring sensor,
5. The camera according to claim 1, wherein the high-speed feedback exposure control unit includes a smooth display unit that reduces a feedback amount so that the exposure state does not vibrate across an appropriate value. 6. .   The high-speed exposure control means stores a plurality of exposure setting values in advance, selects one exposure setting value from the plurality of exposure setting values based on the output of the distance measuring sensor, and selects the selected The camera according to claim 1, further comprising a selection unit that sets the initial state or the reference state based on an exposure setting value.   The distance measuring sensor is a sensor used for automatic focus adjustment, and does not project the auxiliary light for distance measurement onto the subject, but measures the distance using light from the subject, and the subject 7. The active AF sensor according to claim 1, further comprising: an active AF sensor which projects auxiliary light for distance measurement on the object and measures distance using light from a subject at the time of projection. The camera according to any one of the above.   In the passive AF sensor, a separator lens or two lenses and a plurality of photoelectric conversion elements are linearly arranged, and light collected by the separator lens or the two lenses is any of the plurality of photoelectric conversion elements. The camera according to claim 7, further comprising a line sensor disposed so as to be irradiated.   The high-speed exposure control means sets at least an initial state or a reference state of variable control in the automatic exposure adjustment means based on an integrated value of the output of the distance measuring sensor. The camera according to claim 8. Imaging means for imaging a subject;
It comprises at least one of an aperture variable unit that changes the aperture, a shutter speed variable unit that changes the shutter speed, and a gain variable unit that varies the amplification degree of the output of the imaging unit. Exposure changing means for changing the exposure state;
Automatic exposure adjusting means for variably controlling the state of the exposure changing means based on the output of the imaging means;
A flash that emits light toward the subject;
A flash light control sensor for detecting the brightness of the subject when light is irradiated by the flash;
Based on the output of the sensor for flash dimming, it possesses a high-speed exposure control means for setting an initial state or standard state variable control in at least the automatic exposure adjusting means,
The high-speed exposure control means determines whether or not the change in luminance of the subject at a predetermined time interval is greater than or equal to a reference value based on the output of the imaging means or the output of the flash light control sensor. when it is determined that the camera, characterized by chromatic luminance sudden change setting unit for setting a state of the variable control in the automatic exposure adjusting means based on an output of the sensor for flash light adjustment. When at least excluding immediately after the camera is turned on and when the luminance change value of the subject is above the reference value , the exposure is controlled based on the output of the imaging means,
Immediately after the camera is turned on and when the brightness change value of the subject is greater than or equal to the reference value , the exposure control is based on the output of the distance measuring sensor , and
The exposure control process determines whether the change value of the luminance of the subject at a predetermined time interval is greater than or equal to a reference value based on the output of the imaging unit or the output of the distance measuring sensor, and determines that the exposure value is greater than or equal to the reference value. An exposure control method, comprising: a process for controlling the exposure based on an output of the distance measuring sensor .

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