RU2756375C1 - Method for processing images of speckle structures from scattered laser radiation on ferrofluid nanoparticles oriented in a magnetic field - Google Patents

Abstract

FIELD: checkout technique.

SUBSTANCE: invention relates to the field of checkout technique and concerns a method for processing images of speckle structures. The method consists in processing images of speckle structures formed by nanoparticles of ferrofluid placed in a magnetic field formed in laser radiation transmitted through a cell with ferrofluid or reflected from speckle structures. Images are recorded using a camera without focusing optics with autofocus disabled and processed using the RGB color space. To exclude the influence of the intensity of channels B and G associated with the hardware completion of the computer image to improve its perception by the eye, the brightness, color gamut and shades are aligned to the average value. The remaining part of the light noise is compensated by adjusting the RGB channels. In the case of using high-intensity laser radiation to compensate for noise associated with the hardware completion of the computer on the G and B channels, the curves of the RGB channels are adjusted. At the final stage of processing, the choice of the color radiation intensity from the pixel sequence number is implemented.

EFFECT: improving of the obtained images quality.

1 cl, 12 dwg

Description

A method for processing images of speckle structures from scattered laser radiation on nanoparticles oriented in a magnetic field

The invention relates to instrumentation, namely to methods and devices for monitoring the parameters of the magnetic field in various magnetic systems, in the area of magnetic anomalies for the search for minerals, as well as to low-frequency optical switching elements that have increased resistance to various negative external influences ... An optical image formed from speckle structures of ferrofluid nanoparticles placed in a magnetic field, both in transmitted and reflected laser radiation from speckle structures, contains information on various parameters of the magnetic field (induction value, homogeneity, field line density, etc. .). Image data processing makes it possible to decipher the information contained in the images of speckle structures. When decoding the information contained in the images, it is necessary to take into account a number of features associated with both the measurements themselves, the registration conditions and variations in the magnetic field. The accuracy of the results obtained and the quality of the picture of the structure of the magnetic field lines depend on this. During the measurement process, contact of the measuring elements of the measuring device with the object, which creates a magnetic field, is excluded, which makes it possible to carry out research at a certain distance, for example, from the zone of action of a strong non-uniform magnetic field. Measuring elements used in this method do not change the structure of the object's magnetic field.

The essence of the method is that the signal is recorded from laser radiation scattered or reflected from speckle structures consisting of ferrofluid nanoparticles. Speckle structures are located in the area of magnetic field lines and reflect its structure, especially if the magnetic field is uniform. In this case, speckle structures have a certain periodicity (alternation of zones with transparent and opaque layers for laser radiation). At the location of the camera for recording images, a semblance of a diffraction pattern is formed, which contains maxima and minima. These maxima and minima, due to the peculiarities of registration, contain various light flares and noises. The choice of a line, processing area with a certain size and number of pixels, comparison of the obtained image with images in adjacent areas, re-coding of signals can significantly reduce the influence of parasitic light noise, additional reflections on the roughness of speckle structures and flares on the image of speckle structures. As a result, after processing on a computer screen, a contrast image is formed, which is a semblance of a diffraction pattern with the presence of pronounced maxima and minima.

A large number of methods have been developed for processing images of speckle structures. For the prototype, a method for processing images from speckle structures was chosen to determine the authenticity of security holograms in the express control mode (patent RU 139535 U1, published: 20.04.2014). The task of this method, which is closest to the proposed method, is to isolate a part of the diffraction image in reflected light when it moves in space and compare it with the diffraction pattern obtained from the initial structure of the object before the start of movement. The disadvantages of this method include the fact that the comparison of the displacement of the images on the hologram occurs mainly visually in natural light. To measure image displacement, it is necessary to carry out experiments in a stationary laboratory using complex calculation algorithms based on solving difference equations for the Maxwell system of equations. In this case, it is necessary to determine with high accuracy the distance over which the hologram was displaced and the angles of its rotation relative to the incident light. All this does not allow, after processing the images of speckle structures, to construct a large continuous spatial image, for example, the distribution of the magnetic field between the poles of the magnetic system, which is one of the tasks to which our invention is directed.

The tasks to be solved by the invention claimed by us are to increase mobility, improve accuracy and expand the functionality for registering images of speckle structures associated with ensuring control of changes in the structure of the magnetic field in a given area of space under the influence of various factors. Especially great difficulties arise in the study of the spatial structure of the magnetic field lines in the interpolar space of magnetic systems of various configurations with a high value of induction. In these cases, the previously developed methods using magnetic films, sawdust, and Hall sensor systems are extremely difficult to use.

The method is illustrated by the following images:

FIG. 1 Image of the distribution of ferrofluid nanoparticles into cells in the absence of a magnetic field.

FIG. 2 Image of the distribution of ferrofluid nanoparticles into cells in a uniform magnetic field.

FIG. 3 Experimental setup for recording images of speckle structures of nanoparticles in transmitted and reflected laser radiation.

FIG. 4 Logitech C920 camera

FIG. 5 Image taken from a web camera using autofocus

FIG. 6 Image obtained using matrix only

web - cameras

FIG. 7 Adjusting the contrast, brightness and gamma of the input image: (a) - original image, (b) - processed image

FIG. 8 Adjusting RGB channel levels: (a) - original image, (b) - processed image

FIG. 9 Adjustment of RGB channels curves: (a) - original image, (b) - processed

FIG. 10 Image of speckle structures after processing.

FIG. 11 Image of speckle structures from laser radiation transmitted through a ferrofluid placed in cells: a) - corresponds to a uniform magnetic field; b) - an inhomogeneous magnetic field.

FIG. 12 Image of speckle structures from laser radiation reflected from a ferrofluid placed in a cell: a) - corresponds to a magnetic field with a low degree of inhomogeneity; b) - a magnetic field with a high degree of inhomogeneity.

To study the structure of the magnetic field lines in the interpolar space of the magnetic system, it is most expedient to use laser radiation and rectangular cells with a ferrofluid. This cell can be placed both between the poles of the magnetic system and next to the magnetic system of various configurations. Under the influence of a magnetic field, ferromagnetic nanoparticles (the ferrofluid consists of magnetite particles with a size of 12 to 14 nm or hematite with a size of 13 to 16 nm) are magnetized and placed in the zones of the magnetic field lines. The smaller the size of the ferromagnetic nanoparticles, the more clearly the structure of the magnetic field lines will be reproduced by them. In addition, in the case of a very high density of field lines, the use of small particles makes it possible to eliminate the "sticking" of the field lines and the formation of clumps in comparison with the case of using iron filings. FIG. Figures 1 and 2 show images of field lines on which ferrofluid nanoparticles are located, obtained using a microscope.

Analysis of the obtained images allows us to conclude that in the case of a uniform magnetic field, nanoparticles are distributed in the ferrofluid in a certain periodic sequence (with the formation of transparent and opaque zones for laser radiation). This makes it possible to use images of speckle structures from the scattered laser radiation on nanoparticles transmitted through the cell or reflected from the nanoparticles of a ferrofluid to study the distribution of the magnetic field structure.

FIG. 3 shows a block diagram of an experimental setup for recording images of speckle structures of nanoparticles from transmitted and reflected laser radiation through a cell with a ferrofluid. The experimental setup consists of the following components:

1. Semiconductor laser based on heterostructures with λ = 632.8 nm, with a transverse spatial coherence length Ltk = 10 mm, a radiation divergence angle θ ≈ 0.02 mrad to create coherent, monochramic radiation;

2. Optical system (polarizer) for controlling the intensity of laser radiation;

3. Focusing lens with a focal length of 20 cm;

4. A cell with flat faces with a ferrofluid consisting of an aqueous solution of magnetite with a volume concentration of 0.025 and a surfactant - oleic acid;

5. Aperture with focusing lens. The diaphragm is designed to limit the penetration of parasitic multiple reflected images of laser radiation onto the photosensitive layer of the camera;

6. Video camera Logitech C920 for registration of speckle-structure images;

7. A laptop for processing the registered images of the speckle structure of the reflected and transmitted laser radiation and for determining the necessary operations to adjust the optical system to the maximum contrast.

We neglect the phenomena associated with repeated reflection of laser radiation in the walls of the cell, as well as from a ferrofluid with the walls of the cell, due to the low intensity of the reflected laser radiation, since the cell is made of quartz glass with a refractive index of 1.46. The distance between the laser and the cell during image registration was 30 cm, the distance between the cell and the video camera was 60 cm.The entire size of the experimental setup did not exceed 120 cm.A Logitech c920 camera was used for recording images with a maximum frame rate of 30 Hz, the resolution of the matrix was 1920x1080 (Fig. 4). To eliminate various phenomena associated with multiple reflections of laser radiation, the camera has been modified. All optical lenses were removed from the camera, which formed reflections and glare. It has also been found that using in-camera autofocus results in all images being captured. FIG. 5 shows the captured image using autofocus. It was found that the position of the diffraction maxima and minima of the speckle images is blurred and measurements are impossible. Therefore, the autofocus element was removed from the Logitech c920 camera (Fig. 4). This made it possible to obtain the following image (Fig. 6). Analysis of this image shows that it must be processed to obtain the required contrast image on the computer monitor screen, which will help determine the diffraction order.

Currently, there are a huge number of monitor models from various manufacturers. Monitors vary considerably. This creates problems in the reproduction of the registered images of speckle patterns when the signal registration system is connected to various computers. Therefore, we have developed a method for image processing using a unified system of RGB color spaces (red, green, blue). This system is a cube with 1x1x1 faces. Each face is represented as an octet (28) and can have 256 intensity values, where 0 is the minimum and 255 is the maximum.

The experimental results showed that the input image is inaccurate due to the presence of BG channels, which each have their own color histogram. In this case, the presence of BG intensity is a side effect due to the fact that the computer hardware tries to complete the input image for better perception of it by the eye. As a result, a large amount of noise appears, which significantly affects the visualization of the magnetic field through the value of the intensity of the input radiation. For more accurate intensity information, equalize brightness, contrast, gamma, and hue to average. FIG. 7 shows the results of this image processing.

The results obtained showed that this is not enough, there is still a large amount of noise in the recorded image (Fig. 8.a). Therefore, the developed method uses RGB channels adjustment. This allows you to significantly improve the image (Fig.8b)

When using in experiments laser radiation with high intensity in cases of studies of small variations in magnetic fields (close to the magnetic field of the Earth), the noise in the recorded image remains (Fig. 9.a). Therefore, in the developed method, adjustment of RGB channels curves is used, which makes it possible to make insignificant the influence of noise associated with computer hardware on G and B channels on the image from hell structures (Fig. 9.b). The final stage of processing in the developed method is the selection of the intensity of the color radiation from the ordinal number of the pixel. This makes it possible to obtain a contrasting image of speckle structures for studying the structure of magnetic fields.

Example

FIG. 10 shows an example of an image of speckle structures after processing it by the method developed by us in the case of placing a ferrofluid in a cell in a uniform magnetic field.

Comparison of the results obtained with studies of the structure of the magnetic field (Fig. 10) using a microscope and a camera confirms the efficiency of the proposed method for processing images of speckle structures, the use of which is necessary to study the structure of magnetic field lines.

FIG. 11 shows images of speckle structures for various cases of a magnetic field in which a cell with a ferrofluid is located. The image in FIG. 11.a corresponds to the case of placing a ferrofluid in cells in a uniform magnetic field. The shape of the stripes in the image is repeated in a specific sequence. If an inhomogeneous magnetic field is created in the area where the ferrofluid is located in the cell, the appearance and shape of the stripes on the recorded image (Fig. 11.b) changes significantly.

FIG. 12 shows images of speckle structures from laser radiation reflected from a ferrofluid placed in a cell for various degrees of inhomogeneity of the magnetic field.

The result obtained in FIG. 12 shows that in the image of speckle structures obtained in reflected radiation, there is also symmetry between the stripes (Fig. 12.a) with a weak inhomogeneity of the magnetic field. With the deterioration of the inhomogeneity of the magnetic field, this symmetry is violated (Fig. 12.b).

An analysis of the experimental results of the study of magnetic fields using the method developed by us for processing images of speckle structures showed that the information provided on the image of speckle structures makes it possible to select a row by cell height and plot the intensity distribution. This will make it possible to determine the position of the maxima and minima and to estimate the distance between the lines of force of the magnetic field.

In addition, our experimental results allowed us to establish one more feature. The degree of contrast of the image of the speckle structures from the laser radiation transmitted through the ferrofluid is higher than in the recorded image of the speckle structures in the reflected radiation. Therefore, in the case of determining the distance between the lines of force from the recorded image of the speckle structures, the measurement accuracy will be higher when using the image from the laser radiation passed through the cell with the ferrofluid.

Claims (1)

A method for processing images of speckle structures, which consists in processing images of speckle structures formed by nanoparticles of a ferrofluid, which is located in a quartz glass cell placed in a magnetic field, formed in laser radiation transmitted through a cell with a ferrofluid or reflected laser radiation from these speckle structures , characterized in that contrast stripes are obtained to determine the position of maxima and minima corresponding to the location of nanoparticles on the magnetic field lines or their absence at a given point of the ferrofluid; for this, images are recorded using a camera without focusing optics, with autofocus turned off and processed using color RGB space (red, green, blue), which is a cube with 1x1x1 faces, each face is represented as an octet (2 ^ 8) and can have 256 intensity values, where 0 is the minimum and 255 is the maximum, to exclude the influence of intensity channels B and G, link Anna with a computer hardware extension of the picture to improve its perception by the eye, the brightness, color gamut and shades are equalized to the average value, the remaining part of the light noise is compensated by adjusting the RGB channels, in the case of using high-intensity laser radiation in experiments to compensate for noise associated with hardware extension by the computer on the G and B channels, the RGB channels curves are adjusted, the use of which makes it possible to make their influence on the image insignificant; at the final stage of processing, the developed method implements the choice of the intensity of color radiation from the ordinal number of the pixel.

Images