JP4859194B2 - IMAGING DEVICE, ITS CONTROL METHOD, PROGRAM, AND STORAGE MEDIUM - Google Patents

Description

  The present invention relates to an autofocus technique in an imaging apparatus such as a digital camera.

  In a conventional single-lens reflex camera using a silver salt film or a recent digital single-lens reflex camera, there is a technology called a TTL (Through The Lens) phase difference method in order to perform autofocus (hereinafter also simply referred to as AF). Has been applied. In the TTL phase difference type autofocus mechanism, a plurality of subject images are formed on a phase difference detection sensor having a line sensor by light beams that have passed through different portions of the photographing lens. Then, the deviation amount between the imaging surface and the in-focus position can be calculated based on the distance between the images (phase difference) at that time. The line sensor is configured by linearly arranging a CCD (Charge Coupled Device), a CMOS (Complimentary Metal Oxide Semiconductor), or a similar photoelectric conversion element. Therefore, the imaging surface can be made to coincide with the in-focus position only by driving the lens once in accordance with the obtained shift amount. The TTL phase difference type AF is described in detail, for example, in Patent Document 1.

  However, although the phase difference detection sensor is optically equivalent to the imaging surface, the position accuracy of the phase difference detection sensor is affected by various factors such as sensor mounting errors and body and lens manufacturing errors. . Therefore, it is difficult to completely match the in-focus position detected by the TTL phase difference method with an actual imaging surface such as a film or an imaging device.

  On the other hand, in a video camera or a digital compact camera, a so-called contrast method (or a hill-climbing method or a TV-AF method) is applied to perform autofocus. In this contrast method, the focusing lens included in the imaging lens or the imaging device is driven in the optical axis direction, and the contrast of the captured image obtained at each driving stage is acquired as an evaluation value. This is a focal position method. Contrast AF is described in detail, for example, in Patent Document 2.

Since the contrast method performs AF on the actual imaging surface, the in-focus position by AF and the imaging surface position can be matched. However, in order to obtain the evaluation value, it is necessary to drive the focusing lens and the image sensor many times each time, and there is a problem that it takes time to focus as compared with the TTL phase difference method. Also, if the lens or image sensor is not driven, the in-focus direction cannot be determined. If the in-focus position is far from the imaging surface (so-called large blur), the contrast changes even if the lens or image sensor is driven by a small amount. There are also problems such as being weak against large blurring because it is difficult to occur. In a digital single-lens reflex camera, the image sensor is usually shielded by a mirror or a shutter except during exposure, and it is difficult to adopt the contrast AF method because of its structure.
Japanese Patent Publication No. 07-074855 Japanese Patent No. 028121414 JP-A-5-64056 JP 2001-281530 A

  To complement each other's weak points of the TTL phase difference method and the contrast method, both AF methods are combined, and after first adjusting the approximate focus position by the TTL phase difference method, the focus position is accurately imaged by the contrast method. A technique for matching the surface has been proposed. In addition, a technique for improving the accuracy of the TTL phase difference method by feeding back the focusing result in the contrast method to the TTL phase difference method has been proposed. Patent documents 3 and 4 are such known examples.

  First, the contrast method AF is performed after focusing with the TTL phase difference method, thereby eliminating the weak points such as the contrast method that takes time until focusing, and it is difficult to determine the in-focus direction in a large blurred state. Is done. Further, by performing contrast AF after the TTL phase difference method, the in-focus surface and the imaging surface can be made to coincide completely.

  However, since the range of signal values indicating luminance is limited in a digital camera, a so-called whiteout phenomenon occurs in which the signal value of the bright portion sticks to the maximum value depending on the exposure conditions. Since the actual brightness state cannot be reflected in the part where the whiteout occurs, the correct contrast cannot be obtained. Therefore, if the contrast method AF is performed in the area where the whiteout occurs, the distance measurement result is incorrect. May occur.

  FIG. 9 is a diagram for explaining the operation of contrast AF in an inappropriate exposure state that causes overexposure.

  For example, consider a case where contrast AF is performed using a high contrast test chart in which two white lines are written on a black background as shown in FIG.

  FIG. 9B shows the change in the luminance value in the horizontal direction when the exposure is determined so that the bright portion does not white out the chart. When whiteout does not occur as shown in FIG. 9B, correct AF can be performed with contrast AF.

  However, in general, the exposure at the time of shooting is determined so that the average value of the entire screen becomes a predetermined value. When the exposure condition is determined by this method in the case of a subject with many black portions as shown in FIG. 9A, the exposure amount is controlled to be increased because there are many black portions. Then, the white part will cause whiteout. FIG. 9C shows a change in luminance in the horizontal direction when exposure control is performed in this way. Due to whiteout, the bright part sticks to the maximum value side of the luminance value, and a correct contrast value cannot be obtained. For this reason, even if the lens is controlled at the peak position of the evaluation value, a phenomenon may occur in which the true focus position is not achieved.

  In addition to the above-mentioned average metering, there are methods for determining exposure at the time of shooting, such as partial metering based on a part of the screen and evaluation metering that performs weighting according to the position in the screen. For subjects with a large amount of light, the bright part tends to be overexposed.

  Regarding the prior art, Patent Document 3 does not describe what kind of exposure control is performed, and the above-described problem cannot be avoided.

  Patent Document 4 discloses a single-lens reflex digital camera that performs exposure determination after phase difference AF operation. However, there is a description that the contrast method AF can be performed under the same exposure conditions as at the time of photographing, and there is no description that the exposure determination for contrast AF is performed separately from that at the time of photographing. If the contrast AF is performed under the same exposure conditions as those at the time of shooting as described above, the problem that whiteout occurs depending on the scene and the correct focus position cannot be obtained cannot be solved.

  Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide an error in a contrast method in a single-lens reflex digital camera capable of performing two types of AFs, a TTL phase difference method and a contrast method. To reduce the possibility of ranging.

In order to solve the above-described problems and achieve the object, an image pickup apparatus according to the present invention includes an image pickup device that photoelectrically converts a subject image formed by a shooting lens and outputs an image signal, and an output from the image pickup device. Based on the phase difference of the images corresponding to the two main subject focus detection areas divided by the conversion means for amplifying the signal to be converted into a digital signal and the optical system for dividing the subject image into two images , Based on the first autofocus means for performing the first autofocus operation for adjusting the photographing lens to the in-focus position, and the contrast of the image signal corresponding to the main subject focus detection area output from the image sensor. the second auto focusing means for the photographic lens performing a second auto focusing operation to adjust the focus position, exposure conditions set for setting an exposure condition of the imaging device Means and, by the exposure condition setting means, the exposure condition of the imaging device, Oite said second auto focusing when the image corresponding to the main subject focus detection area is set in such exposure conditions as overexposure when performing operation, amplifies the signal from the imaging device with a smaller gain than the gain of the case of photographing by performing the first auto focusing operation without performing the second auto focusing operation in the same exposure conditions Control means for controlling to convert the signal into a digital signal, and the control means performs the second autofocus operation by the second autofocus means and then performs the main subject focus detection area. The exposure for photographing is performed under an exposure condition such that an image corresponding to the above is overexposed .

The image pickup apparatus control method according to the present invention includes an image pickup device that photoelectrically converts a subject image formed by a photographing lens and outputs an image signal, a signal output from the image pickup device is amplified, and a digital signal Based on the phase difference of the images corresponding to the two main subject focus detection areas divided by the converting means for converting the subject image into two images and the optical system for dividing the subject image into two images. Based on the first autofocus means for performing the first autofocus operation to be adjusted and the contrast of the image signal corresponding to the main subject focus detection area output from the image sensor, the photographing lens is brought into the in-focus position. a second auto focusing means for performing a second auto focusing operation, the imaging apparatus including an exposure condition setting means for setting an exposure condition of the image pickup device control to adjust A subject in need thereof by the exposure condition setting means, the exposure condition of the imaging device, the main object focal In no event where the image corresponding to the detection area is set in such exposure conditions as overexposure second of when performing an autofocus operation, in the same exposure conditions and the second auto focusing operation of the first without autofocus smaller gain than the gain in the case of operation for capturing performed from the imaging element A control step of controlling the signal to be amplified and converted into a digital signal , wherein the main subject focus detection is performed after performing the second autofocus operation by the second autofocus means in the control step. The exposure for photographing is performed under an exposure condition in which an image corresponding to the region is overexposed .

  A program according to the present invention causes a computer to execute the above control method.

  A storage medium according to the present invention stores the above program.

  According to the present invention, in a single-lens reflex digital camera capable of executing two types of AF, that is, a TTL phase difference method and a contrast method, it is possible to reduce the possibility of erroneous distance measurement in the contrast method.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the digital camera according to the first embodiment of the present invention.
As shown in FIG. 1, a photographic lens 100 is detachably attached to a digital camera 200 via a lens mounting mechanism of a mount unit (not shown). An electrical contact unit 107 is provided in the mount portion. The digital camera 200 communicates with the photographic lens 100 via the electrical contact unit 107 to control the driving of the focus lens 101 in the photographic lens 100 and the diaphragm 102 that adjusts the amount of light. In FIG. 1, only the focus lens 101 is shown as a lens in the photographic lens 100, but in addition to this, a variable power lens and a fixed lens are provided, and a lens unit is configured including these.

  A light beam from a subject (not shown) is guided to a quick return mirror 203 in the digital camera 200 through a lens unit including a focus lens 101 in the photographing lens 100 and a diaphragm 102. The quick return mirror 203 is disposed obliquely with respect to the optical axis in the photographing optical path, and retracts to the first position (illustrated position) for guiding the light beam from the subject to the upper finder optical system and out of the photographing optical path. Movement to the second position is possible.

  The central portion of the quick return mirror 203 is a half mirror. When the quick return mirror 203 is down to the first position, a part of the light beam from the subject is transmitted through the half mirror portion. The transmitted light beam is reflected by a sub mirror 204 provided on the back side of the quick return mirror 203 and guided to a phase difference AF sensor 205 that constitutes an automatic focus adjustment unit together with a focus detection circuit 206. The focus detection circuit 206 uses the phase difference AF sensor 205 to detect the focus state as shown in FIG. Specifically, detection of the focus state of the photographic lens 100 (focal point) in a focus detection area selected by the user or a system controller 230 described later among a plurality of regions (focus detection area: focus detection region) in the shooting screen. Detection).

  On the other hand, the light beam reflected by the quick return mirror 203 reaches the eyes of the photographer through a finder optical system including a finder screen 202, a pentaprism 201, and an eyepiece lens 207 existing on the focus surface.

  When the quick return mirror 203 is raised to the second position, the light beam from the photographing lens 100 reaches the image sensor 212 via the focal plane shutter 210 and the optical filter 211 that are mechanical shutters. The image sensor 212 is an image sensor typified by a CCD or CMOS sensor. The optical filter 211 has a function of cutting infrared rays and guiding only visible light to the image sensor 212 and a function as an optical low-pass filter.

  The focal plane shutter 210 has a front curtain and a rear curtain, and controls transmission and blocking of a light beam from the photographing lens 100.

  When the quick return mirror 203 is raised to the second position, the sub mirror 204 is also folded with respect to the quick return mirror 203 and retracts out of the photographing optical path.

  In addition, the digital camera 200 of the present embodiment includes a system controller 230 that controls the entire digital camera. The system controller 230 is configured by a CPU, an MPU, and the like, and controls operations of respective circuits described later.

  The system controller 230 communicates with the lens control circuit 104 and the aperture control circuit 106 in the photographing lens 100 via the electrical contact unit 107. The lens control circuit 104 controls the lens driving mechanism 103 that performs focusing by driving the focus lens 101 in the optical axis direction in accordance with a signal from the system controller 230. The lens driving mechanism 103 has a stepping motor or a DC motor as a driving source.

  The diaphragm control circuit 106 controls the diaphragm driving mechanism 105 that drives the diaphragm 102 in accordance with a signal from the system controller 230.

  The system controller 230 is also connected to the shutter control circuit 215 and the photometry circuit 209. The shutter control circuit 215 controls the driving of the front and rear curtains of the focal plane shutter 210 in accordance with a signal from the system controller 230.

  The system controller 230 also includes an EEPROM (memory) that stores parameters that need to be adjusted to control the digital camera 200 and camera ID (identification) information that is unique information for identifying the individual digital camera. Means) 223 is also connected. The EEPROM 223 also stores adjustment values of parameters related to shooting, which are adjusted using a reference lens (photographing lens used when the digital camera is adjusted in a factory).

  The photometric circuit 209 is connected to a photometric sensor 208 disposed in the vicinity of the eyepiece lens 207, and measures the luminance of the subject through the photometric sensor 208. The measurement result of the photometry circuit 209 is sent to the system controller 230.

  Here, as shown in FIG. 4 to be described later, the photometric sensor 208 is divided so that photometry can be performed in a plurality of photometric areas in the photographing screen.

  Further, the system controller 230 controls the lens driving mechanism 103 to form a subject image on the image sensor 212. Further, the system controller 230 controls the aperture driving mechanism 105 based on the set Av value, and further outputs a control signal to the shutter control circuit 215 based on the set Tv value.

  The drive source of the front curtain and rear curtain of the focal plane shutter 210 is constituted by a spring, and after the shutter travels, a spring charge is required for the next operation. The shutter charge mechanism 214 controls this spring charge. Also, the click return mirror 203 is driven up and down by the mirror drive mechanism 213.

  In addition, a camera DSP 227 is connected to the system controller 230. The camera DSP 227 is a correction data sample circuit and a correction circuit configured by a DSP (digital signal processor). Then, control of the image sensor 212 and correction and processing of image data input from the image sensor 212 are executed based on a command from the system controller 230. Auto white balance is also included in the items of image data correction / processing.

  The auto white balance is a function for correcting the maximum luminance portion in the photographed image to a predetermined color (white). For auto white balance, the correction amount can be changed by a command from the system controller 230.

  An A / D converter 217, a video memory 221, and a work memory 226 are connected to the camera DSP 227 via a timing generator 219 and a selector 222.

  The electrical signal from the image sensor 212 is amplified by the CDS / AGC circuit 216 to a predetermined signal level while reset noise and the like are removed by a known method such as correlated double sampling. The output signal of the CDS / AGC circuit 216 is converted into a predetermined digital signal by the A / D converter 217 in order for each pixel.

  Here, the image sensor 212 is driven by the output from the driver circuit 218 for horizontal driving and vertical driving for each pixel based on the signal from the timing generator 219 that determines the overall driving timing. The image signal is output. Similarly, the CDS / AGC circuit 216 and the A / D converter 217 that process the image signal output from the image sensor 212 in an analog manner and convert it into a predetermined signal level are also based on the timing signal from the timing generator 218. Operate.

  The output from the A / D converter 217 is input to the memory controller 228 via the selector 222 that selects a signal based on the signal from the system controller 230, and is all transferred to the DRAM 229 that is a frame memory.

  After the shooting operation is completed, the contents of the DRAM 229 storing the shooting data are transferred to the camera DSP 227 via the selector 222 under the control of the memory controller 228. The camera DSP 227 generates RGB color signals based on the pixel data of the shooting data stored in the DRAM 229.

  In a video camera or a compact digital camera, a finder display (live view) or the like is performed by the monitor display unit 220 by periodically transferring the result to the video memory 221 (each frame) in a state before photographing. In a single-lens reflex digital camera, since the image pickup device 212 is normally shielded by the quick return mirror 203 and the focal plane shutter 210 before shooting, live view cannot be performed. However, the live view operation can be performed by raising the quick return mirror 203 and retracting it from the photographing optical path and then opening the focal plane shutter 210. Further, a contrast evaluation value can be obtained by processing the image signal from the image sensor at the time of live view display by the camera DSP 227 or the system controller 230, and it is possible to perform contrast AF using the evaluation value. .

  At the time of shooting, each pixel data for one frame is read from the DRAM 229 according to a control signal from the system controller 230, subjected to image processing by the camera DSP 227, and temporarily stored in the work memory 226. Then, the data in the work memory 226 is compressed based on a predetermined compression format by the compression / decompression circuit 225, and the result is stored in the external nonvolatile memory (external memory) 224. As the external nonvolatile memory 224, a nonvolatile memory such as a flash memory is usually used. Moreover, a hard disk, a magnetic disk, etc. may be sufficient.

  In addition, when observing captured image data, the data compressed and stored in the external nonvolatile memory 224 is expanded into data for each normal captured pixel through the compression / decompression circuit 225, and the result is connected to the camera DSP 227. The video memory 221 is transferred. Thereby, display can be performed through the monitor display circuit 220.

  Furthermore, an operation display circuit 231, a release switch SW 1 (233), and a release switch SW 2 (234) are connected to the system controller 230. Also, for setting and various selections such as an AF mode SW (235) for switching between a normal shooting mode in which only phase difference AF is performed and a high-precision AF mode in which phase difference AF and contrast AF are used together, and other shooting modes. The operation switches 232 are also connected.

  The operation display circuit 231 displays the operation state of the camera set or selected by the above switches by a display element such as a liquid crystal element, LED (light emitting diode), or organic EL.

  The release switch SW1 (233) is a switch for starting photographing preparation operations such as photometry and focus detection. The release switch SW2 (234) is a switch for starting a photographing operation (charge accumulation and charge read operation for acquiring a still image).

  On the other hand, in the photographic lens 100, the lens control circuit 104 stores performance information such as the focal length and open aperture value of the photographic lens 100 and lens ID (identification) information that is unique information for identifying the photographic lens 100. A memory (not shown) is provided. This memory also stores information received from the system controller 230 through communication. The performance information and the lens ID information are transmitted to the system controller 230 by initial communication when the digital camera 200 is mounted, and the system controller 230 stores them in the EEPROM 223.

  Next, correspondence between the distance measuring point of the phase difference AF sensor, the photometric sensor, and the photometric range in this embodiment will be described.

  FIG. 4 is a diagram illustrating correspondence between the distance measurement point arrangement of the phase difference AF sensor 205 and the photometry area of the photometry sensor 208 used for automatic focus detection and adjustment in the present embodiment.

  FIG. 4A shows the arrangement of the line sensors for focus detection, and FIG. 4B shows the arrangement of the focus detection area in the object field (finder). As will be described later, the phase difference AF method uses a pair of light receiving elements. Therefore, as shown in FIGS. 4A and 4B, the focus detection of one area is performed by one set of two line sensors. The center region of the sensor is provided with two sets of four line sensors, and focus detection corresponding to both the vertical and horizontal directions is possible at the center of the finder.

  4 (c) and 4 (d) are schematic views showing the photometric area of the photometric sensor 208 for automatic exposure adjustment, and FIG. 4 (c) shows a divided sensor area for realizing the divided photometry, and FIG. ) Shows each divided photometry area in the viewfinder. In this example, as shown in FIGS. 4C and 4D, a split photometry method is used in which the viewfinder is equally divided into a total of 35 divisions of 7 in the vertical direction and 5 in the horizontal direction.

  FIG. 4E is a diagram showing how the detection areas of the distance measurement and photometry sensors are in a relative positional relationship in the viewfinder. As shown in FIG. 4 (e), each center area of the multipoint focus detection area and the divided photometry area is centered, and when expressed by the divided photometry area, one is above and below the center area, and two are on each side of the center area. A total of 7 areas are areas where both focus detection and photometry are performed.

  FIG. 4F shows the seven divided photometry areas. These consist of continuous areas, and select one focus detection area (hereinafter referred to as the main subject focus detection area) where the main subject is supposed to exist from the seven divided photometry areas according to the distance measurement result. Thus, automatic exposure control is performed. A main subject focus detection area is selected from a plurality of focus detection areas, and the largest first weighting is performed on the photometric value detected in the photometry area corresponding to the main subject focus detection area. In addition, a second weight smaller than the first weight is applied to the photometric value detected in the peripheral photometry area adjacent to the photometry area where the first weighting is performed. Further, a third weighting smaller than the first and second weighting is performed on the photometric values detected in the remaining photometry area. By calculating the exposure control value by the system controller 230 using the weighted photometric value in this way, the photometric value of the main subject can be prioritized, and shooting is performed with the exposure desired by the photographer. be able to.

  It should be noted that the exposure at the time of shooting is not determined using only the value of the photometric area corresponding to the main subject focus detection area. The photometry value in the photometry area corresponding to the main subject focus detection area is weighted to the maximum, but the exposure for photographing is determined in consideration of the photometry values in the peripheral photometry area and the remaining photometry areas. For this reason, when the contrast method AF is performed on the main subject focus detection area, if the exposure condition in the contrast method AF is determined based on the photometric value determined for photographing, erroneous distance measurement of the contrast method AF may occur. There is. This is because, for example, in a scene where the periphery is under and the main subject is bright, the exposure is not determined only for the bright main subject, so the main subject may be saturated and whiteout may occur. It is.

  Next, the detection principle of the defocus amount (focus position deviation amount) of the phase difference AF method of this embodiment will be described with reference to FIGS.

  As shown in FIGS. 5 and 6, when the image sensor is in focus, the interval between the two images on the pair of light receiving elements (line sensors) that are AF sensors takes a certain value. This value can be obtained by design, but in practice, it does not become the same as the design value due to the size, variation and assembly error of parts. Accordingly, the two-image interval (reference two-image interval Lo) is slightly different for each individual camera, and it is difficult to accurately obtain the reference two-image interval Lo unless actually measured for each individual camera. As is clear from FIG. 5, if the two-image interval is narrower than the reference two-image interval Lo, the photographing lens is in a so-called front pin state, and if it is wider than Lo, it is in a so-called rear pin state.

  FIG. 6 is a diagram illustrating a model in which the condenser lens is omitted from the phase difference AF sensor 205. As shown in this figure, when the angle of the principal ray incident on the phase difference AF sensor 205 is θ, the separator lens magnification is β, and the image movement amounts are ΔL and ΔL ′, the defocus amount d is expressed by the following equation. I want.

d = ΔL / tan θ = ΔL ′ / β tan θ
Here, β tan θ is a parameter determined by the design of the phase difference AF sensor 205. ΔL ′ can be obtained from the reference two-image interval (Lo) and the current two-image interval (Lx).

  The phase difference AF sensor 205 has a plurality of the above-described configurations so that focus detection can be performed in a plurality of focus detection areas in the photographing screen as described with reference to FIG.

  For adjustment at the time of manufacture (factory shipment) of the autofocus control function, a reference lens whose focus position is known in advance is used. Then, the value of the two-image interval obtained from the phase difference AF sensor 205 is used as the adjustment value of the AF focus correction parameter so that the focus position comes to the position of the imaging surface of the image sensor 212 (depending on the assembly error of the image sensor). The data is stored in the EEPROM 223.

  However, when the photographing lens attached to the digital camera changes, the focus position varies due to manufacturing errors of the photographing lens itself. Therefore, as will be described later, by using the contrast method AF together, it becomes possible to focus more accurately and without using the photographing lens.

  Next, the outline of the contrast AF according to this embodiment will be briefly described with reference to FIG.

  The contrast AF is an automatic focus detection method used in video equipment such as a video camera and a compact digital camera. In this method, a high-frequency component in a video signal from an image sensor such as a CCD or CMOS is extracted as a focus signal, and the focusing lens of the imaging optical system is driven so that this focus signal (focus evaluation value) is maximized. It is controlled and moved to the in-focus position. This method is called a hill-climbing method or TV-AF method, which does not require a special optical member for focus adjustment, and has the advantage of being able to focus accurately without depending on the distance at a distance or near. is there.

  FIG. 7 is an explanatory diagram of focus detection by contrast AF, in which the focusing lens is moved at a high speed in a large blurred state, and continues to move in the same direction as the evaluation value increases. When the evaluation value is small, the focusing lens is moved in the opposite direction, and the focusing lens is always moved so that the focusing evaluation value based on the focus signal is large. When the focus signal exceeds a predetermined value, the moving speed of the focusing lens is reduced, and the mountain is slowly climbed, and the movement of the imaging lens is stopped at point A where the focus evaluation value is maximized.

  The contrast method AF is a control method that can drive the lens so that it is always in focus and is suitable for moving images and live views. However, in the case of a still image, when the photographing lens is driven and controlled within a predetermined range that is expected to include the in-focus position while capturing the focus evaluation value, the focus evaluation value of the focus evaluation value is It is also possible to focus by controlling to return the peak to the recorded lens position.

  Next, the operation of the digital camera of this embodiment will be described. First, the AF mode selection sequence will be described with reference to FIG. This sequence is executed by the system controller 230 according to a program. The same applies to each sequence described later.

  In this embodiment, there are two types of AF modes: a normal AF mode in which only phase difference AF is performed, and a high-precision AF mode in which phase difference AF and contrast AF are combined to reduce phase difference AF errors. .

  When the AF mode selection sequence is started, the system controller 230 first reads the state of the AF mode SW 235 in step S101. In step S102, the state of the read SW is compared with the state of the previously read AF mode SW 235 stored in the RAM built in the chip by the system controller 230.

  If it is confirmed that the change has occurred by taking XOR (step S103), the process proceeds to step S104, and the state of the AF mode SW235 read this time is stored in the RAM on the system controller 230 as the state of the new AF mode SW235. . If no change is detected in step S103, the sequence of AF mode selection ends.

  If there is a change, it is determined after step S104 whether the new AF mode is the normal AF mode (step S105). Depending on the result, the normal AF mode is stored on the RAM (incorporated by the system controller 230) (step S106), or the high-precision AF mode is stored on the RAM (step S107). ). Then, the AF mode selection sequence ends.

  Next, with reference to FIG. 3, a sequence from SW1 on to photographing in this embodiment will be described.

  When the switch SW1 (233) is turned on, the shooting preparation sequence of the digital camera 200 starts. First, in step S201, a distance measurement operation using phase difference AF is performed. The light beam that has passed through the photographing lens 100 passes through the half mirror portion of the quick return mirror 203, is reflected by the sub mirror 204, and enters the phase difference AF sensor 205. The distance measurement image signal read out by the focus detection circuit 206 is read out by the system controller 230 and calculated according to the principle of the phase difference AF described above, and the amount of focus shift necessary for the focusing operation is calculated. In the automatic selection mode of the distance measuring points, a distance measuring point at which the main subject is supposed to exist is selected from the distance measurement results of the plurality of distance measuring points. Various techniques are known for ranging point selection algorithms, but there is simply a method of selecting the distance measuring point that gives the closest result as the main subject ranging point.

  Next, in step S202, according to the focus shift amount calculated in step S201, the system controller 230 transmits a lens driving amount for focusing to the interchangeable lens 100 through communication through the electrical contact unit 107. . When the interchangeable lens 100 receives the instructed lens driving amount, the interchangeable lens 100 operates the lens driving mechanism 103 through the lens control circuit 104 according to the driving amount, and drives the focus lens 101 by the designated lens driving amount.

  In step S <b> 203, the system controller 230 performs a photometric operation for photographing using the photometric sensor 208 and the photometric circuit 209. At this time, as described above, a weighted photometric operation is performed on the selected distance measuring point, and a photometric value for determining the aperture and shutter speed for photographing is calculated. Then, it is stored on the RAM in the system controller 230.

  In step S204, it is checked whether the switch SW1 (233) remains on. When the switch SW1 (233) is turned off, the photographing preparation operation is finished, and a standby state is entered until the switch is pressed.

  If the switch SW1 (233) is on, the process proceeds to the next step S205, and it is checked whether the switch SW2 (234) is on. When the switch SW2 (234) is in the off state, the process returns to step S204, and the check of the states of SW1 (233) and SW2 (234) is repeated. When SW2 (234) is turned on, the process proceeds to the sequence of shooting operations after step S206.

  In step S206, in response to a command from the system controller 230, first, the quick return mirror 203 is flipped up to the shooting position by the mirror drive mechanism 213. At the same time, the sub mirror 204 is also folded to the shooting standby position in conjunction with the quick return mirror 203.

  In step S207, the system controller 230 reads data in the built-in RAM, and determines which mode is currently set to the AF mode based on the AF mode selection sequence described above. If the normal AF mode is set, the process proceeds to step S216, and a series of normal photographing operations such as aperture driving (step S216), shutter opening (step S217), image sensor exposure (step S218), and shutter closing (step S219). Perform the action.

  If the high-precision AF mode is set in step S207, the sequence for performing contrast AF starting from step S208 is entered.

  In step S208, the focal plane shutter 210 charged by the shutter charge mechanism 214 is opened through the shutter control circuit 215 in accordance with a command from the system controller 230.

  Next, the process proceeds to step S209, and the accumulation operation of the image sensor 212 is performed for the photometry operation for the contrast AF operation. Regarding the accumulation time, since the contrast AF is a moving image operation, the accumulation time may be determined to be 1/60 second or 1/30 second on the assumption of 60 sheet operation or 30 sheet operation. Further, the initial accumulation time may be determined based on the photometric value for photographing determined in step S203.

  After completion of the accumulation, the process proceeds to step S210, and the system controller 230 drives the timing generator 219 according to a command to the camera DSP 227. Then, using the driver 218, the CDS / AGC circuit 216, the A / D converter 217, the selector 222, the memory controller 228, and the like, the image information stored in the image sensor 212 in the range used for contrast AF is read on the DRAM 229.

  In the next step S211, the system controller 230 calculates the maximum value of the brightness from the image information read in step S211, and compares it with a predetermined value, thereby causing a whiteout phenomenon in the focus detection region. Check if is happening. If the maximum luminance value is lower than the predetermined value, it is determined that there is no whiteout phenomenon, and the process proceeds to step S213. Then, based on the above-described known contrast AF, the camera DSP 227 or the system controller 230 calculates the contrast evaluation value while slightly driving the focus lens 101, and stops the lens at the position where the contrast evaluation value is maximized. Thereby, highly accurate AF is performed.

  If it is determined in step S211 that the maximum luminance value exceeds the predetermined value and the whiteout phenomenon has occurred, the reliability of the contrast AF result is lowered as it is, so in step S212 the CDS / AGC circuit 216 is set. Adjust and lower the gain. Then, the process returns to step S209, and the above steps are repeated until the whiteout phenomenon is eliminated.

  During contrast AF, contrast AF is performed on the result of phase difference AF in step S201 or the vicinity of a distance measuring point selected by manual selection by a photographer. For this reason, the shooting AE in step S203 determines the exposure with reference to the entire screen while weighting the vicinity of the distance measuring point, whereas the area for which the exposure is determined by the contrast AF is used for distance measurement. Only the vicinity of the distance measuring point, and the area used for photometry is different. For contrast AF, it is important not to cause whiteout in the area where the evaluation value is calculated. In contrast, in the case of shooting AE, the entire screen is exposed even if there is a high-luminance subject. If there is no bankruptcy, it is not necessarily bad that whiteout occurs. Therefore, the required algorithm is different. Therefore, as described above, it is necessary to separately perform photometry for contrast AF and photometry for photographing.

  Here, in the image pickup device 212, R, G, or B color filters are arranged in front of each pixel, and are usually arranged in a so-called Bayer array.

  The luminance Y depends on the characteristics of the color filter and the image sensor, for example, these characteristics are the international standard ITU-R BT. If it is based on 601, it is obtained by the following equation.

Y = 0.299 × R + 0.587 × G + 0.114 × B
When the contrast AF in step S213 is completed, the process proceeds to step S214, and the shutter needs to be closed once before shooting a still image. Therefore, a shutter closing operation is performed via the shutter control circuit 215 in response to a command from the system controller 203. .

  Next, in step S215, the exposure conditions for contrast AF that have been set up to now are discarded, and an operation for returning to the setting for exposure conditions for photographing that has been measured in advance in step S203 is executed.

  With the above, the contrast AF operation in the high-precision AF mode is completed, and then the photographing operation is performed.

  First, in step S216, the aperture controller drive circuit 106 drives the aperture drive mechanism 105 by the system controller sending an aperture value command to the photographic lens 100 side through the electrical contact unit 107 based on the photometry information at the time of shooting. As a result, the aperture 102 is driven to the commanded aperture value.

  Next, in step S217, the operation of opening the focal plane shutter 210 charged by the shutter charge mechanism 214 is performed through the shutter control circuit 215 in accordance with a command from the system controller 230.

  Next, in step S218, the accumulation operation of the image sensor 212 is performed.

  Next, in step S219, after the time corresponding to the shutter speed predetermined in step S203 has elapsed, the focal plane shutter 210 is closed through the shutter control circuit 215 in accordance with a command from the system controller 230.

  In step S220, the quick return mirror 203 is returned to the photographing optical path via the mirror driving mechanism 213 according to a command from the system controller 230.

  Next, in step S <b> 221, the system controller 230 drives the timing generator 219 according to a command to the camera DSP 227. Then, using the driver 218, the CDS / AGC circuit 216, the A / D converter 217, the selector 222, the memory controller 228, and the like, image information stored in the image sensor 212 on the DRAM 229 is read.

  In step S222, the system controller 230, together with the camera DSP 227, converts the image information on the DRAM 229 into a predetermined format such as white balance, gamma processing, color conversion, and JPEG. Further, thumbnail creation, photographed image display on the monitor display unit 220 through the video memory 221, compression processing in the work memory 226 and the compression / expansion circuit 225, and recording operation in the nonvolatile memory 224 are performed. These series of operations are post-shooting processing operations.

  Thus, the sequence from SW1 on to the shooting operation is completed.

  As described above, when the high-precision AF mode is set, the phase difference AF operation is performed when SW1 is turned on, and then the release operation is performed when SW2 is turned on. Perform a focusing operation. By performing a photographing operation after that, it is possible to perform focusing with higher accuracy than in the normal AF mode with phase difference AF alone.

  In this embodiment, an example is shown in which the contrast AF is activated by turning on SW2 in the high-precision AF mode. However, in the high-precision AF mode, the contrast immediately after the phase difference AF by turning on SW1 without waiting for SW2 on. A method AF operation may be performed. When performing contrast AF, the single-lens reflex type digital camera needs to be in the mirror-up and shutter-open state as already described. In the meantime, the optical viewfinder image disappears, and instead, live view display may be performed on the monitor display 220 during the contrast AF. After the contrast AF is completed, the shutter is charged after the shutter is closed, the quick return mirror 203 is lowered, and SW2 is turned on in that state.

  In the present embodiment, an example in which contrast AF is performed in the high-precision AF mode has been described. However, a calibration mode may be provided separately from the time of shooting, and high-precision AF using contrast AF may be performed, and an error from phase difference AF may be stored in the EEPROM 223 as a correction value. Then, during normal photographing, the error of the phase difference AF is corrected with the correction value. In that case, exposure conditions for contrast AF are set before the contrast AF is performed, as in the present embodiment.

(Second Embodiment)
In the first embodiment, focusing on the highlight portion of the region used for calculating the evaluation value in the photographed image, an example is shown in which the gain adjustment is performed so that the value of the highlight portion is equal to or less than a predetermined value to suppress whiteout. .

  However, the means for suppressing overexposure is not limited to this. A simpler means may be used, and the second embodiment is such an example.

  FIG. 8 is a flowchart showing a sequence from SW1 on to imaging processing in the second embodiment.

  In FIG. 8, steps that perform the same operations as in FIG. Explanation of the same operation steps is omitted.

  In the second embodiment, during the step of performing the AE operation for contrast AF, it is checked in step S231 whether or not the gain has already been adjusted after the data reading in step S210.

  If the gain has not been adjusted in step S231, the process proceeds to step S211 for determining whether or not whiteout has occurred. If already adjusted, the process proceeds to step S213, and the contrast AF operation is performed.

  If it is determined in step S211 that no whiteout has occurred, the process proceeds to the contrast AF operation in step S213. On the other hand, if it is determined that overexposure has occurred, the process proceeds to step S232, and the CDS / AGC circuit 216 sets the gain to 2 steps under, that is, 1/4.

  When performing the contrast AF AE, if the initial photometry value of the contrast AF is determined based on the result of the shooting AE in step S203, the result of the contrast AF AE and the shooting AE do not necessarily match. However, since they are looking at the same scene, there is no significant difference. Therefore, when a whiteout phenomenon occurs as in this embodiment, it is possible to avoid the whiteout phenomenon in most cases by performing a predetermined amount of gain reduction processing.

  In this way, in most cases, the gain adjustment process described in the first embodiment can be omitted, and the effect of shortening the entire distance measurement operation can be obtained.

  With respect to the gain reduction amount, in the present embodiment, an example in which the two-stage under setting is set is shown, but the present invention is not limited to this. For example, it is needless to say that it may be set to 2.5 steps under or 3 steps under.

  The first and second embodiments have been described above with reference to FIGS.

  As described above, in the above embodiment, the exposure method setting for the contrast AF is performed independently of the shooting AE so that the contrast AF is not affected by the whiteout phenomenon in the distance measurement area. Yes. Further, since it is impossible to determine whether or not whiteout occurs in a largely blurred state, exposure conditions for contrast AF are set so as not to cause whiteout after being substantially focused by phase difference AF.

  In the present invention, various modifications other than those described in the above embodiments are possible.

  For example, the present invention is not limited to the arrangement of the phase difference AF sensor and the photometric area arrangement of the photometric sensor shown in the above embodiment.

  In the description of the embodiment, the camera DSP 227 or the system controller 230 is configured to have the evaluation value calculation for contrast and the peak hold function of the luminance value. However, it goes without saying that this function may be assigned to hardware such as a dedicated IC.

  In addition to the above, various modifications may be made without departing from the scope of the present invention.

(Other embodiments)
The object of each embodiment is also achieved by the following method. That is, a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded is supplied to the system or apparatus. Then, the computer (or CPU or MPU) of the system or apparatus reads and executes the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but the present invention includes the following cases. That is, based on the instruction of the program code, an operating system (OS) running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  Furthermore, the following cases are also included in the present invention. That is, the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion card or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  When the present invention is applied to the above storage medium, the storage medium stores program codes corresponding to the procedure described above.

1 is a block diagram illustrating a configuration of a digital camera according to a first embodiment of the present invention. It is a flowchart explaining AF mode selection sequence of the digital camera of 1st Embodiment. It is a flowchart explaining the sequence from ON of SW1 of the digital camera of 1st Embodiment to imaging | photography. It is a figure which shows a response | compatibility with the ranging point of the phase difference AF sensor of 1st Embodiment, and the photometry area of a photometry sensor. It is a figure explaining the operation | movement of phase difference AF of 1st Embodiment. It is a figure explaining the operation | movement of phase difference AF of 1st Embodiment. It is a figure explaining the operation | movement of contrast system AF of 1st Embodiment. It is a flowchart explaining the sequence from ON of SW1 of the digital camera of 2nd Embodiment to imaging | photography. It is a figure explaining the operation | movement of contrast system AF in case exposure is improper.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Shooting lens 101 Focus lens 205 Phase difference AF sensor 212 Image pick-up element 227 Camera DSP
230 System Controller

Claims (6)

An image sensor that photoelectrically converts a subject image formed by a photographing lens and outputs an image signal; and
Conversion means for amplifying the signal output from the image sensor and converting it to a digital signal;
A first autofocus that adjusts the photographing lens to a focus position based on a phase difference between images corresponding to the two main subject focus detection areas divided by the optical system that divides the subject image into two images. First autofocus means for performing the operation ;
A second autofocus means for performing a second autofocus operation for adjusting the photographing lens to a focus position based on a contrast of an image signal corresponding to the main subject focus detection area output from the image sensor;
Exposure condition setting means for setting an exposure condition of the image sensor;
By the exposure condition setting means, the exposure condition of the imaging device, performs Oite said second auto focusing operation when the image corresponding to the main subject focus detection area is set in such exposure conditions as overexposure case, digital amplifies the signal from the imaging device with a smaller gain than the gain of the case of photographing by performing the first auto focusing operation without performing the second auto focusing operation in the same exposure conditions Control means for controlling to convert to a signal ,
The control means performs exposure for shooting under an exposure condition in which an image corresponding to the main subject focus detection area is blown out after performing the second autofocus operation by the second autofocus means. imaging apparatus for causing.   The exposure condition in which the image corresponding to the main subject focus detection area is overexposed is an exposure condition in which the signal level of the highlight portion of the image signal output from the image sensor exceeds a predetermined value. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is provided. An image sensor that photoelectrically converts a subject image formed by a photographic lens and outputs an image signal; a conversion unit that amplifies a signal output from the image sensor and converts it into a digital signal; and Based on the phase difference between the images corresponding to the two main subject focus detection areas divided by the optical system that divides the image, a first autofocus operation for adjusting the photographing lens to the in-focus position is performed . And a second autofocus operation for adjusting the photographing lens to the in-focus position based on the contrast of the image signal corresponding to the main subject focus detection area output from the image sensor and the autofocus means. A method of controlling an imaging apparatus comprising autofocus means and exposure condition setting means for setting exposure conditions of the image sensor,
By the exposure condition setting means, the exposure condition of the imaging device, performs Oite said second auto focusing operation when the image corresponding to the main subject focus detection area is set in such exposure conditions as overexposure case, digital amplifies the signal from the imaging device with a smaller gain than the gain of the case of photographing by performing the first auto focusing operation without performing the second auto focusing operation in the same exposure conditions Comprising a control step of controlling to convert to a signal ,
In the control step, after performing the second autofocus operation by the second autofocus means, exposure for shooting is performed under an exposure condition such that an image corresponding to the main subject focus detection area is overexposed. A method for controlling an image pickup apparatus. The exposure condition in which the image corresponding to the main subject focus detection area is overexposed is an exposure condition in which the signal level of the highlight portion of the image signal output from the image sensor exceeds a predetermined value. The method for controlling an image pickup apparatus according to claim 3 , wherein: A program for causing a computer to execute the control method according to claim 3 or 4 . A computer-readable storage medium storing the program according to claim 5 .

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