文章目录[隐藏]
Faster R-CNN 目标检测算法
Towards Real-Time Object Detection with Region Proposal Networks
R-CNN：Regions with CNN features
- Input image
- Extract region proposals(~2k)
- Compute CNN features
- Classify regions
IoU Intersection over Union
测量在特定数据集中检测相应物体准确度的一个标准
预测范围： bounding boxex
ground-truth bounding boxes（人为在训练集图像中标出要检测物体的大概范围）
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IoU = \frac{Area\quad of\quad Overlap}{Area \quad of \quad Union}
IoU=AreaofUnionAreaofOverlap
![[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-IldTlrdy-1639284143003)(Detecting%20Text%20in%20Natural%20Image%20with%20Connectionist%20Text%20Proposal%20Network.assets/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2dhb3l1MTI1MzQwMTU2Mw==,size_16,color_FFFFFF,t_70.png)]](https://sup.51qudong.com/wp-content/uploads/csmbjc/ca3a3adb6710410f9802e8ad594a1103.png)
NMS (Non-Maximum Suppression)
Fast R-CNN
![[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-YaZeS7QC-1639284143006)(Detecting%20Text%20in%20Natural%20Image%20with%20Connectionist%20Text%20Proposal%20Network.assets/image-20211211202345500.png)]](https://sup.51qudong.com/wp-content/uploads/csmbjc/620de8dc9d1542a2b1f865c7de01a4e6.png)
Selection search
Anchor sliding window Feature extraction
RPN Loss
Cls label 二分类，是否有物体，使用IoU gt bounding box anchor box
Loc label
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t_x^* = (x^*-x_a)/w_a, t_y^* = (y^*-y_a)/h_a,\\ t_w^* = log(w^*/w_a), t_h^* = log(t_w^*)
tx∗=(x∗−xa)/wa,ty∗=(y∗−ya)/ha,tw∗=log(w∗/wa),th∗=log(tw∗)
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t_x = (x-x_a)/w_a, t_y = (y-ya)/h_a,\\ t_w = log(w/w_a), t_h = log(h/h_a)
tx=(x−xa)/wa,ty=(y−ya)/ha,tw=log(w/wa),th=log(h/ha)
Cls loss
Cross Entropy交叉熵
Loc Loss
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z_i = 0.5(x_i-y_i)^2/beta, \quad if |x_i-y_i|<beta\\ z_i = |x_i-y_i|-0.5*beta, \quad otherwise
zi=0.5(xi−yi)2/beta,if∣xi−yi∣<betazi=∣xi−yi∣−0.5∗beta,otherwise
RoI Head Region of Interest
Mask R-CNN
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L = L_{cls}+L_{box}+L_{mask}
L=Lcls+Lbox+Lmask
To this we apply a per-pixel sigmoid,and define
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Lmask as the average binary cross-entropy loss. For an RoI associated with gorund-truth k,
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Lmask is only defined o the k-th mask(other mask outputs do not contribute to the loss).
RoI Align不对齐，保留浮点，在小区域之内继续划分
CTPN 文字检测算法
Detecting Text in Natural Image with Connectionist Text Proposal Network
- Detecting text in fine-scale proposals
- Recurrent connectionist text proposals
- Side-refinement
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v_c= (c_y-c_y^a)/h^a\\ v_c^* = (c_y^*-c_y^a)/h^a\\ v_h = log(h/h_a)\\ v_h^* = log(h^*/h^a)
vc=(cy−cya)/havc∗=(cy∗−cya)/havh=log(h/ha)vh∗=log(h∗/ha)
Text line construction
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o^* = (x^*_{side} -c^a_x)/w^a
o∗=(xside∗−cxa)/wa
Code
bounding box
CRNN 文字识别算法
An End-yo-End Trainable Neural Network for Image-based Sequence Recognition and Its Application to Scene Text Recognition
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CRNN
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CTC
![[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-g467jlT1-1639284143006)(Detecting%20Text%20in%20Natural%20Image%20with%20Connectionist%20Text%20Proposal%20Network.assets/image-20211209220712175.png)]](https://sup.51qudong.com/wp-content/uploads/csmbjc/def2c7893e4d443a8f31b3fe64e0f785.png)
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lexicon-based
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lexicon-free
feature sequence —— receptive field感受野
CRNN——CTC
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\pi = --hh-e-l-ll-oo--\\ B(\pi) = hello\\ p(l|y) = \sum_{\pi:B(\pi)=1} p(\pi|y), \quad p('hello'|y) = \sum_{\pi:B(\pi)='hello'} p(\pi|y)
π=−−hh−e−l−ll−oo−−B(π)=hellop(l∣y)=π:B(π)=1∑p(π∣y),p(′hello′∣y)=π:B(π)=′hello′∑p(π∣y)
CTC Theory
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p(l|x) = \sum_{\pi \in B^{-1}(1)} p(\pi|x).\\ h(x) = arg\quad max_{1\in L\leq T} \quad p(l|x).\\ O^{ML}(S,N_w) = -\sum_{(x,z)\in S} ln(p(z|x))=-\sum_{(x,z) \in S} ln(\sum_{\pi \in B^{-1}(z)} p(\pi |x))
p(l∣x)=π∈B−1(1)∑p(π∣x).h(x)=argmax1∈L≤Tp(l∣x).OML(S,Nw)=−(x,z)∈S∑ln(p(z∣x))=−(x,z)∈S∑ln(π∈B−1(z)∑p(π∣x))
为了让所有的path都能在图中唯一、合法的表示，结点转换有如下约束：
- 转换只能往右下方向，其他方向不允许
- 相同的字符之间起码要有一个空字符
- 非空字符不能被跳过
- 起点必须从前两个字符开始
- 终点必须落在结尾两个字符
forward-backward
定义在时刻t经过节点s的全部前缀子路径的概率总和为前向概率
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αt(s)
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\alpha_3(4) = p(_ap)+p(aap)+p(a_p)+p(app)
α3(4)=p(ap)+p(aap)+p(ap)+p(app)
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情况1：第s个符号为空符号blank
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\alpha_t(s) = (\alpha_{t-1}(s)+\alpha_{t-1}(s-1))·y^t_{seq(s)}
αt(s)=(αt−1(s)+αt−1(s−1))⋅yseq(s)t
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情况2：第s个符号等于第s-2个符号
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\alpha_t(s) = (\alpha_{t-1}(s)+\alpha_{t-1}(s-1))·y^t_{seq(s)}
αt(s)=(αt−1(s)+αt−1(s−1))⋅yseq(s)t
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情况3：既不属于情况1，也不属于情况2
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\alpha_t(s) = (\alpha_{t-1}(s)+\alpha_{t-1}(s-1)+\alpha_{t-1}(s-2))·y^t_{seq(s)}
αt(s)=(αt−1(s)+αt−1(s−1)+αt−1(s−2))⋅yseq(s)t
![[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-GAanawON-1639284143009)(Detecting%20Text%20in%20Natural%20Image%20with%20Connectionist%20Text%20Proposal%20Network.assets/image-20211209231338595.png)]](https://sup.51qudong.com/wp-content/uploads/csmbjc/f2b41e43d1cc4060b260944dd61e735d.png)
不属于情况2
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\alpha_t(s) = (\alpha_{t-1}(s)+\alpha_{t-1}(s-1)+\alpha_{t-1}(s-2))·y^t_{seq(s)}
αt(s)=(αt−1(s)+αt−1(s−1)+αt−1(s−2))⋅yseq(s)t
![[外链图片转存中...(img-GAanawON-1639284143009)]](https://sup.51qudong.com/wp-content/uploads/csmbjc/4e556e33b2f6460d931f0697950a0a7f.png)
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原文链接：https://blog.csdn.net/weixin_46530492/article/details/121885721
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