CN111586384A - Projection image geometric correction method based on Bessel curved surface - Google Patents
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Abstract
The invention discloses a projection image geometric correction method based on a Bessel curved surface, which belongs to the technical field of virtual reality projection image processing and comprises the steps of 1) collecting distorted projection images which are not subjected to geometric correction by a camera, and establishing a coordinate conversion model of a projection coordinate space and a camera coordinate space through a bicubic Bessel curved surface; 2) making uniform marking points in an ideal area of a screen space and carrying out geometric correction; 3) performing local geometric pre-distortion on the detected screen space pixel offset area; 4) and carrying out Bessel surface pre-distortion on the original image by the obtained coordinate conversion model, eliminating the overall geometric distortion of the projection picture and finishing geometric correction. The invention adopts a Bezier curved surface model to establish the conversion relation of different coordinate space characteristic points, and then carries out error compensation on the area with larger pixel deviation by using an image local Bezier curved surface distortion algorithm.
Description
Technical Field
The invention belongs to the technical field of virtual reality projection image processing, and particularly relates to a projection image geometric correction method based on a Bessel curved surface.
Background
The virtual reality technology is a computer technology which is started at the end of the 20 th century, and enables a user to observe scenes and objects in a three-dimensional space in real time without limitation and immerse the scenes and the objects in a simulation environment. Along with the development of the times, people require more and more to the virtual world, wear VR glasses and can influence the real experience sense, consequently, bore hole virtual reality technique can provide a better VR for people and experience, and multichannel projection concatenation technique is on virtual picture projection wall around, and the user need not wear any auxiliary device when experiencing this technique and using, just can immerse in the picture and have the impression of being personally on the scene. However, in practical applications, due to a series of factors such as the placement of the projectors being inclined or the models of the projectors being different, the projection pictures on the projection screen inevitably have geometric distortion, so that the projection pictures cannot be aligned with each other. At present, many projection image geometric correction methods exist, wherein a bezier curved surface model is typical and is suitable for projection images in various shapes, but one control point of the bezier curved surface is changed to affect each pixel point of the whole image, so that local geometric error compensation is difficult to perform on the image.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a projection image geometric correction method based on a Bezier curved surface, which is characterized in that a transformation relation of different coordinate space characteristic points is established by adopting a Bezier curved surface model, and an area with larger pixel deviation is subjected to error compensation by an image local Bezier curved surface warping algorithm.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a projection image geometric correction method based on Bessel curved surface includes the following steps:
step 1) acquiring a distorted projection picture without geometric correction by using a camera, and establishing a coordinate conversion model of a projection coordinate space and a camera coordinate space by using a bicubic Bessel curved surface;
step 2) making uniform marking points in an ideal area of a screen space and carrying out geometric correction;
step 3) local geometric pre-distortion is carried out on the detected screen space pixel offset area;
and 4) carrying out Bezier curved surface pre-distortion on the original image by the coordinate conversion model obtained in the step 4), eliminating the overall geometric distortion of the projection picture and finishing geometric correction.
The technical scheme of the invention is further improved as follows: in the step 1), the projection picture in the coordinate space is taken as an image before transformation, the projection image in the projection coordinate space is taken as an image after transformation, in the step 2), the original image in the image coordinate space is taken as an image before transformation, and the point set of the ideal area in the screen space is taken as an image after transformation, so that the coordinate conversion model obtained in the step 4) has no reverse Bezier curve operation.
The technical scheme of the invention is further improved as follows: in the step 4), the coordinate conversion models obtained in the step 2) and the step 1) are fused into one-step Bessel surface transformation.
The technical scheme of the invention is further improved as follows: in the step 3), when local geometric pre-distortion is performed on the pixel region corresponding to the image, four edges of the region are fixed through the control points.
Due to the adoption of the technical scheme, the invention has the technical progress that:
the invention provides a projection image geometric correction method based on a Bezier curve, which comprises the steps of 1) shooting a projection picture in a coordinate space as an image before transformation, projecting a projection image in the coordinate space as an image after transformation, and in step 2), taking an original image in the image coordinate space as an image before transformation and taking a point set of an ideal area in a screen space as an image after transformation, so that a coordinate conversion model obtained in step 4) has no reverse Bezier curve operation, thereby reducing the complexity of a mathematical expression.
The invention provides a projection image geometric correction method based on a Bezier curved surface, wherein in the step 4), the coordinate conversion models obtained in the step 2) and the step 1) are fused into one step of Bezier curved surface transformation, so that edge sawteeth after image distortion are reduced.
According to the projection image geometric correction method based on the Bessel curved surface, provided by the invention, in the step 3), when local geometric pre-distortion is carried out on a pixel region corresponding to an image, the continuity and the integrity of the whole image are ensured by fixing four edges of the region through control points.
Drawings
FIG. 1 is an overall flow chart of a projection image geometric correction method based on a Bezier curved surface provided by the invention;
FIG. 2 is an original image before projection provided by the present invention;
FIG. 3 is a two-channel projection display image without geometric correction provided by the present invention;
FIG. 4 is a two-channel projection display image after geometric correction as provided by the present invention;
FIG. 5 is a two-channel projection display image after geometric error compensation provided by the present invention;
FIG. 6 is an effect diagram of the CAVE immersive system provided by the present invention.
Detailed Description
The invention is described in further detail below with reference to the following figures and examples:
the invention relates to a projection image geometric correction method based on a Bezier curved surface, which adopts a Bezier curved surface model to establish the conversion relation of different coordinate space characteristic points and carries out error compensation on a region with larger pixel offset by an image local Bezier curved surface warping algorithm.
As shown in fig. 1 to 5, the device comprises the steps of 1) collecting distorted projection pictures without geometric correction by a camera, and establishing a coordinate conversion model of a projection coordinate space and a camera coordinate space by a bicubic bezier surface;
step 2) making uniform marking points in an ideal area of a screen space and carrying out geometric correction;
step 3) local geometric pre-distortion is carried out on the detected screen space pixel offset area;
and 4) carrying out Bezier curved surface pre-distortion on the original image by the coordinate conversion model obtained in the step 4), eliminating the overall geometric distortion of the projection picture and finishing geometric correction.
In the embodiment provided by the invention, the projection picture in the image coordinate space is taken as an image before transformation in the step 1), the projection image in the projection coordinate space is taken as an image after transformation, in the step 2), the original image in the image coordinate space is taken as an image before transformation, the point set of the ideal area in the screen space is taken as an image after transformation, so that the coordinate transformation model obtained in the step 4) has no reverse Bessel surface operation, the complexity of the mathematical expression is reduced, the algorithm is simplified, and the error rate is reduced.
Further, in the step 4), the coordinate conversion models obtained in the step 2) and the step 1) are fused into one-step Bessel surface transformation, so that edge sawteeth after image distortion are reduced, and the picture adjustment step is simpler and more convenient.
Further, in step 3), when local geometric pre-distortion is performed on the pixel region corresponding to the image, the four edges of the region are fixed by the control points to ensure the continuity and integrity of the whole image and improve the adjustment efficiency.
Specifically, in the embodiment provided by the present invention, the method for geometrically correcting a projection image based on a bezier surface disclosed by the present invention provides a method for recognizing an image by using OpenCV on a Windows operating system of a CAVE immersion system shown in fig. 6, and distorting the image by using OpenGL, and the specific implementation manner includes the following steps: step 1) projecting regular rectangular chessboard grids serving as original images of a projection coordinate space to a projection screen, collecting projection chessboard grid images on the projection screen to a shooting coordinate space by a camera, taking grid corner points as feature points, and establishing a matching relation between the projection coordinate space and corresponding feature points of the shooting coordinate space through a bicubic Bessel curved surface, wherein the following formula is shown:
PP＝C(PC)·pC→P
wherein, PCThe coordinate set of the camera shooting space characteristic points is obtained; c (P)C) A Bessel basis function set which is a coordinate of the shooting space characteristic point; p is a radical ofC→PConverting the camera space into a control point coordinate set of a projection space; pPA coordinate set of projection space characteristic points is obtained;
step 2) uniform marking points are made in an ideal area of a screen space, so that a computer can identify the marking points in a picture after the camera collects the marking points, and a coordinate conversion model of an image coordinate space and a camera coordinate space is established through a bicubic Bessel curved surface, wherein the following formula is shown:
PCS＝C(PI)·pI→C
wherein, PIA point coordinate set which is uniformly distributed in an image space; c (P)I) A Bessel basis function set of point coordinates which are uniformly distributed in an image space; p is a radical ofI→CConverting the image space into a control point coordinate set of an ideal area in a shooting space; pCSA coordinate set of points uniformly distributed in an ideal area in a shooting space;
carrying out Bessel surface pre-distortion on the original image through the coordinate conversion model obtained in the steps 1) and 2), eliminating the overall geometric distortion of the projection picture, and completing geometric correction, as shown in the following formula:
PA＝C(C(PB)·pI→C)·pC→P
wherein, PBSets of coordinate values, P, for all points of the original image before geometric pre-warpingASets of coordinate values for all points after geometric pre-warping of the original image.
The image has edge sawtooth after each pre-distortion, so that the edge sawtooth can be reduced by fusing two steps of Bessel surface distortion transformation into one step, and the obtained P is usedABack calculation control point pI→P(i.e., the set of control point coordinates that the image space is transformed into projection space) as shown by:
PA＝C(PB)·pI→P
by pI→PPerforming geometric pre-distortion on an original image;
step 3), random errors can occur when marking is inevitably performed in step 2), and system errors can also be caused by the projection environment, the shooting angle of the camera and the self characteristics of the mark points, so that after the geometric correction is completed, the offset area of the pixel points in the screen space needs to be detected, and the coordinate space conversion relation between the distortion area in the projection screen space and the area corresponding to the original image is shown as the following formula:
PS′＝CI′·pS→I
wherein, CI' Bessel basis function set, P, as coordinates of corresponding region of original imageSIs distortion in the screen spaceSet of coordinates of the region, pS→IAnd converting the distorted area of the projection screen space into a coordinate control point set of the corresponding area of the original image. Due to bicubic Bessel surface distortion, pS→IThere are 16 control points, wherein 12 control points on four sides of the region are constants to fix the region contour to ensure the continuity and integrity of the whole image, and the other 4 control points are used for pre-distorting the inside of the corresponding region of the original image to realize geometric error compensation;
step 4), performing local geometric pre-distortion on the pixel region corresponding to the image to reduce the pixel offset of the projection picture before performing overall geometric pre-distortion on the original image through the pixel offset region in the screen space detected in the step 3), as shown in the following formula:
wherein, P0The coordinate value set P of all the points before geometric pre-distortion outside the corresponding region of the original image KkThe coordinate value set of all points before geometric pre-distortion of the corresponding area at the kth position of the original image is represented by K which is more than or equal to 1 and less than or equal to K and PTSets of coordinate values for all points after geometric pre-warping of the original image. The invention provides a projection image geometric correction method based on a Bezier curve, which provides a scheme for compensating geometric errors of a pre-distorted original image by an image local Bezier curve distortion algorithm aiming at the problem of larger errors of a projection image geometric correction result fed back by a camera. Firstly, by solving the characteristic points of an original image of a projection space and a projection image of a shooting space, the corresponding relation between the projection space and the shooting space is deduced by utilizing a Bessel surface algorithm; secondly, deducing a corresponding relation of an ideal region of a shooting space and a feature point of an image space by utilizing a Bessel surface algorithm; pre-distorting the original image in the projection space through the two-step corresponding relation; and finally, measuring the error of the pre-distorted image projected to the projection screen, and performing geometric error compensation on the pre-distorted original image by using an image local Bessel curved surface distortion algorithm to reduce the error. The method of the invention is simple, the operation is easy,and additional technical equipment is not needed, so that the maintenance and the use of technicians are facilitated.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are intended to be within the scope of the invention.
Claims (4)
1. A projection image geometric correction method based on Bessel curved surface is characterized in that: the method comprises the following steps:
step 1) acquiring a distorted projection picture without geometric correction by using a camera, and establishing a coordinate conversion model of a projection coordinate space and a camera coordinate space by using a bicubic Bessel curved surface;
step 2) making uniform marking points in an ideal area of a screen space and carrying out geometric correction;
step 3) local geometric pre-distortion is carried out on the detected screen space pixel offset area;
and 4) carrying out Bezier curved surface pre-distortion on the original image by the coordinate conversion model obtained in the step 4), eliminating the overall geometric distortion of the projection picture and finishing geometric correction.
2. The Bezier surface-based projection image geometric correction method according to claim 1, characterized in that: in the step 1), the projection picture in the coordinate space is taken as an image before transformation, the projection image in the projection coordinate space is taken as an image after transformation, in the step 2), the original image in the image coordinate space is taken as an image before transformation, and the point set of the ideal area in the screen space is taken as an image after transformation, so that the coordinate conversion model obtained in the step 4) has no reverse Bezier curve operation.
3. The Bezier surface-based projection image geometric correction method according to claim 1, characterized in that: in the step 4), the coordinate conversion models obtained in the step 2) and the step 1) are fused into one-step Bessel surface transformation.
4. The Bezier surface-based projection image geometric correction method according to claim 1, characterized in that: in the step 3), when local geometric pre-distortion is performed on the pixel region corresponding to the image, four edges of the region are fixed through the control points.
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