A projection light path calibration method based on chessboard center point extraction

Abstract

The present invention discloses a method for calibrating a projection light path based on the extraction of chessboard center points. First, the physical world coordinates of the chessboard center point are calculated. The pixel coordinates of the chessboard center point are calculated based on the extracted coordinates of the chessboard corner points. Then, the phase value corresponding to the center point pixel coordinates is mapped to the target surface pixel coordinates of the projector. Finally, the projection light path is calibrated based on the obtained physical coordinates of the chessboard center point and the projector target surface pixel coordinates at the corresponding position. This method first calculates the projector target surface pixel coordinates corresponding to the chessboard center point, and then uses the target surface pixel coordinates and the physical coordinates of the chessboard center point to calibrate the projection light path. Compared with the traditional elliptical calibration plate for calibrating the projector, the complexity of the calculation is reduced, and the result is not affected by the perspective transformation and is more accurate.

Description

Technical Field

[0001] The present invention relates to the field of structured light three-dimensional measurement, and in particular to a projection light path calibration method based on chessboard center point extraction. Background Art

[0002] In the field of structured light 3D measurement, projector calibration has always been a tedious problem. Traditionally, a circular calibration plate has been used for calibration. However, this requires not only identifying the ellipse boundary but also performing ellipse fitting to extract the center, which reduces the accuracy of the center extraction. This computational complexity is also affected by perspective transformations. Due to perspective transformations, when extracting the center using the circular calibration plate, the center of the ellipse fitting is not the true center, resulting in calibration errors. Therefore, it is crucial to find a calibration method that is unaffected by perspective transformations and computationally simple. Summary of the Invention

[0003] In order to more simply implement projector calibration, the present invention provides a projection light path calibration method based on chessboard center point extraction.

[0004] The technical solution adopted by the present invention is as follows: a projection light path calibration method based on chessboard center point extraction, the steps are as follows:

[0005] Step 1: Calculate the coordinates of the center point of the chessboard in the world coordinate system ;

[0006] Step 2: Read the checkerboard calibration image taken by the camera and extract the coordinates of the checkerboard corner points. Calculate the pixel coordinates of the center point of the checkerboard based on the extracted pixel coordinates of the checkerboard corner points. ;

[0007] Step 3: Calculate the corresponding horizontal and vertical phase values ​​at the pixel coordinates of the projector center point , map the phase value to the projection target surface to calculate the pixel coordinates of the projector target surface ;

[0008] Step 4: According to the coordinates of the center point of the chessboard in the world coordinate system and the pixel coordinates on the projector target surface Calibrate the projector optical path.

[0009] Preferably, step one is as follows:

[0010] The side length of a single grid in the calibration board is calculated according to the checkerboard Define the coordinates of the center point of the chessboard, the long side is Axis direction, short side is Direction, determined by the right-hand screw rule Axis direction; and assuming that the center of the chessboard The axis coordinate is 0, where the upper left corner is the origin coordinate .

[0011] Preferably, step 2 is as follows:

[0012] Extract the coordinates of the four nearest corner points of the chessboard center point through the corner point coordinates 、 、 and ,in and , and are points on each other's diagonals;

[0013] From this we can get the equations of the two diagonal lines of the chessboard:

[0014]

[0015] Solve the above equations to get the coordinates of the center point of the white square .

[0016] Preferably, step three is as follows:

[0017] First, the phase shift method is used to Axis direction, Directional unwrapping yields the unwrapped phase;

[0018] Then through the coordinates of the center point of the chessboard Extract the horizontal and vertical phase values ​​of the center point and , the corresponding projector target surface pixel coordinates are calculated by the following formula:

[0019]

[0020] in and are the periods of the sinusoidal fringes of the projection pattern, and is the number of pixels occupied by the unit phase.

[0021] Preferably, step four is as follows:

[0022] According to the physical coordinates of the center point of the chessboard obtained in step 1 and the pixel coordinates obtained in step 3 , and solve the corresponding calibration parameters according to Zhang’s calibration method.

[0023] The present invention has the following beneficial effects: the present invention proposes a projection light path calibration method based on chessboard center point extraction, which is simpler to calculate than previous calibration methods and is not affected by perspective transformation errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a system block diagram of an embodiment of the present invention.

[0025] Figure 2 This is the checkerboard calibration plate used in the embodiments of the present invention.

[0026] Figure 3 It is the calibration plate pattern of the normal image in the embodiment of the present invention.

[0027] Figure 4 It is an image of a single checkerboard pattern after perspective transformation in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the embodiments and drawings.

[0029] like Figure 1 The following is the steps of this embodiment. First, calculate the coordinates of the center point of the chessboard in the world coordinate system. Then read the camera shot Figure 2 The checkerboard calibration image shown above is used to extract the coordinates of the checkerboard corner points. The pixel coordinates of the center point of the checkerboard are calculated based on the extracted pixel coordinates of the checkerboard corner points. The calculated midpoint coordinates are used to calculate the corresponding horizontal and vertical phase values ​​at the projector center pixel coordinates. Then map the phase value to the projection target surface to calculate the pixel coordinates of the projector target surface Finally, according to the coordinates of the center point of the chessboard in the world coordinate system and the pixel coordinates on the projector target surface Calibrate the projector optical path.

[0030] The specific steps are as follows:

[0031] Step 1: Calculate the world coordinates of the center point of the chessboard. According to the side length of a single grid in the chessboard calibration board Defines the coordinates of the center point of the chessboard. The long side is Axis direction, short side is Direction. And according to the right-hand screw rule, Axis direction. And assuming that the center of the chessboard is The axis coordinate is 0. The upper left corner is the origin coordinate .

[0032] Step 2: Find the pixel coordinates of the center point of the chessboard The coordinates of the four nearest corner points of the chessboard center are extracted through the corner point coordinates. 、 、 and .in and , and They are points on the diagonals of each other.

[0033] From this we can get the equations of the two diagonal lines of the chessboard:

[0034]

[0035] Solving the above equations can get the coordinates of the center point of the white square .

[0036] Step 3: Calculate the pixel coordinates of the projector target corresponding to the center point of the chessboard First, the phase shift method is used to Axis direction, Directional unwrapping gives the unfolded phase. Then the coordinates of the center point of the chessboard are used Extract the horizontal and vertical phase values ​​of the center point and The corresponding projector target surface pixel coordinates are calculated by the following formula:

[0037]

[0038] in and are the periods of the sinusoidal fringes of the projection pattern. and is the number of pixels occupied by the unit phase.

[0039] Step 4: Solve the calibration parameters. According to the physical coordinates of the center point of the chessboard obtained in step 1 and the pixel coordinates obtained in step 3 The corresponding calibration parameters are solved according to Zhang's calibration method.

[0040] Obviously, the above embodiments of the present invention are merely examples for illustrating the present invention and are not intended to limit the implementation of the present invention. Other obvious changes or modifications derived from the essence of the present invention still fall within the scope of protection of the present invention.

Claims

1. A projection light path calibration method based on chessboard center point extraction, characterized in that Here are the steps: Step 1: Calculate the coordinates of the center point of the chessboard in the world coordinate system ; Step 2: Read the checkerboard calibration image taken by the camera, extract the coordinates of the checkerboard corner points, and calculate the pixel coordinates of the checkerboard center point based on the extracted pixel coordinates of the checkerboard corner points , as follows: Extract the coordinates of the four nearest corner points of the chessboard center point through the corner point coordinates 、 、 and ,in and , and They are points on the diagonal lines of each other, so the equations of the two diagonal lines of the chessboard can be obtained as: Solve the above equations to get the coordinates of the center point of the white square ; Step 3: Calculate the corresponding horizontal and vertical phase values ​​at the pixel coordinates of the projector center point , map the phase value to the projection target surface to calculate the pixel coordinates of the projector target surface , as follows: First, the phase shift method is used to Axis direction, Directional unwrapping obtains the unfolded phase, and then the coordinates of the center point of the chessboard are used Extract the horizontal and vertical phase values ​​of the center point and , the corresponding projector target surface pixel coordinates are calculated by the following formula: in and are the periods of the sinusoidal fringes of the projection pattern, and is the number of pixels occupied by the unit phase; Step 4: According to the coordinates of the center point of the chessboard in the world coordinate system and the pixel coordinates on the projector target surface Calibrate the projector optical path.

2. The projection light path calibration method based on chessboard center point extraction according to claim 1, characterized in that: Step 1 is as follows: calibrate the side length of a single grid in the board according to the checkerboard Define the coordinates of the center point of the chessboard, the long side is Axis direction, short side is Direction, determined by the right-hand screw rule Axis direction; And assume that the center of the chessboard is The axis coordinate is 0, where the upper left corner is the origin coordinate .

3. The projection light path calibration method based on chessboard center point extraction according to claim 1, characterized in that: Step 4 is as follows: According to the physical coordinates of the center point of the chessboard obtained in step 1 and the pixel coordinates obtained in step 3 , and solve the corresponding calibration parameters according to Zhang’s calibration method.

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