CN104123725B - A kind of computational methods of single line array camera homography matrix H - Google Patents

Abstract

A kind of computational methods of single line array camera homography matrix H, the method uses Cross ration invariability principle, and the 4 lines scaling boards that the present invention is provided, 4 lines to meet following rule：,,,, with reference to line-scan digital camera imaging characteristicses, (x, y, the z) coordinate on D4 lines can be calculated with Cross ration invariability, and then calculate homography matrix H according to the double ratio of conllinear 4 points of image plane.

Description

A kind of computational methods of single line array camera homography matrix H

Technical field

The invention belongs to camera calibration neighborhood, it is related to single line array camera impact point to the meter of the homography matrix H of imaging point Calculation method.

Background technology

The demarcation of video camera be to determine the three-dimensional geometry position of space object surface point with its in the picture corresponding points it Between correlation.It is the geometrical model according to the video camera imaging set up, is sat by the image coordinate and the world of known features point Mark solves the parameter model of video camera.Camera calibration is unusual the key link, the precision of its calibration result and algorithm it is steady It is qualitative to directly affect the accuracy that camera operation produces result.Therefore, it is camera calibration to improve camera calibration precision Emphasis.

A wherein important step is exactly homography matrix H of the impact point to imaging point.Homography matrix H is obtained, is just needed It is to be understood that coordinate of ground point and imaging point coordinates.Method therefor obtains this two kinds of coordinates of point using scaling board.It is common at present Punctuate plate has chessboard calibration plate, circular scaling board and equidistant striped scaling board.Chessboard calibration plate can very easily obtain target The coordinate of point, such as will obtain accurate imaging point coordinates, it is necessary to do relative uniform motion between single line array camera and scaling board, this is just System complexity is caused to increase.With circular scaling board, if doing relative uniform motion between single line array camera and scaling board Speed setting is bad, and the circle of the imaging plane for obtaining will deform, it is impossible to effectively calculate the center of circle, so cannot obtain accurately into Picpointed coordinate.Equidistant striped scaling board can quickly obtain the x-axis or the value of y-axis of impact point and imaging point, but cannot obtain The value of another reference axis.

To sum up, existing single line array camera impact point, to the computational methods of the homography matrix H of imaging point, is also present at present Some shortcomings：Relative uniform motion is done between single line array camera and scaling board, speed setting is difficult.Phase is done between camera and scaling board To non-uniform movement, it is impossible to calculate homography matrix H.

The content of the invention

It is an object of the invention to provide a kind of computational methods of single line array camera homography matrix H, to reach camera and mark Relative non-uniform movement is done between fixed board, it is also possible to calculate single line array camera homography matrix H.

To achieve the above object, the computational methods of single line array camera homography matrix H of the invention, the method is using special 4 line scaling boards, using the imaging characteristicses and conllinear 4 points of Cross ration invariability of single line array camera, calculating single line array camera list should Property matrix H.The step of the method, is as follows：

（1）The lines in single line array camera image are extracted with Hough operation methods, in the lines in a capture plane A line, this journey is intersected with 4 lines in the image of the 4 lines scaling boards for photographing, and takes intersection point for a, b, c and d；

（2）Ask for the double ratio of imaging point a, b, c and d。

（3）The double ratio of imaging point a, b, c impact point A, B, C and D corresponding with d is obtained using Cross ration invariability, and then calculate D points（X, y, z）Coordinate.

（4）D points and D points are imaged point coordinates accordingly and substitute into impact point to the homography matrix H formula of imaging point, can counted Calculate corresponding H-matrix.

Described step（1）In 4 lines scaling boards, 4 lines meet following rule：,,,,For that can set certainly according to demand.

The step（2）The double ratio of four points a, b, c and d is on cathetus, ac is a and c two Distance between point.Bc, ad and bd are similarly.

The step（3）Middle Cross ration invariability is

The step（3）Middle calculating D points（X, y, z）The step of coordinate, is as follows：

（1）, it is considered to a dummy line D5, it and D1, D2, D3 parallel co-planar, D1, D2, D3 and by D points D5 this four Parallel lines are A', B', C' and D' with y-axis intersection point.There are Cross ration invariability, Wo Menyou

Therefore,

（2）A, B, C and D can be obtained on four calibration lines of scaling board

Can further obtain：

Because 4 calibration lines of scaling board are coplanar, it is in the z coordinate of this target board space coordinate, being can according to demand certainly Setting, can obtain D points（X, y, z）Coordinate.

The step（4）The step of middle calculating homography matrix H, is as follows：

（1）By common line-scan digital camera homography formula

Derive outlet list array camera homography formula

It is scale parameter；

Therefore homography matrix H is

（2）By common line-scan digital camera homography formula, according to impact point D（X, y, z）With corresponding imaging point coordinates d（u）, Zero coordinate points of imager coordinate are the summit in da directions, can calculate homography matrix H.The beneficial effects of the invention are as follows：This hair The computational methods of bright single line array camera homography matrix H, using 4 special line scaling boards, using the imaging of single line array camera Feature and conllinear 4 points of Cross ration invariability, calculate single line array camera homography matrix H, solve single line array camera and scaling board Between make non-uniform movement and cannot calculate the problem of homography matrix H.This method simple system, restrictive condition is few, for single line Array camera demarcate application is significant and practical value.

Brief description of the drawings

Fig. 1 is the inventive method schematic flow sheet；

Fig. 2 is single line array camera imaging schematic diagram；

In Fig. 2, F is the focus of line-scan digital camera.A, b, c, d are picture point, and A, B, C, D are picture point a, b, c, d are corresponding Impact point.A', B', C' and D' are the value of A, B, C, D in y-axis.D1, D2, D3, D4 are 4 coplanar calibration lines, dummy line D5 Cross the line of D points and D1, D2, D3 parallel co-planar.

Specific embodiment

Embodiments of the present invention are carried out in detail by technical scheme for a better understanding of the present invention below in conjunction with the accompanying drawings Explanation.

As shown in figure 1, the present invention carries out the straight line during Hough computings obtain image to gained image first, target is chosen Point calculates double ratio.According to the characteristics of single line array camera imaging system, the double ratio of impact point is obtained with reference to Cross ration invariability.Using mark The equation of calibration line in fixed board, tries to achieve the coordinate of D points.

Specific implementation of the invention is as follows：

1. with Hough operation methods extract single line array camera to image in lines, a line in capture plane, this Row gives the 4 lines scaling boards for photographing（4 line meets following rule：,,,,For that can set certainly according to demand）Image in 4 lines, take intersection point for a, b, c and d；

2. with the double ratio of imaging point a, b, c and d

, ac is a and c distance between two points.Bc, ad and bd are similarly.

3. the double ratio of imaging point a, b, c impact point A, B, C and D corresponding with d is obtained using Cross ration invariability, And then calculate D points（X, y, z）Coordinate.

Step 1：Obtained using Cross ration invariability

Step 2：As shown in Figure 2, it is considered to a dummy line D5, it and D1, D2, D3 parallel co-planar, D1, D2, D3 and by D This four parallel lines of point D5 are A', B', C' and D with y-axis intersection point '.By Cross ration invariability, Wo Menyou

Therefore,

Step 3：A, B, C and D can be obtained on four calibration lines of scaling board

Can further obtain：

Step 4：Because 4 calibration lines of scaling board are coplanar, it is in the z coordinate of this target board space coordinate, being can basis Demand can obtain D points from setting（X, y, z）Coordinate.

4. impact point can calculate corresponding H-matrix to the homography matrix H formula of imaging point

Described step（1）In 4 lines scaling boards, 4 lines meet following rule：,,,,For that can set certainly according to demand.

Step 1：By common line-scan digital camera homography formula

Derive outlet list array camera homography formula

It is scale parameter；

Therefore homography matrix H is

Step 2：By common line-scan digital camera homography formula, according to impact point（X, y, z）With corresponding imaging point coordinates d （u）, zero coordinate points of imager coordinate are the summit in da directions, can calculate homography matrix H.

In order to verify effectiveness of the invention, line-scan digital camera model DALSA Piranha Series Ps 2-2x- is used 04K30, resolution ratio is 1 × 4096, and pixel dimension is 7 μm.The lines parameter of scaling board 4Mm, demarcates board space z-axis coordinate It is zero.

It should be noted last that, the above embodiments are merely illustrative of the technical solutions of the present invention and it is unrestricted.Although real Example is applied to be described in detail the present invention, it will be understood by those within the art that, technical scheme is entered Row modification or equivalent, without departure from the spirit and scope of technical solution of the present invention, it all should cover in power of the invention In the middle of sharp claimed range.

Claims (4)

1. a kind of computational methods of single line array camera homography matrix H, it is characterised in that：The step of the method, is as follows：

(1) lines in single line array camera image are extracted with Hough operation methods, in a capture plane in lines one OK, this journey is intersected with 4 lines in the image of the 4 lines scaling boards for photographing, takes intersection point for a, b, c and d；4 lines scaling boards, 4 Bar line meets following rule：D1:Y=0, D2:Y=α, D3:Y=2 α, D4:Y=x+3 α, α are can according to demand from setting；

(2) double ratio CR (a, the b of imaging point a, b, c and d are asked for；c,d)；

(3) double ratio CR (A, the B of imaging point a, b, c impact point A, B, C and D corresponding with d are obtained using Cross ration invariability；C, D), And then calculate D point (x, y, z) coordinate；

Wherein, the calculation procedure of D points (x, y, z) coordinate is as follows：

Step one, a dummy line D5, it and D1, D2, D3 parallel co-planar, D1, D2, D3 and by this four parallel lines of D points D5 It is A', B', C' and D with y-axis intersection point ', there is Cross ration invariability, there are CR (A, B；C, D)=CR (A', B'；C',D')；

Step 2, A, B, C and D can be obtained on four calibration lines of scaling board

$r=\frac{2\mathrm{\α}}{\mathrm{\α}}/\frac{x+3\mathrm{\α}}{x+2\mathrm{\α}}=2/\frac{x+3\mathrm{\α}}{x+2\mathrm{\α}}$

Can further obtain：

$x=\frac{\mathrm{\α}(4-3r)}{r-2}$

$y=\frac{\mathrm{\α}(4-3r)}{r-2}+3\mathrm{\α}$

It is β in the z coordinate of this target board space coordinate because 4 calibration lines of scaling board are coplanar, is to set certainly according to demand, D point (x, y, z) coordinate can be obtained；

(4) D points and D points are imaged point coordinates accordingly and substitute into impact point to the homography matrix H formula of imaging point, can calculated Corresponding H-matrix.

2. computational methods of a kind of single line array camera homography matrix H according to claim 1, it is characterised in that：It is described The double ratio of four points a, b, c and d is on step (2) cathetus

Ac is a and c distance between two points, and bc is b and c distance between two points, ad is the distance between 2 points of a and d, and bd is b and d 2 points of distances between this.

3. computational methods of a kind of single line array camera homography matrix H according to claim 1, it is characterised in that：It is described Cross ration invariability is CR (A, B in step (3)；C, D)=CR (a, b；c,d).

4. computational methods of a kind of single line array camera homography matrix H according to claim 1, it is characterised in that：It is described The step of homography matrix H is calculated in step (4) is as follows：

Step one, by common line-scan digital camera homography formula

$s\left[\begin{array}{c}u\\ v\\ 1\end{array}\right]=\left[\begin{array}{cccc}{h}_{11}& h_{21}& h_{31}& h_{41}\\ h_{12}& h_{22}& h_{32}& h_{42}\\ h_{13}& h_{23}& h_{33}& h_{43}\end{array}\right]\left[\begin{array}{c}x\\ y\\ z\\ 1\end{array}\right]$

Derive outlet list array camera homography formula

$s\left[\begin{array}{c}u\\ 1\end{array}\right]=\left[\begin{array}{cccc}{h}_{11}& h_{21}& h_{31}& h_{41}\\ h_{13}& h_{23}& h_{33}& h_{43}\end{array}\right]\left[\begin{array}{c}x\\ y\\ z\\ 1\end{array}\right]$

S is scale parameter；

Therefore homography matrix H is

Step 2, by common line-scan digital camera homography formula, according to impact point D (x, y, z) and corresponding imaging point coordinates d (u), Zero coordinate points of imager coordinate are the summit in da directions, can calculate homography matrix H.