# Copyright (c) 2019 PaddlePaddle Authors. 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. from __future__ import absolute_import from __future__ import division from __future__ import print_function from collections import OrderedDict import copy from paddle import fluid from paddle.fluid.param_attr import ParamAttr from paddle.fluid.initializer import Xavier from paddle.fluid.regularizer import L2Decay from ppdet.core.workspace import register from ppdet.modeling.ops import ConvNorm __all__ = ['FPN'] @register class FPN(object): """ Feature Pyramid Network, see https://arxiv.org/abs/1612.03144 Args: num_chan (int): number of feature channels min_level (int): lowest level of the backbone feature map to use max_level (int): highest level of the backbone feature map to use spatial_scale (list): feature map scaling factor has_extra_convs (bool): whether has extral convolutions in higher levels norm_type (str|None): normalization type, 'bn'/'sync_bn'/'affine_channel' """ __shared__ = ['norm_type', 'freeze_norm'] def __init__(self, num_chan=256, min_level=2, max_level=6, spatial_scale=[1. / 32., 1. / 16., 1. / 8., 1. / 4.], has_extra_convs=False, norm_type=None, freeze_norm=False): self.freeze_norm = freeze_norm self.num_chan = num_chan self.min_level = min_level self.max_level = max_level self.spatial_scale = spatial_scale self.has_extra_convs = has_extra_convs self.norm_type = norm_type def _add_topdown_lateral(self, body_name, body_input, upper_output): lateral_name = 'fpn_inner_' + body_name + '_lateral' topdown_name = 'fpn_topdown_' + body_name fan = body_input.shape[1] if self.norm_type: initializer = Xavier(fan_out=fan) lateral = ConvNorm( body_input, self.num_chan, 1, initializer=initializer, norm_type=self.norm_type, freeze_norm=self.freeze_norm, name=lateral_name, norm_name=lateral_name) else: lateral = fluid.layers.conv2d( body_input, self.num_chan, 1, param_attr=ParamAttr( name=lateral_name + "_w", initializer=Xavier(fan_out=fan)), bias_attr=ParamAttr( name=lateral_name + "_b", learning_rate=2., regularizer=L2Decay(0.)), name=lateral_name) shape = fluid.layers.shape(upper_output) shape_hw = fluid.layers.slice(shape, axes=[0], starts=[2], ends=[4]) out_shape_ = shape_hw * 2 out_shape = fluid.layers.cast(out_shape_, dtype='int32') out_shape.stop_gradient = True topdown = fluid.layers.resize_nearest( upper_output, scale=2., actual_shape=out_shape, name=topdown_name) return lateral + topdown def get_output(self, body_dict): """ Add FPN onto backbone. Args: body_dict(OrderedDict): Dictionary of variables and each element is the output of backbone. Return: fpn_dict(OrderedDict): A dictionary represents the output of FPN with their name. spatial_scale(list): A list of multiplicative spatial scale factor. """ spatial_scale = copy.deepcopy(self.spatial_scale) body_name_list = list(body_dict.keys())[::-1] num_backbone_stages = len(body_name_list) self.fpn_inner_output = [[] for _ in range(num_backbone_stages)] fpn_inner_name = 'fpn_inner_' + body_name_list[0] body_input = body_dict[body_name_list[0]] fan = body_input.shape[1] if self.norm_type: initializer = Xavier(fan_out=fan) self.fpn_inner_output[0] = ConvNorm( body_input, self.num_chan, 1, initializer=initializer, norm_type=self.norm_type, freeze_norm=self.freeze_norm, name=fpn_inner_name, norm_name=fpn_inner_name) else: self.fpn_inner_output[0] = fluid.layers.conv2d( body_input, self.num_chan, 1, param_attr=ParamAttr( name=fpn_inner_name + "_w", initializer=Xavier(fan_out=fan)), bias_attr=ParamAttr( name=fpn_inner_name + "_b", learning_rate=2., regularizer=L2Decay(0.)), name=fpn_inner_name) for i in range(1, num_backbone_stages): body_name = body_name_list[i] body_input = body_dict[body_name] top_output = self.fpn_inner_output[i - 1] fpn_inner_single = self._add_topdown_lateral(body_name, body_input, top_output) self.fpn_inner_output[i] = fpn_inner_single fpn_dict = {} fpn_name_list = [] for i in range(num_backbone_stages): fpn_name = 'fpn_' + body_name_list[i] fan = self.fpn_inner_output[i].shape[1] * 3 * 3 if self.norm_type: initializer = Xavier(fan_out=fan) fpn_output = ConvNorm( self.fpn_inner_output[i], self.num_chan, 3, initializer=initializer, norm_type=self.norm_type, freeze_norm=self.freeze_norm, name=fpn_name, norm_name=fpn_name) else: fpn_output = fluid.layers.conv2d( self.fpn_inner_output[i], self.num_chan, filter_size=3, padding=1, param_attr=ParamAttr( name=fpn_name + "_w", initializer=Xavier(fan_out=fan)), bias_attr=ParamAttr( name=fpn_name + "_b", learning_rate=2., regularizer=L2Decay(0.)), name=fpn_name) fpn_dict[fpn_name] = fpn_output fpn_name_list.append(fpn_name) if not self.has_extra_convs and self.max_level - self.min_level == len( spatial_scale): body_top_name = fpn_name_list[0] body_top_extension = fluid.layers.pool2d( fpn_dict[body_top_name], 1, 'max', pool_stride=2, name=body_top_name + '_subsampled_2x') fpn_dict[body_top_name + '_subsampled_2x'] = body_top_extension fpn_name_list.insert(0, body_top_name + '_subsampled_2x') spatial_scale.insert(0, spatial_scale[0] * 0.5) # Coarser FPN levels introduced for RetinaNet highest_backbone_level = self.min_level + len(spatial_scale) - 1 if self.has_extra_convs and self.max_level > highest_backbone_level: fpn_blob = body_dict[body_name_list[0]] for i in range(highest_backbone_level + 1, self.max_level + 1): fpn_blob_in = fpn_blob fpn_name = 'fpn_' + str(i) if i > highest_backbone_level + 1: fpn_blob_in = fluid.layers.relu(fpn_blob) fan = fpn_blob_in.shape[1] * 3 * 3 fpn_blob = fluid.layers.conv2d( input=fpn_blob_in, num_filters=self.num_chan, filter_size=3, stride=2, padding=1, param_attr=ParamAttr( name=fpn_name + "_w", initializer=Xavier(fan_out=fan)), bias_attr=ParamAttr( name=fpn_name + "_b", learning_rate=2., regularizer=L2Decay(0.)), name=fpn_name) fpn_dict[fpn_name] = fpn_blob fpn_name_list.insert(0, fpn_name) spatial_scale.insert(0, spatial_scale[0] * 0.5) res_dict = OrderedDict([(k, fpn_dict[k]) for k in fpn_name_list]) return res_dict, spatial_scale