JPH0327483A - Method and device for deciding circular pattern - Google Patents

Abstract

PURPOSE:To precisely recognize whether a prescribed picture element designated on a radiation picture is the picture element in a circular pattern or not by obtaining the component of each normalized gradient in the direction of the prescribed picture element. CONSTITUTION:The gradient DELTAf1 of each picture data f1 corresponding to each picture element Pi which is distant from the picture element P0 by distance ri and is positioned on each of plural segments of line Li (i=1,2... n) extending toward the circumference of the radiation picture from the prescribed picture element P0 is obtained, and the normalized gradient DELTAfi/¦DELTAfi¦ in which the size ¦DELTAfi¦ is normalized is obtained. Then, the component DELTAfi/¦DELTAfi¦*e1 (e1 is a unit vector going from each picture element P1 to the picture element P0, and *shows a scalar product) in the direction of the picture element P0 of the normalized gradient is obtained, and the mean value of the component DELTAfi/¦DELTAfi¦*e1 is obtained. It is decided whether the picture element P0 is the picture element in the circular pattern or not based on this means value. Thus, it can be precisely decided whether the prescribed picture element P0 is the picture element of the circular pattern or not.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image pattern recognition method and apparatus, and more specifically, the present invention relates to an image pattern recognition method and apparatus. The present invention relates to a circular pattern determination method and apparatus for determining whether a predetermined pixel Po is a pixel within a circular pattern constituting the radiation image.

(Prior Art) It is practiced in various fields to read a recorded radiation image to obtain image data, perform appropriate image processing on this image data, and then reproduce and record the image. For example, an X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with later image processing, and the X-ray image is read from the film on which the X-ray image was recorded and electrical signals ( By performing image processing on this image data and then reproducing it as a visible image in a copy photograph, etc., a reproduced image with good image quality performance such as contrast sharpness and graininess can be obtained. ing(
(See Japanese Patent Publication No. 81-5193).

In addition, the applicant has proposed radiation (X-rays, α-rays, β-rays, γ-rays, etc.)
When irradiated with excitation light such as visible light, some of this radiation energy is accumulated, and when excitation light such as visible light is irradiated, a stimulable phosphor (stimulable phosphor) that exhibits stimulated luminescence depending on the accumulated energy Radiation image information of a subject such as a human body is recorded on a sheet of stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to produce stimulated luminescence. Generate light, photoelectrically read the resulting stimulated luminescent light to obtain image data, and based on this image data, output a radiation image of the subject as a visible image to a recording material such as a photographic light-sensitive material, CRT, etc. A radiation image recording and reproducing system has already been proposed (Japanese Unexamined Patent Publication No. 55-1
No. 2429. 5B-11395, 55-1634
No. 72. 5B-104645, 55-1163
No. 40, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electric signal and using this electric signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

In recent years, in systems using the above-mentioned X-ray film, stimulable phosphor sheets, etc., especially systems designed for medical diagnosis of the human body, reproduced images with good image quality suitable for simple observation (diagnosis) have been developed. In addition to image recognition, pattern recognition of images has also been carried out (for example, in Japanese Patent Application Laid-Open No.
(See Publication No. 125481).

Here, image pattern recognition refers to the operation of extracting a target pattern from a complex radiographic image by performing various processes on image data.
This refers to the operation of extracting, for example, a substantially circular shadow corresponding to a tumor from a very complex image such as a line image that is a mixture of various linear and circular patterns.

A target pattern (for example, a tumor shadow) in such a complex radiographic image (for example, a chest X-ray image of a human body)
By extracting the pattern and reproducing and displaying a visible image clearly showing the extracted pattern, it is possible to assist the observer in observation (for example, assist the doctor in diagnosis).

(Problem to be Solved by the Invention) In the above-mentioned Japanese Patent Application Laid-Open No. 62-125481, for example, a circular pattern is extracted by scanning a chest X-ray image of a human body using a real space filter consisting of three concentric circles. It describes how to do this.

However, this extraction method uses the difference (contrast) between the center and surrounding image data as the feature quantity that is the basis for determining whether the pattern is circular or not. The shape of whether or not a circular pattern exists does not necessarily correspond to the size of the above-mentioned feature amount, and therefore, the accuracy of extracting circular patterns is not necessarily sufficient to extract circular patterns without omission and exclude non-circular patterns. The problem is that there is no.

In view of the above-mentioned problems, the present invention places emphasis on the shape of a circular shape regardless of the contrast, and the predetermined pixel P specified on the radiation image. It is an object of the present invention to provide a circular pattern determination method and apparatus that can accurately recognize whether or not a pixel is a pixel within a circular pattern.

(Means for Solving the Problems) As described above, in the circular pattern determination method and apparatus of the present invention, based on image data representing a radiation image of a subject, a predetermined pixel Po in the radiation image is The present invention relates to a method and apparatus for determining whether a pixel is within a circular pattern constituting an image.

The circular pattern determination method of the present invention is characterized in that, in the above method, the predetermined pixel P. Each of the image data corresponding to each pixel P- located a predetermined distance ri away from the predetermined pixel Po on each of a plurality of line segments L l (1=1, 2..., n) extending around the radiation image from f. Find the gradient fi of each gradient fi, and obtain the normalized gradient V f + / l Vfi1 in which the magnitude of each gradient fi |∇fi| is normalized.
Find the component f + /lfil of the normalized gradient Vfi /lfil in the direction of the predetermined pixel Po.
*e+ (e+ is a unit vector directed from each pixel Pi to the predetermined pixel Po, * represents an inner product), and the average value of the component fi/|∇fi|I 1*e+ is determined, Based on the average value, the predetermined pixel P. The present invention is characterized in that it is determined whether 11 12 is a pixel within the circular pattern.

In the circular pattern determination method of the present invention, each line segment L +
(1-1, 2,..., n), a plurality of predetermined distances r+r (j-L2.
..., m) Each image data f corresponding to each distant pixel Pl,
．． may also be used.

In this case, the circular pattern determination method of the present invention includes the following steps: From the predetermined pixel Po on each of a plurality of line segments Li (i=1, 2,..., n) extending from the predetermined pixel Po to the periphery of the radiation image. A plurality of predetermined distances ri (j-1, 2
,... +n) Each said image data f.corresponding to each distant pixel Pij. gradient f. , and each gradient f. The size of |∇fi|. The normalized gradient f. /|∇fi|Bl is determined, and each normalized gradient f. /|∇fi|+11 in the direction of the predetermined pixel Po fi+/lf II l
* e + (e I is a unit vector directed from each pixel P. to the predetermined pixel Po, * represents an inner product), and for each line segment L, the component fi + /lfllll'k is calculated.
e. Representative value of {V f t+/l V f +''l
'ke+)r is determined, and the representative value {f. An average value of /|∇fi|Bl'l'e+lr is determined, and based on the average value, it is determined whether the predetermined pixel Po is a pixel within the circular pattern. shall be.

Further, in the circular pattern determination device of the present invention, in the device, the predetermined a gradient calculation means for calculating a gradient fi of each of the image data fi corresponding to each pixel Pi separated by a predetermined distance r from the pixel Po of the gradient f. The normalized gradient f where the magnitude of |∇fi|+ is normalized
normalization means for determining I/lf1 1, a component f I/lfi l*e+ of the normalized gradient fl/lfi l in the direction toward the predetermined pixel Po;
(e+ represents a unit vector directed from each pixel Pi toward the predetermined pixel P. * represents an inner product), an average calculation means for calculating an average value of the component fI/lflI*eI , and determining means for determining whether the predetermined pixel Po is a pixel within the circular pattern based on the average value.

Further, the circular pattern determination device of the present invention, like the circular pattern method of the present invention described above, each of the line segments L + (1
= 1, 2, ..., n), a plurality of predetermined distances r +1 (j-1, 2, ...) from the predetermined pixel Po.
・1) Each image data fi corresponding to each distant pixel Pl
j may also be used.

In this case, the circular pattern determination device of the present invention includes the following: The predetermined pixel Po on each of a plurality of line segments L + (1=1, 2,..., n) extending from the predetermined pixel Po around the radiation image. A plurality of predetermined distances rij (j-1, 2
,..., river) corresponding to each of the distant pixels Pl. A gradient calculating means for calculating the gradient fij of the above, a normalized gradient vf/|∇fi|11 in which the magnitude of each gradient f1 |∇fi|++l is normalized.
1, each normalized gradient fi
The predetermined pixel P of j/lfi+1. component fi in the direction of
+/lfi+l*e+ (e+ is a unit vector directed from each pixel P. to the predetermined pixel P0, * represents an inner product); I VfB
l*e+(7) Representative value (Vfi+/l'7fi+l*e
+) representative value calculating means for calculating r; said representative value {V f . / l V f ++ l *
The method further comprises an average calculation means for calculating an average value of e+lr, and a determination means for determining whether the predetermined pixel Po is a pixel within the circular pattern based on the average value. Features.

15 16 Here, each of the plurality of line segments L + (1"1.2.
. . , n)" (that is, the value of n) is not limited to a specific number, but can be arbitrarily determined, taking into consideration, for example, the required determination accuracy, calculation time, etc.

In addition, the above-mentioned "predetermined distance r. and setting a large predetermined distance ri, etc.
The predetermined distance r, is for each line segment L. It may be different for each.

In addition, the above-mentioned “a plurality of predetermined distances r H (j−1, 2, ·
... m) The value of m in J is not limited to a specific value like the value of n above, and, like the predetermined distance rI, for example, it has a major axis in a predetermined direction on the radiographic image. When an elliptical pattern is included in the circular pattern according to the present invention, the predetermined direction has a m
The value of m is determined by increasing the value of each line segment L l
(i=1, 2...", n) may be different.

In addition, the above-mentioned "gradient" means that the xy coordinates of a certain pixel P on an X-ray image are (IIl.n), and that the pixel P and the X direction,
The coordinates of pixels P' and P' adjacent to each other in the y direction are (
m+1. n), (m.n+1), and the image data of those pixels PiP', P' are respectively f(n+.
n), f(m+1,n), f(Ill,
n+1), f (m.n) = ( f (
m+l. n) − f (IIl.n), f (m.
n+1) − f (n+.n) ) −(1).

In addition, the "representative value" refers to the likelihood of a circular pattern on the image profile along each line segment Li by the certain fth/fth/
｜∇fi｜++l*e. Typically, when the target is a circular pattern in which the central image data has a smaller value than the surrounding image data, for example, the above-mentioned value for each line segment Li f+r
/ l V f +r*eI refers to the maximum value, and in the case of a circular pattern in which the central image data has a larger value than the surrounding image data, it refers to the minimum value, for example.

However, for example, in the case where the maximum value is adopted as the representative value, each of the above-mentioned certain segments V f with respect to a certain line segment L,
+r/lf When the effective maximum value cannot be found for the line segment L, such as when all of the 1*e- are negative,
In addition to using the maximum value by simple calculation as the representative value,
For example, 0:0 etc. may be used as the representative value. Also, (maximum value) - (constant value), (minimum value) + (constant value)
Values that substantially represent the maximum value or minimum value are also included in the above-mentioned representative values.

For example, when e,' is a unit vector directed outward from a predetermined pixel P0 along each line segment Li, the above-mentioned certain amount fi/|∇fi|l 1'l'e+ or V f +r
/ l V f ul *e, +; : yi x te V f
+ / l Vfll*e+' or V f +r/
Even if the calculation of l V f zl *el' is performed, they are substantially the same except that the maximum value and the minimum value are reversed, and the present invention does not include various embodiments that are substantially the same. be.

Furthermore, the above-mentioned "average value" typically refers to an average value obtained by ordinary arithmetic mean calculation, but is not limited to this, for example, a value obtained by geometric mean calculation, or two representative values. It may be a value obtained by weighting and then performing an average calculation.

(Function) The circular pattern determination method and device of the present invention can be applied to a normalized gradient fl /lfl l (or fB/l
After calculating fi+l), a certain fraction 1+/fil*el (also V f 1/ l V f .l *e+) of the normalized gradient in the direction of a predetermined pixel Po is calculated. The influence of the contrast of the pattern is eliminated, and it is possible to make a determination based on the shape, whether or not it is circular.

Further, for each line segment L, a plurality of predetermined distances r. Each image data fi corresponding to each distant pixel P
When determining the representative value described above using Even if a predetermined pixel P. It is possible to accurately determine whether or not the pixel is a pixel within those circular patterns. Even in this case, the basic feature of the present invention, which is that the contrast can be abstracted and the determination can be made based on the shapes of these circular patterns, remains unchanged.

The present invention determines whether or not a predetermined pixel Po designated on a radiographic image is a pixel within a circular pattern, but repeating this calculation over the entire radiographic image,
That is, by scanning a radiographic image using the filter of the present invention, a circular pattern of the radiographic image can be extracted.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. Here, the above-mentioned stimulable phosphor sheet was used,
An example of extracting the shadow of a tumor that typically occurs in a roughly spherical shape within the lungs of a human body will be described. This tumor shadow typically appears on a visible image as a substantially circular shadow that is whitish (low density, that is, image data S1 described below has a small value) compared to the surrounding area.

FIG. 4 is a schematic diagram of an example of an X-ray imaging apparatus.

The X-rays 12 from the X-ray source 11 of the X-ray imaging device 10 are irradiated toward the chest 13a of the human body 13, and the X-rays 12a that have passed through the human body 13 are irradiated onto the stimulable phosphor sheet 14. Transmission X-ray image of human chest 18a is sheet l
4 is accumulated and recorded.

FIG. 5 is a perspective view showing an example of an X-ray image reading device and a computer system incorporating an embodiment of the present invention.

A stimulable phosphor sheet 14 on which an X-ray image has been recorded is set at a predetermined position in the X-ray image reading device 20.

The stimulable phosphor sheet 14 set at a predetermined position is transported in the direction of arrow Y (sub-scanning) by a sheet transporting means 22 such as an endless belt driven by a motor 2l.
be done. On the other hand, the light beam 24 emitted from the laser light source 23 is reflected and deflected by the rotating polygon mirror 2B which is driven by the motor 25 and rotates at high speed in the direction of the arrow, and after passing through the focusing lens 27 such as an fθ lens, the light beam 24 is focused on the optical path by the mirror 28. Instead, it enters the sheet 14 and performs main scanning in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y). Sheet l
4, a stimulated luminescence light 29 is emitted from the part irradiated with the excitation light 24 in an amount corresponding to the stored and recorded X-ray image information, and this stimulated luminescence light 29 is guided by a light guide 30. It is photoelectrically detected by a photomultiplier (photomultiplier tube) 3l. The light guide 30 is made by molding a light-guiding material such as an acrylic plate, and has a linear entrance end surface 30a extending along the main scanning line on the stimulable phosphor sheet l4. The light receiving surface of the photomultiplier 3l is coupled to the annularly shaped exit end surface 30b. Light guide 30 from entrance end surface 30a
The stimulated luminescence light 29 that has entered the light guide 30 travels through the interior of the light guide 30 through repeated total reflection, exits from the exit screen 80b, is received by the photomultiplier 8l, and becomes stimulated luminescence light representing an X-ray image. 29 is converted into an electrical signal by a photomultiplier 8l.

The analog output signal SO output from the photomultiplier 31 is logarithmically amplified by the logarithmic amplifier 32, and the A/D
The data is digitized by a converter 33, and image data S1 as an electrical signal is obtained.

The obtained image data S1 is stored in the computer system 40.
is input. This computer system 40 has a configuration that includes an example of the circular pattern determination device of the present invention, and includes a main body 41 in which a CPU and an internal memory are built-in, and a drive into which a floppy disk as an auxiliary memory is inserted and driven. 42, a keyboard 43 for an operator to input necessary instructions to the computer system 40, and a CRT display 44 for displaying necessary information.

Image data S1 manually input to the computer system 40
, each pixel of the X-ray image is assigned a predetermined pixel P. Then, it is determined whether the predetermined pixel Po is a pixel within the tumor shadow (circular pattern), and by repeating this over the entire X-ray image, the tumor shadow on the X-ray image is extracted. .

In order to explain a real space filter as an embodiment of the present invention for extracting the tumor shadow, FIG. This is a diagram drawn in a typical manner. It is determined whether the predetermined pixel Po is a pixel within the tumor shadow. By scanning an X-ray image using a filter like the one shown here,
A tumor shadow on the X-ray image is extracted.

FIG. 2 is a diagram showing an example of the profile of an X-ray image in the direction (X direction) in which line segments Li and L5 in FIG. 1 extend, centered on the predetermined pixel Po. Here, it is assumed that the predetermined pixel Pi is located approximately at the center of the tumor shadow 7 which is very close to the rib shadow 6.

The tumor shadow 7 typically appears as a substantially bilaterally symmetrical profile, but it may not be bilaterally symmetrical, such as when the tumor shadow 7 is located very close to the rib shadow 6 as in this example. It is important to be able to extract this tumor shadow 7 even in such a case. Note that the broken line 8 in FIG. 2 is an example of a profile when there is no tumor.

As shown in FIG. 1, a plurality of (here, 8) line segments Li (1 = 1, 2..., 8) extending from a predetermined pixel Po in the X-ray image to the periphery of the X-ray image are Furthermore, each radius '1 + r centered on a predetermined stroke Po
2+ r3 three circles R+ (j = 1, 2.3
) is assumed. A predetermined pixel P. The image data of is fo, and each pixel P located at each intersection of each line segment Li and each circle R,
ij (Figure 1 shows PII+ p, ■, Pl31P 51
Symbols are shown for + P , 2+ P 53.

) is assumed to be f1.

Here, each pixel Pi1 (1 - LL..., 8; j = 1,
2.3) Image data f. The gradient Vfi+ of is calculated.

FIG. 3 is a diagram showing the above gradient and the calculation method described below.

After the gradient f■ is determined, the lengths of the vectors of these gradients fij are made equal to 1.0. That is, the gradient f. When the magnitude of is fiII, the normalized gradient fi+/lfi+I is obtained.

Next, the component of this normalized gradient f1/1fi+I in the direction of the line segment L is determined.

That is, when eI is a unit vector directed from each pixel Pi1 to a predetermined pixel Po, fi+/lVf*e1 (where * represents an inner product) is obtained.

After that, each line segment Li (i
= 1, 2, ..., 8), each maximum value {f. /｜∇fi｜l
ll*el}m (1 = 1.2..., 8>) is obtained. In this embodiment, this maximum value is the representative value according to the present invention.

Furthermore, each of these maximum values {fi+/lfi, l*e+lm The additional value obtained by adding Σ{fi+/lfi1l'ke+lm is obtained.

The average value is obtained by dividing this added value by the number of line segments L (eight in this embodiment). Therefore, this added value is simply the average value multiplied by a constant, and can be equated with the average value, and in this embodiment, this added value is considered to be the average value of the present invention.

This added value Σ {V f ++/ l V f + r l * e
+lm is the feature amount Cl, this feature amount C, is compared with a predetermined threshold Thl, and whether C1≧Thl or C
A predetermined pixel P depending on whether I<Thl. It is determined whether each pixel is within the tumor shadow.

This filter uses a gradient f. Normalize the size fi + l, and calculate its direction (degree of difference in direction from line segment Li)
By focusing only on the feature C1, which has a large value due to the circular shape, regardless of the contrast with the surroundings, the tumor shadow can be extracted with high accuracy.

In addition, as seen in FIG. 2, each component f regarding the line segment Li
u/lVfi+l *e+ (j = 1, 2.3)
27 28 are all negative, so their maximum value {fi+/l
Vful $e,lm is also negative. Therefore, in this case, the formally determined maximum value {f1+/lful*e+]lI
l is not a valid maximum value in the present invention, so the line segment L. For example, instead of the maximum value above, set 0.
0 may be used as the representative value for the line segment Li.

Further, in the above embodiment, each image data f1 corresponding to each pixel Pij on eight line segments Li to L8 was used as shown in FIG. 1, but it is not necessary that there be eight line segments. Of course, there may be 16 pieces, for example, instead of 16 pieces. Also, regarding the distance from a predetermined pixel Po, ri+
Although calculations were performed on three distances of r2 + r3, this is not limited to three distances,
If the size of the tumor shadow to be extracted is almost constant, a single distance is sufficient (in this case, the calculation to find the representative value is unnecessary). In order to extract well, calculations may be performed for a large number of substantially continuous distances from distance ri to distance r.

The above embodiment is an example of extracting a tumor shadow that typically appears as a circle in a chest X-ray image of a human body obtained using a stimulable phosphor, but the present invention is limited to the extraction of tumor shadows. The present invention is not limited to chest X-ray images, and is not limited to systems using stimulable phosphors, and is not limited to chest X-ray images, and is not limited to systems using stimulable phosphors. This can be widely used when determining whether Po is a pixel within a circular pattern that constitutes the radiation image.

Furthermore, in the present invention, it is not always necessary to scan a radiographic image using the above-described filter. It may be determined whether or not there is one.

(Effects of the Invention) As explained in detail above, the circular pattern determination method and device of the present invention are characterized by the use of a normalized gradient in which the magnitude f1 (|∇fi|++1) of the gradient f(fi+) is standardized. After determining fi /lf1 (fi+/lfi+l), the component f/lVfi l*e+ (Vf./lVf.
l*el), information on the contrast of the circular pattern is abstracted and information representing the shape is extracted, and based on this information representing the shape, a predetermined pixel Po specified on the radiation image is circular. It is possible to accurately recognize whether a pixel is within a pattern.

Further, for each line segment Li, a predetermined pixel Po
By determining the representative value using each image data fi1 corresponding to each pixel Pij located a predetermined distance ril from , it is possible to calculate the shape of circular patterns of various sizes or slightly deformed circular patterns. Based on this, it is possible to accurately determine whether a predetermined pixel Po is a pixel within those circular patterns.

[Brief explanation of drawings]

In order to explain a spatial filter as an embodiment of the present invention for extracting a circular tumor shadow, FIG. Figure 2 is a diagram showing an example of the profile of an X-ray image in the direction (X direction) in which line segments 1l and L5 in Figure 1 extend, with the predetermined pixel P0 as the center. The figure shows image data f
．． FIG. 4 is a schematic diagram of an example of an X-ray image capturing device, and FIG. 5 is a diagram showing an example of an X-ray image reading device and an example of a circular pattern determining device of the present invention. 1 is a perspective view showing a computer system including an embodiment; FIG. 6... Rib shadow lO... X-ray imaging device 20... X-ray image reading device 23... Laser light source 2B... Rotating polygon mirror 29
... Stimulated luminescence light 30 ... Light guide 31 ...
Photo multilayer 40...computer system 7...tumor shadow l4...stimulable phosphor sheet 31 32

Claims (4)

[Claims] (1) In a circular pattern determination method that determines whether a predetermined pixel P_0 in the radiographic image is a pixel within a circular pattern constituting the radiographic image, based on image data representing a radiographic image of a subject. , each pixel P located a predetermined distance r_i from the predetermined pixel P_0 on each of a plurality of line segments L_i (i=1, 2,..., n) extending from the predetermined pixel P_0 to the periphery of the radiation image.
Find the gradient ∇f_i of each of the image data f_i corresponding to _i, and obtain a normalized gradient ∇f_i/I|∇f_i in which the size of each gradient ∇f_i |∇f_i| is normalized.
Find the component ∇f_i/|∇f_i| of the normalized gradient ∇f_i/|∇f_i| in the direction of the predetermined pixel P_0.
*e_i (e_i is a unit vector directed from each pixel P_i to the predetermined pixel P_0, * represents an inner product), find the average value of the component ∇f_i/|∇f_i|*e_i, and calculate the average value A method for determining a circular pattern, characterized in that it is determined whether the predetermined pixel P_0 is a pixel within the circular pattern based on a value. (2) In a circular pattern determination method for determining whether a predetermined pixel P_0 in the radiographic image is a pixel within a circular pattern constituting the radiographic image, based on image data representing a radiographic image of a subject. , a plurality of predetermined distances r_i_j(j
= 1, 2, ..., m) Gradient ∇f_i_ of each image data f_i_j corresponding to each distant pixel P_i_j
Find j and calculate the size of each gradient ∇f_i_j |
Normalized gradient ∇f where ∇f_i_j| is normalized
Find _i_j/|∇f_i_j|, and calculate each normalized gradient ∇f_i_j/|∇f_i_
j| in the direction of the predetermined pixel P_0 ∇f_i_j
/｜∇f_i_j｜*e_i (e_i is each pixel P_
Find the unit vector from i_j to the predetermined pixel P_0 (* represents the inner product), and for each line segment L_i, calculate the component ∇f_i_j/|∇f
＿i＿j｜*e＿i representative value {∇f_i＿j/｜∇f＿
Find i_j|*e_i}r, and calculate the representative value {∇f_i_j/|∇f_i_j|*e_i
} An average value of r is determined, and based on the average value, it is determined whether the predetermined pixel P_0 is a pixel within the circular pattern. (3) In a circular pattern determination device that determines whether a predetermined pixel P_0 in the radiographic image is a pixel within a circular pattern constituting the radiographic image, based on image data representing a radiographic image of a subject. , each pixel P located a predetermined distance r_i from the predetermined pixel P_0 on each of a plurality of line segments L_i (i=1, 2,..., n) extending from the predetermined pixel P_0 to the periphery of the radiation image.
Gradient calculating means for calculating gradient ∇f_i of each of the image data f_i corresponding to _i, a normalized gradient ∇f_i/|∇f_i| in which the size of each gradient ∇f_i |∇f_i| is standardized normalization means for determining the component ∇f_i/|∇f_i| of the normalized gradient ∇f_i/|∇f_i| in the direction of the predetermined pixel P_0;
Inner product calculating means for calculating *e_i (e_i is a unit vector directed from each pixel P_i to the predetermined pixel P_0, * represents an inner product), calculating an average value of the component ∇f_i/|∇f_i|*e_i A circular pattern determination device comprising an average calculation means and a determination means for determining whether or not the predetermined pixel P_0 is a pixel within the circular pattern based on the average value. (4) In a circular pattern determination device that determines whether a predetermined pixel P_0 in the radiographic image is a pixel within a circular pattern constituting the radiographic image, based on image data representing a radiographic image of a subject. , a plurality of predetermined distances r_i_j(j
= 1, 2, ..., m) Gradient ∇f_i_ of each image data f_i_j corresponding to each distant pixel P_i_j
gradient calculation means for calculating j, the size of each gradient ∇f_i_j |∇f_i_
Normalized gradient ∇f_i_j/
Normalization means for determining |∇f_i_j|, each of the normalized gradients ∇f_i_j/|∇f_i_
j| in the direction of the predetermined pixel P_0 ∇f_i_j
/｜∇f_i_j｜*e_i (e_i is each pixel P_
inner product calculation means for calculating a unit vector from i_j toward the predetermined pixel P_0 (* represents an inner product); for each line segment L_i, the component ∇f_i_j/|∇f
＿i＿j｜*e＿i representative value {∇f_i＿j/｜∇f＿
representative value calculation means for calculating i_j|*e_i}r, the representative value {∇f_i_j/|∇f_i_j|*e_i
} average calculation means for calculating an average value of r; and determination means for determining whether the predetermined pixel P_0 is a pixel within the circular pattern based on the average value. Characteristic circular pattern determination device.