CN110940294B - Image coding and decoding method in surface structured light measurement system - Google Patents

Image coding and decoding method in surface structured light measurement system Download PDF

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CN110940294B
CN110940294B CN201911155686.0A CN201911155686A CN110940294B CN 110940294 B CN110940294 B CN 110940294B CN 201911155686 A CN201911155686 A CN 201911155686A CN 110940294 B CN110940294 B CN 110940294B
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李晨
张旭
赵欢
丁汉
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Huazhong University of Science and Technology
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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
    • G01B11/254—Projection of a pattern, viewing through a pattern, e.g. moiré
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Abstract

The invention belongs to the field of optical measurement and discloses a method for encoding and decoding an image in a surface structured light measurement system. The method comprises the following steps: (a) for a surface structured light measurement system, setting each parameter value of a projector, establishing a relational expression of winding phase shift coordinates and phase shift of each point in a projection image of the projector, and projecting by the projector by combining the set parameter value and the relational expression so as to realize image coding and obtain a plurality of phase shift images; (b) the camera shoots the phase shift image to obtain a plurality of shot images, and a relational expression is established to calculate and obtain the winding phase shift and the winding phase corresponding to each point in the shot images; (c) and obtaining the pixel coordinate of each point by using the wrapping phase shift and the wrapping phase of each point in the shot image, thereby realizing the decoding of the image. According to the invention, the propagation of the phase shift error to the phase inversion error is obviously reduced, and the surface structured light measurement system is improved to improve the phase shift decoding precision, thereby improving the three-dimensional measurement precision.

Description

Image coding and decoding method in surface structured light measurement system
Technical Field
The invention belongs to the field of optical measurement, and particularly relates to a method for encoding and decoding an image in a surface structured light measurement system.
Background
For the study of phase measurement profilometers, the documents "Zhang, x., Li, c., Zhang, q., and Tu, D, Optics & Laser Technology,108, 69-80" studied phase measurement profilometry, the documents "Li, c., Zhang, x., and Tu, D, Optical Engineering,57(3), 034103" studied phase measurement deviators, etc. Optical metrology plays an increasingly important role in modern manufacturing. The phase shift technology is a very key technology, and is a bridge for connecting information of a measured object and a sensor. The phase inversion accuracy is used as the basis of error propagation and directly influences the measurement accuracy of the system. Conventional phase encoding methods, such as "Zhang, x., Zhu, L., Tu, d., & Fan, L, Chinese Journal of Lasers,39(11), 1108009-6", generally reduce phase retrieval errors by increasing phase shift step size, temporal phase unwrapping, or fourier phase unwrapping techniques. These methods have no significant effect on reducing phase retrieval errors because the light intensity error is suppressed to the phase recovery error only by one layer of suppressor.
Disclosure of Invention
In view of the above drawbacks or needs for improvement in the prior art, the present invention provides a method for encoding and decoding an image in a surface structured light measurement system, which sets an image by constructing an expression of a winding phase shift coordinate and a phase shift, so as to encode a projected image by a projector, and then decodes a captured image by constructing an expression of a winding phase shift coordinate and a phase shift for an image captured by a camera, so as to implement a decoding process of the image, and improve the surface structured light measurement system to improve the phase shift decoding accuracy, thereby improving the three-dimensional measurement accuracy.
To achieve the above object, according to the present invention, there is provided a method for encoding and decoding an image in a surface structured light measurement system, the method comprising the steps of:
(a) for the surface structure light measurement system, setting various parameter values of a projector, wherein the parameter values comprise the number, the average brightness and the amplitude of phase shift images and the number and the amplitude of winding phase shift images, establishing a relational expression (I) of winding phase shift coordinates of each point in a projection image of the projector relative to the amplitude, the number and the coordinates of the winding phase shift images and a relational expression (II) of phase shift coordinates of each point relative to the number, the average brightness and the amplitude of the phase shift images, and projecting by the projector according to the set parameter values and the relational expressions (I) and (II) so as to realize the coding of the images and obtain a plurality of phase shift images;
(b) the camera shoots the phase shift image to obtain a plurality of shot images, relational expressions (three) and (four) of winding phase shift coordinates and winding phases in the shot images are established by utilizing the phase shift of the phase shift image, and the winding phase shift and the winding phase corresponding to each point in the shot images are obtained through calculation according to the relational expressions (three) and (four);
(c) and (c) obtaining the pixel coordinate of each point according to the wrapping phase shift and the wrapping phase of each point in the shot image obtained in the step (b), thereby realizing the decoding of the image.
Further preferably, in step (a), the relation (one) is preferably performed according to the following expression:
Figure BDA0002284739260000021
wherein, In'(x, y) is the wrapped phase-shift coordinate for point (x, y), B '(x, y) is the amplitude of the wrapped phase-shift image for point (x, y), Φ' (x, y) is the wrapped phase for point (x, y), N 'is the number of wrapped phase-shift images, N' is 1, 2.
Further preferably, in step (a), the relation (two) is preferably performed according to the following expression:
Figure BDA0002284739260000022
wherein, In(x, y) is the phase shift corresponding to point (x, y), a (x, y) is the average luminance of the point (x, y) phase shifted image, B (x, y) is the amplitude of the point (x, y) phase shifted image, N is the number of phase shifted images, N is 1,2n'(x, y) is the wrap phase shift coordinate corresponding to point (x, y).
Further preferably, in step (b), the relation (iii) is preferably performed according to the following expression:
Figure BDA0002284739260000031
wherein the content of the first and second substances,
Figure BDA0002284739260000032
is the wrapped phase shift coordinate, I, of a point (x, y) on the captured imagen(x, y) is the phase shift corresponding to point (x, y).
Further preferably, in step (b), the relation (iv) is preferably performed according to the following expression:
Figure BDA0002284739260000033
where φ (x, y) is the wrap-around phase of a point (x, y) on the captured image, In'(x, y) is the wrap phase shift coordinate corresponding to point (x, y).
Further preferably, in the step (a), the phase shift image is a fringe image with different brightness.
Further preferably, the standard deviation σ of the wrapped phase of the captured imageφ*It is preferable to proceed according to the following expression,
Figure BDA0002284739260000034
a standard deviation σ of the wrapped phase shift coordinates of the taken imageI*Preferably according to the following expression:
Figure BDA0002284739260000035
wherein σIIs the standard deviation of the luminance error of the phase shifted image.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
1. the invention provides an image phase nested encoding and decoding method, which is characterized in that two layers of error suppressors are designed, the phase shift from image phase shifting to winding phase shifting is first layer error suppression, the phase shift from winding phase shifting to winding phase shifting is second layer error suppression, the propagation of image noise errors to decoding phase is greatly suppressed, and the method can be used for improving the phase shift decoding precision of a surface structure optical measurement system so as to improve the three-dimensional measurement precision. According to theoretical calculation, under the condition of adopting the same number of phase shift pictures, the precision of the nested phase shift coding method is the precision of the traditional phase shift coding method
Figure BDA0002284739260000041
Doubling;
2. the invention sets two layers of phase shift images and winding phase shift images, the two layers encode images projected by a projector, the two layers of structures are simultaneously used as error suppressors, errors in the decoding process can be effectively suppressed, and under the condition that the error level of an image source is the same and the number of images is the same, the phase precision of the method is more than twice of that of the traditional phase encoding method.
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Fig. 1 is a schematic diagram of an image encoding and decoding method in a surface structured light measurement system constructed according to a preferred embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, a method for encoding and decoding an image in a surface structured light measurement system includes the following steps:
s101, initializing setting of parameters, and accordingly coding the brightness of each point under the imaging pixel coordinate of the projector, specifically: setting a phase shiftIs composed of
Figure BDA0002284739260000042
The number of phase nested encoding steps is N-N', and the phase shift between two images is
Figure BDA0002284739260000051
Wrap-around phase shift I of the phase phi (x, y) nested encoding of N-N' stepsn'(x, y), phase shift In(x,y)；
According to the embodiment of the invention, it is set that one winding phase shift image is converted into 4 phase shift images; as shown in fig. 1, the coordinates of the points are first converted into a wrapping phase, then the wrapping phase is converted into a wrapping phase shift image, and then the wrapping phase shift image is converted into a phase shift image, so as to realize the encoding process of the projector image and obtain a plurality of phase shift images, wherein the phase shift image is the first layer and the wrapping phase shift image is the second layer.
In the encoding process, the winding phase shift coordinates are set according to the following expression:
Figure BDA0002284739260000052
wherein, In'(x, y) is the phase shift coordinates of the convolution corresponding to point (x, y), B ' (x, y) is the amplitude of the convolution phase-shifted image corresponding to point (x, y), typically chosen as pi or-pi, (x, y) is the phase of the convolution for point (x, y), N ' is the number of convolution phase-shifted images, N ' is the total number of phase-shifted images, x is the abscissa of point (x, y), and y is the ordinate of point (x, y).
The phase shift is set according to the following expression:
Figure BDA0002284739260000053
wherein, In(x, y) is the phase shift corresponding to point (x, y), a (x, y) is the average luminance of the point (x, y) phase shifted image, B (x, y) is the amplitude of the point (x, y) phase shifted image, N is the number of phase shifted images, N is 1,2Total amount of (2), In'(x, y) is the wrap phase shift coordinate corresponding to point (x, y).
S102, shooting the image transmitted on the surface of the object by the projector through the camera to obtain a shot image, decoding the shot image, and calculating the winding phase shift through decoding
Figure BDA0002284739260000054
And winding phase coordinates phi (x, y);
Figure BDA0002284739260000055
Figure BDA0002284739260000061
wherein the content of the first and second substances,
Figure BDA0002284739260000062
is the wrapped phase shift coordinate, I, of a point (x, y) on the captured imagen(x, y) is the phase shift corresponding to point (x, y), φ (x, y) is the wrap-around phase of point (x, y) on the captured image, In'(x, y) is the wrap phase shift coordinate corresponding to point (x, y).
S103, obtaining the pixel coordinate of each point according to the wrapping phase shift and the wrapping phase of each point in the captured image, so as to implement decoding of the image, wherein the process of obtaining the pixel coordinate of each point through the wrapping phase shift and the wrapping phase of each point adopts the existing conventional method, for example: the multi-frequency heterodyne method, the robust chinese remainder theorem, the dual-frequency heterodyne method, etc., will not be described herein again.
Theoretical calculation the precision of the nested phase shift coding method is that of the traditional phase shift coding method under the condition of adopting the same number of phase shift pictures
Figure BDA0002284739260000063
The amount of the solvent to be used is, in particular,
phase shift InThe relationship between the error of (c) and the error of the phase phi is expressed by the error propagation principle, so that the standard deviation sigma of the phase shiftI*And phase standard deviation sigmaφ*Is expressed as
Figure BDA0002284739260000064
Figure BDA0002284739260000065
σIIs the standard deviation of the luminance error of the phase shifted image. B is the abbreviation of B (x, y), B ' is the abbreviation of B ' (x, y), when B ' is chosen as pi or-pi, the wrap-around phase decoding precision of the phase nested encoding method is the one of the traditional phase shift encoding method
Figure BDA0002284739260000066
And (4) doubling.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (2)

1. A method for encoding and decoding images in a surface structured light measurement system is characterized by comprising the following steps:
(a) for the surface structure light measurement system, setting various parameter values of a projector, wherein the parameter values comprise the number, the average brightness and the amplitude of phase shift images and the number and the amplitude of winding phase shift images, establishing a relational expression (I) of winding phase shift coordinates of each point in a projection image of the projector relative to the amplitude, the number and the coordinates of the winding phase shift images and a relational expression (II) of phase shift coordinates of each point relative to the number, the average brightness and the amplitude of the phase shift images, and projecting by the projector according to the set parameter values and the relational expressions (I) and (II) so as to realize the coding of the images and obtain a plurality of phase shift images;
(b) the camera shoots the phase shift image to obtain a plurality of shot images, relational expressions (three) and (four) of winding phase shift coordinates and winding phases in the shot images are established by utilizing the phase shift of the phase shift image, and the winding phase shift and the winding phase corresponding to each point in the shot images are obtained through calculation according to the relational expressions (three) and (four);
(c) obtaining the pixel coordinates of each point according to the wrapping phase shift and the wrapping phase of each point in the shot image obtained in the step (b), thereby realizing the decoding of the image;
in step (a), the relation (one) is performed according to the following expression:
Figure FDA0002779651600000011
wherein, In'(x, y) is the wrapped phase-shift coordinate for point (x, y), B '(x, y) is the amplitude of the wrapped phase-shift image for point (x, y), Φ' (x, y) is the wrapped phase for point (x, y), N 'is the number of wrapped phase-shift images, N' is 1, 2.
In step (a), the relation (ii) is performed according to the following expression:
Figure FDA0002779651600000012
wherein, In(x, y) is the phase shift corresponding to point (x, y), a (x, y) is the average luminance of the point (x, y) phase shifted image, B (x, y) is the amplitude of the point (x, y) phase shifted image, N is the number of phase shifted images, N is 1,2n'(x, y) is the wrap phase shift coordinate corresponding to point (x, y);
in the step (b), the relation (iii) is performed according to the following expression:
Figure FDA0002779651600000021
wherein the content of the first and second substances,
Figure FDA0002779651600000022
is a wrap-around phase shift coordinate, I, obtained by decoding a point (x, y) on the captured phase-shifted imagen(x, y) is the phase shift corresponding to point (x, y);
in the step (b), the relational expression (iv) is performed according to the following expression:
Figure FDA0002779651600000023
where φ (x, y) is the wrap-around phase of a point (x, y) on the captured image, In'(x, y) is the wrap phase shift coordinate corresponding to point (x, y).
2. The method according to claim 1, wherein in step (a), the phase-shifted image is a fringe image with different brightness.
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