SIFT特征提取算法详解

1、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。尺度克同抛生蕉尺废空间理论目的是惶龌镣数局的要尺度特fit.iW斯塞蹦是实现尺度变换的唯Trtfe.予是一同二隼圈隙的尺度空间定义Lx,y.cr）G（x.ytcr）*/（x,j.）其中一gj.cr）是尺度可枭/本心股1.471.L''.'r'工Ttr0（.y）是交间里标曾是尺度坐标的大小决定昭弊的平滑慢度r大尺度对应图瞰的慨貌恃抵；小尺酬心口像的细节恃SL大曲值对宓相忸尺度（低分辨罩）

2、.反渴正精细尺直僖分测路网m引或或分尺度w间旧。g和:才出冲金分。与J；6=（G七F幽-tX，V.1；e）*/（XV）="X,JLfer）-2（.七4b）L（x,y,o-）,o-=1.6agoodtradeoffinstrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,theinstrumentaccordingtothestand-alonetrialsscheduled,withtheprocesspreparationoftestsolutions,equippedwit

3、hprofessionaltechniciansandskilledworkers,toensuresafetyandquality.6.constructionspecification6.1.1siteequipment,andindustrialpipelineweldingengineeringconstructionandtheacceptancespecificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionandtheacceptancespecificat

4、ionSH3501-20026.1.3oilchemicallowtemperaturesteelweldingproceduresSH/T352020046.1.4oilchemicalchromenickelAustrian'sbodysteel,andironnickelalloyandnickelalloypipelineweldingproceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-MOheat-resistantsteelpipe

5、6.1.6ofthepressurevesselNDT4730-946.2JBweldpreparation6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmethods,providingqualifiedweldingprocedurequalificationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstruction,guidethewelderweldingop

6、erations.6.2.3whereparticipationinsitewelding,mustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6.2.4whereinvolvedinthepipeandsteelstructureweldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewithinthescopeandeligibilitya

7、pprovedbythequalityandtechnologysupervisiondepartmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingtheweldingprocess.D(x,y,o-),o-=1.6agoodtradeoffinstrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,theinstrumentaccordingtothestandalone

8、trialsscheduled,withtheprocesspreparationoftestsolutions,equippedwithprofessionaltechniciansandskilledworkers,toensuresafetyandquality.6.weldingengineeringconstructionprogramme6.1thisengineeringusedconstructionspecification6.1.1siteequipment,andindustrialpipelineweldingengineeringconstructionandthea

9、cceptancespecificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionandtheacceptancespecificationSH3501-20026.1.3oilchemicallowtemperaturesteelweldingproceduresSH/T3520-20046.1.4oilchemicalchromenickelAustrian'sbodysteel,andironnickelalloyandnickelalloypipeline

10、weldingproceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-MOheat-resistantsteelpipe6.1.6ofthepressurevesselNDT4730-946.2JBweldpreparation6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmethods,providingqualifiedweldingprocedu

11、requalificationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstruction,guidethewelderweldingoperations.6.2.3whereparticipationinsitewelding,mustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6.2.4whereinvolvedinthepipeandsteels

12、tructureweldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewithinthescopeandeligibilityapprovedbythequalityandtechnologysupervisiondepartmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingtheweldingprocess.关于尺度空间的理解说明:图中的2是必须

13、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。4 nGriUliSidn 0DG J降采样得到（如2）nextoctave是由firstoctave2Tg.kok'b:k'fb）上二2%尺度空间的所有取值，s为每组层数，一般为35在DOCX度空间下的极值点检例尺度空同硬低点F丁手粒尺&三司的蔓值口，拒一个三件点要和个"有的相部点比校,看其是

14、否比它的图骤域和用翻闵相部点大戒者小.如区.不同然吟测电和它同尺度的8小相曾二F帽铜尺.爸"底的9*我电步茂个点曦.以痛保在尺度空图和工国修堂间都住恻到超值点.如累一个,瑞在口。物度壬闻t理4马上F网层的26八酒瓶牡是最大或最小值时.就认为误点是图埋在该尺痍下的一个樗任员Q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instrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,theinstrumentaccordingtothestandalonetrials

15、scheduled,withtheprocesspreparationoftestsolutions,equippedwithprofessionaltechniciansandskilledworkers,toensuresafetyandquality.6.weldingengineeringconstructionprogramme6.1thisengineeringusedconstructionspecification6.1.1siteequipment,andindustrialpipelineweldingengineeringconstructionandtheaccepta

16、ncespecificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionandtheacceptancespecificationSH3501-20026.1.3oilchemicallowtemperaturesteelweldingproceduresSH/T3520-20046.1.4oilchemicalchromenickelAustrian'sbodysteel,andironnickelalloyandnickelalloypipelineweldin

17、gproceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-MOheat-resistantsteelpipe6.1.6ofthepressurevesselNDT4730-946.2JBweldpreparation6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmethods,providingqualifiedweldingprocedurequal

18、ificationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstruction,guidethewelderweldingoperations.6.2.3whereparticipationinsitewelding,mustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6.2.4whereinvolvedinthepipeandsteelstructu

19、reweldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewithinthescopeandeligibilityapprovedbythequalityandtechnologysupervisiondepartmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingtheweldingprocess.在极值比较的过程中，每一组图像的首末两层是无法进行

20、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。DO陵字塔每组有S+2层图像.instrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,theinstrumentaccordingtothestandalonetrialsscheduled,withtheprocesspreparationoftestsolutions,equippedwithprofessionaltechniciansandskilledwor

21、kers,toensuresafetyandquality.6.weldingengineeringconstructionprogramme6.1thisengineeringusedconstructionspecification6.1.1siteequipment,andindustrialpipelineweldingengineeringconstructionandtheacceptancespecificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionan

22、dtheacceptancespecificationSH3501-20026.1.3oilchemicallowtemperaturesteelweldingproceduresSH/T3520-20046.1.4oilchemicalchromenickelAustrian'sbodysteel,andironnickelalloyandnickelalloypipelineweldingproceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-

23、MOheat-resistantsteelpipe6.1.6ofthepressurevesselNDT4730-946.2JBweldpreparation6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmethods,providingqualifiedweldingprocedurequalificationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstructio

24、n,guidethewelderweldingoperations.6.2.3whereparticipationinsitewelding,mustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6.2.4whereinvolvedinthepipeandsteelstructureweldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewith

25、inthescopeandeligibilityapprovedbythequalityandtechnologysupervisiondepartmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingtheweldingprocess.通过哪三维二次性融以精蝎网定关植威驹位置源度（这手画博素精度同时去除低对闿S的关键良刹不楣定的边缘响应点,因为DOG算子会产生软老的辿族呵匠），以图箱匹叱便定旦.苣方忖师生挹J，R空间尺度通鞅11)IMj；工，&2&*亲导3H算为。

26、13到精琳的位室次-值在己及检测到的捋征点中要去掉（0对比庶居而怔最坏穗定的边舞喧瞪点.锵低对比度的点上把公式（2戕人公式（11只翱耐项可得，1>jVJ?r-Ivcr-+-yX=(x,y.af2&若乔。吗谈特征点就保留下来否则舍科醛埠响座的瑞.一个定义不好的高斯差分算子的极值础聘边部的地方有较大的主曲本.而在垂直边算的方向有软石州主向电主曲本通过一个丁工7的Ha筋相牛冲茎上f口D1ff=+'=DfD1,L®«身裁由采样点相邻差估tt得到.D的主曲率和H的特亚值成正比.力最大特征值.耳为量”的恃征值.迎| l' f I | I -"J

27、J. 一 内即 N W”U IIII « I i11II-=Flpi+%=ei*'i令S-Rr贝"iIfratio>(r+1)2/(r),throwitout(SIFTusesr=10)表示DOG&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）,instrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,theinstrumentaccordingtothestandalonetrialssch

28、eduled,withtheprocesspreparationoftestsolutions,equippedwithprofessionaltechniciansandskilledworkers,toensuresafetyandquality.6.weldingengineeringconstructionprogramme6.1thisengineeringusedconstructionspecification6.1.1siteequipment,andindustrialpipelineweldingengineeringconstructionandtheacceptance

29、specificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionandtheacceptancespecificationSH3501-20026.1.3oilchemicallowtemperaturesteelweldingproceduresSH/T3520-20046.1.4oilchemicalchromenickelAustrian'sbodysteel,andironnickelalloyandnickelalloypipelineweldingpr

30、oceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-MOheat-resistantsteelpipe6.1.6ofthepressurevesselNDT4730-946.2JBweldpreparation6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmethods,providingqualifiedweldingprocedurequalifi

31、cationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstruction,guidethewelderweldingoperations.6.2.3whereparticipationinsitewelding,mustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6.2.4whereinvolvedinthepipeandsteelstructurew

32、eldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewithinthescopeandeligibilityapprovedbythequalityandtechnologysupervisiondepartmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingtheweldingprocess.为每个关键点指定方向参蚣刎以关犍点都城镰素的悌度方向分布

33、持性为法个关键电指定方间参班变单于具善芯转齐变忖RCidJ-tUw缸工晴Nhjz+D-Ki-LxM)式中出汉力姓怜芟的国道如内间公式严其中时用的尺度为福个美维点台自斫在晌尺度.一至比，图球的美硬点已喊完毕,每广寺提点有二个倍品心系所处尺度.方向.由此可以碉定一个8格喃诙域.直方图中的峰值就是主方向，其他的达到最大值80%勺方向可作为辅助方向IdentifypeakandassignorientationandsumofmagnitudetokeypointTheusermaychooseathresholdtoexcludekeypointsbasedontheirassignedsumofm

34、agnitudes.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instrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,theinstrumentaccordingtothestandalonetria

35、lsscheduled,withtheprocesspreparationoftestsolutions,equippedwithprofessionaltechniciansandskilledworkers,toensuresafetyandquality.6.weldingengineeringconstructionprogramme6.1thisengineeringusedconstructionspecification6.1.1siteequipment,andindustrialpipelineweldingengineeringconstructionandtheaccep

36、tancespecificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionandtheacceptancespecificationSH3501-20026.1.3oilchemicallowtemperaturesteelweldingproceduresSH/T3520-20046.1.4oilchemicalchromenickelAustrian'sbodysteel,andironnickelalloyandnickelalloypipelineweld

37、ingproceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-MOheat-resistantsteelpipe6.1.6ofthepressurevesselNDT4730-946.2JBweldpreparation6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmethods,providingqualifiedweldingprocedurequ

38、alificationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstruction,guidethewelderweldingoperations.6.2.3whereparticipationinsitewelding,mustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6.2.4whereinvolvedinthepipeandsteelstruc

39、tureweldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewithinthescopeandeligibilityapprovedbythequalityandtechnologysupervisiondepartmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingtheweldingprocess.关键点描述子的生成步骤旋转主将坐揉轴旋转为关键

40、点的方向，以硅.蜂旅华不变烂生成描 述子它于一.卜H淳古丁二128卜文据,M最终形或128绝的SIFT特征店量将特工亢量由姓笠臼一化.则可以进一步去除光照变化的影响.通过对关键点周围图像区域分块，计算块内梯度直方图，生成具有独特性的向量，这个向量是该区域图像信息的一种抽象，具有唯一性。关键点撰述十的生成首光书坐标旗耨为关慨氨的方向.以源保簟辅就性.以特征点为中心里8彝邻域作为崇祥窗口，将崇祥点与特髭您的相前方向通工高勘印在后闩入巨吉R个K同直方图，呆后滨得29”8的8罗特於拦苜二.不苣困也下，讪y 卯依疔心巾ticst npior每一个小格都代表了特征点邻域所在的尺度空间的一个像素，箭头方向代

41、表了像素梯度方向，箭头长度代表该像素的幅值。然后在4X4的窗口内计算8个方向的梯度方向直方图。绘制每个梯度方向的累加可形成一个种子点。instrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,theinstrumentaccordingtothestandalonetrialsscheduled,withtheprocesspreparationoftestsolutions,equippedwithprofessionaltechniciansandskilledworkers,toe

42、nsuresafetyandquality.6.weldingengineeringconstructionprogramme6.1thisengineeringusedconstructionspecification6.1.1siteequipment,andindustrialpipelineweldingengineeringconstructionandtheacceptancespecificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionandtheacce

43、ptancespecificationSH3501-20026.1.3oilchemicallowtemperaturesteelweldingproceduresSH/T3520-20046.1.4oilchemicalchromenickelAustrian'sbodysteel,andironnickelalloyandnickelalloypipelineweldingproceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-MOheat-r

44、esistantsteelpipe6.1.6ofthepressurevesselNDT4730-946.2JBweldpreparation6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmethods,providingqualifiedweldingprocedurequalificationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstruction,guidet

45、hewelderweldingoperations.6.2.3whereparticipationinsitewelding,mustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6.2.4whereinvolvedinthepipeandsteelstructureweldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewithinthesco

46、peandeligibilityapprovedbythequalityandtechnologysupervisiondepartmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingtheweldingprocess.每个直方图有8方向的梯度方向，每一个描述符包含一个位于关键点附近的四个直方图数组.这就导致了SIFT的特征向量有128维.（先是一个4X4的来计算出一个直方图，每个直方图有8个方向。所以是4X4X8=128维）将这个向量归一化之后，就进一步去除了光照的影响。旋转为

47、主方向instrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,theinstrumentaccordingtothestandalonetrialsscheduled,withtheprocesspreparationoftestsolutions,equippedwithprofessionaltechniciansandskilledworkers,toensuresafetyandquality.6.weldingengineeringconstructionprogramme6

48、.1thisengineeringusedconstructionspecification6.1.1siteequipment,andindustrialpipelineweldingengineeringconstructionandtheacceptancespecificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionandtheacceptancespecificationSH3501-20026.1.3oilchemicallowtemperaturestee

49、lweldingproceduresSH/T3520-20046.1.4oilchemicalchromenickelAustrian'sbodysteel,andironnickelalloyandnickelalloypipelineweldingproceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-MOheat-resistantsteelpipe6.1.6ofthepressurevesselNDT4730-946.2JBweldprep

50、aration6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmethods,providingqualifiedweldingprocedurequalificationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstruction,guidethewelderweldingoperations.6.2.3whereparticipationinsitewelding,m

51、ustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6.2.4whereinvolvedinthepipeandsteelstructureweldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewithinthescopeandeligibilityapprovedbythequalityandtechnologysupervisiondepa

52、rtmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingtheweldingprocess.工2A雄美健点描述于生或步Jft勒之计珏述F所名的图像坦墩留述于梯度方向比牙盘由关键点所旄又腐的模糊用体计”产生.明停回联的串在通道下式计R：加父,上*3-1，+1mdw-=-=2G门算美所后维（oC”E）的顿内尺龙,=4instrumenthasasingletestcondition,willbetransferredtothecoordinationofthetestphase,th

53、einstrumentaccordingtothestandalonetrialsscheduled,withtheprocesspreparationoftestsolutions,equippedwithprofessionaltechniciansandskilledworkers,toensuresafetyandquality.6.weldingengineeringconstructionprogramme6.1thisengineeringusedconstructionspecification6.1.1siteequipment,andindustrialpipelinewe

54、ldingengineeringconstructionandtheacceptancespecificationGB50268-976.1.2oilchemicaltoxic,andcanburningmediapipelineengineeringconstructionandtheacceptancespecificationSH3501-20026.1.3oilchemicallowtemperaturesteelweldingproceduresSH/T3520-20046.1.4oilchemicalchromenickelAustrian'sbodysteel,andir

55、onnickelalloyandnickelalloypipelineweldingproceduresSH/T3523-19996.1.5SHJ520-92petrochemicalengineeringtechnicalspecificationforweldingofCR-MOheat-resistantsteelpipe6.1.6ofthepressurevesselNDT4730-946.2JBweldpreparation6.2.1constructionaccordingtothematerialsoftheprojectspecificationsandweldingmetho

56、ds,providingqualifiedweldingprocedurequalificationreport.6.2.2qualifiedweldingprocedurequalificationbasedonthepreparationofweldinginstruction,guidethewelderweldingoperations.6.2.3whereparticipationinsitewelding,mustbeinpossessionofboilerandpressurevesselweldercertificatesissuedbytheLaborDepartment.6

57、.2.4whereinvolvedinthepipeandsteelstructureweldingwelders,welderbeforeentryexaminationsshouldattendtheowners,andconstructionshouldbemadewithinthescopeandeligibilityapprovedbythequalityandtechnologysupervisiondepartmentsandowners.6.2.5qualifyforweldingwelder,weldingprocess,shouldbeapprovedbyweldingth

58、eweldingprocess.己-将坐标移至关找点主方向哪次羡转再度后新生杼为二3 ： I cosfl -sin 3 | x，疝6 gs8 J yy)工旄幽像专桂区域内对奉个通及蛋求其梯度幄役和方向，蜷后对每个株 展幅小来以昌有桢贵舞敦，生蝇方尚击者用.uergijj =匐匕叫± jx.j i)| exp - k : R更与美逢袅为列Q& K ;行感与关蜒忠的行照奉j 0 - if, b (i-</L )x(1 - )a -等于揩生子贸工式9, m力图比龙EM 的一半:instrument has a single test condition, will be tr

59、ansferred to the coordination of the test phase, the instrument according to the standalone trials scheduled, with the process preparation of test solutions, equipped with professional technicians and skilled workers, to ensure safety and quality. 6. welding engineering construction programme 6.1 this engineering used construction specification 6.1.1 s