generate_proposals_op.cc

/* Copyright (c) 2018 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. */

#include <string>
#include <vector>
#include "paddle/fluid/framework/op_registry.h"
#include "paddle/fluid/operators/gather.h"
#include "paddle/fluid/operators/math/math_function.h"

namespace paddle {
namespace operators {

using Tensor = framework::Tensor;
using LoDTensor = framework::LoDTensor;

struct AppendProposalsFunctor {
  LoDTensor *out_;
  int64_t offset_;
  Tensor *to_add_;

  AppendProposalsFunctor(LoDTensor *out, int64_t offset, Tensor *to_add)
      : out_(out), offset_(offset), to_add_(to_add) {}

  template <typename T>
  void apply() const {
    auto *out_data = out_->data<T>();
    auto *to_add_data = to_add_->data<T>();
    memcpy(out_data + offset_, to_add_data, to_add_->numel() * sizeof(T));
  }
};

class GenerateProposalsOp : public framework::OperatorWithKernel {
 public:
  using framework::OperatorWithKernel::OperatorWithKernel;

  void InferShape(framework::InferShapeContext *ctx) const override {
    PADDLE_ENFORCE(ctx->HasInput("Scores"), "Input(Scores) shouldn't be null.");
    PADDLE_ENFORCE(ctx->HasInput("BboxDeltas"),
                   "Input(BboxDeltas) shouldn't be null.");
    PADDLE_ENFORCE(ctx->HasInput("ImInfo"), "Input(ImInfo) shouldn't be null.");
    PADDLE_ENFORCE(ctx->HasInput("Anchors"),
                   "Input(Anchors) shouldn't be null.");
    PADDLE_ENFORCE(ctx->HasInput("Variances"),
                   "Input(Variances) shouldn't be null.");

    auto scores_dims = ctx->GetInputDim("Scores");
    auto bbox_deltas_dims = ctx->GetInputDim("BboxDeltas");
    auto im_info_dims = ctx->GetInputDim("ImInfo");
    auto anchors_dims = ctx->GetInputDim("Anchors");
    auto variances_dims = ctx->GetInputDim("Variances");

    ctx->SetOutputDim("RpnRois", {-1, 4});
    ctx->SetOutputDim("RpnRoiProbs", {-1, 1});
  }

 protected:
  framework::OpKernelType GetExpectedKernelType(
      const framework::ExecutionContext &ctx) const override {
    return framework::OpKernelType(
        framework::ToDataType(ctx.Input<Tensor>("Anchors")->type()),
        platform::CPUPlace());
  }
};

template <class T>
void BoxCoder(const platform::DeviceContext &ctx, Tensor *all_anchors,
              Tensor *bbox_deltas, Tensor *variances, Tensor *proposals) {
  T *proposals_data = proposals->mutable_data<T>(ctx.GetPlace());

  int64_t row = all_anchors->dims()[0];
  int64_t len = all_anchors->dims()[1];

  auto *bbox_deltas_data = bbox_deltas->data<T>();
  auto *anchor_data = all_anchors->data<T>();
  const T *variances_data = nullptr;
  if (variances) {
    variances_data = variances->data<T>();
  }

  for (int64_t i = 0; i < row; ++i) {
    T anchor_width = anchor_data[i * len + 2] - anchor_data[i * len];
    T anchor_height = anchor_data[i * len + 3] - anchor_data[i * len + 1];

    T anchor_center_x = (anchor_data[i * len + 2] + anchor_data[i * len]) / 2;
    T anchor_center_y =
        (anchor_data[i * len + 3] + anchor_data[i * len + 1]) / 2;

    T bbox_center_x = 0, bbox_center_y = 0;
    T bbox_width = 0, bbox_height = 0;

    if (variances) {
      bbox_center_x =
          variances_data[i * len] * bbox_deltas_data[i * len] * anchor_width +
          anchor_center_x;
      bbox_center_y = variances_data[i * len + 1] *
                          bbox_deltas_data[i * len + 1] * anchor_height +
                      anchor_center_y;
      bbox_width = std::exp(variances_data[i * len + 2] *
                            bbox_deltas_data[i * len + 2]) *
                   anchor_width;
      bbox_height = std::exp(variances_data[i * len + 3] *
                             bbox_deltas_data[i * len + 3]) *
                    anchor_height;
    } else {
      bbox_center_x =
          bbox_deltas_data[i * len] * anchor_width + anchor_center_x;
      bbox_center_y =
          bbox_deltas_data[i * len + 1] * anchor_height + anchor_center_y;
      bbox_width = std::exp(bbox_deltas_data[i * len + 2]) * anchor_width;
      bbox_height = std::exp(bbox_deltas_data[i * len + 3]) * anchor_height;
    }

    proposals_data[i * len] = bbox_center_x - bbox_width / 2;
    proposals_data[i * len + 1] = bbox_center_y - bbox_height / 2;
    proposals_data[i * len + 2] = bbox_center_x + bbox_width / 2;
    proposals_data[i * len + 3] = bbox_center_y + bbox_height / 2;
  }
  // return proposals;
}

template <class T>
void ClipTiledBoxes(const platform::DeviceContext &ctx, const Tensor &im_info,
                    Tensor *boxes) {
  T *boxes_data = boxes->mutable_data<T>(ctx.GetPlace());
  const T *im_info_data = im_info.data<T>();
  for (int64_t i = 0; i < boxes->numel(); ++i) {
    if (i % 4 == 0) {
      boxes_data[i] =
          std::max(std::min(boxes_data[i], im_info_data[1] - 1), 0.0f);
    } else if (i % 4 == 1) {
      boxes_data[i] =
          std::max(std::min(boxes_data[i], im_info_data[0] - 1), 0.0f);
    } else if (i % 4 == 2) {
      boxes_data[i] =
          std::max(std::min(boxes_data[i], im_info_data[1] - 1), 0.0f);
    } else {
      boxes_data[i] =
          std::max(std::min(boxes_data[i], im_info_data[0] - 1), 0.0f);
    }
  }
}

template <class T>
void FilterBoxes(const platform::DeviceContext &ctx, Tensor *boxes,
                 float min_size, const Tensor &im_info, Tensor *keep) {
  const T *im_info_data = im_info.data<T>();
  T *boxes_data = boxes->mutable_data<T>(ctx.GetPlace());
  min_size *= im_info_data[2];
  keep->Resize({boxes->dims()[0], 1});
  int *keep_data = keep->mutable_data<int>(ctx.GetPlace());

  int keep_len = 0;
  for (int i = 0; i < boxes->dims()[0]; ++i) {
    T ws = boxes_data[4 * i + 2] - boxes_data[4 * i] + 1;
    T hs = boxes_data[4 * i + 3] - boxes_data[4 * i + 1] + 1;
    T x_ctr = boxes_data[4 * i] + ws / 2;
    T y_ctr = boxes_data[4 * i + 1] + hs / 2;
    if (ws >= min_size && hs >= min_size && x_ctr <= im_info_data[1] &&
        y_ctr <= im_info_data[0]) {
      keep_data[keep_len++] = i;
    }
  }
  keep->Resize({keep_len});
}

bool SortScorePairDescend(const std::pair<float, int> &pair1,
                          const std::pair<float, int> &pair2) {
  return pair1.first > pair2.first;
}

template <class T>
void GetMaxScoreIndex(const std::vector<T> &scores,
                      std::vector<std::pair<T, int>> *sorted_indices) {
  for (size_t i = 0; i < scores.size(); ++i) {
    sorted_indices->push_back(std::make_pair(scores[i], i));
  }
  // Sort the score pair according to the scores in descending order
  std::stable_sort(sorted_indices->begin(), sorted_indices->end(),
                   SortScorePairDescend);
}

template <class T>
T BBoxArea(const T *box, const bool normalized) {
  if (box[2] < box[0] || box[3] < box[1]) {
    // If coordinate values are is invalid
    // (e.g. xmax < xmin or ymax < ymin), return 0.
    return static_cast<T>(0.);
  } else {
    const T w = box[2] - box[0];
    const T h = box[3] - box[1];
    if (normalized) {
      return w * h;
    } else {
      // If coordinate values are not within range [0, 1].
      return (w + 1) * (h + 1);
    }
  }
}

template <class T>
T JaccardOverlap(const T *box1, const T *box2, const bool normalized) {
  if (box2[0] > box1[2] || box2[2] < box1[0] || box2[1] > box1[3] ||
      box2[3] < box1[1]) {
    return static_cast<T>(0.);
  } else {
    const T inter_xmin = std::max(box1[0], box2[0]);
    const T inter_ymin = std::max(box1[1], box2[1]);
    const T inter_xmax = std::min(box1[2], box2[2]);
    const T inter_ymax = std::min(box1[3], box2[3]);
    const T inter_w = inter_xmax - inter_xmin;
    const T inter_h = inter_ymax - inter_ymin;
    const T inter_area = inter_w * inter_h;
    const T bbox1_area = BBoxArea<T>(box1, normalized);
    const T bbox2_area = BBoxArea<T>(box2, normalized);
    return inter_area / (bbox1_area + bbox2_area - inter_area);
  }
}

template <class T>
Tensor NMS(const platform::DeviceContext &ctx, Tensor *bbox, Tensor *scores,
           const T nms_threshold, const float eta) {
  PADDLE_ENFORCE_NOT_NULL(bbox);
  int64_t num_boxes = bbox->dims()[0];
  // 4: [xmin ymin xmax ymax]
  int64_t box_size = bbox->dims()[1];

  std::vector<T> scores_data(num_boxes);
  std::copy_n(scores->data<T>(), num_boxes, scores_data.begin());
  std::vector<std::pair<T, int>> sorted_indices;
  GetMaxScoreIndex<T>(scores_data, &sorted_indices);

  std::vector<int> selected_indices;
  int selected_num = 0;
  T adaptive_threshold = nms_threshold;
  const T *bbox_data = bbox->data<T>();
  bool flag;
  while (sorted_indices.size() != 0) {
    int idx = sorted_indices.front().second;
    flag = true;
    for (size_t k = 0; k < selected_indices.size(); ++k) {
      if (flag) {
        const int kept_idx = selected_indices[k];
        T overlap = JaccardOverlap<T>(bbox_data + idx * box_size,
                                      bbox_data + kept_idx * box_size, false);
        flag = (overlap <= adaptive_threshold);
      } else {
        break;
      }
    }
    if (flag) {
      selected_indices.push_back(idx);
      selected_num++;
    }
    sorted_indices.erase(sorted_indices.begin());
    if (flag && eta < 1 && adaptive_threshold > 0.5) {
      adaptive_threshold *= eta;
    }
  }
  Tensor keep_nms;
  keep_nms.Resize({selected_num});
  int *keep_data = keep_nms.mutable_data<int>(ctx.GetPlace());
  for (int i = 0; i < selected_num; ++i) {
    keep_data[i] = selected_indices[i];
  }

  return keep_nms;
}

template <typename DeviceContext, typename T>
class GenerateProposalsKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext &context) const override {
    auto *scores = context.Input<Tensor>("Scores");
    auto *bbox_deltas = context.Input<Tensor>("BboxDeltas");
    auto *im_info = context.Input<Tensor>("ImInfo");
    auto *anchors = context.Input<Tensor>("Anchors");
    auto *variances = context.Input<Tensor>("Variances");

    auto *rpn_rois = context.Output<LoDTensor>("RpnRois");
    auto *rpn_roi_probs = context.Output<LoDTensor>("RpnRoiProbs");

    int pre_nms_top_n = context.Attr<int>("pre_nms_topN");
    int post_nms_top_n = context.Attr<int>("post_nms_topN");
    float nms_thresh = context.Attr<float>("nms_thresh");
    float min_size = context.Attr<float>("min_size");
    float eta = context.Attr<float>("eta");

    auto &dev_ctx = context.template device_context<DeviceContext>();

    auto scores_dim = scores->dims();
    int64_t num = scores_dim[0];
    int64_t c_score = scores_dim[1];
    int64_t h_score = scores_dim[2];
    int64_t w_score = scores_dim[3];

    auto bbox_dim = bbox_deltas->dims();
    int64_t c_bbox = bbox_dim[1];
    int64_t h_bbox = bbox_dim[2];
    int64_t w_bbox = bbox_dim[3];

    rpn_rois->mutable_data<T>({bbox_deltas->numel() / 4, 4},
                              context.GetPlace());
    rpn_roi_probs->mutable_data<T>({scores->numel(), 1}, context.GetPlace());

    Tensor bbox_deltas_swap, scores_swap;
    bbox_deltas_swap.mutable_data<T>({num, h_bbox, w_bbox, c_bbox},
                                     dev_ctx.GetPlace());
    scores_swap.mutable_data<T>({num, h_score, w_score, c_score},
                                dev_ctx.GetPlace());

    math::Transpose<DeviceContext, T, 4> trans;
    std::vector<int> axis = {0, 2, 3, 1};
    trans(dev_ctx, *bbox_deltas, &bbox_deltas_swap, axis);
    trans(dev_ctx, *scores, &scores_swap, axis);

    framework::LoD lod;
    std::vector<size_t> lod0(1, 0);
    Tensor *anchor = const_cast<framework::Tensor *>(anchors);
    anchor->Resize({anchors->numel() / 4, 4});
    Tensor *var = const_cast<framework::Tensor *>(variances);
    var->Resize({var->numel() / 4, 4});

    int64_t num_proposals = 0;
    for (int64_t i = 0; i < num; ++i) {
      Tensor im_info_slice = im_info->Slice(i, i + 1);
      Tensor bbox_deltas_slice = bbox_deltas_swap.Slice(i, i + 1);
      Tensor scores_slice = scores_swap.Slice(i, i + 1);

      bbox_deltas_slice.Resize({h_bbox * w_bbox * c_bbox / 4, 4});
      scores_slice.Resize({h_score * w_score * c_score, 1});

      std::pair<Tensor, Tensor> tensor_pair =
          ProposalForOneImage(dev_ctx, im_info_slice, *anchor, *var,
                              bbox_deltas_slice, scores_slice, pre_nms_top_n,
                              post_nms_top_n, nms_thresh, min_size, eta);
      Tensor proposals = tensor_pair.first;
      Tensor scores = tensor_pair.second;

      framework::VisitDataType(
          framework::ToDataType(rpn_rois->type()),
          AppendProposalsFunctor(rpn_rois, 4 * num_proposals, &proposals));
      framework::VisitDataType(
          framework::ToDataType(rpn_roi_probs->type()),
          AppendProposalsFunctor(rpn_roi_probs, num_proposals, &scores));

      num_proposals += proposals.dims()[0];
      lod0.emplace_back(num_proposals);
    }

    lod.emplace_back(lod0);
    rpn_rois->set_lod(lod);
    rpn_roi_probs->set_lod(lod);
    rpn_rois->Resize({num_proposals, 4});
    rpn_roi_probs->Resize({num_proposals, 1});
  }

  std::pair<Tensor, Tensor> ProposalForOneImage(
      const DeviceContext &ctx, const Tensor &im_info_slice,
      const Tensor &anchors, const Tensor &variances,
      const Tensor &bbox_deltas_slice,  // [M, 4]
      const Tensor &scores_slice,       // [N, 1]
      int pre_nms_top_n, int post_nms_top_n, float nms_thresh, float min_size,
      float eta) const {
    auto *scores_data = scores_slice.data<T>();

    // Sort index
    Tensor index_t;
    index_t.Resize({scores_slice.numel()});
    int *index = index_t.mutable_data<int>(ctx.GetPlace());
    for (int i = 0; i < scores_slice.numel(); ++i) {
      index[i] = i;
    }
    std::function<bool(const int64_t &, const int64_t &)> compare =
        [scores_data](const int64_t &i, const int64_t &j) {
          return scores_data[i] > scores_data[j];
        };

    if (pre_nms_top_n <= 0 || pre_nms_top_n >= scores_slice.numel()) {
      std::sort(index, index + scores_slice.numel(), compare);
    } else {
      std::nth_element(index, index + pre_nms_top_n,
                       index + scores_slice.numel(), compare);
      index_t.Resize({pre_nms_top_n});
    }

    Tensor scores_sel, bbox_sel, anchor_sel, var_sel;
    scores_sel.mutable_data<T>({index_t.numel(), 1}, ctx.GetPlace());
    bbox_sel.mutable_data<T>({index_t.numel(), 4}, ctx.GetPlace());
    anchor_sel.mutable_data<T>({index_t.numel(), 4}, ctx.GetPlace());
    var_sel.mutable_data<T>({index_t.numel(), 4}, ctx.GetPlace());

    CPUGather<T>(ctx, scores_slice, index_t, &scores_sel);
    CPUGather<T>(ctx, bbox_deltas_slice, index_t, &bbox_sel);
    CPUGather<T>(ctx, anchors, index_t, &anchor_sel);
    CPUGather<T>(ctx, variances, index_t, &var_sel);

    Tensor proposals;
    proposals.mutable_data<T>({index_t.numel(), 4}, ctx.GetPlace());
    BoxCoder<T>(ctx, &anchor_sel, &bbox_sel, &var_sel, &proposals);

    ClipTiledBoxes<T>(ctx, im_info_slice, &proposals);

    Tensor keep;
    FilterBoxes<T>(ctx, &proposals, min_size, im_info_slice, &keep);

    Tensor scores_filter;
    bbox_sel.mutable_data<T>({keep.numel(), 4}, ctx.GetPlace());
    scores_filter.mutable_data<T>({keep.numel(), 1}, ctx.GetPlace());
    CPUGather<T>(ctx, proposals, keep, &bbox_sel);
    CPUGather<T>(ctx, scores_sel, keep, &scores_filter);
    if (nms_thresh <= 0) {
      return std::make_pair(bbox_sel, scores_filter);
    }

    Tensor keep_nms = NMS<T>(ctx, &bbox_sel, &scores_filter, nms_thresh, eta);

    if (post_nms_top_n > 0 && post_nms_top_n < keep_nms.numel()) {
      keep_nms.Resize({post_nms_top_n});
    }

    proposals.mutable_data<T>({keep_nms.numel(), 4}, ctx.GetPlace());
    scores_sel.mutable_data<T>({keep_nms.numel(), 1}, ctx.GetPlace());
    CPUGather<T>(ctx, bbox_sel, keep_nms, &proposals);
    CPUGather<T>(ctx, scores_filter, keep_nms, &scores_sel);

    return std::make_pair(proposals, scores_sel);
  }
};

class GenerateProposalsOpMaker : public framework::OpProtoAndCheckerMaker {
 public:
  void Make() override {
    AddInput("Scores", "The scores of anchors should be foreground.");
    AddInput("BboxDeltas", "bbox_deltas.");
    AddInput("ImInfo", "Information for image reshape.");
    AddInput("Anchors", "All anchors.");
    AddInput("Variances", " variances");

    AddOutput("RpnRois", "Anchors.");
    AddOutput("RpnRoiProbs", "Anchors.");
    AddAttr<int>("pre_nms_topN", "pre_nms_topN");
    AddAttr<int>("post_nms_topN", "post_nms_topN");
    AddAttr<float>("nms_thresh", "nms_thres");
    AddAttr<float>("min_size", "min size");
    AddAttr<float>("eta", "eta");
    AddComment(R"DOC(
Generate Proposals OP

This operator proposes rois according to each box with their probability to be a foreground object and 
the box can be calculated by anchors. Bbox_deltais and scores are the output of RPN. Final proposals
could be used to train detection net.

Scores is the probability for each box to be an object. In format of (N, A, H, W) where N is batch size, A is number
of anchors, H and W are height and width of the feature map.
BboxDeltas is the differece between predicted box locatoin and anchor location. In format of (N, 4*A, H, W)

For generating proposals, this operator transposes and resizes scores and bbox_deltas in size of (H*W*A, 1) and (H*W*A, 4) and 
 calculate box locations as proposals candidates. Then clip boxes to image and remove predicted boxes with small area. 
Finally, apply nms to get final proposals as output.
)DOC");
  }
};

}  // namespace operators
}  // namespace paddle

namespace ops = paddle::operators;
REGISTER_OPERATOR(generate_proposals, ops::GenerateProposalsOp,
                  ops::GenerateProposalsOpMaker,
                  paddle::framework::EmptyGradOpMaker);
REGISTER_OP_CPU_KERNEL(
    generate_proposals,
    ops::GenerateProposalsKernel<paddle::platform::CPUDeviceContext, float>);