CN114813579A - Method and device capable of eliminating glare on surface of high-light-reflection fruits and vegetables - Google Patents

Abstract

The invention discloses a method and a device capable of eliminating glare on the surface of highly reflective fruits and vegetables, relating to the technical field of fruit and vegetable grading, wherein the method comprises the following steps: s1: the light source emits light; s2: shaping a light beam; s3: adjusting polarization; s4: scattering of an object to be detected; s5: polarized filtering of scattered light; s6: collecting by a lens detector; s7: and (5) computer image acquisition and processing. The device comprises a fruit and vegetable transmission device, fruits and vegetables to be detected, an illumination light source, a light beam shaping module, a first polarization adjusting module, a second polarization adjusting module, a lens and an image detector. The method and the device can eliminate local bright spots, enable the fruits and vegetables to be imaged uniformly in a view field, facilitate the identification of surface characteristics and improve the accuracy of characteristic identification.

Description

Method and device capable of eliminating glare on surface of high-light-reflection fruits and vegetables

Technical Field

The invention belongs to the field of optical detection, is applied to the field of fruit and vegetable classification, relates to a visual system for sorting fruits and vegetables with smooth surfaces (strong light reflection), and particularly relates to a method and a device capable of eliminating surface glare of high light reflection fruits and vegetables.

Background

The quality of the fruits and vegetables is uneven due to congenital and acquired factors, and the classification of the fruits and vegetables has important significance in the aspects of improving the utilization rate of products, reducing waste, facilitating processing and the like. The grading premise of the fruits and vegetables is that the grading features of the fruits and vegetables are extracted, and the extraction of the features needs a good imaging effect, so that a machine vision scheme aiming at grading of different types of fruits and vegetables is particularly important.

In the prior art, patent application publication No. CN113751355A introduces an automatic cherry tomato sorting method and system based on computer vision technology, and the patent technical scheme ignores the problem of cherry tomato surface reflection, and particularly, when identifying cherry tomato defects, the algorithm easily misjudges local overexposure (glare) caused by surface reflection as a defect. Similarly, in the patent application with publication number CN113751355A, the optical system for sorting fruits and vegetables uses LEDs, halogen lamps or laser to collect the images of fruits and vegetables to be tested by shaping and lighting, and uses a conventional area array or linear array camera, and this way, the image collection of fruits and vegetables with rough surfaces (not strong mirror reflection) meets the requirements, but is not suitable for fruits and vegetables with smooth surfaces and strong reflection, because the surfaces of strong reflection fruits and vegetables can generate local overexposure (glare), that is, local bright spots are generated on the reflection surfaces, the existence of bright spots affects the extraction of the characteristics of the fruits and vegetables by the algorithm, and misjudgment is easily generated during the characteristic extraction.

Disclosure of Invention

The invention aims to solve the problem of local overexposure (glare) caused by directional strong light reflection on the surface of a smooth fruit and vegetable in a fruit and vegetable sorting system, the problem is not favorable for algorithm identification, misjudgment is easy to generate during characteristic extraction, and the accuracy of algorithm identification is influenced.

In order to realize the functions and the purposes, the invention provides a method and a device for eliminating glare on the surfaces of highly reflective fruits and vegetables, and the technical scheme is as follows:

first, a method flow diagram is shown in fig. 3.

Secondly, the device comprises a fruit and vegetable transmission device, fruits and vegetables to be detected, an illumination light source, a light beam shaping module, a first polarization adjusting module, a second polarization adjusting module, a lens and an image detector.

The fruit and vegetable transmission device is used for bearing and transmitting fruits and vegetables to be detected, and particularly, the color of the fruit and vegetable transmission device and the color of the fruits and vegetables to be detected are preferably complementary. Complementary colors, i.e. any two colors mixed can be combined into white light, one is complementary color of the other, and the complementary color selection may be a reference hue circle (as shown in fig. 4), preferably a pair of colors within an angle of 120-.

An illumination light source: the imaging system is provided with a light source, the illumination light source can be a halogen light source, and further preferably an LED light source and a laser light source.

A beam shaping module: the light distribution is adjusted, and the light can be homogenized according to the actual functional requirements, and the light homogenizing mode can be a scattering plate light guide plate, a micro-lens array and the like; possibly aperture shaping, beam expanding and beam shrinking and the like; possibly a combination of light sources, etc.

A first polarization adjustment module: the function is to adjust the polarization state of the light emitted by the illumination light source, and select different types of polarization adjusting modules according to the light source type, such as a halogen light source and an LED light source, wherein the working wavelength is 400-760nm, and can also be 400-700 nm. The linear polarizer is formed by gluing a dichroic material and glass or a high-molecular transparent film. The linear polarizer functions as a polarizer, i.e., converts unpolarized light into polarized light, and since the polarization direction of transmitted light is always the same as that of the polarizer, polarized light of any angle can be obtained by adjusting the polarization direction of the polarizer, as shown in fig. 5.

The linear polarizer transmission extinction ratio is required to be larger than 100, the transmission extinction ratio is preferably larger than 500, and the transmission extinction ratio is equal to the ratio of the transmission light intensity when the linear polarizer polarization direction is respectively parallel to and vertically incident on the linear polarizer, so that the linear polarizer transmission and cut-off capability of the linear polarizer to linear polarization is represented. Besides dichroic material polarizers, linear thin film polarizers can be selected, which are manufactured according to the selective transmission effect of the elongated silver nanoparticles to polarized light, and have the advantages of high damage threshold and high price.

The half wave plate is selected when the illumination light is a laser light source, most of laser light is linearly polarized light, the transmission light is still linearly polarized after the linearly polarized light passes through the half wave plate, the polarization direction depends on the included angle between the polarization direction of the incident polarized light and the fast axis direction of the half wave plate, and the half wave plate only delays the phase of the incident light and does not perform extinction.

A second polarization adjustment module: the second polarization adjusting module preferably selects a linear polarizer, the polarization direction and the polarization direction of the polarized light adjusted by the first polarization adjusting module form a certain included angle, the function is to filter the direct reflected light of the linear polarized illumination light through the smooth surface, only the unpolarized light scattered through the surface and the polarized light in the non-polarization direction are reserved, and the local overexposure (glare) of the reflecting surface is caused by the direct reflected light of the part.

Lens and detector: for imaging a target test object.

The invention can be used for sorting and identifying some fruits and vegetables with smooth and reflective surfaces, such as cherry tomatoes, grapes, cherries, nectarines, ginseng fruits and the like.

Compared with the prior art, the invention has the following beneficial effects:

the technical scheme of the invention can effectively eliminate the glare problem in figure 1, embody the image of a sample to be identified, eliminate the image distortion caused by external interference, enable fruits and vegetables to be uniformly imaged in a view field, facilitate the identification of surface characteristics and improve the accuracy of characteristic identification.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is an image of a smooth fruit and vegetable surface with local overexposure problems;

FIG. 2 is an image of FIG. 1 with local bright spots removed;

FIG. 3 is a flow chart of the general concept of the present invention;

FIG. 4 is a color wheel diagram;

FIG. 5 is a polarization adjustment schematic;

FIG. 6 is a schematic view of a scheme of example 1;

FIG. 7 is a schematic view of a scheme of example 2;

FIG. 8 is a schematic illustration of a laser beam combining scheme;

fig. 9 is a schematic diagram of a multiplexed polarization maintaining fiber laser beam combining scheme.

Labeled as:

101: a light source;

102: a light guide plate;

103: a first linear polarizer;

104: a fruit and vegetable conveying device;

105: fruits and vegetables to be detected;

106: a second linear polarizer;

107: an imaging lens;

108: a sensor;

109: a computer;

201: a laser beam combining module;

202: a half wave plate;

203: a point laser shaping line laser module;

204: a fruit and vegetable conveying device;

205: fruits and vegetables to be detected;

206: a third linear polarizing plate;

207: an imaging lens;

208: a sensor;

209 is labeled 204 direction of motion, which can be left or right as shown in the diagram;

210 is a computer;

301. 302, 303 are lasers;

304. 305, 306, 307 are high reflection mirrors corresponding to the laser wavelength;

308. 309 is a dichroic mirror with corresponding wavelength, such as 308 high reflection for 301 and high transmission for 302; 309 high-reflection for 303 and high-transmission for 301 and 302;

310 is a multiplexed polarization maintaining fiber;

311 is a fiber collimator.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.

Example 1

Referring to fig. 6, the background color of the fruit and vegetable transmission device 104 is preferably complementary to the color of the fruit and vegetable 105 to be tested, and taking red cherry tomatoes as an example, the background color of the fruit and vegetable transmission device is preferably blue-cyan; the light source 101 is preferably an LED white light area light source which is composed of a driving circuit, an LED packaging chip array and a light guide plate 102, the light guide plate has the function of enabling illumination to be more uniform, and LED light emission belongs to spontaneous radiation and is unpolarized light; the first polarization adjusting module is a first linear polarizer 103, the working wavelength is 400-.

The energy of the LED light source 101 through the first linear polarizer 103 is calculated as follows:

let the total intensity of light incident on the first linear polarizer be I ₀ When the total light intensity after passing through the first linear polarizer is I, the light intensity I' in any polarization direction is as follows (1):

according to the Malus law which describes the intensity of transmitted light after polarized light is linearly polarized, the intensity I' in any one polarization direction after passing through the first linear polarizer is expressed as the following formula (2):

I″＝I′cos ² θ

wherein θ is an included angle between the polarization direction of the incident polarized light and the polarization direction of the first linear polarizer, and the total light intensity of the unpolarized light after passing through the first linear polarizer is I, which is as follows (3):

the following formula (4) can be obtained by bringing the above formulae (1) and (2) into the formula (3):

the formula (4) shows that unpolarized light enters the first linear polarizer, the transmitted light intensity is at most half of the incident light intensity, and other losses such as surface reflection and impurity absorption are considered, so that the transmitted light intensity is lower than 50%.

In order to improve the illumination uniformity, the two light sources 101 are further required to be symmetrically arranged for the illumination uniformity requirement: if the maximum illumination intensity of the imaging area is Emax and the minimum illumination intensity is Emin, the formula (5) is required:

the recognition error caused by uneven illumination can be avoided.

The second polarization adjusting module is a second linear polarizer 106, the working wavelength is 400-,

an imaging lens 107 and a sensor 108, which may be a CCD or CMOS area array image sensor, and is further preferably a color area array image sensor.

Example 2

In embodiment 1, as can be seen from equation (4), on the premise of considering other losses, the first polarizer causes that more than 50% of light emitted by the LED chip does not participate in illumination, which results in energy waste, so in embodiment two, imaging is proposed by using a line laser + line camera scanning manner, which is beneficial to improving the energy utilization rate of the light source, as shown in fig. 7, compared to the symmetrically placed LED area light source of embodiment 1, in embodiment 2, the light source is replaced by a laser light source (a laser beam combining module 201) which includes three laser beams, and the laser wavelength ranges of the three laser beams can be respectively red: 615-620nm, green: 530-540nm, blue light: 460 and 470 nm. Further, the three laser beams are required to be linearly polarized light. The energy ratio of red light to green light to blue light is 6:3:1, and the three laser beams are further required to have similar light spots and have the size of about 1-2 mm.

Combining the three lasers, as in fig. 8, specifically using two dichroic mirrors to combine the three lasers, and in some other embodiments also combining the lasers may be as in fig. 9, specifically using a multiplexed polarization maintaining fiber 310 to combine the three lasers.

The first polarization adjusting module is an achromatic half-wave plate 202, the working wavelength comprises 460 and 620nm, and the adjustment of any linear polarization direction in the cross section of the light beam transmission direction can be realized by rotating the fast axis of the half-wave plate, and no extinction phenomenon exists, namely, no energy loss exists when the polarization direction is adjusted.

The combined laser beam is incident to a powell prism, which is an optical element (a point laser shaping line laser module 203) capable of shaping point laser into line laser, and further requires a line laser incidence angle of 0-15 °. The length direction of the linear laser is perpendicular to the movement direction of the fruit and vegetable transmission device, and the width direction of the linear laser is less than 2 mm.

The point laser is shaped into a line laser, and the point laser can be a cylindrical lens group, a rod lens, a scanning galvanometer, a polygon mirror and the like without being limited to the Powell prism.

The second polarization adjusting module is a third linear polarizer, and the polarization direction of the third linear polarizer is perpendicular to the polarization direction of the linearly polarized light emitted by the first polarization module.

The fruit and vegetable transmission device comprises an imaging lens 207 and a sensor 208, wherein a slit diaphragm is arranged in the imaging lens, the sensor is a color linear array image sensor, further, three lines of the fruit and vegetable transmission device position irradiated by linear laser, the slit diaphragm arranged in the lens and a target surface of the linear array image sensor are required to be coplanar, the collection angle of the lens is 0-15 degrees, and the lens is the same as incident light or is positioned in the normal direction.

In addition, it should be noted that the terms in the examples of the present application are explained as follows:

(1) LED: a light-emitting diode, which is a spontaneous emission light emitting diode, and emits unpolarized light;

(2) laser: light Amplification by Stimulated Emission of Radiation (LASER), which is polarized Light;

(3) polarized light: the light is an electromagnetic wave, the light is a result of combined action of an electric field component and a magnetic field component, and the vibration direction of the electric field component is defined as the polarization direction of the light, namely the light is linearly polarized when the track of the vibration direction of the electric field is a line;

(4) linear polarizer: the optical component only allows light with the polarization direction being the same as that of the linear polarizer to pass through, and linearly polarized light passes through the polarizer and follows the Malus law;

(5) the transmission extinction ratio represents the transmission and extinction capabilities of linearly polarized light to linearly polarized light which is parallel to and perpendicular to the polarization direction of the linearly polarized light, and the larger the numerical value is, the better the representation performance is;

(6) CCD: a charge coupled device, an image sensor;

(7) CMOS: a complementary metal oxide semiconductor, an image sensor;

(8) a dichroic mirror: an optical element, one direction is highly reverse to a wave band, the other direction is highly transparent to another wavelength, is used for laser beam combination;

(9) a half wave plate: the phase delay optical element is made of a birefringent material, linearly polarized light enters a half wave plate, phase delay pi of ordinary light (o light) and non-ordinary light (e light) is achieved, if the included angle between the polarization direction of the linearly polarized light entering the half wave plate and the fast axis of the half wave plate is theta, the included angle between the refracted emergent light and the fast axis of the half wave plate is 2 theta, and when the half wave plate rotates 90 degrees, the polarization direction rotates 180 degrees, the phase delay optical element is mainly used for adjusting the direction of the linearly polarized light.

In the description of the present invention, it is to be noted that, unless otherwise specified, "a plurality" means two or more; the terms "upper", "lower", "left", "right", "inner", "outer", "front", "rear", "top", "bottom", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience in describing and simplifying the description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. It should also be noted that, unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are intended to be construed broadly, as meaning, for example, permanently connected, removably connected, or integrally connected; the connection can be mechanical connection or circuit connection; may be directly connected or indirectly connected through an intermediate. The specific meaning of the above terms in the present invention can be understood as appropriate to those of ordinary skill in the art.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (19)

1. A method for eliminating glare on the surfaces of highly reflective fruits and vegetables is characterized by comprising the following steps:

s1: the light source emits light;

s2: beam shaping, which comprises adjusting light distribution and adopting light homogenizing, aperture shaping, beam expanding and beam contracting or light source beam combining modes;

s3: polarization adjustment, including polarization state adjustment of light emitted by the illumination light source;

s4: scattering an object to be detected;

s5: the polarization filtering of scattered light comprises filtering out direct reflected light of the linear polarized illumination light through a smooth surface, and only keeping unpolarized light scattered from the surface and polarized light in a direction which is not polarized;

s6: collecting by a lens detector;

s7: and (5) computer image acquisition and processing.

2. The method of claim 1, wherein step S1 comprises two symmetrically disposed light sources, and the illumination uniformity requirement is as follows: the maximum illumination intensity of the imaging area is set to be Emax, and the minimum illumination intensity is Emin, so that the following requirements are met:

3. the method of claim 1, wherein the light homogenizing means is a diffuser plate light guide plate or a micro-lens array.

4. The method as claimed in claim 1, wherein when the light source is a halogen light source or an LED light source, the linear polarizer is used for polarization adjustment, and the working wavelength of the linear polarizer is 400-760nm or 400-700 nm.

5. The method of claim 4, wherein the linear polarizer transmission extinction ratio is greater than 100.

6. The method of claim 5, wherein the linear polarizer transmission extinction ratio is greater than 500.

7. The method of claim 1, wherein when the light source is a laser light source, the illumination light polarization uses a half-wave plate, and the reflected light filtering uses a linear polarizer.

8. The method as claimed in claim 7, wherein the operating wavelength of the half-wave plate comprises 460-620 nm.

9. The method of claim 7, wherein the laser source comprises three lasers, and the three laser wavelength ranges are respectively selected from red: 615-620nm, green: 530-540nm, blue light: 460 and 470 nm.

10. The method of claim 9, wherein the three lasers are linearly polarized light and have an energy ratio of red light to green light to blue light of 6:3: 1.

11. The method of claim 10, wherein the three laser spots are similar in size and are 1-2mm in size.

12. The method as claimed in claim 9, wherein the laser combination uses two dichroic mirrors to combine three laser beams, or uses a multiplexing polarization maintaining fiber to combine three laser beams, and the combined laser beams are incident into an optical element of spot laser shaping line laser, wherein the incident angle of the line laser is 0-15 °, the length direction of the line laser is perpendicular to the moving direction of the fruit and vegetable transmission, and the width direction is less than 2 mm.

13. The method of claim 12, wherein the optical element for shaping the point laser into a line laser is any one of a Powell prism, a cylindrical lens group, a rod lens, a scanning galvanometer, or a polygon mirror.

14. The method as claimed in claim 12, wherein the line laser irradiates the fruit and vegetable bearing position, the slit diaphragm built in the lens and the linear array sensor target surface to form a three-line coplanar lens, the collection angle of the lens is 0-15 degrees, and the lens is positioned at the same side of the incident light or in the normal direction.

15. A device capable of eliminating glare on surfaces of highly reflective fruits and vegetables is characterized by comprising:

the fruit and vegetable transmission device is used for bearing and transmitting fruits and vegetables to be detected;

an illumination source providing a light source for the imaging system;

the beam shaping module is used for adjusting light distribution;

the first polarization adjusting module is used for adjusting the polarization state of the light emitted by the illumination light source;

the second polarization adjusting module, the polarization direction of which forms a certain included angle with the polarization direction of the polarized light adjusted by the first polarization adjusting module, is used for filtering the direct reflected light of the linear polarized illumination light through the smooth surface, and only the unpolarized light scattered from the surface and the polarized light in the non-polarization direction are reserved;

the device comprises a lens and a detector, wherein the lens is used for imaging a target object to be measured.

16. The apparatus of claim 15, wherein the fruit and vegetable conveyor color is complementary to the color of the fruit and vegetable to be tested.

17. The device of claim 16 wherein the complementary colors are a pair of colors within an angle of 120 and 180 °.

18. The apparatus of claim 15, wherein the polarization direction of the second polarization adjustment module is perpendicular to the polarization direction of the polarized light adjusted by the first polarization adjustment module.

19. The apparatus of claim 15, further comprising:

a laser beam combining module;

and a point laser shaping line laser module.

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