SIFT 特征提取算法详解.docx

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SIFT 特征提取算法详解.docx

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SIFT 特征提取算法详解.docx

SIFT特征提取算法详解

SIFT特征提取算法总结

主要步骤

1）、尺度空间的生成;

2）、检测尺度空间极值点;

3）、精确定位极值点;

4）、为每个关键点指定方向参数;

5）、关键点描述子的生成。

L（x,y,σ）,σ=1.6agoodtradeoffsafetycatch.Anyproductionsafetyaccidentwillcauseanadditionalburdenonthecountyshouldbearjointandseveralliability,notworththecandle.Soenterprisesshouldconscientiouslyassumetheproductionsafetyofthemainresponsibilityforthesafetyproductionandthencatchproduction.Allunitsanddepartmentsresponsibleforsafetyproductionresponsibility,asthemainpartyleadersmustintervene.Third,derelictionofdutywillpursueresponsibility.Stablenowoutofthequestiontoresponsibilityandaccountabilityisverystrict.Asfaraspossibletochecktheproductionisthesame,thefirstfewdaysofthemainlandoccurredinproductionsafetyaccidents,theaccidentinvestigationresultsalsodidnotcomeout,thecountyPartySecretary,countymagistrate,deputymagistrateanddeputycountymagistrateallinsituremoval,lateralsoshallbeinvestigatedforcriminalresponsibility.Thisisthederelictionofdutyshallbeaccountable,wemustattachgreatimportanceto.Thefourth,preventionfirst,safetyinproductioninplace.Safetyinproductiontopreventthemain,lesstrouble,notafterwardstosolve.Preventionisthekeytoimplementthesafetyproductionresponsibilitysystemandthesafetymeasures.Thedangerofenterprisesshouldtaketheinitiativetopaycloseattentiontothetimetodoprocedures,thereisnolegalcomplianceprocedures,onceoutoftroubleandregret.Unannouncedvisitstoenterprisestoactivelytaketheinitiativetoseizethetimetoformalities.Inimportantholidaystoincreasepublicityandeducation

D（x,y,σ）,σ=1.6agoodtradeoff

safetycatch.Anyproductionsafetyaccidentwillcauseanadditionalburdenonthecountyshouldbearjointandseveralliability,notworththecandle.Soenterprisesshouldconscientiouslyassumetheproductionsafetyofthemainresponsibilityforthesafetyproductionandthencatchproduction.Allunitsanddepartmentsresponsibleforsafetyproductionresponsibility,asthemainpartyleadersmustintervene.Third,derelictionofdutywillpursueresponsibility.Stablenowoutofthequestiontoresponsibilityandaccountabilityisverystrict.Asfaraspossibletochecktheproductionisthesame,thefirstfewdaysofthemainlandoccurredinproductionsafetyaccidents,theaccidentinvestigationresultsalsodidnotcomeout,thecountyPartySecretary,countymagistrate,deputymagistrateanddeputycountymagistrateallinsituremoval,lateralsoshallbeinvestigatedforcriminalresponsibility.Thisisthederelictionofdutyshallbeaccountable,wemustattachgreatimportanceto.Thefourth,preventionfirst,safetyinproductioninplace.Safetyinproductiontopreventthemain,lesstrouble,notafterwardstosolve.Preventionisthekeytoimplementthesafetyproductionresponsibilitysystemandthesafetymeasures.Thedangerofenterprisesshouldtaketheinitiativetopaycloseattentiontothetimetodoprocedures,thereisnolegalcomplianceprocedures,onceoutoftroubleandregret.Unannouncedvisitstoenterprisestoactivelytaketheinitiativetoseizethetimetoformalities.Inimportantholidaystoincreasepublicityandeducation

关于尺度空间的理解说明:

图中的2是必须的，尺度空间是连续的。

在Lowe的论文中，

将第0层的初始尺度定为1.6，图片的初始尺度定为0.5.在检测极值点前对原始图像的高斯平滑以致图像丢失高频信息，所以Lowe建议在建立尺度空间前首先对原始图像长宽扩展一倍，以保留原始图像信息，增加特征点数量。

尺度越大图像越模糊。

nextoctave是由firstoctave降采样得到（如2）

，

尺度空间的所有取值，s为每组层数，一般为3~5

在DOG尺度空间下的极值点

同一组中的相邻尺度（由于k的取值关系，肯定是上下层）之间进行寻找safetycatch.Anyproductionsafetyaccidentwillcauseanadditionalburdenonthecountyshouldbearjointandseveralliability,notworththecandle.Soenterprisesshouldconscientiouslyassumetheproductionsafetyofthemainresponsibilityforthesafetyproductionandthencatchproduction.Allunitsanddepartmentsresponsibleforsafetyproductionresponsibility,asthemainpartyleadersmustintervene.Third,derelictionofdutywillpursueresponsibility.Stablenowoutofthequestiontoresponsibilityandaccountabilityisverystrict.Asfaraspossibletochecktheproductionisthesame,thefirstfewdaysofthemainlandoccurredinproductionsafetyaccidents,theaccidentinvestigationresultsalsodidnotcomeout,thecountyPartySecretary,countymagistrate,deputymagistrateanddeputycountymagistrateallinsituremoval,lateralsoshallbeinvestigatedforcriminalresponsibility.Thisisthederelictionofdutyshallbeaccountable,wemustattachgreatimportanceto.Thefourth,preventionfirst,safetyinproductioninplace.Safetyinproductiontopreventthemain,lesstrouble,notafterwardstosolve.Preventionisthekeytoimplementthesafetyproductionresponsibilitysystemandthesafetymeasures.Thedangerofenterprisesshouldtaketheinitiativetopaycloseattentiontothetimetodoprocedures,thereisnolegalcomplianceprocedures,onceoutoftroubleandregret.Unannouncedvisitstoenterprisestoactivelytaketheinitiativetoseizethetimetoformalities.Inimportantholidaystoincreasepublicityandeducation

在极值比较的过程中，每一组图像的首末两层是无法进行极值比较的，为了

满足尺度

变化的连续性，我们在每一组图像的顶层继续用高斯模糊生成了3幅图像，

高斯金字塔有每组S+3层图像。

DOG金字塔每组有S+2层图像.

Ifratio>（r+1）2/（r）,throwitout（SIFTusesr=10）

表示DOG金字塔中某一尺度的图像x方向求导两次

通过拟和三维二次函数以精确确定关键点的位置和尺度（达到亚像素精度）,

直方图中的峰值就是主方向，其他的达到最大值80%的方向可作为辅助方向

Identifypeakandassignorientationandsumofmagnitudetokeypoint

Theusermaychooseathresholdtoexcludekeypointsbasedontheir

assignedsumofmagnitudes.

利用关键点邻域像素的梯度方向分布特性为每个关键点指定方向参数，使算子具备

旋转不变性。

以关键点为中心的邻域窗口内采样，并用直方图统计邻域像素的梯度

方向。

梯度直方图的范围是0,360度，其中每10度一个柱，总共36个柱。

随着距

中心点越远的领域其对直方图的贡献也响应减小.Lowe论文中还提到要使用高斯函

数对直方图进行平滑，减少突变的影响。

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