bbox_head.py

# 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

from paddle import fluid
from paddle.fluid.param_attr import ParamAttr
from paddle.fluid.initializer import Normal, Xavier
from paddle.fluid.regularizer import L2Decay

from ppdet.modeling.ops import MultiClassNMS
from ppdet.core.workspace import register, serializable

__all__ = ['BBoxHead', 'TwoFCHead']


@register
@serializable
class BoxCoder(object):
    __op__ = fluid.layers.box_coder
    __append_doc__ = True

    def __init__(self,
                 prior_box_var=[0.1, 0.1, 0.2, 0.2],
                 code_type='decode_center_size',
                 box_normalized=False,
                 axis=1):
        super(BoxCoder, self).__init__()
        self.prior_box_var = prior_box_var
        self.code_type = code_type
        self.box_normalized = box_normalized
        self.axis = axis


@register
class TwoFCHead(object):
    """
    RCNN head with two Fully Connected layers

    Args:
        num_chan (int): num of filters for the fc layers
    """

    def __init__(self, num_chan=1024):
        super(TwoFCHead, self).__init__()
        self.num_chan = num_chan

    def __call__(self, roi_feat):
        fan = roi_feat.shape[1] * roi_feat.shape[2] * roi_feat.shape[3]
        fc6 = fluid.layers.fc(input=roi_feat,
                              size=self.num_chan,
                              act='relu',
                              name='fc6',
                              param_attr=ParamAttr(
                                  name='fc6_w',
                                  initializer=Xavier(fan_out=fan)),
                              bias_attr=ParamAttr(
                                  name='fc6_b',
                                  learning_rate=2.,
                                  regularizer=L2Decay(0.)))
        head_feat = fluid.layers.fc(input=fc6,
                                    size=self.num_chan,
                                    act='relu',
                                    name='fc7',
                                    param_attr=ParamAttr(
                                        name='fc7_w', initializer=Xavier()),
                                    bias_attr=ParamAttr(
                                        name='fc7_b',
                                        learning_rate=2.,
                                        regularizer=L2Decay(0.)))
        return head_feat


@register
class BBoxHead(object):
    """
    RCNN bbox head

    Args:
        head (object): the head module instance, e.g., `ResNetC5` or `TwoFCHead`
        box_coder (object): `BoxCoder` instance
        nms (object): `MultiClassNMS` instance
        num_classes: number of output classes
    """
    __inject__ = ['head', 'box_coder', 'nms']

    def __init__(self,
                 head,
                 box_coder=BoxCoder().__dict__,
                 nms=MultiClassNMS().__dict__,
                 num_classes=81):
        super(BBoxHead, self).__init__()
        self.head = head
        self.num_classes = num_classes
        self.box_coder = box_coder
        self.nms = nms
        if isinstance(box_coder, dict):
            self.box_coder = BoxCoder(**box_coder)
        if isinstance(nms, dict):
            self.nms = MultiClassNMS(**nms)
        self.head_feat = None

    def get_head_feat(self, input=None):
        """
        Get the bbox head feature map.
        """

        if input is not None:
            feat = self.head(input)
            if isinstance(feat, OrderedDict):
                feat = list(feat.values())[0]
            self.head_feat = feat
        return self.head_feat

    def _get_output(self, roi_feat):
        """
        Get bbox head output.

        Args:
            roi_feat (Variable): RoI feature from RoIExtractor.

        Returns:
            cls_score(Variable): Output of rpn head with shape of
                [N, num_anchors, H, W].
            bbox_pred(Variable): Output of rpn head with shape of
                [N, num_anchors * 4, H, W].
        """
        head_feat = self.get_head_feat(roi_feat)
        # when ResNetC5 output a single feature map
        if not isinstance(self.head, TwoFCHead):
            head_feat = fluid.layers.pool2d(
                head_feat, pool_type='avg', global_pooling=True)
        cls_score = fluid.layers.fc(input=head_feat,
                                    size=self.num_classes,
                                    act=None,
                                    name='cls_score',
                                    param_attr=ParamAttr(
                                        name='cls_score_w',
                                        initializer=Normal(
                                            loc=0.0, scale=0.01)),
                                    bias_attr=ParamAttr(
                                        name='cls_score_b',
                                        learning_rate=2.,
                                        regularizer=L2Decay(0.)))
        bbox_pred = fluid.layers.fc(input=head_feat,
                                    size=4 * self.num_classes,
                                    act=None,
                                    name='bbox_pred',
                                    param_attr=ParamAttr(
                                        name='bbox_pred_w',
                                        initializer=Normal(
                                            loc=0.0, scale=0.001)),
                                    bias_attr=ParamAttr(
                                        name='bbox_pred_b',
                                        learning_rate=2.,
                                        regularizer=L2Decay(0.)))
        return cls_score, bbox_pred

    def get_loss(self, roi_feat, labels_int32, bbox_targets,
                 bbox_inside_weights, bbox_outside_weights):
        """
        Get bbox_head loss.

        Args:
            roi_feat (Variable): RoI feature from RoIExtractor.
            labels_int32(Variable): Class label of a RoI with shape [P, 1].
                P is the number of RoI.
            bbox_targets(Variable): Box label of a RoI with shape
                [P, 4 * class_nums].
            bbox_inside_weights(Variable): Indicates whether a box should
                contribute to loss. Same shape as bbox_targets.
            bbox_outside_weights(Variable): Indicates whether a box should
                contribute to loss. Same shape as bbox_targets.

        Return:
            Type: Dict
                loss_cls(Variable): bbox_head loss.
                loss_bbox(Variable): bbox_head loss.
        """

        cls_score, bbox_pred = self._get_output(roi_feat)

        labels_int64 = fluid.layers.cast(x=labels_int32, dtype='int64')
        labels_int64.stop_gradient = True
        loss_cls = fluid.layers.softmax_with_cross_entropy(
            logits=cls_score, label=labels_int64, numeric_stable_mode=True)
        loss_cls = fluid.layers.reduce_mean(loss_cls)
        loss_bbox = fluid.layers.smooth_l1(
            x=bbox_pred,
            y=bbox_targets,
            inside_weight=bbox_inside_weights,
            outside_weight=bbox_outside_weights,
            sigma=1.0)
        loss_bbox = fluid.layers.reduce_mean(loss_bbox)
        return {'loss_cls': loss_cls, 'loss_bbox': loss_bbox}

    def get_prediction(self, roi_feat, rois, im_info, im_shape):
        """
        Get prediction bounding box in test stage.

        Args:
            rois (Variable): Output of generate_proposals in rpn head.
            im_info (Variable): A 2-D LoDTensor with shape [B, 3]. B is the
                number of input images, each element consists of im_height,
                im_width, im_scale.
            cls_score (Variable), bbox_pred(Variable): Output of get_output.

        Returns:
            pred_result(Variable): Prediction result with shape [N, 6]. Each
                row has 6 values: [label, confidence, xmin, ymin, xmax, ymax].
                N is the total number of prediction.
        """
        cls_score, bbox_pred = self._get_output(roi_feat)

        im_scale = fluid.layers.slice(im_info, [1], starts=[2], ends=[3])
        im_scale = fluid.layers.sequence_expand(im_scale, rois)
        boxes = rois / im_scale
        cls_prob = fluid.layers.softmax(cls_score, use_cudnn=False)
        bbox_pred = fluid.layers.reshape(bbox_pred, (-1, self.num_classes, 4))
        decoded_box = self.box_coder(prior_box=boxes, target_box=bbox_pred)
        cliped_box = fluid.layers.box_clip(input=decoded_box, im_info=im_shape)
        pred_result = self.nms(bboxes=cliped_box, scores=cls_prob)
        return {'bbox': pred_result}