JP2008053809A - Camera and subject area extracting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To extract a subject area including a range-finding point from a photographed image. <P>SOLUTION: A camera determines photographic conditions, based on information regarding a previously set position in a field. The camera includes an imaging means for outputting an image of the field, an extracting means of extracting an area that includes the subject from the image, and a changing means of changing the extraction conditions of the extracting means, according to the number of positions, determining photographic conditions, in the area that includes the subject. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a camera that determines shooting conditions at a predetermined position in a subject field such as a distance measurement position and a photometry position, and an extraction method that extracts a subject area from a captured image.

  A camera is known in which an image of an object scene is acquired before shooting, a portion where a subject exists is extracted based on a luminance distribution in the image, and a focus is detected in that region (for example, a patent) Reference 1).

Prior art documents related to the invention of this application include the following.
Japanese Patent Laid-Open No. 2001-100087

  However, in the above-described conventional camera, as a result of analysis using luminance information, there is no focus point in the region extracted as the subject, or there is a focus point even if the focus point exists. Detection may not be possible. On the other hand, when there are many distance measuring points in the region extracted as the subject, there is a problem that another determination means must be provided in order to determine the distance measuring point for actual focus detection.

(1) The invention of claim 1 is a camera that determines a shooting condition based on information relating to a preset position in the object scene, and that captures an image of the object scene and outputs the image. And an extracting means for extracting an area including the subject from the image, and a changing means for changing the extraction condition of the extracting means in accordance with the number of positions in the area including the subject for determining the photographing condition.
(2) The camera according to claim 2 is configured such that the area including the subject is distinguished from the area not including the subject by the extraction unit.
(3) In the camera according to claim 3, the position for determining the photographing condition is a position corresponding to the distance measuring point for performing focus detection, and the distance measuring point is within the region extracted by the extracting means by the changing means. If there is no focus, or if focus detection is impossible at a distance measuring point in the area including the subject, the extraction condition is changed so that the area including the subject is enlarged.
(4) In the camera according to claim 4, the position for determining the photographing condition is a position corresponding to a distance measuring point for performing focus detection, and the changing means includes a predetermined number or more of distance measuring points in the area including the subject. If it exists, the extraction condition is changed so that the area extracted by the extraction means is reduced.
(5) In the camera according to claim 5, the position for determining the photographing condition is a position corresponding to the photometric point for performing photometry, and when the photometric point is not present in the area including the subject by the changing means, or the subject The extraction condition is changed so that the area extracted by the extraction means is enlarged when the photometry is not possible at the photometry point in the area including.
(6) In the camera according to claim 6, the position for determining the photographing condition is a position corresponding to the photometric point for performing photometry, and the changing means has a predetermined number or more of photometric points in the area including the subject. Is to change the extraction condition so that the area extracted by the extraction means is reduced.
(7) The camera according to claim 7 compares the hue of the edge portion of the image with the hue of the adjacent portion by the extracting means, and determines that the difference between the two is equal to or greater than the threshold value as the region including the subject. The threshold value is changed by changing means.
(8) The camera according to claim 8 sequentially compares the hues of the upper end portion, the left end portion and the right end portion of the image with the hues of the adjacent portions by the extraction means, and the difference between them is equal to or greater than a threshold value. The portion is determined as an area including the subject.

  According to the present invention, a subject area including a distance measuring point can be extracted from a captured image, and focus detection can be reliably performed.

<< First Embodiment of the Invention >>
An embodiment in which the present invention is applied to a single-lens reflex camera will be described. The present invention is not limited to a single-lens reflex camera, and can be applied to all types of cameras. The present invention can be applied not only to a digital camera but also to a film camera.

  FIG. 1 is a cross-sectional view of a camera showing the configuration of the first embodiment. In the figure, a light beam from a subject passes through an imaging lens 101, is reflected by a quick return mirror 102, and is guided upward of the camera. Further, a part of the light beam passes through the half mirror part of the quick return mirror 102 and is reflected downward by the sub mirror 103.

  The light beam reflected above the camera by the quick return mirror 102 forms an image on the finder screen 104. The formed subject image passes through the penta roof prism 105, and a part of the subject image is guided to the area sensor re-imaging optical system 106 and re-imaged on the area sensor 107. The area sensor 107 measures the light flux from the subject and outputs an image signal to the arithmetic device 108. Details of this image signal will be described later with reference to FIG. The arithmetic unit 108 includes a microcomputer (not shown), and extracts a subject area from an input image by a method described later.

  The light beam reflected downward of the camera by the sub mirror 103 is guided to the focus detection device 109. The focus detection device 109 detects the focus adjustment state of the shooting lens 101 at a plurality of distance measuring points on the shooting screen using a known method, and outputs the focus detection result to the calculation device 108. The arithmetic unit 108 adjusts the focus of the imaging lens 101 based on the focus detection result.

  Note that the position of the area sensor 107 is not limited to the upper rear part of the penta roof prism 105, and may be any place where a light beam from the object field can be imaged before shooting is started. In the case of a digital camera, instead of the area sensor 107, an image sensor used for capturing a subject image may be operated before photographing to obtain an image and output it to the arithmetic device 108. Further, in the case of a digital camera, the focus detection device 109 is not necessarily provided if the focus detection can be performed by the arithmetic device based on the output of the image sensor.

  FIG. 2 is a diagram illustrating an image processing method for extracting a subject area from a captured image. FIG. 3 is a flowchart showing the photographing operation of the camera of the first embodiment. The photographing operation of the first embodiment will be described with reference to FIG. When the camera is turned on, the microcomputer of the arithmetic unit 108 starts the photographing operation from step 301. In step 302, it is confirmed whether or not the photographer has half-pressed the release switch 110 of the camera. In step 303, an image of the object scene is acquired from the area sensor 107.

  FIG. 2A shows an example of an image acquired by the area sensor 107. In this embodiment, the pixel configuration of the area sensor 107 is 22 horizontal pixels and 15 vertical pixels. In step 304, a calculation for extracting a subject area from an image acquired by the area sensor 107 is performed.

  The horizontal coordinate of the image acquired from the area sensor 107 is i, and the vertical coordinate is j. Here, the range taken by i is 0-21, and the range taken by j is 0-14. The output of the area sensor 107 is composed of RGB three-color outputs for each pixel. The arithmetic unit 108 calculates the hue of each pixel of the area sensor 107. In this embodiment, the calculated hue is Hue [i] [j].

Next, in step 305, the arithmetic unit 108 creates a background mask M1 [i] [j] for each column of the image using the following conditional expression (1). In this calculation, an image is scanned in the vertical direction, and a background mask is set for pixels similar to the outermost peripheral pixels.
ABS (Hue [i] [j] −Hue [i] [0]) <ThHue (1)
In equation (1), ABS is a function that returns the absolute value of the input hue difference, and ThHue is a threshold value for determination that has been experimentally determined. When the conditional expression (1) is satisfied, the determination is performed again using the following conditional expression (2).
M1 [i] [j-1] ≠ 0 (2)
The above calculation is performed in the order from the smallest j value to the largest value, that is, from the top to the bottom of the image. When the conditional expression (2) is satisfied, the arithmetic unit 108 increments M1 [i] [j]. Note that the initial value of M1 [i] [j] is zero. However, for the pixel corresponding to the outermost periphery of the image, the initial value of the background mask M1 [i] [j] is set to 1, and the determination based on the conditional expressions (1) and (2) is not performed.

  FIG. 2B shows the image after the background mask is created by scanning the image from top to bottom. In FIG. 2 (b), pixels with a shaded pattern are pixels whose background mask M1 [i] [j] is other than 0, that is, pixels masked as the background.

Next, the same calculation is performed in steps 306 and 307 to set a background mask from the left and right directions. When creating a background mask from the left direction, the following conditional expressions (3) and (4) are used.
ABS (Hue [i] [j] −Hue [0] [j]) <ThHue (3)
M2 [i-1] [j] ≠ 0 (4)
When a background mask is created by scanning an image from the left direction, the calculation is performed in the order from the smallest i value to the largest, that is, from the left to the right of the image. For the background mask M2 [i] [j] from the left direction, the initial value is 0 except for the outermost periphery as in the mask from above.

Similarly, the background mask from the right direction is created using the following conditional expressions (5) and (6).
ABS (Hue [i] [j] −Hue [22] [j]) <ThHue (5)
M3 [i + 1] [j] ≠ 0 (6)
When the background mask is created by scanning from the right direction, the calculation is performed in the order from the larger i value to the smaller value, that is, from the right to the left of the image. In this embodiment, the maximum value of i is 21. Also for the background mask M3 [i] [j] from the right direction, the initial value is 0 except for the outermost periphery as in the mask creation from above.

  FIG. 2C shows an image after the background mask is created from the left direction, and FIG. 2D shows an image after the background mask is created from the right direction. In the figure, pixels in a shaded pattern are pixels whose background masks M2 [i] [j] and M3 [i] [j] are other than 0, that is, pixels masked as the background.

In step 308 after the background mask creation calculation is completed, the final mask thickness Mask [i] [j] is calculated by the following equation.
Mask [i] [j] = M1 [i] [j] + M2 [i] [j] + M3 [i] [j] (7)
FIG. 2E is an example of an image after the mask thickness Mask [i] [j] is calculated. In this figure, the illustration of the subject (person and car) is omitted. In the figure, the pixels in the shaded pattern are pixels whose mask thickness Mask [i] [j] is other than 0, that is, pixels masked as a background. On the other hand, a pixel having a mask thickness Mask [i] [j] of 0 is a pixel in an area where an object exists (hereinafter referred to as an object area).

  Next, the focus detection device 109 detects the focus of the photographing lens 101 in a region where Mask [i] [j] has a zero value, that is, a distance measuring point in the subject region. FIG. 2 (f) shows an example of an image showing distance measuring points on the background mask created by the above calculation. A thick cross in the figure indicates the position of a distance measuring point set in advance in the shooting screen. In this example, a distance measuring point exists in an area other than the background mask, that is, a subject area.

  In step 309, it is determined whether or not there is a distance measuring point in the subject area of the mask thickness Mask [i] [j] = 0. If there is no distance measuring point in the subject area, the process proceeds to step 310 to reset the threshold ThHue used in the conditional expressions (1), (3) and (5). Here, a value smaller than the value set so far is set as the threshold value ThHue. Thereafter, the process returns to step 305, and a background mask is created again by the conditional expressions (1) to (6) in which the threshold value ThHue is changed.

  If it is determined in step 309 that a distance measuring point is present in the subject area with the mask thickness Mask [i] [j] = 0, the process proceeds to step 311. In step 311, the focus detection device 109 detects the focus of the photographic lens 101 at a distance measuring point in the subject area, and after the focus of the photographic lens 101 is adjusted based on the focus detection result, the release switch 110 is fully pressed in step 312. Take pictures according to the operation.

  When the photographer holds the camera in the vertical position and shoots, the vertical position of the camera is detected using the attitude sensor 111 shown in FIG. Then, the above-described control content is changed so as not to scan from the lower side of the image.

  According to the first embodiment, when there is no distance measuring point in the extracted subject area, the subject area extraction condition is changed so that the subject area is enlarged. The object region including the distance measuring point can be extracted from the image, and the focus detection can be reliably performed.

<< Second Embodiment of the Invention >>
In the second embodiment, even when a distance measuring point exists in the subject area with the mask thickness Mask [i] [j] = 0, the focus of the subject cannot be detected due to low contrast or the like. The threshold value ThHue in the conditional expressions (1), (3) and (5) is changed to a small value to reduce the background mask setting area, that is, to enlarge the subject area. The configuration of the second embodiment is the same as that shown in FIG. 1, and illustration and description thereof are omitted.

  FIG. 4 is a flowchart showing the photographing operation of the camera of the second embodiment. Note that steps that perform the same processing as the processing shown in FIG. 3 are given the same step numbers, and differences will be mainly described. If it is determined in step 309 that a distance measuring point exists in the subject area, it is confirmed in step 401 whether or not focus detection is possible at the distance measuring point in the subject area. If focus detection is not possible at the distance measurement point in the subject area, the process proceeds to step 310, a value smaller than the value set so far is reset to the threshold value ThHue, and the process returns to step 305 to perform the above-described processing. repeat.

  According to the second embodiment, the subject area extraction condition is changed so that the subject area is enlarged when focus detection is impossible at the distance measuring point in the extracted subject area. The number of distance measuring points increases, and the probability of obtaining a focus detection result at any one of these distance measuring points increases.

<< Third Embodiment of the Invention >>
In the third embodiment, when there are many distance measuring points in the subject area, the background area is enlarged in order to omit the operation or processing for determining the focus detection point at which distance detecting point. The object area is reduced. The configuration of the third embodiment is the same as that shown in FIG. 1, and illustration and description thereof are omitted.

  FIG. 5 is a flowchart showing the photographing operation of the camera of the third embodiment. Note that steps that perform the same processing as the processing shown in FIG. 3 are given the same step numbers, and differences will be mainly described. In step 501, it is determined whether or not there are more than a predetermined number of distance measuring points in the subject area having the mask thickness Mask [i] [j] = 0. If the number of distance measuring points in the subject area is greater than the predetermined number, the process proceeds to step 502, a value larger than the value set so far is reset to the threshold value ThHue, and the process returns to step 305 to perform the above-described processing. repeat.

  According to the third embodiment, when the number of distance measuring points in the extracted subject area is larger than the predetermined number, the subject area extraction condition is changed so that the subject area is reduced. The number of distance measuring points in the subject area can be set to the minimum necessary number, and the operation or processing for determining the distance measuring points for actual focus detection from many distance measuring points can be omitted. .

<< Fourth Embodiment of the Invention >>
In the first to third embodiments described above, the background masks M1, M2, and M3 are obtained by scanning from the top to the bottom of the shooting screen, from left to right, and further from right to left, respectively, and then the background masks. M1 to M3 are added to separate the subject area from the background area. In the fourth embodiment, when it is determined that there is no distance measuring point in the subject area according to the above-described embodiment, first, the creation of the background mask M1 by scanning from top to bottom is omitted, and the horizontal direction The background masks M2 and M3 are added to separate the subject area from the background area. Since the background area is reduced by the amount not including the background mask M1 from the top-to-bottom scan, and the subject area is enlarged, the probability that a distance measuring point exists in the subject area increases.

  When there is no distance measuring point in the subject area sorted by the left and right background masks M2 and M3, the background area and the subject area are sorted using only the background mask M3 obtained by scanning from right to left. As a result, the subject area is further enlarged, and the probability that a distance measuring point exists in the subject area increases. In the fourth embodiment, a variable called Depth that counts the number of times the mask thickness Mask [i] [j] is calculated based on the background masks M1 to M3 is used.

  The configuration of the fourth embodiment is the same as the configuration shown in FIG. 1, and illustration and description thereof are omitted. FIG. 6 is a flowchart showing the photographing operation of the camera of the fourth embodiment. Note that steps that perform the same processing as the processing shown in FIG. 3 are given the same step numbers, and differences will be mainly described. In step 601, an initial value 1 is set to the variable Depth. If it is determined in step 602 that there is no distance measuring point in the subject area, the process proceeds to steps 603 to 605 to initialize the background masks M1 to M3 to zero. In step 606, the variable Depth is incremented, and the process branches according to the current variable Depth.

  If the number of times Depth for calculating the mask thickness Mask [i] [j] based on the background masks M1 to M3 is 2, the process returns to step 306, and the creation of the background mask M1 by scanning from the top to the bottom of the screen is omitted. Then, background masks M2 and M3 are created by scanning in the left-right direction, and the background masks M2 and M3 are added to obtain the mask thickness Mask [i] [j], and the background region and the subject region are separated. . If there is no distance measuring point in the subject area with the variable Dep = 2, the background masks M1 to M3 are initialized again at steps 603 to 605, and the variable Depth is incremented at step 606. Since the variable Depth is 3 this time, the process returns to step 307, where only the background mask M3 is created by scanning from right to left, and the background area and the subject area are separated by the background mask M3.

  If there is no distance measuring point in the subject area of the variable Depth = 3, the background masks M1 to M3 are initialized again in steps 603 to 605, and the variable Depth is incremented in step 606. Since the variable Depth exceeds 3 this time, the process returns to Step 308. In step 308, the background masks M1 to M3 initialized to 0 are added to obtain the mask thickness Mask [i] [j]. In this case, of course, the mask thickness Mask [i] [j] is 0, and all mask thickness Mask [i] [j] of the pixels in the entire screen range are 0. Therefore, the subject area of Mask [i] [j] = 0 is the entire range of the shooting screen. In step 602, there are of course distance measuring points within the entire range of the photographing screen, so the process proceeds to step 311 to perform distance measuring and photographing as described above.

  According to the fourth embodiment, when there are no distance measuring points in the subject area obtained by superimposing a plurality of background masks, the subject areas are re-sorted by reducing the number of background masks to be superimposed. Since the background area is reduced and the subject area is enlarged, the probability that a distance measuring point exists in the subject area increases, so that focus detection can be reliably performed.

  In the above-described embodiment, the range-finding point for detecting the focus set in advance in the object field has been described as an example. However, the image capturing condition set in the object field is determined. The position is not limited to a distance measuring point, and can be applied to a position where various shooting conditions are determined, such as a light measuring point for performing light metering.

The figure which shows the structure of 1st Embodiment. The figure explaining the image processing method which extracts a to-be-photographed object area | region from a captured image The flowchart which shows the imaging | photography operation | movement of 1st Embodiment. The flowchart which shows the imaging | photography operation | movement of 2nd Embodiment. Flowchart showing the photographing operation of the third embodiment Flowchart showing the photographing operation of the fourth embodiment

Explanation of symbols

107 area sensor 108 arithmetic unit 109 focus detection unit

Claims (9)

A camera that determines shooting conditions based on information relating to a preset position in the scene,
Imaging means for capturing an image of the object scene and outputting the image;
Extraction means for extracting a region including a subject from the image;
A camera comprising: changing means for changing an extraction condition of the extraction means in accordance with the number of positions for determining the photographing condition in an area including the subject. The camera of claim 1,
The camera according to claim 1, wherein the extracting means discriminates a region including the subject from a region not including the subject. The camera according to claim 1 or 2,
The position for determining the photographing condition is a position corresponding to a distance measuring point for performing focus detection,
The changing means enlarges the area extracted by the extracting means when there is no ranging point in the area including the subject, or when focus detection is impossible at the ranging point in the area including the subject. The camera is characterized in that the extraction condition is changed. The camera according to any one of claims 1 to 3,
The position for determining the photographing condition is a position corresponding to a distance measuring point for performing focus detection,
The change means changes the extraction condition so that an area extracted by the extraction means is reduced when a predetermined number or more of distance measuring points exist in the area including the subject. . The camera according to claim 1 or 2,
The position for determining the photographing condition is a position corresponding to a photometric point for performing photometry,
The changing means expands the area extracted by the extracting means when there is no photometric point in the area including the subject, or when photometry is not possible at the photometric point in the area including the subject. A camera characterized in that the extraction condition is changed. The camera according to any one of claims 1, 2, and 5,
The position for determining the photographing condition is a position corresponding to a photometric point for performing photometry,
The change means changes the extraction condition so that the area extracted by the extraction means is reduced when there are a predetermined number or more of photometry points in the area including the subject. The camera according to any one of claims 1 to 6,
The extraction means compares the hue of the edge portion of the image with the hue of a portion adjacent thereto, and determines a portion where the difference between the two is a threshold value or more as a region including the subject,
The camera characterized in that the changing means changes the threshold value. The camera according to claim 7, wherein
The extraction means sequentially compares the hues of the upper end portion, the left end portion and the right end portion of the image with the hues of portions adjacent thereto, and a portion where the difference is a threshold value or more is determined as an area including the subject. A camera characterized by discrimination. A method for extracting a subject area of a camera that determines a shooting condition based on information about a preset position in a scene,
Subject area extraction characterized by changing a condition to be extracted by the extraction means in accordance with the number of positions for determining the photographing condition in an area including a subject extracted from an image obtained by capturing an image of the object scene Method.

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