RU2295713C2 - Spherical aberration correction device - Google Patents

Abstract

FIELD: optical engineering.

SUBSTANCE: spherical aberration correction device has biconvex lens, electro-optical detector, image input unit and controller. Biconvex lens is optically conjugated with detector. Signal, Image characterizing signal from output of detector enters input of image input unit, which has output connected with input of controller. Controller measures radius of blur circle, as well as dependence of brightness of points on distance from center of blur circle to those points, areas of image which need to be corrected, and restoration of brightness of points to get corrected image. Control signal of controller enters input of electro-optical detector to control its magnification factor and to change in image brightness. Correction of spherical aberration is provided in image while design is kept the same as well as weight-and-size characteristics of objectives; introduction of additional members in construction is not required.

EFFECT: improved efficiency of operation.

5 dwg

Description

The invention relates to computer technology and can be used to correct the spherical aberration of the lens of an optoelectronic sensor (OED) in the development and study of vision systems.

A known method and device for correcting spherical aberration and focusing (US patent No. 6091549, MKI G 02 B 27/14; G 02 B 3/02, published July 18, 2000), consisting of a focusing lens and a correction lens separated by an air gap.

The disadvantage of this device is the low accuracy of aberration correction, due to the impossibility of accurate selection of lenses for a given optical system, the complexity of their manufacture.

Closest to the proposed device is a lens (RF patent No. 2244330, IPC ⁷ G 02 B 9/34; G 02 B 13/18, published January 10, 2005) containing a positive component, including a biconvex lens and a negative meniscus lens, with sides of the subject, and the negative component, made in the form of a meniscus, on the side of the image. In the lens, on one of the optical surfaces of the lenses of the positive component, a hologram optical element is applied with an optical power of 0.01-0.1 of the optical power of the lens, and the characteristic equation of the hologram optical element has the form V _H = A ₁ y ² + A ₂ y ⁴ + A ₃ y ⁶ , where A ₁ , A ₂ , A ₃ are the coefficients; y is the height on the surface of the hologram optical element. The coefficient A _{1 is} proportional to the optical power of the hologram optical element, and the coefficients A ₂ and A _{3 are} respectively proportional to the spherical aberration of the positive and negative components of the lens. The negative component on the image side is convex towards it. The negative lens of the positive component is located between the biconvex lens and the object and is convex towards the object. In this case, the lens is equipped with an additional component in the form of a biconvex lens placed between the negative and positive components.

The disadvantage of this device is the inability to correct aberration without introducing additional corrective elements into the lens, which requires calculating the coefficients of the correcting elements, changing the design of the lens and increasing its overall dimensions.

An object of the invention is to provide correction of spherical aberration while maintaining the design and weight and size characteristics of any lenses without introducing additional elements into their design.

The problem is solved in that an optical-electronic sensor, an image input unit, a controller are introduced into a known device containing a biconvex lens, the lens being optically connected to the OED, the output of the OED is connected to the input of the image input unit, the output of which is connected to the controller input, the controller output connected to the input of the OED.

The invention can be used to improve the quality of the resulting image and meets the criterion of "industrial applicability".

The invention is illustrated by drawings, where Fig. 1 shows a block diagram of a device for correcting spherical aberration, Fig. 2 shows a diagram of the path of rays in a lens with spherical aberration, Fig. 3 shows the path of rays for a point outside the optical axis, Fig. 4 shows explanations for the process of correction of aberration, figure 5 presents the algorithms used in the correction of spherical aberration.

The device comprises (FIG. 1) OED 1, a biconvex lens 2, an image input unit 3, a controller 4, the lens 2 being optically connected to the OED 1, the output of the OED 1 is connected to the input of the image input unit 3, the output of which is connected to the input of the controller 4, the output of controller 4 is connected to the input of the OED 1.

The device operates as follows. The image enters through the biconvex lens 2 to the OED 1, from the output of which an analog signal characterizing the image is sent to the image input unit 3, which converts the analog signal to digital form, and the image is input to the controller 4. Controller 4 performs the calculation operations according to the algorithms in FIG. 5 and image correction.

Spherical aberration is a type of monochromatic aberration and causes a violation of the homocentricity of the beam of rays transmitted through the optical system while maintaining their symmetry about the optical axis. Manifestations of aberration are especially noticeable at night, when the image is distorted in areas close to bright light sources.

The presence of spherical aberration in the system leads to the fact that the image of a bright point object is distorted by changing the brightness of the region around the object, called the scattering circle, radius R

where σ is the aperture angle [Theory of optical systems. Textbook for high schools / B.N. Begunov, N.P. Zakaznov, S.I. Kiryushin, V.I. Kuzichev. - 2nd ed., Revised. and add. - M .: Mechanical Engineering, 1981. - P.157], g - longitudinal spherical aberration (figure 2).

Longitudinal spherical aberration is represented by a polynomial:

where k ₁ , k ₂ - constant for this system parameters characterizing aberration, m - radius of the diaphragm.

To correct the brightness of the points, find the radius R of the scattering circle, inside which a correction is made.

To determine the radius R of the scattering circle of spherical aberration, we compose a system of equations using the relations from the triangles MOS and SO ^/ P ^/ (Fig. 2) and the expressions (1), (2):

where f is the focal length of the optical system.

From the system of equations we obtain

The radius R of the scattering circle is determined depending on the values of the aperture radius and focal length, after which the functional dependence of the brightness I _aber (r) of the points on the distance r to the center of the circle is determined by forming a test image from a point light source on a dark background.

Knowing the radius of the scattering circle R and the function I _aber (r) for a given optical system, the brightness of the image points of any bright object is restored, regardless of its shape according to the formula:

where I _restore (x, y) is the restored brightness value for the point with coordinates (x, y), I (x, y) is the brightness value before correction.

For a light source lying outside the optical axis, the distortion caused by spherical aberration takes the form of an ellipse, and not a circle (figa, b), the major axis of which is directed to the center of the frame. Half the length of the major axis is

where α is the angle between the direction of the light source and the main optical axis.

The determination of the angle α is based on the geometric model of the OED with the front image plane:

where X _OED is half the length of the OED image receiver in meters, X is the horizontal frame size of the image.

Thus, to increase the accuracy of the correction of the brightness of points located outside the main optical axis, a scattering ellipse is used instead of the scattering circle.

To correct spherical aberration, areas are determined where spherical aberration is most pronounced. Then adjust the brightness of the points in the found areas.

The areas requiring correction are determined by dividing the image into rectangles (Fig. 4a), changing the brightness of the image (Fig. 4b) by controlling the gain of the OED, for this, from the controller output, the control signal is input to the OED, then rectangular regions are found in which the brightness I _{cp i, j} has changed slightly compared to the average image brightness I _cp (figure 4):

where I (x, y) is the brightness of the pixel at the frame point (x, y), Y is the vertical size of the image frame, x _i , y _j are the coordinates of the upper left vertex of the rectangle (Fig. 4a), i, j is the beginning index the analyzed rectangle (figa), I _then - the threshold value of brightness.

The algorithm of functioning of the device for correcting spherical aberration is shown in the image in Fig.5b.

At the beginning of the execution of the algorithm (block 1, FIG. 5b), the focal length f, aperture radius m, spherical aberration parameters k ₁ , k ₂ and the functional dependence I (r), which is determined by the algorithm in FIG. 5a, are introduced.

Then, according to the formula (4), the radius R of the scattering circle is determined for given values of f, m, k ₁ , k ₂ (block 2, fig. 5b).

In block 3 (Fig.5b) using the formulas (8), (9), (10) determine the rectangles in which there are areas that require correction (figa).

In block 4 (Fig.5b) according to the formula (5), the brightness of the points is restored, obtaining the corrected image.

To determine the dependence I (r), the algorithm shown in Fig. 5a is used, according to which, based on the entered values f, m, k ₁ , k ₂ (block 1, Fig. 5a), the radius R of the scattering circle is determined, inside which the dependence I is established (r) the brightness of the points from the distance from the center of the circle to these points (block 3, figa).

As the image input block, the image input blocks described in the reference book “Systems of technical vision” (Systems of technical vision: Reference book / V.I.Syryamkin, BCTitov. Yu.G. Yakushenkov and others // // Under the general revision of V .I.Syryamkina, BC Titova, Tomsk: MGP "RASCO", 1992. 367 pp., Ill.) On pages 100-117 in chapter 3.7 "Image input devices in microcomputers", as well as in the patent of A.E. Arkhipov, S.V. Degtyareva, A.F. Rubanova, BCTitova "Device for image input into a computer" No. 2166790 IPC G 06 F 3/00.

The controller can be implemented on the basis of a microcomputer or a personal computer described in the reference book "Systems of technical vision" (Systems of technical vision: Reference book / V.I.Syryamkin, BCTitov. Yu.G. Yakushenkov and others // Edited by V. I. Syryamkina, BC Titova, Tomsk: MGP "RASCO", 1992. 367 pp., Ill.) On cc.93-100 in chapter 3.6 "Microprocessors and microcomputers for vision systems." In particular, on p.94 in the last paragraph it is written: “The microprocessor software is used to adapt the optical information sensor (video camera) of the vision system to the object or environment parameters that change or are tuned during operation and makes possible the operation of all elements of the converter (device). "

Thus, the invention allows you to programmatically correct image distortions caused by the influence of spherical aberration without introducing corrective elements into the lens, thereby preserving the dimensions of the lenses, and expand the scope (the device can be used to correct the spherical aberration of camera lenses and cameras without parsing them).

Claims (1)

A spherical aberration correction device comprising a biconvex lens, characterized in that an optical-electronic sensor, an image input unit and a controller are introduced, the biconvex lens being optically connected to an optical-electronic sensor, from the output of which a signal characterizing the image is input to the image input unit the output of which is connected to the input of the controller, which determines the radius of the scattering circle, the dependence of the brightness of the points on the distance from the center of the scattering circle to these points, her images that require correction, and restore the brightness of the points to obtain a corrected image, while the control signal of the controller is fed to the input of an optoelectronic sensor to control its gain and change the brightness of the image.

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