WO2025032549A1

WO2025032549A1 - Dartboard with a scoring system, scoring system and method for counting points using the scoring system

Info

Publication number: WO2025032549A1
Application number: PCT/IB2024/057736
Authority: WO
Inventors: Cyril DE VROOM; Klaas NAGEL
Original assignee: Triplescore BV
Current assignee: Triplescore BV
Priority date: 2023-08-10
Filing date: 2024-08-09
Publication date: 2025-02-13
Anticipated expiration: 2026-02-10
Also published as: NL2035582B1

Abstract

The present invention relates to a dartboard with a scoring system, comprising a target area, a lighting ring, at least three cameras for capturing images of darts, and a processing unit for processing the images and calculating the points, wherein the dartboard comprises a tool with a number of equal arcs for calibrating the scoring system, wherein the dartboard comprises fixed mounting points for detachably placing the tool, wherein after placing the tool each camera is positioned at a center of a circle of only one arc and wherein on each arc left and right of an intersection of the optical axis with the arc over a total range of at least 50° indicators of angles between radii of the circle and the optical axis of the camera are arranged. The current invention also relates to a method for counting points.

Description

DARTBOARD WITH A SCORING SYSTEM, SCORING SYSTEM AND METHOD FOR COUNTING POINTS USING THE SCORING SYSTEM

TECHNICAL FIELD

The invention relates to a dartboard with a scoring system, more specifically a dartboard with a detachable tool for calibrating the scoring system. The invention also relates to a scoring system and a method for counting points using the scoring system.

PRIOR ART

Darts is a game that is gaining more and more popularity. It requires not only dexterity and precision with the darts but also a head for numbers to quickly count points after throwing each dart, so that a game strategy can be quickly adjusted based on the points scored. This prevents some players from fully enjoying the game. Therefore, in recent years, dartboards have been introduced to the market to which an automated scoring system has been added.

An example of such a dartboard is described in CN112013721. Herein is described a dartboard with a system for recognizing a coordinate where a dart has hit the dartboard. The dartboard comprises for this purpose a camera system with four cameras that are placed on an arc at the top side of the dartboard. After throwing a dart, a system of equations is solved, with which the coordinate is calculated. After the coordinate is known, a score for the dart can be determined and the points can be counted.

A problem with the known solution is that the system must be calibrated in a rather cumbersome way. To this end, darts must be placed along the circumference of the physical target of the dartboard at transitions between physical sectors of the target, images of which are then captured using the cameras. This is time consuming and prone to errors.

The present invention aims to find a solution for at least some of the above problems.

SUMMARY OF THE INVENTION

In a first aspect, the present invention relates to a dartboard with a scoring system for automatically calculating points scored after throwing a dart according to claim 1. The dartboard is very advantageous because it can be calibrated very quickly using the tool. The tool only needs to be placed on the dartboard, after which an image can be captured simultaneously with all cameras. There is no need to manually place darts at transitions between sectors on the dartboard. The captured images can then be used to determine an angle, relative to each camera, where a dart has landed in the circular target area of the dartboard during a game. Any deviations due to a different orientation of a camera or due to aberrations in a camera lens can be compensated for in this way. Because the positions of the at least three cameras and the angles relative to the at least three cameras are known, it is then possible to use triangulation to calculate where the dart landed in the circular area and to calculate the points scored. A very advantageous feature of the tool is that the angle indicators are very evenly distributed in a captured image, whereas in a prior art method, because darts are placed as indicators along the circumference of the physical target of the dartboard at transitions between physical sectors of the target, there are more indicators on an outside in a camera image. Thus, a scoring system cannot be calibrated equally accurately everywhere, and errors may possibly be introduced when calculating the points scored. By means of the tool, it is possible to very accurately translate an X-coordinate of a dart in a camera image directly into an angle relative to the camera.

Further preferred forms of the dartboard are described in claims 2-9.

In a second aspect, the invention relates to a method for automatically counting points when throwing a dart at a dartboard with a scoring system according to claim 10.

A particular advantage of this method is that points can be counted very quickly because an X-coordinate of the dart in an image captured by a camera is translated directly to an angle relative to that camera using a lookup table, after which a position in the circular target area can be determined by triangulation. Consequently, no complex techniques are required to determine the position of the dart. The game is not held up by the scoring system and the method can be executed on a simple processing unit.

Further preferred embodiments of the method are described in claims 11-15.

In a third aspect, the invention relates to a scoring system according to claim 16.

The scoring system is very advantageous because it can be calibrated very easily and quickly with the aid of the tool for the scoring system after being placed over a dartboard without a scoring system, after which an accurate determination of a position of a dart on the dartboard is possible and points can be counted automatically.

DESCRIPTION OF THE FIGURES

Figure 1A and IB show perspective views of a dartboard according to an embodiment of the present invention.

Figure 2 shows a cross-section of a dartboard according to an embodiment of the present invention.

Figure 3 shows a perspective view of a tool according to an embodiment of the invention.

Figure 4 shows a schematic representation of a calibration of a dartboard according to the prior art.

Figure 5 shows a schematic representation of a calibration of a dartboard according to an embodiment of the present invention.

Figure 6 shows a schematic representation of an X-coordinate of a dart in a captured image according to an embodiment of the present invention.

Figure 7 shows a schematic block diagram of a method for determining a position of a dart according to an embodiment of the present invention.

DETAILED DESCRIPTION

Unless otherwise defined, all terms used in the description of the invention, including technical and scientific terms, have the meaning as commonly understood by a person skilled in the art to which the invention pertains. For a better understanding of the description of the invention, the following terms are explained explicitly.

In this document, "a" and "the" refer to both the singular and the plural, unless the context presupposes otherwise. For example, "a segment" means one or more segments. The terms "comprise," "comprising," "consist of," "consisting of," "provided with," "have," "having," "include," "including," "contain," "containing" are synonyms and are inclusive or open terms that indicate the presence of what follows, and which do not exclude or prevent the presence of other components, characteristics, elements, members, steps, as known from or disclosed in the prior art.

Quoting numeric intervals by the endpoints comprises all integers, fractions, and/or real numbers between the endpoints, including those endpoints.

In the context of this document, an LED is a Light Emitting Diode.

In the context of this document, MEMS means micro-electromechanical system.

In the context of this document, a centerline is a line that runs through the middle of an object. In a symmetrical object, the centerline is an axis of symmetry.

In the context of this document, "substantially parallel" means that two directions form an angle of a maximum of 10°, preferably a maximum of 5°, more preferably a maximum of 3°, even more preferably a maximum of 2°, and most preferably a maximum of 1°.

In a first aspect, the invention relates to a dartboard with a scoring system for automatically calculating points scored after throwing a dart.

The dartboard comprises a circular target area for darts, a lighting ring around the target area for lateral lighting of the circular target area, at least three cameras for capturing images of darts in the circular target area, and a processing unit for processing the images of the darts in the circular target area and for calculating the points.

The circular target area is preferably made of a soft material suitable for receiving a tip of a dart. The circular target area preferably comprises colored zones, each zone being associated with a predetermined score. Preferably, each transition between two zones is indicated by means of a metal wire, wherein the metal wire is applied on the circular target area. The metal wires form a physical boundary between the different zones.

It will be apparent to one skilled in the art that in this context the target area can also comprise black and white zones and that these should also be considered colored zones. The lighting ring and the circular target area are concentric. The lighting ring has a larger diameter than the circular target area. The lighting ring preferably comprises multiple LED elements as a light source. The lighting ring illuminates the circular target area laterally on a side of the circular target area which is directed towards a player. The lighting ring preferably emits white light. This is thus the side on which the colored zones are applied. The lateral lighting of the circular target area is advantageous because it creates a significant contrast difference in the images captured by the at least three cameras between light emitted by the lighting ring and a dart that has landed in the circular target area. The dart locally blocks the light of the lighting ring and contrasts darkly against the lighting ring, creating a high contrast between the lighting ring and the dart. This makes it easier to locate a dart in an image. The lighting ring is preferably located as close as possible to the plane in which the circular target area lies, so that there is the greatest possible contrast at a tip of a dart.

The at least three cameras preferably have an equal viewing angle, focal length, and resolution. The at least three cameras are directed towards the circular target area. The at least three cameras are positioned on the side of the circular target area that faces the player. The at least three cameras are directed towards a center of the circular target area. This means that an optical axis of each camera passes through the said center. The at least three cameras are placed on a first circumference. The first circumference and the circular target area are concentric. The first circumference has a larger diameter than the circular target area. The at least three cameras are placed evenly distributed on the first circle circumference. This means that an arc on the first circumference between each two cameras is of equal length, or in other words, that seen from the center of the circular target area, an angle between each two cameras is equal. This is an advantage because as a result, a dart in the circular target area can never be in line with the optical axes of all the cameras. This is also advantageous for reducing errors through triangulation when determining a position of a dart in the circular target area. Preferably, the dartboard comprises at least four cameras to further reduce errors through triangulation. In the remainder of this document, where "at least three cameras" is stated, this should be interpreted as "at least four cameras" if the dartboard contains at least four cameras, unless it is clear from the description that this is not the case.

The processing unit comprises a processor or a controller, working memory, and preferably non-volatile memory. The processor or controller is communicatively connected to the at least three cameras for retrieving and processing the captured images. Alternatively, each camera comprises its own processing unit for processing the images and the processing units of the at least three cameras are communicatively connected to each other for calculating the points. Preferably, the processing unit of one camera is the master. It is also possible to provide a dedicated processing unit that acts as a master and calculates the points.

According to a preferred embodiment, the dartboard comprises a detachable tool for calibrating the scoring system. The tool comprises a number of circular arcs. The arcs are preferably the same. The number of arcs is equal to the number of cameras of the dartboard. Most preferably, the tool thus comprises at least four equal arcs.

The dartboard comprises fixed mounting points for the detachable placing of the tool on the dartboard. The fixed mounting points are for example magnets or clamps. Preferably, the fixed mounting points are clamps that detachably secure the tool at the ends of the arcs of the tool. Preferably, the number of fixed mounting points is equal to the number of arcs, with one fixed mounting point being common to two arcs. Preferably, the fixed mounting points are placed on a second circumference, with the second circumference and the circular target area being concentric. The second circumference has a larger diameter than the circular target area, so that the fixed mounting points do not disturb the circular target area. Preferably, the second circumference has a smaller diameter than the first circumference. The fixed anchor points are reference points for the tool, which always causes the tool to be positioned in the same way with respect to the at least three cameras. The fixed mounting points can be part of the circular target area or a component of the lighting ring.

After the detachable placing of the tool on the fixed mounting points, each camera of the at least three cameras is located in a center of a circle of only one arc. It is clear that the arc is part of a circumference of the said circle. The optical axis of any camera is thus a radius of the circle in whose center the camera is located. Each camera is thus aimed at an inner curvature of one arc.

On each arc, to the left and right of an intersection of the optical axis of the camera located at the center of the circle with the arc, indicators are provided over a range of at least 50° of angles between radii of said circle and the optical axis of said camera. The range is preferably at least 54°, more preferably at least 56°, even more preferably at least 60° and even more preferably at least 64°. These angles are suitable for indicating the direction a dart is facing relative to the camera in question. The range is symmetrical with respect to the intersection of the optical axis with the arc. The indicators are points, lines, blocks, numbers, or another suitable indicator. The indicators should preferably be placed at equal intervals. Preferably, there is an indication at least every 5°, more preferably at least every 4°, even more preferably at least every 3°, even more preferably at least every 2°, and most preferably at least every 1° degree.

The dartboard can be calibrated very quickly with the tool. The tool only needs to be placed on the dartboard, after which an image is captured simultaneously with all cameras. There is no need to manually place darts at transitions between sectors on the dartboard. The captured images of each arc can then be used to determine an angle relative to each camera where a dart has landed in the circular target area of the dartboard during a game. After all, an indication of an angle relative to the optical axis of a camera has an X-coordinate in the captured image according to an X-axis that can be expressed in pixels. The X-axis is a lying axis in the captured image and is substantially parallel to a plane in which the circular target area lies. The Y-axis is a standing axis in the image, transverse to the X-axis. During the game, a dart in an image captured by a camera likewise has an X-coordinate along the X-axis which is expressed in pixels. By comparing the X coordinate of the dart with the indication corresponding to the X-coordinate in the image of the arc captured by the same camera, the angle relative to that camera can be determined. It will be apparent that each camera has its own XY-axis system to determine the position of a pixel in an image. Any deviations due to a different camera orientation, for example due to an optical axis that is not perfectly aligned with the center of the circular target area, or due to aberrations in a lens of a camera, can be compensated for by the image of the arc recorded by that camera. Compensating for aberrations in the camera lens is additionally advantageous because it allows working with simple and inexpensive cameras. Because positions of the at least three cameras in a plane containing the circular target area and the angles relative to the at least three cameras are known, it is then possible to use triangulation to calculate where the dart landed in the circular area and to calculate the points scored. A very advantageous feature of the tool is that the angle indicators are very evenly distributed in a captured image. In a method according to the prior art, because darts are placed as indicators along the circumference of the physical target of the dartboard at transitions between physical sectors of the target, there are more indicators on the outside in a camera image. Thus, a scoring system cannot be calibrated equally accurately everywhere, and errors may possibly be introduced when calculating the points scored. By means of the tool, it is possible to very accurately translate an X-coordinate of a dart in a camera image directly into an angle relative to the camera. According to an embodiment, the arcs are fixed on a plate. The plate is preferably a disk. The plate can be detachably placed on the dartboard on the fixed mounting points. The plate preferably has a thickness of at most 3 mm, more preferably at most 2 mm, and even more preferably at most 1 mm. As a result, the plate does not prevent the three or more cameras from viewing the arcs. The plate is advantageous for a simpler construction of the tool. Because of the plate, the arcs do not need to have structural strength. The plate also allows the position and the number of fixed mounting points to be chosen flexibly. For example, the fixed mounting points can be placed on the optical axes of the at least three cameras, so that the fixed mounting points can be used as a direct indication of the positions of the at least three cameras.

According to a preferred embodiment, after placing the tool, each arc has a radius that corresponds to a focal length of the camera that is located in the center of the corresponding arc. This makes the indicators on the arc sharply visible in the captured image, which is advantageous for accurate calibration. Additionally advantageous is that a focal length of a camera is chosen such that a dart is sharply visible in the captured image in as large a portion of the circular target area as possible, whereby the camera is immediately calibrated at a relevant distance.

According to a preferred embodiment, the optical axis of each camera lies in a plane that is parallel to the circular target area. The mentioned plane is located at a distance of at least 1 mm and at most 5 mm from the circular target area. The mentioned distance is measured in a direction perpendicular to the circular target area.

Preferably, the mentioned distance is at most 4 mm, more preferably at most 3 mm, and even more preferably at most 2 mm.

The optical axis of the cameras is preferably as close as possible to the plane in which the circular target area lies, so that the cameras look as straight as possible at the darts, resulting in as few deformations in the image as possible that need to be corrected. Additionally, darts very often land at an angle in the circular target area. The closer to the plane in which the circular target area lies the darts are viewed, the smaller any errors are when determining a position of a dart in the circular target area. A distance of at least 1 mm is advantageous to avoid as much obstruction of the cameras as possible by objects, such as for example the metal wires that physically separate the zones in the circular target area, clamps for retaining the circular target area, or staples that secure these metal wires. According to an embodiment, the circular target area is interchangeable. This is advantageous because it makes the dartboard usable for various game variants. This is additionally advantageous because the circular target area can be replaced when worn. This is particularly advantageous because it allows the scoring system to be used for a dartboard without a scoring system, by replacing the circular target area with the dartboard without a scoring system.

According to a preferred embodiment, the dartboard comprises a control mechanism for regulating a position of the circular target area relative to the optical axes of the at least three cameras. This embodiment is advantageous to ensure that the optical axes of the at least three cameras lie in a plane parallel to the circular target area, as in previously described embodiments. This also allows any production margins during the manufacture of the dartboard to be accommodated. This is also advantageous for positioning the circular target area at a suitable distance from a parallel plane in which the optical axes lie, as described in a previous embodiment. This is particularly advantageous for a dartboard with an interchangeable circular target area. These interchangeable circular target areas can be from different manufacturers and may have different dimensions.

The control mechanism may comprise a mechanism, such as for example three adjusting screws, which allows to adjust the circular target area in height, but also to make the circular target area parallel with the plane in which the optical axes of the at least three cameras lie. The control mechanism may comprise, for each of the at least three cameras, an individual mechanism, such as, for example, an adjusting screw, for adjusting a height position of the cameras relative to the circular target area. The control mechanism can also be a combination of both mechanisms.

According to a preferred embodiment, the lighting ring comprises an annular light source and an annular reflector. The annular reflector is directed towards the circular target area. The annular light source is directed towards the annular reflector, either directly or indirectly. Indirect means that the annular light source is directed towards the annular reflector with the aid of, for example, a second annular reflector. The annular light source is preferably located lower than the circular target area. This means that, as seen in a direction perpendicular to the circular target area, the target area lies at a different height than the side of the circular target area that is directed towards a player and in a direction away from the player. In this way, the annular light source does not obstruct the at least three cameras. The annular light source preferably comprises a plurality of LED elements. The annular reflector is advantageous for the most uniform possible lateral emission of light to the circular target area. This avoids LED elements being directly visible in the images captured by the at least three cameras, which could cause overexposure and possibly hinder detection of a dart that is positioned just between two LED elements.

According to a further embodiment, the at least three cameras are placed outside a perimeter of the annular reflector. The annular reflector has a viewing opening for each camera. The viewing opening has an opening that is preferably large enough to obtain a viewing angle of the camera of 100°, more preferably at least 110° and even more preferably at least 120°. This embodiment is advantageous because it ensures that each camera is hidden as well as possible from other cameras. This maintains a sharp contrast between a dart and the annular reflector, even if the dart is beside or in front of the viewing opening.

According to one embodiment, the annular reflector is a shell of a truncated cone. The truncated cone has an apex angle of preferably less than 45°, even more preferably less than 30°. The truncated cone has a base. Preferably, the base is on a side of the target area that is directed towards the player. This embodiment is advantageous to avoid dirt or dust from remaining on the annular reflector, which could locally cause lower contrast and thereby disrupt the determination of the position of the darts. Examples of dirt comprise fragments of the target area or feathers from darts that become loose. In combination with a second lighting ring from a later embodiment, the dartboard preferably comprises at a bottom side an opening in the second lighting ring for evacuating the dust or dirt. It will be apparent that the bottom of the dartboard is determined in a suspended state.

According to a preferred embodiment, the indicators of the angles between the radii of a circle and the optical axis of the camera located at the center of the circle are blocks that alternately have a first color and a second color. For example, the indicators are blocks alternating between a blue color and a white color. It is clear that as long as there is sufficient contrast between the first color and the second color, many colors are suitable as the first color and the second color. Each block represents an equal number of degrees on the arc.

It will be apparent to one skilled in the art that black and white are suitable as the first and second colors.

This embodiment is very advantageous because it allows a simple relation between an X-coordinate expressed in pixels and a marker of an angle. Each transition from a first color to a second color or from a second color to a first color is an additional step of the same number of degrees. Color transitions are simple to detect in images by means of image processing algorithms. By starting from a fixed point on the arc and by counting the number of transitions, the angle can be determined for that X-coordinate in the image each time. For intermediate pixels in the image, the angle can be interpolated. Additionally advantageous when using a block is that an object, such as for instance a staple for retaining the metal wires that physically separate the zones in the circular target area or a clamp for retaining the circular target area, does not completely hide the block from the camera, allowing detection of a transition between colors to remain possible.

According to a further embodiment, the block that is immediately to the left or immediately to the right of the optical axis of the camera has a third color. The third color is different from the first color and the second color. The third color is for example red. It is again clear that multiple colors are suitable as a third color, as long as there is enough contrast to distinguish the first color, the second color, and the third color from each other. Assuming that a block adjacent to the optical axis on the opposite side has the first color, then the transition between the first color and the third color is the fixed point for counting the transitions. The transition between the first color and the third color is then 0°. This embodiment is advantageous because it allows for a very simple determination of the direction in which the center of the circular target area is located in the image of the camera. It can also be used as a measure to check whether a camera is sufficiently aimed at the center of the circular target area, namely with perfect orientation this transition should lie in the center of the camera's image.

According to an embodiment, the dartboard comprises a marker opposite each of the at least three cameras as an indication of the optical axis of the camera. The marker is preferably applied to the annular reflector. The marker is for example a stripe on the annular reflector. The marker is advantageous because it makes it very easy to determine in which direction the center of the circular target area lies in the camera image. It can also be used as a measure to check whether a camera is sufficiently aimed at the center of the circular target area, namely with perfect orientation this marker should lie in the center of the camera's image. When using the scoring system, the marker can be used to check that a camera is still correctly pointed at the center of the circular target area, without having to place the tool. The marker can be used as an alternative to the third color on the tool. Determining the center of the circular target area can then occur both before and after calibrating with the tool. In the case the dartboard comprises an even number of cameras, the marker is preferably the viewing opening in the annular reflector for an opposite camera. A center of the viewing opening can then be used to determine in which direction the center of the circular target area lies.

According to a preferred embodiment, the dartboard comprises a sensor for detecting the landing of a dart in the circular target area. The sensor is for example a vibration sensor, such as a MEMS. Preferably, the sensor is a piezoelectric sensor that generates an electrical signal under the influence of pressure. The sensor is preferably coupled with the processing unit. This embodiment is advantageous for saving energy. The processing unit only needs to process images if the sensor detects the landing of a dart in the circular target area, instead of continuously processing and comparing images to detect the landing of a dart as a difference between images.

According to an embodiment, the dartboard comprises a scoring ring. The scoring ring comprises score indications that are associated with zones on the circular target area. The scoring ring is placed at a distance of at least 5 mm from the circular target area, preferably at least 6 mm, more preferably at least 7 mm, even more preferably at least 8 mm, and even more preferably at least 9 mm. The distance is measured in a direction transverse to the circular target area. This embodiment is advantageous because the scoring ring does not obstruct a view of the at least three cameras on the circular target area.

According to an embodiment, the dartboard comprises a second lighting ring for the frontal lighting of the circular target area. The second lighting ring is concentric with the circular target area. This embodiment is advantageous for avoiding shadows cast by the first lighting ring on the circular target area.

Preferably, an emitted power of the second lighting ring is adjustable. This is beneficial for adjusting the amount of light with which the target area is illuminated. For competition, for example, a minimum amount of light is prescribed. Particularly advantageous is that adjustments in the emitted power of the second lighting ring have no influence on the detection of a dart, as the second lighting ring shines directly onto the target area.

According to an embodiment, the processing unit of the dartboard is configured to perform a method according to the second aspect. In a second aspect, the invention relates to a method for automatically counting points when throwing a dart at a dartboard with a scoring system.

The method comprises the steps of:

- detecting landing of a dart in a circular target area of a dartboard;

- capturing images of the dart in the circular target area using at least three cameras;

- determining for each of the at least three cameras an angle between an optical axis of the camera and a line between an intersection of the optical axis with the lens of the camera and the dart;

- calculating a position of the dart in the circular target area by means of triangulation;

- determining a score based on the specific position of the dart in the circular target area;

- adding the score to points already scored.

The detection of the landing of the dart in the circular target area can, for example, happen by comparing consecutive images captured by the at least three cameras, whereby the appearance of a previously absent object can be considered as the detection of the landing of the dart. The previously absent object is then treated as the dart whose position must be determined. A disadvantage of this method is that the images from the three cameras constantly need to be processed and compared, which results in high energy consumption of the scoring system.

The images captured by the at least three cameras are stored in a volatile working memory or a non-volatile memory. Preferably, the captured images are stored in a volatile working memory.

The at least three cameras are positioned on a side of the circular target area that faces the player. The at least three cameras are placed at a known position and evenly distributed on a first circumference. This means that an arc on the first circumference between any two cameras is equally long. The at least three cameras are directed towards the circular target area. The at least three cameras are directed towards a center of the circular target area. The first circumference and the circular target area are concentric. The first circumference has a larger diameter than the circular target area. At least three cameras are advantageous because the dart can never lie in line with all the cameras.

A coordinate system is defined in a plane containing the circular target area. The origin of the coordinate system is preferably located at the center of the circular target area. The position of the dart can be determined in the circular target area by means of triangulation, because the positions of the at least three cameras are known and because the angles of the dart relative to the cameras are known. Hereby, at least three elements of a triangle formed by two cameras and a dart are known, namely a side of the triangle with as endpoints the two mentioned cameras and the two adjacent angles, whereby a two-dimensional coordinate of the dart in the plane in which the circular target area lies, can be calculated. In fact, the two angles are known relative to the optical axes of the cameras, but these can be recalculated via triangulation to angles of the triangle formed by the two cameras and the dart. It is obvious that such a calculation can be performed for multiple combinations of two cameras. The final position can be a weighted or non-weighted average of all calculated positions. Deviations between all calculated positions is also a measure of the accuracy of the calculated position of the dart. It is clear that if a dart and two cameras are aligned, this combination is not suitable for calculating the position of the dart. Preferably, images of the dart in the circular target area are captured with at least four cameras. This increases the accuracy of determining the position of the dart and reduces the chance that a dart is hidden in the circular target area by other darts for all combinations of cameras.

The circular target area preferably comprises colored zones, each zone being associated with a predetermined score. Preferably, coordinates of boundaries between zones are also known. Alternatively, formulas are known for calculating the coordinates of these boundaries. Based on the calculated position, it is determined in which zone the dart has landed. The score for the dart is the score associated with the zone. This score is then subtracted from or added to the points already scored depending on the rules of the game. The circular target area is preferably laterally illuminated by a lighting ring around the target area.

In a preferred embodiment, for each of the at least three cameras, the angle between the optical axis of the camera and the line between the point of intersection of the optical axis with the lens of the camera and the dart is determined, by determining according to an X-axis the X-coordinate of the dart in the image captured by the camera. The X- axis is substantially parallel with a plane in which the circular target area is located. The X-axis is thus a lying axis in an image captured by the camera. The Y-axis is a standing axis in the image, transverse to the X-axis. During the game, a dart in an image that has been captured by the camera, has an X-coordinate along the X-axis that is expressed in pixels. The X-coordinate is translated into an angle for the camera using a lookup table. It is clear that the X-axis and the Y-axis are specific to each camera and independent of the coordinate system defined in the plane in which the circular target area lies. If the X-coordinate is not comprised in the lookup table, the angle is interpolated between known values. The X-coordinate is determined as an X-coordinate of a point on a centerline of the dart, with said point preferably taken as close as possible to the plane in which the circular target area lies. This results in the smallest possible error if the dart sticks obliquely in the circular target area. The centerline runs in the longitudinal direction of the dart.

The direct translation of an X-coordinate of the dart in an image captured by a camera using a lookup table to an angle relative to that camera is particularly advantageous because this allows points to be counted very quickly. Immediately after searching for the angles relative to the optical axis of the cameras, the position of the dart can be determined by triangulation, so no complicated techniques are required. The game is not held up by the scoring system and the method can be executed on a simple processing unit. An additional advantage is that the position of the dart can be determined based on a single image from each of the at least three cameras. It is not necessary for determining the position of the dart to continually store captured images in non-volatile memory. This is particularly advantageous in combination with an embodiment described later wherein the landing of the dart is detected by means of a sensor.

According to a preferred embodiment, the method comprises the additional step of calibrating each of the at least three cameras. An arc is placed in front of each of the at least three cameras. Each camera of the at least three cameras is located at a center of a circle of only one arc. It is clear that the arc is part of a circumference of the said circle. The optical axis of each of the at least three cameras is a radius of the circle of the arc placed in front of it. Each camera is thus aimed at an inner curvature of one arc. On each arc, to the left and right of an intersection of the optical axis of the camera located at the center of the circle with the arc, indicators are provided over a range of at least 50° of angles between radii of said circle and the optical axis of said camera. The range is preferably at least 54°, more preferably at least 56°, even more preferably at least 60° and even more preferably at least 64°. These angles are suitable for indicating the direction a dart is facing relative to the camera in question. The range is symmetrical with respect to the intersection of the optical axis with the arc. The indicators are points, lines, blocks, numbers, or another suitable indicator. The indicators should preferably be placed at equal intervals. Preferably, there is an indication at least every 5°, more preferably at least every 4°, even more preferably at least every 3°, even more preferably at least every 2°, and most preferably at least every 1° degree. An X-coordinate is determined for each indicator along the X-axis of the corresponding camera in an image captured by the corresponding camera of the arc. The X-coordinate is expressed in pixels. Then, an angle corresponding to the indicator is stored in the lookup table for the X-coordinate. This embodiment is particularly advantageous because it allows the at least three cameras to be calibrated in a simple manner and in a single step, whereby any deviations due to a differing orientation of a camera or due to aberrations in a lens of a camera can be compensated for. It is particularly advantageous that the indicators of the angles are very uniformly distributed in a captured image during calibration, resulting in a precise calibration.

It is clear that the step of calibrating each of the at least three cameras can occur both beforehand, during production of the scoring system and/or dartboard, and afterwards, during use by a user.

According to a preferred embodiment, the method for each of the at least three cameras comprises the additional step of determining a search area in an image captured by the camera. A dart is only searched for in the search area. This is advantageous because it reduces the number of pixels that need to be processed in an image. The circular target area is laterally illuminated by a lighting ring around the target area. The lighting ring preferably emits white light. As described in the first aspect, the lateral lighting of the circular target area is advantageous because it provides a large contrast difference in the images captured by the at least three cameras between light emitted by the lighting ring and a dart that has landed in the circular target area. The search area is at least limited to a part of the image on which the lighting ring is depicted. This limits the searching for a dart to an area where the contrast is greatest. Determining the search area is preferably carried out when the lighting ring is in operation and before darts have landed in the circular target area, so that there is an unobstructed view of the lighting ring. Determining the search area when a lighting ring is in operation is advantageous because the lighting ring appears as bright white pixels in a captured image, while a background or possible other objects such as a metal wire for separating zones in the circular target area, clamps for retaining the circular target area, or staples that secure these wires are displayed as dark pixels. The search area can now be easily determined by taking all pixels with a value above a predetermined threshold. For example, all pixels with a luminance above a predetermined luminance, which can be considered as white pixels.

The determination of the search area is preferably performed in combination with a previously described calibration step for calibrating each of the at least three cameras. This has the same advantage that not all pixels in a captured image need to be processed to calibrate a camera.

According to a further embodiment, the X-coordinate of the dart in an image is determined at a point where the dart in the search area has a smallest Y-coordinate in the image along the Y-axis. The X-axis and the Y-axis in an image are as in a previously described embodiment regarding the translation of the X-coordinate to an angle using a lookup table. As previously described, the X-coordinate is determined as an X- coordinate of a point on a centerline of the dart, with the said point preferably taken as close as possible to the plane in which the circular target area lies, to obtain the greatest possible accuracy for the position of a dart when the dart lands at an angle in the circular target area. It is therefore advantageous to take a point on the centerline of the dart with the smallest possible Y-coordinate, that still lies within the search area.

According to a further embodiment, when determining the search area it is detected whether an object partially obstructs a view of a camera on the lighting ring. The lighting ring is typically a white bar that extends along the X-axis over a full width of a captured camera image. An object that, for example, may obstruct the view of a camera on the lighting ring is a staple with which metal wires for separating zones in the circular target area are secured, or a staple with which a scoring ring is secured, or a clamp for retaining the circular target area. Such staples or clamps will be visible as a dark protrusion in the white bar. These dark protrusions can, for example, be detected by moving a sliding window along the X-axis from a lower side of the white bar through the captured image, wherein an abrupt reduction in luminance indicates the presence of such an object. If an object is detected that partially obstructs a view of a camera on the lighting ring, the search area is then expanded with a virtual search area, as if the object were not obstructing the camera's view of the lighting ring. If a dart is partially located in the virtual search area, the X-coordinate of the dart in the search area is extrapolated to a point where the dart has the smallest Y-coordinate in the virtual search area according to the Y-axis.

If a dart is partially within the virtual search area, then the part of the dart within the virtual search area will most likely not be visible due to reduced contrast or physical obstruction by the object that hinders the camera's view of the lighting ring. The lighting ring above the object is still visible to the camera, so that the dart above the virtual search area is still visible in the search area and where the centerline of the dart can still be determined. The extrapolation of the X-coordinate of the dart can now take place by, for example, taking a first X-coordinate of the centerline at a point where the dart has a maximum Y-coordinate in the image, in other words at the top of the search area and taking a second X-coordinate of the centerline, for example at a point along the Y- axis halfway through the search area or, for example, at a point at the transition from the search area to the virtual search area and extending the centerline through these two points to the bottom of the virtual search area, in other words where the dart has the minimum Y-coordinate in the virtual search area along the Y-axis. This embodiment has the advantage that despite the object partially obstructing the camera's view, a more accurate X-coordinate for the dart is obtained.

According to a preferred embodiment, a score is determined for each combination of two cameras out of the at least three cameras, after which the score that occurs the most frequently among all combinations of two cameras is added to the points already scored. This embodiment is advantageous for compensating for any inaccurate positions that are calculated for a dart. An inaccurate position usually results in a score that deviates from the other determined scores.

According to a preferred embodiment, a score is determined for each combination of two cameras out of the at least three cameras, after which a weight is assigned to the score. The weight is a measure of the reliability of the determined score. The higher the weight, the more reliable the determined score. Based on the weights, a final score is determined. The final score is added to the points already scored.

For example, the final score is the determined score with the greatest weight. For example, for equal scores, an average of the weights assigned to them is calculated, after which the largest average weight determines the final score. For example, for equal determined scores, a sum of the weights assigned to them is calculated, after which the largest sum of weights determines the final score. For example, the weights are a factor, for instance between 0 and 1, whereby for equal determined scores the assigned weights are multiplied by each other, after which the largest product determines the final score.

Optionally, certain scores with an assigned weight that falls below a threshold value are ignored for determining the final score.

Optionally, different weights are determined for each of the determined scores. From the various weights, as previously described, a largest weight, an average weight, a sum of weights, a product of weights, etc., can then be calculated. It is clear that the weights can be taken into account in many different ways. The invention is not limited to the examples given above.

According to an embodiment, a first weight is assigned to the score. The first weight is proportional to a smallest angle between a first line and a second line. The first line is a line from the dart to a first camera of a combination of two cameras and the second line is a line from the dart to a second camera of the combination of two cameras. The intersection of the first line and the second line determines the position of the dart in the circular target area. The smaller the angle, the more the intersection of the first line and the second line shifts in the event of a triangulation error. This means that with a small angle, the score determined on the basis of the first and second camera is less reliable and therefore receives a lower weight.

According to an embodiment, a second weight is assigned to the score. The second weight depends on the position of the dart in the image of a camera. The second weight is the highest in the middle of the image and the lowest at the edges of the image. In the middle of the image, possible deviations due to aberrations and/or curvature of the lens are minimal.

According to an embodiment, a third weight is assigned to the score. The third weight is higher if in the image of a camera only a single or multiple completely separate darts are visible. The third weight is lower if multiple darts are visible in the image of the camera that intersect or are positioned one behind the other. If only a single dart is visible or if the darts are completely separated visibly, the X-coordinate for the dart can be determined more accurately, making the determined score more reliable and thus a higher weight can be assigned to the determined score.

According to an embodiment, a fourth weight is assigned to the score. The fourth weight is lower if the dart is in the virtual search area. As previously described, in that case the X-coordinate of the dart is extrapolated, which may make the determined score possibly less reliable and thus a lower weight is assigned to the determined score.

It will be apparent to one skilled in the art that in this context, second, third, or fourth weight does not necessarily mean that multiple weights are assigned to a determined score. First, second, third and fourth are used here solely to indicate the weight. This does not exclude, as previously described, that multiple weights are assigned. According to an embodiment, the detecting of the landing of the dart is detected by means of a sensor, such as for example a vibration sensor or a piezoelectric sensor. A signal from this sensor activates the next steps of the method, so that images do not have to be processed continuously and the method can be performed more energy- efficiently. An additional advantage is that this eliminates the need to continuously store captured images in a non-volatile memory and to compare currently captured images from the at least three cameras with previously captured images in order to detect the landing of the dart.

If darts had previously landed in the circular target area, then by comparing past images that were captured by the at least three cameras with current images that were captured by the at least three cameras, a previously absent object can be detected. The previously absent object is then treated as the dart whose position must be determined. For this, it is only necessary to temporarily store only one recorded image of each already thrown dart by each of the at least three cameras. These are only a very limited number of images, so they can be stored perfectly in volatile working memory. After a turn of a player, usually after throwing three darts, the darts are removed from the circular target area and these images can be erased from the volatile working memory. Alternatively, for all darts in the circular target area the X-coordinate of the dart is determined for each of the at least three cameras, after which only for the dart with an up to then still unknown X-coordinate, in other words the last dart, the position is determined. In this case, the captured images can be deleted from the volatile working memory after each throw. It is clear that other ways are possible to determine which is the last thrown dart.

According to an embodiment, a frontal central photo is taken of the circular target area. In the photo, fixed reference points with known coordinates in the coordinate system in the plane in which the circular target area lies are preferably visible. An example of suitable fixed reference points are a center of the circular target area or fixed mounting points for placing a tool for calibrating a scoring system of a dartboard, as described in the first aspect. Based on these fixed reference points, coordinates for transitions between zones on the circular target area can be determined in an automated manner. This happens, for example, in an application that runs on a computer, after which the determined coordinates for the transitions are loaded into a processing unit of a dartboard with a scoring system. Alternatively, the said photo is loaded directly into the processing unit of the dartboard, after which the coordinates of the transitions between the zones are determined directly in the processing unit of the dartboard. This embodiment is particularly advantageous if the circular target area is interchangeable, as in a previously described embodiment.

It is clear that the computer on which the application is run can be a personal device such as a tablet or a smartphone. Such a device is particularly advantageous for taking a frontal central photo due to a typically built-in camera.

According to an embodiment, the method comprises the additional step of improving a silhouette of a dart. A dart is normally, by the lateral lighting of the circular target area using a lighting ring, a dark silhouette against a bright background. If within the silhouette bright pixels are visible, then this is more than likely not correct and these bright pixels can be replaced by dark pixels. If indentations of bright pixels are present at an edge of a silhouette, then this is also more than likely incorrect and these bright pixels can also be replaced by dark pixels. This provides a more accurate silhouette of the dart, which also allows for a more accurate determination of the dart's centerline.

According to an embodiment, the method comprises the additional step of virtually translating and/or rotating the circular target area. The circular target area is virtually translated by a player by inputting a distance over which the circular target area must be shifted in an X-direction and/or a Y-direction. The circular target area is virtually rotated by a player by inputting an angle over which the circular target area must be rotated around the center of the circular target area. The distance and/or the angle are entered using buttons on the scoring system or in a user application that is communicatively connected to the scoring system. After virtually translating or rotating the circular target area, a correction in accordance with the translation or rotation is performed at each calculated position of the dart in the circular target area. This embodiment is particularly advantageous with an interchangeable circular target area, more particularly with a circular target area that is approved for official darts competitions. These have fixed dimensions and fixed zones in the circular target area. This would theoretically make it unnecessary to enter coordinates of the zones into the scoring system after changing the circular target area. When producing circular target areas, there are margins allowing the zones to be translated and/or rotated with respect to the center of the circular target area. This can be simply compensated for by virtually translating and/or rotating the circular target area, making it unnecessary to determine the coordinates of the zones.

The user application can be executed on a computer, but equally on a personal device, such as a smartphone or a tablet. In an alternative embodiment, the distance over which the circular target area must be displaced in an X-direction and/or a Y-direction and/or the angle over which the circular target area must be rotated around the center of the circular target area is determined in an automated manner based on the frontal central photo from a previously described embodiment. As previously described, coordinates for transitions between zones on the circular target area can be determined automatically from the frontal central photo. These are compared with expected coordinates, after which a virtual translation and/or rotation is calculated.

In an embodiment, the circular target area is rotated when worn. The circular target area usually comprises alternating colored zones. In an official dartboard, the colored zones with which a score of twenty points or a multiple thereof is associated, are used most often. These colored zones will also wear out first. By rotating the circular target area, an almost worn colored zone can be associated with a less frequently used one. Preferably, after rotating the circular target area, a virtual translation and/or rotation is determined, as in previously described embodiments. This is beneficial to compensate for small deviations in the coordinates for transitions between zones on the circular target area due to rotation.

In a third aspect, the invention relates to a scoring system for automatically calculating points scored after throwing a dart.

The scoring system comprises a lighting ring suitable for the lateral lighting of a circular target area of a dartboard, at least three cameras suitable for capturing images of darts in the circular target area and a processing unit for processing the images of the darts in the circular target area and for calculating the points.

The scoring system is suitable for placing over a dartboard, preferably a dartboard approved for official darts competitions.

The lighting ring preferably comprises multiple LED elements as a light source. The lighting ring preferably emits white light.

The at least three cameras preferably have an equal viewing angle, focal length, and resolution. The at least three cameras are directed at a center of the lighting ring. This means that an optical axis of each camera passes through the said center. The at least three cameras are placed on a first circumference. The first circumference and the lighting ring are concentric. The at least three cameras are placed evenly distributed on the first circle circumference. The processing unit comprises a processor or a controller, working memory, and preferably non-volatile memory. The processor or controller is communicatively connected to the at least three cameras for retrieving and processing the captured images. Alternatively, each camera comprises its own processing unit for processing the images and the processing units of the at least three cameras are communicatively connected to each other for calculating the points. Preferably, the processing unit of one camera is the master. It is also possible to provide a dedicated processing unit that acts as a master and calculates the points.

The scoring system comprises a detachable tool for calibrating the scoring system. The tool comprises a number of circular arcs. The arcs are preferably the same. The number of arcs is equal to the number of cameras of the scoring system.

The lighting ring comprises fixed mounting points for removably placing the tool on the scoring system. The fixed mounting points are for example magnets or clamps. Preferably, the fixed mounting points are clamps that detachably secure the tool at the ends of the arcs of the tool. Preferably, the number of fixed mounting points is equal to the number of arcs, with one fixed mounting point being common to two arcs. The fixed anchor points are reference points for the tool, which always causes the tool to be positioned in the same way with respect to the at least three cameras.

One skilled in the art will appreciate that a method according to the second aspect is preferably carried out with a dartboard according to the first aspect, that a dartboard according to the first aspect is preferably configured for carrying out a method according to the second aspect, and that a scoring system according to the third aspect combined with a dartboard without a scoring system corresponds to a dartboard according to the first aspect. Each feature described in this document, both above and below, can therefore relate to any of the three aspects of the present invention.

It will be apparent to one skilled in the art that the method and the scoring system can not only be used for darts, but also for other sports such as archery and crossbow shooting.

In what follows, the invention is described by means of non-limiting figures illustrating the invention, which are not intended or should be interpreted to limit the scope of the invention.

DESCRIPTION OF THE FIGURES

Figure 1A shows a dartboard (1) with a scoring system for automatically calculating points scored after throwing a dart. The dartboard (1) comprises a circular target area (2) for darts. The circular target area (2) is interchangeable in this embodiment. The circular target area (2) comprises colored zones (3). Each colored zone (3) has a score associated with it. The circular target area (2) is held in the dartboard (1) by four clamps (4). The dartboard (1) comprises a scoring ring (5). The scoring ring (5) comprises score indications associated with the zones (3) on the circular target area (2). The scoring ring (5) is detachably attached to the dartboard (1) with four magnetic fasteners (6). This is advantageous when exchanging the circular target area (2). The scoring ring (5) and the circular target area (2) are concentric. The scoring ring (5) is placed at a distance of 5 mm from the circular target area (2), the distance being measured in a direction transverse to the circular target area (2). The dartboard (1) comprises a lighting ring (7) around the circular target area (2) for the lateral lighting thereof. The lighting ring (7) and the circular target area (2) are concentric. The lighting ring (7) comprises an annular light source (8), consisting of LED elements and an annular reflector (9). The annular reflector (9) is directed towards the circular target area (2). The lighting ring (7) in this embodiment comprises a second annular reflector (10) for reflecting light from the annular light source (8) to the annular reflector (9). The annular reflector (9) reflects the light thereon laterally to the circular target area (2). This is better visible in the cross-section in Figure 2. The annular light source (8) is located lower than the circular target area (2). The annular reflector (9) has viewing openings (11) for four cameras (12). The four cameras (12) are almost completely hidden by the annular reflector (9). The four cameras (12) are placed evenly on a first circumference (13). Between the four cameras (12), there is thus an angle of 90° with respect to a center of the circular target area (2) each time. The first circumference (13) and the circular target area (2) are concentric. The four cameras (12) are directed at the circular target area (2). The four cameras (12) have an optical axis that passes through the center of the circular target area (2). Each camera (12) also comprises its own processing unit. The processing units are not shown in Figure 1A and Figure IB. The dartboard (1) comprises four fixed mounting points (14) for the detachable placement of a tool for calibrating the scoring system. The tool is not shown in Figure 1A and Figure IB. The four fixed mounting points (14) in this embodiment are the clamps (4). The fixed mounting points (14) are evenly distributed on a second circumference (15). Between the four fixed mounting points (14) there is therefore an angle of 90° each time with respect to the center of the circular target area (2). The four fixed mounting points (14) are rotated 45° relative to the center of the circular target area (2) with respect to the four cameras (12). The second circumference (15) is smaller than the first circumference (13). The first circumference (13) is larger than the circular target area (2). The second circumference (15) is concentric with the circular target area (2).

Figure IB shows the same dartboard (1) as in Figure 1A, but now also shows a second lighting ring (16) for the frontal lighting of the circular target area. The second lighting ring (16) is concentric with the circular target area (2). The second lighting ring (16) is discussed in more detail in Figure 2. The dartboard (1) is finished with a decorative ring (17). The decorative ring (17) is on the one hand decorative and, for example, a brand name can be depicted on it. On the other hand, the decorative ring (17) serves to shield light from the second lighting ring (16). Figure 2 shows a cross-section of a dartboard according to an embodiment of the present invention.

The dartboard (1) corresponds to the dartboard (1) from Figure 1A and Figure IB. Figure 2 shows the placement of a camera (12) hidden by the annular reflector (9), where the camera (12) is directed through a viewing opening (11) in the annular reflector (9) toward the circular target area (2). Figure 2 also shows how an optical axis of the camera (12) is positioned at a very small distance above the plane in which the circular target area (2) lies. In this embodiment, this small distance is 1 mm. Further, it is also visible how the annular light source is directed toward the second annular reflector (10) and the second annular reflector (10) reflects the light to the annular reflector (9), after which the circular target area (2) is laterally illuminated by the annular light source (8). Finally, it can also be seen how the second lighting ring (16) comprises an annular light source (18) for the frontal lighting of the circular target area (2). The annular light source (18) comprises LED elements. The decorative ring (17) shields the light from the annular light source (18) for a player.

The tool (19) comprises four equal arcs (20). The tool (19) is suitable to be placed removably with ends of the four arcs (20) on the four fixed mounting points (14) of the dartboard (1) from Figure 1A. The number of arcs (20) is equal to the number of cameras (12). After placing the tool (19) on the four fixed mounting points (14), each camera (12) is located in a center of a circle of only one arc (20). This is further clarified in Figure 5. Op

On each arc (20), to the left and right of an intersection of the optical axis of the camera (12), which is placed at the center of the circle of the corresponding arc (20), with the arc (20), indicators (25) of angles between radii of the circle of the corresponding arc (20) and the optical axis of the camera (12) are applied. The indicators (25) are arranged over a total range of 64°, namely 32° to the left and 32° to the right of the said intersection. The indicators (25) of the angles are in this embodiment blocks that alternately have a first color (21) and a second color (22). Each block represents 1° on the arc (20). The block that is immediately to the right of the optical axis of the camera (12) has a third color (23), which is different from the first color (21) and the second color (22). The transition between the block with the third color (23) and the block on the left with the first color (21) is a reference point (24) and represents an angle between a radius of the circle and the optical axis of the camera (12) of 0°. The transition between the block with the first color (21) to the next block on the left with the second color (22) represents an angle between a radius of the circle and the optical axis of the camera (12) of 1° counterclockwise. The following transition in the same direction between the second color (22) and the first color (21) is then an angle of 2° counterclockwise, and so on. The transition between the block with the third color (23) and the block on the right with the first color (21) represents an angle between a radius of the circle and the optical axis of the camera (12) of 1° clockwise. The next transition in the same direction between the first color (21) and the second color (22) is then an angle of 2° clockwise, and so on.

During calibration of a prior art dartboard, darts (26) are placed along a circumference of the circular target area (2) at transitions between physical sectors of the circular target area (2). An image of these darts (26) is then captured with the cameras (12). The manual placement of the darts (26) is labor-intensive. Figure 6 only shows a situation for a single camera (12). It is clear that points used for calibration will be distributed very unevenly in the image. There will be more points on the sides of the captured image. It is also clear that there are only a very limited number of points available for calibration. An additional difficulty is that from certain transitions between the physical sectors, the darts (26) will again be displayed more inward on the captured image. This makes it virtually impossible during calibration to determine which dart (26) belongs to which transition. These darts (26) are no longer placed in Figure 6

When calibrating, the tool (19) is detachably placed on the four fixed mounting points (14). The tool (19) is similar to the tool (19) as in Figure 2. After placing the tool (19), each camera (12) is located in a center of a circle of one arc (20). The circles have a radius that corresponds to a focal length of the cameras (12). Hereinafter only one camera (12) and the corresponding arc (20) will be discussed, but it is clear that the description also applies to the other cameras (12) and arcs (20). The intersection of the optical axis of the camera (12) with the arc (20) is a reference point (25) that represents an angle of 0° between the optical axis of the camera (12) and a radius of the arc. Every next indicator (25) represents an equal increase of the angle between the optical axis and a radius of the circle. For the clarity of Figure 5, each subsequent indicator (25) represents an increase of the angle by 5°. It is clear that all cameras (12) can be calibrated simultaneously and that the indicators (25) are evenly distributed over an entire width of an image captured by a camera (12) of the tool (19). This is advantageous for accurate calibration.

Figure 6 shows a schematic representation of an X-coordinate of darts in a captured image according to an embodiment of the present invention.

The captured image mainly shows the lighting ring (7) as a white bar. The white bar determines a search area (27). The image is dark above the search area (27). Under the search area (27) lies the circular target area (2) which is also shown darkly. To the right of the search area (27) is a clamp (4). The clamp (4) hides a part of the lighting ring (7) from the camera (12) that captured the image. The clamp (4) is also shown dark. The search area (27) is extended with a virtual search area (28) that corresponds to the dark display of the clamp (4). In the captured image, there are two darts (26). The darts (26) are normally also displayed dark by backlighting from the lighting ring (7). For the clarity of Figure 6, the darts (26) are drawn clearly. For the left dart (26), the X-coordinate is a point on a centerline (29) of the dart (26) with a smallest Y- coordinate. This is thus a lower X-coordinate (30) at a lower side of the search area (27). A right dart (26) is partially hidden by the clamp (4). This means that the X- coordinate of the right dart (26) lies in the virtual search area (28) and is therefore not visible in the captured image. For the right dart (26) an upper X-coordinate (31) is determined. This is a point on the centerline (29) of the right dart with a largest Y- coordinate, so at the top of the search area (27). In addition, a middle X-coordinate (32) is determined as a point on the centerline (29) of the right dart with a Y-coordinate that lies along the Y-axis in the center (34) of the search area (27). The X-coordinate of the right dart (26) is an extrapolated X-coordinate (33) from the upper X-coordinate (31) and the lower X-coordinate (32).

The method is carried out using a dartboard (1) according to the first aspect. In a first step (35), a search area (12) is determined for each of the at least three cameras (27). In a next step (36), for each camera (12), it is verified whether there are any objects that partially obstruct the view of a camera (12), and the search area (27) of the corresponding camera (12) is extended there with a virtual search area (28). The step (36) is repeated until no new objects are found that obstruct the view of a camera (12). In a subsequent step (37), the at least three cameras (12) are calibrated simultaneously using a tool (19). Each camera (12) captures an image of an arc (20) of the tool (19). For each of the at least three cameras (12), indicators (25) of angles together with a corresponding X-coordinate of the indicator (25) are stored in a lookup table. After this the scoring system is calibrated and ready for use. The method is now in a step (38) where a detection of the landing of a dart (26) in the circular target area (2) is awaited. As long as there is no detection, the scoring system remains in step (38). After detecting the landing of a dart (26) in the circular target area (2), a next step (39) is taken, during which each of the at least three cameras (12) captures an image. In each of the recorded images, a silhouette of the dart (26) is searched for. If no silhouette of the dart (26) can be found or if only silhouettes of darts (26) can be found that had previously landed in the circular target area, the method returns to step (38) to wait for the landing of a new dart (26). For each of the at least three cameras (12) for which a silhouette of the dart (26) is found in the captured image, the silhouette of the dart (40) is enhanced in a next step (26). Thereafter, in step (41), for each of the captured images in which the silhouette of the dart (26) is found, a lower X-coordinate (30) is determined. If the silhouette of the dart (26) is partially located in the virtual search area (28) in a captured image, an extrapolated X-coordinate (42) is calculated using an upper X-coordinate (31) and a middle X-coordinate (32) in a step (33) and used as a lower X-coordinate (30). Next, in step (43), all lower X-coordinates (30) are translated into angles using the lookup table for the corresponding camera (12) in order to subsequently calculate, in step (44), for each combination of two cameras (12), for which in the captured images a silhouette of the dart (26) has been detected, a position of the dart (26) by triangulation. In step (45), a score is determined for each of the calculated positions, after which the score that occurs most frequently is considered the final score. Finally, in step (46) the final score is added to the points already scored. Depending on the rules of the game, this can mean either adding or subtracting the final score from the points already scored. There is now a wait again for the landing of the next dart (26) in the circular landing area (2).

The described method is based on a single player. It is clear that the method can be adapted to a different number of players. Several steps will remain the same. It is also evident that the method can be adjusted and steps can be added or omitted. This method is intended to be illustrative and not limiting.

The numbered elements in the figures are:

1. Dartboard

2. Circular target area 3. Zones

4. Clamp

5. Scoring ring

6. Magnet fastener

7. Lighting ring

8. annular light source

9. annular reflector

10. Second annular reflector

11. Viewing opening

12. Camera

13. First circumference

14. Fixed mounting point

15. Second circumference

16. Second lighting ring

17. Decorative ring

18. annular light source second lighting ring

19. Tool

20. Arc

21. First color

22. Second color

23. Third color

24. Reference point

25. Angle indicator

26. Dart

27. Search area

28. Virtual search area

29. Centerline

30. Lower X-coordinate

31. Upper X-coordinate

32. Middle X-coordinate

33. Extrapolated X-coordinate

34. Middle search area

35. Determine search area

36. Determine virtual search area

37. Camera calibration

38. Wait for dart detection

39. Capture images dart

40. Improve silhouette 41. Determine X-coordinate

42. Extrapolate X-coordinate

43. Translate X-coordinate to angle

44. Calculate dart position 45. Determine score

46. Add score to the points already scored

Claims

1. Dartboard with a scoring system for automatically calculating points scored after throwing a dart, comprising a circular target area for darts, a lighting ring around the circular target area for lateral lighting of the circular target area, at least three cameras for capturing images of darts in the circular target area, wherein the at least three cameras are evenly distributed on a first circumference and are directed towards the circular target area and wherein the first circumference, the lighting ring, and the circular target area are concentric, and a processing unit for processing the images of the darts in the circular target area and for calculating the points, characterized in that the dartboard comprises a detachable tool for calibrating the scoring system, wherein the tool comprises a number of arcs that is equal to the number of cameras of the dartboard, wherein the dartboard comprises fixed mounting points for the removable placement of the tool on the dartboard, wherein, after placing the tool, each camera of the at least three cameras is located at a center of a circle of only one arc, wherein an optical axis of the mentioned camera is a radius of the mentioned circle and wherein on each arc to the left and right of an intersection of the optical axis with the arc over a total range of at least 50° indicators of angles between radii of the mentioned circle and the optical axis of the mentioned camera are arranged.

2. The dartboard according to claim 1, characterized in that after placing the tool, each arc has a radius that corresponds to a focal length of the camera that is located at the center of the circle of the arc.

3. The dartboard according to claim 1 or 2, characterized in that the optical axis of each camera lies in a plane that is parallel to the circular target, wherein the aforementioned plane is situated at a distance of at least 1 mm and at most 5 mm from the circular target area, wherein the aforementioned distance is measured in a direction perpendicular to the circular target area.

4. The dartboard according to any of the preceding claims 1-3, characterized in that the dartboard comprises a control mechanism for adjusting a position of the circular target area relative to the optical axes of the at least three cameras.

5. The dartboard according to any of the preceding claims 1-4, characterized in that the lighting ring comprises an annular light source and an annular reflector, wherein the annular reflector is directed towards the circular target area and wherein the annular light source is directed directly or indirectly towards the annular reflector.

6. The dartboard according to claim 5, characterized in that the at least three cameras are placed outside a circumference of the annular reflector, wherein a viewing opening for the camera is provided in the annular reflector for each camera.

7. The dartboard according to any of the preceding claims 1-6, characterized in that the indicators of the angles between the radii of a circle and the optical axis of the camera located at the center of the circle are blocks alternating between a first color and a second color, each block representing an equal number of degrees on the arc.

8. The dartboard according to claim (7), characterized in that the block that is immediately to the left or immediately to the right of the optical axis of the camera has a third color, different from the first color and the second color.

9. The dartboard according to any of the preceding claims 1-8, characterized in that the dartboard comprises a sensor for detecting the landing of a dart in the circular target area.

10. Method for automatically counting points when throwing a dart at a dartboard with a scoring system, comprising the steps of:

- detecting landing of a dart in a circular target area of a dartboard;

- capturing images of the dart in the circular target area using at least three cameras; wherein the at least three cameras are placed at a known position and evenly distributed on a first circumference and directed at the circular target area, and wherein the first circumference and the circular target area are concentric;

- determining a score based on the specific position of the dart in the circular target area; - adding the score to points already scored; characterized in that for each of the at least three cameras, the angle between the optical axis of the camera and the line between the intersection of the optical axis with the lens of the camera and the dart is determined by determining, according to an X-axis, an X-coordinate of the dart in the image captured by the camera, wherein the X-axis is substantially parallel with a plane in which the circular target area is located, and wherein the X-coordinate is translated to an angle by means of a lookup table for the camera.

11. The method according to claim 10, characterized in that the method comprises the additional step of calibrating each of the at least three cameras, wherein for each of the at least three cameras an arc is placed, wherein each camera of the at least three cameras is positioned at a center of a circle of only one arc, wherein the optical axis of each of the at least three cameras is a radius of the circle of the arc placed in front of it, wherein on each arc to the left and right of an intersection of the optical axis with the arc over a total range of at least 50° indicators of angles between radii of the mentioned circle and the optical axis of the corresponding camera are arranged, wherein for each indicator according to the X-axis of the corresponding camera in an image captured by the corresponding camera of the arc, an X-coordinate is determined, after which an angle corresponding to the indicator is stored in the lookup table for the X- coordinate.

12. The method according to claim 10 or 11, characterized in that the method comprises for each of the at least three cameras the additional step of determining a search area in an image captured by the camera, wherein a dart is searched for only in the search area, wherein the circular target area is laterally illuminated by a lighting ring around the target area, wherein the search area is at least limited to a part of the image on which the lighting ring is depicted.

13. The method according to claim 12, characterized in that the X-coordinate of the dart in an image is determined at a point where the dart in the search area has a smallest Y-coordinate along a Y-axis in the image, and where the Y-axis is directed away from the dartboard.

14. The method according to claim 13, characterized in that in determining the search area, it is detected whether an object partially obstructs a camera's view of the lighting ring, after which the search area is expanded with a virtual search area as if the object didn't obstruct the camera's view of the lighting ring, wherein if a dart is partially located in the virtual search area, the X-coordinate of the dart in the search area is extrapolated to a point where the dart in the virtual search area has a smallest Y-coordinate according to the Y-axis.

15. The method according to any of the preceding claims 10-14, characterized in that for each combination of two cameras of the at least three cameras, a score is determined, after which the score that occurs most frequently among all combinations of two cameras is added to the points already scored.

16. Scoring system for automatically calculating points scored after throwing a dart, comprising a lighting ring suitable for the lateral lighting of a circular target area of a dartboard, at least three cameras suitable for capturing images of darts in the circular target area, wherein the at least three cameras are evenly distributed on a first circumference and are directed towards a center of the lighting ring, and wherein the first circumference and the lighting ring are concentric, and a processing unit for processing the images of the darts in the circular target area and for calculating the points, characterized in that the scoring system comprises a detachable tool for calibrating the scoring system, wherein the tool comprises a number of arcs that is equal to the number of cameras of the scoring system, wherein the lighting ring comprises fixed mounting points for removably placing the tool on the scoring system, wherein, after placing the tool, each camera of the at least three cameras is located at a center of a circle of only one arc, wherein an optical axis of the mentioned camera is a radius of the mentioned circle and wherein on each arc to the left and right of an intersection of the optical axis with the arc over a total range of at least 50° indicators of angles between radii of the mentioned circle and the optical axis of the mentioned camera are arranged.