319 lines
11 KiB
Python
319 lines
11 KiB
Python
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# Taken and modified from https://github.com/lucifer443/SpineNet-Pytorch/blob/master/mmdet/models/backbones/spinenet.py
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import torch.nn as nn
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import torch.nn.functional as F
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from torch.nn.init import kaiming_normal
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from torchvision.models.resnet import BasicBlock, Bottleneck
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from torch.nn.modules.batchnorm import _BatchNorm
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from models.archs.arch_util import ConvBnRelu
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def constant_init(module, val, bias=0):
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if hasattr(module, 'weight') and module.weight is not None:
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nn.init.constant_(module.weight, val)
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if hasattr(module, 'bias') and module.bias is not None:
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nn.init.constant_(module.bias, bias)
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def kaiming_init(module,
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a=0,
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mode='fan_out',
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nonlinearity='relu',
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bias=0,
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distribution='normal'):
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assert distribution in ['uniform', 'normal']
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if distribution == 'uniform':
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nn.init.kaiming_uniform_(
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module.weight, a=a, mode=mode, nonlinearity=nonlinearity)
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else:
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nn.init.kaiming_normal_(
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module.weight, a=a, mode=mode, nonlinearity=nonlinearity)
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if hasattr(module, 'bias') and module.bias is not None:
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nn.init.constant_(module.bias, bias)
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FILTER_SIZE_MAP = {
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1: 32,
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2: 64,
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3: 128,
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4: 256,
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5: 256,
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6: 256,
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7: 256,
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}
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def make_res_layer(block,
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inplanes,
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planes,
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blocks,
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stride=1,
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dilation=1):
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downsample = None
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if stride != 1 or inplanes != planes * block.expansion:
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downsample = nn.Sequential(
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nn.Conv2d(
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inplanes,
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planes * block.expansion,
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kernel_size=1,
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stride=stride,
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bias=False),
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nn.BatchNorm2d(planes * block.expansion),
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)
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layers = []
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layers.append(
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block(
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inplanes=inplanes,
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planes=planes,
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stride=stride,
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dilation=dilation,
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downsample=downsample))
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inplanes = planes * block.expansion
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for i in range(1, blocks):
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layers.append(
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block(
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inplanes=inplanes,
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planes=planes,
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stride=1,
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dilation=dilation))
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return nn.Sequential(*layers)
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# The fixed SpineNet architecture discovered by NAS.
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# Each element represents a specification of a building block:
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# (block_level, block_fn, (input_offset0, input_offset1), is_output).
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SPINENET_BLOCK_SPECS = [
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(2, Bottleneck, (None, None), False), # init block
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(2, Bottleneck, (None, None), False), # init block
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(2, Bottleneck, (0, 1), False),
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(4, BasicBlock, (0, 1), False),
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(3, Bottleneck, (2, 3), False),
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(4, Bottleneck, (2, 4), False),
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(6, BasicBlock, (3, 5), False),
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(4, Bottleneck, (3, 5), False),
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(5, BasicBlock, (6, 7), False),
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(7, BasicBlock, (6, 8), False),
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(5, Bottleneck, (8, 9), False),
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(5, Bottleneck, (8, 10), False),
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(4, Bottleneck, (5, 10), True),
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(3, Bottleneck, (4, 10), True),
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(5, Bottleneck, (7, 12), True),
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(7, Bottleneck, (5, 14), True),
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(6, Bottleneck, (12, 14), True),
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]
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SCALING_MAP = {
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'49S': {
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'endpoints_num_filters': 128,
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'filter_size_scale': 0.65,
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'resample_alpha': 0.5,
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'block_repeats': 1,
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},
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'49': {
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'endpoints_num_filters': 256,
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'filter_size_scale': 1.0,
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'resample_alpha': 0.5,
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'block_repeats': 1,
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},
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'96': {
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'endpoints_num_filters': 256,
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'filter_size_scale': 1.0,
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'resample_alpha': 0.5,
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'block_repeats': 2,
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},
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'143': {
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'endpoints_num_filters': 256,
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'filter_size_scale': 1.0,
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'resample_alpha': 1.0,
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'block_repeats': 3,
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},
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'190': {
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'endpoints_num_filters': 512,
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'filter_size_scale': 1.3,
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'resample_alpha': 1.0,
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'block_repeats': 4,
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},
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}
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class BlockSpec(object):
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"""A container class that specifies the block configuration for SpineNet."""
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def __init__(self, level, block_fn, input_offsets, is_output):
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self.level = level
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self.block_fn = block_fn
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self.input_offsets = input_offsets
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self.is_output = is_output
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def build_block_specs(block_specs=None):
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"""Builds the list of BlockSpec objects for SpineNet."""
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if not block_specs:
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block_specs = SPINENET_BLOCK_SPECS
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return [BlockSpec(*b) for b in block_specs]
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class Resample(nn.Module):
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def __init__(self, in_channels, out_channels, scale, block_type, alpha=1.0):
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super(Resample, self).__init__()
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self.scale = scale
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new_in_channels = int(in_channels * alpha)
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if block_type == Bottleneck:
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in_channels *= 4
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self.squeeze_conv = ConvBnRelu(in_channels, new_in_channels, kernel_size=1)
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if scale < 1:
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self.downsample_conv = ConvBnRelu(new_in_channels, new_in_channels, kernel_size=3, stride=2)
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self.expand_conv = ConvBnRelu(new_in_channels, out_channels, kernel_size=1, relu=False)
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def _resize(self, x):
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if self.scale == 1:
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return x
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elif self.scale > 1:
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return F.interpolate(x, scale_factor=self.scale, mode='nearest')
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else:
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x = self.downsample_conv(x)
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if self.scale < 0.5:
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new_kernel_size = 3 if self.scale >= 0.25 else 5
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x = F.max_pool2d(x, kernel_size=new_kernel_size, stride=int(0.5/self.scale), padding=new_kernel_size//2)
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return x
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def forward(self, inputs):
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feat = self.squeeze_conv(inputs)
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feat = self._resize(feat)
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feat = self.expand_conv(feat)
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return feat
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class Merge(nn.Module):
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"""Merge two input tensors"""
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def __init__(self, block_spec, alpha, filter_size_scale):
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super(Merge, self).__init__()
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out_channels = int(FILTER_SIZE_MAP[block_spec.level] * filter_size_scale)
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if block_spec.block_fn == Bottleneck:
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out_channels *= 4
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self.block = block_spec.block_fn
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self.resample_ops = nn.ModuleList()
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for spec_idx in block_spec.input_offsets:
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spec = BlockSpec(*SPINENET_BLOCK_SPECS[spec_idx])
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in_channels = int(FILTER_SIZE_MAP[spec.level] * filter_size_scale)
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scale = 2**(spec.level - block_spec.level)
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self.resample_ops.append(
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Resample(in_channels, out_channels, scale, spec.block_fn, alpha)
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)
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def forward(self, inputs):
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assert len(inputs) == len(self.resample_ops)
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parent0_feat = self.resample_ops[0](inputs[0])
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parent1_feat = self.resample_ops[1](inputs[1])
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target_feat = parent0_feat + parent1_feat
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return target_feat
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class SpineNet(nn.Module):
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"""Class to build SpineNet backbone"""
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def __init__(self,
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arch,
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in_channels=3,
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output_level=[3, 4, 5, 6, 7],
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zero_init_residual=True):
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super(SpineNet, self).__init__()
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self._block_specs = build_block_specs()[2:]
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self._endpoints_num_filters = SCALING_MAP[arch]['endpoints_num_filters']
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self._resample_alpha = SCALING_MAP[arch]['resample_alpha']
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self._block_repeats = SCALING_MAP[arch]['block_repeats']
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self._filter_size_scale = SCALING_MAP[arch]['filter_size_scale']
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self._init_block_fn = Bottleneck
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self._num_init_blocks = 2
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self.zero_init_residual = zero_init_residual
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assert min(output_level) > 2 and max(output_level) < 8, "Output level out of range"
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self.output_level = output_level
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self._make_stem_layer(in_channels)
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self._make_scale_permuted_network()
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self._make_endpoints()
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def _make_stem_layer(self, in_channels):
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"""Build the stem network."""
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# Build the first conv and maxpooling layers.
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self.conv1 = ConvBnRelu(
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in_channels,
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64,
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kernel_size=7,
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stride=2) # Original paper had stride=2 and a maxpool after.
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# Build the initial level 2 blocks.
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self.init_block1 = make_res_layer(
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self._init_block_fn,
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64,
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int(FILTER_SIZE_MAP[2] * self._filter_size_scale),
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self._block_repeats)
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self.init_block2 = make_res_layer(
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self._init_block_fn,
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int(FILTER_SIZE_MAP[2] * self._filter_size_scale) * 4,
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int(FILTER_SIZE_MAP[2] * self._filter_size_scale),
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self._block_repeats)
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def _make_endpoints(self):
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self.endpoint_convs = nn.ModuleDict()
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for block_spec in self._block_specs:
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if block_spec.is_output:
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in_channels = int(FILTER_SIZE_MAP[block_spec.level]*self._filter_size_scale) * 4
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self.endpoint_convs[str(block_spec.level)] = ConvBnRelu(in_channels,
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self._endpoints_num_filters,
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kernel_size=1,
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relu=False)
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def _make_scale_permuted_network(self):
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self.merge_ops = nn.ModuleList()
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self.scale_permuted_blocks = nn.ModuleList()
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for spec in self._block_specs:
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self.merge_ops.append(
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Merge(spec, self._resample_alpha, self._filter_size_scale)
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)
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channels = int(FILTER_SIZE_MAP[spec.level] * self._filter_size_scale)
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in_channels = channels * 4 if spec.block_fn == Bottleneck else channels
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self.scale_permuted_blocks.append(
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make_res_layer(spec.block_fn,
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in_channels,
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channels,
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self._block_repeats)
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)
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def init_weights(self, pretrained=None):
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for m in self.modules():
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if isinstance(m, nn.Conv2d):
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kaiming_init(m)
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elif isinstance(m, (_BatchNorm, nn.GroupNorm)):
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constant_init(m, 1)
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if self.zero_init_residual:
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for m in self.modules():
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if isinstance(m, Bottleneck):
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constant_init(m.norm3, 0)
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elif isinstance(m, BasicBlock):
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constant_init(m.norm2, 0)
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def forward(self, input):
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feat = self.conv1(input)
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feat1 = self.init_block1(feat)
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feat2 = self.init_block2(feat1)
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block_feats = [feat1, feat2]
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output_feat = {}
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num_outgoing_connections = [0, 0]
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for i, spec in enumerate(self._block_specs):
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target_feat = self.merge_ops[i]([block_feats[feat_idx] for feat_idx in spec.input_offsets])
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# Connect intermediate blocks with outdegree 0 to the output block.
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if spec.is_output:
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for j, (j_feat, j_connections) in enumerate(
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zip(block_feats, num_outgoing_connections)):
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if j_connections == 0 and j_feat.shape == target_feat.shape:
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target_feat += j_feat
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num_outgoing_connections[j] += 1
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target_feat = F.relu(target_feat, inplace=True)
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target_feat = self.scale_permuted_blocks[i](target_feat)
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block_feats.append(target_feat)
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num_outgoing_connections.append(0)
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for feat_idx in spec.input_offsets:
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num_outgoing_connections[feat_idx] += 1
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if spec.is_output:
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output_feat[spec.level] = target_feat
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return [self.endpoint_convs[str(level)](output_feat[level]) for level in self.output_level]
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