{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 目标检测"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import torchvision\n",
    "from torchvision.models.detection.faster_rcnn import FastRCNNPredictor\n",
    "\n",
    "# load a model pre-trained pre-trained on COCO\n",
    "model = torchvision.models.detection.fasterrcnn_resnet50_fpn(pretrained=True)\n",
    "\n",
    "# replace the classifier with a new one, that has\n",
    "# num_classes which is user-defined\n",
    "num_classes = 2  # 1 class (person) + background\n",
    "# get number of input features for the classifier\n",
    "in_features = model.roi_heads.box_predictor.cls_score.in_features\n",
    "# replace the pre-trained head with a new one\n",
    "model.roi_heads.box_predictor = FastRCNNPredictor(in_features, num_classes)"
   ]
  }
 ],
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