JP5911122B2 - Straight line detection apparatus and straight line detection method - Google Patents

Description

  The present invention relates to a technique for detecting a straight line included in an image.

  As a technique for detecting a straight line included in an image, Hough transformation is used. A straight line passing through an arbitrary point of the image having the XY coordinate system is converted into coordinates (θ, ρ) in the Hough space. The number of straight lines converted into the coordinates (θ, ρ) of the Hough space is tabulated using a two-dimensional array [θ] [ρ]. Then, a straight line in the XY coordinate system is detected from coordinates (θ, ρ) having a total value exceeding a predetermined threshold in the two-dimensional array [θ] [ρ].

  In Patent Document 1 below, in order to divide an image into local regions, line segments in the image are detected using Hough transform. In the following Patent Document 2, an attempt is made to optimize the sampling interval of the parameters θ and ρ on the Hough space according to the length of the straight line. Also in Patent Document 3 below, Hough transform is used to detect a line segment included in an image.

JP-A-10-283476 JP-A-11-66302 JP 2006-107034 A

  The straight line detection method using the Hough transform focuses on the number of points existing on the straight line in the XY coordinate system. The greater the number of points existing on the same straight line, the higher the possibility of being detected as a straight line. For this reason, if the image is longer in the horizontal direction than in the vertical direction, straight lines are easily detected in the horizontal direction. On the contrary, even if the straight line in the vertical direction is somewhat dense, there is a possibility that it will not be detected as a straight line if the total value becomes small.

  Alternatively, straight lines that exist at the four corners of the image have a short straight line distance, and therefore, the possibility of being detected as a straight line is further reduced.

  It is an object of the present invention to provide a technique for detecting a straight line based on the same reference without being influenced by the direction or position where the straight line exists.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a straight line detection device, wherein a length ρ of a perpendicular line dropped from a reference point of the target image to an arbitrary straight line in the target image and the vertical line are the reference line By expressing an arbitrary straight line in the target image using an angle θ formed with a reference axis passing through the point, the straight line passing through the arbitrary point in the target image is represented by coordinates (θ, ρ) in the Hough space. A Hough transform unit to be transformed and an intersection for calculating a distance between the intersections while obtaining an intersection where a straight line in the target image corresponding to an arbitrary coordinate (θ, ρ) in the Hough space intersects the outer periphery of the target image The distance calculation unit and the coordinates (θ, ρ) in the Hough space are totaled for the number of times converted by the Hough transform unit, and the total value of each coordinate (θ, ρ) is calculated by the distance between the corresponding points. A normalization unit that normalizes and calculates a normalized aggregate value, and a normalization collection By value specifying the coordinates exceeds the first threshold value (theta, [rho), and a detector for detecting a straight line in the target image.

  The invention according to claim 2 is the straight line detection device according to claim 1, further comprising a conversion unit that performs binary conversion on the target image before the Hough conversion is performed, When a certain point is converted into coordinates (θ, ρ) in the Hough space, 1 is added to the total value.

  Invention of Claim 3 is the straight line detection apparatus of Claim 1 or Claim 2, Comprising: When each point in the said object image is converted into the coordinate ((theta), (rho)) in Hough space, A value weighted by the size of the feature amount of each point in the target image is added to the total value.

  A fourth aspect of the present invention is the straight line detection apparatus according to the third aspect, wherein the feature amount includes a line segment intensity.

  A fifth aspect of the present invention is the straight line detection device according to any one of the first to fourth aspects, wherein the detection unit is configured to perform a normal operation with respect to a straight line whose distance between the intersection points is equal to or less than a second threshold value. Regardless of the value of the totalization value, it is excluded from the line detection target.

  A sixth aspect of the present invention is the straight line detection device according to any one of the first to fifth aspects, wherein the inter-intersection distance calculation unit corresponds to the coordinates (θ, ρ) in the Hough space. When calculating the distance between the intersections of the straight lines in the target image, a simple calculation unit that calculates the distance between the intersections after replacing with ρ = 0.

  A seventh aspect of the present invention is the straight line detection device according to any one of the first to sixth aspects, wherein the reference point is set at an arbitrary coordinate in the target image.

  The invention according to claim 8 is a straight line detection device, wherein a conversion unit that generates a square image by executing an aspect ratio conversion process for converting an aspect ratio to 1: 1 with respect to a target image; An arbitrary straight line in the square image is obtained by using a length ρ of a perpendicular line drawn from a reference point of the square image to an arbitrary straight line in the square image and an angle θ formed by the vertical line and a reference axis passing through the reference point. By expressing, a Hough transform unit that converts a straight line passing through an arbitrary point in the square image into coordinates (θ, ρ) in the Hough space, and each coordinate (θ, ρ) in the Hough space, the Hough A detection unit that counts the number of times of conversion by the conversion unit and detects a straight line in the square image by specifying a coordinate (θ, ρ) whose total value of each coordinate (θ, ρ) exceeds the first threshold value And comprising.

  The invention according to claim 9 is the straight line detection device according to claim 8, further comprising: a conversion unit that performs binary conversion on an image before aspect ratio conversion or after conversion before the Hough conversion is performed. When a certain point in the square image is converted into coordinates (θ, ρ) in the Hough space, 1 is added to the total value.

  The invention according to claim 10 is the straight line detection device according to claim 8 or 9, wherein each point in the square image is converted into coordinates (θ, ρ) in the Hough space. A value weighted according to the feature value of each point in the square image is added to the total value.

  An eleventh aspect of the present invention is the straight line detection device according to the tenth aspect, wherein the feature amount includes a line segment intensity.

  A twelfth aspect of the present invention is the straight line detection device according to any one of the eighth to eleventh aspects, wherein the reference point is set at an arbitrary coordinate in the square image.

  A thirteenth aspect of the present invention is the straight line detection device according to any one of the first to twelfth aspects of the present invention, wherein when the target image is a color image, the color image is detected before the Hough transform is performed. A luminance image generation unit for generating a luminance image;

  A fourteenth aspect of the present invention is the straight line detection device according to the second or ninth aspect, wherein the conversion unit performs a binary conversion after performing a feature amount extraction process on the target image.

  A fifteenth aspect of the present invention is the straight line detection device according to the fourteenth aspect, wherein the feature amount extraction processing includes contour extraction processing.

  The invention according to claim 16 is a straight line detection method, wherein the length ρ of the perpendicular line dropped from a reference point of the target image to an arbitrary straight line in the target image and the perpendicular line serve as a reference axis passing through the reference point. A Hough transform step of converting a straight line passing through an arbitrary point in the target image into coordinates (θ, ρ) in a Hough space by expressing an arbitrary straight line in the target image using an angle θ; A process for calculating a distance between intersections in which a straight line in the target image corresponding to an arbitrary coordinate (θ, ρ) in the Hough space intersects the outer periphery of the target image and calculates a distance between the intersections; For each coordinate (θ, ρ) in space, the number of times converted by the Hough transform step is totaled, and the total value of each coordinate (θ, ρ) is normalized by the corresponding distance between intersections, and the normalized total value The normalization process for calculating and the normalized aggregate value is the first threshold By identifying the more than coordinates (theta, [rho), and a detection step of detecting lines in the target image.

  The invention according to claim 17 is a straight line detection method, wherein a conversion step of generating a square image by executing an aspect ratio conversion process for converting an aspect ratio to 1: 1 with respect to a target image; An arbitrary straight line in the square image is obtained by using a length ρ of a perpendicular line drawn from a reference point of the square image to an arbitrary straight line in the square image and an angle θ formed by the vertical line and a reference axis passing through the reference point. By expressing, a Hough transform step for converting a straight line passing through an arbitrary point in the square image into coordinates (θ, ρ) in the Hough space, and for each coordinate (θ, ρ) in the Hough space, the Hough A detection step of detecting a straight line in the square image by adding up the number of times converted by the conversion step and specifying a coordinate (θ, ρ) where the total value of each coordinate (θ, ρ) exceeds the first threshold value And comprising.

  By using the straight line detection device of the present invention, it is possible to detect a straight line from the Hough transformed information on the same basis without depending on the direction and position of the straight line. Even if the image has an aspect ratio other than 1: 1, it is possible to solve the problem that it is difficult to detect any straight line in the vertical direction or the horizontal direction. Straight lines that exist at the four corners of the image can also prevent detection omissions.

It is a block diagram of the straight line detection apparatus which concerns on 1st Embodiment. It is a figure which shows the expression method of the straight line in binary image data. It is a figure which shows Hough space. It is a figure which shows the straight line which cuts off binary image data. It is a block diagram of the straight line detection apparatus which concerns on 4th Embodiment.

{First embodiment}
<1. Overall flow of processing>
FIG. 1 is a block diagram of a straight line detection apparatus 1 according to the first embodiment. The straight line detection device 1 includes a luminance image generation unit 11, a contour extraction processing unit 12, a binary conversion unit 13, a Hough conversion unit 14, a Hough table 15, and a straight line detection unit 16.

  In the present embodiment, the luminance image generation unit 11, the contour extraction processing unit 12, the binary conversion unit 13, the Hough conversion unit 14, and the straight line detection unit 16 are configured by hardware circuits. However, you may comprise these function parts by the software which operate | moves on CPU and CPU.

  The luminance image generation unit 11 inputs color image data 101. The color image data 101 is, for example, an image acquired by an image sensor (not shown). The color image data 101 is, for example, image data in a YCbCr color space or an RGB color space. The luminance image generation unit 11 generates luminance image data 102 from the color image data 101. For example, if the color image data 101 is image data in the YCbCr color space, the luminance image generation unit 11 generates the luminance image data 102 by extracting the Y signal.

  The contour extraction processing unit 12 inputs luminance image data 102. The contour extraction processing unit 12 generates contour image data 103 from the luminance image data 102. In the present embodiment, the contour extraction processing unit 12 performs contour extraction processing using a Sobel filter. The Sobel filter is a filter that detects an outline by a spatial first-order differential operation. The contour extraction processing unit 12 outputs the absolute value of the filter output as the line segment intensity. The filter to be used is not particularly limited. For example, a Laplacian filter may be used.

  The binary conversion unit 13 receives the contour image data 103. The binary conversion unit 13 generates binary image data 104 from the contour image data 103. The contour image data 103 is grayscale image data. The binary conversion unit 13 converts the pixel value of each pixel of the contour image data 103 into 0 or 1 based on a preset threshold value.

  The Hough conversion unit 14 inputs the binary image data 104. The Hough conversion unit 14 performs Hough conversion on the binary image data 104 and writes the converted result in the Hough table 15. Specifically, the Hough transform unit 14 stores the converted result in a two-dimensional array [θ] [ρ]. The contents of the Hough transform process will be described in detail later.

  The straight line detection unit 16 includes an intersection distance calculation unit 161 and a normalization unit 162. The straight line detection unit 16 detects a straight line included in the binary image data 104 by referring to the Hough table 15. The details of the processing of the straight line detection unit 16 including the inter-intersection distance calculation unit 161 and the normalization unit 162 will be described in detail later.

<2. Hough transform>
The processing content of the Hough converter 14 will be described in detail. The Hough conversion unit 14 converts a straight line passing through each point into coordinates (θ, ρ) in the Hough space for an arbitrary point included in the binary image data 104.

  FIG. 2 is a diagram showing the binary image data 104. In the binary image data 104, an origin O and XY coordinates are defined as shown in FIG. FIG. 2 illustrates some of the points 51 to 55 among the points included in the binary image data 104. Here, the point included in the binary image data 104 is a point to which a pixel value 1 is given by binary conversion. A straight line 61 passing through the point 51 can be expressed as in Equation 1 using θ and ρ.

  In Equation 1, ρ is the length of the perpendicular line 62 drawn from the origin to the straight line 61. θ is an angle formed by the vertical line 62 and the positive direction of the X axis.

  There are many straight lines passing through the point 51. The number of straight lines passing through the point 51 is determined based on the sampling intervals of θ and ρ. Therefore, one point on the binary image data 104 is associated with a plurality of coordinates (θ, ρ) on the Hough space.

  As shown in FIG. 2, the points 51 to 53 are arranged on the same straight line. The straight lines passing through the points 52 and 53 are also converted into coordinates (θ, ρ) on a plurality of Hough spaces, respectively. Then, the straight line 61 is subjected to the Hough transform for all the points 51 to 53 and is associated with the same coordinates (θ, ρ).

  FIG. 3 is a diagram illustrating the Hough space. The sine curves 71 to 75 represent sets of points on the Hough space obtained by performing the Hough transform on the points 51 to 55, respectively. The coordinates (θ1, ρ1) where the sine curves 71 to 73 intersect correspond to the straight line 61.

  Thus, when there are a plurality of points on the same straight line in the binary image data 104, the plurality of points on the binary image are converted to the same point on the Hough space. A straight line can be detected by summing up the points converted into coordinates (θ, ρ) in the Hough space. The Hough table 15 has a two-dimensional array T [θ] [ρ]. That is, the Hough transform is performed on all the points of the binary image data 104, and the results are aggregated in the two-dimensional array T [θ] [ρ].

<3. Straight line detection processing>
The straight line detection unit 16 refers to the Hough table 15 and detects a straight line included in the binary image data 104. The straight line detection unit 16 does not detect a straight line using the conversion result from the Hough conversion unit 14 as it is, but detects a straight line after correcting the contents of the Hough table 15. The correction process is performed by the inter-intersection distance calculation unit 161 and the normalization unit 162.

  The processing content of the distance calculation part 161 between intersections is demonstrated. FIG. 4 shows a straight line 81 included in the binary image data 104. The length of the perpendicular 82 drawn from the origin O to the straight line 81 is ρ. The angle formed by the perpendicular 82 with the positive direction of the X axis is θ.

  In FIG. 4, the binary image data 104 is rectangular image data having a length in the horizontal direction (X-axis direction) of 2w and a length in the vertical direction (Y-axis direction) of 2h. An origin O is set at the center of the binary image data 104.

  The straight line 81 intersects the outer periphery of the binary image data 104 at a point P0 (x0, y0) and a point P1 (x1, y1). In other words, when the straight line 81 cuts out the binary image data 104, the two intersections between the straight line 81 and the outer periphery of the binary image data 104 are the point P0 (x0, y0) and the point P1 (x1, y1). The intersection calculation unit 161 calculates a distance between two intersections, that is, a distance between the points P0 (x0, y0) and P1 (x1, y1) (inter-intersection distance Len).

  The distance calculation method in the present embodiment will be specifically described. First, a method for determining the coordinates (x0, y0) of the point P0 and the coordinates (x1, y1) of the point P1 will be described. In the present embodiment, the X coordinate x0 of the point P0 is obtained from the intersection of the straight line 81 and the straight line y = h, and the X coordinate x1 of the point P1 is obtained from the intersection of the straight line 81 and the straight line y = −h. Further, the Y coordinate y0 of the point P0 is obtained from the intersection of the straight line 81 and the straight line x = w, and the Y coordinate y1 of the point P1 is obtained from the intersection of the straight line 81 and the straight line x = −w.

  First, consider a case where the straight line 81 is parallel to the X axis or the Y axis. In this case, the inter-intersection distance Len is obtained by the following method without obtaining the coordinates of the points P0 and P1 by the above method.

  When cos θ = 0, that is, when the straight line 81 is a straight line parallel to the X axis, the inter-intersection distance Len is expressed by the following equation (2).

  When sin θ = 0, that is, when the straight line 81 is a straight line parallel to the Y axis, the inter-intersection distance Len is expressed by the following equation (3).

  Next, the X coordinate x0 of the point P0 that is the intersection of the straight line 81 and the straight line y = h is obtained. x0 is expressed by Formula 4.

  Next, the X coordinate x1 of the point P1, which is the intersection of the straight line 81 and the straight line y = −h, is obtained. x1 is expressed by Formula 5.

  Next, the Y coordinate y0 of the point P0 that is the intersection of the straight line 81 and the straight line x = w is obtained. y0 is expressed by Equation 6.

  Next, the Y coordinate y1 of the point P1, which is the intersection of the straight line 81 and the straight line x = −w, is obtained. y1 is expressed by Equation 7.

  If x0 is smaller than −w, x0 is set to −w as shown in Equation 8. That is, when the intersection point extends beyond the frame end of the binary image, the frame end is set as the X coordinate of the intersection point. When the X coordinate of the intersection point protrudes from the frame end of the binary image, the X coordinate is set to the frame end in all cases as shown in Equation 8. That is, when x0 is larger than w, x0 is set to w. If x1 is less than -w, set x1 to -w. When x1 is larger than w, x1 is set to w.

  When the Y coordinate of the intersection protrudes from the frame end of the binary image, the Y coordinate is set to the frame end in all cases as shown in Equation 9. That is, when y0 is smaller than -h, y0 is set to -h. When y0 is larger than h, y0 is set to h. If y1 is less than -h, set y1 to -h. When y1 is larger than h, y1 is set to h.

  As described above, when the coordinates of the point P0 (x0, y0) and the point P1 (x1, y1) are determined, the inter-intersection distance calculation unit 161 performs the calculation expressed by Equation 10 to obtain the inter-intersection distance. Find Len.

  In Formula 10, x0, x1, y0, and y1 are values calculated by Formula 4 to Formula 7 when they do not apply to Formula 8 or Formula 9, Formula 8 or Formula 9 When the above is true, it is a value set by Equation 8 or Equation 9.

  By the calculation method as described above, the inter-intersection distance calculation unit 161 refers to the Huff table 15 and calculates the inter-intersection distance Len for all coordinates (θ, ρ) that are straight line candidates. That is, the inter-intersection distance Len is calculated for each coordinate (θ, ρ) in which one or more total values are stored in the two-dimensional array [θ] [ρ]. Alternatively, the inter-intersection distance Len may be calculated for all the two-dimensional arrays [θ] [ρ] including the array whose total value is zero. For example, the intersection distance Len may be calculated for all combinations (θ, ρ) in advance, and Len [θ] [ρ] may be held as a lookup table.

  The normalizing unit 162 normalizes the total value by dividing the total value of each coordinate (θ, ρ) by the inter-intersection distance Len calculated for each coordinate (θ, ρ). The normalization unit 162 divides the total value by the inter-intersection distance Len for each coordinate (θ, ρ) in which one or more total values are stored in the two-dimensional array [θ] [ρ]. Alternatively, as described above, the inter-intersection distance Len is calculated for all the two-dimensional arrays [θ] [ρ], and all the total values are normalized by the corresponding inter-intersection distance Len. In other words, the normalization unit 162 corrects the total value of the straight lines on the binary image to a numerical value per unit length. Thereby, the correction process of the Hough table 15 (two-dimensional array [θ] [ρ]) is completed.

  The straight line detection unit 16 performs straight line detection with reference to the Hough table 15 corrected by normalization. In the straight line detection unit 16, a straight line determination threshold (first threshold) is set in advance. The straight line detection unit 16 specifies coordinates (θ, ρ) in which the total value exceeding the first threshold is stored in the two-dimensional array [θ] [ρ]. The straight line detection unit 16 specifies a straight line included in the binary image data 104 from the specified coordinates (θ, ρ). The straight line detection unit 16 outputs detection information.

  Thus, the straight line detection device 1 of the present embodiment detects a straight line after correcting the Huff table 15 by normalization. Normalization is performed by dividing the total value of the two-dimensional array [θ] [ρ] by the inter-intersection distance Len. In the example shown in FIG. 4, the inter-intersection distance L is long for the horizontal straight line and short for the vertical straight line. Accordingly, the total value stored in the two-dimensional array [θ] [ρ] is divided by a larger value for the horizontal line than for the vertical line.

  As a result, in the binary image data 104, there is no problem that a horizontal straight line is easily detected and a vertical straight line is difficult to detect. Alternatively, there is no problem that it is difficult to detect straight lines that exist at the four corners of the image. Even if the aspect ratio of the image is not 1: 1, straight lines in every direction or position in the image can be detected with the same reference.

{Second Embodiment}
Next, a second embodiment of the present invention will be described. The functional blocks of the straight line detection device 1 in the second embodiment are the same as those shown in FIG. However, in the second embodiment, the processing in the straight line detection unit 16 is different from that in the first embodiment.

  In the first embodiment, the total value of each coordinate (θ, ρ) in the Hough space is divided by the distance Len between the intersections and normalized. That is, normalized total values are calculated for all straight line candidates and compared with the first threshold value.

  In the second embodiment, a straight line whose intersection distance Len is less than a predetermined threshold value (second threshold value) is excluded from straight line detection targets. For example, straight lines that exist at the four corners of the binary image data 104 and have a short intersection distance Len are excluded from detection targets. Thereby, although the density of the points arranged on the straight line is not high, it is possible to prevent the normalized total value from being increased because the distance Len between the intersections is very small, thereby preventing erroneous recognition as a straight line. Alternatively, it is possible to prevent a problem that a large number of straight lines having a very short distance are detected at the four corners of the image.

  For example, when the information on the four corners on the image is not so important, it is possible to detect a straight line by placing a spot near the center of the image by adjusting the second threshold value to be relatively large.

{Third embodiment}
Next, a third embodiment of the present invention will be described. The functional blocks of the straight line detection device 1 in the third embodiment are the same as those shown in FIG. However, in the third embodiment, the processing in the straight line detection unit 16 is different from that in the first embodiment.

  In the first embodiment, the inter-intersection distance Len is calculated by obtaining the coordinates of the points P0 and P1 by the method shown in the equations (4) to (7). In the third embodiment, the distance Len between the intersections is calculated by setting the distance between the straight line and the origin O to zero.

  That is, when calculating the distance Len between the intersections of the straight lines in the binary image corresponding to the coordinates (θ, ρ), the intersection distance calculation unit 161 calculates the distance Len between the intersections after replacing ρ = 0. .

  By calculating the distance Len between the intersections in this way, the amount of calculation of the distance calculation unit 161 between the intersections can be reduced and the processing speed can be improved. Specifically, in Equation 4 to Equation 7, it can be replaced with ρ = 0, so that the arithmetic expression is simplified.

{Fourth embodiment}
Next, a fourth embodiment of the present invention will be described. FIG. 5 is a block diagram of a straight line detection apparatus 1A according to the fourth embodiment.

  As with the straight line detection device 1 of the first embodiment, the straight line detection device 1A of the fourth embodiment is a luminance image generation unit 11, contour extraction processing unit 12, binary conversion unit 13, Hough conversion unit 14, and A huff table 15 is provided. The functions of these functional units are the same as those in the first embodiment.

  Unlike the first embodiment, the straight line detection unit 16 in the fourth embodiment does not include the inter-intersection distance calculation unit 161 and the normalization unit 162. In the fourth embodiment, the straight line detection unit 16 detects a straight line without normalizing the Hough table 15.

  The straight line detection device 1 </ b> A includes an aspect ratio conversion unit 17. The aspect ratio conversion unit 17 receives the color image 101 and converts the color image into a color square image having an aspect ratio of 1: 1. When converting the aspect ratio, it is necessary to decompress or reduce the image. A method for performing the expansion is not particularly limited, and for example, the image is expanded by using linear interpolation or the like. When performing reduction, for example, image thinning may be performed. Even if the aspect ratio is converted, the straight line is converted into a straight line.

  The luminance image generation unit 11, the contour extraction processing unit 12, the binary conversion unit 13, and the Hough conversion unit 14 execute the same processing as in the first embodiment. However, the process is executed for a square image whose aspect ratio is converted to 1: 1.

The Hough table 15 aggregates the coordinates (θ, ρ) converted by the Hough conversion unit 14 using a two-dimensional array [θ] [ρ]. In the straight line detection unit 16, a straight line determination threshold (first threshold) is set in advance. The straight line detection unit 16 specifies coordinates (θ, ρ) in which the total value exceeding the first threshold is stored in the two-dimensional array [θ] [ρ]. The straight line detection unit 16 identifies a straight line included in the binary image data 1 14 from the identified coordinates (θ, ρ). The straight line detection unit 16 outputs detection information. The first threshold value can be set to a value different from that in the first embodiment.

  Thus, the straight line detection device 1A of the present embodiment performs Hough conversion after converting the aspect ratio to 1: 1. Therefore, the problem that the possibility of straight line detection differs depending on the direction in the image can be solved.

  In this embodiment, the aspect ratio is converted before the luminance image is generated. However, the aspect ratio conversion process may be performed at any timing before the Hough conversion is performed. For example, the aspect ratio may be converted after the luminance image generation process, after the contour extraction process, or after the binary conversion process. Note that the straight line detected on the square image is converted into a straight line included in the color image 101 by performing an operation to restore the aspect ratio.

{Fifth embodiment}
In each of the above embodiments, the image is binarized before the Hough transform is performed. In the fifth embodiment, image binarization is not performed. The image has, for example, multivalued pixel values such as 0 to 255.

  The block diagram of the straight line detection device in the fifth embodiment is the same as the straight line detection devices 1 and 1A shown in FIG. 1 or FIG. However, the binary conversion unit 13 is not provided.

  The Hough transform unit 14 performs Hough transform on all points included in the contour image data 103 or 113. The points included in the contour image data 103 or 113 have, for example, multivalued pixel values such as 0 to 255, and Hough transform is performed on all these points.

  In each of the above embodiments, the Hough transform unit 14 stores the number of times that the points included in the binary image data 104 or 114 are subjected to the Hough transform in the binary array [θ] [ρ]. In other words, if the number of times of Hough transform to a certain coordinate (θ, ρ) is N, the value N is stored as a total value in the two-variable array [θ] [ρ].

  In this embodiment, values corresponding to the line segment intensities of points included in the contour image data 103 or 113 are stored in the two-variable array [θ] [ρ]. For example, the pixel values are added to the two-variable array [θ] [ρ] as they are and totaled. Alternatively, a predetermined conversion may be performed on the pixel value, and the conversion value may be added to the two-variable array [θ] [ρ]. That is, the number of conversions can be totaled in the two-variable array [θ] [ρ] after weighting according to the size of the feature amount of the pixel.

  Subsequent processing is the same as in the above embodiments. According to the present embodiment, since binary conversion is not performed, it is effective when it is desired to detect a relatively weak straight line.

{Modifications}
In the first to fifth embodiments, the straight line in the binary image data 104 is expressed using θ and ρ with the center of the binary image data 104 as the origin. However, the origin can be set at any place in the image. Alternatively, the origin may be set outside the frame of the binary image data 104.

  In the first to fourth embodiments, the binarization process is performed after the contour extraction process. The contour extraction process is an example of a process for extracting a feature amount of an image. The binarization process may be performed after extracting the feature amount of the image by another method.

DESCRIPTION OF SYMBOLS 11 Luminance image generation part 12 Contour extraction process part 13 Binary conversion part 14 Hough conversion part 15 Hough table 16 Straight line detection part 17 Aspect ratio conversion part 101 Color image data 102 Luminance image data 103 Contour image data 104 Binary image data

Claims (11)

An arbitrary straight line in the target image is obtained by using a length ρ of a perpendicular drawn from the reference point of the target image to an arbitrary straight line in the target image and an angle θ formed by the vertical line and a reference axis passing through the reference point. A Hough transforming unit that transforms a straight line passing through an arbitrary point in the target image into coordinates (θ, ρ) in the Hough space by expressing,
A straight line in the target image corresponding to an arbitrary coordinate (θ, ρ) in the Hough space obtains an intersection where the outer periphery of the target image intersects, and calculates a distance between the intersections;
For each coordinate (θ, ρ) in the Hough space, the number of times converted by the Hough transform unit is totaled, and the total value of each coordinate (θ, ρ) is normalized by the corresponding distance between intersections, and normalized tabulation A normalization unit for calculating a value;
A detection unit that detects a straight line in the target image by specifying coordinates (θ, ρ) whose normalized total value exceeds the first threshold;
A straight line detection device. The straight line detection device according to claim 1, further comprising:
A binary conversion unit that performs binary conversion on the target image before the Hough conversion is performed;
With
A straight line detection device in which 1 is added to a total value when a certain point in the target image is converted into coordinates (θ, ρ) in a Hough space. The straight line detection device according to claim 1 or 2,
When each point in the target image is converted into coordinates (θ, ρ) in the Hough space, a value weighted by the size of the feature amount of each point in the target image is added to the total value Straight line detection device. The straight line detection device according to claim 3,
The feature detection amount is a straight line detection device including a line segment intensity. The straight line detection device according to any one of claims 1 to 4,
The detection unit is a straight line detection device that excludes a straight line whose distance between the intersections is equal to or smaller than a second threshold from a detection target of a straight line regardless of a value of the normalized total value. A straight line detection device according to any one of claims 1 to 5,
The inter-intersection distance calculation unit
When calculating the distance between the intersections of the straight lines in the target image corresponding to the coordinates (θ, ρ) in the Hough space, a simple calculation unit that calculates the distance between the intersections after replacing ρ = 0.
A linear detection device including: The straight line detection device according to any one of claims 1 to 6,
The straight line detection device in which the reference point is set at an arbitrary coordinate in the target image. The straight line detection device according to any one of claims 1 to 7 , further comprising:
When the target image is a color image, a luminance image generation unit that generates a luminance image from the color image before the Hough transform is performed,
A linear detection device including: The straight line detection device according to claim 2,
A straight line detection apparatus in which the binary conversion is performed after a feature amount extraction process is performed on the target image. The straight line detection device according to claim 9 ,
The feature amount extraction process is a straight line detection device including a contour extraction process. An arbitrary straight line in the target image is obtained by using a length ρ of a perpendicular drawn from the reference point of the target image to an arbitrary straight line in the target image and an angle θ formed by the vertical line and a reference axis passing through the reference point. A Hough transforming step of transforming a straight line passing through an arbitrary point in the target image into coordinates (θ, ρ) in the Hough space by expressing,
An intersection distance calculation step of calculating an intersection point at which a straight line in the target image corresponding to an arbitrary coordinate (θ, ρ) in the Hough space intersects an outer periphery of the target image, and calculating a distance between the intersection points;
For each coordinate (θ, ρ) in the Hough space, the number of times converted by the Hough transformation step is totalized, and the total value of each coordinate (θ, ρ) is normalized by the corresponding distance between the intersections, and normalized tabulation A normalization step to calculate a value;
A detection step of detecting a straight line in the target image by specifying coordinates (θ, ρ) where the normalized total value exceeds the first threshold;
A straight line detection method comprising:

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