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nf_resnet.py
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nf_resnet.py
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# Copyright 2021 DeepMind Technologies Limited. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Norm-Free Residual Networks."""
# pylint: disable=invalid-name
import haiku as hk
import jax
import jax.numpy as jnp
from nfnets import base
class NF_ResNet(hk.Module):
"""Norm-Free preactivation ResNet."""
variant_dict = {'ResNet50': {'depth': [3, 4, 6, 3]},
'ResNet101': {'depth': [3, 4, 23, 3]},
'ResNet152': {'depth': [3, 8, 36, 3]},
'ResNet200': {'depth': [3, 24, 36, 3]},
'ResNet288': {'depth': [24, 24, 24, 24]},
'ResNet600': {'depth': [50, 50, 50, 50]},
}
def __init__(self, num_classes, variant='ResNet50', width=4,
alpha=0.2, stochdepth_rate=0.1, drop_rate=None,
activation='relu', fc_init=None, skipinit_gain=jnp.zeros,
use_se=False, se_ratio=0.25,
name='NF_ResNet'):
super().__init__(name=name)
self.num_classes = num_classes
self.variant = variant
self.width = width
# Get variant info
block_params = self.variant_dict[self.variant]
self.width_pattern = [item * self.width for item in [64, 128, 256, 512]]
self.depth_pattern = block_params['depth']
self.activation = base.nonlinearities[activation]
if drop_rate is None:
self.drop_rate = block_params['drop_rate']
else:
self.drop_rate = drop_rate
self.which_conv = base.WSConv2D
# Stem
ch = int(16 * self.width)
self.initial_conv = self.which_conv(ch, kernel_shape=7, stride=2,
padding='SAME', with_bias=False,
name='initial_conv')
# Body
self.blocks = []
expected_std = 1.0
num_blocks = sum(self.depth_pattern)
index = 0 # Overall block index
block_args = (self.width_pattern, self.depth_pattern, [1, 2, 2, 2])
for block_width, stage_depth, stride in zip(*block_args):
for block_index in range(stage_depth):
# Scalar pre-multiplier so each block sees an N(0,1) input at init
beta = 1./ expected_std
# Block stochastic depth drop-rate
block_stochdepth_rate = stochdepth_rate * index / num_blocks
self.blocks += [NFResBlock(ch, block_width,
stride=stride if block_index == 0 else 1,
beta=beta, alpha=alpha,
activation=self.activation,
which_conv=self.which_conv,
stochdepth_rate=block_stochdepth_rate,
skipinit_gain=skipinit_gain,
use_se=use_se,
se_ratio=se_ratio,
)]
ch = block_width
index += 1
# Reset expected std but still give it 1 block of growth
if block_index == 0:
expected_std = 1.0
expected_std = (expected_std **2 + alpha**2)**0.5
# Head. By default, initialize with N(0, 0.01)
if fc_init is None:
fc_init = hk.initializers.RandomNormal(0.01, 0)
self.fc = hk.Linear(self.num_classes, w_init=fc_init, with_bias=True)
def __call__(self, x, is_training=True, return_metrics=False):
"""Return the output of the final layer without any [log-]softmax."""
# Stem
outputs = {}
out = self.initial_conv(x)
out = hk.max_pool(out, window_shape=(1, 3, 3, 1),
strides=(1, 2, 2, 1), padding='SAME')
if return_metrics:
outputs.update(base.signal_metrics(out, 0))
# Blocks
for i, block in enumerate(self.blocks):
out, res_avg_var = block(out, is_training=is_training)
if return_metrics:
outputs.update(base.signal_metrics(out, i + 1))
outputs[f'res_avg_var_{i}'] = res_avg_var
# Final-conv->activation, pool, dropout, classify
pool = jnp.mean(self.activation(out), [1, 2])
outputs['pool'] = pool
# Optionally apply dropout
if self.drop_rate > 0.0 and is_training:
pool = hk.dropout(hk.next_rng_key(), self.drop_rate, pool)
outputs['logits'] = self.fc(pool)
return outputs
def count_flops(self, h, w):
flops = []
flops += [base.count_conv_flops(3, self.initial_conv, h, w)]
h, w = h / 2, w / 2
# Body FLOPs
for block in self.blocks:
flops += [block.count_flops(h, w)]
if block.stride > 1:
h, w = h / block.stride, w / block.stride
# Count flops for classifier
flops += [self.blocks[-1].out_ch * self.fc.output_size]
return flops, sum(flops)
class NFResBlock(hk.Module):
"""Normalizer-Free pre-activation ResNet Block."""
def __init__(self, in_ch, out_ch, bottleneck_ratio=0.25,
kernel_size=3, stride=1,
beta=1.0, alpha=0.2,
which_conv=base.WSConv2D, activation=jax.nn.relu,
skipinit_gain=jnp.zeros,
stochdepth_rate=None,
use_se=False, se_ratio=0.25,
name=None):
super().__init__(name=name)
self.in_ch, self.out_ch = in_ch, out_ch
self.kernel_size = kernel_size
self.activation = activation
self.beta, self.alpha = beta, alpha
self.skipinit_gain = skipinit_gain
self.use_se, self.se_ratio = use_se, se_ratio
# Bottleneck width
self.width = int(self.out_ch * bottleneck_ratio)
self.stride = stride
# Conv 0 (typically expansion conv)
self.conv0 = which_conv(self.width, kernel_shape=1, padding='SAME',
name='conv0')
# Grouped NxN conv
self.conv1 = which_conv(self.width, kernel_shape=kernel_size, stride=stride,
padding='SAME', name='conv1')
# Conv 2, typically projection conv
self.conv2 = which_conv(self.out_ch, kernel_shape=1, padding='SAME',
name='conv2')
# Use shortcut conv on channel change or downsample.
self.use_projection = stride > 1 or self.in_ch != self.out_ch
if self.use_projection:
self.conv_shortcut = which_conv(self.out_ch, kernel_shape=1,
stride=stride, padding='SAME',
name='conv_shortcut')
# Are we using stochastic depth?
self._has_stochdepth = (stochdepth_rate is not None and
stochdepth_rate > 0. and stochdepth_rate < 1.0)
if self._has_stochdepth:
self.stoch_depth = base.StochDepth(stochdepth_rate)
if self.use_se:
self.se = base.SqueezeExcite(self.out_ch, self.out_ch, self.se_ratio)
def __call__(self, x, is_training):
out = self.activation(x) * self.beta
shortcut = x
if self.use_projection: # Downsample with conv1x1
shortcut = self.conv_shortcut(out)
out = self.conv0(out)
out = self.conv1(self.activation(out))
out = self.conv2(self.activation(out))
if self.use_se:
out = 2 * self.se(out) * out
# Get average residual standard deviation for reporting metrics.
res_avg_var = jnp.mean(jnp.var(out, axis=[0, 1, 2]))
# Apply stochdepth if applicable.
if self._has_stochdepth:
out = self.stoch_depth(out, is_training)
# SkipInit Gain
out = out * hk.get_parameter('skip_gain', (), out.dtype,
init=self.skipinit_gain)
return out * self.alpha + shortcut, res_avg_var
def count_flops(self, h, w):
# Count conv FLOPs based on input HW
expand_flops = base.count_conv_flops(self.in_ch, self.conv0, h, w)
# If block is strided we decrease resolution here.
dw_flops = base.count_conv_flops(self.width, self.conv1, h, w)
if self.stride > 1:
h, w = h / self.stride, w / self.stride
if self.use_projection:
sc_flops = base.count_conv_flops(self.in_ch, self.conv_shortcut, h, w)
else:
sc_flops = 0
# SE flops happen on avg-pooled activations
se_flops = self.se.fc0.output_size * self.width
se_flops += self.se.fc0.output_size * self.se.fc1.output_size
contract_flops = base.count_conv_flops(self.width, self.conv2, h, w)
return sum([expand_flops, dw_flops, se_flops, contract_flops, sc_flops])