KR20180085981A - Apparatus and method for modifying position of reference posiiton mark - Google Patents

Abstract

The present invention relates to a device to correct the position of a reference position marker. According to an embodiment of this invention, the correcting device includes: an image obtaining part generating a photographed image of a subject including a reference position marker by photographing the subject; a motion control part connected with the image obtaining part, selecting an effective preparatory reference position marker candidate group from the image applied from the image obtaining part, selecting a final reference position marker candidate group including a final reference position marker candidate from the selected effective preparatory reference position marker candidate group, determining a final reference position marker by comparing information about a reference position marker to information about the final reference position marker candidate of the final reference position marker candidate group, and adjusting the current position of the final reference position marker to a reference position of the reference position marker by comparing the current position of the determined final reference position marker to the reference position of the reference position marker; and a storage part storing information about the reference position marker, including an angular value between the two reference position markers and the distance between the two reference position markers.

Description

Field of the Invention [0001] The present invention relates to an apparatus and method for correcting the position of a reference position marker,

The present invention relates to an apparatus and method for correcting the position of a reference position marker.

Most image processing systems acquire an image of a target object using a photographing device such as a camera, process the acquired image in a desired manner, and determine a correction operation or desired information for the acquired image.

In this way, when processing the acquired image, accurate position information of the acquired image is required.

Various methods are used to obtain position information in the image processing system depending on whether the position of the photographing apparatus is changed or not and whether the position of the object is changed or not.

For example, when an image is acquired through air or satellite equipment, the object to be photographed is fixed, but the position of the photographing apparatus for acquiring the image changes with time.

When the position of the photographing apparatus changes with time, position information of the photographing apparatus is required when the image is acquired in order to calculate the position information of the image obtained through the photographing operation of the photographing apparatus.

On the other hand, in a photographing apparatus such as CCTV or MRI, the position of the photographing apparatus is fixed, but the position of the object to be photographed is not constant but variable.

In this way, in order to calculate the positional information of the object whose position is not fixed, the position of the object is aligned with the already known reference position and then the photographing operation is performed.

For example, when a DNA chip (DNA chip) having thousands to hundreds of thousands of DNAs attached to a glass plate or a silicon plate of a predetermined size is taken to acquire an image, the user sets the position of the DNA chip at the reference position After adjustment, the DNA chip is photographed.

As such, since the user must manually adjust the position of the DNA chip to the reference position at each photographing, it takes a lot of time and cost.

In order to reduce such an economical cost wastage, a method of calculating the positional information of an object by using a reference position marker after taking a predetermined reference position marker together with a target object is used.

However, there is a problem that the reference position marker is not correctly recognized according to the accuracy of the captured image of the reference position marker, or the wrong position is recognized as the reference position marker.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art.

According to an aspect of the present invention, there is provided an apparatus for correcting a position marker of a reference position marker, the apparatus comprising: an image obtaining unit for capturing an object having a reference position marker and generating an image of the object; And a final reference position marker candidate group having a final reference position marker candidate in the selected valid spare reference position marker candidate group is selected from among the candidates of the final reference position marker candidate, The final reference position marker candidate is compared with the information about the final reference position marker candidate and the information about the reference position marker to determine the final reference position marker and the comparison between the current position of the final reference position marker and the reference position of the reference position marker To adjust the current position of the final reference position marker to the reference position And a storage unit for storing information on the reference position marker including a distance between two reference position markers and an angle formed by two reference position markers, A pixel group including a plurality of pixels arranged in a row direction and a column direction in a row direction and a gradation value is determined, and the determined pixel group is determined as a plurality of preliminary reference position marker candidates, and each preliminary distance is calculated, A distance associated with each of the preliminary reference position marker candidates and a distance related to the reference position marker corresponding to each of the preliminary reference position marker candidates is compared with each of distances related to the reference position marker corresponding to each of the preliminary reference position marker candidates, A distance having the same value exists at a distance related to each of the calculated preliminary reference position marker candidates The candidate preliminary reference position marker candidates are determined as candidates of the effective preliminary reference position marker candidates that are candidates of the corresponding reference position marker, the valid preliminary reference position marker candidates are determined from the plurality of preliminary reference position marker candidates, And the operation control unit judges whether or not there is a final reference position marker candidate group in the selected valid spare reference position marker candidate group by combining the valid spare reference position marker candidate candidates It is determined that there is no candidate of one reference position marker in the preliminary reference position marker candidate and the remaining reference position marker except for one reference position marker assumed to be nonexistent using the plurality of preliminary reference position marker candidates To determine if the candidate is a new valid preliminary criterion It provides an operation for determining a marker value candidate.

The operation control unit may determine the final reference position marker candidate group by deleting the effective spare reference position marker candidate group in which the same effective spare reference position marker is set as a candidate of the reference position marker different from the selected effective spare reference position marker candidate group.

The operation control unit may calculate, at the last reference position marker candidate of the final reference position marker candidate group, the distance between the assumed reference position marker, which is the information about the hypothetical reference position marker for each final reference position marker candidate, And the final reference position marker candidate belonging to the final reference position marker candidate group having the same information as that of the reference position marker can be determined as the final reference position marker.

In the method of correcting the position of the reference position marker, a process of increasing the brightness value of the acquired reference image is performed. After the process of increasing the brightness value is performed, a circle is detected by performing Hough transform. Searching for an optimal circle among the detected circles and selecting the selected circle as a pixel group, performing a process of removing noise existing outside the pixel group on the basis of the searched pixel group, Determining a group of pixels consisting of a plurality of pixels arranged in a row direction and a column direction in a row direction and determining the determined pixel group as a plurality of preliminary reference position marker candidates,

Calculating a distance between each of the preliminary reference position marker candidates and each of the remaining preliminary reference position marker candidates to calculate a distance related to each of the preliminary reference position marker candidates, Comparing the distances associated with the reference position markers corresponding to the preliminary reference position marker candidates,

When a distance having the same value as each of distances related to the reference position marker corresponding to each of the preliminary reference position marker candidates is present in a distance related to each of the calculated preliminary reference position marker candidates, A step of determining an effective preliminary reference position marker candidate as a candidate of a reference position marker and a valid preliminary reference position marker candidate as a plurality of preliminary reference position marker candidates, A step of selecting an effective preliminary reference position marker candidate group for a reference position marker, a step of selecting an effective preliminary reference position marker candidate group for a reference position marker, a final reference position marker candidate having a final reference position marker candidate in the selected valid preliminary reference position marker candidate group, , Selecting the final reference position marker candidate group Comparing the information on the reference position marker candidate with the information on the reference position marker, determining whether a final reference position marker candidate group having the same information as the reference position marker exists, Determining a final reference position marker as a hypothetical reference position marker belonging to the existing final reference position marker candidate group if the final reference position marker candidate group having the same information as the current reference position marker candidate exists, Comparing the current position of the final reference position marker with the reference position of the reference position marker to adjust the current position of the final reference position marker to the reference position, and if there is no final reference position marker candidate group having the same information as the reference position marker , One of the plurality of preliminary reference position marker candidates Determining that there is no candidate of the quasi-position marker, and determining whether the candidate of the remaining reference position marker is one of the remaining reference position markers excluding the one reference position marker that is not supposed to exist using the plurality of preliminary reference position marker candidates And performing an operation to determine a new valid preliminary reference position marker candidate for the new effective preliminary reference position marker candidate.

In the step of selecting the final reference position marker candidate group, the valid preliminary position marker candidate group in which the same effective preliminary reference position marker is determined as a candidate of the reference position marker different from the selected effective preliminary reference position marker candidate group is deleted, The candidate group can be determined.

The step of determining the final reference position marker may further include determining a final reference position marker candidate based on the distance between the assumed reference position marker, which is information on the assumed reference position marker for each final reference position marker candidate in the final reference position marker candidate of the final reference position marker candidate group, Comparing the information about the reference position marker with information about the calculated assumed reference position marker, and comparing the information about the reference position marker with the calculated hypothesized reference position marker And determining that the final reference position marker candidate belongs to the final reference position marker candidate group if the final reference position marker candidate group having the same information about the position marker exists.

Obtaining a center line between the markers in the step of comparing the information about the reference position marker with the information about the calculated assumed reference position marker, calculating the center line, and then calculating the angle between the two markers using the reference line vector and the starting point of the optimal center line , And rotating the image by the obtained angle.

According to this aspect, the position marker corresponding to the reference position marker is determined in the photographed image, and the position of the determined reference position marker is moved to the reference position of the reference position marker.

Therefore, since the position adjustment operation to the reference position manually performed is automatically performed, cost and time are saved.

If the determined number of the reference position markers does not coincide with the number of the reference position markers and a part of the determined reference position markers is not detected and the remaining final reference position marker candidates are used, The position marker is detected. This improves the accuracy of the position detecting operation of the reference position marker.

1 is a schematic block diagram of an apparatus for correcting the position of a reference position marker according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating an operation of a reference position marker position correcting apparatus according to an exemplary embodiment of the present invention.
FIG. 3 is an operation flowchart of a method for calculating information on an existing position marker in FIG.
FIG. 4 is a flowchart illustrating a method for generating a candidate candidate of an effective preliminary reference position marker in FIG.
5 is a view showing a position of a reference position marker used in a position correcting device of a reference position marker according to an embodiment of the present invention.
6 is a diagram showing a vector formed by the reference position marker shown in Fig.
7 (a) and 7 (b) are diagrams showing the values of angles formed by two vectors, respectively.
FIG. 8 is a view showing an example of a photographed image for a test train according to an embodiment of the present invention.
9A and 9B are diagrams showing examples of vectors formed by the final reference position marker candidate group, in which FIG. 9A is a diagram showing a vector formed in the first final reference position marker candidate group, 2 is a diagram showing vectors formed in the final reference position marker candidate group.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but it should be understood that there may be other elements in between do. On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

Hereinafter, an apparatus and method for correcting a reference position marker position according to an embodiment of the present invention will be described with reference to the accompanying drawings.

First, a reference position marker position correcting apparatus according to an embodiment of the present invention will be described in detail with reference to FIG.

An apparatus for correcting the position of a reference position marker according to an embodiment of the present invention includes an image obtaining unit 11, an operation control unit 20 connected to the image obtaining unit 11, (30), and a display unit (40) connected to the operation control unit (20).

The image acquiring unit 10 includes a camera such as a CCD (Charge Coupled Device) camera or the like. The image acquiring unit 10 photographs an object having a predetermined reference position marker and generates a corresponding image, .

The operation control unit 20 includes a controller 21 connected to the image acquisition unit 10 and a storage unit 22 connected to the controller 21. [

The controller 21 selects a candidate group of the preliminary reference position marker for the reference position marker (hereinafter, referred to as a 'preliminary reference position marker candidate group') from the photographed image input from the image obtaining unit 10 The final reference position marker candidate group having the final reference position marker candidate is selected from the selected candidate reference position marker candidate group, and the information about the final reference position marker candidate of the final reference position marker candidate group, And determines a final reference position marker corresponding to the reference position marker, and compares the current position of the determined final reference position marker with the position of the reference position marker (hereinafter referred to as 'reference position marker' Is referred to as a 'reference position'), and the current position of the final reference position marker is adjusted to the reference position.

By the operation of the controller 21 of the operation control unit 20, the position of the reference position marker is not manually positioned to the reference position before shooting the object.

The storage unit 22 is for storing data generated during the control operation of the controller 21. [

The storage unit 30 stores information about each reference position marker, that is, a distance between two reference position markers calculated using two vectors for two reference position markers, a magnitude of an angle between two reference position markers (i.e., The magnitude of the angle between the two vectors) and the direction of each reference position marker (i.e., the sign of the magnitude of the angle).

In this example, the storage unit 22 for storing the data generated during the control operation of the controller 21 and the storage unit 30 for storing the information about the position of the reference position marker are separately provided. However, Only the portion 22 or 30 can be used.

The display unit 40 is connected to the control unit 21 of the operation control unit 20 and may be a liquid crystal display (LCD), an organic light emitting diode (OLED) display, or the like.

The corresponding image according to the control operation of the controller 21 of the display unit 40 is outputted so that the user can visually check the position adjustment process for the photographed image.

Next, with reference to Fig. 2, the control operation of the position correcting device for a reference position marker having such a structure will be described.

In this example, an image captured by the image acquisition unit 10 is an image for confirming a reaction result after applying a reaction material to a test sample such as blood or DNA, (I.e., tone value) of the image photographed by the user is different, and the reference position marker is already located at a predetermined position of the inspection tray containing the inspection sample.

However, the present invention is applied not only to inspection samples such as blood and DNA but also to inspection objects for judging whether defects such as semiconductor devices or electronic parts are defective or other objects on which reference position markers are located, Is adjusted to a reference position using a reference position marker.

When the operation of the position correcting device of the reference position marker is started, the controller 21 of the operation controller 20 starts operation (S10).

The controller 21 starts the operation and calculates information about the reference position markers P1-Pn (n = 1, 2, 3, 4, ...) and stores them in the storage unit 30 (S20) (M = 1, 2, 3, 4, ...) for the reference position marker P1-Pn from the photographed image photographed by the camera 10, (S30).

Next, the controller 21 determines a final reference position marker corresponding to the reference position marker P1-Pn among the identified preliminary reference position marker candidate groups C1-Cm (S40) The position of the last reference marker is rearranged using the reference position of the last reference marker and the position of the last reference marker, and the position of the final reference marker is corrected to the reference position (S50).

First, with reference to FIG. 3, the operation of the controller 21 for calculating information about the reference position markers P1-Pn and storing them in the storage unit 30 will be described.

The operation of calculating and storing the information about the reference position markers P1-Pn is performed by changing at least one of the position and the number of the reference position markers P1-Pn so that the information of the reference position markers P1-Pn is changed Every time.

5, the inspection tray T11 is provided with a plurality of grooves H11 and H12 containing desired inspection specimens. At this time, the grooves H11 function as reference position markers P1-Pn And the other groove (H12) is the groove containing the test sample.

In the case of FIG. 5, the number of reference position markers P1-P4 (n = 4) is four, but the number and position of these reference position markers P1-P4 are changed as necessary.

The groove H11 functioning as the reference position marker P1-P4 is expressed in the same color (e.g., white) as when the inspection food according to the inspection result at the time of photographing by the image obtaining unit 10 reacts, When the position markers P1 to P4 are in a normal state, the portion corresponding to the reference position markers P1 to P4 in the photographed image by the image obtaining unit 10 has a predetermined color (e.g., white).

In this embodiment, as an example, the case where the reference position markers P1 to P4 are located at the corresponding positions of the inspection tray T11 as shown in Fig. 5 will be described as an example.

The controller 21 of the operation control unit 20 uses the image obtaining unit 10 to scan the inspection tray T11 in which only the reference position markers P1 to P4 located in the corresponding grooves H11 are displayed in the set colors, (See FIG. 5), and only the reference position marker P1-P4 acquires a reference image having a set color (that is, a set tone value) (S21).

And the brightness value of the obtained reference image is increased. By doing this, the feature points of the marker and the pixel group become more visible, and high accuracy can be obtained in the subsequent pixel group search and marker detection.

After performing the process of increasing the brightness value, a Hough transform is performed to detect a circle. The optimal circle among the detected circles is searched and selected as the pixel group.

By performing such a process, since there is a lot of noise outside the pixel group, the marker detection rate is remarkably lowered when the marker is detected, so that the error can be eliminated in advance.

A process of removing noise existing outside the pixel group based on the searched pixel group is performed (S00).

Then, each pixel group made up of pixels in which pixels having a set gradation value (e.g., 255) in the reference image having a plurality of pixels are arranged continuously in the row direction and the column direction are determined, It is determined that each of the reference position markers P1 to P4 is located at a position where each pixel group is located and the image in which the reference position markers P1 to P4 are positioned in the reference image is determined to be the reference position markers P1 to P4 (S22).

Next, the center position (x _n ) of the pixel located in the middle of the pixels arranged in the row direction and the center (x _n ) of the pixels arranged in the column direction of the center of the corresponding pixel group with respect to the determined reference position markers P1- and in calculating the position (y _n)] of the pixel, and to determine the calculated position (x _n, y _n) to the position for each reference position marker (P1-P4) stored in the storage unit (22) (S23) .

When the position of each reference position marker P-P4 is determined, the controller 21 defines a vector generated by the reference position markers P1-P4 (S24) The distances between the position markers P1-P4 and the two different vectors are calculated and stored in the storage unit 30 as information about the reference position markers P1-Pn (S25).

6, the vector formed with reference to the first reference position marker P1 is a vector V (P1-P2) formed by the first reference position marker P1 and the second reference position marker P2 A vector V (P1-P3) formed by the first reference position marker P1 and the third reference position marker P3 and a vector V (P1-P3) formed by the first reference position marker P1 and the fourth reference position marker P4, (V (P1-P4)).

The vector formed based on the second reference position marker P2 is a vector V (P2-P1) formed by the second reference position marker P2 and the first reference position marker P1, A vector V (P2-P3) formed by the marker P2 and the third reference position marker P3 and a vector V (P2-P3) formed by the second reference position marker P2 and the fourth reference position marker P4. P2-P4).

The vector formed on the basis of the third reference position marker P3 is a vector V (P3-P1) formed by the third reference position marker P3 and the first reference position marker P1, A vector V (P3-P2) formed by the reference position marker P3 and the second reference position marker P2 and a vector V (P3-P2) formed by the third reference position marker P2 and the fourth reference position marker P4 V (P3 - P4)).

The vector formed based on the fourth reference position marker P4 is a vector V (P4-P1) formed by the fourth reference position marker P4 and the first reference position marker P1, A vector V (P4-P2) formed by the marker P4 and the second reference position marker P2 and a vector V (P4-P2) formed by the fourth reference position marker P4 and the third reference position marker P3. P4-P3).

At this time, only two vectors (for example, V (P1-P2) and V (P2-P1)) whose directions are opposite to each other are regarded as the same vector to define only one vector (for example, V (P1-P2)).

Therefore, when four reference position markers P1-P4 as shown in FIG. 6 are defined, the vectors for the two reference position markers defined by the operation of the controller 21 are V (P1-P2) = V1, V ( (P2 - P3) = V2, V (P1 - P4) = V3, V (P2 - P3) = V4, V (P2 - P4) = V5 and V (P3 - P4) = V6.

When the vectors for the reference position markers P1 to P4 are defined as described above, the control unit 22 sets the vectors V (P1-P2), V (P1-P3) (I.e., the absolute value of the distance between the center positions of the two reference position markers) of the two reference position markers in the reference position marker P (P4), V (P2-P3), V (P2- P2, P4, and P3-P4 are calculated and stored in the storage unit 30 (steps S1 to S3) S25).

Types of two reference position markers forming a vector Position marker vector Distance between position markers P1-P2 V (P1-P2) = V1 | P1-P2 | P1-P3 V (P1-P3) = V2 | P1-P3 | P1-P4 V (P1-P4) = V3 | P1-P4 | P2-P3 V (P2-P3) = V4 | P2-P3 | P2-P4 V (P2-P4) = V5 | P2-P4 | P3-P4 V (P3 - P4) = V6 | P2-P4 |

Next, the controller 21 compares the vectors [V (P1-P2), V (P1-P3), V (P1-P4) (Clockwise or anticlockwise) of the vector and the angle [theta] formed between the two vectors are calculated in the following equation (P2-P4) and V (P3-P4)

(Where, θ is the vector (other vectors (such as the following, reference to the term "line vector"), when the formation is referred to "after the vector "), and the angle between the line vector and a vector, x _q and y _q are the position of the row direction and the position of the column direction with respect to the reference position marker corresponding to the end point at the start point and the end point of the line vector and x _r and y _r is the location of the position of the row direction and the column direction with respect to a reference position marker corresponding to the end point after forming the vector as a component of the vector after each of the _{line vector} V and the hidden line vector, _{then vector} V neunhu vector.)

In Equation (1), if the time of the line vector is not the same as the time of the posterior vector, the position of the posterior vector is shifted horizontally or vertically with respect to the position of the line vector, (X _q , y _q , x _r , y _r ) of the posterior vector and the posterior vector.

Therefore, an angle [theta] formed by two different vectors (i.e., a line vector and a posterior vector) is calculated using [Equation 1]. At this time, the angle between the two vectors (for example, the angle between V (P1-P2) and V (P1-P3) and V (P1-P2) and V θ) is '0 °'.

The calculated angle? Has a positive value or a negative value, and if the value is positive, the direction indicated by the posterior vector on the basis of the line vector is counterclockwise, If the angle (-) is negative (-), the direction indicated by the posterior vector with respect to the line vector is clockwise.

For example, as shown in Fig. 7 (a), the value of the angle [theta] between the vector (V (P1-P2)) and the vector (V (P1-P3) The value of the angle? Between the vector V (P1-P2) and the vector V (P2-P4) becomes -60 degrees in the case of FIG. 7 (b) The direction indicated by the vector (V (P2-P4) (e.g., rear vector) with respect to the vector V (P1-P2) (line vector) is clockwise.

In this way, the values of the inter-vector angles calculated in all the vectors V1, V2, V2, V4, V5 and V6 are calculated as shown in Table 2 and stored in the storage unit 30 (S26)

The types of the two vectors forming the angle [theta] The value of the calculated angle? V1-V2 PA1 V1-V3 PA2 V1-V4 PA3 V1-V5 PA4 V1-V6 PA5 V2-V3 PA6 V2-V4 PA7 V2-V5 PA8 V2-V6 PA9 V3-V4 PA10 V3-V5 PA11 V3-V6 PA12 V4-V5 PA13 V4-V6 PA14 V5-V6 PA15

The operation of the controller 21 of the operation control unit 20 determines the distance between two reference position markers which are information on the reference position markers P1 to P4 and the value of the angle between the vectors formed by the reference position markers The control unit 21 photographs a corresponding inspection tray T12 to inspect the inspection tray T12 and displays the captured image on the inspection tray T12 After the acquisition, the operation of correcting the acquired position of the photographed image to the reference position is performed.

To this end, the controller 21 of the operation control unit 20 first selects an effective preliminary reference position marker from the preliminary reference position marker, and generates an effective preliminary reference position marker candidate group using the selected effective preliminary reference position marker (S30).

4, the controller 21 of the operation control unit 20 first determines whether or not the operation preliminary reference position marker candidate group is an active preliminary reference position marker candidate group, The control unit 10 activates the inspection tray T12 to capture an image of the inspection tray T12 (S31).

In this example, an example of the photographed image of the inspection tray T12 obtained in the image acquisition unit 10 is as shown in FIG. 8. At this time, a portion where the same color as the reference position marker P1-P4 is expressed by S1 S9.

Next, in step S32, the controller 21 determines a preliminary reference position marker candidate using pixels having the same tone value as the image for the reference position markers P1-P4 in the acquired image. That is, at least one of the reference position markers is included in the preliminary reference position marker candidate.

To this end, the controller 21 uses the respective tone values of the plurality of pixels constituting the photographed image to determine whether the pixels having the tone value representing the corresponding color (for example, white) are continuously arranged in the row direction and the column direction (P = 1, 2, 3,...) Of the preliminary reference position marker, that is, the preliminary reference position marker candidates S1-Sp.

At this time, the number of pixels arranged consecutively in each row direction and column direction is increased or decreased by a predetermined number based on the number of adjacent pixels in the row direction and column direction of the pixel group corresponding to the reference position marker, The margin of determination of the position marker can be varied.

That is, the controller 21 determines that the preliminary reference position marker candidates S1-Sp are located at the positions where the respective pixel groups are located, and determines that the preliminary reference position marker candidates S1-Sp are located at the center of the pixels arranged in the row direction, by calculating the position (xs _p) and the position of the pixel in the center of the pixel array in the column direction (ys _p) is stored in the storage unit 22 as the position of each set preliminary reference position marker candidates (S1-Sp) ( S32).

8, the total number of the preliminary reference position marker candidates S1-Sp detected in FIG. 8 is nine (p = 9), and the first to ninth preliminary reference positions Marker candidates S1 to S9.

Next, the controller 21 performs an operation of determining each of the preliminary reference position marker candidates S1-S9 as candidates of the effective preliminary reference position marker to be a candidate of any reference position marker among the reference position markers P1-P4 ( S33).

Therefore, the controller 21 first calculates the distance between the first preliminary reference position marker candidate S1 and the remaining preliminary reference position marker candidates S2 to S9 (i.e., the distance related to the first preliminary reference position marker candidate) And stores it in the storage unit 22.

At this time, in the same manner as described with reference to step S25 of FIG. 3, the distance calculation operation is performed by calculating the distance between the position of the first preliminary reference position marker candidate S1 and the position of one remaining preliminary reference position marker candidate S2- And calculates the distance related to the first preliminary reference position marker candidate S1.

The controller 21 compares the calculated first preliminary reference position marker candidate S1 and the remaining respective preliminary reference positions S1 and S2 to check whether the first preliminary reference position marker candidate S1 is a candidate of the first reference position marker P1. S1-S2 |, | S1-S3 |, | S1-S4 |, | S1-S5 |, and | S1-S2} related to the first preliminary reference position marker candidate S1, which is the distance between the marker candidates S2- P1-P2 |, | P1-P3 |, and | P1-P3 associated with the first reference position marker P1, S1-S6, S1-S7, S1- S1-S2 |, S1-S3 |, S1-S4 |, S1-S5 |, and S1-S2 relative to the calculated first preliminary reference position marker candidate S1 P1-P2 |, | P1-P3 |, | P1-P3 | associated with the first reference position marker P1 among the first reference position marker P1, -S6, P4 < / RTI >

S1-S5, S1-S6, S1-S7, S1-S8, S1, S2, S3, S4, P1-P3 |, and P1-P4 | associated with the first reference position marker P1 in the first and second reference positions P1, P2, P3, The selector 21 selects the first preliminary reference position marker candidate S1 as the effective preliminary reference position marker candidate that is the candidate of the first reference position marker P1.

The distances P1-P2 |, P1-P3 | and P1-P4 | associated with the first reference position marker P1 are stored as information of the reference position markers P1-P4, (30).

In the same manner, in order to check again whether the first preliminary reference position marker candidate S1 is a candidate for the second reference position marker P2, the controller 21 compares the calculated first preliminary reference position marker candidate S1 and S1-S2 |, | S1-S3 |, | S1-S4 |, and S1-S2 | associated with the first preliminary reference position marker candidate S1, which is the distance between each of the remaining preliminary reference position marker candidates S2- | P1-P2 |, | S1-S5 | associated with the second reference position marker P2 among the reference position markers S1-S5, S1-S6, S1-S7, P2-P3 |, and | P2-P4 |).

S1-S2 |, | S1-S3 |, | S1-S4 |, | S1-S5 |, | S1-S6 |, | S1-S7 P1-P2 |, | P2-P3 |, and | P2-P4 | associated with the second reference position marker P2 among the first reference position markers S1, S2, The controller 21 determines that the first preliminary reference position marker candidate S1 is a candidate for the second reference position marker P2. In this case, the first preliminary reference position marker candidate S1 is an effective preliminary reference position marker candidate that is a candidate for the first and second reference position markers P1 and P2 at the same time.

Thus, in this way, it is determined whether or not the first preliminary reference position marker candidate S1 is a candidate for each of the first to fourth reference position markers P1-P4.

In the same manner, in order to determine which of the first to fourth reference position markers P1 to P4 are candidates for the second preliminary reference position marker candidate S2, the second preliminary reference position marker candidate S2 S2-S3 |, | S3-S4 |, | S2-S5) related to the second preliminary reference position marker candidate S2, which is the distance between the remaining preliminary reference position marker candidates S1 and S3- | S2-S6 |, S2-S7 |, S2-S8 |, S2-S9 | At this time, the distance (S2-S1 |) between the second preliminary reference position marker candidate S2 and the first preliminary reference position marker candidate S1 is already the first preliminary reference position marker candidate S1 (| S1 -S2 |), it is omitted.

S2-S3 |, | S3-S4 |, | S2-S5 |, | S2-S6 |, | S2-S7 |, | P 1 -P 3 |, | P 1 -P 4 |, | P 2 -P 4 associated with the first to fourth reference position markers S 1 to S 8 and S 2 to S 9 | The second preliminary reference position marker candidate S2 is compared with any one of the first to second reference position markers P1 to P4 by comparing the preliminary reference position marker candidates S2 to P3, Is judged.

This operation is also applied to each of the remaining preliminary reference position markers S3 to S9 to determine which of the reference position markers P1 to P4 are candidates for the preliminary reference position markers P3 to P9, P9) of the at least one reference position marker (P1-P4).

Therefore, when the first to ninth preliminary reference position marker candidates S1 to S9 are judged as the preliminary reference position marker candidates as shown in Fig. 8, the effective preliminary reference position marker candidates S1, S2, S3, S4, S7 and S9 .

At this time, the first effective preliminary reference position marker candidate S1 is the candidate of the first reference position marker P1, and the second and fourth effective preliminary reference position marker candidates S2 and S4 are the second reference position marker P2 The third and seventh effective preliminary reference position marker candidates S3 and S7 are candidates of the third reference position marker P3 and the ninth effective spare reference position marker candidate S9 is the candidate of the fourth reference position marker P3, (P4).

Next, the controller 21 generates all possible combinations by using the valid preliminary reference position marker candidates S1, S2, S3, S4, S7, and S9 determined as the candidates of the reference position markers P1-P4 And generates an effective preliminary reference position marker candidate group (C1-Cm) (S34).

In the case of this example, all possible candidate positions of the preliminary reference position marker C1-Cm are all four (C1-C4), as shown in Table 3 below.

P1 P2 P3 P4 C1 S1 S2 S3 S9 C2 S1 S2 S7 S9 C3 S1 S4 S3 S9 C4 S1 S4 S7 S9

Next, the controller 21 deletes candidate groups that are practically impossible in the calculated plurality of effective preliminary position marker candidate groups (C1-C4), and selects the final reference position marker candidate group (S35). At this time, the effective preliminary reference position marker candidate included in the final reference position marker candidate group becomes the final reference position marker candidate.

That is, in the same effective preliminary reference position marker candidate group (C1-C4), the same effective spare reference position marker candidate can not be a candidate for the different reference position markers P1-P4. Accordingly, the controller 21 removes candidates of reference position marker candidates having the same effective spare reference position marker candidates from among the effective spare reference position marker candidate groups C1-C4.

The final reference position marker candidate S1 belonging to the final reference position marker candidate group C1 is S1, S2, S3, and S9. At this time, the final reference position marker candidate S1 is a candidate for the first reference position marker P1, The position candidate marker S2 is the candidate of the second reference position marker P2 and the final reference position marker candidate S3 is the candidate of the third reference position marker P3 and the final reference position marker candidate S9 is the candidate of the second reference position marker P2, 4 reference position marker P4.

Then, the controller 21 calculates the final reference position marker candidates C1-C4 in each of the selected final reference position marker candidate groups C1-C4 using the same method as that for calculating information on the reference position markers P1-P4, Assuming that the candidate is a corresponding reference position marker, the distance between the assumed reference position markers, which is information on each final reference position marker assumed as a corresponding reference position marker (hereinafter, referred to as 'assumed reference position marker'), The value of the angle between the vectors (i.e., the magnitude of the angle and the vector direction) is calculated (S36).

Then, the controller 21 compares the information about the assumed reference position marker and the information about the reference position marker with each other (S37). Then, the controller 21 compares the last reference position marker candidate (Step S38).

If there is a final reference position marker candidate group having the same information as that of the reference position marker, the controller 21 determines the assumed reference position marker belonging to the final reference position marker group as the final reference position marker (S39) . That is, each of the hypothesized reference position markers belonging to the final reference position marker candidate group is the reference position marker located at the current position instead of being located at the reference position which is the initial position of the reference position marker.

The candidate group (C1-C4) selected as the last reference position marker candidate group in Table 3 will be described in more detail, for example.

P2, P3, and P4 belong to the final reference position marker candidate group C1 as the reference position markers P1, P2, P3, and P4, respectively, corresponding to Table 3, , The distance between two assumed reference position markers and the angle between two assumed reference position markers calculated using two vectors for two assumed reference position markers are calculated, 5]. In the case of the first final reference position marker candidate group C1, the formed vector becomes (a) in Fig.

Two assumed reference position markers forming a vector The distance between the assumed reference position markers Same Distance between reference position markers S1-S2 | S1-S2 | same | P1-P2 | S1-S3 | S1-S3 | same | P1-P3 | S1-S9 | S1-S9 | same | P1-P4 | S2-S3 | S2-S3 | same | P2-P3 | S2-S9 | S2-S9 | same | P2-P4 | S3-S9 | S3-S9 | same | P3-P9 |

The value of the angle ([theta]) between the assumed reference position markers Same The value of the angle (?) Between the reference position markers SA1 same PA1 SA2 same PA2 SA3 same PA3 SA4 same PA4 SA5 same PA5 SA6 same PA6 SA7 same PA7 SA8 same PA8 SA9 same PA9 SA10 same PA10 SA11 same PA11 SA12 same PA12 SA13 same PA13 SA14 same PA14 SA15 same PA15

In the case of the final reference position marker candidate group (C1), the distance between the two assumed reference position markers and the value of the angle formed by the two assumed reference position markers are the same as those of the reference position marker, respectively.

Therefore, the hypothetical reference position markers S1, S2, S3, and S9 belonging to the final reference position marker candidate group C1 are finally set to the final reference position markers P1, P2, P3, P4, -P4) but becomes the reference position marker located at the current position rather than the reference position which is the initial position of the reference position markers P1-P4.

Assuming that the assumed reference position markers S1, S2, S7, and S9 are the reference position markers P1, P2, P3, and P4 in the case of the final reference position marker candidate group C2, Are shown in [Table 6] and [Table 7]. At this time, the vector formed in the second final reference position marker candidate group C2 is as shown in FIG. 9 (b).

Two assumed reference position markers forming a vector The distance between the assumed reference position markers Same Distance between reference position markers S1-S2 | S1-S2 | same | P1-P2 | S1-S7 | S1-S7 | same | P1-P3 | S1-S9 | S1-S9 | same | P1-P4 | S2-S7 | S2-S7 | disparity | P2-P3 | S2-S9 | S2-S9 | same | P2-P4 | S7-S9 | S7-S9 | same | P3-P9 |

The value of the angle ([theta]) between the assumed reference position markers Same The value of the angle (?) Between the reference position markers SA1 disparity PA1 SA2 same PA2 SA3 disparity PA3 SA4 same PA4 SA5 disparity PA5 SA6 disparity PA6 SA7 disparity PA7 SA8 disparity PA8 SA9 disparity PA9 SA10 disparity PA10 SA11 same PA11 SA12 disparity PA12 SA13 disparity PA13 SA14 disparity PA14 SA15 disparity PA15

As shown in [Table 6] and [Table 7], since the information on the two assumed reference position markers and the information on the reference position marker are not the same, The reference position markers S1, S2, S7, S9 are not final reference position markers.

In this manner, information on the hypothetical reference position marker belonging to each of the final reference position marker candidate groups (C1-C4) is calculated, and until the last reference position marker candidate group having the same information as the information about the reference position marker is found A comparison operation is performed.

However, if there is no final reference position marker candidate group having the same information as the information about the reference position marker in all final reference position marker candidate groups (C1-C4) (S38), the controller 21 of the operation control unit 20 It is determined that the image of the portion corresponding to one of the reference position markers P1-P4 is not accurately obtained and thus is not detected as a candidate for the preliminary reference position marker.

Therefore, the controller 21 determines that the reference position markers corresponding to the assumed reference position markers are lost one by one in each of the last reference position marker candidate groups (C1-C4) (S310), and the process goes to step S33 And a new effective preliminary reference position marker candidate is determined using the determined preliminary reference position marker candidate.

For example, it is assumed that there is no candidate of the first reference position marker P1 among the preliminary reference position marker candidates S1-S9 determined in step S33.

Therefore, the controller 21 reads the distance related to the first preliminary reference position marker candidate S1 stored in the storage unit 22 and calculates the distances (| P2-P3 |, | P2 -P4 |), it is determined whether or not the first preliminary reference position marker candidate S1 is a candidate for the second reference position marker P2.

In a similar manner, the controller 21 compares the distance associated with the first preliminary reference position marker candidate S1 and the distance related to the third reference position marker P3 to determine whether the first preliminary reference position marker candidate S1 is It is determined whether or not the first reference position marker P3 is a candidate for the first reference position position marker P3 and the distance related to the first reference position position marker candidate S1 is compared with the distance related to the fourth reference position marker P4, (S1) is a candidate of the fourth reference position marker P4.

In this way, since there are no candidates of the first reference position marker P1 among the plurality of preliminary reference position marker candidates S1-S9, the distance associated with the first reference position marker P1 is used to calculate each anticipated reference position marker candidate S1-S9) is a candidate of the first reference position marker P1 is omitted.

In this manner, it is determined whether the remaining preliminary reference position marker candidates S2 to S9 are candidates of the reference position markers P2 to P4 among the second to fourth reference position markers P2 to P4, The effective preliminary reference position marker candidate which is a candidate of at least one of the reference position markers P2-P4 is calculated.

Next, the controller 21 generates a new effective preliminary reference position marker candidate group by combining all of the calculated effective preliminary reference position marker candidates.

At this time, as described above, the candidates of the first reference position marker P1 do not exist in each of the generated preliminary position marker candidate groups (C1-Cm) (see, for example, Table 8).

Effective preliminary position marker candidate P1 P2 P3 P4 C1 Loss S2 S3 S9

As described above, a plurality of effective preliminary position marker candidate groups (C1-Cm) in which candidates of the first reference position marker P1 do not exist are generated, and as described above, the effective preliminary position marker candidates C1- It is determined whether the preliminary position marker candidates C1 to Cm exist at the same time as two or more reference position marker P2-P4 candidates. If the same effective preliminary position marker candidate exists at the same time on two or more criteria If there is an effective preliminary position marker candidate group (C1-Cm) that is a candidate of the position marker P2-P4, the effective preliminary position marker candidate group is deleted to select the final reference position marker candidate group.

Next, it is the same as the operation in step S36, and information on each assumed reference position marker belonging to each final reference position marker candidate group is calculated, and information on the calculated assumed reference position marker and information on the reference position marker If there is a final reference position marker candidate group having the same information (i.e., information on the reference position marker whose information on the first reference position marker is deleted), the assumed reference position marker belonging to the candidate group is the final reference position marker.

However, in this process, information on the calculated assumed reference position marker and information on the reference position marker (i.e., information on the reference position marker whose information on the first reference position marker is deleted) If there is no candidate group, the controller 21 again determines that there is no candidate of the second reference position marker P2 among the plurality of preliminary reference position marker candidates S1-S9.

Therefore, under the assumption that there is no candidate of the second reference position marker P2 among the plurality of the preliminary reference position marker candidates S1-S9, the valid spare reference position marker candidate is again re-evaluated A new effective preliminary reference position marker candidate group is generated and a final reference position marker candidate group is selected from among the generated effective preliminary reference position marker candidate groups to determine a final reference position marker.

If the final reference position marker can not be determined through this process, the controller 21 again determines that there is no candidate of the third reference position marker P3 among the plurality of preliminary reference position marker candidates S1-S9 , The above operation is repeated again.

This operation is repeated until it is determined that the assumed reference position marker of the final reference position marker candidate group corresponds to the finally corresponding reference position marker.

As a result, even if the reference position marker is lost in the photographed image, it is possible to select the final reference position marker among a plurality of hypothesized reference position markers using another detected hypothesized reference position marker.

In the case of this example, the case where there is no candidate of one reference position marker P1-P4 among the plurality of spare reference position marker candidates S1-Sp has been described, however, the number of the reference position marker to be lost can be changed .

When the last reference position marker corresponding to the reference position marker is selected from the plurality of final reference position marker candidates, the controller 21 of the operation control unit 20 sets the current position of the final reference position marker and the reference position of the reference position marker (Step S50).

At this time, the storage unit 22 and the storage unit 30 store information on the final reference position marker and information on the reference position marker, respectively.

Therefore, the controller 21 can know the positions of the final reference position marker and the reference position marker corresponding to each other using the contents stored in the corresponding storage units 22 and 30. Therefore, based on Equation (2) The movement amount and the rotation angle are calculated in the row direction and the column direction using the position difference between the reference position marker and the reference position marker, and the position of the captured image is moved using the calculated movement amount and rotation angle.

Therefore, the position of the final reference position marker is moved to the reference position of the reference position marker by the movement of the captured image, and the position of the captured image is aligned to the reference position before processing the taken image.

The spacing between the Equation 2 in, x _t is the current position of the corresponding reference position line of the moved end reference position marker direction corresponding to the line reference position and the reference position in the direction of the marker, y _t is the standard The distance between the reference position in the column direction of the position marker and the current position in the column direction of the final reference position marker to be moved corresponding to the reference position, x is a final reference position to be shifted Y is the current position in the column direction of the last reference position marker to be moved corresponding to the reference position marker in the shot image

Is the angle between one of the vectors associated with the final reference position marker and the vector associated with the reference position marker corresponding to this vector. For example, if one of the vectors associated with the final reference position marker is V (S1-S4) when the final reference position marker is S1, then the vector of the corresponding reference position marker is V (P1-P4) do.

After completing the series of steps, one more precise calibration step is performed to accurately correct the positions of the markers.

The correcting step first finds the centerline between the markers. At this time, the method for obtaining the center line between the markers uses [Equation 3] to obtain the coefficients of the linear equations of "

only,

는 Y,

는 A,

는 C로 정의한다. (즉,Y= AC)At this time

Y ,

A ,

Is defined as C. (I.e., Y = AC )

Here, a is the coefficient of the straight line x to be obtained, and b is the intercept of y.

x is the current position in the row direction of the last reference position marker to be moved corresponding to the reference position marker in the captured image and y is the current position in the column direction of the last reference position marker to be moved corresponding to the reference position marker in the captured image Your current location.

C can be expressed as [Equation 4] using a pseudo inverse formula.

[Equation 4] is calculated, and a geometric error r is obtained to minimize the error of the algebraic error. The formula of error (r) is as shown in Equation (5).

If the above-mentioned expression (5) is partially differentiated, the expression (6) is obtained.

Using the a and b values of the C matrix as the initial estimated values by calculating the above equations (4) to (6), the Gauss-Newton elimination method is repeated ten times to calculate the optimal center line between the markers To obtain a linear equation.

를 구한다.Referring to FIG. 10, the optimal center line is obtained, and the angle (?) Of the two straight lines is calculated using the reference line vector and the starting point of the optimal center line.

.

The equation for obtaining the angle [theta] is obtained by using [Equation 7].

The angle? Is calculated using the above-described expression (7), and the image is rotated by the obtained angle?.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

10: Image acquisition unit 20: Operation control unit
21: controller 22, 30:
40: Display P1-Pn: Reference position marker
C1-Cm: candidate for preliminary reference position marker
S1-Sp: candidate for preliminary reference position marker

Claims (7)

In the position correcting device of the reference position marker,
An image acquiring unit for photographing an object having a reference position marker and generating an image of the object,
A candidate valid reference position marker candidate group for the reference position marker is selected from the captured image applied from the image obtaining unit and a final reference position marker candidate is selected from the selected valid spare reference position marker candidate group, Determining a final reference position marker candidate by comparing information on a final reference position marker candidate of the final reference position marker candidate group with information on a reference position marker, The current position of the final reference position marker is compared with the reference position of the reference position marker to adjust the current position of the final reference position marker to the reference position,
A distance between two reference position markers, and a value of an angle formed by two reference position markers,
Lt; / RTI >
The operation control unit,
Determining a pixel group having a plurality of pixels arranged in the row direction and the column direction in a manner that has a tone value already set in the photographed image and is arranged in a row direction and a column direction and judges the determined pixel group as a plurality of preliminary reference position marker candidates,
Compares the distances between the calculated preliminary reference position marker candidates and the distances related to the reference position marker corresponding to the respective preliminary reference position marker candidates,
When a distance having the same value as each of distances related to the reference position marker corresponding to each of the preliminary reference position marker candidates is present in a distance related to each of the calculated preliminary reference position marker candidates, A candidate preliminary reference position marker candidate is determined as a candidate of a reference position marker, and a candidate of a preliminary reference position marker candidate is determined in a plurality of preliminary reference position marker candidates,
The effective preliminary reference position marker candidate group is determined by combining the effective spare preliminary position position marker candidates, which are candidates of the reference position position marker,
The operation control unit,
Determining that there is no candidate of one reference position marker among the plurality of preliminary reference position marker candidates if the final reference position marker candidate group does not exist in the selected candidate group of candidate effective reference position markers, A position correcting device for a reference position marker which performs an operation of determining a new effective preliminary reference position marker candidate to judge whether or not it is a candidate of the remaining reference position markers other than one reference position marker assumed to be absent using the marker candidate . The method of claim 1,
The operation control unit may further include a reference position marker candidate group determining unit for determining a candidate reference position marker candidate group by deleting the effective preliminary reference position marker candidate group in which the same effective preliminary reference position marker is set as a candidate of a reference position marker group having the same effective preliminary reference position marker, . The method of claim 1,
The operation control unit may calculate, at the last reference position marker candidate of the final reference position marker candidate group, the distance between the assumed reference position marker, which is the information about the hypothetical reference position marker for each final reference position marker candidate, And determines a final reference position marker candidate belonging to the last reference position marker candidate group having the same information as that of the reference position marker as a final reference position marker. In the position correction method of the reference position marker,
Performing a process of increasing a brightness value of the acquired reference image,
After performing the process of increasing the brightness value, a Hough transform is performed to detect a circle. Searching for an optimal circle among the detected circles and selecting the group as a pixel group,
Performing a process of removing noise existing outside the pixel group based on the searched pixel group,
Determining a group of pixels having a plurality of pixels arranged in a row direction and a column direction with preset gradation values from the image obtaining unit and determining the determined pixel group as a plurality of preliminary reference position marker candidates,
Calculating a distance between each of the preliminary reference position marker candidates and each of the remaining preliminary reference position marker candidates to calculate a distance related to each of the preliminary reference position marker candidates,
Comparing the distance between each of the calculated preliminary reference position marker candidates and the distance related to the reference position marker corresponding to each of the preliminary reference position marker candidates,
When a distance having the same value as each of distances related to the reference position marker corresponding to each of the preliminary reference position marker candidates is present in a distance related to each of the calculated preliminary reference position marker candidates, Determining an effective preliminary reference position marker candidate from among a plurality of preliminary reference position marker candidates by judging the effective preliminary reference position marker candidate as a candidate of the reference position marker,
Determining an effective preliminary reference position marker candidate group by combining effective preliminary reference position marker candidates that are candidates of the reference position marker,
Selecting an effective preliminary reference position marker candidate for the reference position marker,
Selecting a final reference position marker candidate group having a final reference position marker candidate in the selected effective spare reference position marker candidate group,
Comparing information of a final reference position marker candidate of the final reference position marker candidate group with information of a reference position marker,
Determining whether a final reference position marker candidate group having the same information as the reference position marker exists,
Determining a final reference position marker candidate that belongs to the last reference position marker candidate group that exists if there is a final reference position marker candidate group having the same information as the information about the reference position marker,
Comparing the current position of the determined final reference position marker with the reference position of the reference position marker to adjust the current position of the final reference position marker to the reference position,
Determining that there is no candidate of one reference position marker among the plurality of preliminary reference position marker candidates if there is no final reference position marker candidate group having the same information as the information about the reference position marker,
An operation of determining a new effective preliminary reference position marker candidate to determine whether or not a candidate of the remaining reference position markers other than one reference position marker assumed to be nonexistent is a candidate using the plurality of preliminary reference position marker candidates A method for correcting a position of a reference position marker comprising: 5. The method of claim 4,
In the step of selecting the final reference position marker candidate group, the valid preliminary position marker candidate group in which the same effective preliminary reference position marker is determined as a candidate of the reference position marker different from the selected effective preliminary reference position marker candidate group is deleted, A method for correcting a position of a reference position marker for determining a candidate group. 5. The method of claim 4,
Wherein determining the final reference position marker comprises:
Calculating a distance between an assumed reference position marker and an angle between two vectors, which is information on an assumed reference position marker for each final reference position marker candidate in the final reference position marker candidate of the final reference position marker candidate group,
Comparing the information about the reference position marker with information about the calculated assumed reference position marker, and
Determining a final reference position marker candidate as a final reference position marker candidate when the final reference position marker candidate group having the same information about the reference position marker and the calculated information about the assumed reference position marker exists; , And the position of the reference position marker. The method of claim 6,
A step of comparing the information on the reference position marker with the information on the calculated assumed reference position marker to obtain the center line between the markers,
Obtaining an angle between the two markers using the reference line vector and the starting point of the optimal centerline;
Further comprising the step of rotating the image by the obtained angle.

Images