WO2021143331A1 - 基于高频图案干涉的二进制光栅图像投影反光抑制方法 - Google Patents

基于高频图案干涉的二进制光栅图像投影反光抑制方法 Download PDF

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WO2021143331A1
WO2021143331A1 PCT/CN2020/128627 CN2020128627W WO2021143331A1 WO 2021143331 A1 WO2021143331 A1 WO 2021143331A1 CN 2020128627 W CN2020128627 W CN 2020128627W WO 2021143331 A1 WO2021143331 A1 WO 2021143331A1
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binary
grating
binary grating
coherent
image
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PCT/CN2020/128627
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French (fr)
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何再兴
李沛隆
赵昕玥
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浙江大学
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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
    • G01B11/2509—Color coding
    • 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
    • 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
    • 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
    • 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
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/50—Depth or shape recovery
    • G06T7/521—Depth or shape recovery from laser ranging, e.g. using interferometry; from the projection of structured light

Definitions

  • the present invention relates to the field of active three-dimensional shape measurement, and mainly relates to reverse engineering based on binary grating projection method, which uses high-frequency pattern interference to remove reflective areas distributed on the surface of a measured object, and in particular relates to a high-frequency pattern-based reverse engineering An interference suppression method for binary grating image projection.
  • the binary grating projection method is a structured light three-dimensional measurement technology, which has the advantages of fast measurement speed and high measurement accuracy. In recent years, it has developed into one of the main technologies for structured light three-dimensional measurement.
  • the binary grating projection method it is necessary to project a periodically distributed grating field on the measured object, and the height of the object's topography is contained in the distribution of the grating field.
  • the distribution of the grating field is collected by the camera and decoded by binary threshold segmentation to obtain the shape and height information of the object.
  • the grating is easy to form a high-brightness reflective area on the surface of the measured object, which interferes with the result of threshold segmentation, affects the decoding accuracy, reduces the measurement accuracy of the three-dimensional shape, and even causes the three-dimensional shape.
  • the appearance measurement results show holes and defects in the reflective area.
  • the existing methods for suppressing the reflective area in the binary grating projection method are mainly developed from two aspects: avoiding the generation of the reflective area and overcoming the influence of the reflective area.
  • Feng Wei et al. used interpolation prediction and search algorithm to obtain the best projection gray value, reduce the intensity of raster projection, and avoid the occurrence of reflective phenomena to a certain extent.
  • Budianto et al. based on the distribution characteristics of the grating projection, restored the missing grating information in the reflective area through image restoration, and overcome the impact of the reflective area on the grating projection and three-dimensional measurement accuracy.
  • the existing method to avoid the generation of reflective areas is based on reducing the intensity of the grating projection; in actual measurement, reducing the intensity of the grating projection will reduce the quality of the camera's collection of the grating field and increase the background light intensity of the projection grating.
  • Field interference leads to a reduction in the accuracy of three-dimensional measurement; in addition, it is difficult to suppress excessively strong reflections only by reducing the intensity of the grating projection, and it depends on more complex fitting algorithms to determine the degree of reduction in the intensity of the grating projection, the efficiency of the method, and the efficiency of the method. The convenience of operation needs to be improved;
  • the existing method to overcome the influence of the reflective area because it uses the grating information near the reflective area that is not interfered by the reflective area as a basis to realize the estimation and repair of the missing grating information in the reflective area. Because the estimation results inevitably have errors, Therefore, while suppressing reflections, the image restoration process may destroy the grating field distribution and introduce additional measurement errors.
  • the present invention proposes a method for suppressing light reflection in binary grating image projection based on high-frequency pattern interference.
  • high-frequency pattern interference an interference binary grating is generated; through projection interference binary grating, the reflected light component is removed from The output image is separated to achieve reflection suppression, effectively eliminate the influence of the reflection area on the binary grating field distribution, and improve the accuracy of the three-dimensional profile measurement based on the binary grating projection method.
  • Step 1) generating multiple high-frequency patterns for reflection suppression
  • Step 2 Generate a binary grating for three-dimensional shape measurement.
  • the binary grating is a grating composed of a binary 0-1 coded stripe code, and the binary grating is inverted to generate a reverse binary grating.
  • the reverse binary grating is used For reflection suppression;
  • Step 3 generating multiple coherent binary gratings, the coherent binary grating is obtained by performing interference operation on the coded value in the high-frequency pattern and the coded value in the binary grating/inverted binary grating, and the coherent binary grating is used for reflection suppression ;
  • Step 4 the projection images of multiple coherent binary gratings collected by the projector and captured by the camera are used as the output image, and all the output images are synthesized in a certain way to obtain an output image after reflection suppression, which is regarded as the output image to be projected.
  • the suppression of the reflection of the binary grating image the suppression of the reflection of the output image corresponding to the binary grating projection is realized.
  • the reflection suppression is to suppress the reflection area that appears in the output image when the binary grating used for three-dimensional profile measurement is projected.
  • the reflective area is a high-brightness area formed by the accumulation of reflected light generated by the grating light source irradiating the surface of the object to be measured in a specific position.
  • the high-frequency pattern is a pattern composed of array encoding using a binary 0-1 encoding method, and the encoding value in the high-frequency pattern has high-frequency periodic changes in both the horizontal and vertical directions; multiple high-frequency The pattern satisfies the following conditions: multiple high-frequency patterns have the same number of rows and columns, and for each pixel at each position, the encoding value of the multiple high-frequency patterns at this pixel is not all 0 or all 1.
  • the inversion operation in the step 2) is to perform a "not" logic operation on all the coded values in the binary raster, that is, to set the element with a code value of 0 to 1, and to set the element with a code value of 1 to 0.
  • the multiple high-frequency patterns are respectively interfered with the binary grating to obtain multiple forward coherent binary gratings, and the multiple high-frequency patterns are respectively interfered with the reverse binary grating to obtain multiple reverse coherents.
  • Binary grating is composed of multiple forward coherent binary gratings and multiple reverse coherent binary gratings together to form multiple coherent binary gratings; the interference operation is performed for each row/column using the interference logic operation shown in Table 1 Traverse, perform the interference logic operation shown in Table 1 on the binary elements p1 and p2 at the same position in the middle:
  • p1 is the code value located in the xth row and yth column of the high-frequency pattern
  • p2 is the code value located in the xth row and yth column in the binary raster/reverse binary raster
  • ⁇ is the interference logic operator
  • P1(x,y) ⁇ p2(x,y) represents the output result of the interference logic operation, and the output result is taken as the code value of the xth row and yth column in the coherent binary raster.
  • the above-mentioned interference logic operation guarantees: the pixel with a code value of 0 in the grating before the interference operation is still 0 after the interference operation; in the grating before the interference operation
  • the encoding value after the interference operation depends on the encoding value of the pixel in the high-frequency pattern, that is, if the encoding value of the high-frequency pattern at the pixel is 1, then the interference operation The result is 1; if the code value of the high-frequency pattern at the pixel point is 0, the result of the interference operation is 0.
  • the multiple forward/reverse coherent binary gratings are located at this pixel
  • the coding value of is not all 0 nor all 1; for each pixel with a coding value of 0 in the binary raster, the coding value at this pixel in the multiple positive coherent binary rasters is all 0.
  • the code value in the coherent grating obtained by the interference operation also has a high-frequency periodic change in the horizontal direction/vertical direction. Therefore, the projection result of the coherent grating also satisfies the light intensity decomposition formula. Based on this, in step 4), the light intensity decomposition formula is fully utilized to achieve reflection suppression.
  • a grating projection system is adopted.
  • the grating projection system includes a projector (1), a camera (2), and an object to be measured (3).
  • the projector (1) and the camera (2) are respectively placed on the object to be measured (3)
  • the lens of the projector (1) and the lens of the camera (2) are all facing the object to be measured (3);
  • the coherent binary grating is input to the projector (1) and projected onto the object to be measured (3)
  • the camera (2) collects the image projected by the coherent binary grating onto the object to be measured (3) as an output image.
  • step 4 the synthesis process of the output image is traversed in the following manner for each row/column, specifically:
  • Step 4.1 the forward coherent binary grating is input to the projector (1) is projected onto the object to be measured (3) and the output image is collected by the camera (2), and the N output images corresponding to the forward coherent binary grating are expressed as
  • the inverse coherent binary grating is input to the projector (1) and projected onto the object to be measured (3), and the output image is collected by the camera (2).
  • the N output images corresponding to the inverse coherent binary grating are expressed as For each pixel (x, y) in the output image, perform the following processing to obtain the forward auxiliary image A + and the reverse auxiliary image A - for subsequent reflection suppression:
  • (x, y) is the pixel in the x-th row and y-th column in the output image;
  • max[...] represents the maximum value of all gray values in the square brackets;
  • the code value at this pixel in the multiple positive coherent binary rasters is not all 0 or all 1.
  • a code value of 0 indicates that the light source at the coded pixel is off, and a code value of 1 indicates that the light source at the coded pixel is on.
  • the light source generated at the above-mentioned pixel points guarantees: for any scene point (x, y) that may be illuminated by the light source on the surface of the object under test, multiple light sources generated by multiple positive coherent binary gratings may directly illuminate the scene point (such as As shown in the left image of Figure 3(b)), the scene point may not be irradiated directly (as shown in the right image of Figure 3(b)), and the above two situations must exist.
  • the light intensity at the scene point in the output image I + (x, y) I d (x, y) + I g (x, y) ); FIG.
  • the reflective component is removed and the direct component is retained by the following calculation, and the forward auxiliary image A + is calculated to achieve the reflection suppression:
  • Step 4.2 the forward auxiliary image A + and the reverse auxiliary image A -are subjected to a differential operation to obtain an output image R after reflection suppression.
  • the differential operation refers to each pixel (x, y) in the output image, Expressed as:
  • R (x, y) A + (x, y) -A - (x, y).
  • the present invention linearly decomposes the light intensity reflected by the binary grating field in the output image into two components: the direct component Id and the reflective component Ig, as shown in Figure 3(a).
  • the reflective component is the high-brightness light intensity component formed by the grating light source irradiated to the surface of the object to be measured, after at least two reflections, and accumulated in a specific area on the surface of the object to be measured, as shown in Figure 3(a).
  • the components of the reflected light at point A in) include the direct component Id of the optical path of Op-A-Oc, and the reflective component Ig of the path of Op-BA-Oc.
  • the reflective component is the cause of the reflective area.
  • the direct component is a light intensity component formed by a beam of reflected light that is directly irradiated by the grating light source to the surface of the object to be measured, and is reflected only once.
  • the present invention has found through experiments that for a grating with high-frequency light and dark changes in the horizontal/vertical direction, the light intensity I(x,y) at the pixel point in the x-th row and y-th column in the output image conforms to the following light intensity decomposition formula , As shown in Figure 3(a):
  • the invention calibrates the direct component Id and the reflective component Ig generated by the binary grating field irradiated to the surface of the object to be measured by projecting multiple interference binary gratings, removes the reflective component Ig from the light intensity I, and retains the direct component Id, thereby achieving Reflective suppression.
  • the present invention uses multiple projected coherent binary gratings to separate the reflective components that cause reflections in the output image, retain the direct components after the reflection suppression, and simply take the maximum value, the minimum value, and the subtraction operation. Realizes reflection suppression, avoids the complex fitting algorithm that traditional methods need to reduce the light intensity of the grating projection, and also avoids the complex restoration algorithms that traditional methods need to perform image restoration on the reflective area, and improves the efficiency and convenience of reflection suppression It also guarantees the anti-reflective effect.
  • the present invention avoids the additional error introduced to the grating site by the reflection suppression method based on image restoration, and ensures the accuracy of the three-dimensional shape measurement based on the binary grating projection method after the reflection suppression.
  • the present invention can eliminate the reflection phenomenon caused by the background light intensity, and can realize the reflection suppression when there is a strong reflection phenomenon, and overcome the limitation of the reflection suppression method based on reducing the projection light intensity.
  • the present invention effectively suppresses the reflection phenomenon existing in the output image of the binary grating projection collected by the camera, and improves the accuracy of the three-dimensional shape measurement based on the binary grating projection.
  • Figure 1 is a schematic diagram of the layout and connection of the projection grating system of the present invention
  • Figure 2 is a flow chart of the present invention to achieve reflection suppression
  • Figure 3(a) is a model diagram established by the present invention for the reflection phenomenon
  • Figure 3(b) a schematic diagram of light intensity decomposition
  • Figure 4 is a schematic diagram of the high-frequency patterns, binary stripes, and coherent binary stripes used in an embodiment of the present invention
  • Figure 4(a) shows 6 high-frequency patterns forming multiple high-frequency patterns
  • Figure 4(b) shows The high-frequency pattern and the binary fringe interfere with each other to obtain the coherent binary fringe.
  • Fig. 5 is a comparison diagram of output images before and after reflection suppression in an embodiment of the present invention
  • Fig. 5(a) is an output image captured by a camera without reflection suppression after projection of a binary grating in an embodiment of the present invention
  • Fig. 5 (b) is an embodiment of the present invention, using the method of the present invention to perform reflection suppression on the result shown in Figure 5(a), and the resulting output image after reflection suppression;
  • FIG. 6 is a comparison diagram of three-dimensional topography measurement results before and after light reflection suppression in an embodiment of the present invention.
  • Figure 6(a) is the three-dimensional topography measurement result of the output image without reflection suppression
  • Figure 6(b) is the three-dimensional topography measurement result of the output image after reflection suppression obtained by the method of the present invention.
  • the grating projection system shown in FIG. 1 is adopted.
  • the grating projection system includes a projector 1, a camera 2 and an object 3 to be measured.
  • the projector 1 and the camera 2 are respectively placed on both sides above the object 3 to be measured, and the projector 1
  • the lens of the camera 2 and the lens of the camera 2 both face the object 3 to be measured; the coherent binary grating input projector 1 is projected onto the object 3 to be measured, and the camera 2 collects the image of the coherent binary grating projected onto the object 3 as the output image.
  • Step 1) generate multiple high-frequency patterns;
  • the high-frequency pattern is a pattern used for reflection suppression using a binary 0-1 encoding method, and the encoding value in the high-frequency pattern exists in both the horizontal direction and the vertical direction High frequency periodic change.
  • the high-frequency pattern is composed of a number of square areas of equal size, and each square area is composed of a number of pixels coded as all 0s or all 1, and the code is all 0s. Square areas are shown as white squares, and square areas coded as all ones are shown as black squares. The side length of the square area is 3 pixels.
  • the high-frequency pattern shows alternating high-frequency distribution of black squares and white squares.
  • the multiple high-frequency patterns shown in Figure 4(a) meet the following conditions: the multiple high-frequency patterns have the same number of rows and columns, and the encoding values of two adjacent high-frequency patterns are in the horizontal/vertical direction There is a translation in the same direction at a distance of 1 pixel. For each pixel at a specific position, the encoding value of multiple high-frequency patterns at this pixel is not all 0 nor all 1;
  • Step 2 perform the inversion operation on the binary grating to generate a reverse binary grating
  • the binary grating is a kind of grating that adopts binary 0-1 encoding and is used for three-dimensional shape measurement
  • the inversion operation is performed on the binary All coded values in the raster are subjected to a "not" logic operation, that is, an element with a code value of 0 is set to 1, and an element with a code value of 1 is set to 0
  • the inverted binary grating is used for reflection suppression;
  • Step 3 Interfere the coded value in the high-frequency pattern and the coded value in the binary grating/inverse binary grating to generate multiple coherent binary gratings.
  • the schematic diagram of the interference operation is shown in Figure 4(b).
  • Multiple high-frequency patterns are interfered with binary gratings to obtain multiple forward coherent binary gratings; multiple high-frequency patterns are interfered with reverse binary gratings to obtain multiple reverse coherent binary gratings; multiple forwards Coherent binary grating and multiple inverse coherent binary gratings together form multiple coherent binary gratings;
  • the interference operation in step 3) uses the interference logic operation shown in Table 1 to traverse each row/column, and performs the interference shown in Table 1 on the binary elements p 1 and p 2 at the same position in the logic operation:
  • p 1 is the code value located in the x-th row and y-th column of the high-frequency pattern
  • p 2 is the code value located in the x-th row and y-th column in the binary raster/reverse binary raster
  • ⁇ is the interference logic Operator
  • p 1 (x, y) ⁇ p 2 (x, y) represents the output result of the interference logic operation, and the output result is used as the code value of the xth row and yth column in the coherent binary raster.
  • Step 4 through the projector projection, the camera to collect multiple coherent binary grating projection images as the output image, all the output images are synthesized according to a certain way to obtain an output image after reflection suppression, to achieve the binary grating projection The reflection suppression of the corresponding output image;
  • the reflection suppression is to suppress the reflection area that appears in the output image when the binary grating used for three-dimensional profile measurement is projected.
  • the reflective area is a high-brightness area formed by the accumulation of reflected light generated by the grating light source irradiating the surface of the object to be measured in a specific position.
  • the synthesis process of the output image in the step 4) uses the following methods to traverse for each row/column, including:
  • Step 4.1 the N output images corresponding to the forward coherent binary grating are expressed as Express the N output images corresponding to the inverse coherent binary grating as For each pixel (x, y) in the output image, the following calculation is performed to obtain a forward auxiliary image A + and a reverse auxiliary image A ⁇ for subsequent reflection suppression.
  • (x, y) is the pixel in the x-th row and y-th column in the output image;
  • max[...] represents the maximum value of all gray values in the square brackets;
  • the code value at this pixel in the multiple positive coherent binary rasters is not all 0 or all 1.
  • a code value of 0 indicates that the light source at the coded pixel is off, and a code value of 1 indicates that the light source at the coded pixel is on.
  • the light source generated at the above-mentioned pixel points guarantees: for any scene point (x, y) that may be illuminated by the light source on the surface of the object under test, multiple light sources generated by multiple positive coherent binary gratings may directly illuminate the scene point (such as As shown in the left image of Figure 3(b)), the scene point may not be irradiated directly (as shown in the right image of Figure 3(b)), and the above two situations must exist.
  • the light intensity at the scene point in the output image I + (x, y) I d (x, y) + I g (x, y) ); FIG.
  • the reflective component is removed and the direct component is retained by the following calculation, and the forward auxiliary image A + is calculated to achieve the reflection suppression:
  • Step 4.2 perform a differential operation on the forward auxiliary image A + and the reverse auxiliary image A - to obtain the output image R after reflection suppression;
  • the difference operation means that for each pixel in the output image (x ,y), perform the following calculations:
  • R (x, y) A + (x, y) -A - (x, y)
  • the ceramic bowl is used as the object to be measured, and the binary grating projection obtained by projection by a projector and collected by a camera is shown in Figure 5(a).
  • the result shown in Figure 5(a) is subjected to anti-reflective suppression, and the resulting output image after anti-reflective suppression is shown in Figure 5(b).
  • the three-dimensional morphology measurement result of the ceramic bowl obtained before the reflection suppression is shown in Figure 6(a).
  • the resulting three-dimensional morphology result of the ceramic bowl is shown in Fig. 6(b).

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Abstract

一种基于高频图案干涉的二进制光栅图像投影反光抑制方法，该方法包括：生成用于反光抑制的多幅高频图案；生成用于三维形貌测量的二进制光栅，对二进制光栅进行取反操作生成反向二进制光栅；生成多幅相干二进制光栅，相干二进制光栅是通过将高频图案中的编码值和二进制光栅/反向二进制光栅中的编码值进行干涉操作所得；通过投影仪（1）投影进而相机（2）采集的多幅相干二进制光栅的投影图像作为输出图像，将所有输出图像按照一定方式进行合成处理，获得一幅反光抑制后的输出图像，即作为需投影的二进制光栅图像反光抑制后的结果。该方法对二进制光栅投影法三维测量中由于反光所导致的错误测量结果进行有效消除，提高基于二进制光栅投影法的三维形貌测量精度。

Description

基于高频图案干涉的二进制光栅图像投影反光抑制方法 技术领域
本发明涉及主动式三维形貌测量领域，主要涉及到基于二进制光栅投影法的逆向工程中，利用高频图案干涉对分布在被测物体表面的反光区域进行去除，尤其涉及一种基于高频图案干涉的二进制光栅图像投影反光抑制方法。
背景技术
二进制光栅投影法是一种结构光三维测量技术，具有测量速度快、测量精度高等优势，近年来已发展成为结构光三维测量的主要技术之一。
在二进制光栅投影法的实际应用中，需要对被测物体投影呈周期分布的光栅场，物体的形貌高度蕴含在光栅场的分布中。通过相机采集光栅场的分布，并通过二进制阈值分割进行解编码，获得物体的形貌高度信息。受到被测物体反射特性以及投影面光源分布特性的影响，光栅容易在被测物体表面形成高亮度的反光区域，干扰阈值分割结果，影响解编码精度，降低三维形貌测量精度，甚至造成三维形貌测量结果在反光区域出现空洞和缺失。
现有抑制二进制光栅投影法中反光区域的方法，主要从避免反光区域的产生和克服反光区域影响两方面展开。在避免反光区域产生的方面，冯维等人通过插值预测查找算法，求得最佳投影灰度值，降低光栅投影的强度，一定程度地避免反光现象的发生。在克服反光区域影响的方面，Budianto等人根据光栅投影的分布特性，通过图像修复的方式，对反光区域中缺失的光栅信息进行复原，克服反光区域对光栅投影和三维测量精度的影响。
上述现有方法存在的问题主要有：
其一，现有避免反光区域产生的方法，基于降低光栅投影的强度实现；在实际测量中，降低光栅投影的强度的同时会降低相机采集光栅场的质量，并增大背景光强的投影光栅场的干扰，导致三维测量精度的降低；此外，仅通过降低光栅投影的强度，难以抑制过于强烈的反光现象，且依赖于较为复杂的拟合 算法确定光栅投影强度降低的程度，方法的效率和操作的便利性有待提高；
其二，现有克服反光区域影响的方法，由于其利用反光区域附近未受反光干扰的光栅信息作为依据，实现对反光区域中缺失光栅信息的估计和修复，由于估计结果不可避免地存在误差，所以在抑制反光的同时，图像修复过程可能破坏光栅场地分布，引入附加测量误差。
发明内容
针对上述背景技术中存在的问题，本发明提出了一种基于高频图案干涉的二进制光栅图像投影反光抑制方法，通过高频图案干涉，生成干涉二进制光栅；通过投影干涉二进制光栅，将反光成分从输出图像中分离，从而实现反光抑制，有效地消除反光区域对二进制光栅场分布的影响，提高基于二进制光栅投影法三维形貌测量的精度。
如图2所示，本发明所采用的技术方案是：
步骤1)，生成用于反光抑制的多幅高频图案；
步骤2)，生成用于三维形貌测量的二进制光栅，二进制光栅是采用二进制0-1编码条纹编码构成的光栅，对二进制光栅进行取反操作生成反向二进制光栅，所述反向二进制光栅用于反光抑制；
步骤3)，生成多幅相干二进制光栅，相干二进制光栅是通过将高频图案中的编码值和二进制光栅/反向二进制光栅中的编码值进行干涉操作所得，所述相干二进制光栅用于反光抑制；
步骤4)，通过投影仪投影进而相机采集的多幅相干二进制光栅的投影图像作为输出图像，将所有输出图像按照一定方式进行合成处理，获得一幅反光抑制后的输出图像，即作为需投影的二进制光栅图像反光抑制后的结果，实现了对二进制光栅投影所对应的输出图像的反光抑制。
所述反光抑制，是抑制投影用于三维形貌测量的二进制光栅时，在输出图像中出现的反光区域。所述反光区域，是光栅光源照射至待测物体表面所产生的反射光积聚在某一特定位置所形成的高亮度区域。上述高频图案、反向二进 制光栅、相干二进制光栅均用于实现反光抑制。
所述步骤1)中，高频图案是采用二进制0-1编码方式阵列编码构成的图案，高频图案中的编码值在水平方向和竖直方向上均存在高频周期变化；多幅高频图案满足如下条件：多幅高频图案具有相同的行数和列数，且对于每一个位置的像素点，多幅高频图案在这一像素点处的编码值不全为0也不全为1。
所述步骤2)中的取反操作是对二进制光栅中的所有编码值进行“非”逻辑运算，即将编码值为0的元素置为1，将编码值为1的元素置为0。
所述步骤3)中，多幅高频图案分别与二进制光栅进行干涉操作，得到多幅正向相干二进制光栅，多幅高频图案分别与反向二进制光栅进行干涉操作，得到多幅反向相干二进制光栅，由多幅正向相干二进制光栅和多幅反向相干二进制光栅共同构成多幅相干二进制光栅；所述的干涉操作，是针对每一行/列均采用表1所示的干涉逻辑运算进行遍历，将位于中相同位置的二进制元素p1和p2进行如表1所示的干涉逻辑运算：
表1
Figure PCTCN2020128627-appb-000001
上表中，p1是位于高频图案中第x行、第y列的编码值，p2是位于二进制光栅/反向二进制光栅中第x行、第y列的编码值，⊙是干涉逻辑运算符，p1(x,y)⊙p2(x,y)表示干涉逻辑运算的输出结果，将输出结果作为相干二进制光栅中第x行、第y列的编码值。
如图4所示，对于和高频图案发生干涉的光栅，上述干涉逻辑操作保证：干涉操作前的光栅中编码值为0的像素点，在干涉运算后仍为0；干涉操作前的光栅中编码值为1的像素点，在干涉操作后的编码值取决于高频图案中位于该像素点处的编码值，即，若高频图案在该像素点处的编码值为1，则干涉操作所得结果为1；若高频图案在该像素点处的编码值为0，则干涉操作所得结果为0。 结合步骤1)中所述的多幅高频图案之间的特点，对于每一个在二进制光栅中编码值为1的像素点，多幅正向/反向相干二进制光栅中在这一像素点处的编码值不全为0也不全为1；对于每一个在二进制光栅中编码值为0的像素点，多幅正向相干二进制光栅中在这一像素点处的编码值全为0。
结合图4以及上述干涉操作的原理，干涉操作所得的相干光栅中的编码值在水平方向/竖直方向上同样存在高频周期变化。因此，相干光栅的投影结果同样满足光强分解公式。基于此，在步骤4)中充分利用光强分解公式实现反光抑制。
所述步骤4)中，采用光栅投影系统，光栅投影系统包括投影仪(1)、相机(2)和待测物体(3)，投影仪(1)和相机(2)分别置于待测物体(3)上方的两侧，投影仪(1)的镜头和相机(2)的镜头均朝向待测物体(3)；将相干二进制光栅输入投影仪(1)投影到待测物体(3)上，相机(2)采集相干二进制光栅投影到待测物体(3)后的图像作为输出图像。
所述步骤4)中，对输出图像的合成处理，针对每一行/列均采用以下方式进行遍历，具体为：
步骤4.1)，正向相干二进制光栅输入到投影仪(1)投影到待测物体(3)上被相机(2)采集获得输出图像，将正向相干二进制光栅所对应的N幅输出图像表示为
Figure PCTCN2020128627-appb-000002
反向相干二进制光栅输入到投影仪(1)投影到待测物体(3)上被相机(2)采集获得输出图像，将反向相干二进制光栅所对应的N幅输出图像表示为
Figure PCTCN2020128627-appb-000003
对于输出图像中的每一个像素点(x,y)，进行如下处理获得用于后续反光抑制的正向辅助图像A +和反向辅助图像A -：
Figure PCTCN2020128627-appb-000004
其中，(x,y)是输出图像中位于第x行、第y列的像素点；max[…]表示取方括号内所有灰度值的最大值；
结合图3和光强分解公式，以正向辅助图像A +为例，对上式的计算原理解 释如下：
对于每一个在二进制光栅中编码值为1的像素点，多幅正向相干二进制光栅中在这一像素点处的编码值不全为0也不全为1。编码值为0表示位于编码像素点处的光源关闭，编码值为1表示位于该编码像素点处的光源开启。上述像素点处所产生的光源保证：对于被测物体表面可能被光源照射的任何一个场景点(x,y)，多幅正向相干二进制光栅所产生的多个光源可能直接照射该场景点(如图3(b)左图所示)，也可能不直接照射该场景点(如图3(b)右图所示)，且上述两种情况必然均存在。如图3(b)左图所示，对于直接照射的情况，输出图像中位于该场景点处的光强I +(x,y)＝I d(x,y)+I g(x,y)；如图3(b)右图所示对于不直接照射的情况，输出图像中位于该场景点处的光强I -(x,y)＝I g(x,y)；且必然有I +(x,y)＞I +(x,y)。因此，在正向相干二进制光栅所对应的N幅输出图像中，通过如下取最大值和最小值的方式计算I +(x,y)和I -(x,y)：
Figure PCTCN2020128627-appb-000005
根据上式，通过如下计算去除反光成分、保留直接成分，计算正向辅助图像A +，实现反光抑制：
A +(x,y)＝I d(x,y)＝I +(x,y)-I -(x,y)
反向辅助图像A -的计算原理可以此类推，在此不再赘述。
步骤4.2)，将正向辅助图像A +与反向辅助图像A -进行差分运算，获得反光抑制后的输出图像R，差分运算是指对于输出图像中的每一个像素点(x,y)，表示为：
R(x,y)＝A +(x,y)-A -(x,y)。
上述处理的作用：其一，能增大输出图像的对比度，提高后续对输出图像进行二进制阈值分割的鲁棒性；其二，由于正向辅助图像和反向辅助图像中位于相同像素点(x,y)处的背景光强是相同的，因此，能抵消背景光强对输出图 像的影响，进一步提高后续对输出图像进行二值化阈值分割的鲁棒性。
本发明将二进制光栅场在输出图像中所反映出的光强，线性分解为两种成分：直接成分Id和反光成分Ig，如图3(a)所示。所述反光成分是光栅光源照射至待测物体表面，经过至少两次反射的多束反射光，积聚在被测物体表面某一特定区域所形成的高亮度的光强成分，如图3(a)中A点处的反射光的成分中，即包括光路为Op-A-Oc直接成分Id，也包括路为Op-B-A-Oc反光成分Ig。反光成分是导致出现反光区域的原因。所述直接成分是光栅光源直接照射至待测物体表面，只经过一次反射的一束反射光，所形成的光强成分。
本发明通过实验发现，对于水平/竖直方向存在高频明暗变化的光栅，输出图像中位于第x行、第y列的像素点处的光强I(x,y)符合如下光强分解公式，如图3(a)所示：
I(x,y)＝I d(x,y)+I g(x,y)
本发明通过投影多幅干涉二进制光栅，对二进制光栅场照射至被测物体表面所产生的直接成分Id和反光成分Ig进行标定，从光强I中去除反光成分Ig，保留直接成分Id，进而实现反光抑制。
本发明的有益效果是：
其一，本发明通过多幅投影相干二进制光栅，将输出图像中导致反光的反光成分进行分离，保留反光抑制后的直接成分，仅通过简单地取最大值、取最小值以及减法运算，即可实现反光抑制，避免了传统方法为降低光栅投影光强所需进行的复杂拟合算法，也避免了传统方法对反光区域进行图像复原所需进行的复杂修复算法，提高了反光抑制的效率和便利性，同时也保证了反光抑制的效果。
其二，本发明避免了基于图像复原的反光抑制方法对光栅场所引入的附加误差，保证了反光抑制后基于二进制光栅投影法的三维形貌测量的精度。
其三，本发明可以消除背景光强所产生的反光现象，并可以在存在强烈的反光现象时实现反光抑制，克服了基于降低投影光强的反光抑制方法的局限性。
综合以上，本发明对相机采集的二进制光栅投影的输出图像中存在的反光 现象实现有效抑制，提高了基于二进制光栅投影的三维形貌测量的精度。
附图说明
图1为本发明投影光栅系统布置连接示意图；
图2是本发明实现反光抑制的流程图；
图3(a)是本发明对反光现象所建立的模型图，图3(b)光强分解原理图；
图4是本发明的一个实施例中，所用高频图案、二进制条纹以及相干二进制条纹的示意图；图4(a)为6幅高频图案，构成多幅高频图案；图4(b)表示高频图案与二进制条纹进行干涉操作，获得相干二进制条纹。
图5本发明的一个实施例中，反光抑制前后输出图像的对比图；图5(a)是本发明的一个实施例中，相机采集的二进制光栅投影后未经过反光抑制的输出图像；图5(b)是本发明的一个实施例中，运用本发明所述方法对图5(a)中所示结果进行反光抑制，所得的经过反光抑制后的输出图像；
图6本发明的一个实施例中，反光抑制前后三维形貌测量结果的对比图。图6(a)是未经过反光抑制的输出图像所得的三维形貌测量结果，图6(b)是运用本发明方法所得经过反光抑制后的输出图像所得的三维形貌测量结果。
图中：投影仪1、相机2、待测物体3。
具体实施方式
下面结合图和实例对本发明进行进一步描述。
具体实施方式采用图1所示的光栅投影系统，光栅投影系统包括投影仪1、相机2和待测物体3，投影仪1和相机2分别置于待测物体3上方的两侧，投影仪1的镜头和相机2的镜头均朝向待测物体3；将相干二进制光栅输入投影仪1投影到待测物体3上，相机2采集相干二进制光栅投影到待测物体3后的图像作为输出图像。
本发明实施例如下：
步骤1)，生成多幅高频图案；所述高频图案是采用二进制0-1编码方式、用于反光抑制的图案，且高频图案中的编码值在水平方向和竖直方向上均存在 高频周期变化。如图4(a)所示，在该实施例中，高频图案由若干大小相等的正方形区域构成，每个正方形区域由若干编码为全0或全1的像素点构成，编码为全0的正方形区域表现为白色方块，编码为全1的正方形区域表现为黑色方块。正方形区域的边长为3个像素。在水平方向上，高频图案中表现出黑色方块和白色方块的高频交替分布。将第一幅高频图案分别向右和向下进行整体平移，每次平移距离为1个像素，连续进行多次平移，可以获得6幅互不相同高频图案，平移的次数是正方形区域的边长的两倍；上述6幅高频图案共同构成多幅高频图案。多幅高频图案是后续生成相干二进制光栅的基础。
图4(a)中所示的多幅高频图案满足如下条件：多幅高频图案具有相同的行数和列数，且相邻两幅高频图案的编码值在水平方向/竖直方向存在同方向的、1个像素距离的平移，对于每一个特定位置的像素点，多幅高频图案在这一像素点处的编码值不全为0也不全为1；
步骤2)，对二进制光栅进行取反操作，生成反向二进制光栅；所述二进制光栅，是一种采用二进制0-1编码、用于三维形貌测量的光栅；所述取反操作，对二进制光栅中的所有编码值进行“非”逻辑运算，即将编码值为0的元素置为1，将编码值为1的元素置为0；所述反向二进制光栅用于反光抑制；
步骤3)，将高频图案中的编码值和二进制光栅/反向二进制光栅中的编码值进行干涉操作，生成多幅相干二进制光栅，干涉操作的示意图如图4(b)所示。
多幅高频图案分别与二进制光栅进行干涉操作，得到多幅正向相干二进制光栅；多幅高频图案分别与反向二进制光栅进行干涉操作，得到多幅反向相干二进制光栅；多幅正向相干二进制光栅和多幅反向相干二进制光栅，共同构成多幅相干二进制光栅；
所述步骤3)中的干涉操作，是针对每一行/列均采用表1所示的干涉逻辑运算进行遍历，将位于中相同位置的二进制元素p 1和p 2进行如表1所示的干涉逻辑运算：
表1
Figure PCTCN2020128627-appb-000006
Figure PCTCN2020128627-appb-000007
上表中，p 1是位于高频图案中第x行、第y列的编码值，p 2是位于二进制光栅/反向二进制光栅中第x行、第y列的编码值，⊙是干涉逻辑运算符，p 1(x,y)⊙p 2(x,y)表示干涉逻辑运算的输出结果，将输出结果作为相干二进制光栅中第x行、第y列的编码值。
步骤4)，通过投影仪投影、相机采集多幅相干二进制光栅的投影图像作为输出图像，将所有输出图像按照一定方式进行合成处理，获得一幅反光抑制后的输出图像，实现对二进制光栅投影所对应的输出图像的反光抑制；
所述反光抑制，是抑制投影用于三维形貌测量的二进制光栅时，在输出图像中出现的反光区域。所述反光区域，是光栅光源照射至待测物体表面所产生的反射光积聚在某一特定位置所形成的高亮度区域。上述高频图案、反向二进制光栅、相干二进制光栅均用于实现反光抑制。
所述步骤4)中对输出图像的合成处理，针对每一行/列均采用以下方式进行遍历，包括：
步骤4.1)，将正向相干二进制光栅所对应的N幅输出图像表示为
Figure PCTCN2020128627-appb-000008
Figure PCTCN2020128627-appb-000009
将反向相干二进制光栅所对应的N幅输出图像表示为
Figure PCTCN2020128627-appb-000010
对于输出图像中的每一个像素点(x,y)，进行如下计算，获得用于后续反光抑制的正向辅助图像A +，和反向辅助图像A -。
Figure PCTCN2020128627-appb-000011
其中，(x,y)是输出图像中位于第x行、第y列的像素点；max[…]表示取方括号内所有灰度值的最大值；
结合图3和光强分解公式，以正向辅助图像A +为例，对上式的计算原理解释如下：
对于每一个在二进制光栅中编码值为1的像素点，多幅正向相干二进制光栅中在这一像素点处的编码值不全为0也不全为1。编码值为0表示位于编码像素点处的光源关闭，编码值为1表示位于该编码像素点处的光源开启。上述像素点处所产生的光源保证：对于被测物体表面可能被光源照射的任何一个场景点(x,y)，多幅正向相干二进制光栅所产生的多个光源可能直接照射该场景点(如图3(b)左图所示)，也可能不直接照射该场景点(如图3(b)右图所示)，且上述两种情况必然均存在。如图3(b)左图所示，对于直接照射的情况，输出图像中位于该场景点处的光强I +(x,y)＝I d(x,y)+I g(x,y)；如图3(b)右图所示对于不直接照射的情况，输出图像中位于该场景点处的光强I -(x,y)＝I g(x,y)；且必然有I +(x,y)＞I +(x,y)。因此，在正向相干二进制光栅所对应的N幅输出图像中，通过如下取最大值和最小值的方式计算I +(x,y)和I -(x,y)：
Figure PCTCN2020128627-appb-000012
根据上式，通过如下计算去除反光成分、保留直接成分，计算正向辅助图像A +，实现反光抑制：
A +(x,y)＝I d(x,y)＝I +(x,y)-I -(x,y)
反向辅助图像A -的计算原理可以此类推，在此不再赘述。
步骤4.2)，将正向辅助图像A +，与反向辅助图像A -进行差分运算，获得反光抑制后的输出图像R；所述差分运算，是指对于输出图像中的每一个像素点(x,y)，进行如下计算：
R(x,y)＝A +(x,y)-A -(x,y)
为表明本发明对二进制光栅图像投影的反光抑制效果，以陶瓷碗为待测物体，通过投影仪投影、通过相机采集所获得二进制光栅投影如图5(a)所示。采用本发明所述方法，对图5(a)中所示结果进行反光抑制，所得反光抑制后的输出图像如图5(b)所示。与图5(a)相对应的，反光抑制前，所得的陶瓷 碗的三维形貌测量结果如图6(a)所示。与图5(b)相对应的，利用本发明所述方法进行反光抑制后，所得的陶瓷碗的三维形貌结果如图6(b)所示。
在图5(a)中，未经过反光抑制时，在陶瓷碗的碗底处分布有明显的反光圈，在陶瓷碗的碗壁、碗沿处分布有明显的反光斑点。经过反光抑制后，在图5(b)中，上述反光圈和反光斑点被显著地去除，表明了本发明实现反光抑制的有效性。
在图6(a)中，未经过反光抑制时，所得的三维形貌测量结果在反光区域出现明显的空洞、缺失现象。经过反光抑制后，在图6(b)中，所得三维形貌测量结果未出现空洞、缺失现象，提高了基于二进制光栅投影的三维形貌测量精度，扩大了基于二进制光栅投影的三维形貌测量的适应性。

Claims (6)

  1. 一种基于高频图案干涉的二进制光栅图像投影反光抑制方法，其特征在于，包括如下步骤：
    步骤1)，生成用于反光抑制的多幅高频图案；
    步骤2)，生成用于三维形貌测量的二进制光栅，二进制光栅是采用二进制0-1编码条纹编码构成的光栅，对二进制光栅进行取反操作生成反向二进制光栅；
    步骤3)，生成多幅相干二进制光栅，相干二进制光栅是通过将高频图案中的编码值和二进制光栅/反向二进制光栅中的编码值进行干涉操作所得；
    步骤4)，通过投影仪投影进而相机采集的多幅相干二进制光栅的投影图像作为输出图像，将所有输出图像按照一定方式进行合成处理，获得一幅反光抑制后的输出图像，即作为需投影的二进制光栅图像反光抑制后的结果，实现了对二进制光栅投影所对应的输出图像的反光抑制。
  2. 根据权利要求1所述的一种基于高频图案干涉的二进制光栅图像投影反光抑制方法，其特征在于：所述步骤1)中，高频图案是采用二进制0-1编码方式阵列编码构成的图案，高频图案中的编码值在水平方向和竖直方向上均存在高频周期变化；多幅高频图案满足如下条件：多幅高频图案具有相同的行数和列数，且对于每一个位置的像素点，多幅高频图案在这一像素点处的编码值不全为0也不全为1。
  3. 根据权利要求1所述的一种基于高频图案干涉的二进制光栅图像投影反光抑制方法，其特征在于：所述步骤2)中的取反操作是对二进制光栅中的所有编码值进行“非”逻辑运算，即将编码值为0的元素置为1，将编码值为1的元素置为0。
  4. 根据权利要求1所述的一种基于高频图案干涉的二进制光栅图像投影反光抑制方法，其特征在于：所述步骤3)中，多幅高频图案分别与二进制光栅 进行干涉操作，得到多幅正向相干二进制光栅，多幅高频图案分别与反向二进制光栅进行干涉操作，得到多幅反向相干二进制光栅，由多幅正向相干二进制光栅和多幅反向相干二进制光栅共同构成多幅相干二进制光栅；所述的干涉操作，是针对每一行/列均采用表1所示的干涉逻辑运算进行遍历，将位于中相同位置的二进制元素p1和p2进行如表1所示的干涉逻辑运算：
    表1
    Figure PCTCN2020128627-appb-100001
    上表中，p1是位于高频图案中第x行、第y列的编码值，p2是位于二进制光栅/反向二进制光栅中第x行、第y列的编码值，⊙是干涉逻辑运算符，p1(x,y)⊙p2(x,y)表示干涉逻辑运算的输出结果，将输出结果作为相干二进制光栅中第x行、第y列的编码值。
  5. 根据权利要求1所述的一种基于高频图案干涉的二进制光栅图像投影反光抑制方法，其特征在于：所述步骤4)中，采用光栅投影系统，光栅投影系统包括投影仪(1)、相机(2)和待测物体(3)，投影仪(1)和相机(2)分别置于待测物体(3)上方的两侧，投影仪(1)的镜头和相机(2)的镜头均朝向待测物体(3)；将相干二进制光栅输入投影仪(1)投影到待测物体(3)上，相机(2)采集相干二进制光栅投影到待测物体(3)后的图像作为输出图像。
  6. 根据权利要求1所述的一种基于高频图案干涉的二进制光栅图像投影反光抑制方法，其特征在于：所述步骤4)中，具体为：
    步骤4.1)，将正向相干二进制光栅所对应的N幅输出图像表示为
    Figure PCTCN2020128627-appb-100002
    Figure PCTCN2020128627-appb-100003
    将反向相干二进制光栅所对应的N幅输出图像表示为
    Figure PCTCN2020128627-appb-100004
    对于输出图像中的每一个像素点(x,y)，进行如下处理获得用于后续反光抑制的正向辅助图像A +和反向辅助图像A -：
    Figure PCTCN2020128627-appb-100005
    其中，(x,y)是输出图像中位于第x行、第y列的像素点；max[…]表示取方括号内所有灰度值的最大值；
    步骤4.2)，将正向辅助图像A +与反向辅助图像A -进行差分运算，获得反光抑制后的输出图像R，差分运算是指对于输出图像中的每一个像素点(x,y)，表示为：
    R(x,y)＝A +(x,y)-A -(x,y)。
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