JP5822479B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus having a function of detecting dust in a focus detection optical system.

  2. Description of the Related Art Conventionally, in a phase difference AF type automatic focusing device of a general interchangeable lens type single-lens reflex camera system, two images formed by a subject light flux that has passed through two different exit pupil regions of the interchangeable lens are converted into a line sensor pair. The light is received and photoelectrically converted. A method of detecting a defocus amount, that is, a so-called defocus amount of the interchangeable lens by obtaining a relative position displacement of an image signal that is an output is general. In this case, since the line sensor pair extracts only the luminance distribution of a specific area in the subject space, the defocus amount cannot be detected for a subject having no luminance distribution in that area. In view of this, a method has been proposed in which a plurality of line sensor pairs and corresponding focus detection optical systems are prepared, and focus detection can be performed on a larger number of subjects by extracting luminance distributions of a plurality of subject areas. Yes. In addition, a method has been proposed in which line sensor pairs are arranged so as to be orthogonal to each other in the focus detection areas (hereinafter referred to as cross phase difference AF).

  Specifically, the focus detection optical system of cross phase difference AF will be described with reference to FIG. In order to simplify the explanation in this figure, the focus detection is possible only in the center area on the shooting screen, and the line sensor that is paired with the phase difference AF is within the area in the vertical and horizontal directions of the shooting screen. It is arrange | positioned so that it may orthogonally cross. Therefore, the total number of line sensor pairs is two. Furthermore, a method for improving detection accuracy by arranging a plurality of line sensor pairs in the same direction and shifting the pixels of the plurality of line sensor pairs by 1/2 pixel (hereinafter referred to as a staggered arrangement) has also been proposed. Yes. First, it is possible to reduce a focus detection repetition error by averaging the focus detection results of a plurality of line sensor pairs. Secondly, in each pixel constituting the line sensor, there is a sensitivity characteristic unevenness in which the center of the pixel is high in sensitivity and the end of the pixel is low. Therefore, it is possible to cancel (reduce) the phenomenon of phase-in / out in which the phase shape changes even when the subject image on the line sensor is moved slightly within one pixel range and the focus detection result changes.

  Conventionally, dust that floats in the air, such as dust, when attaching / detaching an interchangeable lens, adheres to the main mirror or sub mirror on the optical path of the AF sensor or the focus detection optical system (hereinafter referred to as focus detection system dust). There has been a problem that the detection accuracy is significantly lowered.

  Specifically, as shown in FIG. 11, if the vertical axis represents the image signal output of the line sensor pair and the horizontal axis represents the pixel position of the line sensor pair, the image signal output of a certain line sensor pair is generated by the focus detection system dust. descend. When the focus detection system dust is reflected in the focus detection optical system, a false defocus amount is detected even when there is no contrast of the subject.

  With respect to this problem, in Patent Document 1, the false defocus amount detected by the focus detection system dust is detected again regardless of how much the focusing lens of the photographing lens is driven. Pay attention. That is, a technique is disclosed that determines that the focus detection system dust is attached when in this state and prohibits focus detection by the line sensor pair.

Japanese Patent No. 2952215

  However, the conventional technique disclosed in Patent Document 1 described above has the following problems.

  First, the focus detection system dust cannot be detected unless the camera actually drives the focusing lens.

  Second, the focus detection system dust may not be detected unless the subject has a very low contrast or no contrast. This is because the influence of the focus detection system dust is reduced when the subject has a high contrast. Similarly, focus detection system dust may not be detected even when the luminance distribution of pixels in a region where focus detection system dust is reflected is relatively lower than pixels in other regions. This is because the luminance distribution of the pixels in the region where the focus detection system dust is reflected is embedded in the low luminance distribution.

  Third, as shown in FIG. 12, depending on the position of attachment, the reflection of the focus detection system dust may affect only one image of the pair of line sensors. In this case, the focus detection system dust is false. May not be detected as the defocus amount.

  Fourth, in the mode in which the automatic focus adjustment follows the moving subject, it is impossible to distinguish the false defocus amount detected by the focus detection system dust from the defocus amount newly generated by the subject moving. Sometimes, there was a possibility of misdetecting the focus detection system dust.

(Object of invention)
An object of the present invention is to provide an imaging apparatus capable of accurately detecting focus detection system dust.

To achieve the above object, an imaging apparatus of the present invention, a focus detection means for detecting a focus state in a focus detection area set in the picture plane, the images in the focus detection area from the focus detection unit acquired, acquires the first contrast detecting means for detecting the contrast of the acquired image, an imaging unit to obtain an image for photometry, the images in the area corresponding to the focus detection area from the image pickup means A second contrast detecting means for detecting the contrast of the acquired image; a first contrast detected by the first contrast detecting means; and a second contrast detected by the second contrast detecting means. comparison, said second contrast is the contrast of the image obtained by the image pickup means in a region corresponding to the focus detection area is smaller than a predetermined threshold value By the first contrast is greater than a predetermined threshold value, it is characterized in that it has a focus detection system dust detection means for detecting a focus detection system dust.
In another imaging apparatus, a focus detection unit that detects a focus state in a focus detection region set in a screen, and an image in the focus detection region is acquired from the focus detection unit, and a contrast of the image is detected. a first contrast detecting means for, Taking a iMAGING means for obtaining images for shadows to acquire an image in a region corresponding to the focus detection area from the image pickup means, the second to detect the contrast of the image A first contrast detected by the first contrast detecting means and a second contrast detected by the second contrast detecting means, and corresponding to the focus detection area. the second contrast is the contrast of the images of the imaging means at the region is smaller than a predetermined threshold value, the first contrast predetermined threshold By large Ri, it is characterized in that it has a focus detection system dust detection means for detecting a focus detection system dust.

  According to the present invention, it is possible to accurately detect the focus detection system dust.

1 is a block diagram of an interchangeable lens digital camera that is Embodiment 1 of the present invention. FIG. FIG. 3 is a diagram illustrating a focus detection area according to the first embodiment. FIG. 3 is a diagram illustrating a photometric area according to the first embodiment. 3 is a flowchart illustrating an automatic focus adjustment and an imaging sequence according to the first exemplary embodiment. 6 is a flowchart illustrating automatic focus detection selection according to the first exemplary embodiment. 6 is a flowchart for explaining optional focus detection according to the first embodiment. 10 is a flowchart illustrating an operation in a focus detection system dust detection mode according to the second embodiment. It is a figure which shows the focus detection type dust detection mode setting screen of Example 2. FIG. It is a figure which shows the imaging type dust data acquisition mode setting screen of Example 2, and a white balance setting mode setting screen. It is a figure for demonstrating a general focus detection optical system. It is a figure which shows an image signal output when focus detection system dust adheres to a line sensor pair. It is a figure which shows an image signal output when focus detection system dust is reflected in one image of a pair of line sensors.

  The mode for carrying out the invention is as described in Examples 1 and 2 below.

  FIG. 1 is a block diagram showing a configuration of an interchangeable lens type digital camera which is an example of an imaging apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a lens MPU (microprocessing unit), which performs control related to the interchangeable photographing lens 100. Reference numeral 2 denotes a lens driving unit for driving the focusing lens 3 of the photographing lens 100, and reference numeral 4 denotes an aperture driving unit for driving the diaphragm 5.

  The taking lens 100 is constituted by the lens MPU 1, the lens driving unit 2 and the aperture driving unit 4. The photographing lens 100 is connected via a mount 6 as shown by a dotted line in the figure, and is detachable from the camera body 110.

  A camera MPU 7 performs control related to the camera body 110. A mirror driving unit 8 retracts the main mirror 9 and the sub mirror 10 arranged on the optical axis at the time of photographing. Reference numeral 11 denotes a defocus amount detection unit. A defocus amount, which is a defocus amount required for automatic focus adjustment, is calculated by an output from the defocus amount detection unit 11.

  As shown in FIG. 2A, the defocus amount detection unit 11 according to the first embodiment has five focus detections including the center in the shooting screen when the area corresponding to one licensor pair is indicated by a rectangle. An area 12 is set, and the focus state can be detected at these five points. In one focus detection region 12, two line sensor pairs are arranged in a staggered arrangement in the vertical direction and horizontal direction of the shooting screen. That is, the total number of line sensor pairs in the shooting screen is 5 × 2 × 2 = 20. The number of pixels of the pair of line sensors is 100 × 2 = 200 pixels, and the total number of pixels of the defocus amount detection unit 11 is 4000 pixels in monochrome. The camera MPU 7 and the defocus amount detection unit 11 constitute a focus detection unit.

  Reference numeral 13 denotes a photographing unit that generates a photographed image of 4800 × 3200 = about 15 million pixels in RGB from the image sensor 21. The photographing unit 13 constitutes an imaging unit that obtains a photographing screen for photographing. 14 is a photometric unit, which generates a photographic image in a photometric area 15 of 640 × 480 = about 300,000 pixels in RGB as shown in FIG. 3 from a subject image guided by a photometric optical system (not shown). Determine the automatic exposure with color. The photometric unit 14 constitutes an imaging unit that obtains a captured image for photometry. Reference numeral 16 denotes a nonvolatile memory EEPROM which stores various camera settings. Reference numeral 17 denotes a recording unit, which records captured images as files on a removable memory card.

  Reference numeral 18 denotes a dial / SW unit for setting various camera settings (focus detection mode, shutter speed, aperture value, ISO sensitivity, etc.). Reference numeral 19 denotes a display unit that displays various camera settings and captured images on the display panel 20.

  When the main SW is turned on, the camera MPU7 and the lens MPU1 are activated, and the camera system functions. SW1 is a switch that is turned on by a first stroke operation (half press) of the release button, and SW2 is a switch that is turned on by a second stroke operation (full press) of the release button. When SW1 is turned on, the automatic focus adjustment device operates.

  Reference numeral 20 denotes a display panel, 21 denotes an image sensor, 22 denotes a focusing plate, 23 denotes a pentaprism, and 24 denotes an optical viewfinder.

  This will be described more specifically with reference to the flowcharts of FIGS.

  When SW1 is turned on, the process proceeds to step 101 in FIG. 4 to start the automatic focus adjustment device and the processing of the imaging sequence. First, in step 102, it is determined whether SW1 is turned on. If SW1 is not on, the process proceeds to step 113 and the automatic focus adjustment is terminated. If SW1 is on, the process proceeds to step 103, where automatic exposure control and contrast calculation are performed. As shown in FIG. 3, the photometric unit 14 is composed of photoelectric conversion elements of RGB of 640 × 480 = about 300,000 pixels, generates a photometric image for photometry, and determines automatic exposure in consideration of the subject color. At the same time, as shown in FIG. 2A, the contrast of the pixel corresponding to the focus detection area 12 corresponding to each individual licensor pair on the photographing screen is calculated from the photographed image of the photometry unit 14 (hereinafter, referred to as “the focus detection area 12”). Photometric contrast = second contrast). The camera MPU 7 that executes Step 103 constitutes a second contrast detecting means.

  Subsequently, the process proceeds to step 104, and the process proceeds to either step 105 or step 106 depending on whether the setting of the focus detection mode of the camera is “automatic selection” or “optional selection”. “Automatic selection” automatically selects an optimum area from the five focus detection areas 12 in FIG. 2A, and “optional selection” means that the user selects any one of the focus detection areas 12 by an operation switch. To choose one. Details of step 105 and step 106 will be described later.

  When step 105 or step 106 is completed, if the focus detection is successful, the defocus amount is calculated. Therefore, it is determined whether or not the defocus amount is equal to or less than a threshold (so-called in-focus defocus width) that can be regarded as in-focus. Judge with. If not in focus, the process proceeds to step 108, lens driving is performed according to the defocus amount, and the processing from step 102 to step 108 is repeated until the in-focus state is obtained. In addition, when focus detection fails, it is determined that focus is not achieved, and the lens drive amount at that time is set to 0, that is, the process from step 102 to step 108 is repeated until focus is achieved without driving the lens.

  If it is determined in step 107 that the subject is in focus, the process proceeds to step 109 to determine again whether SW1 is turned on. If SW1 is not on, the process proceeds to step 113 and the automatic focus adjustment is terminated. If SW1 is on, the process proceeds to step 110 to determine whether SW2 is on.

  If SW2 is on, photographing operation and contrast calculation are performed in step 111. The photographing unit 13 generates a photographed image from the image sensor 21 having 4800 × 3200 = about 15 million pixels in RGB. The captured image is recorded as a file on a removable memory card attached to the recording unit 17. At the same time, as shown in FIG. 2A, the contrast of the pixel corresponding to the focus detection area 12 corresponding to each individual licensor pair on the shooting screen is calculated from the shot image of the shooting unit 13 (hereinafter, referred to as “the focus detection area 12”). Shooting contrast = second contrast). The camera MPU 7 that executes step 111 constitutes a second contrast detecting means.

  Subsequently, the process proceeds to detection of dust in the focus detection system in step 112, and the processing from step 109 to step 112 is repeated until SW1 is not turned on.

  Before describing the focus detection system dust detection in step 112, the above-described “focus detection automatic selection” in step 105 and “focus detection arbitrary selection” in step 106 will be described using the flowcharts of FIGS. 5 and 6, respectively. .

  First, when the “focus detection automatic selection” process is started in step 201 in FIG. 5, accumulation control is started for all line sensor pairs of the defocus amount detection unit 11 in step 202. When the accumulation control is started in step 202, the process proceeds to step 203, and it is determined whether a predetermined time-out period has elapsed since the accumulation start. The line sensor pair according to the first exemplary embodiment has a subject contrast sufficient for focus detection between the pixels of the line sensor by the AGC (auto gain control) circuit or before the charge is saturated in any pixel. Stop accumulation. However, when the subject contrast is low and the subject brightness is low, the accumulation is not completed indefinitely. Therefore, a time-out period in which responsiveness does not become a problem in practical use is provided, and when this time has elapsed, the accumulation is forcibly terminated and the process proceeds to step 209.

  On the other hand, if the time-out period has not elapsed, the process proceeds to step 204, where it is determined whether accumulation of any line sensor pair has been completed. If the accumulation has not been completed, the process returns to step 203. If the accumulation has been completed, the process proceeds to step 205, and the image signal of the corresponding line sensor pair is read. Subsequently, the process proceeds to step 206, where the relative position displacement amount of the image signal is obtained by correlation calculation, and the defocus amount is detected by appropriately calculating the relative position displacement amount. Furthermore, it progresses to step 207 and a reliability determination and contrast calculation are performed. The reliability determination is performed based on whether or not the degree of coincidence of the subject images between the line sensor pairs is equal to or greater than a predetermined threshold value. When ghost light is incident on the focus detection system, the subject image is greatly destroyed, and the focus detection accuracy is significantly reduced. Therefore, when the degree of coincidence of the subject images is less than a predetermined threshold, even if the defocus amount is detected, focus detection is impossible. Subsequently, the contrast of the line sensor pair is calculated (hereinafter, focus detection contrast = first contrast). The camera MPU 7 that executes step 207 constitutes a first contrast detecting means. When the subject has a low contrast or no contrast, the focus detection accuracy is remarkably lowered. Therefore, the focus detection is disabled even when the contrast is less than a predetermined threshold. Further, the line sensor pair in which the focus detection system dust is detected is also disabled for focus detection.

  Proceeding to step 208, it is determined whether or not the accumulation of all line sensor pairs has been completed. If the accumulation has not been completed, the processing from step 203 to step 208 is repeated. On the other hand, if the accumulation is completed, the process proceeds to step 209, and the defocus amount calculated by which line sensor pair is used for each of the five focus detection areas 12, and the final defocus in the focus detection area 12 is performed. Select whether to make a quantity. Specifically, as long as focus detection is not disabled, two pairs of line sensors in the horizontal direction and in the vertical direction average the defocus amount to obtain the horizontal defocus amount and the vertical defocus amount, respectively. . Next, the defocus amount in the direction in which the defocus amount in the closer direction is detected is set as the final defocus amount. This is because the defocus amount that is least affected by the background or the like (distance conflict) becomes the defocus amount in the closest direction.

  If the defocus amount for each of the five focus detection areas 12 is determined in step 209, the process proceeds to step 210, and the final focus detection area is selected. The selection method according to the first embodiment is based on an empirical rule that the closest subject is likely to be the main subject, and the defocus amount in the closer direction is selected from the focus detection areas in which focus detection is not disabled. Is selected. For example, in the example of FIG. 2B, the person is in front of the background building and the person's face is in front of the stomach. Therefore, the defocus amount detected in the central focus detection area is closer to the focus detection area at the center, regardless of the position of the distance ring of the photographic lens. The On the other hand, the focus detection cannot be performed because there is no contrast in the upper and right focus detection areas. Therefore, the defocus amount in the central focus detection area becomes the final defocus amount.

  In this way, the defocus amount of “focus detection automatic selection” is determined, and the process returns to step 107 in step 211.

  Next, “focus detection arbitrary selection” in step 106 will be described with reference to the flowchart of FIG. Many of the processes are the same as the “focus detection automatic selection” in FIG. 5, so only the differences will be described. First, accumulation control is started only for the run sensor pair included in the focus detection area selected by the user with the operation switch among the line sensor pairs of the defocus amount detection unit 11 in the accumulation setting in step 302. . Secondly, since the focus detection area 12 selected by the user with the operation switch is one, processing corresponding to the focus detection area selection in step 210 of FIG. 5 is not required.

  The above is the processing of the automatic focus adjustment device and the imaging sequence. The focus detection system dust detection in step 112 described above will be described. At step 112, photometric contrast, focus detection contrast, and imaging contrast are calculated.

  For example, in the example of FIG. 2B, as described above, since there is no contrast in the upper and right focus detection areas, these three contrasts are usually smaller than a predetermined threshold value. Therefore, when either the photometric contrast or the photographing contrast is smaller than the predetermined threshold, but the focus detection contrast is larger than the predetermined threshold, it is detected and stored that dust is attached to the focus detection system, In the focus detection after the next time, focus detection in the line sensor pair (focus detection region) is disabled.

  As a matter of course, the focus detection dust may be moved by a user's cleaning with a photographing operation or an air brush. Therefore, even in a line sensor pair in which focus detection dust is detected once, if either the photometric contrast or the photographing contrast is smaller than a predetermined threshold and the focus detection contrast is smaller than the predetermined threshold, the focus detection dust is It memorizes that it has disappeared, and again enables focus detection with the line sensor pair that has been disabled.

  Here, the “photometric contrast” or “photographing contrast” is set to “any” because there is a possibility that dust may also adhere to the photometric unit 14 or the photographing unit 13 itself. Even if the contrast of either unit exceeds a predetermined threshold due to the adhesion of dust, focus detection system dust can be correctly detected by the remaining units.

  In the first embodiment, the camera is actually focused by comparing the presence / absence of contrast of a plurality of imaging units (photometry unit 14 and photographing unit 13) that obtain a photographed image other than focus detection in a specific region of the photographed image. Focus detection dust can be accurately detected without driving the lens. Further, even if the reflection of the focus detection system dust affects only one image of the line sensor pair, the focus detection system dust can be accurately detected. Furthermore, focus detection system dust can be accurately detected regardless of whether or not the subject is moving.

  In addition, by using the remaining line sensor pairs by prohibiting the focus adjustment operation using the focus detection result of the line sensor pair in which the focus detection system dust is detected from the plurality of defocus amount detection means. Accurate focus detection is possible.

  Further, even if the line sensor pair in which the focus detection dust is once detected, if the focus detection dust is eliminated, the focus detection can be performed again by the line sensor pair that has been disabled, so that more accurate focus detection can be performed.

(Modification)
In the first embodiment, the focus detection system dust is detected based on the presence / absence of contrast in a plurality of imaging units (photometry unit, focus detection unit, imaging unit) in a plurality of focus detection areas set in the shooting screen. The present invention can be similarly applied even if the focus detection system dust is detected by analyzing the captured images of the imaging means and comparing the contrast similarity of the captured images in the plurality of imaging means.

  In the first embodiment, when the user performs a normal photographing operation, it is determined that there is no contrast in a specific region of the photographed image, and focus detection system dust is detected at that time.

  In the second embodiment, the user (photographer) intentionally captures an image having no contrast (blue sky, plain signboard, gray reflector, etc.) to detect the focus detection system dust.

  This will be described more specifically with reference to the flowchart of FIG. When the user operates the operation switch, the display unit 19 enters the “focus detection system dust detection mode” as shown in FIG. 8, and when the user presses the OK button, the process proceeds to step 401. Subsequently, automatic exposure control and contrast calculation are performed in step 402, focus detection automatic selection is performed in step 403, photographing operation and contrast calculation is performed in step 404, and focus detection system dust detection is performed in step 405. Step 402 is the same as step 103 in FIG. 4, step 403 is the same as step 105 in FIG. 4, step 404 is the same as step 111 in FIG. 4, and step 405 is the same as step 112 in FIG.

  In the second embodiment, the focus detection system dust is detected in accordance with the opportunity for the user to intentionally capture an image having no contrast. In Embodiment 1, since the presence or absence of contrast in the region corresponding to the line sensor pair is determined when performing the photographing operation, whether or not the focus detection system dust can be detected by a single photographing operation is determined. There is no certainty. On the other hand, in the second embodiment, it can be expected in advance that there is no contrast in the specific areas of the captured image corresponding to all the line sensor pairs, so that the focus detection system dust can be detected more reliably.

(Modification)
In the second embodiment, a dedicated mode for detecting dust in the focus detection system is provided. However, it may be combined with another function for capturing an image having no contrast more generally. Specifically, since the user intentionally captures an image with no contrast even in the imaging dust data acquisition mode as shown in FIG. 9A or the white balance setting mode as shown in FIG. 9B. Even if the focus detection system dust is detected when these functions are operated, the present invention can be similarly applied.

7 Camera MPU
11 Defocus amount detection unit 13 Imaging unit 14 Photometric unit 18 Dial / SW unit

Claims (6)

Focus detection means for detecting a focus state in a focus detection area set on the screen within
It acquires images in the focus detection area from the focus detection unit, a first contrast detecting means for detecting the contrast of the obtained image,
Imaging means for obtaining an image for photometry ;
Acquires images of the area corresponding to the focus detection area from the image pickup means, a second contrast detecting means for detecting the contrast of the obtained image,
The first contrast detected by the first contrast detection means is compared with the second contrast detected by the second contrast detection means, and obtained by the imaging means in an area corresponding to the focus detection area. Focus detection system dust detection means for detecting focus detection system dust when the second contrast, which is the contrast of the captured image, is smaller than a predetermined threshold value and the first contrast is greater than the predetermined threshold value. An imaging device that is characterized. Focus detection means for detecting a focus state in a focus detection area set in the screen;
First contrast detection means for acquiring an image in the focus detection area from the focus detection means and detecting contrast of the image;
And an imaging means for obtaining an image for shooting,
An image in a region corresponding to the focus detection region is acquired from the imaging unit, and a second contrast detection unit detects the contrast of the image ,
The first contrast detected by the first contrast detecting means is compared with the second contrast detected by the second contrast detecting means, and the image of the photographing means in an area corresponding to the focus detecting area is compared. It has focus detection system dust detection means for detecting focus detection system dust when the second contrast, which is the contrast of an image, is smaller than a predetermined threshold value and the first contrast is larger than a predetermined threshold value. to imaging device. The focus detection region, a plurality of sets in the picture plane,
The focus detection dust detection unit detects focus detection dust for each of the plurality of focus detection areas, and prohibits a focus adjustment operation using a focus detection result in the focus detection area where the focus detection dust is detected. The imaging apparatus according to claim 1 or 2 , wherein It has a setting means for the photographer to set a focus detection system dust detection mode for detecting a focus detecting system dust by taking the images without contrast,
The imaging means, the imaging apparatus according to any one of claims 1 to 3, characterized in that to obtain images without contrast in the focus detection system dust detection mode. A setting means for setting a white balance setting mode by the photographer to take a picture image without contrast,
The imaging means, the imaging apparatus according to any one of claims 1 to 3, characterized in that in the white balance setting mode obtaining images without contrast. A setting unit for setting an imaging system dust data acquisition mode in which the photographer detects dust attached to the imaging system by capturing an image having no contrast;
The imaging means, the imaging apparatus according to any one of claims 1 to 3, characterized in that to obtain images without contrast in the imaging system garbage data acquisition mode.

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