src/operator/contrib/proposal.cc

/*!
 * Copyright (c) 2015 by Contributors
 * \file proposal.cc
 * \brief
 * \author Piotr Teterwak, Bing Xu, Jian Guo
*/

#include "./proposal-inl.h"

//============================
// Bounding Box Transform Utils
//============================
namespace mxnet {
namespace op {
namespace utils {

// bbox prediction and clip to the image borders
inline void BBoxTransformInv(const mshadow::Tensor<cpu, 2>& boxes,
                             const mshadow::Tensor<cpu, 4>& deltas,
                             const float im_height,
                             const float im_width,
                             const int real_height,
                             const int real_width,
                             mshadow::Tensor<cpu, 2> *out_pred_boxes) {
  CHECK_GE(boxes.size(1), 4);
  CHECK_GE(out_pred_boxes->size(1), 4);
  int anchors = deltas.size(1)/4;
  int heights = deltas.size(2);
  int widths = deltas.size(3);

  for (int a = 0; a < anchors; ++a) {
    for (int h = 0; h < heights; ++h) {
      for (int w = 0; w < widths; ++w) {
        index_t index = h * (widths * anchors) + w * (anchors) + a;
        float width = boxes[index][2] - boxes[index][0] + 1.0;
        float height = boxes[index][3] - boxes[index][1] + 1.0;
        float ctr_x = boxes[index][0] + 0.5 * (width - 1.0);
        float ctr_y = boxes[index][1] + 0.5 * (height - 1.0);

        float dx = deltas[0][a*4 + 0][h][w];
        float dy = deltas[0][a*4 + 1][h][w];
        float dw = deltas[0][a*4 + 2][h][w];
        float dh = deltas[0][a*4 + 3][h][w];

        float pred_ctr_x = dx * width + ctr_x;
        float pred_ctr_y = dy * height + ctr_y;
        float pred_w = exp(dw) * width;
        float pred_h = exp(dh) * height;

        float pred_x1 = pred_ctr_x - 0.5 * (pred_w - 1.0);
        float pred_y1 = pred_ctr_y - 0.5 * (pred_h - 1.0);
        float pred_x2 = pred_ctr_x + 0.5 * (pred_w - 1.0);
        float pred_y2 = pred_ctr_y + 0.5 * (pred_h - 1.0);

        pred_x1 = std::max(std::min(pred_x1, im_width - 1.0f), 0.0f);
        pred_y1 = std::max(std::min(pred_y1, im_height - 1.0f), 0.0f);
        pred_x2 = std::max(std::min(pred_x2, im_width - 1.0f), 0.0f);
        pred_y2 = std::max(std::min(pred_y2, im_height - 1.0f), 0.0f);

        (*out_pred_boxes)[index][0] = pred_x1;
        (*out_pred_boxes)[index][1] = pred_y1;
        (*out_pred_boxes)[index][2] = pred_x2;
        (*out_pred_boxes)[index][3] = pred_y2;

        if (h >= real_height || w >= real_width) {
          (*out_pred_boxes)[index][4] = -1.0;
        }
      }
    }
  }
}

// iou prediction and clip to the image border
inline void IoUTransformInv(const mshadow::Tensor<cpu, 2>& boxes,
                            const mshadow::Tensor<cpu, 4>& deltas,
                            const float im_height,
                            const float im_width,
                            const int real_height,
                            const int real_width,
                            mshadow::Tensor<cpu, 2> *out_pred_boxes) {
  CHECK_GE(boxes.size(1), 4);
  CHECK_GE(out_pred_boxes->size(1), 4);
  int anchors = deltas.size(1)/4;
  int heights = deltas.size(2);
  int widths = deltas.size(3);

  for (int a = 0; a < anchors; ++a) {
    for (int h = 0; h < heights; ++h) {
      for (int w = 0; w < widths; ++w) {
        index_t index = h * (widths * anchors) + w * (anchors) + a;
        float x1 = boxes[index][0];
        float y1 = boxes[index][1];
        float x2 = boxes[index][2];
        float y2 = boxes[index][3];

        float dx1 = deltas[0][a * 4 + 0][h][w];
        float dy1 = deltas[0][a * 4 + 1][h][w];
        float dx2 = deltas[0][a * 4 + 2][h][w];
        float dy2 = deltas[0][a * 4 + 3][h][w];

        float pred_x1 = x1 + dx1;
        float pred_y1 = y1 + dy1;
        float pred_x2 = x2 + dx2;
        float pred_y2 = y2 + dy2;

        pred_x1 = std::max(std::min(pred_x1, im_width - 1.0f), 0.0f);
        pred_y1 = std::max(std::min(pred_y1, im_height - 1.0f), 0.0f);
        pred_x2 = std::max(std::min(pred_x2, im_width - 1.0f), 0.0f);
        pred_y2 = std::max(std::min(pred_y2, im_height - 1.0f), 0.0f);

        (*out_pred_boxes)[index][0] = pred_x1;
        (*out_pred_boxes)[index][1] = pred_y1;
        (*out_pred_boxes)[index][2] = pred_x2;
        (*out_pred_boxes)[index][3] = pred_y2;

        if (h >= real_height || w >= real_width) {
          (*out_pred_boxes)[index][4] = -1.0f;
        }
      }
    }
  }
}

// filter box by set confidence to zero
// * height or width < rpn_min_size
inline void FilterBox(mshadow::Tensor<cpu, 2> *dets,
                      const float min_size) {
  for (index_t i = 0; i < dets->size(0); i++) {
    float iw = (*dets)[i][2] - (*dets)[i][0] + 1.0f;
    float ih = (*dets)[i][3] - (*dets)[i][1] + 1.0f;
    if (iw < min_size || ih < min_size) {
      (*dets)[i][0] -= min_size / 2;
      (*dets)[i][1] -= min_size / 2;
      (*dets)[i][2] += min_size / 2;
      (*dets)[i][3] += min_size / 2;
      (*dets)[i][4] = -1.0f;
    }
  }
}

}  // namespace utils
}  // namespace op
}  // namespace mxnet

//=====================
// NMS Utils
//=====================
namespace mxnet {
namespace op {
namespace utils {

struct ReverseArgsortCompl {
  const float *val_;
  explicit ReverseArgsortCompl(float *val)
    : val_(val) {}
  bool operator() (float i, float j) {
    return (val_[static_cast<index_t>(i)] >
            val_[static_cast<index_t>(j)]);
  }
};

// copy score and init order
inline void CopyScore(const mshadow::Tensor<cpu, 2>& dets,
                      mshadow::Tensor<cpu, 1> *score,
                      mshadow::Tensor<cpu, 1> *order) {
  for (index_t i = 0; i < dets.size(0); i++) {
    (*score)[i] = dets[i][4];
    (*order)[i] = i;
  }
}

// sort order array according to score
inline void ReverseArgsort(const mshadow::Tensor<cpu, 1>& score,
                           mshadow::Tensor<cpu, 1> *order) {
  ReverseArgsortCompl cmpl(score.dptr_);
  std::sort(order->dptr_, order->dptr_ + score.size(0), cmpl);
}

// reorder proposals according to order and keep the pre_nms_top_n proposals
// dets.size(0) == pre_nms_top_n
inline void ReorderProposals(const mshadow::Tensor<cpu, 2>& prev_dets,
                             const mshadow::Tensor<cpu, 1>& order,
                             const index_t pre_nms_top_n,
                             mshadow::Tensor<cpu, 2> *dets) {
  CHECK_EQ(dets->size(0), pre_nms_top_n);
  for (index_t i = 0; i < dets->size(0); i++) {
    const index_t index = order[i];
    for (index_t j = 0; j < dets->size(1); j++) {
      (*dets)[i][j] = prev_dets[index][j];
    }
  }
}

// greedily keep the max detections (already sorted)
inline void NonMaximumSuppression(const mshadow::Tensor<cpu, 2>& dets,
                                  const float thresh,
                                  const index_t post_nms_top_n,
                                  mshadow::Tensor<cpu, 1> *area,
                                  mshadow::Tensor<cpu, 1> *suppressed,
                                  mshadow::Tensor<cpu, 1> *keep,
                                  index_t *out_size) {
  CHECK_EQ(dets.shape_[1], 5) << "dets: [x1, y1, x2, y2, score]";
  CHECK_GT(dets.shape_[0], 0);
  CHECK_EQ(dets.CheckContiguous(), true);
  CHECK_EQ(area->CheckContiguous(), true);
  CHECK_EQ(suppressed->CheckContiguous(), true);
  CHECK_EQ(keep->CheckContiguous(), true);
  // calculate area
  for (index_t i = 0; i < dets.size(0); ++i) {
    (*area)[i] = (dets[i][2] - dets[i][0] + 1) *
                 (dets[i][3] - dets[i][1] + 1);
  }

  // calculate nms
  *out_size = 0;
  for (index_t i = 0; i < dets.size(0) && (*out_size) < post_nms_top_n; ++i) {
    float ix1 = dets[i][0];
    float iy1 = dets[i][1];
    float ix2 = dets[i][2];
    float iy2 = dets[i][3];
    float iarea = (*area)[i];

    if ((*suppressed)[i] > 0.0f) {
      continue;
    }

    (*keep)[(*out_size)++] = i;
    for (index_t j = i + 1; j < dets.size(0); j ++) {
      if ((*suppressed)[j] > 0.0f) {
        continue;
      }
      float xx1 = std::max(ix1, dets[j][0]);
      float yy1 = std::max(iy1, dets[j][1]);
      float xx2 = std::min(ix2, dets[j][2]);
      float yy2 = std::min(iy2, dets[j][3]);
      float w = std::max(0.0f, xx2 - xx1 + 1.0f);
      float h = std::max(0.0f, yy2 - yy1 + 1.0f);
      float inter = w * h;
      float ovr = inter / (iarea + (*area)[j] - inter);
      if (ovr > thresh) {
        (*suppressed)[j] = 1.0f;
      }
    }
  }
}

}  // namespace utils
}  // namespace op
}  // namespace mxnet


namespace mxnet {
namespace op {

template<typename xpu>
class ProposalOp : public Operator{
 public:
  explicit ProposalOp(ProposalParam param) {
    this->param_ = param;
  }

  virtual void Forward(const OpContext &ctx,
                       const std::vector<TBlob> &in_data,
                       const std::vector<OpReqType> &req,
                       const std::vector<TBlob> &out_data,
                       const std::vector<TBlob> &aux_states) {
    using namespace mshadow;
    using namespace mshadow::expr;
    CHECK_EQ(in_data.size(), 3);
    CHECK_EQ(out_data.size(), 2);
    CHECK_GT(req.size(), 1);
    CHECK_EQ(req[proposal::kOut], kWriteTo);
    CHECK_EQ(in_data[proposal::kClsProb].shape_[0], 1)
      << "Sorry, multiple images each device is not implemented.";

    Stream<xpu> *s = ctx.get_stream<xpu>();

    Shape<4> scores_shape = Shape4(in_data[proposal::kClsProb].shape_[0],
                                   in_data[proposal::kClsProb].shape_[1] / 2,
                                   in_data[proposal::kClsProb].shape_[2],
                                   in_data[proposal::kClsProb].shape_[3]);
    real_t* foreground_score_ptr = in_data[proposal::kClsProb].dptr<real_t>()
                                    + scores_shape.Size();
    Tensor<cpu, 4> scores = Tensor<cpu, 4>(foreground_score_ptr, scores_shape);
    Tensor<cpu, 4> bbox_deltas = in_data[proposal::kBBoxPred].get<cpu, 4, real_t>(s);
    Tensor<cpu, 2> im_info = in_data[proposal::kImInfo].get<cpu, 2, real_t>(s);

    Tensor<cpu, 2> out = out_data[proposal::kOut].get<cpu, 2, real_t>(s);
    Tensor<cpu, 2> out_score = out_data[proposal::kScore].get<cpu, 2, real_t>(s);

    int num_anchors = in_data[proposal::kClsProb].shape_[1] / 2;
    int height = scores.size(2);
    int width = scores.size(3);
    int count = num_anchors * height * width;
    int rpn_pre_nms_top_n = (param_.rpn_pre_nms_top_n > 0) ? param_.rpn_pre_nms_top_n : count;
    rpn_pre_nms_top_n = std::min(rpn_pre_nms_top_n, count);
    int rpn_post_nms_top_n = std::min(param_.rpn_post_nms_top_n, rpn_pre_nms_top_n);

    int workspace_size = count * 5 + 2 * count + rpn_pre_nms_top_n * 5 + 3 * rpn_pre_nms_top_n;
    Tensor<cpu, 1> workspace = ctx.requested[proposal::kTempResource].get_space<cpu>(
      Shape1(workspace_size), s);
    int start = 0;
    Tensor<cpu, 2> workspace_proposals(workspace.dptr_ + start, Shape2(count, 5));
    start += count * 5;
    Tensor<cpu, 2> workspace_pre_nms(workspace.dptr_ + start, Shape2(2, count));
    start += 2 * count;
    Tensor<cpu, 2> workspace_ordered_proposals(workspace.dptr_ + start,
                                               Shape2(rpn_pre_nms_top_n, 5));
    start += rpn_pre_nms_top_n * 5;
    Tensor<cpu, 2> workspace_nms(workspace.dptr_ + start, Shape2(3, rpn_pre_nms_top_n));
    start += 3 * rpn_pre_nms_top_n;
    CHECK_EQ(workspace_size, start) << workspace_size << " " << start << std::endl;

    // Generate anchors
    std::vector<float> base_anchor(4);
    base_anchor[0] = 0.0;
    base_anchor[1] = 0.0;
    base_anchor[2] = param_.feature_stride - 1.0;
    base_anchor[3] = param_.feature_stride - 1.0;
    CHECK_EQ(num_anchors, param_.ratios.info.size() * param_.scales.info.size());
    std::vector<float> anchors;
    utils::GenerateAnchors(base_anchor,
                           param_.ratios.info,
                           param_.scales.info,
                           &anchors);
    std::memcpy(workspace_proposals.dptr_, &anchors[0], sizeof(float) * anchors.size());

    // Enumerate all shifted anchors
    for (index_t i = 0; i < num_anchors; ++i) {
      for (index_t j = 0; j < height; ++j) {
        for (index_t k = 0; k < width; ++k) {
          index_t index = j * (width * num_anchors) + k * (num_anchors) + i;
          workspace_proposals[index][0] = workspace_proposals[i][0] + k * param_.feature_stride;
          workspace_proposals[index][1] = workspace_proposals[i][1] + j * param_.feature_stride;
          workspace_proposals[index][2] = workspace_proposals[i][2] + k * param_.feature_stride;
          workspace_proposals[index][3] = workspace_proposals[i][3] + j * param_.feature_stride;
          workspace_proposals[index][4] = scores[0][i][j][k];
        }
      }
    }

    // prevent padded predictions
    int real_height = static_cast<int>(im_info[0][0] / param_.feature_stride);
    int real_width = static_cast<int>(im_info[0][1] / param_.feature_stride);
    CHECK_GE(height, real_height) << height << " " << real_height << std::endl;
    CHECK_GE(width, real_width) << width << " " << real_width << std::endl;

    if (param_.iou_loss) {
      utils::IoUTransformInv(workspace_proposals, bbox_deltas, im_info[0][0], im_info[0][1],
                             real_height, real_width, &(workspace_proposals));
    } else {
      utils::BBoxTransformInv(workspace_proposals, bbox_deltas, im_info[0][0], im_info[0][1],
                              real_height, real_width, &(workspace_proposals));
    }
    utils::FilterBox(&workspace_proposals, param_.rpn_min_size * im_info[0][2]);

    Tensor<cpu, 1> score = workspace_pre_nms[0];
    Tensor<cpu, 1> order = workspace_pre_nms[1];

    utils::CopyScore(workspace_proposals,
                     &score,
                     &order);
    utils::ReverseArgsort(score,
                          &order);
    utils::ReorderProposals(workspace_proposals,
                            order,
                            rpn_pre_nms_top_n,
                            &workspace_ordered_proposals);

    index_t out_size = 0;
    Tensor<cpu, 1> area = workspace_nms[0];
    Tensor<cpu, 1> suppressed = workspace_nms[1];
    Tensor<cpu, 1> keep = workspace_nms[2];
    suppressed = 0;  // surprised!

    utils::NonMaximumSuppression(workspace_ordered_proposals,
                                 param_.threshold,
                                 rpn_post_nms_top_n,
                                 &area,
                                 &suppressed,
                                 &keep,
                                 &out_size);

    // fill in output rois
    for (index_t i = 0; i < out.size(0); ++i) {
      // batch index 0
      out[i][0] = 0;
      if (i < out_size) {
        index_t index = keep[i];
        for (index_t j = 0; j < 4; ++j) {
          out[i][j + 1] =  workspace_ordered_proposals[index][j];
        }
      } else {
        index_t index = keep[i % out_size];
        for (index_t j = 0; j < 4; ++j) {
          out[i][j + 1] = workspace_ordered_proposals[index][j];
        }
      }
    }

    // fill in output score
    for (index_t i = 0; i < out_score.size(0); i++) {
      if (i < out_size) {
        index_t index = keep[i];
        out_score[i][0] = workspace_ordered_proposals[index][4];
      } else {
        index_t index = keep[i % out_size];
        out_score[i][0] = workspace_ordered_proposals[index][4];
      }
    }
  }

  virtual void Backward(const OpContext &ctx,
                        const std::vector<TBlob> &out_grad,
                        const std::vector<TBlob> &in_data,
                        const std::vector<TBlob> &out_data,
                        const std::vector<OpReqType> &req,
                        const std::vector<TBlob> &in_grad,
                        const std::vector<TBlob> &aux_states) {
    using namespace mshadow;
    using namespace mshadow::expr;
    CHECK_EQ(in_grad.size(), 3);

    Stream<xpu> *s = ctx.get_stream<xpu>();
    Tensor<xpu, 4> gscores = in_grad[proposal::kClsProb].get<xpu, 4, real_t>(s);
    Tensor<xpu, 4> gbbox = in_grad[proposal::kBBoxPred].get<xpu, 4, real_t>(s);
    Tensor<xpu, 2> ginfo = in_grad[proposal::kImInfo].get<xpu, 2, real_t>(s);

    // can not assume the grad would be zero
    Assign(gscores, req[proposal::kClsProb], 0);
    Assign(gbbox, req[proposal::kBBoxPred], 0);
    Assign(ginfo, req[proposal::kImInfo], 0);
  }

 private:
  ProposalParam param_;
};  // class ProposalOp

template<>
Operator *CreateOp<cpu>(ProposalParam param) {
  return new ProposalOp<cpu>(param);
}

Operator* ProposalProp::CreateOperator(Context ctx) const {
  DO_BIND_DISPATCH(CreateOp, param_);
}

DMLC_REGISTER_PARAMETER(ProposalParam);

MXNET_REGISTER_OP_PROPERTY(_contrib_Proposal, ProposalProp)
.describe("Generate region proposals via RPN")
.add_argument("cls_score", "NDArray-or-Symbol", "Score of how likely proposal is object.")
.add_argument("bbox_pred", "NDArray-or-Symbol", "BBox Predicted deltas from anchors for proposals")
.add_argument("im_info", "NDArray-or-Symbol", "Image size and scale.")
.add_arguments(ProposalParam::__FIELDS__());

}  // namespace op
}  // namespace mxnet