RU2797508C2 - Method for automatic determination of resolution of digital optoelectronic systems and a test object of its implementation including line patterns with arcuate structure of elements - Google Patents

Abstract

FIELD: information; measuring technology.

SUBSTANCE: invention is related in particular to methods for determining the resolution of digital optoelectronic systems and devices for its implementation. The method includes capturing a test object using a digital optoelectronic system and analysing the resulting digital images. The test object includes 4 line patterns with an arcuate structure of elements with decreasing spatial frequency, located at angles of 0°, 90°, 180°, 270° relative to the central element consisting of four alternating black and white squares. The analysis of the obtained digital images consists in an automated search for the coordinates of the boundary of the separate reproduction of elements corresponding to the spatial frequency that determines the value of the resolution of the digital optoelectronic system.

EFFECT: increasing the accuracy of measuring resolution and reducing the time of the measurement process by providing the possibility of automating the measurement process.

3 cl, 3 dwg

Description

1. Technical field to which the invention belongs

The invention relates to the field of information and measurement technology, and can be used to determine the quality parameters of digital optoelectronic systems (COES) by measuring the resolution (RS) based on the method of automated analysis of digital images obtained when shooting a test object. The invention can also be used in laboratory studies and full-scale tests of COES for various purposes.

2. State of the art

The currently existing methods for experimental evaluation of the quality of digital optoelectronic systems are based on determining the resolution. RS is the main parameter characterizing the ability of the COES to reproduce fine details, as well as to separate the details of the depicted objects, and is quantitatively equal to the largest number of elements (lines) that the COES is capable of overeating, while the RS value along the vertical characterizes the largest number of horizontal lines, and RS horizontal - vertical.

Known standardized methods for determining MS, based on visual evaluation of images of test objects.

There is a known method for determining the resolution of photographic material according to GOST 2819-84, which consists in obtaining a number of images of a resolvometric target (a test object containing a set of groups of strokes - gratings of constant contrast - with a regularly changing spatial frequency) and subsequent visual evaluation of resolvograms (a number of images of a resolvometric worlds) by a decoder specialist who sequentially, as the frequency increases, examines the strokes and determines the number of the allowed group, after which the strokes are no longer distinguished, and the resolution of the photographic material is found from the arithmetic mean of the results of three parallel determinations with a tolerance of up to 20%.

There is a known method for determining the resolution limit of telescopic systems according to GOST 15114-78, which consists in forming an image of dashed worlds of absolute contrast with light, differing in width, strokes located in a certain system on a dark background, and consideration by the decoder operator of successive images of individual elements of the worlds with different stroke frequency, search for an element of the target, in which the strokes of all four directions are still separately visible, and determination of the resolution limit as the smallest angular distance between the midpoints of two adjacent strokes of the target.

There is a known method for measuring the resolution of television tubes according to GOST 18720-90, which consists in projecting an optical image of the test table and visually determining the resolution by the largest number of visually distinguishable lines of a vertical wedge or dashed groups on the screen of a video control device according to marks corresponding to the loss of distinguishability of black and white lines.

There is a known method of working resolution of image intensifier tubes according to GOST 21815.9-86, which consists in focusing the image of the target element on the section of the photocathode of the electron-optical converter, and, three observers, observing it through the ocular optics, considering the target element, find an element with the largest serial number, the image of the strokes in all four directions is still visible separately along the entire length of the stroke and determines the working resolution.

The disadvantages of the described standardized methods include:

- low accuracy of determining RS values, due to the subjective nature of the assessment inherent in the visual method of analysis, as well as the dependence of the results obtained on the qualifications and condition of the decoder operator;

- the impossibility of automating the analysis process based on visual assessment, and, in connection with this, the need to involve a large number of qualified operators-decoders and - an increased time interval for the procedure for analyzing images of test objects and determining the value of RS;

- high relative error (10-12%) in determining the value of RS;

- the need to obtain a large number of images of test objects with different spatial frequencies;

- lack of compatibility of the spatial frequency of the recommended test objects with modern high-resolution COES;

- the need to observe the mutual orientation of the target and the device of the COES, inherent in dashed targets, and wedge-shaped targets, which are the main elements of the recommended test objects.

There is a known method for visual determination of resolution, described in the ISO 12233:2017 standard, which is based on obtaining a test table using an optical image system, consisting of dashed and wedge-shaped targets located at angles of 0°, 45°, 90° and 135°, and image analysis, which consists in the operator's visual assessment of the spatial frequency of the world, at which the lines are separately distinguishable, and, by the obtained values, determining the resolution of the optical system. The disadvantages of the method also include the low accuracy of determining PC values, due to the subjective nature of the assessment inherent in the visual method, the high relative error, and the need to observe the relative orientation of the device and the test object, including dashed and wedge-shaped targets.

A known method for determining the linear resolution on the ground per pixel of an optoelectronic system, described in patent RU 2 732 784, is based on performing aerial surveys of the terrain with horizontally placed canvases of the world with absolutely white strokes, and determining the linear resolution from the obtained aerial photographs as the arithmetic mean estimates obtained by all decoder operators for all images in the world, each of which is the minimum stroke width in recognized groups, in which all strokes are observed separately and along the entire length. The method has all the disadvantages inherent in the previously described methods based on the visual method of analysis.

Currently, the most relevant are automated methods for determining RS, which are based on theoretical, scientific, practical and experimental knowledge in the field of TSOE.

A known method for automated evaluation of the resolution of aviation optical-electronic systems, described in patent RU 2 293 960, based on the implementation of aerial photography of the terrain with the world placed on it, including groups of spatial elements of different spatial frequencies, pre-processing, selection of fragments of the dashed world and the implementation of automated analysis of the image, and obtaining an estimate of the resolution for a given signal-to-noise ratio in the image based on the algorithm for digital analysis of the envelope cross-sections of the image of the world. The disadvantages of this method include the need to observe the relative orientation of the targets and the COES device, which is inherent in the dashed targets, which are the main element of the test object according to this method, as well as the need to carry out the image processing and analysis process twice for two orthogonal directions. In addition, the approximation approach used to obtain the envelope cross sections of the world image distorts the primary data and reduces the accuracy of the results.

There is a known method for measuring resolution on the ground, described in patent RU 2 144 654, based on performing aerial photography of the terrain with a dashed world placed on it, automatically detecting a world located in the central part and representing no more than 10% of the area of the entire frame, and detecting still distinguishable group of strokes using the standard model of the decoder. The disadvantages of this method include the need to orient the test object along the central part of the frame, when placing the test object on an area that is no more than 10 percent of the total frame size, which creates significant limitations in determining RS using this method. The dashed target, proposed as a test object, due to its design features, creates the need to observe the relative orientation of the device with the test object.

In addition, the described methods for determining RS are widely used during flight tests, but are not always applicable for determining the RS of COES for various purposes in laboratory conditions.

A known method for measuring the resolution of a camera is described in patent RU 2 461 853 and is based on the camera receiving images of ring targets, which are a system of concentric dark rings on a light background with a constant width of the dark rings, and determining the resolution at each point of the image according to the resolution of that target. , the minimum width of the dark ring of which still differs at a given point in the image, using the distinguishability criterion, the standard deviation of the brightness of points lying on the segment oriented along the radius vector connecting this point with the center of the target is 3 times higher than the standard deviation of the brightness of points lying on segment of the same length. The disadvantages of this method include the need to obtain images of up to 20 worlds, due to the design feature of the worlds, expressed in the constant spatial frequency of its elements.

A known method for measuring the resolution limit of an information-measuring optoelectronic system is described in patent RU 2 213 335 based on the formation of an image of a dashed world containing an element, consisting of groups of strokes, the frequency of which is the same in the element and increases with increasing element number, and the width of the strokes decreases with the element number increasing exponentially with a denominator of 0.94, and choosing a group of strokes with the same fill factor, finding an element of the stroke world, in whose groups there are no brightness dips, setting the stroke size in the group of strokes with the maximum fill factor and determining the resolution limit. The disadvantages of this method include the disadvantages inherent in methods based on the use of dashed targets: the need to observe the relative orientation of the device with the test object, as well as the need to process the obtained images: highlighting the range of target elements and selecting a group of strokes for further analysis.

For the prototype of the method for determining the resolution of digital optoelectronic systems, it is proposed to take the method described in patent RU 2 673 501, based on the shooting of test objects, subsequent processing and analysis of images, which consists in the process of decoding by reading and decoding information encoded in test symbols -objects depicted on the selected fragments, and characterizing the spatial frequency, the value of which is used to calculate the resolution value. The disadvantages of this method include the need for image processing: selection of decryption fragments for further analysis, which, in turn, does not fully automate the process of determining RS and increases the analysis time. Significant limitations imposed on the distortion distortion inherent in any optical system significantly narrow the scope of this method: the impossibility of reading and/or decoding information of image fragments, taken as limitations of the resolution limit, is observed when the distortion is distorted.

3. Disclosure of the invention

The purpose of the invention is to eliminate the noted shortcomings of the prototype and other known methods for determining RS COES by providing a set of the following qualities:

1) improving the accuracy of determining the values of RS COES in comparison with known methods;

2) increasing the speed of determining the values of RS COES in comparison with known methods;

3) elimination of the factor of subjectivity in determining the RS of the COES due to the exclusion of the human factor in the course of measurements.

This goal is achieved due to the fact that, unlike the considered methods and the prototype, the proposed method for determining the RS includes an automatic search for the coordinates of the border of the separate reproduction of elements, based on the position that the luminance signal of the allowed frequency of the world exceeds the level of digital noise and relies on a test object, including 4 dashed worlds with an arcuate structure of elements with decreasing spatial frequency, located at angles of 0°, 90°, 180°, 270° relative to the central element, consisting of four alternating black and white squares (figure 1).

The technical result consists in increasing the accuracy and speed, as well as simplifying the process of determining the values of RS COES by shooting a test object and subsequent analysis of the obtained digital image, performed automatically by a computer.

The specified technical result is achieved due to the fact that the proposed method for automatically determining RS TSOE is a sequence of steps of the following content.

At the first stage, three images of the test object of the same angle and scale are obtained with the help of the COES device under constant lighting conditions and the COES operating mode. To do this, the test object is installed parallel to the matrix receiver of the COES device. The central element of the test object is placed on the optical axis of the COES device. The test object must be located in the test area of the generated digital image. The method allows deviations during installation of the test object from the optical axis by no more than 5% of the image width, from the plane of the matrix receiver by no more than 10 degrees, from the vertical by no more than 10 degrees.

At the second stage, automatic analysis of digital images using a computer is performed, consisting of the following steps:

(размера

).

- число строк матрицы – соответствует числу пикселов по высоте изображения, Y - число столбцов матрицы - соответствует числу пикселов по ширине изображения).1. Input of a digital image of the worlds with subsequent analysis of the brightness of all pixels of the image and output of the data matrix

(size

).

- number of matrix rows - corresponds to the number of pixels along the image height, Y - number of matrix columns - corresponds to the number of pixels along the image width).

2. Automatic determination of pixel coordinates corresponding to the location of the elements of the test object.

3. Automatic determination of the measurement area of digital noise on the border of the squares of the central element (figure 2).

4. Obtaining the standard deviation of the brightness of the digital noise area pixels:

– последовательность значений яркости пикселов,

– размер центрального элементаWhere

is a sequence of pixel brightness values,

- the size of the central element

последовательности значений яркости пикселов поперечного сечения миры длины

.5. Definition

sequences of brightness values of cross-section pixels worlds of length

.

6. Automatic search for the coordinates of the separation boundary of the elements corresponding to the resolved spatial frequency of the targets, using the distinguishability criterion, which consists in the fact that the brightness values of the pixels of the cross section of the targets exceed the standard deviation of the brightness of the pixels of the boundaries of the central element, based on the position that the brightness signal of the resolved frequency of the targets exceeds the level of digital noise:

– наименьшее значение

, удовлетворяющее условию:Where

- the smallest value

, satisfying the condition:

–

-й элемент -й последовательности

.Where

-

-th element of the -th sequence

.

:7. In accordance with the linear parameters of the measuring elements of the worlds, the corresponding spatial frequency of the test object is determined by the obtained coordinates

:

– сумма толщин всех линий штриховой мирыWhere

- the sum of the thicknesses of all lines of the dashed world

(минимальный размер толщины линии) рассчитывается следующим образом. Выбирается множество всех значений

, удовлетворяющих условию

, далее среди данных значений выбирается наименьшее

.Where

(minimum line thickness dimension) is calculated as follows. The set of all values is chosen

, satisfying the condition

, then among these values the smallest is selected

.

8. Items 5-7 are performed for each measuring element of the worlds.

9. The number of vertical and horizontal lines is determined

и

– индексы соответствия вертикального расположения миры (90°, 270°) на тест объекте, и горизонтального (0°, 180°) соответственно.Where

And

are indices of correspondence between the vertical position of the target (90°, 270°) on the test object and the horizontal position (0°, 180°), respectively.

10. Steps 1-9 are performed for each of the three received digital images of the same angle and scale.

и

, полученные по трем цифровым изображениям одного ракурса и масштаба.11. The final values of the RS vertically and horizontally are the average values,

And

obtained from three digital images of the same angle and scale.

The algorithm described in paragraphs 1-11, from inputting images to obtaining the final values of RS vertically and RS horizontally from 3 digital images of a test object of the same angle and scale, is performed automatically by a computer.

The test object proposed for performing the above method includes 4 dashed worlds with an arcuate structure of elements with decreasing spatial frequency located at angles of 0°, 90°, 180°, 270° relative to the central element, consisting of four alternating black and white squares.

The central element of the test object allows you to:

- measure digital noise at the border of dark and light elements of the digital image of the obtained test object;

-measure the pixel density and the distortion function of the optical system to obtain accurate information about the image quality by generating resolution data at each point of the image;

- serves as a reference point for the automated algorithm and allows you to determine the exact position of the center of the test object and then go to the exact position of the dashed world for their subsequent analysis.

A dashed target with an arcuate structure of elements makes it possible to determine the change in the brightness signal of the digital image pixels in accordance with the changing spatial frequency. The spatial frequency is determined by the width of the pairs of lines starting from 0.1 mm and varies according to the law of increasing arithmetic progression with a difference of 0.05 mm. The arcuate structure of the dashed target ensures the invariance of the angular orientation of the lines with respect to the side of the optical radiation receiver with a component of 10°. The location of the worlds in different orthogonal directions allows you to determine the RS vertically and horizontally.

Such a constructive implementation of the test object ensures the determination of the vertical and horizontal resolution in the described manner, taking into account digital noise, at different distances, while ensuring the invariance of the angular orientation of the test object relative to the matrix receiver of the device.

4. Implementation of the invention

The proposed method for automatically determining the resolution of the COES and the test object for its implementation can be implemented as a test stand.

A possible variant of the test bench designed to implement the proposed method is shown in Fig. 3. When implementing the proposed method, a test object (2) is placed on the surface (1) so that the optical axis (3) of the COES (4) passes through the center of the test object. After that, a test object is surveyed from one angle and scale using the tested TSES, while remote control is carried out using a computer (5). Further, with the help of a computer in automatic mode, the analysis of digital images of the test object obtained with the help of the tested COES is performed.

Claims (3)

1. A method for determining the resolution of digital optoelectronic systems, which includes placing a test object parallel to a matrix receiver in the test area of a digital image being formed on a flat vibration-proof surface, shooting a test object using a digital optoelectronic system, and determining the resolution of the digital optoelectronic system. electronic system based on the results of automatic analysis of the received digital images, characterized in that when analyzing the obtained digital images, the coordinates of the boundary of the separate reproduction of elements corresponding to the allowed spatial frequency of the targets are automatically searched, using the distinguishability criterion, which consists in the fact that the brightness values of the pixels of the cross section of the targets exceed the standard deviation of the pixel luminance of the center element borders, based on the position that the luminance signal of the resolved target frequency exceeds the digital noise floor. 2. The method according to claim 1, characterized in that the final values of the vertical and horizontal resolution are determined by 3 obtained digital images of the same angle and scale. 3. Test object for determining the resolution of a digital optoelectronic system, placed parallel to the matrix receiver in the test area of the generated digital image on a flat vibration-protected surface, characterized in that it includes 4 dashed targets with an arcuate structure of elements that ensures the invariance of the angular orientation of the test object up to 10°, with a decreasing spatial frequency, which is determined by the width of pairs of lines starting from 0.1 mm and changing according to the law of increasing arithmetic progression with a difference of 0.05 mm, located at angles of 0°, 90°, 180°, 270° relative to the central element consisting of four alternating black and white squares of 5 mm.

Images