CN104921697A - Method for quickly measuring longitudinal distances of sight of human eyes - Google Patents

Abstract

The invention relates to a method for measuring longitudinal distances of sight of human eyes. The method includes particular steps of 1, creating an eccentric photographic measuring device comprising a camera, an infrared light source, an infrared filter lens, a telescope, a human face support, an infrared cut-off filter and the like; 2, detecting pupil boundaries, acquiring pupil regions by means of processing by the aid of run algorithms and acquiring boundaries by means of equation fitting; 3, computing the internal brightness distribution of pupils, and computing ratios of certain longitudinal lengths of the pupil regions to the lengths of integral longitudinal axes; 4, measuring longitudinal distances, acquiring the longitudinal distances of the sight by the aid of pre-measurement calibration parameters and current brightness distribution conditions of the pupils by means of computing. Average values of gray values of the integral pupil regions are used as threshold values, and the certain longitudinal lengths of the pupil regions are larger than the threshold values. The method has the advantages that information of the longitudinal distances can be obtained during sight tracking, accordingly, the sight can be truly three-dimensionally tracked, and the method further can be used for improving the precision of the traditional two-dimensional sight tracking systems; the method is low in computational complexity, and quick measuring and real-time tracking effects can be realized.

Description

A kind of method for fast measuring of human eye sight fore-and-aft distance

Technical field

The present invention relates to the field of measuring technique of human eye sighting distance, be specifically related to a kind of method for fast measuring of human eye sight fore-and-aft distance.

Background technology

At present, the measurement of human eye sighting distance is mainly carried out based on visual disparity method, the non-constant of such certainty of measurement.When the eyes of people focus on same point, the eyes due to people have a spacing (about 3-5cm), cause the direction of visual lines vector of two eyes not overlap completely.All, visual disparity method is exactly the direction of visual lines vector by each eyes of independent measurement, and the intersection point of two vectors is the focus place of eye-observation.But, the error that human eye sight direction vector is measured is natively larger, calculating with it second order error brought human eye focal position again can be very large, moreover there are some researches show that the position of direction of visual lines vector intersection point might not be the focus of eye-observation, eye-observation Focus Club appears in front and back one segment distance of direction of visual lines vector intersection point.Traditional visual disparity method certainty of measurement will be caused so lower.

Summary of the invention

The object of the invention is to the method for fast measuring proposing a kind of human eye sight fore-and-aft distance.By the pupil image of photographic head shooting human eye, extract the bright dark distribution characteristics of pupil from image, calculate human eye sight distance.We improve the light path of infrared eccentric Photographic technique, add suitable optics auxiliary (infrared fileter, cutoff filter, infrared light supply, telescopic system), make the restriction of measuring process to people smaller, and time cost is also less.

Object of the present invention is achieved through the following technical solutions.

A measuring method for human eye sight fore-and-aft distance, it comprises the steps:

(1) on optical bench, build eccentric image measuring device, comprise photographic head, infrared light supply, infrared filter, telescope, face support, cutoff filter; Coaxially contour along the cutoff filter on optical path direction, telescope and photographic head, face support is for supporting testee face; Optical path is folded on the right side of face support by cutoff filter; Telescope is for shortening shooting light path; Video camera, at the low order end of light path, establishes diaphragm and infrared light supply between telescope and photographic head, use infrared light supply to obtain sharply marginated pupil image, diaphragm shelters from the latter half of photographic head; An infrared fileter is provided with, for reducing the impact of ambient visible light before photographic head; Photographic head also connects computer by USB interface, carries out image procossing and calculating on computers with on MATLAB software platform;

(2) pupil boundary detects, and obtains pupil region by distance of swimming algorithm process, then obtains pupil boundary by equation model method;

(3) the bright dark distribution of pupil region calculates, diaphragm due to device is the latter half of blocking photographic head, the bright dark distribution of the pupil image of shooting is vertical change, the diameter of vertical direction can be chosen to calculate bright dark distribution characteristics, whole pupil region gray value meansigma methods is as threshold value, and what calculate vertical direction is diametrically greater than the length of threshold value and the ratio of pupil diameter;

(4) measurement of fore-and-aft distance, by the scaling parameter before measuring and the bright dark distribution situation of current pupil, calculates and obtains sight line fore-and-aft distance; Described scaling parameter comprises the oculopupillary distance A of pupil radium R, video camera and people, pupil dark areas and diameter ratio k.

Further optimally, said method uses the infrared eccentric Photographic technique improved directly to measure the fore-and-aft distance of human eye sight, the method of concrete improvement is by the correction of human eye diopter for human eye focal length, and becoming is the correction of diopter to object distance, and then obtains the calculation expression of sight line fore-and-aft distance.

The present invention adopts telescopic system to shorten shooting light path, weakens pupil center and infrared light supply out-of-alignment affects.Infrared light supply and infrared fileter is used to weaken environment interference of stray light.

Further optimally, said method uses the method for image procossing to calculate the bright dark distribution situation of pupil image, first adopts distance of swimming algorithm to obtain pupil region from eye image; Then pupil center is obtained to the method for zone boundary ellipse fitting, and border is modified to ellipse; Then carry out stretching, pupil region is drawn into circle, finally get the diameter of circular vertical to calculate the bright dark distribution characteristics of pupil region.

Further optimally, said method uses cutoff filter to make optical path vertical with human eye sight light path, and measuring process can not affect human eye field range.

Further optimally, the concrete calculation expression of the described calculating acquisition sight line fore-and-aft distance of step (4) is:

$S=\frac{2R\·A\·k}{E+2R\·k},$

S and sight line fore-and-aft distance, R is pupil radium, k is pupil dark areas and diameter ratio, A is photographic head and interpupillary distance, E is that light source departs from optical axis distance, wherein pupil dark areas and diameter ratio k can be obtained from pupil image by image processing techniques, and parameter E, A and R are obtained by calibration process; For each frame eye image, calculate the fore-and-aft distance that pupil dark areas and the diameter ratio k expression formula substituted into above just can calculate current human eye sight.

Compared with prior art, beneficial effect of the present invention comprise following some:

1) use infrared light supply, image processing process is simplified, and certainty of measurement is better.

2) use the battery of lens of telescopic system, shorten light path, weaken the impact that pupil center and infrared light supply disalignment are brought, reduce the restriction to people.

3) each time of measuring is few, can meet real-time measurement, follow the trail of the requirement of measuring.

4) use cutoff filter, reflects infrared light, visible light transmissive, measuring process can not affect the field range of testee.

Accompanying drawing explanation

Fig. 1 a and Fig. 1 b is the structural representation of eccentric photogrammetric apparatus in example.

Fig. 2 is the bright dark distributed effect figure of pupil image.

Fig. 3 is infrared eccentric Photographic technique schematic diagram.

Fig. 4 is actual eye-observation index path.

Fig. 5 is the bright dark distribution measuring figure of pupil.

Fig. 6 is experiment parameter matched curve figure.

Detailed description of the invention

Below in conjunction with accompanying drawing and example, specific embodiment of the invention is described further, but enforcement of the present invention and protection are not limited thereto.

The problem that this example will solve mainly can be divided into following some: from shooting eye image, accurately detect the border of pupil.Measure the bright dark distribution situation in pupil region.According to calibration process, obtain empirical parameter.Actual measurement, with the formulae discovery optical range of empirical parameter.

1. the coaxial adjustment of measuring system

Composition graphs 1 illustrates, whole device is fixed on optical bench, and face support 1 is for supporting testee face; Optical path is folded on the right side of face support by cutoff filter 2; Telescope 3 is for shortening shooting light path; Video camera 5, at low order end, is diaphragm and infrared light supply between telescope 3 and photographic head 5, uses infrared light supply can obtain sharply marginated pupil image; There is an infrared fileter 4 before photographic head, the impact of ambient visible light can be reduced.Adjustment process is as follows: first, regulates photographic head 5, telescope 3, hollow pipe and cutoff filter 2 on optical bench coaxially contour.Then, photographic head 5 takes eye image, is transferred to computer by USB interface.Check real-time eye image, regulate face support 1 height (due to human eye individual variation), eye areas is comprised in the picture.

2. pupil region segmentation

This step is partitioned into pupil region from eye image, and pupil region is drawn into border circular areas as shown in Figure 2.Because pupil is more responsive to infrared light, allow infrared light supply be irradiated on eyeball, lesser ring of Merkel can branch away by image procossing.Infrared light supply is arranged on center on diaphragm, and brightness can regulate.Image processing process is divided into the following steps:

(1) utilize the rectangular histogram of eye image to obtain appropriate threshold that one can be distinguished pupil and other parts.

(2) utilize the threshold value obtained, threshold process is carried out to eye image, divide zones of different.

(3) judgement of Run-Length Coding algorithm and adjacency vector is used, to each zone number.

(4) what comprise each region counts, and adds up, chosen area area maximum as pupil region.

(5) border of pupil and the two ends end to end of each column vector of chosen area, is extracted.

(6) utilize the border obtained, carry out oval matching.Be thought with method of least square, utilize singular value decomposition algorithm to calculate oval fit equation.Obtain ultimate bound and pupil region.

(7) pupil region obtained above is stretched to ellipse short shaft, make pupil region become border circular areas.

3. the bright dark distributions ratios of pupil is measured

The infrared eccentric Photographic technique schematic diagram of composition graphs 3 illustrates, eccentric Photographic technique measures the dioptric method of human eye, and the pupil region Fig. 2 obtained above is that light path shooting as shown in Figure 3 obtains.The expression formula of diopter D can be derived in conjunction with index path from bias photography ratio juris:

$D=\frac{E}{2R\·A\·k}$

Wherein D is diopter, and E is the distance of infrared light supply shown in Fig. 3 302 to diaphragm 301 edge, A be photographic head to pupil 303 distance, R is pupil radium, and k is pupil dark areas and diameter ratio (this can be mentioned below).Composition graphs 3 and Fig. 4 illustrate, the adjustment of diopter to eyes (eyeball 305) focal length are joined, become normal eye, be imaged on retina 304, the Gaussian imaging equation of this light path:

$\frac{1}{X}-\frac{1}{A}=\frac{1}{F}+D$

By formula transposition distortion above, can obtain:

$\frac{1}{X}-(\frac{1}{A}+D)=\frac{1}{F}$

The meaning of being out of shape here is not insignificant, can understand like this: the adjustment of diopter to human eye focal length is transformed into the adjustment of diopter to object distance.If consider that this process is object point imaging on normal retina, so object point is to the distance S of pupil, and namely the fore-and-aft distance of sight line meets:

$\frac{1}{S}=\frac{1}{A}+D$

By relational expression above, the expression formula of diopter D is substituted into the expression formula that can obtain sight line depth S:

$S=\frac{2R\·A\·k}{E+2R\·k}$

Wherein S is sight line fore-and-aft distance, and R is pupil radium, and k is pupil dark areas and diameter ratio, and A is photographic head and interpupillary distance, and E is that infrared light supply is to diaphragm Edge Distance.

Derive as can be seen from principle above, different optical ranges, the bright dark distribution characteristics (pupil dark areas and diameter ratio K) of pupil is different, and along with distance increase, dark areas ratio also increases.Diaphragm due to device is the latter half of blocking photographic head, the bright dark distribution of the pupil image of shooting is vertical change, therefore, the diameter of easy choice vertical direction calculates bright dark distribution characteristics, whole pupil region gray value meansigma methods is as threshold value, and what calculate vertical direction is diametrically greater than the length of threshold value and the ratio of pupil diameter.For a figure measurement as shown in Figure 5.

$k=\frac{2.72}{13.18}=0.21.$

4. calibration process

Use a center be a stain round target as calibration thing, people stares at target center.In eye sight line direction, at 50cm-300cm, each doing every 50cm once calibrates measurement.Obtain the ratio k of optical range s and pupil dark areas corresponding with it and whole vertical axes, number is substituted into the formula of theoretical derivation, obtain scaling parameter by the method for matched curve, fitted figure as shown in Figure 6, like this, the formula after calibration just may be used for actual measurement.The longitudinal expression formula of sight line after calibration is:

$S=\frac{2R\·A\·k}{E+2R\·k}=\frac{40k}{9+4k}$

By the result shown in calibration expression formula calculation chart 5 obtained above, wherein k=0.21, substitutes into above formula: sight line fore-and-aft distance S=0.873m.

Claims (5)

1. a measuring method for human eye sight fore-and-aft distance, is characterized in that comprising the steps:

(1) on optical bench, build eccentric image measuring device, comprise photographic head, infrared light supply, infrared filter, telescope, face support, cutoff filter; Coaxially contour along the cutoff filter on optical path direction, telescope and photographic head, face support is for supporting testee face; Optical path is folded into face support side by cutoff filter; Telescope is for shortening shooting light path; Video camera, at the low order end of light path, establishes diaphragm and infrared light supply between telescope and photographic head, use infrared light supply to obtain sharply marginated pupil image, diaphragm shelters from the latter half of photographic head; An infrared fileter is provided with, for reducing the impact of ambient visible light before photographic head; Photographic head also connects computer by USB interface, carries out image procossing and calculating on computers with on MATLAB software platform;

(2) pupil boundary detects, and obtains pupil region by distance of swimming algorithm process, then obtains pupil boundary by equation model method;

(3) the bright dark distribution of pupil region calculates, diaphragm due to device is the latter half of blocking photographic head, the bright dark distribution of the pupil image of shooting is vertical change, the diameter of vertical direction can be chosen to calculate bright dark distribution characteristics, whole pupil region gray value meansigma methods is as threshold value, and what calculate vertical direction is diametrically greater than the length of threshold value and the ratio of pupil diameter;

(4) measurement of fore-and-aft distance, by the scaling parameter before measuring and the bright dark distribution situation of current pupil, calculates and obtains sight line fore-and-aft distance; Described scaling parameter comprises the oculopupillary distance A of pupil radium R, video camera and people, pupil dark areas and diameter ratio k.

2. the measuring method of a kind of human eye sight fore-and-aft distance according to claim 1, it is characterized in that using the infrared eccentric Photographic technique improved directly to measure the fore-and-aft distance of human eye sight, the method of concrete improvement is by the correction of human eye diopter for human eye focal length, becoming is the correction of diopter to object distance, and then obtains the calculation expression of sight line fore-and-aft distance.

3. the measuring method of a kind of human eye sight fore-and-aft distance according to claim 1, is characterized in that using the method for image procossing to calculate the bright dark distribution situation of pupil image, first adopts distance of swimming algorithm to obtain pupil region from eye image; Then pupil center is obtained to the method for zone boundary ellipse fitting, and border is modified to ellipse; Then carry out stretching, pupil region is drawn into circle, finally get the diameter of circular vertical to calculate the bright dark distribution characteristics of pupil region.

4. the measuring method of a kind of human eye sight fore-and-aft distance according to claim 1, it is characterized in that using cutoff filter to make optical path vertical with human eye sight light path, measuring process can not affect human eye field range.

5. the measuring method of a kind of human eye sight fore-and-aft distance according to claim 1, is characterized in that the described calculating of step (4) obtains the concrete calculation expression of sight line fore-and-aft distance and is:

$S=\frac{2R\·A\·k}{E+2R\·k},$

S and sight line fore-and-aft distance, R is pupil radium, k is pupil dark areas and diameter ratio, A is photographic head and interpupillary distance, E is that light source departs from optical axis distance, wherein pupil dark areas and diameter ratio k can be obtained from pupil image by image processing techniques, and parameter E, A and R are obtained by calibration process; For each frame eye image, calculate the fore-and-aft distance that pupil dark areas and the diameter ratio k expression formula substituted into above just can calculate current human eye sight.