CN103411757A - Measuring system based on optical transfer function of endoscope with special spatial frequency and calibrating method thereof - Google Patents
Measuring system based on optical transfer function of endoscope with special spatial frequency and calibrating method thereof Download PDFInfo
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- CN103411757A CN103411757A CN2013103975545A CN201310397554A CN103411757A CN 103411757 A CN103411757 A CN 103411757A CN 2013103975545 A CN2013103975545 A CN 2013103975545A CN 201310397554 A CN201310397554 A CN 201310397554A CN 103411757 A CN103411757 A CN 103411757A
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- endoscope
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Abstract
The invention relates to a calibrating method and a system of a measuring system based on an optical transfer function of an endoscope with special spatial frequency. The calibrating system comprises a light source 1, a reticle 2, an imaging objective 3, a CCD (Charge Coupled Device) 4 and a standard endoscope 5, wherein the reticle 2 is provided with a raster with special spatial frequency. When the measuring system is calibrated, the standard endoscope 5 is used. The optical transfer function value MTF(fx) of characteristic frequency of the raster used by the standard endoscope is known, then, contrast ratio M1(fx) is obtained by measuring, and M2(fx) is obtained according to a formula and is recorded and stored, and the endoscope is measured. According to the optical transfer function measuring system of the endoscope provided by the invention, before and after the standard endoscope and a measured endoscope are placed, conjugate relations of optical lenses are infinitive conjugation without system errors. Parasitic light impacts of the CCD in the calibrating process and the measuring process are close, and the change on illuminance is smaller, so that the non-linear response impact of the CCD is smaller, and the measuring precision is higher. The measuring result is traced to the source.
Description
Technical field
The present invention relates to a kind of measuring system and calibration steps thereof of endoscope optical transfer function, especially a kind of measuring system and calibration steps thereof of the optical transfer function of the endoscope based on the particular space frequency.
Background technology
Endoscope is the Main Means of the inside and outside section deagnostic test of routine always.The quality of medical image directly affects diagnosis and the treatment of doctor to the state of an illness, and and the communication of families of patients, therefore how to obtain satisfied image and to objective, the comprehensive evaluation of carrying out of image, be how the focus that people study always.Optical transfer function (Optical Transfer Function) can be used for estimating the image quality of optical system, optical transfer function is the general name of modulation transfer function and phase transfer function in the physical sense, and what modulation transfer function (MTF) meaned is the output of different space frequency and the ratio of input degree of modulation (being contrast).MTF has reflected the ability of the image information of optical system transmission different space frequency, can objective and accurately describe the information regeneration rate of imaging system and its ingredient.The mtf value of a certain spatial frequency is higher, illustrates that the optical system imaging ability is better under this spatial frequency, stronger to the reducing power of raw information, and resulting image is also more close to original objects.Therefore, MTF is widely used in the evaluation of imaging quality of various optical imaging systems since the concept of optical transfer function proposes.
Fig. 1 is the system of the optical transfer function of endoscope of measuring in prior art, comprise light source 1, graticule 2, image-forming objective lens 3 and CCD4, when this modulated optical transport function of calibration, do not put tested endoscope, only carry out optical focusing, the imaging lens of this system is accommodated on graticule 2, on graticule 2, be provided with the grating of determining spatial frequency, now can be observed the grating image on graticule, by the signal of CCD, can measure the contrast of particular space frequency
This value is stored.Then in this system, place the endoscope that will measure, then imaging lens is accommodated to infinite distance.Now the grating image on graticule is clear, can measure by the signal of CCD the contrast that can obtain the particular space frequency
And utilize following formula to calculate
Can draw the optical transfer function of last endoscope.
There is following deficiency in existing endoscope optical transfer function measuring system:
1) measuring system is installed before and after endoscope, and the conjugate relation of image-forming objective lens is adjusted to finite conjugate by infinite conjugate.The image-forming objective lens optical transfer function of finite distance, being less than himself focal length below 30 times the time, can produce certain systematic error.The transport function of object lens itself has certain variation.
2) in addition due to CCD at measuring process and calibration process, veiling glare impact differs far away, there is certain deviation in the variation of illuminance, non-linear due to the CCD response, this affects the variation of contrast to a certain extent.
3) measurement result can't be traced to the source, and accuracy can't be guaranteed.
Above-mentioned factor all can cause that the accuracy of measurement of optical transfer function reduces.
Summary of the invention
The object of the invention is to for above-mentioned existing problems, propose a kind of particular space frequency endoscope optical transfer function measuring system and calibration steps thereof, improve the accuracy in detection of endoscope optical modulation function MTF measuring system.
The present invention is based on the calibration steps of particular space frequency endoscope optical transfer function measuring system, depend on the standard endoscope of an optical transfer function precision calibration, set up tracing to the source and calibration steps of endoscope optical transfer function pick-up unit.
A kind of calibration steps based on particular space frequency endoscope optical transfer function measuring system, comprising following steps:
1) use the precision optics transport function measurement mechanism based on Fourier analysis to carry out the optical transfer function precision calibration to a standard endoscope;
2) obtain the continuous curve of 0 degree visual field different space frequency;
3) get the optical transfer function value MTF (f based on the grating characteristic frequency of endoscopy examining system
x)
4) endoscope that will demarcate is placed in an endoscope optical transfer function measuring system, and this endoscope optical transfer function measuring system is calibrated;
5) in above-mentioned endoscope optical transfer function measuring system, the high-high brightness Imax of the endoscope that actual measurement was demarcated and minimum brightness Imin, according to formula
Can calculate the contrast ratio M of particular space frequency
1(f
x);
6) according to formula
MTF (f wherein
x) by step 3), be known, can obtain M
2(f
x), and be recorded preservation;
7) from described endoscope optical transfer function measuring system, taking out standard endoscope, place and need the tested endoscope of measuring, again measure, obtain the contrast of the particular space frequency of tested endoscope
8) utilize following formula to calculate
M wherein
2(f
x) obtained by step 6), can draw the biography letter of last endoscope.
A kind of measuring system based on particular space frequency endoscope optical transfer function, comprise light source, graticule, image-forming objective lens and CCD, also comprise standard endoscope, light source wherein, graticule, endoscope, image-forming objective lens and CCD set gradually, and on graticule, are provided with the grating of particular space frequency.
A kind of measuring system based on particular space frequency endoscope optical transfer function, wherein light source is LED light source.
The invention has the advantages that:
In endoscope optical transfer function measuring system, place before and after standard endoscope and tested endoscope 1) the Application standard endoscope carries out the calibration of measuring system, and the conjugate relation of optical lens is all infinite conjugate, does not have systematic error.2) because CCD approaches in measuring process and the impact of calibration process veiling glare, the variation of illuminance is less.The nonlinear response impact of CCD is less, and measuring accuracy is higher.3) measurement result is traced to the source.
The accompanying drawing explanation
Fig. 1 a is the grating of different space frequency;
Fig. 1 b is the imaging of the grating of different space frequency in Fig. 1 a;
Fig. 2 is existing schematic diagram based on particular space frequency endoscope optical transfer function measuring system;
Fig. 3 is the schematic diagram that the present invention is based on particular space frequency endoscope optical transfer function measuring system.
Embodiment
Fig. 1 a is the grating that illustrates different space frequency, and Fig. 1 b is the grating difference imaging of different space frequency in Fig. 1 a.
The present invention is based on particular space frequency endoscope optical transfer function measuring system, as shown in Figure 3, comprise light source 1, graticule 2, image-forming objective lens 3, CCD4 and standard endoscope 5, on graticule 2, be provided with the grating of particular space frequency, the light source that the present embodiment is used is LED, when calibration measuring system of the present invention, Application standard endoscope 5, the optical transfer function value MTF (f of the characteristic frequency of the grating that uses of known this standard endoscope
x), then, measure contrast ratio M
1(f
x), according to formula
Can obtain M
2(f
x), and be recorded preservation.The work of calibration endoscope optical transfer function measuring system completes.Can carry out the measurement of endoscope.
The present invention is based on the calibration steps of particular space frequency endoscope optical transfer function measuring system, comprising following steps:
(1) use the precision optics transport function measurement mechanism based on Fourier analysis to carry out the optical transfer function precision calibration to a standard endoscope;
(2) obtain the continuous curve of 0 degree visual field different space frequency;
(3) get the optical transfer function value MTF (f based on the grating characteristic frequency of endoscopy examining system
x);
(4) endoscope that will demarcate is placed in endoscope optical transfer function measuring system of the present invention, and this endoscope optical transfer function measuring system is calibrated;
(5) in above-mentioned endoscope optical transfer function measuring system, the high-high brightness Imax of the endoscope that actual measurement was demarcated and minimum brightness Imin, according to formula
Can calculate the contrast ratio M of this particular space frequency
1(f
x);
(6) according to formula
MTF (f wherein
x) by step 3), be known, can obtain M
2(f
x), and be recorded preservation;
(7) from described endoscope optical transfer function measuring system, taking out standard endoscope, place and need the tested endoscope of measuring, again measure, obtain the contrast of this particular space frequency of tested endoscope
(8) utilize following formula to calculate
M wherein
2(f
x) obtained by step 6), can draw the biography letter of last endoscope.
Endoscope optical transfer function measuring system of the present invention, place before and after standard endoscope and tested endoscope, and the conjugate relation of optical lens is all infinite conjugate, does not have systematic error.Because CCD is close at calibration process and the impact of measuring process veiling glare, the variation of illuminance is less, makes the nonlinear response impact of CCD less, and measuring accuracy is higher.Measurement result is traced to the source.
Claims (3)
1. calibration steps based on particular space frequency endoscope optical transfer function measuring system, comprising following steps:
1) use the precision optics transport function measurement mechanism based on Fourier analysis to carry out the optical transfer function precision calibration to a standard endoscope;
2) obtain the continuous curve of 0 degree visual field different space frequency;
3) get the optical transfer function value MTF (f based on the grating characteristic frequency of endoscopy examining system
x)
4) endoscope that will demarcate is placed in an endoscope optical transfer function measuring system, and this endoscope optical transfer function measuring system is calibrated;
5) in above-mentioned endoscope optical transfer function measuring system, the high-high brightness Imax of the endoscope that actual measurement was demarcated and minimum brightness Imin, according to formula
Can calculate the contrast ratio M of particular space frequency
1(f
x);
6) according to formula
MTF (f wherein
x) by step 3), be known, can obtain M
2(f
x), and be recorded preservation;
7) from described endoscope optical transfer function measuring system, taking out standard endoscope, place and need the tested endoscope of measuring, again measure, obtain the contrast of the particular space frequency of tested endoscope
8) utilize following formula to calculate
M wherein
2(f
x) obtained by step 6), can draw the biography letter of last endoscope.
2. measuring system based on particular space frequency endoscope optical transfer function, comprise light source, graticule, image-forming objective lens and CCD, characterized by further comprising standard endoscope, wherein light source, graticule, endoscope, image-forming objective lens and CCD set gradually, and on graticule, are provided with the grating of particular space frequency.
3. a kind of measuring system based on particular space frequency endoscope optical transfer function according to claim 1, wherein light source is LED light source.
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Cited By (2)
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| CN104122077A (en) * | 2014-07-31 | 2014-10-29 | 福州锐景达光电科技有限公司 | Method and device for measuring modulation transfer functions of optic lenses through infinite conjugated light paths |
| CN106153301A (en) * | 2015-03-24 | 2016-11-23 | 北京威斯顿亚太光电仪器有限公司 | A kind of detection method for rigid endoscope modulation transfer function (MTF) |
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| CN103411757B (en) | 2017-01-11 |
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