CN109828381B - Edge enhancement imaging method based on optical erasing frequency domain filter plate - Google Patents
Edge enhancement imaging method based on optical erasing frequency domain filter plate Download PDFInfo
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Abstract
The invention relates to an edge enhancement imaging method based on an optical erasing frequency domain filter plate, which is characterized in that a light beam carrying light field information of a target object is subjected to Fourier transform through a lens, a liquid crystal frequency filter plate is placed on a spatial frequency spectrum surface for spatial frequency spectrum modulation, and then the modulated light beam is subjected to inverse Fourier transform to obtain an edge enhancement image. The filter plate for modulating the spatial frequency spectrum of the light beam is prepared by using a liquid crystal photoalignment technology, has a light erasing function, and can realize the electric control on and off of amplitude type filtering by matching with the polarization and the polarization detection which are parallel to each other.
Description
Technical Field
The invention relates to an edge enhancement imaging method, which is based on a liquid crystal photoalignment technology, and the manufactured erasable liquid crystal panel has a frequency domain filtering function, thereby realizing edge enhancement in any direction of an image.
Background
In image processing and acquisition, image edge enhancement is widely researched and is widely applied to the fields of image processing, astronomical detection, pattern recognition and the like. Image edge enhancement methods can be divided into spatial domain enhancement and frequency domain enhancement. The first method is to process the intensity image of the object light field through a computer, but is limited by factors such as the resolution, quality and the like of the image, and the method cannot obtain more object light field information; the second method is that the edge enhancement effect of the image is directly obtained by preprocessing the object light field information in the imaging process.
In recent years, image edge enhancement in the frequency domain has become a focus of research, and frequency domain filtering is based on a 4f system, which places appropriate optical elements (frequency domain filters) on the spatial frequency spectrum plane of an optical system, removes or selectively passes some spatial frequencies, or changes the amplitude and phase of the spatial frequency domain, so that the imaging result is transformed accordingly or improved as required. The frequency domain filter plate modulates the light intensity distribution on the frequency spectrum surface and is a core device of the system. The edge enhancement imaging method based on the optical erasing frequency domain filter plate is provided, and the optical erasing frequency domain filter plate is designed based on the liquid crystal photoalignment technology, so that the edge enhancement of an image in any direction is realized.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method for realizing edge enhanced imaging based on the liquid crystal filter plate is provided, wherein the liquid crystal filter plate is prepared by using a photoalignment technology and can be subjected to a photo-erasing operation.
The technical solution of the invention is as follows: an edge enhancement imaging method based on a light erasing frequency domain filter plate comprises the following steps: incident light, a polarizer, a first lens, a light erasable liquid crystal frequency domain filter plate, a second lens, an analyzer and a camera are shown in figure 1.
Incident light: carrying light field information of a target object;
polarizer: the first lens is positioned in front of the second lens, so that incident light is changed into linearly polarized light;
a first lens: carrying out Fourier transform on the incident beam to obtain a Fourier spectrum of a target on a focal plane of the lens;
frequency domain filtering board: modulating a Fourier spectrum of the target;
a second lens: the lens carries out inverse Fourier transform imaging on the Fourier spectrum modulated by the liquid crystal frequency domain filtering plate.
A polarization analyzer: the polarization transmission direction is parallel to the polarizer;
a camera: an image is captured.
The invention provides a preparation method of a frequency domain filter plate in the system, and the frequency domain filter plate comprises the following steps: the liquid crystal display panel comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged, and the liquid crystal layer is positioned between the first substrate and the second substrate; as shown in fig. 2.
Wherein, the first base plate is provided with spacing particles to support the liquid crystal layer;
a first electrode and a second electrode are respectively arranged on one sides of the first substrate and the second substrate, which are close to the liquid crystal layer;
and one sides of the first electrode and the second electrode, which are close to the liquid crystal layer, are respectively provided with a light erasing and writing orientation control film layer and a light stability orientation film layer.
Further, the material of the liquid crystal layer is nematic liquid crystal.
Furthermore, a preset voltage difference is formed between the first electrode and the second electrode, and the distribution of liquid crystal molecules in the liquid crystal layer is changed, so that the controllable suppression of the frequency domain filtering function is realized.
The invention has the beneficial effects that: the invention discloses a method for realizing image edge enhancement by utilizing a light erasing frequency domain filter plate. The optical erasing filter plate for modulating the light beam in the frequency domain is prepared by adopting a liquid crystal photoalignment technology and has an optical erasing function.
Drawings
FIG. 1 is a schematic diagram of the present invention;
FIG. 2 is a diagram of a liquid crystal frequency domain filter plate according to the present invention;
FIG. 3 is a flow chart of the frequency domain filter plate preparation of the present invention;
FIG. 4 is a diagram of a frequency domain filter panel embodying the present invention;
FIG. 5 is a test light path diagram of the present invention;
FIG. 6 is a graph showing the results of experiments performed on round hole targets according to the present invention;
FIG. 7 is a graph of the results of experiments performed on a spatial resolution plate according to the present invention;
Detailed Description
Taking an active illumination transmission type object as an example, the principle and experimental results of one-dimensional edge enhancement imaging of the active illumination transmission type object are introduced in detail by using an amplitude type liquid crystal frequency domain filter plate. Based on the Hilbert transform theory, edge enhancement is achieved by enhancing the refractive gradient of the object. Thus, the system can enhance the edges of amplitude-type and phase-type objects.
The hilbert transform is based on a 4f system, as shown in fig. 1. Suppose the object light field is o (x)0,y0) The spectrum of the object field obtained when the object passes through the lens to the back focal plane thereof is O (u, v). In this case, a Hilbert filter H (u, v) is placed on the spectral plane of the object light, and the object light fieldThe spectrum of (a) is modulated by the hilbert filter and becomes the product of O (u, v) and H (u, v). When the modulated light field reaches the output plane through the second lens, the output function o' (x) is obtained1,y1)：
o'(x1,y1)＝o(x,y)*h(x1,y1) (1)
Wherein, denotes convolution, h (x)1,y1) Is the inverse fourier transform of the hilbert filter H (u, v).
The hilbert transform for the one-dimensional P order can be defined as:
HP(u)＝exp(iPπ/2)S(u)+exp(-ipπ/2)S(-u) (2)
wherein S (u) is a unit step function. P is the order of the Hilbert transform, which is the classical Hilbert transform when P ═ 1, and will be discussed below under the condition of P ═ 1. The above formula can be changed into:
HP(u)＝isgn(u) (3)
where sgn (u) is a sign function, the output of the whole system can be expressed as:
o'(x1,y1)＝i{[o(x0,y0)]*(1/iπx)} (4)
where 1/i π x is the Fourier transform of the sign function, thus outputting o' (x)1,y1) May be equivalent to o (x)0,y0) The result of convolution with 1/i π x. The hilbert transform, also known as a 90 ° phase shift transform, essentially shifts the positive frequency part of the signal by pi/2 radians and the negative frequency part by-pi/2 radians.
The frequency domain filter plate is used as a core element of the system, and modulates the frequency spectrum of an object optical field, the embodiment provides an optical erasable frequency domain filter plate, fig. 2 is a schematic sectional structure diagram of the optical erasable frequency domain filter plate of the invention, and as shown in fig. 2, the filter plate comprises: the liquid crystal display panel comprises a first substrate, a second substrate and a liquid crystal layer positioned between the first substrate and the second substrate; wherein, the first substrate is provided with spacing particles to support the liquid crystal layer; a first electrode and a second electrode are respectively arranged on one sides of the first substrate and the second substrate, which are close to the liquid crystal layer; and one sides of the first electrode and the second electrode, which are close to the liquid crystal layer, are respectively provided with a photo-erasing orientation film layer and a photo-stabilizing orientation film layer.
Furthermore, the orientation direction of the optical erasing orientation film layer can be repeatedly erased and written for many times, the orientation direction of the optical erasing orientation film layer can be erased and written by irradiating polarized light with corresponding sensitive wavelength, the pattern of the frequency domain filter plate can be changed in real time, and the frequency domain filter plate with multiple modes is generated.
An embodiment of the present invention provides a method for manufacturing a filter plate in an optical erasing frequency domain, and fig. 3 is a flowchart for manufacturing a filter plate in an optical erasing frequency domain according to the present invention, as shown in fig. 3, the method includes the following steps:
and a light erasing orientation film layer is formed on one side of the first substrate provided with the first electrode, which is close to the liquid crystal layer, and a light stabilizing orientation film layer is formed on one side of the second substrate provided with the second electrode, which is close to the liquid crystal layer.
The formation of the photo-erasable alignment film layer and the photo-stable alignment film layer on the sides of the first substrate provided with the first electrode and the second substrate provided with the second electrode, which are close to the liquid crystal layer, respectively, may be as follows:
and respectively spin-coating a photo-erasing alignment material and a photo-stabilizing alignment material on one side of the first substrate provided with the first electrode, which is close to the liquid crystal layer, and one side of the second substrate provided with the second electrode, which is close to the liquid crystal layer.
And baking the first substrate coated with the optical erasing orientation material and the second substrate coated with the optical stabilizing orientation material in a spinning mode to form an orientation film layer.
First exposure: and placing the first substrate coated with the optical erasing orientation film layer and the second substrate coated with the optical stabilizing orientation film layer on a black exposure platform, then placing polarizing films above the first substrate and the second substrate, and placing the polarizing films into an ultraviolet lamp box for irradiation.
And (3) second exposure: and covering a mask plate on the first substrate coated with the optical erasing orientation film layer, and then exposing again, wherein the polarization direction of linearly polarized light is vertical to that of the first exposure.
Arranging spacing particles between the first substrates provided with the first electrodes and encapsulating the spacing particles with the second substrates provided with the second electrodes; the packaged and poured filter plate in the optical erasing frequency domain is shown in fig. 4 under orthogonal polarization and analysis.
The size of the spacer particles can be selected according to specific needs, and the distance between the first substrate and the second substrate can be adjusted by selecting the spacer particles with different sizes.
After the first substrate and the second substrate are packaged into a box, the first substrate surface coated with the optical erasing orientation film layer faces upwards and is covered by any mask plate, and multiple reorientations can be carried out.
A preset voltage difference is formed between the first electrode and the second electrode, and an included angle between liquid crystal molecules in the liquid crystal layer and a plane where the first substrate is located can be changed, so that controllable suppression of a frequency domain filtering function is achieved.
Results of the experiment
As shown in fig. 5, a test optical path system for edge enhanced imaging in an embodiment of the present invention includes: the device comprises a light source, a spatial filter, a collimation and beam expansion lens, an object, a polarizer, a first lens, a light erasing and writing frequency domain filter plate, a second lens, an analyzer and a camera. The light source is a He-Ne laser, the space filter filters stray light in the light source to generate uniform emergent light, the collimation beam expanding lens conducts collimation beam expansion on the light emitted from the space filter, the space filter is arranged on a front focal plane of the collimation beam expanding lens, the polarizer enables incident light to be changed into polarized light, the lens conducts Fourier transform on light beams irradiating an object, the optical erasing template modulates the frequency spectrum of the light, the two pairs of light after frequency spectrum modulation are imaged through the lens, the light passes through the polarization analyzer with the polarization direction parallel to the polarizer, and finally an image with the enhanced edge is obtained through a camera.
The edge-enhanced imaging test optical path system shown in fig. 5 is built by using the optical erasing frequency domain filter plate prepared in the invention. First, the circular hole having a diameter of 7mm was subjected to edge enhancement imaging, and the experimental results are shown in fig. 6, where (a) is the original, (b) is the result of edge enhancement in the x-direction, (c) is the result of edge enhancement in the y-direction, and (d) is the result of edge enhancement in the 45 ° direction. The 2.52lp/mm resolution plate was then subjected to edge enhanced imaging, the experimental results are shown in fig. 7, where (a) is the original and (b) is the x-direction edge enhanced imaging result.
As can be seen from the experimental results of fig. 6 and fig. 7, the invention provides an edge enhanced imaging method based on a filter plate in a photo-erasing frequency domain, wherein the filter plate in the photo-erasing frequency domain prepared by using a liquid crystal photo-alignment technology realizes the effect of edge enhanced imaging on an object.
Those skilled in the art will appreciate that the invention may be practiced without these specific details.
Claims (8)
1. An edge enhancement imaging method based on a light erasing frequency domain filter plate is characterized by comprising the following steps: changing an incident beam carrying the light field information of the object into polarized light by using a polarizer; fourier transform is carried out on the incident beams by using a lens to obtain a spatial frequency spectrum; modulating the spatial frequency spectrum by using a frequency domain filter plate; carrying out inverse Fourier transform on the modulated light beams by using the lens pair to obtain an image; after passing through an analyzer parallel to the polarization transmission direction of the polarizer, shooting an image by using a camera; the frequency domain filter plate for spatially modulating the light beam is prepared by using a liquid crystal photoalignment technology and has a light erasing function;
the frequency domain filter panel includes: the liquid crystal display panel comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged, and the liquid crystal layer is positioned between the first substrate and the second substrate; wherein, the surface of the first substrate is provided with spacing particles to support the liquid crystal layer; a first electrode is arranged on one side, close to the liquid crystal layer, of the first substrate, and a second electrode is arranged on one side, close to the liquid crystal layer, of the second substrate; one side of the first electrode, which is close to the liquid crystal layer, is provided with a light erasing orientation film layer, and one side of the second electrode, which is close to the liquid crystal layer, is provided with a light stabilizing orientation film layer.
2. The method of claim 1, wherein the lens performs Fourier transform on the incident light beam, and the lens performs inverse Fourier transform on the light modulated by the frequency-domain filter.
3. The method as claimed in claim 1, wherein the polarizer in front of the first lens and the analyzer behind the second lens have polarization directions parallel to each other.
4. The method as claimed in claim 1, wherein the camera is located in the Fourier plane of the second lens.
5. The method of claim 1, wherein the filter panel is prepared by liquid crystal photoalignment and has a photo-erasing function.
6. An optical erasable frequency domain filter board prepared by using a liquid crystal photoalignment technology is characterized by comprising the following components: the liquid crystal display panel comprises a first substrate, a second substrate and a liquid crystal layer, wherein the first substrate and the second substrate are oppositely arranged, and the liquid crystal layer is positioned between the first substrate and the second substrate; wherein, the surface of the first substrate is provided with spacing particles to support the liquid crystal layer; a first electrode is arranged on one side of the first substrate, which is close to the liquid crystal layer, and a second electrode is arranged on one side of the second substrate, which is close to the liquid crystal layer; one side of the first electrode, which is close to the liquid crystal layer, is provided with a light erasing orientation film layer, and one side of the second electrode, which is close to the liquid crystal layer, is provided with a light stabilizing orientation film layer.
7. The optical erasable frequency domain filter plate of claim 6, comprising: the light-stable oriented film layer has light-stable characteristics after being oriented and does not change along with multiple exposures; and carrying out multiple reorientations on the optical erasing orientation film layer by using corresponding sensitive wavelength to realize the erasing and writing of any filter pattern.
8. The optical erasable-programmable frequency-domain filter plate of claim 6, wherein a predetermined voltage difference is formed between said first electrode and said second electrode to change the distribution of liquid crystal molecules in said liquid crystal layer, thereby realizing the controllable suppression of the frequency-domain filter function.
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