CN110443807A - A kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion - Google Patents

A kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion Download PDF

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Publication number
CN110443807A
CN110443807A CN201910568740.8A CN201910568740A CN110443807A CN 110443807 A CN110443807 A CN 110443807A CN 201910568740 A CN201910568740 A CN 201910568740A CN 110443807 A CN110443807 A CN 110443807A
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image
pixel
luminance
value
threshold
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张莉君
郭辉
陈鹏
黄顺
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China University of Geosciences
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China University of Geosciences
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    • G06T5/94
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00Image analysis
    • G06T7/10Segmentation; Edge detection
    • G06T7/11Region-based segmentation
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00Image analysis
    • G06T7/10Segmentation; Edge detection
    • G06T7/136Segmentation; Edge detection involving thresholding
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00Indexing scheme for image analysis or image enhancement
    • G06T2207/10Image acquisition modality
    • G06T2207/10004Still image; Photographic image
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00Indexing scheme for image analysis or image enhancement
    • G06T2207/20Special algorithmic details
    • G06T2207/20021Dividing image into blocks, subimages or windows

Abstract

The present invention provides a kind of even carrying out image threshold segmentation methods of uneven illumination based on luminance proportion, carry out luminance compensation to the different luminance areas in image first, the luminance background of whole image is made to reach unanimity.Then the data such as the corresponding pixel number of each gray level in gained image are fitted, obtain a gauss of distribution function, by carrying out second order derivation to the function, obtain two threshold values.Using dual threshold, to luminance proportion, treated that image is split processing, if the gray value of pixel is between high-low threshold value in image, determines the pixel for background dot;Otherwise, it is determined that the pixel is target point.Pixel all in image is traversed, the bianry image that segmentation finishes is finally obtained.

Description

A kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion
Technical field
The present invention relates to technical field of image segmentation, and in particular to a kind of even image threshold of uneven illumination based on luminance proportion It is worth dividing method.
Background technique
Carrying out image threshold segmentation, the also known as binaryzation of image are widely used in Car license recognition, OCR identification, fingerprint recognition, red The fields such as outer moving target.Bianry image has the characteristics that memory space is small, processing speed is fast, can be convenient carry out Boolean logic Operation.The basic thought of image binaryzation is that one gray threshold of setting makes image show in white and black effect.Binaryzation Method is all the method based on threshold value mostly, that is, finds a suitable threshold value and the pixel grey scale of original image is divided into greater than threshold value Be less than threshold value two classes, to obtain the result of binaryzation.Currently, binarization method can be divided into Global thresholding, local threshold Value method two major classes.Simple for the Global thresholding principle of representative with Da-Jin algorithm (OTSU), processing speed is fast, but is easily lost mesh Mark details and even very sensitive to uneven illumination;Although local thresholding method can preferably handle the even image of uneven illumination, But it will lead to the problems such as partial region is broken there are false target or target object in binarization result.Not for a width illumination For uniform image, the optimal threshold in high luminance area and low-light level area differs greatly, and is difficult at this time using Global thresholding All divide successfully, and be easy to cause local segmentation to be distorted using local thresholding method.Even uneven illumination is frequent in image procossing The problem of encountering, mainly image background ambient lighting was bad and body surface is reflective the reason of causing the problem etc..
Currently, mainly having histogram equalization method for the even algorithm for image enhancement of uneven illumination, based on illumination-reflection Homomorphic filtering method, Retinex Enhancement Method etc..The flat equalization of histogram, substantially carries out Nonlinear extension, weight to image New distribution image pixel value, keeps the quantity of pixel value in certain tonal range roughly equal.In this way, the peak among original histogram Top part contrast is enhanced, and the lowest point part contrast of two sides reduces, and the histogram for exporting image is one more flat The visual effect of rude classification can be generated if the fragmentation value of output data is lesser by being segmented histogram;Homomorphic filtering is one The specific process of picture superposition and compression brightness of image range that kind carries out in a frequency domain.Homomorphic filter can be reduced Low frequency and increase high frequency, to can be reduced illumination variation and sharpen edge details.The homomorphic filtering technology of image foundation be Illumination catoptric imaging principle in image acquisition procedures.It belongs to frequency domain processing, and effect is adjusted to image grayscale range, Uneven problem is illuminated on image by eliminating.But homomorphic filtering method can not cut down multiplying property and convolution noise;It is general Retinex algorithm to light image estimate when, can all assume initial light image be it is slowly varying, i.e., light image is smooth 's.But practical really not so, brightness differs greatly the edge in region, and image irradiation variation is simultaneously unsmooth.So in this feelings Under condition, Retinex, which enhances enhancing image of the algorithm in the big region of luminance difference, can generate halation.
For the defect for avoiding above-mentioned algorithm, the invention proposes a kind of even image thresholds of the uneven illumination based on luminance proportion Dividing method first carries out piecemeal to the background luminance of image and dynamically adjusts, locates adjusted image background brightness substantially It is split in identical level, then using dual-threshold voltage, to solve problems of the prior art.
Summary of the invention
The technical problem to be solved in the present invention is that using Global thresholding to the even image of uneven illumination at present for above-mentioned Or the common Binarization methods such as local thresholding method are difficult to the technical issues of obtaining satisfactory segmentation effect, provide a kind of base Above-mentioned technological deficiency is solved in the even carrying out image threshold segmentation method of the uneven illumination of luminance proportion.
A kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion, comprising:
Step 1, input source picture seek the average gray I of source images;
Step 2 divides the image into M × N block according to a certain size, finds out every piece of average brightness, obtains the bright of sub-block Spend matrix D;Wherein, the average brightness of a sub-block represents an element of luminance matrix D;
Step 3, the average gray I that source images are subtracted with the value of each element of matrix D, obtain the luminance difference square of sub-block Battle array E;
Matrix E is extended to and source images Luminance Distribution matrix R of a size by step 4 with bicubic interpolation method;
The pixel brightness value of source images is subtracted corresponding numerical value in matrix R, then imposes smothing filtering by step 5, can be obtained Image after to luminance proportion;
In step 6, obtaining step 5 equalize after image grey level histogram, measure image in dimensional parameters [s, t] simultaneously Average gray value greay_mean is calculated, counting number T, s, t that each gray level occurs indicates the size of image;
Step 7 goes out intensity histogram diagram data obtained in step 6, including pixel grayscale and each gray level Existing number T is recorded and is fitted to Gaussian distribution curve;
Step 8, the expectation μ and variances sigma that One-Dimensional Normal distribution probability density function is obtained according to Gaussian distribution curve, two The threshold value of value image chooses condition | X- μ |≤σ, and to obtain two threshold Xs1、X2, wherein X1> X2, after luminance proportion The pixel gray value G of image is compared with resulting two threshold values, if X2< G < X1, then G is set to 255, otherwise sets G It is 0, traverses each pixel in image, final bianry image can be obtained.
Further, the specific method of step 2 includes: to divide the image into M × N block according to a certain size, finds out every piece Average value, the luminance matrix D for obtaining sub-block, which refers to, is divided into M × N block for a secondary picture, and gray level is (0 ..., L), then average Brightness are as follows:Wherein p (i, j) is the pixel brightness value that coordinate is in image;With the son of size M × N Block carries out piecemeal to the image, then the luminance mean value of each sub-block are as follows:
Further, in the step 7, input be image after compensation grey level histogram, and by pixel grayscale And its corresponding frequency of occurrence T is fitted to Gaussian distribution curve.
Further, the segmentation threshold of bianry image is chosen in the step 8 | X- μ |≤σ, specific steps include:
S81, the One-Dimensional Normal distribution probability density function that fitting obtains is denoted as f (x):
S82, derivation is carried out to f (x) function, obtains derivative f ' (x),
In gauss of distribution function, abscissa is pixel grey scale, and ordinate is pixel number, when | f ' (x) | take maximum When value, the quantity and gray-value variation of pixel are the most obvious.
S83, by the property of gauss of distribution function it is found that as f " when (x)=0, f ' (x) obtains maximum and minimum, this When
X1=μ-σ, X2=μ+σ;
Enable X1、X2For segmentation threshold, by the pixel gray value G of image after luminance proportion and resulting two threshold values into Row compares, if X2< G < X1, then G is set to 255, G is otherwise set to 0, traversed each pixel in image, obtain final two It is worth image.
Compared with prior art, the invention has the advantages that: the present invention proposes that a kind of uneven illumination based on luminance proportion is even Carrying out image threshold segmentation method, this method, by carrying out luminance compensation to image block, keep image background bright in terms of image enhancement Degree is generally in identical level;In terms of threshold value selection, by carrying out one-dimensional gaussian profile fitting to grey level histogram, obtain Two optimal segmenting thresholds, segmentation effect become apparent from, and the various indexs such as recall rate, precision rate, error rate are improved.
Detailed description of the invention
Present invention will be further explained below with reference to the attached drawings and examples, in attached drawing:
Fig. 1 is a kind of even carrying out image threshold segmentation method flow diagram of uneven illumination based on luminance proportion of the invention.
Specific embodiment
For a clearer understanding of the technical characteristics, objects and effects of the present invention, now control attached drawing is described in detail A specific embodiment of the invention.
A kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion, as shown in Figure 1, comprising:
Step 1, input source picture seek the average gray I of source images;
Step 2 divides the image into M × N block according to a certain size, finds out every piece of average value, obtains the brightness square of sub-block Battle array D;
Step 3, the average gray I that source images are subtracted with the value of each element of matrix D, obtain the luminance difference square of sub-block Battle array E;
Matrix E is extended to and source images Luminance Distribution matrix R of a size by step 4 with bicubic interpolation method;
The pixel brightness value of source images is subtracted corresponding numerical value in matrix R, then imposes smothing filtering by step 5, can be obtained Image after to luminance proportion;
In step 6, obtaining step 5 equalize after image grey level histogram, measure image in dimensional parameters [s, t] simultaneously Average gray value greay_mean is calculated, counting number T, s, t that each gray level occurs indicates the size of image;
Step 7 goes out intensity histogram diagram data obtained in step 6, including pixel grayscale and each gray level Existing number T is recorded and is fitted to Gaussian distribution curve;
The threshold value of step 8, the expectation μ and variances sigma for obtaining One-Dimensional Normal distribution probability density function, bianry image is chosen Condition can be set as | X- μ |≤σ, available two threshold Xs1、X2, wherein X1> X2.By the pixel of image after luminance proportion Gray value G is compared with resulting two threshold values, if X2< G < X1, then G is set to 255, G is otherwise set to 0, traverse image In each pixel, final bianry image can be obtained.
The step 2, in 3,4, background and target should be evenly distributed on image 4 parts up and down, if illumination It is uniformly, then the average value of this 4 part gray value should be not much different;, whereas if difference is larger, then made by processing Its similar mean values shows the effect of similar uniform illumination.The specific method is as follows: dividing the image into M × N according to a certain size Block finds out every piece of average value, and the luminance matrix D for obtaining sub-block, which refers to, is divided into M × N block for a secondary picture, and gray level is (0 ..., L), then average brightness are as follows:Wherein p (i, j) is the pixel intensity that coordinate is in image Value.Piecemeal is carried out to the image with the sub-block of size M × N, then the luminance mean value of each sub-block are as follows:Then the difference of sub-block luminance mean value and full figure luminance mean value is Δlum=Lumav_bm-Lumav, right For ΔlumThe brightness of positive sub-block carries out Weakening treatment, to ΔlumThe brightness for the sub-block being negative carries out enhancing processing.To avoid office The defect of portion's threshold method does not directly add or subtracts the same adjustment numerical value to each sub-block, but according to piecemeal Format interpolation is carried out to the matrix of sub-block, be allowed to expand to entire original image size by using bicubic interpolation method.So Δ after subtracting extension with the value of the pixel of original image afterwardslumMatrix is just able to achieve the luminance proportion adjustment of entire image.
The segmentation threshold of bianry image is chosen in the step 8 | X- μ |≤σ, the specific steps are as follows:
S81, the One-Dimensional Normal distribution probability density function that fitting obtains is denoted as f (x), is shown below:
S82, derivation is carried out to above formula function, obtains derivative f ' (x),
Image binaryzation method will usually find a threshold value when handling grayscale image, so that the difference between profile and background Different maximum.And in gauss of distribution function, abscissa is pixel grey scale, and ordinate is pixel number, when | f ' (x) | take maximum When value, the quantity and gray-value variation of pixel are the most obvious.
S83, by the property of gauss of distribution function it is found that as f " when (x)=0, f ' (x) obtains maximum and minimum, this When X1=μ-σ, X2=μ+σ.
Enable X1、X2For segmentation threshold, by the pixel gray value G of image after luminance proportion and resulting two threshold values into Row compares, if X2< G < X1, then G is set to 255, G is otherwise set to 0, traversed each pixel in image, obtain final two It is worth image.
In summary: the present invention, by carrying out luminance compensation to image block, keeps image background bright in terms of image enhancement Degree is generally in identical level;In terms of threshold value selection, by carrying out one-dimensional gaussian profile fitting to grey level histogram, obtain Two optimal segmenting thresholds, the image segmentation even for uneven illumination becomes apparent from, in recall rate, precision rate, error rate etc. It is better than homomorphic filtering and Retinex algorithm for image enhancement in index.Present invention can apply to aerospaces, UAV Flight Control Deng the military field for needing to carry out feature extraction under complex background environment;Civilian aspect, mobile robot, vision SLAM, Also there is more wide application prospect in the fields such as dam body monitoring.
The embodiment of the present invention is described with above attached drawing, but the invention is not limited to above-mentioned specific Embodiment, the above mentioned embodiment is only schematical, rather than restrictive, those skilled in the art Under the inspiration of the present invention, without breaking away from the scope protected by the purposes and claims of the present invention, it can also make very much Form, all of these belong to the protection of the present invention.

Claims (4)

1. a kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion characterized by comprising
Step 1, input source picture seek the average gray I of source images;
Step 2 divides the image into M × N block according to a certain size, finds out every piece of average brightness, obtains the brightness square of sub-block Battle array D;Wherein, the average brightness of a sub-block represents an element of luminance matrix D;
Step 3, the average gray I that source images are subtracted with the value of each element of matrix D, obtain the luminance difference matrix E of sub-block;
Matrix E is extended to and source images Luminance Distribution matrix R of a size by step 4 with bicubic interpolation method;
The pixel brightness value of source images is subtracted corresponding numerical value in matrix R, then imposes smothing filtering by step 5, can be obtained bright Image after degree equalization;
The grey level histogram of image after equalizing in step 6, obtaining step 5 measures the dimensional parameters [s, t] in image and calculates Average gray value greay_mean, counting number T, s, t that each gray level occurs indicates the size of image;
Step 7, by intensity histogram diagram data obtained in step 6, including pixel grayscale and each gray level occur Number T is recorded and is fitted to Gaussian distribution curve;
Step 8, the expectation μ and variances sigma that One-Dimensional Normal distribution probability density function is obtained according to Gaussian distribution curve, binary map The threshold value of picture chooses condition | X- μ |≤σ, and to obtain two threshold Xs1、X2, wherein X1> X2, by image after luminance proportion Pixel gray value G be compared with resulting two threshold values, if X2< G < X1, then G is set to 255, G is otherwise set to 0, Each pixel in image is traversed, final bianry image can be obtained.
2. a kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion according to claim 1, feature It is, the specific method of step 2 includes: to divide the image into M × N block according to a certain size, finds out every piece of average value, obtains son The luminance matrix D of block, which refers to, is divided into M × N block for a secondary picture, and gray level is (0 ..., L), then average brightness are as follows:Wherein p (i, j) is the pixel brightness value that coordinate is in image;With the sub-block of size M × N to this Image carries out piecemeal, then the luminance mean value of each sub-block are as follows:
3. a kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion according to claim 1, feature Be, in the step 7, input be compensation after image grey level histogram, and by pixel grayscale and its it is corresponding go out Occurrence number T is fitted to Gaussian distribution curve.
4. a kind of even carrying out image threshold segmentation method of uneven illumination based on luminance proportion according to claim 1, feature It is, the segmentation threshold of bianry image is chosen in the step 8 | X- μ |≤σ, specific steps include:
S81, the One-Dimensional Normal distribution probability density function that fitting obtains is denoted as f (x):
S82, derivation is carried out to f (x) function, obtains derivative f ' (x),
In gauss of distribution function, abscissa is pixel grey scale, and ordinate is pixel number, when | f ' (x) | when being maximized, The quantity and gray-value variation of pixel are the most obvious;
S83, by the property of gauss of distribution function, it is found that as f, " when (x)=0, f ' (x) obtains maximum and minimum, at this time
X1=μ-σ, X2=μ+σ;
Enable X1、X2For segmentation threshold, the pixel gray value G of image after luminance proportion and resulting two threshold values are compared Compared with if X2< G < X1, then G is set to 255, G is otherwise set to 0, traversed each pixel in image, obtain final binary map Picture.
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CN114418890A (en) * 2022-01-20 2022-04-29 中国人民解放军国防科技大学 Uneven-illumination text image processing method
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CN114742784A (en) * 2022-03-31 2022-07-12 精诚工坊电子集成技术(北京)有限公司 Skin image red blood silk marking method, evaluation method and system
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Application publication date: 20191112