CN112050751B - Projector calibration method, intelligent terminal and storage medium - Google Patents
Projector calibration method, intelligent terminal and storage medium Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
- G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object
- G01B11/2504—Calibration devices
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
- G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object
Abstract
The invention discloses a projector calibration method, an intelligent terminal and a storage medium, wherein the projector calibration method is applied to a projector calibration system and comprises the following steps: acquiring a calibration image corresponding to the calibration plate, and generating a world coordinate system, a camera image plane coordinate system and a projector image plane coordinate system according to preset coordinate parameters and the calibration image; calculating calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system and the camera image plane coordinate system; correcting a projector image plane coordinate system according to the calibration parameters to generate a first projector coordinate system; and randomly selecting a plurality of collinear correction points in the calibration board, correcting the first coordinate system of the projector according to the world coordinates of the correction points corresponding to the correction points and the corresponding first coordinates of the correction points in the first coordinate system of the projector, and generating a second coordinate system of the projector. The invention can effectively improve the calibration efficiency of the projector.
Description
Technical Field
The invention belongs to the technical field of visual calibration, and particularly relates to a projector calibration method, an intelligent terminal and a storage medium.
Background
The structured light three-dimensional measurement technology is a non-contact three-dimensional measurement method and has the advantages of no damage, high efficiency, low cost, high reliability and the like. The coded structured light in the structured light does not need to be scanned, and the method has high measurement efficiency, so that the method is widely applied. The general three-dimensional measuring system of structured light comprises a camera, a projector and a measured object, wherein the projector sequentially projects coding stripes onto the measured object according to a time sequence, the stripes are distorted on the surface of the object and deform, the camera acquires each deformed stripe image and then decodes the stripe images to acquire three-dimensional coordinates of the object according to an optical triangulation principle, and then three-dimensional reconstruction is completed.
Before measurement, the structured light three-dimensional measurement system needs to be calibrated. Common methods include geometric trigonometry, polynomial fitting, inverse camera, and pseudo-camera. The inverse machine method and the pseudo camera method need to calibrate the camera first and then calibrate the projector, so that the calibration parameters of the projector have accumulated errors. Although the pseudo camera method avoids the accumulation of errors, the problems that the calibration precision is easily influenced by illumination or the calculation efficiency is low exist.
Disclosure of Invention
The invention mainly aims to provide a projector calibration method, an intelligent terminal and a storage medium, and aims to solve the problem of low projector calibration accuracy in the prior art.
In order to achieve the above object, the present invention provides a projector calibration method, which includes the following steps:
acquiring a calibration image corresponding to the calibration plate, and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to preset coordinate parameters and the calibration image;
calculating calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system and the camera image plane coordinate system;
correcting the projector image plane coordinate system according to the calibration parameters to generate a first projector coordinate system;
and randomly selecting a plurality of collinear correction points in the calibration plate, correcting the first coordinate system of the projector according to the world coordinates of the correction points corresponding to the correction points and the first coordinates of the correction points corresponding to the first coordinate system of the projector, and generating a second coordinate system of the projector.
Optionally, the projector calibration method, wherein the obtaining a calibration image corresponding to the calibration plate, and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera, and a projector image plane coordinate system corresponding to the projector according to preset coordinate parameters and the calibration image includes:
controlling the projector to continuously project the coded structured light to the plane where the calibration plate is located, and controlling the camera to shoot calibration images in the processes of non-projection and projection;
decoding the calibration image to generate camera coordinate information corresponding to the calibration plate in a camera image plane and projector coordinate information corresponding to the calibration plate in a projector image plane;
and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to the coordinate parameters, the camera coordinate information and the projector coordinate information.
Optionally, the projector calibration method, wherein the calculating calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system, and the camera image plane coordinate system includes:
calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system according to the calibration image;
and calculating the calibration parameters of the projector according to the world coordinate system and the homography matrix.
Optionally, the projector calibration method, wherein the calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system according to the calibration image includes:
selecting a plurality of calibration points from the calibration plate, and calculating the distance between the coordinates of the calibration point camera and the coordinates of the central point;
calculating the area of a matching region in the calibration image according to the height of the calibration image, the distance, a preset upper area limit threshold and a preset lower area limit threshold;
determining corresponding local areas of the calibration points in the projector image plane coordinate system and the camera image plane coordinate system according to the areas;
based on the local region, a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system is calculated.
Optionally, the projector calibration method, wherein the calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system based on the local area includes:
randomly selecting a plurality of pairs of candidate points in the local area, wherein the coordinates of the same point in the projector image plane coordinate system and the camera image plane coordinate system are a pair of candidate points;
and calculating a homography matrix between the projector image plane coordinate system and the camera image plane coordinate system according to the coordinates of the candidate points.
Optionally, the projector calibration method, wherein the calibration parameters include an internal parameter, an external parameter, and a distortion coefficient, and the calculating the calibration parameters of the projector according to the world coordinate system and the homography matrix includes:
calculating the corresponding coordinate of the fixed point projector in the projector image plane coordinate system according to the homography matrix;
and calculating the internal parameter, the external parameter and the distortion coefficient of the projector according to the coordinate of the fixed point projector and the world coordinate of the fixed point.
Optionally, the projector calibration method, wherein the randomly selecting a plurality of collinear calibration points in the calibration plate, and correcting the first coordinate system of the projector according to a world coordinate of the calibration point corresponding to the calibration point and a first coordinate of the calibration point corresponding to the first coordinate system of the projector, and generating the second coordinate system of the projector includes:
randomly selecting a plurality of collinear correction points in the calibration plate, and randomly selecting a plurality of calculation points in the correction points, wherein the number of the calculation points is less than that of the correction points;
calculating a correction point theoretical coordinate corresponding to each correction point according to a calculation point world coordinate corresponding to the calculation point and a calculation point projector first coordinate;
calculating a corresponding second coordinate of the correction point according to the first coordinate of the correction point and the theoretical coordinate of the correction point;
and mapping the second coordinate of the correction point to the first coordinate system of the projector, correcting each coordinate in the first coordinate system of the projector, and generating a second coordinate system of the projector.
Optionally, the projector calibration method, wherein the calculating, according to the first coordinate of the correction point and the theoretical coordinate of the correction point, a corresponding second coordinate of the correction point includes:
calculating the error between the first coordinate of the correction point and the theoretical coordinate of the correction point;
judging whether each error is larger than a preset error threshold value or not;
if so, deleting the correction points corresponding to the errors;
if not, calculating a corresponding second coordinate of the correction point according to the error.
In addition, to achieve the above object, the present invention further provides an intelligent terminal, wherein the intelligent terminal includes: a memory, a processor and a projector calibration program stored on the memory and executable on the processor, the projector calibration program when executed by the processor implementing the steps of the projector calibration method as described above.
In addition, to achieve the above object, the present invention further provides a storage medium, wherein the storage medium stores a projector calibration program, and the projector calibration program realizes the steps of the projector calibration method as described above when executed by a processor.
The method comprises the steps of firstly projecting a series of coded structured light to a calibration plate, shooting a plurality of calibration images by a camera, calculating calibration parameters of the projector according to the calibration images, a projector image plane coordinate system, a camera image plane coordinate system and a world coordinate system, and correcting the projector according to the calibration parameters. And then, secondary correction is carried out according to the co-linear points in the calibration plate to correspond to coordinates in a world coordinate system and a corrected projector image plane coordinate system by using the cross ratio without deformation, so that the distortion coefficient in the calibration parameters of the projector is further corrected, and the accuracy of projection calibration is improved.
In addition, the invention also calculates different local areas according to the distance between the calibration point in the calibration image and the central point of the calibration image, then selects a plurality of pairs of candidate points in the local areas of the projector image plane coordinate system and the camera image plane coordinate system respectively, and calculates the conversion relation between the two, namely the homography matrix. Through the homography matrix, the coordinates of the projector image plane coordinate system and the coordinates of the world coordinate system can be corresponded, so that the calibration parameters of the projector can be calculated. The distortion of the original image shot by the camera is increased along with the increase of the distance from the central point, so that the difference between the coordinate of the calibration point in the world coordinate system and the coordinate of the camera image plane coordinate system is larger along with the increase of the distance from the calibration point to the central point, namely the difference is more unreliable. Therefore, the credible local area is determined by calibrating the distance between the point and the central point, and the homography matrix is calculated according to the points in the local area, so that the reliability of the homography matrix is improved, and the accuracy of subsequently calculating the calibration parameters of the projector is improved.
Drawings
FIG. 1 is a flow chart of a preferred embodiment of a projector calibration method according to the present invention;
FIG. 2 is a flowchart of step S100 in the preferred embodiment of the calibration method of the projector according to the present invention;
FIG. 3 is a flowchart of step S200 in the preferred embodiment of the calibration method for a projector according to the present invention;
FIG. 4 is a flowchart of step S210 in the preferred embodiment of the calibration method of the projector according to the invention;
FIG. 5 is a flowchart of step S214 in the preferred embodiment of the projector calibration method according to the invention;
FIG. 6 is a flowchart of step S2220 according to the exemplary embodiment of the present invention;
FIG. 7 is a schematic diagram of the cross ratio invariance principle employed in the preferred embodiment of the projector calibration method of the present invention;
FIG. 8 is a flowchart of step S400 of the calibration method of the projector according to the preferred embodiment of the present invention
FIG. 9 is a flowchart of step S430 in the preferred embodiment of the calibration method for a projector according to the invention;
fig. 10 is a schematic operating environment diagram of an intelligent terminal according to a preferred embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, the projector calibration method according to the preferred embodiment of the present invention includes the following steps:
and S100, acquiring a calibration image corresponding to the calibration plate, and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to preset coordinate parameters and the calibration image.
In this embodiment, preset coordinate parameters are first obtained, where the coordinate parameters include an origin of coordinates, directions of coordinate axes, and the like, and then according to the coordinate parameters, coordinate axes of the world coordinate system, the camera image plane coordinate system, and the projector image plane coordinate system are established. And refining the coordinate axis of the world coordinate system according to the parameters of the calibration plate to obtain the world coordinate system. In addition, the projector is controlled to project the coded structured light on the calibration plate, the camera is controlled to shoot a corresponding calibration image, and then the calibration image is decoded, so that points in the camera image plane coordinate system correspond to points in the projector image plane coordinate system, and the camera image plane coordinate system and the projector image plane coordinate system are generated.
Further, referring to fig. 2, step S100 includes:
and step S110, controlling the projector to continuously project the coded structured light to the plane where the calibration plate is located, and controlling the camera to shoot a calibration image in the processes of non-projection and projection.
Specifically, in the embodiment, a gray code in the coded structured light is used for description, the gray code is also called a cyclic code, and any pixel of the gray code is located at the boundary of the black and white stripe at most once, so that the coding value of the adjacent pixel is different by only one bit at most. However, under the same gray code, the higher the screen resolution, the increased number of gray codes with the same code value, so that several line shift patterns are projected to distinguish the pixels with the same code value, and the subsequent decoding of the gray code and the line shift can roughly determine the coordinates of some pixels. In this embodiment, the calibration board is a checkerboard calibration board, a dot calibration board, or the like, which can be used for camera calibration.
Firstly, the focal length and the aperture of the camera and the focal length of the projector are adjusted according to the long-range view of the object to be measured and the light intensity of the environment. The camera is controlled to capture the calibration board separately, and the calibration board is marked as a calibration image 1. And then controlling the projector to project the Gray code onto the plane where the calibration plate is located, and shooting a plurality of calibration images by the camera in the period, wherein the calibration images are marked as calibration images N. And automatically segmenting a threshold value of the calibration image N to obtain a corresponding binary image, then decoding the binary image to obtain pixel points of points on the plane of the calibration plate on the projector image plane, and comparing the calibration image N with the calibration image 1 to further determine the corresponding coordinate information of the points in the calibration plate in the projector image plane.
And step S120, decoding the calibration image to generate camera coordinate information corresponding to the calibration plate in a camera image plane and projector coordinate information corresponding to the calibration plate in a projector image plane.
Specifically, because the calibration image is located on the camera image plane, the pixel point of the calibration image can be used as a unit point, and scales on different coordinate axes can be obtained, so that coordinate information of the camera image plane can be obtained. Meanwhile, by combining the gray code decoded value and the line shift code decoded value in the calibration image, the corresponding position of each point on the calibration plate in the projector image plane can be calculated. In order to better determine the specific positions of the points in the calibration board, the calibration board adopted in this embodiment is a checkerboard calibration board.
And step S140, generating a world coordinate system corresponding to the calibration board, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to the coordinate parameters, the camera coordinate information and the projector coordinate information.
In this embodiment, preset coordinate parameters are first obtained, where the coordinate parameters include an origin of coordinates, a direction of a coordinate axis, and the like. If the coordinate parameters comprise that the origin of the world coordinate system is the origin of the coordinate system which is the upper left corner endpoint of the calibration board, the horizontal right direction is the positive direction of an X axis, the vertical downward positive direction of a Y axis, and the vertical X, Y axial inward direction is the positive direction of a Z axis, the entity of the calibration board is positioned in the world coordinate system, therefore, the scales can be marked on the X axis, the Y axis and the Z axis according to the length and the width of the calibration board, each calibration point and the distance between the calibration points and the like from the calibration board, thereby generating the world coordinate system. Taking the camera image coordinate system as an example, when the direction of the coordinate axis, the position of the origin and the scale of each coordinate axis are determined, the camera image plane coordinate system can be generated, and based on the same principle, the projector image plane coordinate system can be generated.
And S200, calculating calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system and the camera image plane coordinate system.
Further, referring to fig. 3, step S200 includes:
and S210, calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system according to the calibration image.
Specifically, Homography (Homography) is used for describing the position mapping relationship of an object between a world coordinate system and a pixel coordinate system, and a corresponding transformation matrix is a Homography matrix. In the scheme, the calibration image is obtained through the combined action of the projector and the camera, so that a position mapping relation exists between the projector image plane coordinate system and the camera image plane coordinate system, and if a homography matrix between the projector image plane coordinate system and the camera image plane coordinate system is obtained through calculation, the projector can be used as a 'pseudo camera' to calculate the calibration parameters of the projector. The calculation method of the homography matrix mainly comprises the steps of selecting a plurality of pairs of points, and then estimating the transformation matrix of two planes through the transformation relation between the points.
Further, referring to fig. 4, step S210 includes:
step S211, selecting a plurality of calibration points in the calibration plate, and calculating the distance between the coordinates of the calibration point camera and the coordinates of the central point.
Specifically, the calibration board has a plurality of calibration points, the calibration points appear in the calibration image shot by the camera, and the calibration point camera coordinates corresponding to each calibration point are determined according to the camera image plane coordinate system. The embodiment adopts the checkerboard calibration plate, the calibration points are the angular points of the checkerboard calibration plate, and the angular points with longer distance can be preferentially selected for reducing the possibility of overlapping of subsequent local areas. And picking out the central point of the calibration image in the camera image plane coordinate system, and obtaining the coordinate of the central point, namely the coordinate of the central point. The distance between the two is calculated by the Euclidean distance formula which is as follows:
Di＝||pi-oc||2，
wherein p isiRepresenting the calibrated point camera coordinates, ocRepresenting the coordinates of the center point, DiAnd expressing the Euclidean distance between the coordinate of the calibration point camera and the coordinate of the central point.
And S212, calculating the area of the matching region in the calibration image according to the height of the calibration image, the distance, a preset upper area limit threshold and a preset lower area limit threshold.
Specifically, the calibration image has a certain height, and if the specification of the calibration image is 100 × 100 pixels, the height of the calibration image is 100. Presetting the maximum value and the minimum value of the area of the matching region, namely an upper area threshold and a lower area threshold, so as to obtain the size of the area in the calibration image, wherein the area calculation formula of the matching region is as follows:
wherein S is the area, m is the area upper threshold, n is the area lower threshold, h is the height of the calibration image, and S is the area.
And step S213, determining the corresponding local areas of the calibration points in the projector image plane coordinate system and the camera image plane coordinate system according to the areas.
Specifically, if the area of the current region is calculated according to the coordinates of the calibration point camera of the calibration point a and the coordinates of the center point, a local region having the same size as the area is selected from the calibration image with the calibration point a as the center, and the local region may be circular or square.
The current local areas are obtained according to preset numerical values, the local areas can be defined only by performing complex conversion in a calibration image, so that the efficiency is low, the distortion in the calibration image cannot be considered, the subsequent calculation of the coordinates of the projector has larger errors, and different local areas are divided according to different calibration points and aiming at the positions of the calibration points in the calibration image, so that the calculation steps are simplified, and the accuracy of the subsequent calculation is improved.
And S214, calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system based on the local area.
Specifically, the position of the local area in the projector image plane coordinate system may be determined according to the corresponding position of the local area in the camera image plane coordinate system. And a plurality of points in the local area correspond to the position coordinates in the camera image plane coordinate system and the projector image plane coordinate system, so that different position coordinates of the same point in the two coordinate systems can be determined, the conversion relation between the two coordinate systems is calculated, and the homography matrix between the two coordinate systems is calculated.
Further, referring to fig. 5, step S214 includes:
step S2141, a plurality of pairs of candidate points are randomly selected in the local area, wherein the coordinates of the same point in the projector image plane coordinate system and the camera image plane coordinate system are a pair of candidate points.
Specifically, as for a certain point E, there is a world coordinate in the world coordinate system, and by analyzing the calibration image by the camera, the coordinate of the point E in the camera image plane coordinate system and the coordinate of the point E in the projector image plane coordinate system can be obtained, and therefore the coordinates of the local area in the camera image plane coordinate system and the projector image plane coordinate system can be determined. If the randomly selected point is the point E, the corresponding points in the camera image plane coordinate system and the projector image plane coordinate system are respectively the point EcAnd EpThen E iscAnd EpIs a pair of candidate points.
Step S2142, calculating a homography matrix between the projector image plane coordinate system and the camera image plane coordinate system according to the coordinates of the candidate points.
Specifically, since the same pair of candidate points originates from the same point, a conversion formula between the projection image plane coordinate system and the camera image plane coordinate system can be calculated through multiple pairs of candidate points, in this scheme, a homography matrix is used as the conversion formula, and in order to reduce the influence of noise points on the calculation, a Random Sample Consensus (RANSAC) method is used in this embodiment to find a homography matrix between the two.
Selecting a part of the candidate points as known numbers in advance, calculating a corresponding conversion matrix, marking as M, then calculating the distance between the coordinates of the rest part of the candidate points and M, screening out the local points according to the distance, recording the value of the local points, repeating for many times, and selecting the conversion matrix with the maximum local point value as the finally obtained homography matrix.
The calculation formula is as follows:
wherein xcIs the coordinate, x, of a point of said candidate points located in said camera image plane coordinate systempIs the coordinate of a point of said candidate points located in the projector image plane coordinate system, HiFor the purpose of the said transformation matrix,
is the homography matrix.
And S220, calculating calibration parameters of the projector according to the world coordinate system and the homography matrix.
Specifically, the world coordinate system cannot be associated with the projector image plane coordinate system, but the world coordinate system can be associated with the projector image plane coordinate system through the homography matrix, the projector is used as a camera calibration method, the projector is calibrated by adopting the camera calibration method, and the calibration parameters of the projector are calculated.
Further, referring to fig. 6, step S220 includes:
step S221, calculating a corresponding coordinate of the calibration point projector in the projector image plane coordinate system according to the homography matrix;
specifically, according to the homography matrix, a conversion relation between the camera image plane coordinate system and the projector image plane coordinate system can be determined, so that coordinates of a calibration point in the camera image plane coordinate system are obtained, and coordinates of the calibration point in the projector image plane coordinate system can be determined, wherein a calculation formula is as follows:
wherein q isiFor the coordinates of the index point in the projector image plane coordinate system, piTo scale the coordinates of a point in the camera image plane coordinate system,
is the homography matrix.
Step S222, calculating internal parameters, external parameters and distortion coefficients of the projector according to the coordinates of the fixed point projector and the world coordinates of the fixed point.
Specifically, the projector is used as a camera, and the correspondence between the coordinates of the calibration point projector and the coordinates of the calibration point world is established by the coordinates of the calibration point camera, so that the conversion parameter from the calibration plate to the projector image plane, that is, the calibration coefficient of the projector can be calculated. In this embodiment, a calibration parameter of the projector is calculated by using a zhangxiong calibration method, where the calibration parameter includes an internal parameter, an external parameter, and a distortion coefficient. Since the gnomon calibration method is a common calibration technique, it will not be further described in this embodiment.
And step S300, correcting the projector image plane coordinate system according to the calibration parameters to generate a first projector coordinate system.
In this embodiment, since there is distortion between the lenses of the camera and the projector and the light, it is necessary to correct the coordinates in the image plane coordinate systems of the camera and the projector according to the distortion coefficient, so that the subsequently obtained projector image plane coordinate system is closer to the real world, and the corrected projector image plane coordinate system is referred to as a first projector coordinate system.
Step S400, a plurality of collinear correction points are randomly selected in the calibration board, and the first coordinate system of the projector is corrected according to the world coordinates of the correction points corresponding to the correction points and the first coordinates of the correction points corresponding to the first coordinate system of the projector, so that a second coordinate system of the projector is generated.
Specifically, the present embodiment corrects the first coordinate system of the projector using the cross ratio invariance. The cross ratio invariance refers to the characteristic that the cross ratio of four collinear points is unchanged under projective transformation, and the projector image plane coordinate system and the world coordinate system are derived from the same light source, namely the light source of the projector theoretically, so that the collinear points should meet the cross ratio invariance on the world coordinate system and the first coordinate system of the projector. Firstly, collinear points are randomly selected in the calibration plate, and then the first coordinate system of the projector is corrected according to coordinates of the collinear points on the world coordinate system and the first coordinate system of the projector, so that the collinear points are close to or meet a theoretical value obtained based on cross ratio invariance, and a second coordinate system of the projector is generated.
Further, referring to fig. 7, a schematic diagram of the cross ratio invariance principle, and fig. 8, step S400 includes:
step S410, a plurality of collinear correction points are randomly selected in the calibration plate, and a plurality of calculation points are randomly selected in the correction points, wherein the number of the calculation points is smaller than that of the correction points.
Specifically, the calibration board is a checkerboard calibration board, a plurality of black and white grids exist on the checkerboard calibration board, and intersection points of the plurality of black and white grids are randomly selected, that is, calibration points are used as the correction points. In this embodiment, the projector first coordinate system is corrected by using the principle of cross ratio invariance. Firstly, randomly selecting a plurality of calculation points from the correction points, wherein if the number of the selected correction points is 4, the world coordinates of the correction points are A, B, C and D, the correction points are positioned on the same straight line L, the first coordinates of the correction points are a, b, C and D, the correction points are positioned on the same straight line L, the number of the calculation points is 3, and the world coordinates are A, B and C respectively.
And step S420, calculating the theoretical coordinate of the correction point corresponding to each correction point according to the world coordinate of the calculation point corresponding to the calculation point and the first coordinate of the projector of the calculation point.
Specifically, since A, B, C and D are located on the same straight line L, and the A, B, C and D and the a, b, c and D are all projected by the projectionThe luminous point of the instrument being the origin, i.e. OpDetermined after the ray is shot, so that the intersection ratio of the ray and the ray has the following relation:
(a，b；c，d)＝(A，B；C，D)，
thus, the cross ratio of these four correction points is:
therefore, the intersection ratio of a, b, c and D can be calculated from the coordinate values of A, B, C and D. Then, the theoretical value of D, i.e., the projector theoretical coordinates of the correction point D, is calculated using the coordinate values of the calculation points, i.e., a, b, and c.
And step S430, calculating a corresponding second coordinate of the correction point according to the first coordinate of the correction point and the theoretical coordinate of the correction point.
Specifically, by the above method, the projector theoretical coordinates of A, B, C and D are calculated, respectively, and then the average value thereof with the projector reference coordinates, i.e., a, b, c, and D, is calculated, and the average value is taken as the corresponding correction point second coordinate.
Step S440, mapping the second coordinate of the correction point to the first coordinate system of the projector, and correcting each coordinate in the first coordinate system of the projector to generate a second coordinate system of the projector.
Specifically, the second coordinate of the correction point is mapped to the first coordinate system of the projector according to a distortion formula so as to correct the distortion coefficient of the projector and obtain the first coordinate system of the projector again.
It should be noted that, the present embodiment is described with only four correction points and three calculation points, but actually, a plurality of correction points and a plurality of calculation points may be adopted, and the number of correction points to be calculated by the calculation points may be a plurality, and within a certain range, the greater the number, the more the accuracy is improved. In order to further improve the accuracy of the calculation result, the steps of calculating the calibration parameters and correcting can be repeatedly executed for multiple times.
Further, referring to fig. 9, step S430 includes:
and step S431, calculating the error between the first coordinate of the correction point and the theoretical coordinate of the correction point.
In this embodiment, to reduce the error of the correction point selection difference, which results in too large deviation of the second coordinate of the subsequent correction point, the error between the first coordinate of the correction point and the theoretical coordinate of the correction point is calculated first.
And step S432, judging whether each error is larger than a preset error threshold value.
Specifically, an error threshold is preset, and the obtained errors are compared with the error threshold in magnitude.
And step S433, if yes, deleting the correction point corresponding to the error.
Specifically, if the error is greater than the error threshold, if the error corresponding to the correction point a is greater than the error threshold, the correction point a is excluded from the subsequent calculation of the correction point second coordinate.
And step S434, if not, calculating a corresponding second coordinate of the correction point according to the error.
Specifically, if the error corresponding to the correction point a is less than or equal to the error threshold, the second coordinate of the correction point corresponding to the correction point a is calculated.
In this embodiment, the coordinate values with a large error are eliminated by using the error threshold, so as to improve the reliability of the second coordinate of the correction point.
Step S440, mapping the second coordinate of the correction point to the first coordinate system of the projector, and correcting each coordinate in the first coordinate system of the projector to generate a second coordinate system of the projector.
Specifically, the second coordinate of the correction point is mapped into the first coordinate system of the projector according to a distortion formula, so as to correct the distortion coefficient of the projector and generate a second coordinate system of the projector. Because each projector coordinate system can be based on the calibration parameters of the projector, after the second projector coordinate system is generated, calibration parameters such as corrected distortion coefficients and the like can be correspondingly calculated, so that the calibration of the projector is completed.
In order to obtain a better calibration effect, the steps S300 to S400 may be repeatedly performed for multiple times, and then all calibration parameters are integrated to perform more accurate calibration on the projector.
Further, as shown in fig. 10, based on the projector calibration method, the present invention also provides an intelligent terminal, which includes a processor 10, a memory 20, and a display 30. Fig. 10 shows only some of the components of the smart terminal, but it is to be understood that not all of the shown components are required to be implemented, and that more or fewer components may be implemented instead.
The memory 20 may be an internal storage unit of the intelligent terminal in some embodiments, such as a hard disk or a memory of the intelligent terminal. The memory 20 may also be an external storage device of the Smart terminal in other embodiments, such as a plug-in hard disk, a Smart Memory Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), and the like, provided on the Smart terminal. Further, the memory 20 may also include both an internal storage unit and an external storage device of the smart terminal. The memory 20 is used for storing application software installed in the intelligent terminal and various data, such as program codes of the installed intelligent terminal. The memory 20 may also be used to temporarily store data that has been output or is to be output. In an embodiment, the memory 20 stores a projector calibration program 40, and the projector calibration program 40 can be executed by the processor 10 to implement the projector calibration method of the present application.
The processor 10 may be a Central Processing Unit (CPU), a microprocessor or other data Processing chip in some embodiments, and is used for executing program codes stored in the memory 20 or Processing data, such as executing the projector calibration method.
The display 30 may be an LED display, a liquid crystal display, a touch-sensitive liquid crystal display, an OLED (Organic Light-Emitting Diode) touch panel, or the like in some embodiments. The display 30 is used for displaying information at the intelligent terminal and for displaying a visual user interface. The components 10-30 of the intelligent terminal communicate with each other via a system bus.
In one embodiment, the following steps are implemented when the processor 10 executes the projector calibration program 40 in the memory 20:
acquiring a calibration image corresponding to the calibration plate, and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to preset coordinate parameters and the calibration image;
calculating calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system and the camera image plane coordinate system;
correcting the projector image plane coordinate system according to the calibration parameters to generate a first projector coordinate system;
and randomly selecting a plurality of collinear correction points in the calibration plate, correcting the first coordinate system of the projector according to the world coordinates of the correction points corresponding to the correction points and the first coordinates of the correction points corresponding to the first coordinate system of the projector, and generating a second coordinate system of the projector.
The acquiring a calibration image corresponding to the calibration plate, and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera, and a projector image plane coordinate system corresponding to the projector according to preset coordinate parameters and the calibration image includes:
controlling the projector to continuously project the coded structured light to the plane where the calibration plate is located, and controlling the camera to shoot calibration images in the processes of non-projection and projection;
decoding the calibration image to generate camera coordinate information corresponding to the calibration plate in a camera image plane and projector coordinate information corresponding to the calibration plate in a projector image plane;
and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to the coordinate parameters, the camera coordinate information and the projector coordinate information.
Wherein the calculating calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system and the camera image plane coordinate system comprises:
calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system according to the calibration image;
and calculating the calibration parameters of the projector according to the world coordinate system and the homography matrix.
Wherein, according to the calibration image, calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system comprises:
selecting a plurality of calibration points from the calibration plate, and calculating the distance between the coordinates of the calibration point camera and the coordinates of the central point;
calculating the area of a matching region in the calibration image according to the height of the calibration image, the distance, a preset upper area limit threshold and a preset lower area limit threshold;
determining corresponding local areas of the calibration points in the projector image plane coordinate system and the camera image plane coordinate system according to the areas;
based on the local region, a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system is calculated.
Wherein said computing a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system based on the local region comprises:
randomly selecting a plurality of pairs of candidate points in the local area, wherein the coordinates of the same point in the projector image plane coordinate system and the camera image plane coordinate system are a pair of candidate points;
and calculating a homography matrix between the projector image plane coordinate system and the camera image plane coordinate system according to the coordinates of the candidate points.
Wherein, the calibration parameters comprise internal parameters, external parameters and distortion coefficients, and the calculating the calibration parameters of the projector according to the world coordinate system and the homography matrix comprises:
calculating the corresponding coordinate of the calibration point projector in the projector image plane coordinate system according to the homography matrix;
and calculating the internal parameter, the external parameter and the distortion coefficient of the projector according to the coordinate of the calibration point projector and the coordinate of the calibration point world.
Wherein, the randomly selecting a plurality of collinear correction points in the calibration board, and correcting the first coordinate system of the projector according to the world coordinates of the correction points corresponding to the correction points and the first coordinates of the correction points corresponding to the first coordinate system of the projector, and generating the second coordinate system of the projector comprises:
randomly selecting a plurality of collinear correction points in the calibration plate, and randomly selecting a plurality of calculation points in the correction points, wherein the number of the calculation points is less than that of the correction points;
calculating a correction point theoretical coordinate corresponding to each correction point according to a calculation point world coordinate corresponding to the calculation point and a calculation point projector first coordinate;
calculating a corresponding correction point second coordinate according to the correction point first coordinate and the correction point theoretical coordinate;
and mapping the second coordinate of the correction point to the first coordinate system of the projector, correcting each coordinate in the first coordinate system of the projector, and generating a second coordinate system of the projector.
Wherein the calculating the corresponding correction point second coordinate according to the correction point first coordinate and the correction point theoretical coordinate comprises:
calculating the error between the first coordinate of the correction point and the theoretical coordinate of the correction point;
judging whether each error is larger than a preset error threshold value or not;
if so, deleting the correction points corresponding to the errors;
and if not, calculating a second coordinate of the corresponding correction point according to the error.
In addition, in order to achieve the above object, the present invention further provides an intelligent terminal, wherein the intelligent terminal includes: a memory, a processor and a projector calibration program stored on the memory and executable on the processor, the projector calibration program when executed by the processor implementing the steps of the projector calibration method as described above.
The present invention also provides a storage medium, wherein the storage medium stores a projector calibration program, and the projector calibration program when executed by a processor implements the steps of the projector calibration method as described above.
In summary, the present invention provides a projector calibration method, an intelligent terminal and a storage medium, where the method includes: acquiring a calibration image corresponding to the calibration plate, and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to preset coordinate parameters and the calibration image; calculating calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system and the camera image plane coordinate system; correcting the projector image plane coordinate system according to the calibration parameters to generate a first projector coordinate system; and randomly selecting a plurality of collinear correction points in the calibration plate, correcting the first coordinate system of the projector according to the world coordinates of the correction points corresponding to the correction points and the first coordinates of the correction points corresponding to the first coordinate system of the projector, and generating a second coordinate system of the projector. The invention can effectively improve the calibration accuracy of the projector.
Of course, it will be understood by those skilled in the art that all or part of the processes of the methods of the above embodiments may be implemented by a computer program instructing relevant hardware (such as a processor, a controller, etc.), and the program may be stored in a computer readable storage medium, and when executed, the program may include the processes of the above method embodiments. The storage medium may be a memory, a magnetic disk, an optical disk, etc.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.
Claims (9)
1. A projector calibration method is applied to a projector calibration system, wherein the projector calibration system comprises a projector, a camera and a calibration board, and the projector calibration method comprises the following steps:
acquiring a calibration image corresponding to the calibration plate, and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to preset coordinate parameters and the calibration image;
calculating calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system and the camera image plane coordinate system; the calibration parameters comprise internal parameters, external parameters and distortion coefficients;
correcting the projector image plane coordinate system according to the calibration parameters to generate a first projector coordinate system; correcting coordinates in the camera image plane coordinate system and the projector image plane coordinate system according to the distortion coefficient, wherein the corrected projector image plane coordinate system is a first projector coordinate system;
randomly selecting a plurality of collinear correction points in the calibration plate, and correcting the first coordinate system of the projector according to the world coordinates of the correction points corresponding to the correction points and the first coordinates of the correction points corresponding to the first coordinate system of the projector to generate a second coordinate system of the projector;
the calculating the calibration parameters of the projector according to the calibration image, the world coordinate system, the projector image plane coordinate system and the camera image plane coordinate system comprises: calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system according to the calibration image; and calculating the calibration parameters of the projector according to the world coordinate system and the homography matrix.
2. The projector calibration method according to claim 1, wherein the obtaining a calibration image corresponding to the calibration plate, and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera, and a projector image plane coordinate system corresponding to the projector according to preset coordinate parameters and the calibration image comprises:
controlling the projector to continuously project the coded structured light to the plane where the calibration plate is located, and controlling the camera to shoot calibration images in the processes of non-projection and projection;
decoding the calibration image to generate camera coordinate information corresponding to the calibration plate in a camera image plane and projector coordinate information corresponding to the calibration plate in a projector image plane;
and generating a world coordinate system corresponding to the calibration plate, a camera image plane coordinate system corresponding to the camera and a projector image plane coordinate system corresponding to the projector according to the coordinate parameters, the camera coordinate information and the projector coordinate information.
3. The projector calibration method as claimed in claim 1, wherein said calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system from the calibration image comprises:
selecting a plurality of calibration points in the calibration plate, and calculating the distance between the coordinates of the calibration point camera and the coordinates of the center point; selecting a central point of the calibration image in the camera image plane coordinate system to obtain a coordinate of the central point, namely the coordinate of the central point;
calculating the area of a matching region in the calibration image according to the height of the calibration image, the distance, a preset upper area limit threshold and a preset lower area limit threshold;
determining corresponding local areas of each calibration point in the projector image plane coordinate system and the camera image plane coordinate system according to the areas;
based on the local region, a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system is calculated.
4. The projector calibration method as claimed in claim 3, wherein said calculating a homography matrix between the camera image plane coordinate system and the projector image plane coordinate system based on the local area comprises:
randomly selecting a plurality of pairs of candidate points in the local area, wherein the coordinates of the same point in the projector image plane coordinate system and the camera image plane coordinate system are a pair of candidate points;
and calculating a homography matrix between the projector image plane coordinate system and the camera image plane coordinate system according to the coordinates of the candidate points.
5. The projector calibration method as claimed in claim 1, wherein the calibration parameters include an internal parameter, an external parameter and a distortion coefficient, and the calculating the calibration parameters of the projector according to the world coordinate system and the homography matrix comprises:
calculating the corresponding coordinate of the fixed point projector in the projector image plane coordinate system according to the homography matrix;
and calculating the internal parameter, the external parameter and the distortion coefficient of the projector according to the coordinate of the calibration point projector and the coordinate of the calibration point world.
6. The method for calibrating a projector according to claim 1, wherein the randomly selecting a plurality of collinear calibration points in the calibration board, and correcting the first coordinate system of the projector according to world coordinates of the calibration points corresponding to the calibration points and the first coordinates of the calibration points corresponding to the first coordinate system of the projector to generate the second coordinate system of the projector comprises:
randomly selecting a plurality of collinear correction points in the calibration plate, and randomly selecting a plurality of calculation points in the correction points, wherein the number of the calculation points is less than that of the correction points;
calculating a correction point theoretical coordinate corresponding to each correction point according to a calculation point world coordinate corresponding to the calculation point and a first coordinate of a calculation point projector;
calculating a corresponding second coordinate of the correction point according to the first coordinate of the correction point and the theoretical coordinate of the correction point;
and mapping the second coordinate of the correction point to the first coordinate system of the projector, correcting each coordinate in the first coordinate system of the projector, and generating a second coordinate system of the projector.
7. The method for calibrating a projector according to claim 6, wherein the calculating the corresponding second coordinates of the correction point according to the first coordinates of the correction point and the theoretical coordinates of the correction point comprises:
calculating the error between the first coordinate of the correction point and the theoretical coordinate of the correction point;
judging whether each error is larger than a preset error threshold value or not;
if so, deleting the correction points corresponding to the errors;
if not, calculating a corresponding second coordinate of the correction point according to the error.
8. An intelligent terminal, characterized in that, intelligent terminal includes: a memory, a processor and a projector calibration program stored on the memory and executable on the processor, the projector calibration program when executed by the processor implementing the steps of the projector calibration method as claimed in any one of claims 1 to 7.
9. A storage medium, characterized in that the storage medium stores a projector calibration program, which when executed by a processor implements the steps of the projector calibration method according to any one of claims 1 to 7.
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| CN114727073B (en) * | 2021-01-05 | 2023-09-01 | 成都极米科技股份有限公司 | Image projection method and device, readable storage medium and electronic equipment |
| CN114466173A (en) * | 2021-11-16 | 2022-05-10 | 海信视像科技股份有限公司 | Projection equipment and projection display control method for automatically throwing screen area |
| CN115965697B (en) * | 2022-12-31 | 2024-01-26 | 梅卡曼德（北京）机器人科技有限公司 | Projector calibration method, system and device based on Moh's law |
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