net_utils.py 文件源码

def _crop_pool_layer(bottom, rois, max_pool=True):
    # code modified from 
    # https://github.com/ruotianluo/pytorch-faster-rcnn
    # implement it using stn
    # box to affine
    # input (x1,y1,x2,y2)
    """
    [  x2-x1             x1 + x2 - W + 1  ]
    [  -----      0      ---------------  ]
    [  W - 1                  W - 1       ]
    [                                     ]
    [           y2-y1    y1 + y2 - H + 1  ]
    [    0      -----    ---------------  ]
    [           H - 1         H - 1      ]
    """
    rois = rois.detach()
    batch_size = bottom.size(0)
    D = bottom.size(1)
    H = bottom.size(2)
    W = bottom.size(3)
    roi_per_batch = rois.size(0) / batch_size
    x1 = rois[:, 1::4] / 16.0
    y1 = rois[:, 2::4] / 16.0
    x2 = rois[:, 3::4] / 16.0
    y2 = rois[:, 4::4] / 16.0

    height = bottom.size(2)
    width = bottom.size(3)

    # affine theta
    zero = Variable(rois.data.new(rois.size(0), 1).zero_())
    theta = torch.cat([\
      (x2 - x1) / (width - 1),
      zero,
      (x1 + x2 - width + 1) / (width - 1),
      zero,
      (y2 - y1) / (height - 1),
      (y1 + y2 - height + 1) / (height - 1)], 1).view(-1, 2, 3)

    if max_pool:
      pre_pool_size = cfg.POOLING_SIZE * 2
      grid = F.affine_grid(theta, torch.Size((rois.size(0), 1, pre_pool_size, pre_pool_size)))
      bottom = bottom.view(1, batch_size, D, H, W).contiguous().expand(roi_per_batch, batch_size, D, H, W)\
                                                                .contiguous().view(-1, D, H, W)
      crops = F.grid_sample(bottom, grid)
      crops = F.max_pool2d(crops, 2, 2)
    else:
      grid = F.affine_grid(theta, torch.Size((rois.size(0), 1, cfg.POOLING_SIZE, cfg.POOLING_SIZE)))
      bottom = bottom.view(1, batch_size, D, H, W).contiguous().expand(roi_per_batch, batch_size, D, H, W)\
                                                                .contiguous().view(-1, D, H, W)
      crops = F.grid_sample(bottom, grid)

    return crops, grid