CN110940294B - A method for encoding and decoding images in a surface structured light measurement system - Google Patents

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

A method for encoding and decoding images in a surface structured light measurement system

technical field

The invention belongs to the field of optical measurement, and more particularly relates to an image encoding and decoding method in a surface structured light measurement system.

Background technique

For the study of phase measurement profilometry, the literature "Zhang, X., Li, C., Zhang, Q., and Tu, D, Optics & Laser Technology, 108, 69-80" studied the phase measurement profilometry, the literature "Li, C., Zhang, X., and Tu, D, Optical Engineering, 57(3), 034103" studied the phase measurement deviation meter, etc. Optical metrology methods are playing an increasingly important role in modern manufacturing. Among them, the phase shift technology is a very critical technology, it is a bridge connecting the measured object and sensor information. As the basis of error propagation, the phase inversion accuracy directly affects the measurement accuracy of the system. The traditional phase encoding method, such as "Zhang, X., Zhu, L., Tu, D., & Fan, L, Chinese Journal of Lasers, 39(11), 1108009-6", generally by increasing the phase shift step, time Phase unwrapping or Fourier phase unwrapping techniques are used to reduce phase retrieval errors. These methods have little effect on reducing the phase retrieval error, because the light intensity error is only suppressed to the phase recovery error by a layer of suppressor.

SUMMARY OF THE INVENTION

In view of the above defects or improvement requirements of the prior art, the present invention provides an image encoding and decoding method in a surface structured light measurement system, which sets the image by constructing the expression of the winding phase shift coordinates and the phase shift, In this way, the encoding of the projected image by the projector is realized, and then the captured image is decoded by the expression of the winding phase shift coordinates and phase shift constructed from the captured image of the camera, so as to realize the decoding process of the image and improve the measurement of surface structured light. The system improves the phase-shift decoding accuracy so as to improve the three-dimensional measurement accuracy.

In order to achieve the above object, according to the present invention, a method for encoding and decoding images in a surface structured light measurement system is provided, wherein the method comprises the following steps:

(a) For the surface structured light measurement system, set various parameter values of the projector, including the number, average brightness and amplitude of the phase-shifted images, and the number and amplitude of the winding phase-shifted images, to establish the projector projection The relationship between the wrapping phase shift coordinates of each point in the image and the magnitude, number and coordinates of the wrapping phase shift image (1), and the phase shift of each point with respect to the number, average brightness and amplitude of the phase shift image The relational expression (2) of the projector is combined with the set parameter value and relational expressions (1) and (2) to project, thereby realizing the encoding of the image and obtaining a plurality of phase-shifted images;

(b) The camera captures the phase-shifted image to obtain a plurality of captured images, and uses the phase shift of the phase-shifted image to establish a relationship between the winding phase-shift coordinates and the winding phase in the captured image (3 ) and (4), according to the relational expressions (3) and (4), the winding phase shift and the winding phase corresponding to each point in the captured image are obtained by calculating;

(c) Obtaining the pixel coordinates of each point according to the wrapping phase shift and wrapping phase of each point in the captured image obtained in step (b), thereby realizing the decoding of the image.

Further preferably, in step (a), the relational formula (1) is preferably carried out according to the following expression:

Among them, In _' (x, y) is the winding phase shift coordinate corresponding to the point (x, y), B' (x, y) is the amplitude of the winding phase shift image corresponding to the point (x, y), φ'(x,y) is the wrap phase of point (x,y), n' is the number of wrap phase shift images, n'=1,2,...,N', N' is the phase shift image The total number of , where x is the abscissa of the point (x, y), and y is the ordinate of the point (x, y).

Further preferably, in step (a), the relational formula (2) is preferably carried out according to the following expression:

where In (x, y) is the phase shift corresponding to point (x, y), A( _x , y) is the average brightness of the phase-shifted image at point (x, y), and B(x, y) is the point (x, y) x, y) the magnitude of the phase-shifted images, n is the number of phase-shifted images, n=1,2,...,N, N is the total number of phase-shifted images, I _n' (x,y) is the point (x,y) corresponds to the winding phase shift coordinates.

Further preferably, in step (b), the relational formula (3) is preferably carried out according to the following expression:

是拍摄图像上点(x,y)的卷绕相移坐标，I_n(x,y)是点(x,y)对应的相移。in,

is the wrapping phase shift coordinate of point (x, y) on the captured image, and I _n (x, y) is the phase shift corresponding to point (x, y).

Further preferably, in step (b), the relational formula (4) is preferably carried out according to the following expression:

Among them, φ*(x, y) is the winding phase of the point (x, y) on the captured image, and In _' (x, y) is the winding phase shift coordinate corresponding to the point (x, y).

Further preferably, in step (a), the phase shift image is a fringe image with different brightness.

Further preferably, the standard deviation σ _φ* of the wrapping phase of the captured image is preferably performed according to the following expression,

The standard deviation σ _I* of the wrapped phase shift coordinates of the captured image is preferably performed according to the following expression:

where _σI is the standard deviation of the luminance error of the phase-shifted image.

In general, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

倍；1. The present invention proposes a method for image phase nested encoding and decoding. By designing two layers of error suppressors, the first layer of error suppression is the phase shift image to the wrapping phase shift, and the first layer error suppression is the wrapping phase shift to the wrapping phase. The two-layer error suppression greatly suppresses the propagation of image noise errors to the decoding phase, which can be used to improve the surface structured light measurement system, improve the phase shift decoding accuracy, and thus improve the three-dimensional measurement accuracy. According to the theoretical calculation, the accuracy of the nested phase-shift coding method is higher than that of the traditional phase-shift coding method under the condition of using the same number of phase-shifted pictures.

times;

2. The present invention sets two layers of a phase-shift image and a wrap-around phase-shift image, and the two layers encode the image projected by the projector. The two-layer structure acts as an error suppressor at the same time, which can effectively suppress errors in the decoding process. Under the condition of the same image source error level and the same number of images, the phase accuracy of this method is more than twice that of the traditional phase encoding method.

Description of drawings

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 ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

As shown in Figure 1, a method for encoding and decoding images in a surface structured light measurement system includes the following steps:

相位嵌套编码步数为N-N'，两个图像之间的相移为

时，N-N'步的相位φ(x,y)嵌套编码的卷绕相移I_n'(x,y)、相移I_n(x,y)；S101, setting the initialization parameters, so as to realize the encoding of the brightness of each point under the coordinates of the imaging pixel of the projector, specifically: setting the phase shift as

The number of phase nested encoding steps is N-N', and the phase shift between the two images is

When , the phase φ(x, y) of the N-N' step is nested and encoded with the winding phase shift I _n' (x, y) and the phase shift I _n (x, y);

According to the embodiment of the present invention, it is set that one winding phase-shift image is converted into 4 phase-shift images; as shown in FIG. 1 , first, the coordinates of the point are converted into the winding phase, and then the winding phase is converted In order to wrap the phase-shift image, then convert the wrap-phase-shift image into a phase-shift image, so as to realize the encoding process of the projector image, and obtain multiple phase-shift images. Phase-shifted images are the second layer.

During the encoding process, the setting of the winding phase shift coordinates is carried out according to the following expressions:

Among them, In _' (x, y) is the winding phase shift coordinate corresponding to the point (x, y), B' (x, y) is the amplitude of the winding phase shift image corresponding to the point (x, y), Generally selected as π or -π, φ'(x,y) is the winding phase of point (x,y), n' is the number of winding phase shift images, n'=1,2,...,N ', N' is the total number of phase-shifted images, x is the abscissa of point (x, y), y is the ordinate of point (x, y).

The phase shift is set according to the following expression:

where In (x, y) is the phase shift corresponding to point (x, y), A( _x , y) is the average brightness of the phase-shifted image at point (x, y), and B(x, y) is the point (x, y) x, y) the magnitude of the phase-shifted images, n is the number of phase-shifted images, n=1,2,...,N, N is the total number of phase-shifted images, I _n' (x,y) is the point (x,y) corresponds to the winding phase shift coordinates.

和卷绕相位坐标φ*(x,y)；S102 , the camera captures the image transmitted by the projector on the surface of the object, obtains the captured image, decodes the captured image, and decodes and calculates the winding phase shift

and winding phase coordinates φ*(x,y);

是拍摄图像上点(x,y)的卷绕相移坐标，I_n(x,y)是点(x,y)对应的相移，φ*(x,y)是拍摄图像上点(x,y)的卷绕相位，I_n'(x,y)是点(x,y)对应的卷绕相移坐标。in,

is the winding phase shift coordinates of the point (x, y) on the captured image, In (x, y) is the phase shift corresponding to the point (x, y), φ _* (x, y) is the point (x, y) on the captured image , y), and In _' (x, y) is the coordinate of the winding phase shift corresponding to the point (x, y).

S103: Obtain the pixel coordinates of each point according to the wrapping phase shift and wrapping phase of each point in the captured image obtained above, so as to realize the decoding of the image, wherein, obtaining the wrapping phase shift and wrapping phase of each point The process of pixel coordinates of each point can use existing conventional methods, such as: multi-frequency heterodyne method, robust Chinese remainder theorem, dual-frequency heterodyne method, etc., which will not be repeated here.

倍，具体地，Theoretical calculation In the case of using the same number of phase-shifted pictures, the accuracy of the nested phase-shift coding method is higher than that of the traditional phase-shift coding method.

times, specifically,

The relationship between the error of the phase shift In and the error of the phase φ* is expressed by the principle of error propagation, so the relationship between the phase shift standard deviation σ _{I* and} the phase standard deviation σ _φ* is expressed as

倍。σ _I is 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 selected as π or -π, the wrapped phase decoding accuracy of the phase nested coding method is the traditional phase shift encoding method

times.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (2)

1. a method for encoding and decoding an image in a surface structured light measurement system, characterized in that the method comprises the following steps: (a) For the surface structured light measurement system, set various parameter values of the projector, including the number, average brightness and amplitude of the phase-shifted images, and the number and amplitude of the winding phase-shifted images, to establish the projector projection The relationship between the wrapping phase shift coordinates of each point in the image and the magnitude, number and coordinates of the wrapping phase shift image (1), and the phase shift of each point with respect to the number, average brightness and amplitude of the phase shift image The relational expression (2) of the projector is combined with the set parameter value and relational expressions (1) and (2) to project, thereby realizing the encoding of the image and obtaining a plurality of phase-shifted images; (b) The camera captures the phase-shifted image to obtain a plurality of captured images, and uses the phase shift of the phase-shifted image to establish a relationship between the winding phase-shift coordinates and the winding phase in the captured image (3 ) and (4), according to the relational expressions (3) and (4), the winding phase shift and the winding phase corresponding to each point in the captured image are obtained by calculating; (c) obtaining the pixel coordinates of each point according to the wrapping phase shift and wrapping phase of each point in the captured image obtained in step (b), thereby realizing the decoding of the image; In step (a), the relational formula (1) is carried out according to the following expression:

Among them, In _' (x, y) is the winding phase shift coordinate corresponding to the point (x, y), B' (x, y) is the amplitude of the winding phase shift image corresponding to the point (x, y), φ'(x,y) is the wrap phase of point (x,y), n' is the number of wrap phase shift images, n'=1,2,...,N', N' is the phase shift image The total number of , x is the abscissa of the point (x, y), y is the ordinate of the point (x, y); In step (a), the relational formula (2) is carried out according to the following expression:

where In (x, y) is the phase shift corresponding to point (x, y), A( _x , y) is the average brightness of the phase-shifted image at point (x, y), and B(x, y) is the point (x, y) x, y) the magnitude of the phase-shifted images, n is the number of phase-shifted images, n=1,2,...,N, N is the total number of phase-shifted images, I _n' (x,y) is the point (x,y) corresponding winding phase shift coordinates; In step (b), the relational formula (3) is carried out according to the following expression:

in,

is the winding phase shift coordinate obtained by decoding the point (x, y) on the captured phase shift image, and I _n (x, y) is the phase shift corresponding to the point (x, y); In step (b), the relational formula (4) is carried out according to the following expression:

Among them, φ*(x, y) is the winding phase of the point (x, y) on the captured image, and In _' (x, y) is the winding phase shift coordinate corresponding to the point (x, y). 2 . The method for encoding and decoding images in a surface structured light measurement system according to claim 1 , wherein in step (a), the phase-shifted images are fringe images with different brightness. 3 .

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