CN110823129A - Method for improving modulation degree image quality based on pi phase shift - Google Patents
Method for improving modulation degree image quality based on pi phase shift Download PDFInfo
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- CN110823129A CN110823129A CN201910988022.6A CN201910988022A CN110823129A CN 110823129 A CN110823129 A CN 110823129A CN 201910988022 A CN201910988022 A CN 201910988022A CN 110823129 A CN110823129 A CN 110823129A
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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
- G01B11/2531—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 using several gratings, projected with variable angle of incidence on the object, and one detection device
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- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
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Abstract
The invention discloses a method for improving modulation degree image quality based on pi phase shift. The process is as follows: generating two frames of fringe patterns with pi phase shift, projecting the two frames of fringe patterns onto a measured object respectively, collecting the two frames of deformed fringe patterns, subtracting the two frames of deformed fringe patterns, processing the subtracted fringe patterns to obtain a spectrogram, and sequentially filtering, inverse Fourier transform and modulus operation on the spectrogram to obtain a high-quality modulation degree image. According to the invention, through subtracting the two frames of sine fringe patterns with pi phase shift, not only can zero-frequency components in frequency spectrum be eliminated, but also errors caused by aliasing of frequency spectrum can be eliminated, and meanwhile, the filtering range is widened, so that the modulation degree image quality is improved.
Description
Technical Field
The invention belongs to the technical field of three-dimensional measurement of objects, and particularly relates to a method for improving modulation degree image quality based on pi phase shift.
Background
The acquisition of the three-dimensional information of the object has important significance in the development of modern science and technology. Among various three-dimensional measurement techniques, optical three-dimensional measurement methods based on surface structured light, such as fourier transform profilometry, phase measurement profilometry, modulation degree profilometry and the like, have been widely researched and applied in the field of three-dimensional information acquisition due to the characteristics of non-contact, high precision, full-field measurement and the like. In many optical three-dimensional measurement methods, modulation degree image information is extracted, and the precision of a three-dimensional reconstruction object is directly influenced by the quality of the modulation degree image.
The quality of the modulation degree image is directly related to the frequency of the fringe pattern, when the fringe frequency is low, due to the fact that the distance between the fundamental frequency and the zero frequency is short, frequency spectrum aliasing easily exists, and interference of background light intensity exists in the extracted modulation degree image; if the fringe frequency is increased, although the frequency spectrum aliasing phenomenon can be reduced as much as possible, and the modulation degree image quality is improved, the appearance change rate of the measured object is limited, and the universality of the three-dimensional measurement method is reduced.
Disclosure of Invention
The present invention is directed to solve the above-mentioned drawbacks of the prior art, and provides a simple and reliable method for improving modulation image quality based on Π phase shift.
The technical scheme adopted by the invention is as follows: a method for improving the quality of a modulation image based on pi phase shift comprises the steps of generating two frames of fringe patterns with pi phase shift, projecting the two frames of fringe patterns onto an object to be measured respectively, collecting two frames of deformed fringe patterns, subtracting the two frames of deformed fringe patterns, carrying out Fourier transform processing on the subtracted fringe patterns to obtain a spectrogram, and carrying out filtering, inverse Fourier transform and modular operation on the spectrogram in sequence to obtain a high-quality modulation image of the object to be measured.
The invention has the beneficial effects that:
1. the invention can eliminate the zero-frequency component in the frequency spectrum, eliminate the error introduced by the aliasing of the frequency spectrum and widen the filtering range by subtracting the two frames of sine fringe patterns with pi phase shift.
2. Because the influence of the non-linear error introduced by the ambient light, the image projection and the acquisition equipment on the deformed fringe patterns of the two frames is completely consistent, the error can be inhibited by subtracting the images, and the modulation degree image quality is improved.
3. The invention can flexibly design the needed grating stripe, thus obtaining the needed two frames of deformed stripe patterns with pi phase shift in a short time, and the method is simple.
Drawings
FIG. 1 is a schematic frequency spectrum diagram of two frames of deformed fringe patterns with pi phase shift after subtraction.
Fig. 2 is a schematic view of a subject under test.
Fig. 3 is a schematic diagram of a high quality modulation image obtained by the method of the present invention.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. 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. 1-3, the present invention provides a method for improving modulation image quality based on pi phase shift, which generates two frames of fringe patterns with pi phase shift, projects the two frames of fringe patterns onto an object to be measured, collects two frames of deformed fringe patterns, subtracts the two frames of deformed fringe patterns, performs fourier transform processing on the subtracted fringe patterns to obtain a spectrogram, and then sequentially performs filtering, inverse fourier transform and modulo operation on the spectrogram to obtain a high-quality modulation image of the object to be measured.
The detailed process is as follows:
two frames of sine fringe patterns with pi phase shift are generated by computer coding, and are projected onto a measured object through image projection equipment, the measured object is modulated by the height of the measured object to deform the measured object, and the light intensity of the two frames of deformed fringe patterns acquired by image acquisition equipment is as shown in formulas (1) and (2):
I1(x,y)＝R(x,y)[A(x,y)+B(x,y)·cos(2πfx+φ(x,y))](1)
wherein (x, y) is the pixel point coordinate of the collected stripe in the system, R (x, y) is the reflectivity distribution of the measured object, A (x, y) and B (x, y) are the background light intensity and the sine stripe contrast distribution respectively, f is the stripe frequency,
is the phase shift due to the height modulation of the object under test. Subtracting equation (2) from equation (1) yields:
I3(x,y)＝R(x,y)[2B(x,y)·cos(2πfx+φ(x,y))](3)
wherein the background light intensity is eliminated, and then fourier transform is performed on equation (3) to obtain a spectrogram:
G′(fx,fy)＝G1(fx,fy)+G-1(fx,fy) (4)
wherein G is1(fx,fy) Is a primary spectrogram, G-1(fx,fy) Is a negative first-order spectrogram, and the zero-frequency component corresponding to the background light in the frequency spectrum is caused by I1(x, y) and I2The subtraction of the two (x, y) equations, which is eliminated, will not interfere with the extraction of the positive order component of the fundamental frequency in the spectral distribution. Filtering out the primary spectrum component in the spectrogram (namely equation (4)) by using a spatial filter, and performing inverse Fourier transform on the filtered primary spectrum to obtain:
then, performing modular operation on the formula (5) to obtain a high-quality modulation degree image based on the pi phase shift algorithm:
M'(x,y)＝abs[p'(x,y)]＝R(x,y)B(x,y) (6)
since the nonlinear effect of the system and the random noise have approximately the same effect on the deformed fringe patterns of the two frames, when I is equal to I1(x, y) and I2When the two formulas (x, y) are subtracted, the zero frequency component in the frequency spectrum is eliminated, and meanwhile, errors caused by the nonlinear effect of the system and random noise can be restrained, so that the modulation degree image quality is improved.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Those not described in detail in this specification are within the skill of the art.
Claims (2)
1. A method for improving modulation degree image quality based on pi phase shift is characterized in that: generating two frames of fringe patterns with pi phase shift, projecting the two frames of fringe patterns onto a measured object respectively, collecting the two frames of deformed fringe patterns, subtracting the two frames of deformed fringe patterns, processing the subtracted fringe patterns and acquiring a spectrogram, and sequentially filtering, inverse Fourier transform and modulus operation on the spectrogram to obtain a high-quality modulation degree image of the measured object.
2. The method for improving the image quality of the modulation degree based on the pi phase shift according to claim 1, wherein: and performing Fourier transform on the subtracted fringe pattern to obtain a spectrogram with zero frequency and spectrum aliasing eliminated.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112203099A (en) * | 2020-09-24 | 2021-01-08 | 太原科技大学 | 3D data compression algorithm based on virtual orthogonal structure light coding |
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| CN109631798A (en) * | 2018-12-28 | 2019-04-16 | 成都信息工程大学 | A kind of 3 d shape vertical measurement method based on π phase shifting method |
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| CN1529122A (en) * | 2003-10-09 | 2004-09-15 | 四川大学 | Method for realizing Fourier transfrom contour by generating pi phase shift by two-colour grating template |
| CN102147492A (en) * | 2011-01-06 | 2011-08-10 | 南京大学 | Micro-structure quasi-phase-matching based method for preparing multidimensional target waveguide grating and bulk grating |
| CN107044833A (en) * | 2017-03-24 | 2017-08-15 | 南京理工大学 | A kind of ultrafast 3 D measuring method and its system based on improved Fourier transform outline technology |
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