详解目标检测之anchor-box生成

野性酷女 2023-05-21 15:16 13阅读 0赞

无论前端backbone如何，总会输出一个feature map 如何在这个feature map上得到pred的 box呢？

#### 第一步先得到 feature map上所有的 中心点x，y ####

举例：  
以特征图大小（4， 4 ，5， 6）表示，4为batch，4 为channel， 5为h, 6为w

#以feature的大小5*6 生成单位网格
    import torch
    yy, xx =torch.meshgrid(torch.arange(5), torch.arange(6)
    print(yy,xx)
    #得到如下
    tensor([[0, 0, 0, 0, 0, 0],
            [1, 1, 1, 1, 1, 1],
            [2, 2, 2, 2, 2, 2],
            [3, 3, 3, 3, 3, 3],
            [4, 4, 4, 4, 4, 4]]) 
    tensor([[0, 1, 2, 3, 4, 5],
            [0, 1, 2, 3, 4, 5],
            [0, 1, 2, 3, 4, 5],
            [0, 1, 2, 3, 4, 5],
            [0, 1, 2, 3, 4, 5]])
    #堆叠起来
    mesh = torch.stack([xx, yy], dim=0)
    print(mesh)
    #输出如下，shape为[2, 5, 6]
    tensor([[[0, 1, 2, 3, 4, 5],
             [0, 1, 2, 3, 4, 5],
             [0, 1, 2, 3, 4, 5],
             [0, 1, 2, 3, 4, 5],
             [0, 1, 2, 3, 4, 5]],
    
            [[0, 0, 0, 0, 0, 0],
             [1, 1, 1, 1, 1, 1],
             [2, 2, 2, 2, 2, 2],
             [3, 3, 3, 3, 3, 3],
             [4, 4, 4, 4, 4, 4]]])
     #增加一个batch 位置的维度 shape为 [4, 2, 5, 6] 
    mesh = mesh.unsqueeze(0).repeat(4,1,1,1).float() 
    print(mesh)
    tensor([[[[0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.]],
    
             [[0., 0., 0., 0., 0., 0.],
              [1., 1., 1., 1., 1., 1.],
              [2., 2., 2., 2., 2., 2.],
              [3., 3., 3., 3., 3., 3.],
              [4., 4., 4., 4., 4., 4.]]],
    
    
            [[[0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.]],
    
             [[0., 0., 0., 0., 0., 0.],
              [1., 1., 1., 1., 1., 1.],
              [2., 2., 2., 2., 2., 2.],
              [3., 3., 3., 3., 3., 3.],
              [4., 4., 4., 4., 4., 4.]]],
    
    
            [[[0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.]],
    
             [[0., 0., 0., 0., 0., 0.],
              [1., 1., 1., 1., 1., 1.],
              [2., 2., 2., 2., 2., 2.],
              [3., 3., 3., 3., 3., 3.],
              [4., 4., 4., 4., 4., 4.]]],
    
    
            [[[0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.],
              [0., 1., 2., 3., 4., 5.]],
    
             [[0., 0., 0., 0., 0., 0.],
              [1., 1., 1., 1., 1., 1.],
              [2., 2., 2., 2., 2., 2.],
              [3., 3., 3., 3., 3., 3.],
              [4., 4., 4., 4., 4., 4.]]]])

#### \#\#\#\# 然后 以预设定的anchor box 比率生成 ####

anchor\_wh=\[  
\[ 5.0174, 15.0521\],  
\[ 7.0833, 21.2500\],  
\[10.0347, 24.7917\],  
\[20.0694, 18.8889\]\]

anchor_offset_mesh = anchor_wh.unsqueeze(-1).unsqueeze(-1).repeat(1, 1, nGh,nGw)
    print(anchor_offset_mesh)
    tensor([[[[ 5.0174,  5.0174,  5.0174,  5.0174,  5.0174,  5.0174],
              [ 5.0174,  5.0174,  5.0174,  5.0174,  5.0174,  5.0174],
              [ 5.0174,  5.0174,  5.0174,  5.0174,  5.0174,  5.0174],
              [ 5.0174,  5.0174,  5.0174,  5.0174,  5.0174,  5.0174],
              [ 5.0174,  5.0174,  5.0174,  5.0174,  5.0174,  5.0174]],
    
             [[15.0521, 15.0521, 15.0521, 15.0521, 15.0521, 15.0521],
              [15.0521, 15.0521, 15.0521, 15.0521, 15.0521, 15.0521],
              [15.0521, 15.0521, 15.0521, 15.0521, 15.0521, 15.0521],
              [15.0521, 15.0521, 15.0521, 15.0521, 15.0521, 15.0521],
              [15.0521, 15.0521, 15.0521, 15.0521, 15.0521, 15.0521]]],
    
    
            [[[ 7.0833,  7.0833,  7.0833,  7.0833,  7.0833,  7.0833],
              [ 7.0833,  7.0833,  7.0833,  7.0833,  7.0833,  7.0833],
              [ 7.0833,  7.0833,  7.0833,  7.0833,  7.0833,  7.0833],
              [ 7.0833,  7.0833,  7.0833,  7.0833,  7.0833,  7.0833],
              [ 7.0833,  7.0833,  7.0833,  7.0833,  7.0833,  7.0833]],
    
             [[21.2500, 21.2500, 21.2500, 21.2500, 21.2500, 21.2500],
              [21.2500, 21.2500, 21.2500, 21.2500, 21.2500, 21.2500],
              [21.2500, 21.2500, 21.2500, 21.2500, 21.2500, 21.2500],
              [21.2500, 21.2500, 21.2500, 21.2500, 21.2500, 21.2500],
              [21.2500, 21.2500, 21.2500, 21.2500, 21.2500, 21.2500]]],
    
    
            [[[10.0347, 10.0347, 10.0347, 10.0347, 10.0347, 10.0347],
              [10.0347, 10.0347, 10.0347, 10.0347, 10.0347, 10.0347],
              [10.0347, 10.0347, 10.0347, 10.0347, 10.0347, 10.0347],
              [10.0347, 10.0347, 10.0347, 10.0347, 10.0347, 10.0347],
              [10.0347, 10.0347, 10.0347, 10.0347, 10.0347, 10.0347]],
    
             [[24.7917, 24.7917, 24.7917, 24.7917, 24.7917, 24.7917],
              [24.7917, 24.7917, 24.7917, 24.7917, 24.7917, 24.7917],
              [24.7917, 24.7917, 24.7917, 24.7917, 24.7917, 24.7917],
              [24.7917, 24.7917, 24.7917, 24.7917, 24.7917, 24.7917],
              [24.7917, 24.7917, 24.7917, 24.7917, 24.7917, 24.7917]]],
    
    
            [[[20.0694, 20.0694, 20.0694, 20.0694, 20.0694, 20.0694],
              [20.0694, 20.0694, 20.0694, 20.0694, 20.0694, 20.0694],
              [20.0694, 20.0694, 20.0694, 20.0694, 20.0694, 20.0694],
              [20.0694, 20.0694, 20.0694, 20.0694, 20.0694, 20.0694],
              [20.0694, 20.0694, 20.0694, 20.0694, 20.0694, 20.0694]],
    
             [[18.8889, 18.8889, 18.8889, 18.8889, 18.8889, 18.8889],
              [18.8889, 18.8889, 18.8889, 18.8889, 18.8889, 18.8889],
              [18.8889, 18.8889, 18.8889, 18.8889, 18.8889, 18.8889],
              [18.8889, 18.8889, 18.8889, 18.8889, 18.8889, 18.8889],
              [18.8889, 18.8889, 18.8889, 18.8889, 18.8889, 18.8889]]]])
    
    anchor_offset_mesh=torch.cat([mesh2, anchor_offset_mesh],dim=1)
    f=anchor_offset_mesh.permute(0,2,3,1).contiguous().view(-1, 4) 
    print(f)
    # 生成 x,y, w,h 格式的bounding box
    tensor([[ 0.0000,  0.0000,  5.0174, 15.0521],
            [ 1.0000,  0.0000,  5.0174, 15.0521],
            [ 2.0000,  0.0000,  5.0174, 15.0521],
            [ 3.0000,  0.0000,  5.0174, 15.0521],
            [ 4.0000,  0.0000,  5.0174, 15.0521],
            [ 5.0000,  0.0000,  5.0174, 15.0521],
            [ 0.0000,  1.0000,  5.0174, 15.0521],
            [ 1.0000,  1.0000,  5.0174, 15.0521],
            [ 2.0000,  1.0000,  5.0174, 15.0521],
            [ 3.0000,  1.0000,  5.0174, 15.0521],
            [ 4.0000,  1.0000,  5.0174, 15.0521],
            [ 5.0000,  1.0000,  5.0174, 15.0521],
            [ 0.0000,  2.0000,  5.0174, 15.0521],
            [ 1.0000,  2.0000,  5.0174, 15.0521],
            [ 2.0000,  2.0000,  5.0174, 15.0521],
            [ 3.0000,  2.0000,  5.0174, 15.0521],
            [ 4.0000,  2.0000,  5.0174, 15.0521],
            [ 5.0000,  2.0000,  5.0174, 15.0521],
            [ 0.0000,  3.0000,  5.0174, 15.0521],
            [ 1.0000,  3.0000,  5.0174, 15.0521],
            [ 2.0000,  3.0000,  5.0174, 15.0521],
            [ 3.0000,  3.0000,  5.0174, 15.0521],
            [ 4.0000,  3.0000,  5.0174, 15.0521],
            [ 5.0000,  3.0000,  5.0174, 15.0521],
            [ 0.0000,  4.0000,  5.0174, 15.0521],
            [ 1.0000,  4.0000,  5.0174, 15.0521],
            [ 2.0000,  4.0000,  5.0174, 15.0521],
            [ 3.0000,  4.0000,  5.0174, 15.0521],
            [ 4.0000,  4.0000,  5.0174, 15.0521],
            [ 5.0000,  4.0000,  5.0174, 15.0521],
            [ 0.0000,  0.0000,  7.0833, 21.2500],
            [ 1.0000,  0.0000,  7.0833, 21.2500],
            [ 2.0000,  0.0000,  7.0833, 21.2500],
            [ 3.0000,  0.0000,  7.0833, 21.2500],
            [ 4.0000,  0.0000,  7.0833, 21.2500],
            [ 5.0000,  0.0000,  7.0833, 21.2500],
            [ 0.0000,  1.0000,  7.0833, 21.2500],
            [ 1.0000,  1.0000,  7.0833, 21.2500],
            [ 2.0000,  1.0000,  7.0833, 21.2500],
            [ 3.0000,  1.0000,  7.0833, 21.2500],
            [ 4.0000,  1.0000,  7.0833, 21.2500],
            [ 5.0000,  1.0000,  7.0833, 21.2500],
            [ 0.0000,  2.0000,  7.0833, 21.2500],
            [ 1.0000,  2.0000,  7.0833, 21.2500],
            [ 2.0000,  2.0000,  7.0833, 21.2500],
            [ 3.0000,  2.0000,  7.0833, 21.2500],
            [ 4.0000,  2.0000,  7.0833, 21.2500],
            [ 5.0000,  2.0000,  7.0833, 21.2500],
            [ 0.0000,  3.0000,  7.0833, 21.2500],
            [ 1.0000,  3.0000,  7.0833, 21.2500],
            [ 2.0000,  3.0000,  7.0833, 21.2500],
            [ 3.0000,  3.0000,  7.0833, 21.2500],
            [ 4.0000,  3.0000,  7.0833, 21.2500],
            [ 5.0000,  3.0000,  7.0833, 21.2500],
            [ 0.0000,  4.0000,  7.0833, 21.2500],
            [ 1.0000,  4.0000,  7.0833, 21.2500],
            [ 2.0000,  4.0000,  7.0833, 21.2500],
            [ 3.0000,  4.0000,  7.0833, 21.2500],
            [ 4.0000,  4.0000,  7.0833, 21.2500],
            [ 5.0000,  4.0000,  7.0833, 21.2500],
            [ 0.0000,  0.0000, 10.0347, 24.7917],
            [ 1.0000,  0.0000, 10.0347, 24.7917],
            [ 2.0000,  0.0000, 10.0347, 24.7917],
            [ 3.0000,  0.0000, 10.0347, 24.7917],
            [ 4.0000,  0.0000, 10.0347, 24.7917],
            [ 5.0000,  0.0000, 10.0347, 24.7917],
            [ 0.0000,  1.0000, 10.0347, 24.7917],
            [ 1.0000,  1.0000, 10.0347, 24.7917],
            [ 2.0000,  1.0000, 10.0347, 24.7917],
            [ 3.0000,  1.0000, 10.0347, 24.7917],
            [ 4.0000,  1.0000, 10.0347, 24.7917],
            [ 5.0000,  1.0000, 10.0347, 24.7917],
            [ 0.0000,  2.0000, 10.0347, 24.7917],
            [ 1.0000,  2.0000, 10.0347, 24.7917],
            [ 2.0000,  2.0000, 10.0347, 24.7917],
            [ 3.0000,  2.0000, 10.0347, 24.7917],
            [ 4.0000,  2.0000, 10.0347, 24.7917],
            [ 5.0000,  2.0000, 10.0347, 24.7917],
            [ 0.0000,  3.0000, 10.0347, 24.7917],
            [ 1.0000,  3.0000, 10.0347, 24.7917],
            [ 2.0000,  3.0000, 10.0347, 24.7917],
            [ 3.0000,  3.0000, 10.0347, 24.7917],
            [ 4.0000,  3.0000, 10.0347, 24.7917],
            [ 5.0000,  3.0000, 10.0347, 24.7917],
            [ 0.0000,  4.0000, 10.0347, 24.7917],
            [ 1.0000,  4.0000, 10.0347, 24.7917],
            [ 2.0000,  4.0000, 10.0347, 24.7917],
            [ 3.0000,  4.0000, 10.0347, 24.7917],
            [ 4.0000,  4.0000, 10.0347, 24.7917],
            [ 5.0000,  4.0000, 10.0347, 24.7917],
            [ 0.0000,  0.0000, 20.0694, 18.8889],
            [ 1.0000,  0.0000, 20.0694, 18.8889],
            [ 2.0000,  0.0000, 20.0694, 18.8889],
            [ 3.0000,  0.0000, 20.0694, 18.8889],
            [ 4.0000,  0.0000, 20.0694, 18.8889],
            [ 5.0000,  0.0000, 20.0694, 18.8889],
            [ 0.0000,  1.0000, 20.0694, 18.8889],
            [ 1.0000,  1.0000, 20.0694, 18.8889],
            [ 2.0000,  1.0000, 20.0694, 18.8889],
            [ 3.0000,  1.0000, 20.0694, 18.8889],
            [ 4.0000,  1.0000, 20.0694, 18.8889],
            [ 5.0000,  1.0000, 20.0694, 18.8889],
            [ 0.0000,  2.0000, 20.0694, 18.8889],
            [ 1.0000,  2.0000, 20.0694, 18.8889],
            [ 2.0000,  2.0000, 20.0694, 18.8889],
            [ 3.0000,  2.0000, 20.0694, 18.8889],
            [ 4.0000,  2.0000, 20.0694, 18.8889],
            [ 5.0000,  2.0000, 20.0694, 18.8889],
            [ 0.0000,  3.0000, 20.0694, 18.8889],
            [ 1.0000,  3.0000, 20.0694, 18.8889],
            [ 2.0000,  3.0000, 20.0694, 18.8889],
            [ 3.0000,  3.0000, 20.0694, 18.8889],
            [ 4.0000,  3.0000, 20.0694, 18.8889],
            [ 5.0000,  3.0000, 20.0694, 18.8889],
            [ 0.0000,  4.0000, 20.0694, 18.8889],
            [ 1.0000,  4.0000, 20.0694, 18.8889],
            [ 2.0000,  4.0000, 20.0694, 18.8889],
            [ 3.0000,  4.0000, 20.0694, 18.8889],
            [ 4.0000,  4.0000, 20.0694, 18.8889],
            [ 5.0000,  4.0000, 20.0694, 18.8889]])