RU2429509C1 - Method of image optical processing and optical system to this end - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: optical system comprises pulse radiation source to expose object, stationary first lens or set of lenses to collimate radiation, second lens or set of lenses moving along system optical axis to transfer first intermediate image into plane of second intermediate image, third lens or set of lenses to transfer second intermediate image into fixed plane of receiver, and image receiver. Parameters of first and second lenses or set of lenses obey relationships specified in claims.

EFFECT: auto focusing and stabilisation of image scale.

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Description

The present invention relates to optics and can be used in bioidentification systems, in particular according to the iris of the eye, in metrology, as well as in reportage and artistic shooting.

Optical image processing has long been widely known.

However, in conventional systems, when changing the distance to the object, both auto and manual focusing is accompanied by a change in the image scale, which in some cases (bio-identification, metrology and others) seems extremely undesirable, since additional measures for adjusting the scale require additional time, complicate the design and ultimately lead to poor image quality.

Currently, there are many technical solutions aimed at eliminating this drawback and based on various techniques.

Known optical systems containing the first, second and third groups of lenses, the first and second of which are movable [see, for example, patent analogues of Panavision Inc. US 6961188, publ. 02/05/2004, WO 2004/010199, publ. 01/29/2004, TW 263797, publ. 10/11/2006]. In such systems, one intermediate real image is formed, which can be further enlarged.

Known optical systems with zooming and autofocus [see, for example, patents US 4890132 firm Asahi Kogaku Kogio KK, publ. 12/26/1989, US 5055932 by Victor Campani of Japan, Ltd., publ. 10/08/1991, BY 8411. OJSC "Peleng". Publ. 08/30/2006, RU 2262727, N.E. Kundeleva et al., Publication of 10/20/2005, application US 2008204893 of Samsung Electromechanics Co. Ltd., publ. 08/28/2008, and CN 101300525 of Flextronix AP LLS company, publ. 11/05/2008]. These optical systems are made with two separate movable groups of lenses for zooming and for focusing.

Known optical systems containing several groups of lenses, at least two of which are movable [see, for example, patents JP 60090318 by Sankio Seiki Seisakusho KK, publ. 05/21/1985, JP 2071214 by Kopal Co. Ltd., publ. 03/09/1990, US 5748387 from Nippon Kogaku KK, publ. 05/05/1998, US 7330316 company Nippon Kogaku KK, publ. 02/12/2008]. In these systems, both zooming and image size correction are carried out by the coordinated movement of these movable lens groups.

The closest analogue of both the claimed method and the claimed optical system is the method and optical system disclosed in the patent US 7330316 company Nippon Kogaku KK, publ. 02/12/2008. The optical system according to the patent includes a source of pulsed radiation for exhibiting an object, a first lens for collimating the radiation scattered by the object, a second lens for transferring the first intermediate image to the plane of the second intermediate image, a third lens for transferring the second intermediate image to the fixed plane of the receiver and the image receiver. At least two of these lenses are movable. The optical image processing method in this system involves both zooming and image size correction due to the coordinated movement of these movable lenses.

The disadvantage of such an optical system and the corresponding method is the complexity of the task of matching the autonomous movement of two (or more) lenses or groups of lenses.

The inventors of the present invention have found that there are ratios of parameters of a fixed and a movable lens or a group of lenses, the selection of which allows for autofocus and image stabilization by moving only one group of lenses while the object is within or within the operating range of distances from the first lens or group of lenses.

Thus, it is an object of the present invention to provide an optical image processing method and an optical system capable of autofocusing and image stabilization of an object when this object is located or moved along the optical axis within the working distance.

The problem in the method of optical image processing, comprising the following steps:

- exposure of an object moving or within the limits of the working distance by pulsed radiation,

- the collimation of radiation scattered by the object using the first lens or group of lenses made stationary, and the construction of the first intermediate image, the size of which and its location in space are determined by the distance from the object to the entrance pupil of the optical system;

- transfer of the first intermediate image into a spatially fixed plane of the second intermediate image and the construction of the second intermediate image with a constant linear increase using the second lens or group of lenses made movable along the optical axis,

- transfer of the second intermediate image to a fixed plane of the image receiver and the construction of the image of the object using the third lens or group of lenses,

is solved due to the fact that

- the parameters of the first and second lenses or lens groups are selected in accordance with the following ratios:

where d ₁ is the distance from the object to the front main plane of the first lens or group of lenses,

l _max and l _min - the limits of the change in the working distance to the object,

d ₂ is the distance from the rear main plane of the 1st lens or group of lenses to the front main plane of the 2nd group of lenses,

d ₃ - the distance from the second intermediate image to the nearest main plane of the 2nd group of lenses,

F ₁ and F ₂ are the focal lengths of the first and second lens or group of lenses,

α _AD - linear increase in the second intermediate image

and Δα / α _AD is the permissible relative error of the finish linear increase in the optical system.

F ₁ , F ₂ > 0, if the refraction is positive,

F ₁ , F ₂ <0, if the refraction is negative,

d ₃ > 0 if the second intermediate image is valid,

d ₃ <0 if the second intermediate image is imaginary.

The exposure of the object is preferably carried out by monochromatic, including laser, radiation, particularly preferably visible or infrared radiation.

Both the first intermediate image and the second intermediate image can be imaginary or real.

The problem is solved in an optical system containing a source of pulsed radiation for exposing an object moving or within the working distance, the first lens or group of lenses made stationary, for the collimation of radiation scattered by the object, the second lens or group of lenses moving along the optical axis systems for transferring the first intermediate image to the plane of the second intermediate image, a third lens or group of lenses for transferring the second intermediate image niya in a fixed plane of the image receiver and the image receiver,

due to the fact that

- the first and second lenses or groups of lenses are designed so that their parameters satisfy the following relationships:

where d ₁ is the distance from the object to the front main plane of the first lens or group of lenses,

l _max and l _min - the limits of the change in the working distance to the object,

d ₂ is the distance from the rear main plane of the 1st lens or group of lenses to the front main plane of the 2nd group of lenses,

d ₃ - the distance from the second intermediate image to the nearest main plane of the 2nd group of lenses,

F ₁ and F ₂ are the focal lengths of the first and second lens or group of lenses,

α _AD - linear increase in the second intermediate image

and Δα / α _AD is the permissible relative error of the finish linear increase in the optical system.

F ₁ , F ₂ > 0, if the refraction is positive,

F ₁ , F ₂ <0, if the refraction is negative,

d ₃ > 0 if the second intermediate image is valid,

d ₃ <0 if the second intermediate image is imaginary.

The radiation source can be made to create a monochromatic, including laser, radiation flux, preferably to create a visible or infrared radiation flux.

The drawings show non-limiting examples of the implementation of the present invention.

Figure 1 presents a possible implementation scheme of the claimed invention, given to simplify the approximation of thin lenses. Figure 2 presents the design scheme used to justify the claimed invention. Figure 3 shows a schematic diagram of one example of the implementation of the claimed optical system in the approximation of thin lenses with the first imaginary and second real images of the object at its various positions. Figure 4 shows an example implementation of the claimed optical system in the approximation of thin lenses with a second imaginary image. Fig. 5 shows photographs of an extended object obtained using the optical scheme shown in Fig. 3 (Fig. 5a) and using a conventional lens with the same focal length (Fig. 5b). Figure 6 shows the industrial implementation of the optical system for identifying a person by the iris of the eye with parameters adequate to the implementation example shown in figure 4.

Identical elements in all drawings are assigned the same designations.

In figure 1 A is the plane of the object Im ₀ located at a distance d ₁ from the input surface of the 1st fixed lens (group of lenses) L ₁ with a focal length F ₁ (plane B). The value of d _{1 is} adequate to the working distance to the object. The range of changes d ₁ is set a priori. The lens (group of lenses) L ₁ forms the first intermediate image Im ₁ . The segment d ₂ and the plane C reflect the position of the 2nd movable lens (group of lenses) with a focal length F ₂ forming the 2nd intermediate image Im ₂ in the plane D.

The inventive method with reference to figure 1 includes the following steps.

- Exposure of object A moving or within the working distance Δl by a pulsed source of visible or infrared radiation.

- The collimation of the radiation scattered by the object using the first fixed lens L ₁ and the construction of the first imaginary or real intermediate image B, the size of which and its location in space are determined by the distance l from the object to the entrance pupil of the optical system. When moving an object along the axis, its first, in the example of figure 1, imaginary image B will also move. Together with moving the image, its size also changes — here the length of the arrow.

- Transfer of the first intermediate image to the fixed plane of the second intermediate real or imaginary image C and the construction of the specified second intermediate image using a movable group of lenses L ₂ , the parameters of which are related to the parameters of the first group of lenses L ₁ , as well as the working distance Δl and scaling error Δα, given mathematical relations (1) - (4), which provide, along with optical conjugation of the system, object A - a fixed plane C stabilization of the linear increase in volume kta (normalization). Regardless of the movement of object A, its second intermediate image in a fixed plane C remains almost constant in magnitude (with a small error Δα). That is, if when moving object A, its first intermediate image B increases by a certain number of times, the second intermediate image C in the plane C is proportionally reduced. Thus, the size of the second intermediate image C and its position in space remain stable.

- Transferring the second intermediate image C and building the image of the object in the plane of the image receiver D (photomatrix, transmitting television tube, etc.) with a manually or automatically zooming scale and preserving the optical conjugation of the CD planes, which is ultimately equivalent to optical conjugation the plane of the object A and the plane of its final image D or, in other words, the creation in the plane of the receiver of a focused image with a fixed magnification (scale).

Justification of the claimed invention with reference to figure 2

The conversion of a light beam propagating in the meridional plane of a centered optical system is described in matrix form as follows [A. Gerrard, J.M. Burch. Introduction to Matrix Methods in Optics. Publication John Willey & Sons, London, New York, Toronto, 1976]:

- матрица передачи оптической системы, содержащей N элементов;Where

- transmission matrix of an optical system containing N elements;

- матрица отдельного элемента оптической схемы.y ₁ and u ₁ are the radial and angular coordinates of the beam at the input of the optical system, respectively; y _N and u _N are the coordinates of the beam at the output of the optical system. In the simplest case, the elements of an optical scheme are understood to mean individual spherical surfaces (thin lenses), as well as the gaps between them, filled with a medium with a refractive index n. In the formula (5)

- matrix of an individual element of the optical scheme.

In figure 2 A is the plane of the object Im ₀ located at a distance d ₁ from the input surface of the 1st fixed lens (group of lenses) L ₁ with a focal length F ₁ (plane B). The value of d _{1 is} adequate to the working distance to the object. The range of changes d ₁ is set a priori. The lens (group of lenses) L ₁ forms the first intermediate image Im ₁ .

Similarly, the segment d ₂ and the plane C reflect the position of the 2nd movable lens (group of lenses) with a focal length F ₂ forming the 2nd intermediate image Im ₂ in the plane D.

To solve the problem posed in the claimed invention, the position of the plane D should not change with a change in the distance to the object (d ₁ ), and variations in the linear magnification of the 2nd intermediate image, defined as the ratio y ₂ / y ₁ , should not go beyond the permissible inaccuracies.

The second intermediate image is transferred to the plane of the photodetector G by the lens system L ₃ , which, depending on specific conditions, can have both fixed and variable focal length F ₃ , for example, for controlling the scale of the final image Im ₃ independent of the lens system L ₁ and L ₂ .

рассматриваемой оптической системы на участке A-D объединяет N=5 элементов: интервал d₁, линзу L₁, промежуток d₂, линзу L₂ и отрезок D₃.Transmission Matrix

of the considered optical system in the area AD combines N = 5 elements: the interval d ₁ , the lens L ₁ , the gap d ₂ , the lens L ₂ and the segment D ₃ .

In accordance with the formula (5)

Here, the values of y ₁ and y ₂ correspond to the notation shown in figure 2.

According to [A. Gerrard], the condition for optical conjugation of the planes A and D (the object is its image) is that the parameter β of the transfer matrix is equal to zero:

When condition (7) is fulfilled according to formula (6), the expression for linear increase in the segment AD takes the form:

It can be shown that in the paraxial approximation for the optical system shown in FIG. 2, the parameters α _AD and β _{AD are} determined by the following relationships:

Here F ₁ , F ₂ > 0, if the spherical surface is convex (positive lens);

F ₁ , F ₂ <0, if the spherical surface is concave (negative lens);

d ₃ > 0 if the second intermediate image is valid;

d ₃ <0 if the second intermediate image is imaginary.

Thus, to solve the problem posed in the claimed invention, it is necessary to require the following conditions:

- предельно допустимая относительная погрешность линейного увеличения оптической системы в целом.

- the maximum permissible relative error of the linear increase in the optical system as a whole.

It is also obvious that conditions (1) and (2) must be supplemented by the requirement of stability of the position in space of the second intermediate image (plane D in FIG. 2) and independence of this position from variations in the distance d ₁ . This requirement may be expressed in the following form:

As an initial condition for the calculation, the permissible error of increasing Δα and the working distance boundary Δl are set.

Equations (1-4) combine the set of conditions necessary for forming an object image in the plane of the photodetector with a constant, fixed increase (scale) when moving the specified object along the optical axis within the specified working distance Δl (formula (4)). These conditions are as follows:

1. the condition of optical conjugation of the object and its second intermediate and, therefore, the final image - equation (1);

2. the condition for the stability of the linear increase (scale) of the object is equation (2);

3. The condition for the constancy of the spatial position of the second intermediate image is equation (3).

The system of equations (1) - (4) has many solutions, which is confirmed by the following implementation examples.

Example 1

Optical system for photographic recording and subsequent identification of a person by the features of the structure of the face

The optical system shown in figure 3, provides photographic registration of a person's face with a constant increase in the range of distances from 700 to 1000 mm. The system for registering and identifying a person according to the features of the structure of the face in this case does not require image scaling during its primary computer processing and additionally allows the absolute sizes of individual anatomical elements to be used in the recognition process.

The principle of operation of the optical system is as follows.

The object Im ₀ (plane A) is located (or moves) along the axis of the optical system within the working distance d ₁ -d ₁ '= Δl. A negative lens (lens system) L ₁ (plane B) builds the first imaginary intermediate image Im ₁ . The magnitude and localization of Im ₁ on the optical axis change as the object moves and depend on the distance d ₁ from the object Im ₀ . The first intermediate image Im _{1 is} transferred using a moving positive lens (lens system) L ₂ (plane C) to the plane D. The position of the plane D on the axis is fixed, and the second intermediate image Im ₂ constructed in this way is valid. The fulfillment of conditions (1) - (4) (see the claims) ensures the formation in the plane D of the image Im ₂ with an almost constant increase in α ± Δα (where Δα is a small value). The choice of distance d ₂ can be carried out manually (with a fixed position of the subject) or automatically in autofocus mode (moving subject). The second image Im ₂ stabilized in magnitude and localization is transferred by the lens system L ₃ (plane E) to the surface of the photodetector, for example, a CCD array (plane G, image Im ₃ ) for registration and subsequent computer processing.

The paraxial calculation of the optical system in question using formulas (1) - (4) for a working distance of 1000 mm <d ₁ <700 mm gives the following parameters:

- the focal length of the first lens (group of lenses) F ₁ = -588 mm;

- the focal length of the second lens (group of lenses) F ₂ = + 294 mm;

- the position of the 2nd intermediate image d ₂ + d ₃ = 882 mm;

- when changing the distance to the object from 700 to 1000 mm, the distance between the lenses (groups of lenses) L ₁ and L ₂ (value d ₂ ) varies from 188.2 to 102.9 mm.

Under the specified parameters and conditions, the linear increase in the second intermediate image is minus 0.62 ± 0.01 when moving the object along the axis within the working distance.

The focal length of the lens group L ₃ and the position of this group on the optical axis are determined by the specific parameters of the photodetector matrix and the requirements for the final increase in the lens as a whole.

The result of the described example implementation of the claimed invention is presented in figa, while on figb is a control image obtained in close conditions using a conventional lens. To increase the depth of field, sequential single-frame shooting and subsequent integration of images using the Helicon Focus program were used.

The recorded width of the objects in figa in accordance with the claims is practically independent of the distance to the lens. This effect here is the basis of the visual illusion of broadening (in the general case, an increase in size) of an object as it moves away from the observer. In reality (this can easily be verified by a simple measurement) there is no such broadening. The effect can be used in art photography, reportage filming and other similar cases.

Example 2

Photographic registration system for subsequent identification of the person by the iris

Consider the lens-camera system, shown in figure 4, can provide photorecording of the iris of a person’s eyes with a constant increase in the range of distances from 205 to 305 mm. It, as in the previous example, does not require scaling of the image during its primary computer processing, which reduces the time required for identification of a person and helps to improve the quality of the final image. The range of applications of this system can be significantly expanded. In particular, it can be useful in the metric of moving micro-objects, in art photography and other areas.

Here, the input fixed positive lens L ₁ (plane B) constructs the first virtual real image (not shown in the drawing) of object A. This image is transformed by a movable negative lens L ₂ into an imaginary second intermediate image localized in plane D. The spatial position of plane D is fixed. The fulfillment of conditions (1) - (4) ensures the formation in the plane D of the image with a constant increase of α ± Δα (where Δα is a small value that does not depend on the distance to the object). The second, in this case, imaginary, image is transferred to the photodetector matrix G using the third lens L ₃ . The parameters of the optical scheme calculated in the paraxial approximation — the focal lengths of the lenses and their position in space — are shown in Fig. 4. The dimensions in parentheses correspond to the maximum working distance to the object. The calculated magnification of the second intermediate image when changing the working distance to the object within 205-305 mm does not go beyond A = + 0.2 ± 0.005. The magnification of the lens L ₃ on the segment of the second intermediate image - the image on the matrix of the photodetector G - is 1.1. Thus, the final magnification of the object is 0.22.

Example 3

Industrial implementation of the photographic registration system discussed in Example 2

A sample of the lens for the photographic registration system of the iris shown in Fig.6, is calculated using the data given in Example 2. It is manufactured under industrial conditions and tested. As in the previous case, in Fig. 5 in parentheses are the parameters corresponding to the maximum working distance. The designations SH _i and SH _i 'correspond to the front and rear main planes of the lens groups L ₁ , L ₂ , L ₃ . The lens is achromatized in the near infrared region of the spectrum.

The system shown in Fig.6, contains three groups of lenses, the second of which is installed with the possibility of movement along the optical axis, and an aperture diaphragm.

The first lens of the first group I is the positive meniscus 1, facing concavity to the plane of objects.

The second lens is glued from a positive biconvex lens 2 and a negative biconcave lens 3.

The third lens is a negative meniscus 4, facing concavity to the plane of objects.

The second group of lenses II is made of glued from two lenses - a negative biconcave lens 5 and a positive meniscus 6, convex to the plane of objects.

The third group of lenses III is also made of glued from two lenses - a positive biconvex lens 7 and a negative meniscus 8, facing a concavity to the plane of objects.

The aperture diaphragm is located between the second and third groups of lenses.

The proposed lens is designed to operate in the spectral range of wavelengths λ = (650 ÷ 890) nm. The image scale is β = -0.22 ^x , the numerical aperture in the image space is NA '= 0.08, and the diameter of the working field of the image is 2Y' = 3.3 mm. The working range of distances from the first surface of the first component to the plane of objects is 300–400 mm. The image plane is located at a distance of 50 mm from the last surface of the third component and remains constant when the distance to the plane of objects changes.

The table shows the results of technical testing of the lens according to Example 2, shown in Fig.6. The test bench included a LED backlight source sequentially located on the optical bench in the spectral range of 650 ± 20 nm, transparent myrrh No. 4 as the object of photographic recording, the test lens complete with a CMOS camera with a photographic resolution of 1600 × 1200 pixels. The object sequentially moved along the optical axis within the working distance. The lens was focused and the magnification was determined using an extremely high resolution image of the myrrh. The nominal image scale (magnification) is 0.22.

The distance from the object to the lens, mm Lens resolution, lin./mm Image zoom, horizontal,% Image zoom, vertical,% 300 175 0 0 320 125 +0.985 +0.985 340 175 +1.724 +1.724 360 175 0 +2.217 380 175 +0.985 +0.985 400 175 +2.217 0

The test results show that the instability of the image scale when moving an object along the optical axis within the working distance does not exceed 2.5%.

Claims (8)

1. A method of optical image processing, comprising the following steps:
exposure of an object moving or within the limits of the working distance by pulsed radiation,
the collimation of radiation scattered by the object using the first lens or a group of lenses made stationary, and the construction of the first intermediate image, the size of which and the location in space are determined by the distance from the object to the entrance pupil of the optical system;
transferring the first intermediate image into a spatially fixed plane of the second intermediate image and constructing the second intermediate image using a second lens or group of lenses made movable along the optical axis,
transferring the second intermediate image to a fixed plane of the image receiver and constructing an image of the object using a third lens or group of lenses,
characterized in that
the parameters of the first and second lenses or lens groups are selected in accordance with the following ratios:

Where

Where

d ₂ + d ₃ = const,
l _max ≥d ₁ ≥l _min ,
where d ₁ is the distance from the object to the front main plane of the first lens or group of lenses;
l _max and l _min - the limits of the change in the working distance to the object;
d ₂ - the distance from the rear main plane of the 1st lens or group of lenses to the front main plane of the 2nd group of lenses;
d ₃ - the distance from the second intermediate image to the nearest main plane of the 2nd group of lenses;
F ₁ and F ₂ are the focal lengths of the first and second lens or group of lenses;
α _AD is a linear increase in the second intermediate image; and
Δα / α _AD is the permissible relative error of the finish linear increase in the optical system;
F ₁ , F ₂ > 0 if the refraction is positive;
F ₁ , F ₂ <0, if the refraction is negative;
d ₃ > 0 if the second intermediate image is valid;
d ₃ <0 if the second intermediate image is imaginary. 2. The method according to claim 1, characterized in that the exposure of the object is carried out monochromatic, including laser, radiation. 3. The method according to claim 1, characterized in that the first intermediate image is imaginary or real. 4. The method according to claim 1, characterized in that the second intermediate image is real or imaginary. 5. The method according to claim 1, characterized in that the exposure of the object is carried out by visible or infrared radiation. 6. An optical system containing a source of pulsed radiation for exhibiting an object, a first lens or group of lenses made stationary to collimate the radiation scattered by the object, a second lens or group of lenses movable along the optical axis of the system to transfer the first intermediate image to the plane of the second an intermediate image, a third lens or a group of lenses for transferring the second intermediate image to a fixed plane of the receiver and the image receiver, characterized in that
the first and second lenses or groups of lenses are designed so that their parameters satisfy the following relationships:

Where

Where

d ₂ + d ₃ = const,
l _max ≥d ₁ ≥l _min ,
where d ₁ is the distance from the object to the front main plane of the first lens or group of lenses;
l _max and l _min - the limits of the change in the working distance to the object;
d ₂ is the distance from the rear main plane of the 1st lens or group of lenses to the front main plane of the 2nd group of lenses;
d ₃ - the distance from the second intermediate image to the nearest main plane of the 2nd group of lenses;
F ₁ and F ₂ are the focal lengths of the first and second lens or group of lenses;
α _AD is a linear increase in the second intermediate image; and
Δα / α _AD is the permissible relative error of the finish linear increase in the optical system;
F ₁ , F ₂ > 0 if the refraction is positive;
F ₁ , F ₂ <0, if the refraction is negative;
d ₃ > 0 if the second intermediate image is valid;
d ₃ <0 if the second intermediate image is imaginary. 7. The system according to claim 6, characterized in that the radiation source is made to create a stream of monochromatic, including laser, radiation. 8. The system according to claim 6, characterized in that the radiation source is made to create a stream of visible or infrared radiation.

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