CN1188660C - Camera calibrating method and its implementing apparatus - Google Patents
Camera calibrating method and its implementing apparatus Download PDFInfo
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- CN1188660C CN1188660C CNB031096492A CN03109649A CN1188660C CN 1188660 C CN1188660 C CN 1188660C CN B031096492 A CNB031096492 A CN B031096492A CN 03109649 A CN03109649 A CN 03109649A CN 1188660 C CN1188660 C CN 1188660C
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- circular hole
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Abstract
The present invention discloses a camera calibrating method and an implementing apparatus thereof and relates to the field of computer vision detection. The present invention solves the problems of calibration range, coordinate origin, nonideal environmental background light, and too small visual field of a camera, or solves the problem that imaging on the space coordinate origin set on the edge of the target is not clear or is outside of the visual field range when an included angle between the travel direction of a target and the light axle of the camera. The present invention has the technical scheme that the present invention adopts a circular target, the radiuses of circular holes for marking of the circular target are 120% to 150% of the radiuses of the rest of circular holes, the position of the camera is determined by a method for space positioning of characteristic points through a method for the noise filtering of images, threshold segmentation, contour tracing, ellipse identification, ellipse fitting and center extraction according to the space positions of the centers of the circular holes for marking and the centers of circular holes which are closest to the circular holes for marking, the distance of the centers of the circular holes for marking and the rest of circular holes, and the movement distance of the circular target which moves along one direction of space. The present invention is suitable for occasions where a camera is calibrated so as to acquire the coincidence relation from space points to the points of the image elements of computer images.
Description
Technical field
The present invention relates to the Computer Vision Detection field, relate in particular in order to obtain spatial point, the occasion that video camera is demarcated to the corresponding relation of computer picture picture element.
Background technology
In the Computer Vision Detection process, in order to obtain the corresponding relation of spatial point to the computer picture picture element, camera calibration is absolutely necessary.Camera calibration is exactly geometry and the optical characteristics that obtains video camera inside, i.e. inner parameter, and camera coordinate system is with respect to the position relation of space coordinates, i.e. external parameter.
The RAC standardization of Tsai is the most commonly used at present, and this method adopts process of iteration to obtain other parameters earlier by the most of parameter that radially collimates the constraint solving camera model then.A step very crucial in the demarcation is exactly the processing of characteristic point data on the target, promptly determines the volume coordinate and the image coordinate of the unique point on the target.The form of Camera calibration target is varied, and wherein target disc is the most frequently used.Because circular insensitive to the threshold value of image, and the unique point coordinate is definite easily, so can be relatively easy to obtain the stated accuracy of sub-pixel.Traditional target disc is an evenly distributed circular hole of the same size on surface plate, and the centre distance between the circular hole is accurately known, and the center of circular hole can be used as unique point.Because special without comparison circular hole is difficult to determine automatically the space coordinates true origin.At timing signal, generally to manually on image, select calibration range and true origin.Have and a kind ofly can realize that the method for automatically demarcating is to set up coordinate system with the circular hole center on a certain edge of target as initial point, but, when environmental background light undesirable, camera field of view is too little, or target moving direction and camera optical axis angle be when big, and the volume coordinate initial point of setting at the target edge is can imaging unintelligible or shift out field range.So this method can't be obtained the object space true origin fully automatically, can not realize real robotization demarcation.
Summary of the invention
For overcoming the deficiencies in the prior art, a kind of speed and automaticity that ccd video camera is demarcated that improve is provided, make more reliable and more stable method of application and true device thereof, the technical solution used in the present invention is:
A kind of camera marking method comprises the following steps:
Adopting the marked circle pore radius is 120% to 150% target disc of all the other circle hole radius, and the mark circular hole is positioned at target disc central authorities;
A certain direction moves target disc along the space;
Noise filtering by image, Threshold Segmentation, profile is followed the tracks of, oval identification, before ellipse fitting and center extracting method are sought in camera field of view and are moved and target disc and the enough a plurality of circular holes that comprise the mark circular hole of target disc epipodium after moving, and find from the near circular hole of marked circle Kongzui, determine that the mark circular hole reaches the locus from the center of circle of the near circular hole of marked circle Kongzui;
According to the marked circle hole circle heart and from the distance of center circle of locus, mark circular hole and all the other circular holes in the center of circle of the near circular hole of marked circle Kongzui and described a certain direction moves the displacement of target disc along the space, employing unique point space-location method is determined the position of video camera.
Be applicable to the target disc of said method, its structure is to make a series of printing opacity array of circular apertures M * N on the light tight sheet glass by lithography, and ranks are strict vertical, and the centre distance of circular hole equates and is known, and the circular hole of target central authorities is that the radius of mark circular hole is 120% to 150% of all the other circle hole radius.
Because the present invention has adopted the target structure of the radius of central circular hole (being called marked circle) greater than all the other circle hole radius, and the noise filtering of image, Threshold Segmentation, profile is followed the tracks of, oval identification, and extract and unique point space orientation step at ellipse fitting and center, in the CCD calibration process, set up space coordinates automatically, and obtain and handle the data of unique point on the target automatically, thereby improve speed and the automaticity that ccd video camera is demarcated, make application more reliable and more stable.
Description of drawings
Fig. 1 is a target disc structural representation of the present invention.
Fig. 2 sets up schematic diagram automatically for space of the present invention 3D coordinate.
Embodiment
Further specify the present invention below in conjunction with drawings and Examples.
Fig. 1 is a target disc of the present invention, and this target disc is to make a series of printing opacity array of circular apertures M * N on light tight sheet glass by lithography, and ranks are strict vertical, and the centre distance of circular hole equates and known (Δ x, Δ y).The radius that is the mark circular hole of target disc central authorities with traditional target difference is greater than all the other circular holes.In calibration process, be initial point O with the mark circular hole center of first position of target disc
w, laterally the straight line at place, the center of circle is X
wAxle, vertically the straight line at place, the center of circle is Y
wAxle is Z with the target disc moving direction
wAxle is set up space coordinates, and coordinate system meets the right-hand rule, as shown in Figure 2.Because the mark circular hole is positioned at target central authorities, so,, must find the mark circular hole and from its nearest circular hole by Flame Image Process and oval identification as long as occur abundant circular hole in the camera field of view.Target disc of the present invention has overcome conventional target target defective, can finish Camera calibration more flexible automatic and exactly.
Automatically demarcate in order to realize video camera, design, used a whole set of image processing algorithm according to target disc characteristics of the present invention: the noise filtering of image, Threshold Segmentation, profile is followed the tracks of, oval identification, ellipse fitting and center extraction and unique point space orientation etc.
Because the histogram of target disc image has apparent in view bimodal, represented printing opacity circular hole and the light tight base plate of black in the target respectively, and the gap of bimodal is bigger, so can directly adopt bimodal method that image is carried out Threshold Segmentation; Adopt the profile tracing then, obtain the marginal point of target; Because through the perspective transform of lens, circle has become ellipse, so we adopt oval similarity recognizer to reject the marginal point of non-ellipse, determines the point of mark circular hole simultaneously; Remaining point is carried out ellipse fitting, extract oval centre coordinate, they are exactly the image coordinate of unique point; Determine the position relation of marked circle hole circle heart coordinate and all the other central coordinate of circle at last, the distance that moves according to target disc in known target disc distance of center circle and the calibration process, set up space coordinates, can be easy to the pairing volume coordinate of unique point on definite image.Stress key algorithm wherein below: oval similarity recognizer.
Though, still have good similarity between the ellipse on the uncalibrated image through perspective transform.A tree name this, we have designed two-step approach and have discerned ellipse target.The first step is preliminary identification of profile and mark ellipse search, and to pick impurity point and non-elliptical point, second step was to utilize similarity accurately to discern ellipse:
1) preliminary identification of profile and mark ellipse search:
Certain bar has the closed outline { (x of N marginal point
i, y
j) | 1≤i≤N}, its institute's area surrounded area is:
From marginal point, search high order end point p
0, low order end point p
1, topmost put p
2, put p bottom
3, wantonly 2 distance is D
I, j, then they between any two half of ultimate range be the circumradius of this profile:
R=max (D
I, j) (i, j=0,1,2,3) (2) when lens distortion is little, circularity index C=S/ (π r
2) value can be very not little.Because the circumradius of ellipse size close with the marginal point number (removing marked circle) in the target image.So the method that can adopt similar image histogram to add up is selected and is demarcated circle.Adding up the circumradius r and the edge number N of all profiles, serves as at interval as histogrammic division with 5 and 20 respectively, count fall into each interval in the number of profile; Find both maximal values respectively, i.e. circumradius histogram peak P
RMaxWith with marginal point number histogram peak P
NMaxThe little one-level of getting both is as threshold value:
Threshold value is deleted the point that meets the following conditions: marginal point number N＜T according to this
nCircumradius r＜T
rCircularity index C＜0.5.In the residue point, search for the marked circle that is of circumradius r maximum.
2) accurately discern based on the oval of similarity:
Through the operation of the first step, the point of having removed most non-ellipse in order to define more accurately with oval point, also will be utilized oval similarity, the similarity between promptly common ellipse and the mark ellipse, further search.According to Hu square unchangeability, promptly identical shape is done translation, rotation back Hu square value remains unchanged, and defines three shape likeness coefficients:
Wherein, A, B are the some set of two elliptic contours;
h
kBe k rank Hu square.When two profiles are identical, I
1=I
2=I
3=0; And the similarity of two profiles is poor more, and the value of three likeness coefficients is just big more.A large amount of experimental results show that likeness coefficient oval in the target image can be deleted I much smaller than 0.001
i＞0.001 point.So far finished the whole process of the oval identification of similarity.
In the experiment, video camera to be calibrated is the MTV-368P of Mintron, and its parameter is: pixel number 500 (H) * 582 (V), and effectively image sensing surface is of a size of 4.9mm * 3.7mm, and minimal illumination is 0.1lux; The nominal focal length f=16mm of optical lens, relative aperture l/F=1.4.Select for use the specification of target disc to be: 11 * 9 circular array, circular hole center distance Δ x=Δ y=15mm, the radius of mark circular hole are respectively 120%, 135% to 150% totally three kinds of all the other circle hole radius.They are placed on respectively on the automatically controlled automatic travelling table, gather a width of cloth target image every Δ z=10mm, gather the image of 5 positions altogether, obtain the coordinate data of individual features point through Flame Image Process, choose the image of 3 positions wherein, adopt the RAC scaling method of Tsai ' s to demarcate, obtained the inner parameter and the external parameter of ccd video camera.Do the calibrated error analysis with the image of other 2 positions, by analysis as can be known calibrated error less than 0.4 pixel.
Claims (2)
1. a gamma camera scaling method is characterized in that, comprises the following steps:
Adopting the marked circle pore radius is 120% to 150% target disc of all the other circle hole radius, and the mark circular hole is positioned at target disc central authorities;
Target disc is to make a series of printing opacity array of circular apertures M * N on light tight sheet glass by lithography, and ranks are strict vertical, and the centre distance of circular hole equates and is known;
A certain direction moves target disc along the space;
Noise filtering by image, Threshold Segmentation, profile is followed the tracks of, oval identification, before ellipse fitting and center extracting method are sought in the gamma camera visual field and are moved and target disc and the enough a plurality of circular holes that comprise the mark circular hole of target disc epipodium after moving, and find from the near circular hole of marked circle Kongzui, determine that the mark circular hole reaches the locus from the center of circle of the near circular hole of marked circle Kongzui;
According to the marked circle hole circle heart and from the distance of center circle of locus, mark circular hole and all the other circular holes in the center of circle of the near circular hole of marked circle Kongzui and described a certain direction moves the displacement of target disc along the space, employing unique point space-location method is determined the position of gamma camera.
2. one kind is used for the target disc that gamma camera is demarcated, its structure is to make a series of printing opacity array of circular apertures M * N on the light tight sheet glass by lithography, ranks are strict vertical, the centre distance of circular hole equates and is known, it is characterized in that the circular hole of target central authorities is that the radius of mark circular hole is 120% to 150% of all the other circle hole radius.
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| CN1188660C true CN1188660C (en) | 2005-02-09 |
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Cited By (1)
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| CN100462668C (en) * | 2005-09-07 | 2009-02-18 | 北京航空航天大学 | Flexible plane target for vision system scaling |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100462668C (en) * | 2005-09-07 | 2009-02-18 | 北京航空航天大学 | Flexible plane target for vision system scaling |
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