JP6490951B2 - Drawing image erasing method - Google Patents

Description

  The present invention relates to a drawn image erasing method, and more particularly, in a display screen along sample points of a coordinate sequence by a series of erasing operations obtained by sampling coordinates that move based on a time series during a drawn image erasing operation. The present invention relates to a drawn image erasing method for erasing a drawn image.

  2. Description of the Related Art Conventionally, in a drawing display device such as an electronic blackboard or a tablet, an application (software) that can write a figure or a character using a pen (drawing member) is used.

  In such an application, in many cases, a line (drawing image) written with a pen can be erased using an eraser (for example, a pen set to function as an erasing member). There are roughly two methods for erasing the drawn image. One method is to erase the lines touched by the eraser one by one, and the other method is to overlap a trajectory of a pen that functions as an eraser (hereinafter referred to as “eraser stroke”). This is a method of erasing only the part. Some lines drawn with a pen are held as vector data and others are held as image data.

  In the method of erasing the part that overlaps the eraser stroke, the coordinates of the eraser are recorded as a point sequence in time series for the convenience of processing performance. It is called “data”.) At a certain timing, for example, when the eraser leaves the screen of the tablet (when touched up), the data is erased.

  In this way, in the line segment extraction method for obtaining a line segment that passes through a point sequence that forms a line drawn with a pen or an eraser stroke when erasing a portion that overlaps the eraser stroke, as a conventional technique, for example, Hough transform There is known a method of obtaining a tangent at a coordinate position where a point sequence is used and extracting a line segment.

  However, the Hough transform requires much more time than the case of using the above-mentioned difference in order to determine which straight line is appropriate after performing calculation by converting all candidate points into polar coordinates. There was a problem. In particular, when the figure is large and the length of the contour line is long, there is a problem that enormous calculation time is required.

  Therefore, as a conventional technique, in the line segment extraction method, the size of the area to be subjected to the Hough transform is set according to the curve before and after the target point to be processed, and within the set area A method has been proposed that enables highly accurate line segment extraction by performing Hough transform (see Patent Document 1).

JP 09-259279 A

  However, when the eraser stroke is extracted using the above-described conventional line segment extraction method, for example, since the Hough conversion is performed on all the eraser stroke data within the region set in the curved portion of the eraser stroke, the eraser stroke is performed. If the number of points in the data point sequence is large, there is a problem that the processing time is greatly affected. Therefore, when extracting the eraser stroke, it is desirable to reduce the number of eraser stroke data as much as possible within a range where a similar shape can be obtained.

  On the other hand, if the score of the eraser stroke data is reduced too much, the shape of the eraser stroke changes, which causes a problem that the result after the eraser is applied is affected. Therefore, a method for reducing the number of eraser stroke data without changing the shape of the eraser stroll as much as possible has been desired.

  Further, if the processing for reducing the number of eraser stroke data is complicated, it takes time to reduce the number of points for the eraser stroke data. Therefore, a processing method that is as simple as possible has been desired.

  The present invention has been made in view of the above-described conventional problems, and by a simple process, the number of coordinate rows for performing a series of erase processes is reduced, and the shape of the strol (eraser stroke) for performing the erase processes is changed. An object of the present invention is to provide a drawing image erasing method capable of shortening the time required for the drawing image erasing process without causing the above.

  The present invention relates to a drawing image erasing method for erasing a drawing image in a display screen along a sample point of a coordinate sequence by a series of erasing operations obtained by sampling coordinates that move based on a time series during a drawing image erasing operation. The sample is based on the angle formed by the straight line derived from the sampled sample points and the straight line derived from the last sample point of the sampled sample points and the newly sampled sample point candidate point. A step of determining whether or not to use the point candidate as a new sample point.

  Further, the present invention is a step of determining whether to use the sample point candidate as a new sample point based on the length of a straight line derived from the last sample point sampled and the point of the sample point candidate, It is preferable to provide.

  Further, the present invention provides a straight line derived from the last sample point sampled and the sample point candidate point, and a straight line derived from the sample point candidate point and the newly sampled next sample point candidate point. Preferably, the method includes a step of determining whether to use the sample point candidate as a new sample point based on the angle.

  Further, the present invention uses the sample point candidate point as a new sample point based on the length of a straight line derived from the sample point candidate point and the next newly sampled sample point candidate point. It is preferable to include a step of determining whether or not.

  Further, the present invention does not reduce the data amount of the coordinate sequence by the erasure operation in the curved portion derived from the plurality of sampled sample points, and the coordinate sequence by the erasure operation in the linear portion derived from the plurality of sampled sample points. It is preferable to reduce the amount of data.

  In addition, the present invention includes a step of obtaining an extreme value of the curve based on a coordinate sequence of discrete points of a curve derived from a plurality of sampled sample points, and the extreme value of the curve and / or the periphery thereof is provided. It is preferable not to reduce the data amount of the coordinate string by the erasing operation, and to reduce the data amount of the coordinate string by the erasing operation in other portions.

  The present invention also relates to a drawing image erasing method for erasing a drawing image on a display screen along a coordinate sequence by a series of erasing operations obtained by sampling coordinates that move based on a time series during a drawing image erasing operation. And a step of approximating data obtained from a sampled curve obtained from a plurality of sampled points by using a sequence of points sampled by discrete points, and obtaining points as sample points where the tangent of the curve satisfies a specific condition However, sampling is not performed or the sampling frequency is lowered for a portion where the slope of the tangent of the curve does not satisfy a specific condition.

  In the present invention, it is preferable that the specific condition of the tangent of the curve is set to “0” as the slope of the tangent.

  The present invention also relates to a drawing image erasing method for erasing a drawing image on a display screen along a coordinate sequence by a series of erasing operations obtained by sampling coordinates that move based on a time series during a drawing image erasing operation. , Comprising a step of approximately converting a curve derived from a plurality of sampled sample points into a point sequence sampled by discrete points, and changing a sampling frequency according to a derivative value of the curve It is characterized by making it.

  In the present invention, it is preferable that the sampling frequency is increased (the sampling frequency near the extreme value is increased) as the absolute value of the derivative of the curve is smaller.

  The present invention also relates to a drawing image erasing method for erasing a drawing image on a display screen along a coordinate sequence by a series of erasing operations obtained by sampling coordinates that move based on a time series during a drawing image erasing operation. And a step of approximating the curve derived from a plurality of sampled sample points with a sequence of points sampled by discrete points, wherein the curve is expressed as f (x, y) = 0, f (x, y). The frequency of sampling is changed according to the values of fx (x, y) and fy (x, y) when the partial derivative of fx is fx (x, y), fy (x, y) It is characterized by.

  In the present invention, it is preferable that the sampling frequency is increased (the sampling frequency near the extreme value is increased) as the absolute value of the derivative of the curve is smaller.

  The present invention also relates to a drawing image erasing method for erasing a drawing image on a display screen along a coordinate sequence by a series of erasing operations obtained by sampling coordinates that move based on a time series during a drawing image erasing operation. A step of approximating the curve derived from a plurality of sampled sample points with a sequence of points sampled by discrete points, wherein the curve is expressed as f (x, y) = 0, f (x, y ) Is expressed as fxy (x, y), fxy (x, y), fxx (x, y), fyy (x, y), fxy (x, y), fyx (x , Y), fxx (x, y), and fyy (x, y), the sampling condition is changed.

  The present invention also provides a sampling frequency when the absolute values of the above fxy (x, y), fyx (x, y), fxx (x, y), and fyy (x, y) exceed a preset value. It is preferable to change the sampling method so as to be high.

  In the present invention, it is preferable that the sampling frequency is increased as the absolute values of fxy (x, y), fyx (x, y), fxx (x, y), and fyy (x, y) are larger.

  According to the drawn image erasing method of the present invention, the drawn image on the display screen is erased along the coordinate sequence obtained by a series of erasing operations obtained by sampling the coordinates moving based on the time series during the drawn image erasing operation. In the drawn image erasing method, the sample point candidate is determined based on an angle formed by a straight line derived from a plurality of sampled sample points and a straight line derived from a sampled last sample point and a newly sampled sample point candidate point. A step of determining whether or not to use as a new sample point, for example, by setting a threshold value for the angle formed by the above-mentioned straight line, if the angle has not been reached, the newly sampled sample point candidate is The simple process of avoiding using as a new sample point reduces the number of points in the series of eraser coordinate lines, and the angle change is small. Without changing the shape of the eraser strike roll, it is possible to shorten the time required for erasure processing of the drawing image.

  Further, according to the drawn image erasing method of the present invention, the drawn image on the display screen is displayed along the coordinate sequence by a series of erasing operations obtained by sampling the coordinates moving based on the time series at the time of drawing image erasing operation. In the drawn image erasing method for erasing, the method comprises a step of approximately converting a curve derived from a plurality of sampled sample points into a point sequence obtained by sampling discrete points, wherein the tangent of the curve satisfies a specific condition As a sample point, the sampling point is not sampled or the sampling frequency is reduced at a location where the slope of the tangent of the curve does not satisfy a specific condition, thereby reducing the data amount of the coordinate sequence by the erasing operation. With a simple process, the number of points in the coordinate sequence of the eraser is reduced, and the shape of the eraser strol is changed because the angle change is small. Without, it is possible to shorten the time required for erasure processing of the drawing image.

  Further, according to the drawn image erasing method of the present invention, the drawn image on the display screen is displayed along the coordinate sequence by a series of erasing operations obtained by sampling the coordinates moving based on the time series at the time of drawing image erasing operation. In the drawn image erasing method for erasing, the method includes a step of approximating data of a curve derived from a plurality of sampled sample points by a sequence of points sampled by discrete points, and depending on a value of a derivative of the curve The simple processing of changing the sampling frequency reduces the number of points in the coordinate sequence of the eraser, and the angle change is small, so the erased image can be erased without changing the shape of the eraser stroller. Such time can be shortened.

  Further, according to the drawn image erasing method of the present invention, the drawn image on the display screen is displayed along the coordinate sequence by a series of erasing operations obtained by sampling the coordinates moving based on the time series at the time of drawing image erasing operation. In the drawn image erasing method for erasing, the method includes a step of approximating data of a curve derived from a plurality of sampled sample points by a sequence of points sampled by discrete points, wherein the curve is f (x, y) = 0. , F (x, y), when the partial derivative is fx (x, y), fy (x, y), sampling according to the values of fx (x, y) and fy (x, y) The time taken to erase the drawn image without changing the shape of the eraser stroller because the angle change is reduced by reducing the number of points in the series of eraser coordinates by a simple process of changing the frequency of the eraser. Shorten can do.

  Further, according to the drawn image erasing method of the present invention, the drawn image on the display screen is displayed along the coordinate sequence by a series of erasing operations obtained by sampling the coordinates moving based on the time series at the time of drawing image erasing operation. In the drawn image erasing method for erasing, the method includes a step of approximating data of a curve derived from a plurality of sampled sample points by a sequence of points sampled by discrete points, wherein the curve is f (x, y) = 0. , F (x, y) is expressed as fxy (x, y), fxy (x, y), fxx (x, y), fyy (x, y). y), fyx (x, y), fx (x, y), fyy (x, y) according to the value of sampling, a simple process of changing the sampling condition, the score of a series of eraser coordinate series Because there is little angle change , Without changing the shape of the eraser strike roll, it is possible to shorten the time required for erasure processing of the drawing image.

It is explanatory drawing which shows an example drawn on the display of the electronic blackboard by which the drawing image deletion method which concerns on 1st Embodiment of this invention was employ | adopted. It is explanatory drawing which shows an example which erase | eliminates a part of drawing image of the said display. It is a block diagram which shows the structure of the said electronic blackboard. It is explanatory drawing which shows an example which performs drawing operation with a pen on the display of the said electronic blackboard. It is explanatory drawing which shows an example which erases a part of drawing image of the said display with an eraser. It is explanatory drawing explaining the algorithm which thins out the eraser coordinate in the drawing image erasing method which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows an example of the eraser stroke in the said display. It is a flowchart which shows an example of the process process which discards eraser stroke data when deleting a drawing image in the said electronic blackboard. It is a block diagram which shows the structure of the electronic blackboard by which the drawing image deletion method which concerns on 2nd Embodiment of this invention was employ | adopted. It is explanatory drawing explaining the algorithm which thins out the eraser coordinate in the drawing image deletion method which concerns on 2nd Embodiment of this invention. It is a flowchart which shows a part of process process which discards eraser stroke data when erasing a drawing image in the electronic blackboard adopting the drawing image erasing method. 12 is a flowchart illustrating a process following the flowchart of FIG. 11. It is a block diagram which shows the structure of the electronic blackboard by which the drawing image deletion method which concerns on 3rd Embodiment of this invention was employ | adopted.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is an example of an embodiment for carrying out the invention, and is an explanatory diagram showing an example of drawing on a display of an electronic blackboard adopting the drawn image erasing method according to the first embodiment of the present invention. FIG. FIG. 3 is an explanatory diagram showing an example of erasing a part of a drawn image, and FIG. 3 is a block diagram showing a configuration of the electronic blackboard.

  In the first embodiment of the present invention, as shown in FIG. 1, a part or all of a drawn image 113 drawn by a pen 112 in a display (display screen) 101 functions as an eraser as shown in FIG. A drawing image erasing method is adopted that erases along the sample points of the coordinate sequence by a series of erasing operations obtained by sampling the coordinates moving based on the time series during the erasing operation of the drawing image with the pen 112 set to be performed. In the electronic blackboard (drawing display device) 100, the drawn image erasing method according to the present invention is adopted as the drawn image erasing method.

  As shown in FIG. 3, the electronic blackboard 100 according to the first embodiment mainly includes a display (display screen) 101 that performs drawing, a storage unit (memory) 102, and a control unit 103 that performs operation / processing control of each unit. I have.

  The display 101 includes a touch panel 111, detects an input by the pen 112, and displays a drawing image based on the input drawing information.

  The storage unit 102 includes a pen stroke group storage unit 121 and an eraser stroke group storage unit 122. The pen stroke group storage unit 121 stores pen stroke coordinate string data (hereinafter referred to as “pen stroke data”) input as drawing information to be drawn by the pen 112. The eraser stroke group storage unit 122 stores eraser coordinate string data (hereinafter referred to as “eraser stroke data” by an erasing operation) input as eraser information to be erased by the pen 112 set to function as an eraser. To do.

  The control unit 103 mainly includes a display control unit 104, an input reception unit 105, a pen processing unit 106, an eraser processing unit 107, and further includes an input point filtering determination unit 108.

  The display control unit 104 displays a drawing image on the display 101 based on the drawing information input on the touch panel 111 or part or all of the drawing image displayed based on the eraser information input on the touch panel 111. Is displayed as if deleted.

  The input receiving unit 105 accepts drawing information input by the pen 112 on the touch panel 111 and eraser information input by the pen 112 set to function as an eraser as pen stroke data and eraser stroke data, and stores them. It is stored in the pen stroke group storage part 121 and the eraser stroke group storage part 122 of the unit 102.

The pen processing unit 106 performs pen processing (drawing processing) based on pen stroke data input as drawing information by the pen 112 on the touch panel 111.
The eraser processing unit 107 performs eraser processing (erasing process) based on eraser data input as eraser information by the pen 112 on the touch panel 111.

  The input point filtering determination unit 108 includes a straight line derived from a plurality of sampled eraser coordinates as sample points, a straight line derived from the last sample point of the sampled sample points and a newly sampled sample point candidate point. Whether or not the sample point candidate is to be used as a new sample point is determined based on the angle formed by.

  The eraser coordinate data determined not to be a new sample point by the input point filtering determination unit 108 is deleted.

Here, a drawing operation and a drawing image erasing operation with the pen 112 in the electronic blackboard 100 according to the first embodiment will be described with examples.
FIG. 4 is an explanatory view showing an example of performing a drawing operation with a pen on the display of the electronic blackboard adopting the drawn image erasing method according to the first embodiment of the present invention, and FIG. It is explanatory drawing which shows an example erase | eliminated by.

First, the electronic blackboard 100 is loaded with a handwriting pen application.
With this application, as shown in FIG. 4, the pen 112 can freely draw on the display 101 of the electronic blackboard 100.
The drawn handwritten data is stored as vector data in the storage unit 102 and also displayed on the display 101.

In addition, this application has a function of erasing a drawn image.
The function of erasing the drawn image is that when the drawn image displayed on the display 101 of the electronic blackboard 100 is touched with the set eraser (or blackboard eraser) 114, the handwritten data drawn on the touched portion is deleted. In this example, the handwritten data is not deleted in units of strokes, but the part touching the eraser 114 is deleted.

  Instead of the eraser 114, the pen 112 may be set to function as an eraser.

Here, a case where a drawn image is erased using the eraser 114 will be described.
As shown in FIG. 5, when the eraser 114 is moved so as to cross the central portion of the straight line 115 drawn by the pen 112, the central portion of the straight line 115 is deleted and divided into two straight lines 115A and 115B. A plurality of handwritten lines can be deleted simultaneously.

  In the erasing process by the eraser 114, while the display 101 is moved after being touched by the eraser 114, the same image as the background is displayed at the position touched by the eraser 114, and the part appears to have disappeared. .

  While the display 101 is touched with the eraser 114 and until the eraser 114 is separated from the display 101, the position of the eraser 114 is recorded as eraser stroke data while displaying the background image.

Next, an algorithm for deleting (thinning out) eraser stroke data in the electronic blackboard 100 of the first embodiment will be described.
FIG. 6 is an explanatory diagram illustrating an algorithm for thinning out eraser coordinates in the drawn image erasing method according to the first embodiment of the present invention, and FIG. 7 is an explanatory diagram illustrating an example of an eraser stroke in the display.

  The operation of deleting the actual eraser stroke data is performed using stroke points (coordinate sequences) that form an eraser stroke that is a locus when the eraser recorded before the eraser 114 moves away from the display 101 moves. .

The stroke points of the eraser 114 are collected as follows.
The position information (coordinates) of the eraser 114 is notified from the touch panel 111 to the application every 10 (ms).

  The application determines whether or not to store the newly acquired point as the sample point (position information) of the eraser 114 by the input point filtering determination unit 108 as follows.

(1) The first two points after the eraser 114 touches the display 101 (unless they are the same point) are stored unconditionally.
(2) The point acquired at the moment when the eraser 114 leaves the display 101 is stored.
(3) Ignore the same points as previously stored points.
(4) The angle θ1 between the extension line (two-dot chain line) of the straight line AB formed by the two points A and B stored previously and the line BC formed by the point B and the new point C stored previously is obtained (see FIG. 6). ), If the angle θ1 is greater than or equal to a certain value (for example, more than 10 degrees), the new point C is stored as a standard point, and if it is less than that, the new point C is deleted.

In addition, the following conditions may be added as auxiliary conditions.
(5) Ignore points that are less than a certain distance from the previously stored point.
(6) When the number of stroke points of the eraser 114 is below a certain value, all points are stored.

  The displacement of the stroke point of the eraser 114 includes the previously stored straight line formed by the two points, the angle between the previously stored point and the straight line formed by the new point, the previously stored point (last sample point), and the new point. Considering that it depends on the distance to the next sample point publicity point, it can also be as follows.

(7) The angle θ1 between the extension line (two-dot chain line) of the straight line AB formed by the two points A and B stored previously and the line BC formed by the previously stored point B and the new point C is obtained (see FIG. 6). ), If sin θ1 × (the length of the line BC) is greater than or equal to a certain value, the new point C is stored, and if it is less than that, the new point C is deleted.

  In this way, the stroke point of the eraser 114 is collected until the eraser 114 moves away from the display 101, and when the eraser 114 moves away from the display 101, the collected coordinate sequence data of the eraser 114 is selected. In addition to deleting, the handwritten line is deleted based on the selected stroke point of the eraser.

  Since this algorithm does not require future point information, it is suitable for selecting the position information of the eraser 114 in real time.

  In the case where the selection is performed using future point information, the position information of the eraser 114 may be selected when the eraser 114 leaves the display 101.

  In addition, as shown in FIG. 7, when the eraser stroke drawn on the display 101 of the electronic blackboard 100 includes a straight line portion a and a curved portion b, the erased portion is erased in the curved portion b derived from a plurality of sampled sample points. Instead of reducing the data amount of the coordinate sequence by the operation, the data amount of the coordinate sequence by the erasing operation may be reduced at the straight line portion a derived from the plurality of sampled sample points. The black star mark is a point adopted as a sample point of the eraser stroke, and the x mark indicates a point that can be deleted from the coordinate sequence of the eraser stroke.

  By doing in this way, the data of the eraser coordinate sequence can be greatly reduced in the straight line portion a, and the drawn image can be erased in the curved portion b without changing the shape of the eraser stroke.

  Specifically, when erasing a wide area with the eraser 114, the user may erase by repeatedly reciprocating the eraser 114 in the left-right direction or the up-down direction so as to fill one area of the plane on the display 101.

  In such a case, the eraser stroke is a repetition of a straight portion and a folded portion (curved portion), and the shape of the eraser stroke does not change greatly even if the number of points is reduced for the straight portion. For this reason, if the direction of the eraser stroke has hardly changed from the previous time at a certain point on the eraser stroke, it is not necessary to acquire this point.

  Therefore, the sample points are acquired at a high frequency in the folded portion (curved portion), and the sample points are acquired at a low frequency in the straight line portion, thereby reducing the influence on the shape of the eraser stroke. The score can be reduced.

Next, a process for discarding eraser stroke data when the drawn image is erased in the electronic blackboard 100 of the first embodiment will be described with reference to a flowchart.
FIG. 8 is a flowchart showing an example of processing steps for discarding eraser stroke data when the drawn image is erased on the electronic blackboard adopting the drawn image erasing method according to the first embodiment of the present invention.

  When erasing a drawn image drawn on the electronic blackboard 100, first, as shown in FIG. 8, the eraser stroke data input by the eraser 114 (or a pen functioning as an eraser) is sampled and the first two points ( The points A and B) shown in FIG. 6 are recorded as standard points (step S1).

  Then, the next point (point C shown in FIG. 6) is acquired (step S2). Then, it is determined whether or not the next point C is the last point (step S3).

  If it is determined in step S3 that the next point C is the last point, the point C is recorded as a new standard point (step S4).

  On the other hand, if it is determined in step S3 that the next point C is not the last point, it is determined whether or not it is the same coordinate as the previously acquired point (step S5).

  If it is determined in step S5 that the coordinates are the same as the previously acquired point, the point C is deleted without being recorded (step S6), and the process returns to step S2.

  On the other hand, if it is determined in step S5 that the coordinates are not the same as the previously acquired point, a line AB (see FIG. 6) connecting the previous two points A and B is obtained (step S7).

Next, a line BC (see FIG. 6) connecting the next point C and the previous point B is obtained (step S8).
Then, an angle θ1 (see FIG. 6) formed by the extension line of the line AB and the line BC is obtained (step S9).
And it is judged whether angle (theta) 1 is 10 degrees or less (step S10).

  In step S10, when it is determined that the angle θ1 is 10 degrees or less, the process proceeds to step S6, the point C is deleted without being recorded, and the process returns to step S2.

  On the other hand, if it is determined in step S10 that the angle θ1 is not less than 10 degrees, the point C is recorded as a new standard point (step S11), and the process returns to step S2.

  In this way, the data amount of the eraser stroke data to be recorded is determined by selecting whether or not the point (coordinates) obtained by sampling the point input by the eraser 114 is a new standard point, and selecting the data. Can be minimized.

  Since it comprised as mentioned above, according to 1st Embodiment, in the display screen along the coordinate row | line | column by a series of deletion operation obtained by sampling the coordinate which moves based on a time series at the time of drawing image deletion operation In the electronic blackboard 100 that employs a drawn image erasing method for erasing a drawn image, an input point filtering determination unit 108 is provided to extend the straight line AB derived from the two sampled points A and B and the last sampled. Whether or not to use the sample point candidate point C as a new sample point is determined based on the angle θ1 between the sample point B and the line BC derived from the newly sampled sample point candidate point C. Therefore, by setting a threshold value for the angle θ1 and not reaching the angle, the newly sampled sample point candidate point C is not used as a new sample point. With this simple processing, it is possible to delete sample point candidate points with little angle change. As a result, the time taken for the erasing process of the drawn image can be reduced without changing the number of the eraser stroke data and changing the shape of the eraser stroke.

  In the first embodiment, the input point filtering determination unit 108 functions as an extension of the straight line AB derived from the two sampled points A and B, and the last point B among the plurality of sampled sample points. Whether or not to use the sample point candidate point C as a new sample point is determined based on the angle θ1 formed with the line BC derived from the sampled sample point candidate point C. However, the present invention is not limited to this.

  For example, as a function of the input point filtering determination unit 108, the sample point candidate point C is used as a new sample point based on the length of the line BC derived from the last sampled point B and the sample point candidate point C. It may be determined whether or not to do so. For example, if a threshold value is provided for the length of the line BC and the length has not been reached, the newly sampled sample point candidate point C may not be used as a new sample point.

  Further, as a function of the input point filtering determination unit 108, in addition to the above-described function, a function for obtaining an extreme value of a curve based on a coordinate sequence of discrete points of a curve derived from a plurality of sampled sample points is provided. Therefore, the extremum of the curve and / or the periphery thereof are not reduced in the data amount of the coordinate string by the erasing operation, and the data amount of the coordinate string is reduced in the other portions by the erasing operation. May be.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.
FIG. 9 is a block diagram showing the configuration of an electronic blackboard that employs the drawn image erasing method according to the second embodiment of the present invention.

  Note that the configuration of the electronic blackboard according to the second embodiment has the same configuration and function as the electronic blackboard 100 of the first embodiment, and therefore has the same configuration as the configuration of the electronic blackboard 100 of the first embodiment. Components are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 9, the electronic blackboard 200 according to the second embodiment includes an input point filtering determination unit 208 as a configuration of the control unit 203, and a coordinate sequence by a series of erasing operations obtained when erasing a drawn image. The amount of data is reduced by the input point filtering determination unit 208.

  The electronic blackboard 200 mainly includes a display 101 that performs drawing, a storage unit 102, and a control unit 203 that controls operation and processing of each unit. The electronic blackboard 200 is loaded with a handwriting pen application.

  The control unit 203 mainly includes a display control unit 104, an input reception unit 105, a pen processing unit 106, an eraser processing unit 107, and further includes an input point filtering determination unit 208.

  In addition to the function of the input point filtering determination unit 108 of the first embodiment, the input point filtering determination unit 208 includes a straight line derived from the last sampled sample point and a newly sampled sample point candidate point, and the sample point candidate. A function for determining whether to use the sample point candidate as a new sample point based on the angle between the point and the straight line derived from the point of the next sample point candidate that has been newly sampled. It is a feature.

  The eraser coordinate data determined not to be a new sample point by the input point filtering determination unit 208 is deleted.

Next, an algorithm for deleting (thinning out) the coordinate sequence data of the eraser 114 in the electronic blackboard 200 of the second embodiment will be described.
FIG. 10 is an explanatory diagram for explaining an algorithm for thinning out eraser coordinates in the drawn image erasing method according to the second embodiment of the present invention.

  In the second embodiment, the collection of the stroke points of the eraser 114 is performed in the same manner as in the first embodiment, and a description thereof will be omitted.

  The application installed in the electronic blackboard 200 determines whether or not to store a newly input point as the sample point (position information) of the eraser 114 by the input point filtering determination unit 208 as follows.

  First, as shown in FIG. 10, the point (standard point candidate point) for determining whether to memorize is a point T, and the point one point after the point T for determining whether to memorize (the point for the next standard point candidate) Is point N, and point P is the point one point before point T for determining whether or not to store.

  Whether or not to store the newly acquired point T is determined by prefetching from the point T for determining whether to store the point T to the point N one point ahead.

(1) The first point after the eraser 114 touches the display 101 is stored unconditionally.
(2) The point acquired at the moment when the eraser 114 leaves the display 101 is stored.
(3) Ignore consecutive points at the same position.
(4) An angle θ2 between an extended line (two-dot chain line) of the straight line PT formed by the point P and the point T and a straight line TN formed by the point T and the point N is obtained (see FIG. 10), and the angle θ2 is not less than a certain value. If it is (for example, more than 10 degrees), the point T is stored as a standard point, and if it is less than that, the point T is deleted.

  In this manner, the stroke point of the eraser 114 is collected until the eraser 114 leaves the display 101, and when the eraser 114 leaves the display 101, the collected eraser stroke data is selected and deleted, Erase the handwritten line based on the selected eraser stroke point.

  This algorithm requires future point information, but since only one point is read ahead, it is suitable for selecting the position information of the eraser 114 in real time.

  In the case where the selection is performed using future point information, the position information of the eraser 114 may be selected when the eraser 114 leaves the display 101.

Next, a process for discarding eraser stroke data when erasing a drawn image on the electronic blackboard 200 of the second embodiment will be described with reference to a flowchart.
FIG. 11 is a flowchart showing a part of a processing step of discarding eraser stroke data when erasing a drawn image on an electronic blackboard adopting the drawn image erasing method according to the second embodiment of the present invention. 12 is a flowchart illustrating a process following the flowchart of FIG. 11.

  When erasing a drawn image drawn on the electronic blackboard 200, as shown in FIG. 11, first, the eraser stroke data input by the eraser 114 (or a pen functioning as an eraser) is sampled and the first point ( The point P) shown in FIG. 10 is recorded as a standard point (step S101).

  Then, the next point (point T shown in FIG. 10) is acquired (step S102), and the next point (point N shown in FIG. 10) is acquired (step S103). Then, it is determined whether or not the point N is the last point (step S104).

  When it is determined in step S104 that the point N is the last point, a line PT (see FIG. 10) connecting the previous point P and the next point T is obtained (step S105).

Next, a line TN (see FIG. 10) connecting the next point T and the next point N is obtained (step S106).
Then, an angle θ2 (see FIG. 10) formed by the extension line of the line PT and the line TN is obtained (step S107).
Then, it is determined whether or not the angle θ2 is 10 degrees or less (step S108).

  If it is determined in step S108 that the angle θ2 is 10 degrees or less, the point T is deleted without being recorded (step S111).

  Then, the point N is recorded as a new standard point (step S110). As a result, the eraser stroke becomes a straight line PN.

  On the other hand, if it is determined in step S108 that the angle θ2 is not less than 10 degrees, the point T is recorded as a new standard point (step S109).

  Then, the point N is recorded as a new standard point (step S110).

  On the other hand, if it is determined in step S104 that the point N is not the last point, the process proceeds to step S121, and it is determined whether or not the point is the same coordinate as the previously acquired point.

  If it is determined in step S121 that the coordinates are the same as the previously acquired point, the point T is deleted without being recorded (step S122), and the point N is recorded as a new standard point (step S128). Then, the process returns to step S102.

  On the other hand, if it is determined in step S121 that the coordinates are not the same as the previously acquired point, a line PT (see FIG. 10) connecting the previous point P and the next point T is obtained (step S123).

Next, a line TN (see FIG. 10) connecting the next point T and the next point N is obtained (step S124).
Then, an angle θ2 (see FIG. 10) formed by the extension line of the line PT and the line TN is obtained (step S125).
Then, it is determined whether or not the angle θ2 is 10 degrees or less (step S126).

  If it is determined in step S126 that the angle θ2 is 10 degrees or less, the point T is deleted without being recorded (step S122), and the point N is recorded as a new standard point (step S128). Then, the process returns to step S102.

  On the other hand, if it is determined in step S126 that the angle θ2 is not less than 10 degrees, the point T is recorded as a new standard point (step S127), and the point N is recorded as a new standard point (step S128). Then, the process returns to step S102.

  In this way, the data amount of the eraser stroke data to be recorded is determined by selecting whether or not the point (coordinates) obtained by sampling the point input by the eraser 114 is a new standard point, and selecting the data. Can be minimized.

  Since it was configured as described above, according to the second embodiment, a display screen is displayed along a coordinate sequence by a series of erasure operations obtained by sampling coordinates that move based on a time series during a drawn image erasure operation. An electronic blackboard 200 that employs a drawn image erasing method for erasing a drawn image includes an input point filtering determination unit 208, and a line PT derived from the last sampled point P (sample point) and the sample point candidate point T, Based on the angle θ2 between the point T of the sample point candidate and the straight line TN derived from the newly sampled point N of the next sample point, it is determined whether to use the sample point candidate as a new sample point As a result, a threshold is set for the angle θ2, and if the angle is not reached, the sample point candidate point T is not used as a new sample point. Sample point candidate points with little angle change can be deleted. As a result, the time taken for the erasing process of the drawn image can be reduced without changing the number of the eraser stroke data and changing the shape of the eraser stroke.

  In the second embodiment, as the function of the input point filtering determination unit 208, the extension line of the straight line PT derived from the last sampled point P and the sample point candidate point T, and the sample point candidate point T are further updated. Whether or not to use the sample point candidate point T as a new sample point is determined based on the angle θ2 formed by the straight line TN derived from the sampled point N of the next sample point candidate. However, the present invention is not limited to this.

  For example, as a function of the input point filtering determination unit 208, based on the length of the straight line TN derived from the sample point candidate point T and the newly sampled next sample point candidate point N, the sample point candidate point T May be used as a new sample point. For example, if a threshold is provided for the length of the straight line TN and the length has not been reached, the sample point candidate point T may not be used as a new sample point.

  Further, as a function of the input point filtering determination unit 208, in addition to the above-described function, a function for obtaining an extreme value of a curve based on a coordinate sequence of discrete points of a curve derived from a plurality of sampled sample points is provided. Therefore, the extremum of the curve and / or the periphery thereof are not reduced in the data amount of the coordinate string by the erasing operation, and the data amount of the coordinate string is reduced in the other portions by the erasing operation. May be.

(Third embodiment)
Next, a third embodiment of the present invention will be described.
FIG. 13 is a block diagram showing the configuration of an electronic blackboard that employs the drawn image erasing method according to the third embodiment of the present invention.

  Note that the configuration of the electronic blackboard according to the third embodiment has the same configuration and function as the electronic blackboard 100 of the first embodiment, and therefore has the same configuration as the configuration of the electronic blackboard 100 of the first embodiment. Components are denoted by the same reference numerals and description thereof is omitted.

  As illustrated in FIG. 13, the electronic blackboard 300 according to the third embodiment includes a function approximation processing unit 308 as a configuration of the control unit 303, and samples curves derived from a plurality of sampled sample points using discrete points. A function approximation that approximates data by a point sequence is performed, and the sampling frequency is changed in accordance with the value of the derivative of the curve.

  The electronic blackboard 300 mainly includes a display 101 that performs drawing, a storage unit 102, and a control unit 303 that controls operation and processing of each unit. The electronic blackboard 300 is loaded with a handwriting pen application.

  The control unit 303 mainly includes a display control unit 104, an input reception unit 105, a pen processing unit 106, an eraser processing unit 107, and further includes a function approximation processing unit 308.

  The function approximation processing unit 308 performs function approximation to approximately convert a curve derived from a plurality of sampled sample points into data using a sequence of points sampled by discrete points, and according to the value of the derivative of the curve, It has a function of changing the frequency of sampling.

  In the third embodiment, the collection of stroke points (coordinate sequences) of the eraser 114 is performed in the same manner as in the first embodiment. Then, the position information (coordinates) of the eraser 114 is notified from the touch panel 111 to the application every 10 (ms).

  The application temporarily stores the notified position information of the eraser 114 in the eraser stroke group storage unit 122 and performs function approximation in the function approximation processing unit 308. Note that a function approximation may be performed for each stroke portion of the eraser 114 as necessary.

The curve thus obtained is expressed as y = f (x).
Then, a region where the absolute value of the derivative f ′ (x) of f (x) is equal to or smaller than a certain value is obtained.
Then, sampling of points is performed for this region.

  This can be dealt with when the erased image is erased by reciprocating the eraser stroke in the vertical direction.

Depending on the method of function approximation, a unique explicit function may not be obtained.
At that time, h (x, y) = 0 is expressed as an implicit function.

  Also, y = f (x) is expressed as h (x, y) = 0, and sampling is performed for a region where the absolute value of the partial derivative hx (x, y) or hy (x, y) is equal to or less than a certain value. If implemented, it is possible to cope with the case where the erased image is erased by reciprocating the eraser stroke in either the vertical or horizontal direction.

  Further, there is a possibility that the drawn image is erased by moving the eraser stroke back and forth in an oblique direction instead of vertically and horizontally. In this case, if the sampling is performed on the region where the absolute value of the second-order partial derivative | f ″ (x) |

  As an approximate function of the eraser stroke, when h (x, y) = 0, the second order partial derivatives are hxx (x, y), hyy (x, y), hxy (x, y), hyx (x , Y). If sampling is performed in a region where the absolute value of any one of these second-order partial derivatives is a certain value or more, it is possible to cope with an eraser stroke that reciprocates in any direction.

  If it is known that hxy (x, y) and hyx (x, y) are the same, only one of them need be calculated.

  Further, it is desirable to obtain a function that does not have a point that cannot be partially differentiated. However, if there is a point that cannot be partially differentiated, sampling is also performed on that point or its surroundings.

  Since it comprised as mentioned above, according to 3rd Embodiment, in the display screen along the coordinate row | line | column by a series of deletion operation obtained by sampling the coordinate which moves based on a time series at the time of drawing image deletion operation In the electronic blackboard 300 that employs a drawn image erasing method for erasing a drawn image, the control unit 303 includes a function approximation processing unit 308 and samples curves derived from a plurality of sampled sample points using discrete points. By performing function approximation that approximates data by the sequence of points and changing the frequency of sampling according to the derivative value of the curve, the number of eraser stroke data can be reduced.

  In addition, the function approximation processing unit 308 can perform the erasure process of the drawn image without changing the shape of the eraser stroller by increasing the sampling frequency as the absolute value of the derivative of the curve is smaller. .

  When the function approximation processing unit 308 sets the curve to f (x, y) = 0 and the partial derivative of f (x, y) to fx (x, y), fy (x, y), fx By changing the frequency of sampling according to the values of (x, y) and fy (x, y), and increasing the sampling frequency as the absolute value of the derivative of the curve is smaller, The drawn image can be erased without changing the shape of the eraser stroller.

  In addition, the function approximation processing unit 308 determines whether the absolute value of any of the second-order partial derivatives of hxx (x, y), hyy (x, y), hxy (x, y), and hyx (x, y) is By increasing the sampling frequency as the absolute value increases, the drawn image can be erased without changing the shape of the eraser stroller.

  In addition, as a function of the function approximation processing unit 308, a point where a curve tangent satisfies a specific condition is acquired as a sample point, and sampling is not performed for a point where the slope of the curve tangent does not satisfy a specific condition, or The sampling frequency may be lowered.

  Specifically, by setting the slope of the curve tangent to “0” as a specific condition of the curve tangent, sampling is not performed in the straight line portion, and the score of the eraser stroke data is reduced. Can do.

  In the third embodiment, there are places where mathematical expressions are used, such as f (x, y) = 0, but this does not necessarily mean that mathematical expressions are used, and implementation is performed using another method. It is also possible.

  In the third embodiment, in two dimensions, function approximation is performed in which a curve derived from a plurality of sampled sample points is converted into data approximately by a sequence of points sampled by discrete points. The drawn image erasing method of the invention is not limited to two dimensions but can be extended to n dimensions.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described.
In the fourth embodiment, the drawn image erasing method of the present invention is applied to design software for a 3D printer, and a three-dimensional eraser expressed as a cube in a three-dimensional space is used as an erasing member for erasing a drawn image. It is characterized in that it can be used.

  In the fourth embodiment, a three-dimensional eraser is moved on a touch panel (input device) such as an electronic blackboard or a tablet to delete a drawing image in space.

  The position information (coordinates) of the three-dimensional eraser is notified to the application every 10 (ms) from the touch panel.

  The application temporarily stores the notified position information of the three-dimensional eraser in the storage unit, and performs function approximation. If necessary, function approximation may be performed for each stroke portion of the three-dimensional eraser.

  If the eraser stroke is three-dimensional in an area on a three-dimensional space, the partial derivative fx (x, y, z) with respect to x is expressed when this stroke is expressed as f (x, y, z) = 0. ) = 0, the partial derivative fy (x, y, z) = 0 for y, and the partial derivative fz (x, y, z) = 0 for z are obtained as sample points. can do.

  As described above, according to the fourth embodiment, since the drawn image erasing method of the present invention can acquire the standard point in the eraser stroke even in the three-dimensional space, the same as in the third embodiment described above. It is possible to reduce the number of eraser stroke data by performing function approximation that approximates data based on a plurality of sampled points and changing the frequency of sampling according to the derivative value of the curve. it can.

  In addition, this invention is not limited to embodiment mentioned above, A various change is possible in the range shown to the claim. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the claims, that is, changes are made as appropriate without departing from the scope of the present invention. Embodiments obtained by combining technical means are also included in the technical scope of the present invention.

  In particular, there are various methods for deleting a drawn image using a given eraser stroke other than a method using a Hough transform, and the present invention falls within the scope of the claims and other drawing methods. It can also be applied to an image deletion method.

100, 200, 300 Electronic blackboard 101 Display 102 Storage units 103, 203, 303 Control unit 104 Display control unit 105 Input reception unit 106 Pen processing unit 107 Eraser processing unit 108, 208 Input point filtering determination unit 111 Touch panel 112 Pen 113 Drawing image 114 Eraser 121 Pen Stroke Group Storage Unit 122 Eraser Stroke Group Storage Unit 308 Function Approximation Processing Unit

Claims (6)

In a drawing image erasing method for erasing a drawing image in a display screen along a sample point of a series of erasing processing coordinate sequences obtained by sampling coordinates that move based on a time series during a drawing image erasing operation,
The sample point candidate based on the angle formed by the straight line derived from the sampled sample points and the straight line derived from the last sample point of the sampled sample points and the newly sampled sample point candidate point And a step of determining whether or not to use as a new sample point. Determining whether to use the sample point candidate as a new sample point based on the last sample point sampled and the length of a straight line derived from the sample point candidate point;
The drawn image erasing method according to claim 1, further comprising: Based on the angle between the last sample point sampled and the straight line derived from the sample point candidate point, and the straight line derived from the sample point candidate point and the newly sampled next sample point candidate point, Determining whether to use a sample point candidate as a new sample point;
The drawn image erasing method according to claim 1, further comprising: Whether or not to use the sample point candidate point as a new sample point is determined based on the length of a straight line derived from the sample point candidate point and the newly sampled next sample point candidate point. Process,
The drawn image erasing method according to claim 3, further comprising:   In the curve portion derived from a plurality of sampled sample points, the data amount of the coordinate sequence by the erasure operation is not reduced, and in the straight line portion derived from the plurality of sampled sample points, the data amount of the coordinate sequence is reduced. The drawn image erasing method according to claim 1, wherein the drawn image is erased. Obtaining an extreme value of the curve based on a coordinate sequence of discrete points of the curve derived from a plurality of sampled sample points,
In the extreme value of the curve and / or the periphery thereof, the data amount of the coordinate string is not reduced by the erasing operation, and the data amount of the coordinate string is reduced by the erasing operation in the other portions. The drawn image erasing method according to any one of claims 1 to 4.

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