Class RAFT

core/raft.py:25–150

class RAFT(nn.Module):
    def __init__(self, args):
        super(RAFT, self).__init__()
        self.args = args

        if args.small:
            self.hidden_dim = hdim = 96
            self.context_dim = cdim = 64
            args.corr_levels = 4
            args.corr_radius = 3
        
        else:
            self.hidden_dim = hdim = 128
            self.context_dim = cdim = 128
            args.corr_levels = 4
            args.corr_radius = 4

        if 'dropout' not in self.args:
            self.args.dropout = 0

        if 'alternate_corr' not in self.args:
            self.args.alternate_corr = False

        # feature network, context network, and update block
        if args.small:
            self.fnet = SmallEncoder(output_dim=128, norm_fn='instance', dropout=args.dropout)        
            self.cnet = SmallEncoder(output_dim=hdim+cdim, norm_fn='none', dropout=args.dropout)
            self.update_block = SmallUpdateBlock(self.args, hidden_dim=hdim)

        else:
            if self.args.fnet == 'CNN':
                self.fnet = BasicEncoder(output_dim=256, norm_fn='instance', dropout=args.dropout)        
                self.cnet = BasicEncoder(output_dim=hdim+cdim, norm_fn='batch', dropout=args.dropout)
            elif self.args.fnet == 'twins':
                self.fnet = twins_svt_large(pretrained=True)
                self.cnet = twins_svt_large(pretrained=True)
            self.update_block = BasicUpdateBlock(self.args, hidden_dim=hdim)

    def freeze_bn(self):
        for m in self.modules():
            if isinstance(m, nn.BatchNorm2d):
                m.eval()

    def initialize_flow(self, img):
        """ Flow is represented as difference between two coordinate grids flow = coords1 - coords0"""
        N, C, H, W = img.shape
        coords0 = coords_grid(N, H//8, W//8, device=img.device)
        coords1 = coords_grid(N, H//8, W//8, device=img.device)

        # optical flow computed as difference: flow = coords1 - coords0
        return coords0, coords1

    def upsample_flow(self, flow, mask):
        """ Upsample flow field [H/8, W/8, 2] -> [H, W, 2] using convex combination """
        N, _, H, W = flow.shape
        mask = mask.view(N, 1, 9, 8, 8, H, W)
        mask = torch.softmax(mask, dim=2)