Interference out-of-focus image speckle steering discrimination method based on autocorrelation
Technical Field
The invention relates to the technical field of measurement of ellipsoidal particles in an optical system, in particular to a method for distinguishing speckle turning of an interference defocused image of a complex particle.
Background
The interference particle imaging method has the advantages of high precision, wide measurement range, non-contact and the like, the research technology is mature, most of research objects are spherical particles with the same size, and the information such as the size, the movement speed, the concentration and the like of the particles can be obtained by processing the interference focusing image and the interference defocusing image. Suspended particles in the atmosphere contain a large number of non-spherical particles, the shape of the particles is close to an ellipsoid, the aspect ratio and the surface curvature and the steering of the ellipsoid particles can influence scattered light distribution, further influence the speckle distribution of interference defocused images, the change of particle steering causes the change of speckle steering of the interference defocused images, and the steering information of the ellipsoid particles can be obtained by analyzing the speckle steering of the interference defocused images, so that the speckle steering judgment of the interference defocused images has important significance in the measurement of the ellipsoid particles.
In the measurement of the transparent ellipsoid particles by using the interference particle imaging technology, patent CN103868831A proposes a cloud particle spectral distribution measurement method and measurement system, which uses an interference particle imaging system to collect an interference defocused image of particles and a depolarized interference defocused image, and distinguishes the phase state of the cloud particles by distinguishing the two images.
At present, no example for realizing speckle steering discrimination of the interference out-of-focus image through an autocorrelation algorithm exists.
Disclosure of Invention
On the basis of the prior art, the invention provides an interference defocused image speckle steering distinguishing method based on autocorrelation, which obtains speckle steering through autocorrelation processing of an interference defocused image and is suitable for measurement of transparent ellipsoid particles in an optical system.
The invention discloses an interference out-of-focus image speckle steering discrimination method based on autocorrelation, which comprises the following steps:
step 1, acquiring an interference defocused image of transparent ellipsoid particles under any steering by using an interference particle imaging system;
step 2, carrying out autocorrelation processing on the interference defocused image by using MATLAB, and carrying out binarization processing on a result image of the autocorrelation processing to obtain a central bright spot of the autocorrelation processing;
step 3, utilizing the ellipse to circle out bright spots, and drawing lines along the long axis direction of the ellipse to obtain bright spot steering;
and 4, steering the bright spots in the step 3, namely steering the interference defocused image speckles.
The method can realize speckle turning discrimination of the interference defocused image of the transparent ellipsoid particles, further realize turning discrimination of the transparent ellipsoid particles, and provide technical support for complex particle field measurement.
Reference numerals
FIG. 1 is a flow chart of the interference out-of-focus image speckle steering discrimination method based on autocorrelation.
FIG. 2 is a block diagram of an example interference particle imaging system, wherein: 1. the device comprises a laser, 2, a microscope objective, 3, a spatial filter, 4, a collimating lens, 5, a first cylindrical mirror, 6, a second cylindrical mirror, 7, a glass slide, 8, an imaging lens, 9 and a CCD.
FIG. 3 is a schematic diagram of an interference defocused image and a processing result, wherein: (a) - (d) is a transparent ellipsoidal particle interference defocused image with different speckle steering; (e) - (h) is the result of autocorrelation processing of the interference defocused image; (i) - (l) a combined image of interferometric out-of-focus image speckle magnification and interferometric out-of-focus image autocorrelation bright spot magnification.
Detailed Description
Embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
Example 1: interference particle imaging system
An interference particle imaging system adopted by the invention is shown in figure 2, the wavelength of laser beam emitted by a laser 1 is 532nm, the maximum output power is 6W, the laser beam is expanded by a microscope objective lens 2, filtered by a spatial filter 3 and collimated by a collimating lens 4, and then compressed into a sheet-shaped laser beam with the thickness of 1mm by a first cylindrical mirror 5 and a second cylindrical mirror 6, an imaging lens 8 for collecting particle scattered light is a Nikon 50mm f/1.4D focusing lens, a receiving device 9 is a CCD with the pixel size of 6.45 mu m and the effective pixel number of 1384 multiplied by 1036, the scattering angle theta of the system is 90 degrees, the magnification of the system is 1.67, the object distance is 79.88mm, the image distance is 133.68mm, the particle to be detected is an ellipsoid particle obtained by stretching polystyrene spherical particle with the particle size of 80 mu m, and the axial ratio range of the long particle and the short particle of the ellipsoid is 1.5-2.5.
In the observation process, the particles are distributed on the glass slide 7 in any direction, and the glass slide is parallel to a receiving plane of the CCD9 positioned on the defocused image surface, so that the ellipsoid particles only have a deflection angle on the plane, and interference defocused images of the transparent ellipsoid particles under different speckle turning directions are collected.
Example 2: and (3) obtaining a processing result of the speckle turning of the transparent ellipsoid particle interference defocused image by adopting an autocorrelation processing algorithm, and comparing the processing result:
FIG. 3 is a schematic diagram of an interference defocused image and a processing result. Wherein: (a) - (d) is a transparent ellipsoidal particle interference defocused image with different speckle steering; (e) - (h) is the result of autocorrelation processing of the interference defocused image; (i) - (l) a combined image of interferometric out-of-focus image speckle magnification and interferometric out-of-focus image autocorrelation bright spot magnification. The interference defocused images of the ellipsoidal particles with different rotation directions are obtained to obtain interference images with different speckle rotation directions, representative speckles in the interference defocused images are taken as speckle rotation directions and marked out by dotted lines, and the autocorrelation result of the interference defocused images is taken and marked out by solid lines, and as can be seen from fig. 3, the autocorrelation bright spot rotation directions are the same as the speckle rotation directions of the interference defocused images.