RU2449491C1 - Method of compensating for signal irregularity of photosensitive elements of multielement photodetector - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: method includes receive of radiation flux and processing the signal from photodetector by formula

where S_i,j is aligned image array; T_iny - output array of image incoming from multielement photodetector and formed as result of recorded radiation effect; Tfon_i,j - array of compensated constant components of signals from photosensitive elements, resulting from defocusing; k_i,j - array of correction factors of multielement photodetector elements sensitivity; i - number of pixel in image array row; j - number of image array row. Tfon_i,j is obtained due to insertion of defocusing element in optical path of optical system which element shifts image plane to cold diaphragm plane or to intermediate plane between cold diaphragm plane and photosensitive elements plane. To obtain Tin _i,j the defocusing element is drawn from optical path.

EFFECT: lower hardware costs, higher processability, flexibility and reliability of compensation of elements signal constant component irregularity, achieving its quality independence from range of changing of external background radiation and incoming flux dynamics, higher image quality.

3 cl, 3 dwg

Description

The invention relates to techniques for imaging, in particular, to systems of optoelectronic devices for forming and processing infrared images (IR), in which the task of correcting a thermal image associated with compensating for heterogeneity of the DC component of the signal of photosensitive elements is relevant, and can be used to develop and creating thermal imaging systems and devices for various purposes with matrix photodetectors (MFPU).

A technical solution is known that describes a method for compensating for signal heterogeneity of photosensitive elements of a multi-element photodetector (RF patent No. 2066057 for invention, IPC: 6 H04N 5/33), which consists in generating a compensation code for the background signal and signal drift for each photosensitive element photodetector; generating a sensitivity correction code for each photosensitive element of the photodetector; reception of the radiation flux to be recorded. The first reference radiation stream is supplied to the photodetector when there is no reception of the radiation stream to be registered with the formation and storage of the electrical signal generated by responding to the first reference radiation stream, and the background component of the photodetector is compensated for when the radiation stream to be registered is received by summing the electric signal from the detected stream radiation with an electrical signal in respect of which memorization is made. At the same time, during the reception of the first reference radiation flux, an electrical signal for compensating the background signal and signal drift is generated and stored for each photosensitive element of the photodetector. Additionally, in the absence of reception of the radiation flux to be recorded, a second reference radiation flux is supplied with the formation and storage of an electric sensitivity correction signal for each photosensitive element of the photodetector. Upon receipt of the radiation flux to be recorded simultaneously with the compensation of the background signal and signal drift for each photosensitive element of the photodetector by summing the pre-processed signal of the corresponding element with the compensation signal of its background signal, for which the memorization was carried out, and the signal drift, sensitivity correction is performed for each photosensitive element of the photodetector by changing the amplitude of the summed signal for each photosensitivity itelnogo element in accordance with its sensitivity correction signal in respect of which effected memorization. In the method, the magnitude of the first reference radiation flux is set in proportion to the magnitude of the external background radiation flux. The compensation process consists of a periodically performed procedure for determining correction factors and a continuously performed procedure for adjusting signals.

The disadvantages of the above technical solutions include: the relatively high hardware costs of the electronic system of a thermal imaging device (TVP) for the implementation of compensation for heterogeneity of the constant component of the signal of photosensitive elements; low manufacturability and universality of compensation for heterogeneity of the DC component of the signal; insufficiently satisfactory quality of a thermal imaging image, in particular, obtained from a photodetector based on a solid solution of cadmium tellurides and mercury; low reliability of compensation for heterogeneity of the constant component of the signal elements; the dependence of the quality of compensation for heterogeneity of the constant component of the signal elements in a wide range of changes in the external background radiation; the dependence of the quality of compensation for heterogeneity of the constant component of the signal of the elements from the dynamics of changes in the input stream of external background radiation.

The disadvantages are caused by the following reasons. First, there is a need to set the magnitude of the first reference radiation flux in proportion to the magnitude of the external background radiation flux, which requires the use of a reference radiation source with the ability to adjust the radiation flux. This circumstance, respectively, requires additional means of monitoring and evaluating the magnitude of the input stream from the reference source. Secondly, to ensure high-quality and reliable compensation of the dark component of the signal of the MFPU photocells, it is necessary to provide continuous monitoring of the input flux of external background radiation, in accordance with which it is necessary to establish the flux of the reference radiation source. This circumstance limits the possibility of observing scenes with high dynamics, in which a rapid change in the magnitude of the external background radiation flux is characteristic. This is due, first of all, to the speed of the control system for the radiation flux of the reference source, to the ability of the control system to quickly adjust the radiation flux of the reference source in accordance with the value of the input flux of external background radiation. Thirdly, the implementation of the method leads to the large dimensions, mass and power consumption of the TVP electronic system, providing compensation for the heterogeneity of the DC component of the photosensitive elements, and in addition to the large dimensions and mass of the optical-mechanical TVP system, which provides compensation for the inhomogeneity of the constant component of the photosensitive signals elements.

A known method of compensating for signal heterogeneity of the photosensitive elements of a multi-element photodetector (V.N. Solyakov, S.I. Zhegalov, L.D. Saganov, A.M. Filachev, K.O. Boltar, I.D. Burlakov, A.N. Sviridov “Method for correcting the heterogeneity of multi-element photodetectors based on scene signals.” Applied Physics. - 2008 - No. 1. - pp. 60-70), taken as the closest analogue, consisting in the fact that the radiation flux to be recorded is received and they process the signal generated by the photodetector, according to the signals received when reg tration scene determined interelement communication inhomogeneities of adjacent elements, then the correction factors for all elements providing outputs of eliminating nonuniformity produce the dynamic correction signals in the range of register photodetector. For each element, a pair of correction coefficients is determined - by offset and sensitivity, with a sufficient level of scene variability on the element. With insufficient scene variability, a one-point correction is performed. According to the implementation, the method is based on the two-point correction method, depending on the scene, adaptation to one or two-point and one-point correction is used. The correction process consists of a periodically performed procedure for determining correction factors and a continuously performed procedure for adjusting signals.

The result of the correction depends on the scene. It is shown that the condition for accurate correction is the inter-element equality of average flows and average deviations of the scene.

The disadvantages of the technical solution include: high hardware costs of the TVP electronic system for the implementation of compensation for the heterogeneity of the constant component of the signal of the photosensitive elements; low manufacturability and universality of compensation for heterogeneity of the DC component of the signal; insufficiently satisfactory quality of the thermal imaging image, in honesty, obtained from a photodetector based on a solid solution of cadmium and mercury tellurides; low reliability of compensation for heterogeneity of the constant component of the signal elements, depending on the contrast of the observed scenes; the dependence of the quality of compensation for heterogeneity of the constant component of the signal elements in a wide range of changes in the external background radiation; the dependence of the quality of compensation for heterogeneity of the constant component of the signal of the elements from the dynamics of changes in the input stream of external background radiation.

The reason for the disadvantages is that the compensation method is based on the use of scene signals.

The use of compensation for scene signals, on the one hand, allows us to simplify the optomechanical part of the TVP, however, on the other hand, it requires significant computational resources. In turn, this circumstance entails an increase in the mass, dimensions and energy consumption of the TVP electronic system. Compensation based on scene signals requires the use of sophisticated computational algorithms and high accuracy analysis, which determines the task of achieving high-quality and reliable scene compensation as difficult to implement.

The use of one-point correction of sensitivity with insufficient scene variability indicates a clearly worse quality of alignment, in this case, than if the alignment was carried out at two points when using reference emitters.

The technical result of the invention is:

- reduction of hardware costs of the TVP electronic system for the implementation of compensation for heterogeneity of the constant component of the signal of photosensitive elements;

- improving the manufacturability and versatility of compensating for the heterogeneity of the constant component of the signal;

- improving the quality of the thermal imaging image, in particular, obtained from a photodetector based on a solid solution of cadmium and mercury tellurides;

- improving the reliability of compensation for heterogeneity of the constant component of the signal elements regardless of the contrast of the observed scenes;

- achieving independence of the quality of compensation for heterogeneity of the constant component of the signal elements in a wide range of changes in the external background radiation;

- achieving independence of the quality of compensation for heterogeneity of the constant component of the signal elements from the dynamics of changes in the input stream of external background radiation.

, где S_i,j - выровненный массив изображения; Tin_i,j - выходной массив изображения, поступающего с многоэлементного фотоприемника, формируемый в результате воздействия излучения, подлежащего регистрации от объекта наблюдения; Tfon_i,j - массив скомпенсированных постоянных составляющих сигналов с фоточувствительных элементов, полученных в результате выполнения расфокусирования; k_i,j - массив коэффициентов коррекции чувствительности элементов многоэлементного фотоприемника, i - номер пикселя в строке массива изображения, j - номер строки массива изображения; при этом Tfon_i,j - массив скомпенсированных постоянных составляющих сигналов с фоточувствительных элементов получают в результате расфокусирования за счет введения в оптический тракт оптической системы тепловизионного прибора расфокусирующего элемента, формирующего на входе фотоприемника равномерный поток излучения или поток с заданной равномерностью и, в результате расфокусирования, смещающего плоскость изображения в плоскость холодной диафрагмы или в промежуточную плоскость между плоскостью холодной диафрагмы и плоскостью фоточувствительных элементов, соответственно; затем осуществляют регистрацию расфокусированного излучения и запись массива Tfon_i,j, формируемого на выходе фотоприемника в ответ на воздействие потока расфокусированного излучения, в память электронной системы; после чего для получения на выходе фотоприемника массива сигналов Tin_i,j, формируемого на выходе фотоприемника в ответ на воздействие подлежащего регистрации излучения от объекта наблюдения, расфокусирующий элемент выводят из оптического тракта; далее выполняют обработку сигналов в соответствии с приведенной формулой, получая выровненный массив изображения.The technical result is achieved by the fact that in the method of compensating for signal inhomogeneity of the photosensitive elements of the multi-element photodetector, which consists in receiving the radiation to be detected and processing the signal generated by the photodetector, the processing being carried out in accordance with the formula

where S _{i, j} is the aligned image array; Tin _{i, j} is the output array of the image coming from the multi-element photodetector formed as a result of exposure to radiation to be registered from the object of observation; Tfon _{i, j} is an array of compensated dc components from photosensitive elements obtained as a result of defocusing; k _{i, j} is the array of sensitivity correction coefficients of the elements of the multi-element photodetector, i is the pixel number in the line of the image array, j is the line number of the image array; in this case, Tfon _{i, j} - an array of compensated constant components of the signals from the photosensitive elements is obtained as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, which forms a uniform radiation stream or a stream with a given uniformity at the input of the photodetector and, as a result of defocusing, shifting the image plane to the plane of the cold diaphragm or to the intermediate plane between the plane of the cold diaphragm and the photo plane vstvitelnyh elements respectively; then the defocused radiation is recorded and the array Tfon _{i, j} formed at the output of the photodetector in response to the influence of the defocused radiation flux is recorded in the memory of the electronic system; then, to receive at the output of the photodetector an array of signals Tin _{i, j} formed at the output of the photodetector in response to the effect of the radiation to be detected from the observation object, the defocusing element is removed from the optical path; further, signal processing is performed in accordance with the above formula, obtaining a aligned image array.

In the method, upon receipt of Tfon _{i, j} , an array of compensated constant signal components from photosensitive elements as a result of defocusing by introducing a defocusing element into the optical path of the optical system of a thermal imaging device, the required field of view of the thermal imaging device is retained - full or partial.

In the Tfon _{i, j} method _{, an} array of compensated constant signal components from photosensitive elements is obtained as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, which forms a uniform radiation stream or a stream with a given uniformity at the input of the photodetector and, as a result of defocusing, shifting the image plane to the plane of the cold diaphragm or to the intermediate plane between the plane of the cold diaphragm and the photo plane sensitive elements, respectively, namely, displacing the image plane into the plane of the cold diaphragm, located at a distance of 10 mm from the plane of the photosensitive elements, or shifting into the intermediate plane between the plane of the cold diaphragm and the plane of the photosensitive elements, located at a distance of less than 10 mm from the plane of the photosensitive elements .

The invention is illustrated by the following description and the accompanying figures. Figure 1 shows a diagram of the implementation of the compensation of the inhomogeneity of the constant component of the signal of the photosensitive elements of a multi-element photodetector with an optical system, implemented at least as two optical components, constructing an intermediate image and transferring the intermediate image to the plane of the image formed in the plane of the photosensitive elements of the photodetector matrices, with the plane of the intermediate image being the plane of the intermediate of the image, where 1 is the input lens, 2 is the projection lens, 3 is the defocusing element (in the position of its entry into the optical path of the optical system it is shown by a solid line, in the position of its output from the optical path of the optical system it is shown by a dashed line), 4 - multi-element photodetector. Figure 2 schematically shows the course of the rays in the absence of a defocusing element in the optical path of the optical system designed to compensate for the heterogeneity of the constant component of the signals of the photosensitive elements, with the image being built behind the plane of the cold diaphragm, in the plane of the photosensitive elements of the photodetector array. Figure 3 schematically shows the course of the rays in the presence of a defocusing element in the optical path of the optical system designed to compensate for the heterogeneity of the constant component of the signals of the photosensitive elements, while performing full compensation for the heterogeneity of the constant component of the signals of the photosensitive elements, with the image being built in the plane of the cold diaphragm.

Currently, the most common and most effective among the methods used in practice for correcting geometric noise in MFPs is the linear or two-point correction method, based on the well-known formula (N. I. Solina, “Aligning sensitivity and correcting geometric noise in thermal imaging images using the two-point correction method”. Information Technologies for Modeling and Control: International Scientific Scientific Library - Edited by Prof. O.Ya. Kravets, Issue 15 - Voronezh: Scientific Book Publishing House - 2004 .; N.I. Solina "Calculation of correction factors in the high-temperature calibration mode on the neuroprocessor L1879VM1 ", International conference" Mathematics. Computer. Education ": Abstracts - Edited by G.Yu. Riznichenko, issue 11, Moscow - Izhevsk: Publishing House" Regular and chaotic dynamics "- 2004; K.O. Boltar, R.V. Grachev, V.V. Poluneev" Determination of defective elements of matrix thermal imaging receivers in the procedure of two-point correction "; Applied Physics. - 2009 - No. 109 (1) - pp. 42-45; R.V. Grachev “Calibration of the parameters of the thermal imaging matrix for two-point correction in the electronic processing unit based on the MC-24 microcontroller”, Questions of radio electronics, ser. EVT - 2008 - issue 3 - pp. 148-156):

,

,

where S _{i, j} is the aligned image array;

Tin _{i, j} is the output array of the image coming from the MFP, formed as a result of exposure to radiation to be registered from the object of observation;

Tfon _{i, j} - array of constant components of the signal from photosensitive elements;

k _{i, j} - array of correction factors for the sensitivity of the elements of the MFP, i - pixel number in the line of the image array, j - line number of the image array,

for values of i from 0 to sizeX and j from 0 to sizeY, moreover, sizeX is the number of columns in the array, and sizeY is the number of rows in the array.

Two-point correction is carried out under the assumption of a linear dependence of the output signal, matrix elements on the input signal. In fact, this dependence differs from the linear to a greater or lesser extent for different elements. Therefore, it is not possible to completely eliminate the heterogeneity.

A negative feature of two-point correction is the use of sources of reference signals with the need to adjust them to the scene. Correction is provided subject to the linear dependence of the signals of the elements from the optical flow at their input. In order to minimize the deviation from the linear dependence within the dynamic range of the observed scene, the range of values of the reference flows is consistent with the range of values of the signals of the scene. In addition, it is required to maintain uniformity of illumination of MFPU elements by reference sources, since the accuracy of determination of correction factors depends on the uniformity of illumination. In some cases, the presence of reference sources is unacceptable under the terms of their placement in the equipment.

The formation on the photosensitive region of the receiver of a uniform thermal background and an equivalent array of the constant components of the signals of the photosensitive elements Tfon when performing effective compensation of the constant component of the signals of the MFP devices requires the use of a reference emitter periodically introduced into the optical system of the device (as, for example, in the first of the above analogues) or the use of complex compensation algorithms for the observation scene (as, for example, in the second of the given analogues).

In the proposed method for compensating for heterogeneity, the emphasis is on maintaining the positive features of the above known methods while eliminating their disadvantages. In this regard, in the proposed technical solution, a transition is made to compensate for the heterogeneity of the constant component of the signal of the photosensitive elements, which is based on the formation of an absolutely uniform or predetermined uniformity of illumination of the MFP in the observation scene, and at the same time, which does not require significant computational resources. In the process of compensating for the heterogeneity, in order to obtain the values of the constant components of the signals of the photosensitive elements Tfon _{i, j, a} defocusing operation is introduced, which is carried out by introducing a defocusing element into the optical system of the TVP (see Figure 1).

или потока с заданной равномерностью в оптический тракт оптической системы вводят рассчитанный расфокусирующий элемент, в результате чего происходит смещение плоскости изображения в плоскость холодной диафрагмы при требовании достижения полной компенсации, или в промежуточную плоскость между плоскостью холодной диафрагмы и плоскостью фоточувствительных элементов в случае, когда достаточна частичная компенсация, соответственно. Осуществляют регистрацию излучения и запись массива Tfon в память электронной системы, формируемого на выходе фотоприемника в ответ на воздействие потока излучения

- расфокусированного потока излучения. Для получения на выходе фотоприемника сигнала Tin, формируемого на выходе фотоприемника в ответ на воздействие подлежащего регистрации излучения Р от объекта наблюдения, расфокусирующий элемент выводят из оптического тракта. Далее выполняют обработку сигнала, получая выровненный массив изображения с учетом выполнения компенсации неоднородности, в соответствии с вышеприведенной формулой. Исходные коэффициенты коррекции записаны в память электронной системы ТВП. Процесс компенсации, также и таким же образом, состоит в периодически выполняемой процедуре определения корректирующих коэффициентов и непрерывно выполняемой процедуре корректировки сигналов, с той разницей, что значения Tfon_i,j, необходимые для коррекции, получают не посредством использования источников опорного потока излучения или сложных вычислительных алгоритмов по сигналам сцены, а посредством использования расфокусирующего элемента.To implement the proposed method for compensating for heterogeneity, the optical system is calculated for the range of infrared radiation in which the TVP operates, taking into account an additional defocusing element (defocusing lens) that meets the following conditions. Depending on the achievement of the required completeness of compensation, the defocusing element, when introduced into the optical path, should shift the image plane into the plane of the cold diaphragm of the MFP or into the plane located between the plane of the cold diaphragm and the plane in which the photosensitive elements of the photodetector matrix are located. In addition, when a defocusing element is inserted into the optical path, the property of preserving a given field of view of the optical system is inherent. To form a uniform radiation flux at the input of the photodetector

or a stream with a given uniformity, the calculated defocusing element is introduced into the optical path of the optical system, as a result of which the image plane is shifted to the plane of the cold diaphragm when full compensation is required, or to the intermediate plane between the plane of the cold diaphragm and the plane of the photosensitive elements when partial compensation, respectively. The radiation is recorded and the Tfon array is recorded in the memory of the electronic system formed at the output of the photodetector in response to the influence of the radiation flux

- defocused radiation flux. In order to receive at the output of the photodetector a signal Tin generated at the output of the photodetector in response to the effect of the radiation P to be detected from the observation object, the defocusing element is removed from the optical path. Next, the signal processing is performed, obtaining a aligned image array taking into account the performance of heterogeneity compensation, in accordance with the above formula. The initial correction coefficients are recorded in the memory of the TVP electronic system. The compensation process, also in the same way, consists of a periodically performed procedure for determining correction coefficients and a continuously performed procedure for correcting signals, with the difference that the values Tfon _{i, j} necessary for correction are not obtained using sources of the reference radiation flux or complex computational algorithms for scene signals, and through the use of a defocusing element.

The coefficients are stored in the read-only memory (ROM) of the TVP and when the device is turned on, they are loaded from the ROM into the RAM, the same as the Tfon array. In this case, the coefficients are calculated when calibrating the device using an external source of reference radiation, for example, a completely black body (blackbody).

A variant is also possible in which when the device is turned on, the coefficients are calculated using the built-in sources of reference radiation, after which they are loaded into the RAM.

The defocusing element is introduced into the optical path as necessary, which is established experimentally, depending on the receiver used and the operating conditions of the device.

Compensation of the inhomogeneity in accordance with the proposed method can be performed in whole or in part, depending on the defocusing and the shift of the image plane to the plane of the cold diaphragm or to the plane located between the plane of the cold diaphragm and the plane of the photosensitive elements of the photodetector, respectively.

To fully compensate for heterogeneity, it is necessary and sufficient to fulfill the main condition. The component introduced into the optical system should shift the image plane to the plane of the MFP’s cold diaphragm (see Figure 2, Figure 3), since in this case the radiation energy coming from the object and background will uniformly reach the entire photosensitive region of the photodetector matrix. The corresponding defocusing of the incoming radiation for registration with the photodetector array is most optimal when the image plane is shifted to the plane of the MPU cold diaphragm, as a result of which the indicated technical result is achieved with the greatest possible completeness. When a defocusing element 3 is introduced into the optical path (see FIG. 1), the radiation energy coming from the object and background uniformly enters the entire photosensitive region of the photodetector matrix, thereby leading to complete compensation for the inhomogeneity of the DC component of the signal. When the defocusing element 3 is removed from the optical path (see FIG. 1, when the indicated element is indicated by a dashed line), the infrared radiation from the observation object passes through the optical path, focuses with imaging of the object in the plane of the radiation receiver (see FIG. 2 ) When a defocusing element 3 is introduced into the optical path, defocusing occurs, the image of the observation object shifts to the plane of the MPU’s cold diaphragm, the radiation flux that is maximally proportional to the flow of the observation scene always arrives at the photosensitive elements of the photodetector matrix. The specified stream is guaranteed to be maximally proportional to the input stream of the observation scene, in connection with which high quality, reliability and independence of compensation for the heterogeneity of the constant component of the signal of the elements from the dynamics of the change in the radiation energy flux of the observation scene are achieved. The latter is due to the fact that no additional time is required to set the flux of the reference radiation source in proportion to the input flux of observation, adjustment to the scene. The circumstance of guaranteed proportionality also makes it possible to save the TVP from monitoring and control systems of reference radiation sources and, in addition, provides a reduction in the weight, dimensions and energy consumption of the electronic TVP system, thus increasing the manufacturability and universality of the compensation of heterogeneity.

In the second case, when the defocusing element introduced into the optical system shifts the image plane to a plane located between the plane of the MPU cold diaphragm and the original image plane (corresponding to the case of the absence of a defocusing component in the optical system in which the image plane is in the plane of the photodetector, see Fig. .2), then in this case the irregularity of the radiation energy coming from the object and background to the photosensitive region of the photodetector matrix will be adic smoothed. Partial compensation of the inhomogeneity will occur, due to the proportion (relative to the case considered above) of defocusing the incoming radiation to register the photodetector and to shift the image plane in the direction of the cold diaphragm. The achievement of the specified technical result is possible in this case, although the technical result is not achieved with the greatest possible completeness.

In addition, the implementation of the compensation of heterogeneity, during which a defocusing element is introduced into the optical path, makes it possible to compensate for the heterogeneity in a wide temperature range, which is practically limited only by the temperature range of application of the thermal imaging device.

The proportionality of the incoming radiation flux to the photosensitive elements of the photodetector matrix to the input stream of the observation scene makes it possible to compensate with high accuracy the heterogeneity of the constant component of the signal of the elements, thereby improving the quality of the thermal imaging image.

In order to compensate for the inhomogeneity of the DC component of the signal, in addition to the above condition, the image of the observation object is shifted to the plane of the cold diaphragm of the MFP or into the plane located between the plane of the cold diaphragm and the plane of the photosensitive elements of the photodetector, it is desirable to obtain compensation of the heterogeneity with respect to the entire photodetector, to fulfill the condition of maintaining the field of view of the optical system. While maintaining the field of view, compensation is carried out according to the averaged flux of radiation energy coming from the entire field of view. In the case of a change, a decrease in the field of view, the compensation of the inhomogeneity occurs not over the entire photodetector, but over a certain portion of it that corresponds to the given, reduced, now vision value. However, in this case as well, compensation for the inhomogeneity of the constant component of the signal is carried out in the same way, according to the averaged flow, but arriving according to the changed, reduced, field of view corresponding to this certain section. In any of these cases, compensation leads to the achievement of uniformity to one degree or another of the constant component of the signal.

The optical system contains, for example, two optical components (see Figure 1-3). One component is building an intermediate image. The second component is the transfer of the intermediate image into the plane of the image formed in the plane of the photosensitive elements of the photodetector matrix.

The optical system can be implemented with the inner plane of the actual intermediate image and is made up of at least two optical components - the input and projection lenses, with the plane of the intermediate actual image located between these lenses (see Figure 1), or an afocal system with the plane of the intermediate actual image located between the components of the afocal system and the lens.

It should be emphasized that in each case of the existing optical system, it is necessary to calculate the specific parameters of the defocusing element.

The need for full or partial compensation for heterogeneity is determined by the operating conditions of the thermal imaging device, the nature of the tasks being solved.

In the particular case of the implementation of the proposed method, the optical system may be in the following embodiment.

The input lens 1 (see Figure 1) is made up of sequentially located along the rays of the positive meniscus, convex to the space of objects, negative meniscus, convex to the space of objects. The center distance between the concave surface of the first and the convex surface of the second is about 1.4 mm. The projection lens 2 is made up of a successive negative meniscus convex to the space of objects, a biconvex lens, a negative meniscus convex to the image plane, a positive meniscus convex to the image plane, and a positive meniscus convex to the space of objects . The center distance between the concave surface of the first of the menisci of the projection lens and the surface of the biconvex lens facing the space of objects is about 2 mm. The center distance between the surface of the biconvex lens facing the image plane and the concave surface of the second of the menisci of the projection lens is about 2.5 mm. The center distance between the convex surface of the second and the concave surface of the third meniscus of the projection lens is about 2 mm. The center distance between the convex surface of the third and the convex surface of the fourth menisci of the projection lens is about 0.5 mm. The distance between the input and projection lenses, that is, the center distance between the concave surface of the second meniscus of the input lens and the convex surface of the first meniscus of the projection lens, is 95.5 mm. The center distance between the convex surface of the first of the menisci of the input lens and the image plane (see Figure 1) is 150 mm. The radius of curvature of the surface facing the space of objects, the first along the rays in the input lens of the positive meniscus convex to the space of objects, is 60.096 mm, the radius of curvature of the surface facing the image plane is 137.5351 mm. The radius of curvature of the surface facing the space of objects, the second in the direction of the rays in the input lens of the negative meniscus convex to the space of objects, is 220.393 mm, the radius of curvature of the surface facing the image plane is 131.4331 mm. The radius of curvature of the surface facing the space of objects, the first in the direction of the rays in the projection lens of the negative meniscus convex to the space of objects is 27.2 mm, the radius of curvature of the surface facing the image plane is 22.503 mm. The radius of curvature of the surface facing the space of objects in the projection lens of a biconvex lens located along the rays after the first meniscus is 32.716 mm, the radius of curvature of the surface facing the image plane is -54.64 mm. The radius of curvature of the surface facing the space of objects of the second, after the biconvex lens, along the rays in the projection lens of the negative meniscus convex to the image plane is -15.88 mm, the radius of curvature of the surface facing the image plane is -31.551 mm . The radius of curvature of the surface facing the space of objects along the rays in the projection lens of the third positive meniscus convex to the image plane is -27.436 mm, the radius of curvature of the surface facing the image plane is -33.183 mm. The radius of curvature of the surface facing the space of objects along the rays in the projection lens of the fourth positive meniscus convex to the space of objects is 22.19 mm, the radius of curvature of the surface facing the image plane is 31.885 mm. The materials are silicon and germanium. The optical system is equipped with a defocusing element 3 - a negative meniscus, convex to the image plane, with means for its input / output from the optical path. The specified meniscus with input / output means is installed between the plane of the intermediate actual image and the projection lens (see Figure 1 and Figure 3). As input / output means, an electromechanical drive — a stepper motor of the MD 14 series — can be used. In the case of complete compensation, when the image plane is shifted to the plane of the cold diaphragm, the defocusing element 3 — the negative meniscus convex to the image plane — is thus set that the center distance between its concave surface and the concave surface of the second meniscus of the input lens is 72 mm with a tolerance of ± 0.05 mm. To implement partial compensation, the specified distance is reduced. The center distance between the concave surface facing the image plane of the fourth meniscus of the projection lens and the image plane is 20.41 mm. The center distance between the concave surface facing the image plane of the fourth meniscus of the projection lens and the input window of the cryostat is 6.63 mm. The distance between the plane of the cold diaphragm and the image plane, which is the plane of the photosensitive elements of the photodetector matrix, within which the image is shifted during defocusing, is 10 mm.

The initial (before the introduction of its defocusing element 3) the optical system has the following characteristics:

- spectral range of 3-5 microns;

- focal length 60 mm;

- relative aperture 1/3;

- field of view in the space of objects 5.76 × 4.32 degrees.

When a defocusing element 3 is introduced into the optical system in such a way that the center distance between its concave surface and the concave surface of the second meniscus of the input lens is 72 mm, in order to completely compensate for the inhomogeneity, the image plane is shifted to the plane of the cold diaphragm. In this case, the focal length of the lens becomes equal to 30 mm, and the size of the image obtained is equal to the size of the cold diaphragm, the field of view and the relative aperture of the system are preserved, and all the energy coming from the object and background gets onto the multi-element photodetector 4 (see Figure 1).

Obtained (after the introduction of a defocusing element 3), the optical system has the following characteristics:

- spectral range of 3-5 microns;

- focal length 30 mm;

- relative aperture 1/3;

- field of view in the space of objects 5.76 × 4.32 degrees.

The defocusing element 3 is characterized by the following:

- material - silicon;

- thickness 2 mm;

- radius of curvature R1 = -1172.6 mm;

- radius of curvature R2 = -131.4 mm;

- light diameter 9.6 mm;

- weight 2 g.

As information confirming the possibility of implementing the method with the achievement of a technical result, we give the following implementation examples.

Example 1

When compensating for the heterogeneity of the signal of the photosensitive elements of the multi-element photodetector, the radiation flux to be registered is received and the signal generated by the photodetector is processed.

The treatment is carried out in accordance with the formula

,

,

where S _{i, j} is the aligned image array; Tin _{i, j} is the output array of the image coming from the multi-element photodetector formed as a result of exposure to radiation to be registered from the object of observation; Tfon _{i, j} is an array of compensated dc components from photosensitive elements obtained as a result of defocusing; k _{i, j} is the array of sensitivity correction coefficients of the elements of the multi-element photodetector, i is the pixel number in the line of the image array, j is the line number of the image array. In this case, Tfon _{i, j} - an array of compensated constant components of the signals from the photosensitive elements is obtained as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, which forms a uniform radiation flux at the photodetector input and, as a result of defocusing, which shifts the image plane to the plane cold diaphragm located at a distance of 10 mm from the plane of photosensitive elements. Upon receipt of Tfon _{i, j} - an array of compensated constant signal components from photosensitive elements as a result of defocusing by introducing a defocusing element into the optical path of the optical system of a thermal imaging device, the required field of view of the thermal imaging device is kept - complete.

Then, defocused radiation is recorded and the array Tfon _{i, j} formed at the output of the photodetector in response to the influence of the defocused radiation flux is recorded in the memory of the electronic system. Then, in order to receive an array of signals Tin _{i, j} at the output of the photodetector formed at the output of the photodetector in response to the effect of radiation to be detected from the observation object, the defocusing element is removed from the optical path. Next, the signal processing is performed in accordance with the above formula, obtaining a aligned image array.

When processing, coefficients are used that are stored in the memory of the TVP ROM and when the device is turned on, they are loaded from the ROM into the RAM, the same as the array Tfon _{i, j} . The coefficients are calculated when calibrating the device using blackbody.

Example 2

When compensating for the heterogeneity of the signal of the photosensitive elements of the multi-element photodetector, the radiation flux to be registered is received and the signal generated by the photodetector is processed.

The treatment is carried out in accordance with the formula

,

,

where S _{i, j} is the aligned image array; Tin _{i, j} is the output array of the image coming from the multi-element photodetector formed as a result of exposure to radiation to be registered from the object of observation; Tfon _{i, j} is an array of compensated dc components from photosensitive elements obtained as a result of defocusing; k _{i, j} is an array of sensitivity correction coefficients of the elements of a multi-element photodetector, i is the pixel number in the array and image lines, j is the line number of the image array. In this case, Tfon _{i, j} - an array of compensated constant signal components from photosensitive elements is obtained as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, which forms a uniform radiation flux at the input of the photodetector with a given uniformity and, as a result of defocusing, which displaces the plane images in the intermediate plane between the plane of the cold diaphragm and the plane of photosensitive elements located on standing 9 mm from the plane of photosensitive elements. Upon receipt of Tfon _{i, j} - an array of compensated constant signal components from photosensitive elements as a result of defocusing by introducing a defocusing element into the optical path of the optical system of a thermal imaging device, the required field of view of the thermal imaging device is kept - complete.

Then, defocused radiation is recorded and the array Tfon _{i, j} formed at the output of the photodetector in response to the influence of the defocused radiation flux is recorded in the memory of the electronic system. Then, in order to receive an array of signals Tin _{i, j} at the output of the photodetector formed at the output of the photodetector in response to the effect of radiation to be detected from the observation object, the defocusing element is removed from the optical path. Next, the signal processing is performed in accordance with the above formula, obtaining a aligned image array.

When processing, coefficients are used that are stored in the memory of the TVP ROM and when the device is turned on, they are loaded from the ROM into the RAM, the same as the array Tfon _{i, j} . The coefficients are calculated when calibrating the device using blackbody.

Example 3

When compensating for the heterogeneity of the signal of the photosensitive elements of the multi-element photodetector, the radiation flux to be registered is received and the signal generated by the photodetector is processed.

The treatment is carried out in accordance with the formula

,

,

where S _{i, j} is the aligned image array; Tin _{i, j} is the output array of the image coming from the multi-element photodetector formed as a result of exposure to radiation to be registered from the object of observation; Tfon _{i, j} is an array of compensated dc components from photosensitive elements obtained as a result of defocusing; k _{i, j} is an array of sensitivity correction coefficients of the elements of a multi-element photodetector, i is the pixel number in the array and image lines, j is the line number of the image array. In this case, Tfon _{i, j} - an array of compensated constant components of the signals from the photosensitive elements is obtained as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, which forms a uniform radiation flux at the photodetector input and, as a result of defocusing, which shifts the image plane to the plane cold diaphragm located at a distance of 10 mm from the plane of photosensitive elements. Upon receipt of Tfon _{i, j} - an array of compensated constant signal components from photosensitive elements as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, the required field of view of the thermal imaging device is retained - partial, since the method of compensating for inhomogeneity is used in a thermal imaging system with a laser backlight, working simultaneously in passive and active modes, with simultaneous representation in the output image on the body the visual monitor of two images formed in the active and passive modes, moreover, in relation to the image obtained in the active mode, there are more stringent requirements for compensating for signal inhomogeneity.

Then, defocused radiation is recorded and the array Tfon _{i, j} formed at the output of the photodetector in response to the influence of the defocused radiation flux is recorded in the memory of the electronic system. Then, in order to receive an array of signals Tin _{i, j} at the output of the photodetector formed at the output of the photodetector in response to the effect of radiation to be detected from the observation object, the defocusing element is removed from the optical path. Next, the signal processing is performed in accordance with the above formula, obtaining a aligned image array.

When processing, coefficients are used that are stored in the memory of the TVP ROM and when the device is turned on, they are loaded from the ROM into the RAM, the same as the array Tfon _{i, j} . The coefficients are calculated when calibrating the device using blackbody.

Claims (3)

1. A method of compensating for signal heterogeneity of the photosensitive elements of a multi-element photodetector, which consists in receiving the radiation flux to be detected and processing the signal generated by the photodetector, characterized in that the processing is carried out in accordance with the formula

,
where S _{i, j} is the aligned image array;
Tin _{i, j} is the output array of the image coming from the multi-element photodetector formed as a result of exposure to radiation to be registered from the object of observation;
Tfon _{i, j} is an array of compensated dc components from photosensitive elements obtained as a result of defocusing;
k _{i, j} is an array of sensitivity correction coefficients of the elements of a multi-element photodetector;
i - pixel number in the line of the image array;
j is the line number of the image array;
in this case, Tfon _{i, j} - an array of compensated constant components of the signals from the photosensitive elements is obtained as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, which forms a uniform radiation stream or stream with a given uniformity at the input of the photodetector and, as a result of defocusing, shifting the image plane to the plane of the cold diaphragm or to the intermediate plane between the plane of the cold diaphragm and the photo plane vstvitelnyh elements respectively; then the defocused radiation is recorded and the array Tfon _{i, j} formed at the output of the photodetector in response to the influence of the defocused radiation flux is recorded in the memory of the electronic system; then, to receive at the output of the photodetector an array of signals Tin _{i, j} formed at the output of the photodetector in response to the effect of the radiation to be detected from the observation object, the defocusing element is removed from the optical path; further, signal processing is performed in accordance with the above formula, obtaining a aligned image array. 2. The method according to claim 1, characterized in that upon receipt of Tfon _{i, j} - an array of compensated constant signal components from the photosensitive elements as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, the required field of view of the thermal imaging device is maintained - full or partial. 3. The method according to claim 1, characterized in that Tfon _{i, j} - an array of compensated constant components of the signals from the photosensitive elements is obtained as a result of defocusing by introducing a defocusing element into the optical path of the optical system of the thermal imaging device, forming a uniform radiation flux at the input of the photodetector or flow with a given uniformity and, as a result of defocusing, shifting the image plane into the plane of the cold diaphragm or into the intermediate plane between the plane of the cold aphrages and the plane of photosensitive elements, respectively, namely, displacing the image plane to the plane of the cold diaphragm, located at a distance of 10 mm from the plane of the photosensitive elements, or shifting to the intermediate plane between the plane of the cold diaphragm and the plane of the photosensitive elements, located at a distance of less than 10 mm from the plane of the photosensitive elements.

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