first commit

network/core/raft.py

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+import numpy as np
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+
+from update import BasicUpdateBlock, SmallUpdateBlock
+from extractor import BasicEncoder, SmallEncoder
+from corr import CorrBlock, AlternateCorrBlock
+from network.core.utils.utils import bilinear_sampler, coords_grid, upflow8
+
+try:
+    autocast = torch.cuda.amp.autocast
+except:
+    # dummy autocast for PyTorch < 1.6
+    class autocast:
+        def __init__(self, enabled):
+            pass
+        def __enter__(self):
+            pass
+        def __exit__(self, *args):
+            pass
+
+
+class RAFT(nn.Module):
+    def __init__(self, args):
+        super(RAFT, self).__init__()
+        self.args = args
+        #args.small = True
+
+        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:
+            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)
+            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).to(img.device)
+        coords1 = coords_grid(N, H//8, W//8).to(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)
+
+        up_flow = F.unfold(8 * flow, [3,3], padding=1)
+        up_flow = up_flow.view(N, 2, 9, 1, 1, H, W)
+
+        up_flow = torch.sum(mask * up_flow, dim=2)
+        up_flow = up_flow.permute(0, 1, 4, 2, 5, 3)
+        return up_flow.reshape(N, 2, 8*H, 8*W)
+
+
+    def forward(self, image1, image2, iters=12, flow_init=None, upsample=True, test_mode=False):
+        """ Estimate optical flow between pair of frames """
+
+        image1 = 2 * (image1 / 255.0) - 1.0
+        image2 = 2 * (image2 / 255.0) - 1.0
+
+        image1 = image1.contiguous()
+        image2 = image2.contiguous()
+
+        hdim = self.hidden_dim
+        cdim = self.context_dim
+
+        # run the feature network
+        with autocast(enabled=self.args.mixed_precision):
+            fmap1, fmap2 = self.fnet([image1, image2])        
+        
+        fmap1 = fmap1.float()
+        fmap2 = fmap2.float()
+        if self.args.alternate_corr:
+            corr_fn = AlternateCorrBlock(fmap1, fmap2, radius=self.args.corr_radius)
+        else:
+            corr_fn = CorrBlock(fmap1, fmap2, radius=self.args.corr_radius)
+
+        # run the context network
+        with autocast(enabled=self.args.mixed_precision):
+            cnet = self.cnet(image1)
+            net, inp = torch.split(cnet, [hdim, cdim], dim=1)
+            net = torch.tanh(net)
+            inp = torch.relu(inp)
+
+        coords0, coords1 = self.initialize_flow(image1)
+
+        if flow_init is not None:
+            coords1 = coords1 + flow_init
+
+        flow_predictions = []
+        for itr in range(iters):
+            coords1 = coords1.detach()
+            corr = corr_fn(coords1) # index correlation volume
+
+            flow = coords1 - coords0
+            with autocast(enabled=self.args.mixed_precision):
+                net, up_mask, delta_flow = self.update_block(net, inp, corr, flow)
+
+            # F(t+1) = F(t) + \Delta(t)
+            coords1 = coords1 + delta_flow
+
+            # upsample predictions
+            if up_mask is None:
+                flow_up = upflow8(coords1 - coords0)
+            else:
+                flow_up = self.upsample_flow(coords1 - coords0, up_mask)
+            
+            flow_predictions.append(flow_up)
+
+        if test_mode:
+            return coords1 - coords0, flow_up
+            
+        return flow_predictions