CN116878416A - Phase correction method for three-dimensional surface shape measurement reconstruction of structured light - Google Patents
Phase correction method for three-dimensional surface shape measurement reconstruction of structured light Download PDFInfo
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- CN116878416A CN116878416A CN202310833648.6A CN202310833648A CN116878416A CN 116878416 A CN116878416 A CN 116878416A CN 202310833648 A CN202310833648 A CN 202310833648A CN 116878416 A CN116878416 A CN 116878416A
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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
- G01B11/2441—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures using interferometry
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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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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T17/00—Three dimensional [3D] modelling, e.g. data description of 3D objects
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Abstract
The application provides a phase correction method for measuring and reconstructing a three-dimensional surface shape of structured light, which comprises the following steps: s1, constructing four sinusoidal gratings with 90-degree phase difference, and calculating ideal phases of pixel points in the sinusoidal gratings; s2, carrying out logarithmic transformation on the sinusoidal grating, and calculating a logarithmic phase based on a logarithmic transformation result; s3, establishing a lookup table related to the ideal phase and the logarithmic phase, wherein the lookup table comprises the corresponding relation between the logarithmic phase and the ideal phase; s4, the projection device projects the structural grating onto the surface of the object, four projection images projected by the projection device are collected, the projection images are subjected to logarithmic transformation, and the projection phase is calculated; s5, taking the projection phase as a logarithmic phase, searching an ideal phase corresponding to the logarithmic phase through the lookup table, and taking the ideal phase as a corrected phase of the projection image.
Description
Technical Field
The application relates to the technical field of three-dimensional image reconstruction, in particular to a phase correction method for structural light three-dimensional surface shape measurement reconstruction.
Background
In the three-dimensional surface shape measurement of the structured light based on the phase, due to the nonlinear mapping (Gamma correction) of the projection and the CCD, the projected sinusoidal grating stripes are distorted, and finally the errors of the phase and the three-dimensional reconstruction are caused, the current phase correction method is divided into two types, namely, the Gamma value is obtained by the projection and shooting of images with different gray scales after logarithmic transformation and linear fitting, and the grating image obtained by the system has better sine through the pre-correction. The number of images to be projected and captured is large to perform such a method. Secondly, by projecting a phase grating to a white flat plate, the difference between the actual phase and the theoretical phase is calculated, and a lookup table is made. The phase calculated in the measuring process is corrected, the gamma value is required to be calibrated in the mode, the theoretical phase difference and the actual phase difference are required to be acquired through a flat plate, the implementation process is complex, and the accurate and rapid reconstruction of the three-dimensional image is not facilitated.
Disclosure of Invention
The application aims to provide a phase correction method for reconstructing three-dimensional surface shape measurement of structured light, which is used for solving the problems in the background art.
The application is realized by the following technical scheme: the application discloses a phase correction method for reconstructing three-dimensional surface shape measurement of structured light, which comprises the following steps:
s1, constructing four sinusoidal gratings with 90-degree phase difference, and calculating ideal phases of pixel points in the sinusoidal gratings;
s2, carrying out logarithmic transformation on the sinusoidal grating, and calculating a logarithmic phase based on a logarithmic transformation result;
s3, establishing a lookup table related to the ideal phase and the logarithmic phase, wherein the lookup table comprises the corresponding relation between the logarithmic phase and the ideal phase;
s4, the projection device projects the structural grating onto the surface of the object, four projection images projected by the projection device are collected, the projection images are subjected to logarithmic transformation, and the projection phase is calculated;
s5, taking the projection phase as a logarithmic phase, searching an ideal phase corresponding to the logarithmic phase through the lookup table, and taking the ideal phase as a corrected phase of the projection image.
Optionally, in step S1, calculating an ideal phase of the pixel point in the sinusoidal grating includes:
acquiring a light intensity expression of four frames of sinusoidal gratings:
where a denotes the background light intensity, b denotes the modulation degree, ωt denotes the log-phase information,light intensity expression representing a sinusoidal image with a logarithmic phase of 0,/for a sinusoidal image>Light intensity expression representing a sinusoidal image with a logarithmic phase of pi/2,/for a sinusoidal image>Light intensity expression representing a sinusoidal image with a logarithmic phase pi,/and a method for generating the same>Light intensity expression representing sinusoidal image at logarithmic phase 3 pi/2；
Phase a is calculated by:
optionally, the logarithmic transformation is performed on the sinusoidal grating, and the logarithmic phase is calculated based on the logarithmic transformation result, which specifically includes:
acquiring a light intensity expression of the sinusoidal grating:
performing logarithmic transformation on the light intensity expression of the sinusoidal grating:
based on the logarithmic transformation result, carrying out phase calculation, eliminating a factor gamma, and obtaining a logarithmic phase:
in the method, in the process of the application,is a logarithmic phase.
Specifically, after performing logarithmic transformation on the projection image, calculating a projection phase, specifically including:
acquiring a light intensity expression of a projection image;
performing logarithmic transformation on the light intensity expression of the projection image;
and carrying out phase calculation based on the logarithmic transformation result to obtain a projection phase.
In a second aspect, the application discloses an optical three-dimensional measurement system, comprising:
projection means for projecting the structured grating onto a surface of the object;
the image acquisition device is used for acquiring four projection images projected by the projection device and transmitting the acquired projection images back to the control terminal;
the control terminal is used for generating the sine grating, calculating the ideal phase of the sine grating, carrying out logarithmic transformation on the sine grating, carrying out phase correction calculation based on a logarithmic transformation result, eliminating factors, obtaining the logarithmic phase, and establishing a lookup table related to the ideal phase and the logarithmic phase.
Compared with the prior art, the application has the following beneficial effects:
the phase correction method for the structured light three-dimensional surface shape measurement reconstruction provided by the application has the advantages that the gamma value is not required to be calibrated, the corresponding relation between the logarithmic phase and the ideal phase is obtained, the logarithmic phase and the ideal phase are quantitatively analyzed, a lookup table corresponding to the logarithmic phase one by one is established, the ideal phase corresponding to the logarithmic phase of the actual image is searched through the lookup table, and the ideal phase is the corrected phase of the actual image.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only preferred embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a gamma phase correction method for structured light three-dimensional surface shape measurement reconstruction provided by the application;
FIG. 2 is a graph showing the correspondence between logarithmic phase and ideal phase according to the present application;
FIG. 3 is a schematic diagram of an optical three-dimensional measurement system according to the present application;
fig. 4 is a schematic block diagram of an optical three-dimensional measurement system provided by the present application.
In the figure, a projection device 1, an image acquisition device 2 and a control terminal 3.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, exemplary embodiments according to the present application will be described in detail with reference to the accompanying drawings. It should be apparent that the described embodiments are only some embodiments of the present application and not all embodiments of the present application, and it should be understood that the present application is not limited by the example embodiments described herein. Based on the embodiments of the application described in the present application, all other embodiments that a person skilled in the art would have without inventive effort shall fall within the scope of the application.
In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present application. It will be apparent, however, to one skilled in the art that the application may be practiced without one or more of these details. In other instances, well-known features have not been described in detail in order to avoid obscuring the application.
It should be understood that the present application may be embodied in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term "and/or" includes any and all combinations of the associated listed items.
In order to provide a thorough understanding of the present application, detailed structures will be presented in the following description in order to illustrate the technical solutions presented by the present application. Alternative embodiments of the application are described in detail below, however, the application may have other implementations in addition to these detailed descriptions.
The photoelectric conversion characteristics of the current photoelectric conversion parts are all nonlinear. The input-output characteristics are all power functions capable of reflecting the respective characteristics, namely, if the intensity of an input optical signal is L, the intensity of an output electric signal is I. The relationship between input and output satisfies the following equation: i=c·l γ Wherein c is the magnification and is a constant; gamma (gamma) is an exponent of a power function, representing a conversion characteristic of a nonlinear component, which is referred to as a power-law (power-law) conversion characteristic, because the nonlinear characteristic is in the form of a gamma power, and thus, is also referred to as a gamma characteristic.
The actual image system is made up of several components, and if all components have the transfer characteristics of a power function, the transfer function of the whole system is a power function with an exponent y equal to the product of all individual components y. The following gives a derivation of the simple system power law conversion characteristics with two links.
Let the input and output of the first link be x 1 ，y 1 The power law conversion characteristic is thatThe input and output of the second link are x respectively 2 ，y 2 The power law conversion characteristic is->Because the input of the second link is the output of the first link, x 2 ＝y 1 . If the system has only two links, the input of the system is x 1 Output is y 2 The method comprises the following steps:
wherein c=c 1 ·c 2 。
For correcting the image, it is obvious that it is critical to obtain the gamma value, for estimating the gamma value, for
I＝c·Lγ
The logarithm is taken from two sides, and then:
logI＝C+γlogL
in the prior art, by setting a test target diagram and different log L images, detecting to obtain log I, obtaining the corresponding relation between log L and log I, selecting a linear section part of the linear section, and enabling the slope to correspond to a gamma value.
The traditional phase correction method is divided into two types, namely, the gamma value is obtained by linear fitting after logarithmic transformation through projection and shooting of images with different gray scales, and the grating image obtained by the system has better sine through pre-correction. The number of images to be projected and captured is large to perform such a method. Secondly, by projecting a phase grating to a white flat plate, the difference between the actual phase and the theoretical phase is calculated, and a lookup table is made. The phase calculated during the measurement is corrected.
Referring to fig. 1 to 2, the first aspect of the present application discloses a phase correction method for reconstructing three-dimensional surface shape measurement of structured light, which does not need to calibrate a gamma value or acquire a theoretical and actual phase difference through a flat plate. The method has universality, a lookup table which is related to the corresponding relation between the logarithmic phase and the ideal phase is established in advance, the logarithmic phase in the actual image is calculated, the corresponding ideal phase is searched in the lookup table, and the ideal phase is taken as the phase of the actual image, so the method specifically comprises the following steps:
s1, generating four frames of sinusoidal gratings with 90-degree phase difference, calculating ideal phases of pixel points in the sinusoidal gratings, and calculating logarithmic phases based on the ideal phases;
calculating an ideal phase of a pixel point in the sinusoidal grating comprises:
acquiring a light intensity expression of four frames of sinusoidal gratings:
where a denotes the background light intensity, b denotes the modulation degree, ωt denotes the log-phase information,light intensity expression representing a sinusoidal image with a logarithmic phase of 0,/for a sinusoidal image>Light intensity expression representing a sinusoidal image with a logarithmic phase of pi/2,/for a sinusoidal image>Light intensity expression representing a sinusoidal image with a logarithmic phase pi,/and a method for generating the same>A light intensity expression representing a sinusoidal image at a logarithmic phase of 3 pi/2;
the ideal phase is calculated by:
s2, carrying out logarithmic transformation on the sinusoidal grating, and calculating a logarithmic phase based on a logarithmic transformation result, wherein the method specifically comprises the following steps of:
acquiring a light intensity expression of the sinusoidal grating:
performing logarithmic transformation on the light intensity expression of the sinusoidal grating:
phase calculation is performed based on the logarithmic transformation result:
in the method, in the process of the application,the factor γ can be eliminated by the above calculation process to obtain a log phase.
S3, establishing a lookup table related to the ideal phase and the logarithmic phase, wherein the lookup table comprises the corresponding relation between the logarithmic phase and the ideal phase.
S4, the projection device projects the structural grating onto the surface of the object, four projection images projected by the projection device are collected, and projection phases are calculated after logarithmic transformation is carried out on the projection images.
After carrying out logarithmic transformation on the projection image, calculating a projection phase, specifically comprising the following steps:
acquiring a light intensity expression of a projection image;
performing logarithmic transformation on the light intensity expression of the projection image;
and carrying out phase calculation based on the logarithmic transformation result to obtain a projection phase.
S5, taking the projection phase as a logarithmic phase, searching an ideal phase corresponding to the logarithmic phase through the lookup table, and taking the ideal phase as a corrected phase of the projection image
The phase correction look-up table calculation procedure is as follows (Matlab program): % four-step phase shift method to calculate phase
N＝1024；
x＝1:N；
a＝128；
b＝127；
% standard sinusoidal curve
I1＝a+b*cos(2*π*x/N+0*π/2)；
I2＝a+b*cos(2*π*x/N+1*π/2)；
I3＝a+b*cos(2*π*x/N+2*π/2)；
I4＝a+b*cos(2*π*x/N+3*π/2)；
% ideal phase
Phi＝-atan2(I4-I2,I3-I1)+π；
% log transform log i1=log (I1) of standard sinusoid;
logI2＝log(I2)；
logI3＝log(I3)；
logI4＝log(I4)；
% log phase
LogPhi＝-atan2(logI4-logI2,logI3-logI1)+π；
% of the mapping relationship between the two
plot(LogPhi,Phi)
% correction lookup table giving a log phase value, a corresponding ideal phase value can be found in the table
LUT＝[LogPhi，Phi]
In summary, the application eliminates the factor gamma by carrying out logarithmic transformation on the sinusoidal grating, obtains the logarithmic phase, quantitatively analyzes the corresponding relation between the logarithmic phase and the ideal phase, establishes a lookup table corresponding to the logarithmic phase and the ideal phase one by one, and searches the ideal phase corresponding to the logarithmic phase through the lookup table when the logarithmic phase of the actual image is calculated in the step S2, wherein the ideal phase is the corrected phase of the actual image, thereby improving the convenience in the image correction process and further improving the accuracy of image reconstruction.
For the second part, the following steps are included:
1. projecting the formal gratings A1, A2, A3 and A4 on the surface of an object by a projector
2. The camera collects four corresponding images B1, B2, B3 and B4, and the logarithmic phase of the four images B1, B2, B3 and B4 is calculated based on the calculation method disclosed in the step S2;
3. the logarithmic phase is corrected to a phase free from the gamma nonlinear effects according to the lookup table generated in step S3.
Further, the method disclosed in the first aspect of the present application is applied to an optical three-dimensional measurement system, see fig. 3 to 4, the measurement system comprising:
a projection device 1 for projecting a structured grating onto a surface of an object;
the image acquisition device 2 is used for acquiring four projection images projected by the projection device 1 and transmitting the acquired projection images back to the control terminal 3;
and the control terminal 3 is used for generating the sine grating, calculating the ideal phase of the sine grating, carrying out logarithmic transformation on the sine grating, carrying out phase correction calculation based on a logarithmic transformation result, eliminating factors, obtaining the logarithmic phase and establishing a lookup table related to the ideal phase and the logarithmic phase.
The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather to enable any modification, equivalent replacement, improvement or the like to be made within the spirit and principles of the application.
Claims (5)
1. A phase correction method for reconstruction of structured light three-dimensional surface shape measurement, comprising the steps of:
s1, constructing four sinusoidal gratings with 90-degree phase difference, and calculating ideal phases of pixel points in the sinusoidal gratings;
s2, carrying out logarithmic transformation on the sinusoidal grating, and calculating a logarithmic phase based on a logarithmic transformation result;
s3, establishing a lookup table related to the ideal phase and the logarithmic phase, wherein the lookup table comprises the corresponding relation between the logarithmic phase and the ideal phase;
s4, the projection device projects the structural grating onto the surface of the object, four projection images projected by the projection device are collected, the projection images are subjected to logarithmic transformation, and the projection phase is calculated;
s5, taking the projection phase as a logarithmic phase, searching an ideal phase corresponding to the logarithmic phase through the lookup table, and taking the ideal phase as a corrected phase of the projection image.
2. A phase correction method for structured light three-dimensional surface shape measurement reconstruction according to claim 1, wherein in step S1, calculating an ideal phase of a pixel point in the sinusoidal grating comprises:
acquiring a light intensity expression of four frames of sinusoidal gratings:
where a denotes the background light intensity, b denotes the modulation degree, ωt denotes the log-phase information,light intensity expression representing a sinusoidal image with a logarithmic phase of 0,/for a sinusoidal image>Light intensity expression representing a sinusoidal image with a logarithmic phase of pi/2,/for a sinusoidal image>Light intensity expression representing a sinusoidal image with a logarithmic phase pi,/and a method for generating the same>A light intensity expression representing a sinusoidal image at a logarithmic phase of 3/2;
the ideal phase is calculated by:
3. a phase correction method for reconstruction of structured light three-dimensional surface shape measurement according to claim 2, wherein the sinusoidal grating is subjected to logarithmic transformation, and the logarithmic phase is calculated based on the result of the logarithmic transformation, specifically comprising:
acquiring a light intensity expression of the sinusoidal grating:
performing logarithmic transformation on the light intensity expression of the sinusoidal interference image:
based on the logarithmic transformation result, carrying out phase calculation, eliminating a factor gamma, and obtaining a logarithmic phase:
in the method, in the process of the application,is a logarithmic phase.
4. A phase correction method for structured light three-dimensional surface shape measurement reconstruction according to claim 2, wherein the projection phase is calculated by logarithmically transforming the projection image, and specifically comprising:
acquiring a light intensity expression of a projection image;
performing logarithmic transformation on the light intensity expression of the projection image;
and carrying out phase calculation based on the logarithmic transformation result to obtain a projection phase.
5. A phase correction method for reconstruction of structured light three-dimensional surface shape measurement according to any of claims 1-4, wherein the method is applied in an optical three-dimensional measurement system, the measurement system comprising:
projection means for projecting the structured grating onto a surface of the object;
the image acquisition device is used for acquiring four projection images projected by the projection device and transmitting the acquired projection images back to the control terminal;
the control terminal is used for generating the sine grating, calculating the ideal phase of the sine grating, carrying out logarithmic transformation on the sine grating, carrying out phase correction calculation based on a logarithmic transformation result, eliminating factors, obtaining the logarithmic phase, and establishing a lookup table related to the ideal phase and the logarithmic phase.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117168313A (en) * | 2023-11-03 | 2023-12-05 | 武汉工程大学 | Phase error model correction method and system based on grating projection three-dimensional reconstruction |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117168313A (en) * | 2023-11-03 | 2023-12-05 | 武汉工程大学 | Phase error model correction method and system based on grating projection three-dimensional reconstruction |
| CN117168313B (en) * | 2023-11-03 | 2024-01-23 | 武汉工程大学 | Phase error model correction method and system based on grating projection three-dimensional reconstruction |
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