CN103006175A - Method for positioning optic disk for eye fundus image on basis of PC (Phase Congruency) - Google Patents

Abstract

The invention belongs to the field of medical image treatment and relates to a method for positioning an optic disk for an eye fundus image on the basis of PC (Phase Congruency). According to the method, after four relatively prominent single-channel images for the optic disk are selected, a PC function is utilized to treat the selected images, and a logic AND is adopted for enhancing a result. The window scanning and the gray level accumulation are performed on the eye fundus image subjected to the enhancing treatment, so that the optic disk is positioned. The method is not influenced by the noise, luminance and contrast change in the images and is high in accuracy in positioning the optic disk for the eye fundus images of normal fundus, and slight and moderate as well as severe diabetes mellitus lesion.

Description

A kind of eye fundus image optic disc localization method based on phase equalization

Technical field

This patent relates to a kind of eye fundus image optic disc localization method based on phase equalization, the method can be determined the position of optic disc in eye fundus image, normal optical fundus and slight, moderate, severe diabetes pathological changes eye fundus image all there is very high accuracy, belong to technical field of image processing, can be applicable to Clinical Ophthalmology and with diagnosis and the treatment of retinopathy relevant disease.

Background technology

Medical Image Processing always is emphasis and the hot issue of studying in image processing and the analysis field with analysis.By the powerful measure of figure, image technique, quality and the display packing of medical image are greatly improved, so that treatment level improves greatly.Image processing techniques is introduced ophthalmology for many years, computational analysis by eye fundus image, the important fundus tissues such as optic disc, retinal vessel and macula lutea fovea centralis are carried out quantitative measurement, between normal and unusual, make clearly discriminating, can find early, exactly various eye pathological changes and considerable systemic disease, such as diabetes, hypertension, arteriosclerosis etc.Along with society to clinical optical fundus detect in the urgent need to, existing eye fundus image detection method shows many deficiencies in practical application and test, the difficulty of this field face and challenge also increase day by day.

Optic disc is one of the vital tissue on optical fundus, it is the pink circle that a diameter is about 1.5mm, be also referred to as papilla of optic nerve, it is the position of retinal nerve fiber and retinal vessel discrepancy eyeball, the neural impulse that reception produces from the visually-perceptible cell, and further conduct to brain formation vision by optic nerve.Its central authorities are funnel-shaped depression, are called physiological depression.Can see 4 arteria retinas and vein in the central authorities of optic disc, be the important guarantee of keeping retina nutrition.The parameters such as the shape of optic disc, area and the degree of depth are to weigh the important indicator of optical fundus health status, and the optic disc location is that ocular fundus image registration splicing, blood vessel segmentation, macula lutea and pathological changes are extracted and optic disc such as cuts apart at the basis that eye fundus image is processed.The multiformity such as imaging and individual differences causes the feature differences such as optic disc shape, color, size huge, and particularly the existence of various fundus pathological changes brings difficulty in the location automatically to optic disc.Work out and to satisfy the eye fundus image optic disc localization method that desired accuracy, objectivity, repeatable standard are detected in clinical optical fundus, for Clinical Ophthalmology research and with the diagnosis of retinopathy relevant disease with treat significant.

Up to now, the research work of relevant eye fundus image detection technique has been obtained many achievements, and Chinese scholars has proposed a lot of optic disc localization methods.Utilize the method for fuzzy clustering to set up relation between blood vessel and the optic disc such as: Hoover etc., and then obtain preferably locating effect (Hoover A, Goldbaum M.Locating the optic nerve in a retinal image using the fuzzy convergence of theblood vessels[J] .IEEE Transaction on Medical Imaging, 2003,22 (8): 951-958).Tobin etc. are based upon on the accurate extraction of vasoganglion, by analyzing its brightness, width and directional information location optic disc (Tobin K W, Chaum E, Govindasamy VP, et al.Detection of anatomic structures in human retinal imagery[J] .IEEE Transaction on Medical Imaging, 2007,26 (12): 1729-1739).Li Jupeng etc. by make up " class blood vessel " crossover network realize the optic disc location (Li Jupeng, Chen Houjin, Zhang Xinyuan. the optical fundus papilla of optic nerve based on crossover network is located automatically. electronics and information journal, 2009,31 (5): 1170-1174).Based on the different attribute of optical fundus optic disc, generally will have the optic disc localization method now and be divided into two kinds, based on the method for the feature of optic disc own with based on the method for retinal blood tubular construction.First kind method has the characteristic of higher brightness to locate optic disc based on optic disc circular configuration feature roughly with other position, relative optical fundus, for the retina that has pathological changes to occur, the robustness of this method is not strong, especially for the situation that fundus oculi disease occurs, the method can not obtain good positioning result.In addition, these class methods are removed optical fundus blood vessel by the morphology preprocess method mostly first, yet unified, the fixing Morphological Structuring Elements of the overall situation is used in the morphology pretreatment, and morphological transformation exists unintentional nonlinearity and irreversibility, therefore inevitably the optic disc edge feature is introduced larger change, cause the inaccurate of positioning result.The Equations of The Second Kind method is the attribute of retinal vessel networks converge point based on optic disc, need to be partitioned in advance blood vessel, extraction accuracy to vasoganglion has higher requirement, computation complexity is higher, and be only applicable to clearly retinal images of vasoganglion, be difficult to realize the optic disc location under the different images quality.

The eye fundus image background is complicated, and the factors such as the contrast of optic disc and background is low, uneven illumination even, optic disc size disunity all can affect positioning result, cause the inaccurate even track rejection in location.Therefore, need a kind of noise in the image, the impact that the brightness and contrast changes, eye fundus image optic disc localization method with versatility, robustness of not being subjected to.

Summary of the invention

For realizing that the optic disc positioning result is not subjected to the purpose of the factor affecting such as picture noise, brightness, the invention provides a kind of eye fundus image optic disc localization method based on phase equalization, may further comprise the steps: at first, be outstanding optic disc, eye fundus image is transformed to Lab, Yuv, Yiq and four color spaces of Hsv, select respectively the strongest channel image of optic disc and background contrasts in each space; Then, four selected channel image are carried out respectively phase equalization process, strengthen the result by logic "and" operation; At last, utilize the method location optic disc of window scanning and gray accumulation.

1. select to be fit to the color space passage of eye fundus image optic disc location: the inventive method has been selected a passage in Lab space, the u passage in Yuv space, the i passage in Yiq space and the s passage in Hsv space.Eye fundus image optic disc in these 4 passages is obviously outstanding and keep good local edge.

2. 4 single channel images selecting in the step 1 are carried out respectively PC and process, calculate the point of phase equalization maximum in the eye fundus image by estimating the peak value in the local energy function.This patent selects log Gabor wavelet function and its Hilbert conversion as the wave filter that calculates local energy.

3. the PC result of 4 single channel images carried out logic "and" operation, strengthen PC result.

4. select the image after 80 * 80 rectangular window scans whole logical “and”, the pixel mean-max in the calculation window utilizes the center-of-mass coordinate of window this moment just to locate optic disc.

5. in the rectangular window that step 4 obtains, carry out gray accumulation and calculate maximum gradation value X along X, Y-direction respectively _Max, Y _Max, the directions X gray threshold is made as 0.5*X _Max, the Y-direction gray threshold is made as 0.5*Y _Max, keep the image section greater than threshold value, calculate the centre coordinate of reserve part, finally determine the optic disc position with this coordinate.

Compare with existing method, beneficial effect of the present invention is:

1. phase information is not subjected to the impact of the factors such as contrast is low, uneven illumination is even, and therefore, this patent all has very strong robustness to the location of the optic disc under the different images quality.

2. this patent has been considered the skimble-scamble factor of Different Individual optic disc size, has adopted final definite optic disc position, two step location, has guaranteed the accuracy of location.

3. this patent can be realized automatically locating with slight, moderate, severe pathological changes eye fundus image optic disc at the bottom of the normal eyes, can realize the analytic function to patient's eye fundus image, for the diagnostic accuracy and the efficient that improve the doctor, improve the medical diagnosis level, enlarge ophthalmology numerical dialing system range of application important in inhibiting.

Description of drawings

Fig. 1: optic disc localization method flow chart of the present invention.

Fig. 2: the single channel eye fundus image in the different colours space.Fig. 2-1 is a passage eye fundus image in Lab space, and Fig. 2-2 is the u passage eye fundus image in Yuv space, and Fig. 2-3 is the i passage eye fundus image in Yiq space, and Fig. 2-4 is the s passage eye fundus image in Hsv space.

Fig. 3: after PC processes, the single channel eye fundus image in the different colours space.Fig. 3-1 is a passage eye fundus image in Lab space, and Fig. 3-2 is the u passage eye fundus image in Yuv space, and Fig. 3-3 is the i passage eye fundus image in Yiq space, and Fig. 3-4 is the s passage eye fundus image in Hsv space.

Fig. 4: image behind the logical “and”.

Fig. 5: clinical eye fundus image optic disc positioning experiment is figure as a result.First classifies original image as; Second classifies method positioning result of the present invention as.Fig. 5-1 is normal eye fundus image, and Fig. 5-2 is slight pathological changes eye fundus image, and Fig. 5-3 is moderate pathological changes eye fundus image, and Fig. 5-4 is severe pathological changes eye fundus image.

Fig. 6: utilize the STARE storehouse to carry out the optic disc positioning experiment, and with the contrast of the positioning result of Hoover method.First classifies original image as; Second classifies the positioning result of Hoover method as; The 3rd classifies the positioning result of the inventive method as.Fig. 6-1 is normal eye fundus image, and Fig. 6-2～6-5 is the pathological changes eye fundus image.

The specific embodiment

Flow chart of the present invention at first for outstanding optic disc, transforms to Lab, Yuv, Yiq, four color spaces of Hsv with original image as shown in Figure 1; In each space, select a single channel image to carry out PC and process, by logic "and" operation enhancement process result; Utilize the method location optic disc of window scanning and gray accumulation.Below in conjunction with accompanying drawing, the specific implementation process of technical solution of the present invention is illustrated.

1. the color space passage is chosen:

Select a passage, the u passage in Yuv space, the i passage in Yiq space and the s passage in Hsv space in Lab space.As shown in Figure 2, original image transformed to these 4 passages after, optic disc is obviously outstanding and keep good local edge, is beneficial to follow-up optic disc location.

2. based on phase equalization eye fundus image is processed:

The phase equalization function definition is as follows:

$\mathrm{PC}\left(x\right)={\max }_{\stackrel{\‾}{\mathrm{\φ}}\left(x\right)\∈\left[\mathrm{0,2}\mathrm{\π}\right]}\frac{{\mathrm{\Σ}}_n{A}_n\cos ({\mathrm{\φ}}_n\left(x\right)-\stackrel{\‾}{\mathrm{\φ}}\left(x\right))}{{\mathrm{\Σ}}_n{A}_n}$

In the formula, A _nBe the amplitude of nth harmonic cosine component, φ _nThe phase place of n secondary frequency components,

Weighted average for the local phase of all Fourier's items of being positioned at this point.

The point of phase equalization maximum can equivalence be the peak value in the local energy function.Local energy can be estimated by following formula:

$\mathrm{LE}=\left|\right|E\left(x\right)\left|\right|=\sqrt{F^2+H^2}=\sqrt{{(I\left(x\right)*M_{\mathrm{even}})}^2+{(I\left(x\right)*M_{\mathrm{odd}})}^2}$

For one-dimensional signal F (x), local energy is defined as square root sum square of signal F (x) and its Hilbert conversion H (x).Two parts of local energy can be estimated by the convolution of signal I (x) and pair of orthogonal wave filter, and a wave filter is even symmetry, is M _Even, another is odd symmetric, is M _Odd

This patent selects log Gabor wavelet function and its Hilbert conversion as the wave filter that calculates local energy.On the linear frequency yardstick, the form of the transfer function of log Gabor function is:

$g\left(\mathrm{\ω}\right)=e^{\frac{-{\left(\log (\mathrm{\ω}/{\mathrm{\ω}}_0)\right)}^2}{2{\left(\log (\mathrm{\β}/{\mathrm{\ω}}_0)\right)}^2}}$

Here ω ₀Mid frequency for wave filter.For guaranteeing the constant shape of wave filter, for different mid frequency ω ₀, β/ω ₀Must be consistent.

4 single channel images selecting are previously carried out respectively PC process, the result as shown in Figure 3.

3. logic "and" operation:

PC result to 4 single channel images carries out logic "and" operation, and the result as shown in Figure 4.

4. the eye fundus image behind the logical “and” is adopted final definite optic disc position, two step location:

4.1 first location: select the image after 80 * 80 rectangular window scans whole logical “and”, the pixel average in the calculation window, the zone of pixel average maximum namely is the position of optic disc, utilizes the center-of-mass coordinate location optic disc of window this moment.

4.2 accurately locate: in rectangular window obtained in the previous step, carry out gray accumulation and calculate maximum gradation value X along X, Y-direction respectively _Max, Y _Max, the directions X gray threshold is made as 0.5*X _Max, the Y-direction gray threshold is made as 0.5*Y _Max, keep the image section greater than threshold value, calculate the centre coordinate of reserve part, finally determine the optic disc position with this coordinate.

Adopt this patent method that the eye fundus image in clinical collection and STARE, the DRIVE storehouse is tested, the result is shown in Fig. 5, Fig. 6 and table 1.Method of the present invention is positioned with good effect to the eye fundus image optic disc, can to normal optical fundus and in various degree pathological changes optical fundus standard to the location optic disc, have very strong robustness.

Table 1: utilize the DRIVE storehouse to carry out the optic disc positioning experiment, and with the contrast of the position success rate of Tobin, Hoover method.

Claims (4)

1. the eye fundus image optic disc localization method based on phase equalization comprises the following steps:

(1) the space single channel image that gets colors;

(2) utilize the phase equalization function that selected single channel eye fundus image is processed;

(3) the PC result of single channel image carried out logic "and" operation;

(4) select image after 80 * 80 rectangular window scans whole logical “and”, the pixel mean-max in the calculation window utilizes the center-of-mass coordinate of window this moment just to locate optic disc;

(5) in the rectangular window that step (4) obtains, carry out gray accumulation and calculate maximum gradation value X along Y-direction not respectively _Max, Y _Max, the directions X gray threshold is made as 0.5*X _Max, the Y-direction gray threshold is made as 0.5*Y _Max, keep the image section greater than threshold value, calculate the centre coordinate of reserve part, with the final accurately location of this coordinate optic disc.

2. eye fundus image optic disc localization method according to claim 1, it is characterized in that, in the step (1), only choose the color space single channel image that is fit to eye fundus image optic disc location, image is not carried out any morphology pretreatment, guaranteed the accuracy of optic disc edge feature.

3. eye fundus image optic disc localization method according to claim 1, it is characterized in that, in the step (2), use phase equalization sign optic disc feature, need not waveform is carried out any hypothesis, just in Fourier transform domain, seek characteristic point by the consistent order of phase place.

4. eye fundus image optic disc localization method according to claim 1 is characterized in that, in step (4), (5), uses elder generation just to locate pinpoint twice localization method again and determines the optic disc position, improves accurate positioning.

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