CN117781941A - Phase shift coding method of binary stripes - Google Patents
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Abstract
The invention discloses a phase shift coding method of binary stripes, which specifically comprises the following steps: projecting an initial black-white alternate binary stripe, each stripe respectively occupyingEach pixel value, the image is moved leftwards by one pixel value each time, and the image is repeatedSecondary co-acquisition ofBinary fringe patterns with different magnitudes; then, calculating different weights occupied by each image, and multiplying each binary fringe image by different weightsThen the images I are overlapped to obtain the image I, and the image I and the quilt are equally divided in one periodEqual parts of sine stripe intensity values are in one-to-one correspondence, and unknown coefficients can be calculatedFinally, carrying out coefficient adding on specific numerical values, and then, superposing to obtain sine stripes, wherein when the method is combined with a phase shift method, a continuous cyclic binary stripe can be obtained; the characteristic of equidistant binary stripes is utilized to recycle the related stripes so as to reduce the projected stripe width number, only byThe binary stripes with equal spacing can finish four-step, eight-step and sixteen-step phase shifting.
Description
Technical Field
The invention belongs to the field of structured light three-dimensional measurement, and particularly relates to a phase shift coding method of binary stripes.
Background
With the development of measurement technology, structured light three-dimensional measurement plays an increasingly important role in production and life as an important component of the measurement technology. In the existing three-dimensional shape measurement technology, stripe projection profilometry (FPP) is widely used with the advantages of flexibility, rapidness, accuracy and the like. Currently, digital Fringe Projection (DFP) technology has been widely used for fringe projection, since it can be programmed to display arbitrary patterns, it is easy to project sinusoidal fringes and achieve precise phase shifts. Most commercial projectors produce measurement errors because of the non-linearities of the projector itself. That is, an ideal sinusoidal fringe image is sent to the projector, the fringe image produced by the projector will be non-sinusoidal, and the phase error produced by this non-sinusoidal wave is the primary error source for fringe projection.
To eliminate the effect of non-linear errors on the measurement results, a number of correction and compensation algorithms are derived. The binary stripe defocusing projection is an optical three-dimensional morphology measurement technology which is proposed relative to the sinusoidal stripe projection, and image distortion caused by nonlinear response of related equipment can be minimized because binary stripe signals are only composed of '1' and '0'. In this process, the defocus process acts as a low pass filter and harmonic components are suppressed except for the fundamental component of the square wave which is preserved. The prior art passes a binary square wave grating pattern through defocus of a digital projector to produce a pattern of approximately sinusoidal fringes. It requires a high defocus level to get a good sinusoidal fringe, which limits the effective depth of field, resulting in reduced contrast. The prior art uses Sinusoidal Pulse Width Modulation (SPWM) techniques to modulate binary stripes and proposes an Optimal Pulse Width Modulation (OPWM) technique that improves the stripes by purposefully eliminating selected high frequency harmonics by setting breakpoints. In the prior art, the tripolar SPWM technique further reduces the amount of defocus required to obtain high quality sinusoidal-like fringes. Such methods using Pulse Width Modulation (PWM) have better measurement quality and can obtain better sinusoidal effect with smaller defocus compared to binary square waves. However, the disadvantage is that the method is only suitable for the situation when the stripe width is narrow, and the application scene is limited. However, in the actual measurement process, the defocus level of the binary stripe is difficult to accurately determine, and if the defocus level is insufficient, the image reduces the sine of the projected stripe, and conversely, the stripe resolution is reduced, so that information is lost. Therefore, a binary stripe encoding method is provided, and the binary stripe is utilized to encode to obtain the sine stripe, so that the nonlinear response of the projector can be effectively avoided, and the defocusing adjustment is not needed. A plurality of binary images are overlapped to form a triangular fringe pattern by adopting codes, and the triangular fringe pattern is not sine fringes. Secondly, in the prior art, a space-time binary coding method is adopted to divide the sinusoidal fringes into a plurality of binary fringes according to intensity quantization and classification, projection is carried out according to time sequence, and finally the sinusoidal fringes are synthesized. A design and optimization algorithm of a multistage symmetrical mode is provided, and three-layer modes are decomposed into two binary modes for projection. However, the optimization process of this method is very complex.
Disclosure of Invention
The invention aims to: in order to overcome the defects in the prior art, the invention provides a phase shift coding method of binary stripes, which uses the characteristic of equidistant binary stripes to recycle related stripes so as to reduce the number of projected stripe widths.
In order to achieve the above purpose, the invention adopts the following technical scheme: a phase shift encoding method of binary stripes is provided, comprising the following steps:
step one: preparing a projection picture, projecting an initial binary stripe image with black and white phase, moving the image to the left one pixel point at a time, and repeatingHypo-co-acquisition->Equidistant binary fringe patterns with different magnitudes;
step two: the sine intensity value with a period of 2 pi is equally divided intoEqual parts, recording the sine intensity value corresponding to each point;
step three: calculating the proportion of each binary stripe image prepared in the step oneThen obtaining a sine fringe pattern I through superposition;
step four: continuously moving the binary stripe in the first step leftwards by one pixel point number, and repeatingSecondary co-acquisition ofEquidistant binary stripes of different widths, corresponding specific gravity +.>The sine fringe pattern I after phase shift by half a period can be generated after superposition, which is the same as that obtained in the step three;
step five: when combined with N-step phase shift, the method will obtainThe binary stripes and the corresponding coefficients are regarded as one cycle connected end to end; every time will be superimposed +.>The binary stripes are shifted backwards +.>The pattern can generate sine stripe patterns I with different phase shifts.
As a preferred embodiment of the present invention: each stripe in the projected binary stripes with initial black and white phase respectively occupiesA pixel value of +.>The individual pixel length is considered as one period; the generation of the initial black-and-white stripes is shown in the following formula:
wherein T represents the T pixel point, A represents the generated black-white stripe, and M represents the number of projected stripe patterns; the intensity value of white is 1, and the intensity value of black is 0.
As a preferred embodiment of the present invention: in the second step, the sampling formula of the sinusoidal fringe intensity value is as follows:
wherein Y represents a sine value corresponding to different n, when the abscissa increases each timeCorresponding sine values are recorded.
As a best of the inventionSelected embodiments: in step threeThe proportion of the binary stripe image>The solution equation of (2) is as follows:
in the method, in the process of the invention,representing the specific gravity of the nth image, and associating the intensity value of each pixel point of the binary stripes with corresponding +.>Multiplication by->Overlapping the stripes with the +.>The intensity values of the sine stripes are in one-to-one correspondence, so that the imitated sine stripes are obtained, and the required +.>。
As a preferred embodiment of the present invention: in the third and fourth stepsThe equation for generating a sinusoidal fringe by superimposing the binary fringe images and phase shifting the sinusoidal fringe after half a period is as follows:
in the middle ofAnd->Representing the generation of sinusoidal stripes and stripes after half a period of phase shift, respectively,/->Represents the nth binary stripe, +.>Representing the specific gravity occupied by the nth image, wherein +.>Amplitude binary stripe and front->The coefficients of the binary stripes are identical.
As a preferred embodiment of the present invention: in the fifth step, the black and white stripes are equally spaced, i.e. the pixels occupied by the black stripes and the pixels occupied by the white stripes areBit, so that the stripe is shifted pixel by pixel>After this time, the binary stripes obtained when the translation is continued will be identical to the former + ->The webs are identical, forming a cycle of stripe patterns.
As a preferred embodiment of the present invention: in the fifth step, the solving process of synthesizing the sine fringe pattern I with different phase shifts is as follows:
in the middle ofRepresents the synthesized nth phase shift sinusoidal fringe pattern, N represents the selectionN-step phase shift method of->Representing the specific gravity of the a-th binary stripe image calculated in the step three, < ->Representing the b-th binary stripe obtained in the step four;
wherein, since the value of a only takes M, when the value of a is larger than M, M must be subtracted until a is smaller than M; similarly, since the value of b only takes 2M, when the value taken by b is greater than 2M, 2M must be subtracted until b is less than 2M.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention uses the characteristic of the equidistant binary stripes to repeatedly use the relevant stripes so as to reduce the projected stripe width number, and finally only needs toThe binary stripes with equal spacing can finish four-step, eight-step and sixteen-step phase shifting.
2. According to the invention, the binary stripes are projected in the whole process, so that measurement errors caused by nonlinear response of the projector and the camera to the gray level image are avoided, and the stability of operation measurement data is improved.
Drawings
FIG. 1 is a flow chart of a method according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating a process for obtaining equidistant binary stripes according to an embodiment of the present invention;
FIG. 3 is a graph of the average distribution and the value of sinusoidal fringes in an embodiment of the present invention;
FIG. 4 is a schematic diagram of a binary stripe superimposed as a periodic sinusoidal stripe in an embodiment of the present invention;
FIG. 5 is a schematic diagram of performing phase shift encoding on binary stripes in an embodiment of the present invention.
Detailed Description
The present invention is further illustrated in the accompanying drawings and detailed description which are to be understood as being merely illustrative of the invention and not limiting of its scope, and various equivalent modifications to the invention will fall within the scope of the appended claims to the skilled person after reading the invention.
The invention relates to a phase shift coding method for multiplexing equidistant binary stripes, the principle flow chart is shown in figure 1,
step one: preparing a projection picture, projecting an initial binary stripe image with black and white phase, moving the image to the left one pixel point at a time, and repeatingHypo-co-acquisition->Equidistant binary fringe patterns with different magnitudes;
step two: the sine intensity value with a period of 2 pi is equally divided intoEqual parts, recording the sine intensity value corresponding to each point;
step three: calculating the proportion of each binary stripe image prepared in the step oneThen obtaining a sine fringe pattern I through superposition;
step four: continuously moving the binary stripe in the first step leftwards by one pixel point number, and repeatingSecondary co-acquisition ofEquidistant binary stripes of different widths, corresponding specific gravity +.>The sine fringe pattern I after phase shift by half a period can be generated after superposition, which is the same as that obtained in the step three;
step five: when combined with N-step phase shift, the method will obtainThe binary stripes and the corresponding coefficients are regarded as one cycle connected end to end; every time will be superimposed +.>The binary stripes are shifted backwards +.>The pattern can generate sine stripe patterns I with different phase shifts.
Example 1:
the invention relates to a binary stripe coding projection method based on equidistant, which comprises the steps of firstly preparing a projection picture: and projecting an initial black-and-white alternate binary stripe, moving the image to the left one pixel point at a time, and repeating 7 times to obtain 8 different equidistant binary stripe patterns. Then one period is 2The sinusoidal intensity value of (2) is equally divided into 15 equal parts, and the sinusoidal intensity value corresponding to each point is recorded. Then, the weight of the prepared 8 binary fringe images in the finally generated sine fringe pattern is calculated>And then obtaining a sine fringe pattern I through superposition. And finally, continuously moving the binary stripes in the first step to the left by one pixel point number, repeating 8 times to obtain 16 different equidistant binary stripes, wherein the corresponding coefficients are the same as those obtained in the third step, and generating a sine stripe graph after phase shift by half a period through superposition. When applied in combination with the N-step phase shift method, the resulting 16 binary stripes and their corresponding coefficients are considered as one cycle end to end. And shifting the overlapped 8 binary stripes back by 16/N images each time to generate sine stripe patterns with different phase shifts.
The method comprises the following steps:
step one: a projection picture is prepared. And projecting an initial black-and-white alternate binary stripe, wherein each stripe respectively occupies 8 pixel point values, and the length of 16 pixels is regarded as one period. The image is moved one pixel point to the left each time and repeated 7 times to obtain 8 different equidistant binary fringe patterns. The generation of the initial black-and-white stripes is shown in the following formula:
where T represents the T-th pixel point and a represents the black-and-white stripe generated. The intensity value of white is '1', and the intensity value of black is '0'.
Step two: one period is 2The sinusoidal intensity value of (2) is equally divided into 15 equal parts, and the sinusoidal intensity value corresponding to each point is recorded. The sine stripe intensity value sampling formula is as follows:
wherein Y represents a sine value corresponding to a different n, each time the abscissa increasesWhen the corresponding sine value is recorded, only the value corresponding to 8 points is recorded due to the symmetry of the sine stripes. As shown in fig. 2.
Step three: and (3) calculating the proportion K_n of each binary stripe image prepared in the step (I) in the finally generated sinusoidal stripe image, and obtaining a sinusoidal stripe image I through superposition. Coefficients of 8 binary stripe imagesThe solution equation of (2) is as follows:
in the middle ofRepresenting the specific weight of each image, and combining the intensity value of each pixel point of the binary stripes with the corresponding coefficient +.>Multiplying, and superposing 8 stripes to make the two stripes correspond to the 16 sine stripe intensity values obtained in the step two one by one, so as to obtain the imitated sine stripe. Due to the symmetry of the sine stripes, the required coefficient can be calculated only by the first 8 pixel points. As shown in fig. 3.
Step four: continuously moving the binary stripes in the first step leftwards by one pixel point number, and repeating 8 times to obtain 16 different equidistant binary stripes with corresponding specific gravityAnd (3) generating a sine fringe pattern I after phase shifting by half a period through superposition, wherein the sine fringe pattern I is the same as that obtained in the step (III). In the third and fourth steps, 8 binary stripe images are superimposed to generate a sine stripe and an equation of the sine stripe after half a period of phase shift of the sine stripe is as follows:
in the middle ofAnd->Representing the generation of sinusoidal stripes and stripes after half a period of phase shift, respectively,/->Representation->The nth binary stripe and the corresponding coefficient thereof, wherein the coefficient of the last 8 binary stripes is the same as that of the first 8 binary stripes.
Step five: because the projected black and white stripes are equally spaced, i.e. the black stripes occupy 8 bits of pixels and the white stripes occupy 8 bits of pixels, the binary stripes obtained when the stripes are translated 16 times and then continued to be translated will be the same as the first 16 stripes, i.e. a cycle of stripe patterns is formed. And (3) shifting the overlapped M binary stripes back 16/N images each time to generate sinusoidal stripe patterns I with different phase shifts. In the fifth step, the solving process of synthesizing the sine fringe pattern I with different phase shifts is as follows:
in the middle ofRepresenting the synthesized nth phase shift sinusoidal fringe pattern, N representing the selected N-step phase shift method,/->Representing the specific gravity of the a-th binary stripe image calculated in the step three, < ->And (5) representing the b-th binary stripe obtained in the step four. Since the value of a takes only 8, when a takes a value greater than 8, 8 must be subtracted until a is less than 8; similarly, since the value of b is only 16, when b is greater than 16, 16 must be subtracted until b is less than 16.
When the reconstruction is carried out by combining an N-step phase shift method, the superimposed 8 binary stripes are shifted back by 16/N images each time, so that sinusoidal stripe patterns I with different phase shifts can be generated. The sine pattern of one period generated by the method occupies 16 pixel points, so the number of pixel points of each translation should be a factor of 16, namely, in a multi-step phase shift method, only 16 binary stripes generated by the method can be projected to be suitable for four-step, eight-step and sixteen-step phase shift. Taking a four-step phase shift as an example, a schematic diagram is shown in fig. 3.
Based on the steps, the proposed phase shift coding method for multiplexing equidistant binary stripes. And (3) projecting 16 equidistant binary stripes, and sequentially projecting and collecting. Sinusoidal fringe patterns of different phase shifts highly modulated by the object can be obtained by a series of superposition calculations. The four-step, eight-step and sixteen-step phase shift can be completed only by 16 equidistant binary stripes. In addition, because binary stripes are projected in the whole process, measurement errors caused by nonlinear response of the projector and the camera to gray images are avoided.
The foregoing is only a preferred embodiment of the invention, it being noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the invention.
Claims (7)
1. A method for phase shift encoding of binary stripes, comprising the steps of:
step one: preparing a projection picture, projecting an initial binary stripe image with black and white phase, moving the image to the left one pixel point at a time, and repeatingHypo-co-acquisition->Equidistant binary fringe patterns with different magnitudes;
step two: the sine intensity value with a period of 2 pi is equally divided intoEqual parts, recording the sine intensity value corresponding to each point;
step three: calculating the proportion of each binary stripe image prepared in the step oneThen obtaining a sine fringe pattern I through superposition;
step four: continuously moving the binary stripe in the first step leftwards by one pixel point number, and repeatingHypo-co-acquisition->Equidistant binary stripes of different widths, corresponding specific gravity +.>The sine fringe pattern I after phase shift by half a period can be generated after superposition, which is the same as that obtained in the step three;
step five: when combined with N-step phase shift, the method will obtainThe binary stripes and the corresponding coefficients are regarded as one cycle connected end to end; every time will be superimposed +.>The binary stripes are shifted backwards +.>The pattern can generate sine stripe patterns I with different phase shifts.
2. The method for phase-shift encoding of binary stripes of claim 1, wherein: each stripe in the projected binary stripes with initial black and white phase respectively occupiesA pixel value of +.>The individual pixel length is considered as one period; the generation of the initial black-and-white stripes is shown in the following formula:
wherein T represents the T pixel point, A represents the generated black and white stripe, and M represents projectionThe number of the stripe patterns; the intensity value of white is 1, and the intensity value of black is 0.
3. The method for phase-shift encoding of binary stripes of claim 1, wherein: in the second step, the sampling formula of the sinusoidal fringe intensity value is as follows:
wherein Y represents a sine value corresponding to a different n, when the abscissa increases by +.>Corresponding sine values are recorded.
4. The method for phase-shift encoding of binary stripes of claim 1, wherein: in step threeThe proportion of the binary stripe image>The solution equation of (2) is as follows:
in (1) the->Representing the specific gravity of the nth image, and associating the intensity value of each pixel point of the binary stripes with corresponding +.>Multiplication by->Overlapping the stripes with the +.>The intensity values of the sine stripes are in one-to-one correspondence, so that the imitated sine stripes are obtained, and the required +.>。
5. The method for phase-shift encoding of binary stripes of claim 1, wherein: in the third and fourth stepsThe equation for generating a sinusoidal fringe by superimposing the binary fringe images and phase shifting the sinusoidal fringe after half a period is as follows:
in->And->Representing the generation of sinusoidal stripes and stripes after half a period of phase shift, respectively,/->Represents the nth binary stripe, +.>Representing the specific gravity occupied by the nth image, wherein +.>Amplitude binary stripe and front->The coefficients of the binary stripes are identical.
6. According to claimThe binary stripe phase shift encoding method of claim 1, wherein the binary stripe phase shift encoding method is characterized by: in the fifth step, the black and white stripes are equally spaced, i.e. the pixels occupied by the black stripes and the pixels occupied by the white stripes areBit, so that the stripe is shifted pixel by pixel>After this time, the binary stripes obtained when the translation is continued will be identical to the former + ->The webs are identical, forming a cycle of stripe patterns.
7. The method for phase-shift encoding of binary stripes of claim 1, wherein: in the fifth step, the solving process of synthesizing the sine fringe pattern I with different phase shifts is as follows:
in->Representing the synthesized nth phase shift sinusoidal fringe pattern, N representing the selected N-step phase shift method,/->Representing the proportion of the a-th binary stripe image calculated in the step three,representing the b-th binary stripe obtained in the step four;
wherein, since the value of a only takes M, when the value of a is larger than M, M must be subtracted until a is smaller than M; similarly, since the value of b only takes 2M, when the value taken by b is greater than 2M, 2M must be subtracted until b is less than 2M.
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