CN102353519B - Resolving power evaluation method for three-generation dim light image intensifier - Google Patents

Resolving power evaluation method for three-generation dim light image intensifier Download PDF

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CN102353519B
CN102353519B CN 201110150196 CN201110150196A CN102353519B CN 102353519 B CN102353519 B CN 102353519B CN 201110150196 CN201110150196 CN 201110150196 CN 201110150196 A CN201110150196 A CN 201110150196A CN 102353519 B CN102353519 B CN 102353519B
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resolving power
target line
image
value
line unit
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CN102353519A (en
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史继芳
韩占锁
杨斌
李宏光
吉晓
孙宇楠
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205TH INSTITUTE OF CHINA NORTH INDUSTRIES
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Abstract

The invention discloses a resolving power measuring device and a resolving power evaluation method for a three-generation dim light image intensifier, and belongs to the field of optical measurement and metering. The resolving power measuring device is characterized by consisting of a light source component, a resolving power target, a collimator tube, an imaging objective lens, a test camera obscura, a charge coupled device (CCD) camera and a computer. The resolving power evaluation method comprises the following steps of: imaging the resolving power target irradiated by a standard light source to a fluorescent screen by using a measured image intensifier; converting into a frame image of a target line by using the CCD camera, and transmitting into the computer; successively processing a single frame image of the target line by using a normalized cross correlation model and an optical modulation degree model through internal image processing software of the computer to acquire a single frame processing result; and analyzing multi-frame processing results and performing corresponding supplement operation to acquire a final resolving power evaluation result. By the device and the method, the problem of objective evaluation during resolving power measurement of the three-generation dim light image intensifier is solved; and the device and the method can be popularized to other measurement fields such as an intensified charge coupled device (ICCD) measurement field and the like where resolving power is required to be objectively evaluated, and have wide application prospects.

Description

Three generations's gleam image intensifier resolving power evaluation method
Technical field
The invention belongs to field of optical measuring technologies, relate generally to a kind of three generations's gleam image intensifier resolution measurement instrument, relate in particular to the evaluation method of cover three generations's gleam image intensifier resolution measurement device and three generations's gleam image intensifier resolving power.
Background technology
In recent years, along with scientific-technical progress, more and more higher to the requirement of low-light technology in fields such as space astronomy detection, fluorescence detection, military night vision reconnaissances, three generations's gleam image intensifier becomes increasingly conspicuous as this its effect of field core devices.The accurate measurement of three generations's gleam image intensifier parameter has significant meaning to improving its performance in research and production, also be an urgent demand of national defense industry numerous areas.Resolving power is the spatial frequency of gleam image intensifier MTF curve 2%～3% degree of modulation correspondence, is one of important parameter of reflection gleam image intensifier performance, is determining the low-light system 10 -31x～10 -1Operating distance and image definition during the above illumination of 1x.The development that is measured as gleam image intensifier, production and the application of gleam image intensifier resolving power provides and measured the calibration means accurately.
Traditional two generation gleam image intensifier resolution measurement method adopt the visualization method usually, Institutes Of Technology Of Nanjing, Shijiazhuang College Of Arms and China Arms Industry the 205 research institute once developed two generation gleam image intensifier resolution test equipment, all be to adopt the visualization method.Two generation gleam image intensifier resolution test equipment comprise standard sources, integrating sphere, neutral attenuator, power supply, resolving power target, parallel light tube, image-forming objective lens, gleam image intensifier to be measured, eyepiece, by resolving power target image on the eye-observation image intensifier video screen, judge the image intensifier resolving power at last.This method has measures advantage simply and intuitively, but influenced by people's subjective factor, such as to same target, different observer's observed result differences, same observer is because continue the difference of observation time length, age, health, and observed result is difference to some extent all; So visualization method accuracy of measurement is not high, repeatability is relatively poor.Therefore, the low-light level night vision device objective evaluation is very important.
At " optical technology " in the May issue, 2000, the 21st the 2nd phase of volume, among the P451-453, people such as Liu Zhengyun use gray scale-gradient co-occurrence matrix model to two generation low-light level night vision device resolution measurement image texture features analyze, with auxiliary artificial select and turning point is judged as the objective criterion of resolving power of five streak feature parameters such as gray scale entropy, gradient entropy, gray scale mean square deviation.Its algorithm computational accuracy is not high, can't provide quantitative conclusion voluntarily by algorithm, must auxiliary subjective judgement, and when in the visual field, having bright or dark spot or stripe pattern itself small-sized, can cause all that occurrence law is poor as a result.
Three generations's gleam image intensifier belongs to the photoelectronic imaging device, all the video screen imagings of its image and other that becomes are the same, have problems such as screen flicker, dark background noise, ion burn, therefore, performance and index that three generations's gleam image intensifier is new are had higher requirement to resolution measurement, press for and adopt resolving power objective evaluation algorithm development gleam image intensifier resolution measurement system, repeatability and accuracy when improving three generations's gleam image intensifier resolution measurement.
Not seeing both at home and abroad at present has the open report that adopts method for objectively evaluating to measure three generations's gleam image intensifier resolving power.
Summary of the invention
The technical problem to be solved in the present invention is at the deficiencies in the prior art, and the device of a cover measurement three generations gleam image intensifier resolving power and the method for objective evaluation three generations gleam image intensifier resolving power are provided.
Three generations's gleam image intensifier resolution measurement device provided by the invention, comprise light source assembly, the resolving power target, parallel light tube, the image-forming objective lens that has zoom function, the test camera bellows that has input and outgoing window, base platform, the ccd video camera that has function of temperature control, computing machine, described light source assembly, parallel light tube and test camera bellows are fixed on the described base platform by corresponding bracing frame, described resolving power target is connected on the parallel light tube, its target surface is positioned on the object space focal plane of parallel light tube and target surface is centered close on the optical axis of measuring light path, described image-forming objective lens and described ccd video camera are installed in described base platform by two-dimension translational mechanism and D translation mechanism respectively, the target surface center of the optical axis of image-forming objective lens and ccd video camera all is positioned on the optical axis of measuring light path, and is placed on the video screen of the image intensifier to be measured in the described test camera bellows and the object space focal plane and focus that the center correspondence is positioned at described ccd video camera; The light beam that described light source assembly sends illuminates described resolving power target, and the time of the target line pattern of resolving power target through focused on described three generations's gleam image intensifier to be measured behind the described parallel light tube collimation by described image-forming objective lens is on the pole-face; Three generations's gleam image intensifier to be measured forms brighter target line image to collimation target line pattern multiplication back at its video screen; Described ccd video camera is gathered the target line image on three generations's gleam image intensifier video screen to be measured and is converted thereof into electric signal and transfers in the described computing machine; The described ccd video camera of described computer control is finished the setting of dependence test parameter; Gather the target line image of cold-scarce scape image, hot background image and the resolving power target of ccd video camera output; The corresponding signal of gathering is carried out a series of image handle, finally obtain the resolving power evaluation result of described three generations's gleam image intensifier to be measured.
The three generations's gleam image intensifier resolving power evaluation method that adopts three generations's gleam image intensifier resolution measurement device of the present invention to realize may further comprise the steps:
The first step, the running parameter of the described ccd video camera of initialization;
In second step, according to keyboard instruction, gather the cold-scarce scape image A of described ccd video camera output in succession LWith hot background image A RAnd all deposit in the storer,
The 3rd step, according to keyboard instruction, gather a frame resolving power target image F of described ccd video camera output and deposit in the storer, show this image at display screen simultaneously;
In the 4th step, according to keyboard instruction, from storer, call cold-scarce scape image A L, hot background image A RWith resolving power target image F, resolving power target image F is deducted cold-scarce scape image A according to pursuing grey scale pixel value LWith hot background image A RThe gray-scale value of corresponding pixel points obtains testing image G and corresponding two dimensional gray matrix thereof, stores the two dimensional gray matrix and shows testing image G at display screen;
In the 5th step, according to keyboard commands, it is the ROI district that the image processing region is set, the zone that the ROI district limits for the highest distinguishable or inferior high distinguishable resolving power target line group of tested image intensifier;
In the 6th step, generate the standard form that has minimum resolving power target line group and have all target line unit correspondences in the inferior low resolution target line group in the ROI zone;
The 7th step, travel through all pixels in ROI zone successively in the mode of pursuing pixel line by line with each standard form that generates, simultaneously, adopt the normalized crosscorrelation formula to calculate the cross-correlation coefficient NC value of standard form and subgraph in each pixel position, find out the corresponding subgraph that is the coupling target line unit that have maximum cross correlation coefficient NC value with each standard form one by one, record these maximum cross correlation coefficient NC values and corresponding coupling target line unit thereof sequence number (i, j); Cross-correlation coefficient NC value and resolution threshold value NC with these coupling target line unit DifferentiateCompare, in cross-correlation coefficient NC value greater than differentiating threshold value NC DifferentiateCoupling target line unit in, will have best result and distinguish that the coupling target line unit of power is as optimum matching target line unit;
In the 8th step, in optimum matching target line unit, get the gray-scale value I of a row pixel of horizontal target line group switching centre position 1I 2... I kAnd these gray-scale values are carried out size ordering, rejects acquisition selection gray value sequence I after k/Q the maximal value ChoosingAnd Q is positive integer, if k/Q is not integer, then units rounds downwards, and calculates the degree of modulation of the horizontal target line of optimum matching group with following formula:
M = I max - I min I max + I min
In the formula, I AvgFor selecting the average of each gray-scale value in the gray value sequence, I MaxFor selecting in the gray value sequence mean value greater than each gray-scale value of average, I MinFor selecting in the gray value sequence mean value less than each gray-scale value of average; In like manner, calculate the degree of modulation of the perpendicular target line group of optimum matching; Ask the average of optimum matching target line unit horizontal target line group and perpendicular target line group degree of modulation
Figure BSA00000511252300042
That is the optical modulation degree of optimum matching target line unit;
The 9th step is with the optical modulation degree of optimum matching target line unit
Figure BSA00000511252300043
With threshold modulation M cCompare: if
Figure BSA00000511252300044
Continue to judge the optical modulation degree of optimum matching target line unit
Figure BSA00000511252300045
Whether apparently higher than threshold value M c, if
Figure BSA00000511252300046
Then the resolving power value of optimum matching target line unit correspondence is that single frames is handled net result; If
Figure BSA00000511252300047
Then calculate the optical modulation degree that resolving power is higher than the adjacent cells of optimum matching target line unit If the optical modulation degree of high resolution adjacent target line unit
Figure BSA00000511252300049
Satisfy
Figure BSA000005112523000410
Then the resolving power value of high resolution adjacent target line unit correspondence is the net result that single frames is handled, otherwise the resolving power value of keeping optimum matching target line unit correspondence is that single frames is handled net result; If
Figure BSA000005112523000411
Calculate the optical modulation degree that resolving power is lower than the adjacent cells of optimum matching target line unit
Figure BSA000005112523000412
If satisfy And
Figure BSA000005112523000414
Then the resolving power value of low resolution adjacent target line unit correspondence is that single frames is handled net result; If satisfy
Figure BSA000005112523000415
Then utilize the cross-correlation coefficient NC between normalized crosscorrelation formula calculating low resolution adjacent target line unit and the corresponding standard form thereof again AdjacentIf, NC Adjacent〉=0.97NC, then the resolving power value of optimum matching target line unit correspondence is that single frames is handled net result, if NC Adjacent＜0.97NC, then the resolving power value of low resolution adjacent target line unit correspondence is that single frames is handled net result and shown at display screen;
The tenth step, repeatedly repeating the 3rd step to the 9th step handles follow-up multiframe resolving power target image respectively, thereby obtain the single frames resolving power result of respective numbers, if have half and above single frames resolving power result identical, with the net result of this result as three generations's gleam image intensifier resolving power evaluation method; If the single frames resolving power result of multiple image is in a discrete distribution, then the optical modulation degree is asked by the 8th step respectively in the corresponding target line of each single frames resolving power result unit
Figure BSA00000511252300051
And compare the optical modulation degree with degree of modulation criterion Mc one by one
Figure BSA00000511252300052
Near M cThe corresponding resolving power value in target line unit be considered as the net result of described three generations's gleam image intensifier resolving power evaluation method and show at display screen.
Overall technology effect of the present invention is embodied in the following aspects.
(1) the present invention has set up a cover three generations gleam image intensifier resolution measurement device by light source assembly, resolving power target, parallel light tube, image-forming objective lens, ccd video camera and computing machine, wherein, light source assembly has adopted the weak illumination light source of even diffusion, solved the problem of prior art light source lack of homogeneity under the low-light-level measurement background, measured the resolving power of three generations's gleam image intensifier for objective evaluation and lay a good foundation; In addition, used ccd video camera has refrigeration unit and temperature controller, has eliminated the electronic noise of CCD itself and thermonoise etc. greatly, for software analysis and the noise handled as three generations's low-light booster provide hardware guarantee.
(2) in the present invention, be equipped with image processing software in the computing machine, this image processing software carries out objective evaluation to the resolving power target image that becomes with ccd video camera through three generations's low-light booster in succession, its evaluation algorithms adopts the bimodel based on different principle, be normalized crosscorrelation model and optical modulation degree model, two models are independent mutually to complement each other again, obtains final conclusion by dual independent criterion.Thereby the present invention can accurately measure three generations's gleam image intensifier resolving power, the accuracy of measurement height, and good reproducibility is for development, production and the application of three generations's gleam image intensifier provides reliable technical support.
(3) in image processing process, with the matching factor in the normalized crosscorrelation model as independent criterion, not only can qualitative measurement target surface groove group whether clear, but also can search the corresponding target line of a certain particular resolution group position, be subsequent calculations lock image processing region.Thus, not only reduced the operand that image is handled, and the error result of having avoided unnecessary calculating to cause.
(4) the present invention introduces optical modulation degree model in the resolving power objective evaluation originally, because under the low contrast condition of low-light field, the image resolvability that the judgement of employing optical modulation degree criterion draws and the result of eye-observation have the height consistance, therefore, with the optical modulation degree as another independent criterion of the present invention, the resolving power data be can quantitatively obtain, thereby objectivity, accuracy and the accuracy of evaluation method of the present invention improved.
Description of drawings
Fig. 1 is the formation synoptic diagram of three generations's gleam image intensifier resolution measurement device of the present invention.
Fig. 2 is the measurement index path of three generations's gleam image intensifier resolution measurement device.
Fig. 3 is the workflow diagram of three generations's gleam image intensifier resolving power evaluation method of the present invention.
Embodiment
The present invention is described in further detail below in conjunction with accompanying drawing and preferred embodiment.
As shown in Figure 1, the preferred embodiment of three generations's gleam image intensifier resolution measurement device mainly comprises light source assembly 1, resolving power target 2, parallel light tube 3, image-forming objective lens 4, test camera bellows 5, ccd video camera 6, base platform 7, computing machine 8 and power supply 9.
Light source assembly 1 is made up of standard sources 1-1, neutral colour filter and iris 1-2 and integrating sphere 1-3.Standard sources 1-1 selects halogen tungsten lamp for use, and neutral colour filter and iris decay to the light beam that halogen tungsten lamp sends, and forming colour temperature in the exit behind integrating sphere 1-3 integration is the light beam of 2856K, and the illuminance scope of this light beam is 10 -31x～10 -1Between the 1x, the unevenness in effective illuminating area is less than 1%.In the gleam image intensifier resolution measurement, because human eye is highly sensitive, the homogeneity of low light level light source is very little to the influence of measurement result, and the sensitivity of ccd video camera is lower than human eye, and is very high to the uniformity requirement of low light level light source.In the traditional handicraft, the homogeneity of weak illumination light source is one of key index that is difficult to guarantee, in the measurement because the uneven irradiation of light source, each zone of target surface presents inhomogeneous illumination, cause the image intensifier contrast to descend, thereby introduce inestimable uncertain factor, also experimental result is produced unforeseen influence.Thereby in the present invention, for the power supply 9 of standard sources 1-1 power supply is selected high precision high stability degree constant current constant voltage source for use, to satisfy the requirement that light stability and colour temperature change.Integrating sphere 1-3 is the key that forms the diffuse reflection light source, and it is coated with the hemispherical Shell of white diffuse reflector by two inwalls forms.The correlation parameter of integrating sphere 1-3 among the present invention determines that by illumination diffusion computing formula its diameter is taken as 260mm, and the light hole diameter is that 20mm and area are 7.7% of the integrating sphere total area, satisfies the requirement that should not surpass the integrating sphere total area 10%.
Resolving power target 2 is the USAF1951 resolving power target that the low-light field tests is often used, and is of a size of 101.6mm * 82.6mm * 1.5mm, has 10 groups of target line unit on it, i.e. width such as grade and the equally spaced bright dark fringe that forms at target surface.Every group of target line unit constitutes by isometric three horizontal target lines and three vertical target lines, and the length of target line is five times of target line width, and target line width and adjacent target line equate at interval.The spacing of horizontal target line and vertical target line is the twice of target line width, and from maximum one group of target line unit, the target line unit that per two packet sizes approach is all pressed
Figure BSA00000511252300071
Ratio dwindle.
Parallel light tube 3 is for F1000 type zoom lens and innerly have the good two separation object lens of picture element, and its focal length is 1000mm, and the effective aperture is Φ 100mm, resolving power 1.3 ", 1 ° 38 of visual field ', parallax≤0.20mm.Image-forming objective lens 4 has zoom function, and its focal length is 100mm, and the effective aperture is Φ 80mm.All have logical light window on the front and back sidewall of test camera bellows 5, tested image intensifier 5-1 by corresponding fixture support in testing the cavity of camera bellows 5.
Light source assembly 1, parallel light tube 3 and test camera bellows 5 are fixed on the base platform 7 by corresponding bracing frame 7-1,7-2,7-4, resolving power target 2 is connected on the parallel light tube 3, the optical axis that its target surface is positioned on the object space focal plane of parallel light tube 3 and target surface is centered close to parallel light tube 3 is namely measured on the optical axis of light path, simultaneously, the video screen center of image intensifier 5-1 to be measured also is positioned on the optical axis of measuring light path in the test camera bellows 5.Image-forming objective lens 4 and ccd video camera 6 are installed in base platform 7 by the 7-3 of two-dimension translational mechanism and the 7-5 of D translation mechanism respectively, during test, by adjusting the two-dimension translational 7-3 of mechanism and the 7-5 of D translation mechanism, the optical axis of image-forming objective lens 4 and the target surface of ccd video camera 6 are centered close on the optical axis of measuring light path, and guarantee that the video screen of tested image intensifier 5-1 is positioned on the object space focal plane of ccd video camera 6.
According to shown in Figure 2, the light beam that standard sources 1-1 sends is in succession through forming uniform diffusion light beam and illuminating resolving power target 2 behind neutral colour filter and iris 1-2 and the integrating sphere 1-3; Whole target lines unit on the resolving power target 2 is focused on the time of the three generations's gleam image intensifier 5-1 to be measured that tests in the camera bellows 5 on the pole-face by image-forming objective lens 4 through parallel light tube 3 collimation back; Three generations's gleam image intensifier 5-1 to be measured forms brighter target line image to collimation target line pattern multiplication back at its video screen; Ccd video camera 6 is gathered the target line image on the video screen and is converted thereof into electric signal and transfers in the computing machine 8.
Ccd video camera 6 is selected the COOLSNAP K4 video camera of U.S. Photometric company production for use and is subjected to the control of computing machine 8, and this video camera has refrigeration unit and temperature controller, the highest sample frequency 20MHz; Pixel Dimensions 7.4 μ m * 7.4 μ m, pixel count is 2048 * 2048, chip area 15.16m * 15.16mm, frame rate 3fps.In running order following at ccd video camera 6, the image that collects when its shutter close is cold-scarce scape image, and this cold-scarce scape image is real to be ccd video camera 6 intrinsic heat noise own and electronic noises; Open and standard sources 1-1 power supply when not opening when its shutter, its image that collects is hot background image, and this image is produced by experimental enviroment; Open and standard sources 1-1 when opening when its shutter, its image that collects is the target line image.Cold-scarce scape image, hot background image and target line image are bitmap (bitmap) form.
Computing machine 8 built-in capture cards, storer and image processing software also are furnished with mouse and keyboard, and computing machine 8 is connected with ccd video camera 6 by pci bus.Prestore initialization status data, the threshold modulation M of ccd video camera and capture card in the storer c, resolving power target line unit and resolving power value corresponding tables, simultaneously, can also store all kinds of images of ccd video camera 6 outputs.The function of image processing software is that control ccd video camera 6 is finished the setting of dependence test parameter; Gather the target line image of cold-scarce scape image, hot background image and the resolving power target 2 of ccd video camera 6 outputs; The respective image of gathering is carried out a series of image handle, the final objective evaluation result who obtains three generations's gleam image intensifier 5-1 resolving power to be measured.
Resolving power evaluation method of the present invention realizes that by computing machine 8 after three generations's gleam image intensifier 5-1 to be measured was placed into the resolution measurement device, image processing software was according to the following operation steps of flow performing shown in Figure 3.
The first step, initialization
After start powers on, load the driver of ccd video camera, capture card, mouse, keyboard, initialization apparatus.In conjunction with the input data setting ccd video camera 6 of keyboard and the duty of capture card, as the on-keyboard input, then call ccd video camera and capture card initialization status data in the storer, set the duty of the two; This acquiescence duty is focus pattern and video monitoring mode, and lightness and contrast parameter are 50, and working temperature is-25 ℃, and frequency acquisition was 3 frame/seconds, and drainage pattern is the single frames collection, and transfer rate is 20M/s;
In second step, gather cold-scarce scape image and hot background image
After the acquisition of receiving the keyboard input, at first send cold-scarce scape acquisition to ccd video camera 6, gather the cold-scarce scape image A of ccd video camera 6 outputs by pci bus LAnd deposit in the storer; Then, send hot background acquisition to ccd video camera 6, under the situation that light source 1-1 does not open, gather the hot background image A of ccd video camera 6 outputs by pci bus RAnd deposit in the storer.
In the 3rd step, gather resolving power target image
After the acquisition of receiving the keyboard input, send resolving power target acquisition to ccd video camera 6, under the situation that light source 1-1 opens, gather a frame resolving power target image F of ccd video camera 6 outputs and deposit in the storer by pci bus, show this resolving power target image F at display screen simultaneously.
The 4th step, the image pre-service
In the present invention, the image pre-service refers to resolving power target image F according to deduct cold-scarce scape image A by grey scale pixel value LWith hot background image A RA kind of processing mode of corresponding pixel points gray-scale value, its specific algorithm formula is as follows:
G (s, t)=n (s, t)-n L(s, t)-n R(s, t) in the formula, n (s, t), n L(s, t), n R(s t) is followed successively by resolving power target image F, cold-scarce scape image A L, hot background image A RPixel (s, gray-scale value t), g (s, t) for the testing image G that obtains after the pre-service at pixel (s, gray-scale value t).After whole two field picture pre-service finishes, just obtained the two dimensional gray matrix of testing image G and with this matrix stores in storer, simultaneously show testing image G at display screen.
In the 5th step, set the ROI zone
Behind the ROI zone setting command of receiving the keyboard input, calculate the size in ROI zone according to corresponding formula.The ROI zone is the perform region, refers to the image-region that need handle, and this zone is the square area that the group of the highest distinguishable resolving power target of tested image intensifier limits.Since present embodiment at the resolving power target be the USAF1951 target, this target comprises-2 ,-1,0, totally 10 groups of 1......6,7, the length of side L in the ROI zone of every group of correspondence iDetermined by following formula:
L i = ( 1 2 ) i + 1 [ 7 2 ( 1 - 1 2 6 ) - 2 32 6 ]
In the formula, i represents the group of resolving power target, i.e. i=-2 ,-1,0,1......6,7.At present, the three-generation image enhancer best result is distinguished power generally at second group, and therefore, in the present embodiment, correspondence is got i=2, obtains L by calculating 2=3.56.Calculated amount is reduced in the target line zone that definition ROI can avoid handling low resolution in the zone.
In the 6th step, generate target line unit standard form
Standard form refers to target line number and the shape and size generated ideal target line image according to each discrete target line unit on the used resolving power target.
For the present embodiment, the width of standard form is determined by following formula:
D i , j = 12 ( 1 2 ) i + 1 ( 1 2 6 ) j
In the formula, j represents each target line unit number in every group of resolution target line.In the present embodiment, minimum resolving power target line group in the ROI zone is second group, i.e. i=2, and the span of j is 1,2,3......6, the target line unit that has maximum line width in the corresponding resolving power group of j=1, the target line unit that has minimum feature in the corresponding resolving power group of j=6.For USAF1951 resolving power target, its standard form height is 5/12 of width, and three horizontal three perpendicular rectangular target lines are arranged in the template, six roots of sensation target line equal and opposite in direction, and target line length breadth ratio is 5: 1, target line width E I, j(mm of unit) determined by following formula:
E i , j = ( 1 2 ) i + 1 ( 1 2 6 ) j
E I, jAlso be simultaneously the spacing between three horizontal target lines being equally spaced or the three perpendicular target lines, the distance between horizontal target line group and the perpendicular target line group is 2E I, j
According to above-mentioned computing formula and corresponding target line parameters relationship, generate the standard form that has minimum resolving power target line group and have all target line unit correspondences in the inferior low resolution target line group in the ROI zone.For present embodiment, generate i=2 and j=1～6 successively, the standard form of each unit correspondence of i=3 and j=1～6.
In the 7th step, calculate the normalized crosscorrelation coefficient
The standard form that generates is placed the upper left corner, ROI zone of testing image G, and according to moving this standard form by the mode of pixel line by line, every movement once, utilize the normalized crosscorrelation formula to calculate normalized crosscorrelation coefficient (abbreviation cross-correlation coefficient) NC of current standard form and subgraph, all pixels until current standard form traversal ROI zone.Subgraph is testing image G by the part that standard form covered.Find out the subgraph of corresponding maximum cross correlation coefficient NC value then, record maximum cross correlation coefficient NC value and corresponding subgraph position thereof.Specific practice is, according to resolving power standard form order from low to high, travel through all pixels in ROI zone one by one with standard form, finally find out the corresponding subgraph that has maximum cross correlation coefficient NC value with each standard form, that is coupling target line unit, record these maximum cross correlation coefficient NC values and the corresponding target line of corresponding subgraph unit number thereof (i, j).
Cross-correlation coefficient NC value is more big, illustrate that subgraph is more similar to standard form, when cross-correlation coefficient NC value is 1, it is the perfect match position, and in actual conditions, cross-correlation coefficient NC can not be 1, therefore only need find at testing image G to have the corresponding subgraph of maximum cross correlation coefficient NC value position, can think that then the target line unit of this position is exactly the coupling target line unit of current standard form.Like this, the corresponding coupling target line unit of each standard form.Cross-correlation coefficient NC value and resolution threshold value NC with these coupling target line unit DifferentiateCompare, in cross-correlation coefficient NC value greater than differentiating threshold value NC DifferentiateCoupling target line unit in, find out and have that best result is distinguished the target line unit of power and as optimum matching target line unit.
In these coupling target line unit corresponding with whole standard forms, its cross-correlation coefficient NC value too hour, this target line unit is actually and can't differentiates, and cross-correlation coefficient NC value is when too big, the resolving power that can not truly reflect tested image intensifier, therefore a suitable cross-correlation coefficient NC value need be set namely differentiates threshold value NC Differentiate, to find out not only distinguishable and resolving power but also high target line unit.Usually, need at first obtain not only distinguishable and resolving power but also high target line unit by a large amount of experiments, then, with this unit corresponding cross-correlation coefficient NC value as differentiating threshold value NC DifferentiateNC DifferentiateSpan is generally 0.5～0.7, NC in the present embodiment DifferentiateGet 0.68.
Because tested gleam image intensifier is the video screen imaging, there are the bright phaeism flicker of intrinsic screen and screen shake scintillation.For this reason, the present invention utilize normalized crosscorrelation model accuracy height, adaptability good, to the insensitive characteristics of the linear transformation of gradation of image value, subgraph to the testing image G of standard form and covering thereof carries out matching operation, thereby can reduce the influence that the bright phaeism flicker of tested image intensifier screen is estimated resolution measurement; In addition, because the result of calculation of normalized crosscorrelation model is to find the solution optimum matching target line unit, therefore, can solve the influence that screen shake flicker is estimated resolution measurement well.
The 8th step, the calculating optical degree of modulation
The size of optical modulation degree has reflected the resolvability of image to a great extent, can judge the readability of image on the whole.The sharpness of different target lines and the optical modulation degree of its grey scale curve are proportional.Simultaneously, the clear picture degree of the size of optical modulation degree and human eye observation has good consistance, and the optical modulation degree is more high, and image is more clear, and vice versa.Among the present invention, the optical modulation degree calculates according to the following steps:
8.1 in optimum matching target line unit, get the gray-scale value I of a row pixel of horizontal target line group switching centre position 1I 2... I kAnd these gray-scale values are carried out size ordering, rejects acquisition selection gray value sequence I after k/Q the maximal value ChoosingAnd Q is positive integer.If k/Q is not integer, then units rounds downwards.The Q value depends on the fluoroscopic ion burn quantity of tested image intensifier grade, and its size should guarantee effectively to reject ion burn, guarantees as far as possible that again leaving more pixel count is used for subsequent treatment.In the present embodiment, get Q=12.
To selecting gray value sequence I ChoosingAsk the arithmetic mean value to obtain I AvgTo select gray value sequence I ChoosingIn greater than average I AvgGray-scale value ask arithmetic mean to obtain I Max, and to less than I AvgGray-scale value ask the arithmetic mean value to obtain I MinAfterwards, calculate the degree of modulation of horizontal target line group with following formula:
M = I max - I min I max + I min
8.2 get the gray-scale value of perpendicular target line group switching centre position, optimum matching target line unit one-row pixels, the method with 8.1 is calculated the degree of modulation of perpendicular target line group.
8.3 ask the average of optimum matching target line unit horizontal target line group and perpendicular target line group degree of modulation
Figure BSA00000511252300131
It is the optical modulation degree of optimum matching target line unit.Optical modulation degree with this target line unit
Figure BSA00000511252300132
With the threshold modulation M in the storer cCompare, if
Figure BSA00000511252300133
Show that this optimum matching target line unit is distinguishable under the degree of modulation criterion, then enter 9.1 steps; If Show that this optimum matching target line unit can not differentiate under the degree of modulation criterion, then enter 9.2 steps.
Threshold modulation M cIt is through test of many times and the resolution critical point of determining after verifying repeatedly.Generally speaking, degree of modulation is lower than 0.1, and resolving power target image will be difficult to differentiate, thereby, threshold modulation M cValue generally at 0.1≤M c≤ 0.2 scope.
Because three generations's gleam image intensifier is the video screen imaging, has intrinsic ion burn.For this reason, the present invention by removing k/Q maximum gradation value, can effectively reject the big unusual gray-scale value that ion burn causes, thereby remove the interference that ion burn is estimated resolution measurement in the calculating of optical modulation degree.
In the 9th step, obtain single-frame images resolving power result calculated
9.1 work as Continue to judge the optical modulation degree of optimum matching target line unit
Figure BSA00000511252300136
Whether apparently higher than threshold value M c, if
Figure BSA00000511252300137
Then the sequence number of optimum matching target line unit is the single frames result; If
Figure BSA00000511252300138
Then calculate the optical modulation degree that resolving power is higher than the adjacent cells of optimum matching target line unit
Figure BSA00000511252300139
If the optical modulation degree of high resolution adjacent target line unit Satisfy
Figure BSA000005112523001311
Then the sequence number of this high resolution target line unit is the single frames result, otherwise the sequence number of keeping optimum matching target line unit is the single frames result.
9.2 work as
Figure BSA000005112523001312
Calculate the optical modulation degree that resolving power is lower than the adjacent cells of optimum matching target line unit
Figure BSA000005112523001313
If satisfy
Figure BSA000005112523001314
And
Figure BSA000005112523001315
Then the sequence number of this low resolution adjacent target line unit is the single frames result; If satisfy
Figure BSA000005112523001316
Then further utilize the cross-correlation coefficient NC between normalized crosscorrelation formula calculating low resolution adjacent target line unit and the corresponding standard form thereof AdjacentIf, cross-correlation coefficient NC AdjacentThere are not bigger variation, i.e. NC with the cross-correlation coefficient NC of optimum matching target line unit more yet Adjacent〉=0.97NC, then the sequence number of optimum matching target line unit is the single frames result, if NC Adjacent＜0.97NC, then the sequence number of low resolution adjacent target line unit is the single frames result.
The sequence number of above-mentioned resolving power target line unit shows as i and organizes the j unit, also need to search the corresponding resolving power value of this sequence number by (table 1) mode of tabling look-up, and with this resolving power value as the final process result of single frames and be presented on the screen.
In the tenth step, obtain multiple image resolving power result calculated
For making result of calculation more accurate, one width of cloth resolving power target image is carried out the multiframe collection, usually select for use 10 frames to get final product, then repeatedly the 3rd step of (10 times) repetition to the 9th step handles every frame resolving power target image respectively, thereby obtains the single frames resolving power result of respective numbers.Like this, will there be following two kinds of situations:
1). there are half and above single frames resolving power final process result identical, can be with the net result of this result as three generations's gleam image intensifier resolving power evaluation method.
2). the single frames resolving power final process result of multiple image is in a discrete distribution, and does not namely have a kind of single frames resolving power final process result ratio to surpass half, at this moment, the optical modulation degree is asked by the 8th step respectively in the corresponding target line of each single frames resolving power result unit
Figure BSA00000511252300141
And one by one with degree of modulation criterion M cRelatively, optical modulation degree
Figure BSA00000511252300142
Near M cThe resolving power value of target line unit correspondence be considered as the net result of three generations's gleam image intensifier resolving power evaluation method.
Table 1 resolving power target line unit and resolving power value corresponding tables
Unit: line is right
Figure BSA00000511252300143

Claims (2)

1. three generations's gleam image intensifier resolving power evaluation method, this method realizes at three generations's gleam image intensifier resolution measurement device, described three generations's gleam image intensifier resolution measurement device comprises light source assembly (1), resolving power target (2), parallel light tube (3), the image-forming objective lens (4) that has zoom function, the test camera bellows (5) that has input and outgoing window, base platform (7), the ccd video camera (6) that has function of temperature control, computing machine (8), described light source assembly (1), parallel light tube (3) and test camera bellows (5) are by corresponding bracing frame (7-1,7-2,7-4) be fixed on the described base platform (7), described resolving power target (2) is connected on the parallel light tube (3), its target surface is positioned on the object space focal plane of parallel light tube (3) and target surface is centered close on the optical axis of measuring light path, described image-forming objective lens (4) and described ccd video camera (6) are installed in described base platform (7) by two-dimension translational mechanism (7-3) and D translation mechanism (7-5) respectively, the target surface center of the optical axis of image-forming objective lens (4) and ccd video camera (6) all is positioned on the optical axis of measuring light path, and is placed on the video screen of the image intensifier to be measured (5-1) in the described test camera bellows (5) and the object space focal plane and focus that the center correspondence is positioned at described ccd video camera (6); The light beam that described light source assembly (1) sends illuminates described resolving power target (2), and the time of the target line pattern of resolving power target (2) through focused on described three generations's gleam image intensifier to be measured (5-1) behind described parallel light tube (3) collimation by described image-forming objective lens (4) is on the pole-face; Three generations's gleam image intensifier to be measured (5-1) forms brighter target line image to collimation target line pattern multiplication back at its video screen; Described ccd video camera (6) is gathered the target line image on three generations's gleam image intensifier to be measured (5-1) video screen and is converted thereof into electric signal;
It is characterized in that: described computing machine (8) is estimated the resolving power of three generations's gleam image intensifier by following operation steps:
The first step, the running parameter of the described ccd video camera of initialization (6);
In second step, according to keyboard instruction, gather the cold-scarce scape image A of described ccd video camera (6) output in succession LWith hot background image A RAnd all deposit in the storer;
The 3rd step, according to keyboard instruction, gather a frame resolving power target image F of described ccd video camera (6) output and deposit in the storer, show this image at display screen simultaneously;
In the 4th step, according to keyboard instruction, from storer, call cold-scarce scape image A L, hot background image A RWith resolving power target image F, resolving power target image F is deducted cold-scarce scape image A according to pursuing grey scale pixel value LWith hot background image A RThe gray-scale value of corresponding pixel points obtains testing image G and corresponding two dimensional gray matrix thereof, stores the two dimensional gray matrix and shows testing image G at display screen;
In the 5th step, according to keyboard commands, it is the ROI district that the image processing region is set, the zone that the ROI district limits for the highest distinguishable or inferior high distinguishable resolving power target line group of tested image intensifier;
In the 6th step, generate the standard form that has minimum resolving power target line group and have all target line unit correspondences in the inferior low resolution target line group in the ROI zone;
The 7th step, travel through all pixels in ROI zone successively in the mode of pursuing pixel line by line with each standard form that generates, simultaneously, adopt the normalized crosscorrelation formula to calculate the cross-correlation coefficient NC value of standard form and subgraph in each pixel position, find out the corresponding subgraph that is the coupling target line unit that have maximum cross correlation coefficient NC value with each standard form one by one, record these maximum cross correlation coefficient NC values and corresponding coupling target line unit thereof sequence number (i, j); Cross-correlation coefficient NC value and resolution threshold value NC with these coupling target line unit DifferentiateCompare, in cross-correlation coefficient NC value greater than differentiating threshold value NC DifferentiateCoupling target line unit in, will have best result and distinguish that the coupling target line unit of power is as optimum matching target line unit;
In the 8th step, in optimum matching target line unit, get the gray-scale value I of a row pixel of horizontal target line group switching centre position 1I 2... I kAnd these gray-scale values are carried out size ordering, rejects acquisition selection gray value sequence I after k/Q the maximal value ChoosingAnd Q is positive integer, if k/Q is not integer, then units rounds downwards, and calculates the degree of modulation of the horizontal target line of optimum matching group with following formula:
M = I max - I min I max + I min
In the formula, I MaxFor selecting in the gray value sequence mean value greater than each gray-scale value of selecting the gray value sequence average, I MinFor selecting in the gray value sequence mean value less than each gray-scale value of selecting the gray value sequence average; In like manner, calculate the degree of modulation of the perpendicular target line group of optimum matching; Ask the average of optimum matching target line unit horizontal target line group and perpendicular target line group degree of modulation
Figure FSB00001055667300022
That is the optical modulation degree of optimum matching target line unit;
The 9th step is with the optical modulation degree of optimum matching target line unit
Figure FSB00001055667300031
With threshold modulation M cCompare: if
Figure FSB00001055667300032
Continue to judge the optical modulation degree of optimum matching target line unit
Figure FSB00001055667300033
Whether apparently higher than threshold value M c, if
Figure FSB00001055667300034
Then the resolving power value of optimum matching target line unit correspondence is that single frames is handled net result; If
Figure FSB00001055667300035
Then calculate the optical modulation degree that resolving power is higher than the adjacent cells of optimum matching target line unit
Figure FSB00001055667300036
If the optical modulation degree of high resolution adjacent target line unit
Figure FSB00001055667300037
Satisfy
Figure FSB00001055667300038
Then the resolving power value of high resolution adjacent target line unit correspondence is the net result that single frames is handled, otherwise the resolving power value of keeping optimum matching target line unit correspondence is that single frames is handled net result; If
Figure FSB00001055667300039
Calculate the optical modulation degree that resolving power is lower than the adjacent cells of optimum matching target line unit
Figure FSB000010556673000310
If satisfy
Figure FSB000010556673000311
And
Figure FSB000010556673000312
Then the resolving power value of low resolution adjacent target line unit correspondence is that single frames is handled net result; If satisfy
Figure FSB000010556673000313
Then utilize the cross-correlation coefficient NC between normalized crosscorrelation formula calculating low resolution adjacent target line unit and the corresponding standard form thereof again AdjacentIf, NC Adjacent〉=0.97NC, then the resolving power value of optimum matching target line unit correspondence is that single frames is handled net result, if NC Adjacent＜0.97NC, then the resolving power value of low resolution adjacent target line unit correspondence is that single frames is handled net result and shown at display screen;
The tenth step, repeatedly repeating the 3rd step to the 9th step handles follow-up multiframe resolving power target image respectively, thereby obtain the single frames resolving power result of respective numbers, if have half and above single frames resolving power result identical, with the net result of this result as three generations's gleam image intensifier resolving power evaluation method; If the single frames resolving power result of multiple image is in a discrete distribution, then the optical modulation degree is asked by the 8th step respectively in the corresponding target line of each single frames resolving power result unit
Figure FSB000010556673000314
And one by one with degree of modulation criterion M cRelatively, optical modulation degree
Figure FSB000010556673000315
Near M cThe corresponding resolving power value in target line unit be considered as the net result of described three generations's gleam image intensifier resolving power evaluation method and show at display screen.
2. three generations's gleam image intensifier resolving power evaluation method according to claim 1 is characterized in that: described resolution threshold value NC DifferentiateValue in 0.5～0.7 scope; Described threshold modulation M cValue at 0.1≤M c≤ 0.2 scope.
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