CN114838674A - Phase correction method for structured light three-dimensional surface shape measurement reconstruction - Google Patents
Phase correction method for structured light three-dimensional surface shape measurement reconstruction Download PDFInfo
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- CN114838674A CN114838674A CN202210785446.4A CN202210785446A CN114838674A CN 114838674 A CN114838674 A CN 114838674A CN 202210785446 A CN202210785446 A CN 202210785446A CN 114838674 A CN114838674 A CN 114838674A
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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
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- 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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- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
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Abstract
In a structured light scanning system projecting a sinusoidal grating, phase nonlinearity is caused by nonlinearity of a projection system and an image acquisition system, and the phase nonlinearity has an influence on measurement accuracy, so that the phase needs to be corrected, and therefore, the invention provides a phase correction method for structured light three-dimensional surface shape measurement reconstruction, which comprises the following steps: s1, generating four frames of sine interference images with the phase difference of 90 degrees, and calculating the phase A of pixel points in the sine interference images; and S2, projecting the sinusoidal interference image on the surface of an object, collecting four projected images, carrying out logarithmic transformation on the projected images, carrying out phase calculation based on the result of the logarithmic transformation, and eliminating factors to obtain a corrected phase.
Description
Technical Field
The invention relates to the technical field of three-dimensional image reconstruction, in particular to a phase correction method for structured light three-dimensional surface shape measurement reconstruction.
Background
In the phase-based structured light three-dimensional surface shape measurement, due to projection and CCD nonlinear mapping (Gamma correction), projected sinusoidal grating stripes are distorted, and errors of phase and three-dimensional reconstruction are finally caused. A large number of images need to be projected and captured to perform such methods. And secondly, calculating the difference between the actual phase and the theoretical phase by projecting a phase grating to the white flat plate, and making a lookup table. The phase calculated in the measurement process is corrected, the gamma value needs to be calibrated in the mode, the theoretical and actual phase difference needs to be acquired through a flat plate, the implementation process is complex, and the method is not beneficial to accurate and rapid reconstruction of the three-dimensional image.
Disclosure of Invention
The present invention is directed to a phase correction method for structured light three-dimensional profile measurement and reconstruction, so as to solve the problems in the background art.
The invention is realized by the following technical scheme: the invention discloses a phase correction method for structured light three-dimensional surface shape measurement reconstruction, which comprises the following steps:
s1, generating four frames of sine interference images with the phase difference of 90 degrees, and calculating the phase A of pixel points in the sine interference images;
and S2, projecting the sinusoidal interference image on the surface of an object, collecting four projection images, carrying out logarithmic transformation on the projection images, carrying out phase calculation based on the result of the logarithmic transformation, and eliminating a factor gamma to obtain an initial phase.
Optionally, the sinusoidal interference image includes a plurality of ideal sinusoidal grating fringes with an initial phase of 0.
Optionally, in step S1, calculating a phase a of a pixel point in the sinusoidal interference image, including:
acquiring a light intensity expression of four frames of sinusoidal interference images:
where α represents background light intensity, b represents modulation degree, ω t represents initial phase information, and I 1 p Light intensity expression, I, representing a sinusoidal image with an initial phase of 0 2 p Light intensity expression representing a sinusoidal image with an initial phase of π/2, I 3 p Expression for the intensity of light representing a sinusoidal image with an initial phase of pi, I 4 p To representThe light intensity expression of the sinusoidal image when the initial phase is 3 pi/2;
phase a is calculated by:
。
optionally, performing logarithmic transformation on the projection image, further comprising:
acquiring a light intensity expression of the projection image:
carrying out logarithmic transformation on the light intensity expression of the projection image:
optionally, phase calculation is performed based on the result of logarithmic transformation, and factor γ is eliminated to obtain an initial phase:
in the formula (I), the compound is shown in the specification,
is the initial phase.
The second aspect of the present invention discloses an optical three-dimensional measurement system, comprising:
the projection device is used for projecting four frames of sinusoidal interference images with the phase difference of 90 degrees according to the instruction of the control terminal;
the image acquisition device is used for acquiring and projecting four frames of sinusoidal interference images with the phase difference of 90 degrees and transmitting the acquired projection images back to the control terminal;
and the control terminal is used for generating the sinusoidal interference image, driving the projection device to project the sinusoidal interference image, carrying out logarithmic transformation on the projection image acquired by the image acquisition device, carrying out phase correction calculation on the basis of a logarithmic transformation result, eliminating a factor and obtaining a corrected phase.
Compared with the prior art, the invention has the following beneficial effects:
the phase correction method for the structured light three-dimensional surface shape measurement reconstruction provided by the invention does not need to calibrate a gamma value or acquire theoretical and actual phase difference through a flat plate, eliminates the influence of a gamma factor in the structured light three-dimensional surface shape measurement, has universality and can realize accurate and rapid reconstruction of a three-dimensional image.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only preferred embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without inventive exercise.
FIG. 1 is a flow chart of a gamma phase correction method for structured light three-dimensional surface measurement reconstruction according to the present invention;
FIG. 2 is a diagram of a phase mapping relationship between a corrected phase and a phase before correction according to the present invention;
FIG. 3 is a schematic structural diagram of an optical three-dimensional measurement system provided by the present invention;
fig. 4 is a schematic block diagram of an optical three-dimensional measurement system provided by the present invention.
In the figure, 1 projection device, 2 image acquisition device, 3 control terminal.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the described embodiments are only some of the embodiments of the present invention, and not all of the embodiments of the present invention, and it should be understood that the present invention is not limited by the exemplary embodiments described herein. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the invention described herein without inventive step, shall fall within the scope of protection of the invention.
In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.
It is to be understood that the present invention may be embodied in many different 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 invention 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 invention. 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 invention, a detailed structure will be set forth in the following description in order to explain the present invention. Alternative embodiments of the invention are described in detail below, however, the invention may be practiced in other embodiments that depart from these specific details.
The photoelectric conversion characteristics of current photoelectric conversion components are all non-linear. The input-output characteristics are all power functions capable of reflecting the respective characteristics, that is, if the input optical signal intensity is L, the output electrical signal intensity is I. The relationship between the input and the output satisfies the following equation: i = c · L γ Wherein c is a magnification factor and is a constant; gamma (ganma) is a powerThe exponent of the function represents the conversion characteristic of the nonlinear component, which is called power-law conversion characteristic because the nonlinear characteristic is in the form of γ -th power, and is therefore also called γ characteristic.
The actual image system is composed of a plurality of components, and if all the components have the conversion characteristic of a power function, the transfer function of the whole system is a power function, and the exponent gamma of the transfer function is equal to the product of all the single components gamma. The derivation of a simple system power-law conversion characteristic with two links is given below.
Let the input and output of the first link be x 1 ，y 1， The power law conversion characteristic is
The input and output of the second link are x 2 ，y 2 The power law conversion characteristic is
Since the input to the second element is the output of the first element, x 2 =y 1 . If the system has only two links, the input of the system is x 1 Output is y 2 Namely:
wherein
。
For correcting the image, it is clear that it is critical to obtain the gamma value, and to estimate the gamma value, for I = c · L γ Taking logarithm on two sides, then:
in the prior art, a test target graph is set, different logL images are set, logL is obtained through detection, the corresponding relation between the logL and the logL is obtained, a linear section part of the logL is selected, and the slope corresponds to a gamma value.
The conventional phase correction methods are divided into two types, firstly, the gamma value is obtained by projection and shooting of images with different gray scales and linear fitting after logarithmic transformation, and the grating image obtained by the system has better sine property through pre-correction. A large number of images need to be projected and captured to perform such methods. And secondly, calculating the difference between the actual phase and the theoretical phase by projecting a phase grating to the white flat plate, and making a lookup table. The phase calculated during the measurement is corrected.
Referring to fig. 1 to fig. 2, a first aspect of the present invention discloses a phase correction method for structured light three-dimensional profile measurement reconstruction, which neither needs to calibrate a γ value nor needs to obtain a theoretical and actual phase difference through a flat plate. Has universality. The method specifically comprises the following steps:
s1, generating four frames of sine interference images with the phase difference of 90 degrees, and calculating the phase A of pixel points in the sine interference images.
Calculating the phase A of a pixel point in the sinusoidal interference image, including:
acquiring a light intensity expression of four frames of sinusoidal interference images:
where α represents background light intensity, b represents modulation degree, ω t represents initial phase information, and I 1 p Light intensity expression, I, representing a sinusoidal image with an initial phase of 0 2 p Light intensity expression representing a sinusoidal image with an initial phase of π/2, I 3 p Expression for the intensity of light representing a sinusoidal image with an initial phase of pi, I 4 p An expression of light intensity representing a sinusoidal image at an initial phase of 3 pi/2;
phase a is calculated by:
。
and S2, projecting the sinusoidal interference image on the surface of an object, collecting four projection images, carrying out logarithmic transformation on the projection images, carrying out phase calculation based on the result of the logarithmic transformation, and eliminating a factor gamma to obtain an initial phase.
In step S2, a light intensity expression of the projected image is first acquired:
carrying out logarithmic transformation on the light intensity expression of the projection image:
and performing phase calculation based on the logarithmic transformation result, and eliminating a factor gamma to obtain an initial phase.
In the formula,
as the initial phase, the factor γ is cancelled by the above calculation process, and the initial phase is obtained.
In conclusion, the invention eliminates the factor gamma by carrying out logarithmic transformation on the projection image, thereby directly obtaining the corrected phase value, improving the convenience in the image correction process and further improving the accuracy of image reconstruction.
Further, the method disclosed by the first aspect of the present invention is applied to an optical three-dimensional measurement system, referring to fig. 3 to 4, the measurement system includes:
the projection device 1 is used for projecting a sinusoidal interference image according to an instruction of the control terminal 3;
and the image acquisition device 2 is used for shooting the sinusoidal interference image and transmitting the shooting result back to the control terminal 3, wherein the image acquisition device 2 can select an industrial CDC camera.
And the control terminal 3 is used for generating the sinusoidal interference image, driving the projection device 1 to project the sinusoidal interference image, carrying out logarithmic transformation on the projection image acquired by the image acquisition device 2, carrying out phase correction calculation on the basis of a logarithmic transformation result, and eliminating a factor gamma to obtain a corrected phase.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. A phase correction method for structured light three-dimensional surface shape measurement reconstruction is characterized by comprising the following steps:
s1, generating four frames of sine interference images with the phase difference of 90 degrees, and calculating the phase A of pixel points in the sine interference images;
and S2, projecting the sinusoidal interference image on the surface of an object, collecting four projection images, carrying out logarithmic transformation on the projection images, carrying out phase calculation based on the result of the logarithmic transformation, and eliminating a factor gamma to obtain a corrected phase.
2. The method of claim 1, wherein the sinusoidal interference image comprises a plurality of ideal sinusoidal grating fringes with an initial phase of 0.
3. The method of claim 2, wherein in step S1, the calculating the phase a of the pixel point in the sinusoidal interference image comprises:
acquiring a light intensity expression of four frames of sinusoidal interference images:
where α represents background light intensity, b represents modulation degree, ω t represents initial phase information, and I 1 p Light intensity expression, I, representing a sinusoidal image with an initial phase of 0 2 p Light intensity expression representing a sinusoidal image with an initial phase of π/2, I 3 p Expression for the intensity of light representing a sinusoidal image with an initial phase of pi, I 4 p An expression of light intensity representing a sinusoidal image at an initial phase of 3 pi/2;
phase a is calculated by:
。
4. the phase correction method for structured light three-dimensional shape measurement reconstruction according to claim 3, wherein the projection image is logarithmically transformed, further comprising:
acquiring a light intensity expression of the projection image:
carrying out logarithmic transformation on the light intensity expression of the projection image:
and performing phase calculation based on the logarithmic transformation result, and eliminating a factor gamma to obtain an initial phase.
5. The phase correction method for the structured light three-dimensional shape measurement and reconstruction as claimed in claim 4, wherein the phase calculation is performed based on the logarithm transformation result, and the factor γ is eliminated, so as to obtain the corrected phase:
in the formula (I), the compound is shown in the specification,
is the initial phase.
6. The phase correction method for the measurement and reconstruction of the structured light three-dimensional shape according to any one of claims 1 to 5, wherein the method is applied to an optical three-dimensional measurement system, and the measurement system comprises:
the projection device is used for projecting four frames of sinusoidal interference images with the phase difference of 90 degrees according to the instruction of the control terminal;
the image acquisition device is used for acquiring and projecting four frames of sinusoidal interference images with the phase difference of 90 degrees and transmitting the acquired projection images back to the control terminal;
and the control terminal is used for generating the sinusoidal interference image, driving the projection device to project the sinusoidal interference image, carrying out logarithmic transformation on the projection image acquired by the image acquisition device, carrying out phase correction calculation on the basis of a logarithmic transformation result, eliminating a factor and obtaining a corrected phase.
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