from 3d to 2d
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R esto rstio n
featu re d etectio n
p inho le m o d el
p reserved
straig ht lines, incid ence
no t p reserved ang les, leng th
投影到前面平行的平面
fronto-parallel p lanes
all p o ints o n that p lane are at fixed d ep th z
ang els and ratio s of leng ths/areas
vanishing p o int
find vanishing p o int
vanishing line of the g round p lane
the p o ints hig ht that ho rizo n are ab o ve the cam era p rovid es w ay of co m paring heig ht of o b jects
m easuring heig ht
p ersp ective d istortio n e.g. 球投成椭圆
ortho g rap hic p rojectio n
d istance from center of p rojectio n to im ag e p lane is infinite
p rojectio n m atrix
ap erture size 孔径越大越模糊
cam era w ith tin lens
物距的倒数加像距的倒数等于焦距的倒数
circle of co nfusio n 除了特定距离会in fo cus,其他距离光线落在小范围内
depth of field sm all ap erture size m akes the lig ht m o re fo cus b ut m ake the p o int d arker
field of view larger fo cal leng th m eans sm aller FO V
d istortio n is m o re o b vio us at the ed g e of the lens
d ig ital cam era 求RG B 3*3范围每个通道求平均
uniform m ean filter
b o und ary
zero pad d ing
ad just filter kernel 框内有几个算几个，不额外扩展
可以拆成2个1D kernel
g aussian filter
w hy g aussian filter rem o ve no ise lo w pass filter
so b el filter
Lap lacian filter
hig h pass filter
unsharp m ask 原图减去经过uniform m ean filter的图片，结果叠加到原图上
nonlinear fileter m ax,m in,m ed ian filter 子主题
spatial filtering
g aussian no ise
sp eckle no ise
b rig hter than g aussian no ise
d ifficult to rem o ve d ue to m ultip licatio n
no ise and r
salt and p ep p er no ise
m ed ian filter sam e as L2 m inim isatio n（绝对值求和求中值）
outlier rejectio n m etho d
1.set a thesho ld D
2.co m pare the value p w ith surround ing m ean m
3.if |p-m| > D, p is id entified as a no ise and rep lace it b y m
g aussian no ise
sam p le averag e filter
w ind ow size
sm all w ind o w
unifo rm m ean filter o r g aussian filter
no t effective
large w ind o w o ver-sm o o th
b ilateral filter
co nisd er b o th spatial and intensity d istance
fo r intensity d istence, if the p ixel has sim ilar intensity
w ith the centre o ne, the w eig ht w ill b e hig her
p reserve ed g es
no n-lo cal m eans filter
averag es neig hb o r w ith sim ilar neig hb o urho o d s
no spatial term s
g aussian filter
b ilateral filter
N L-m eans
o nly spatial term
lo w no ise and d etails
spatial term and co nsid er intensity d istance
b etter at no ise rem o val
o nly intensity d istance
sharp, lo w no ise, few artifacts
p erio d ic no ise
FT can g et the freq uency of the w aves and use co unter sig nal to rem o ve it
m o d eled as sinuso id w aves
L1 d istance（平方求和求均值）
easily influnced b y no ise
sho uld rem o ve no ise first
d erivative of G aussian Filter
sm o o thed d erivative rem o ves no ise b ut b lurs ed g e
so b el filter ap p o rxim ate to the d erivative of g aussian filter
Lap lacian filter sensitive to no iseLap lacian of G aussian rem o ve no ise first
C anny ed g e d etector first, im ag e filtering next, no n-m axim um sup p resio n third, d o ub le thresho ld ing
basic id ea co rner has a large chang e in intensity in any d irectio n
H arris co rner d etector
first, co m p ut M m atrix f
o r each w ind o w to g et t
heir co nnerness sco res
seco nd, find p o ints w ho se
surround ing w ind o w g ave
larger co rner resp o nse
third, take the p o ints
of lo cal m axim a
resist to co nner relo catio n, affine intensity chang e
no t resist to scaling
no t scaling
feature d escrip tor
feature m eatching
SIFT d iscrip tor
N N m atching
so lutio n: b lo b d etector b y SIFT
b lo b d etector
find m axim a and m inim a resp o nse w ith d ifferent size of filter
LO G/ D O G
b lack fo r m inim a LO G 中心, w hite fo r m axim a LO G 边缘
extrem um 当sigm a与冲击的宽度相同时，产生极值
find keyp o ints at d ifferent scale
1. d etect cand id ates of interest p o ints, w hich are extrem a p o ints in the scale-space d o m ains
2. sub-p ixel lo calizatio n and rem o ve of extrem a p o ints w ith lo w co ntrast
less sensitive to no ise
3. o rientatio n assig nm ent
take 16*16 w ind o w and co m p ute ed g e o rientatio n fo r each 2*2 b lo ck
throw o ut w eak ed g es and create histog ram
o ne feature m atches to ano ther if tho se feature are
the nearest neig hb o ur and their d istance b elo w T
cross-checking techniq ue 两张图相互映射，如果两点匹配，则保留
another techniq ue 一张图向另一张图映射，第一近的点与第二近的点距离之比小于某一阈值，则保留
4. co m p ut g rad ient histog ram o ver 8-d irectio ns fo r esch 4*4 b lo ck
5. co ncatenate 8-d vectors of 4*$ arrays and no m alize the m ag nitud e of 128-d vector to 1
用bolb检测cond id ate of interst p o ints
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