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   "source": [
    "## 1. PP-OCRv2模型简介\n",
    "\n",
    "PP-OCR是PaddleOCR针对OCR领域发布的文字检测识别系统，PP-OCRv2针对 PP-OCR 进行了一些经验性改进，构建了一个新的 OCR 系统。PP-OCRv2系统框图如下所示（粉色框中为PP-OCRv2新增策略）：\n",
    "\n",
    "<div align=\"center\">\n",
    "<img src=\"https://user-images.githubusercontent.com/12406017/200258931-771f5a1d-230c-4168-9130-0b79321558a9.png\"  width = \"80%\"  />\n",
    "</div>\n",
    "\n",
    "从算法改进思路上看，主要有五个方面的改进：\n",
    "1. 检测模型优化：采用 CML 协同互学习知识蒸馏策略；\n",
    "2. 检测模型优化：CopyPaste 数据增广策略；\n",
    "3. 识别模型优化：PP-LCNet 轻量级骨干网络；\n",
    "4. 识别模型优化：UDML 改进知识蒸馏策略；\n",
    "5. 识别模型优化：Enhanced CTC loss 损失函数改进。\n",
    "\n",
    "从效果上看，主要有三个方面提升：\n",
    "1. 在模型效果上，相对于 PP-OCR mobile 版本提升超7%；\n",
    "2. 在速度上，相对于 PP-OCR server 版本提升超过220%；\n",
    "3. 在模型大小上，11.6M 的总大小，服务器端和移动端都可以轻松部署。\n",
    "\n",
    "更详细的优化细节可参考技术报告：https://arxiv.org/abs/2109.03144 。\n",
    "\n",
    "更多关于PaddleOCR的内容，可以点击 https://github.com/PaddlePaddle/PaddleOCR 进行了解。\n",
    "\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2. 模型效果\n",
    "\n",
    "PP-OCRv2的效果如下：\n",
    "\n",
    "<div align=\"center\">\n",
    "<img src=\"https://user-images.githubusercontent.com/12406017/200239467-a082eef9-fee0-4587-be48-b276a95bf8d0.gif\"  width = \"80%\"  />\n",
    "</div>\n",
    "\n",
    "\n",
    "\n"
   ]
  },
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   "metadata": {},
   "source": [
    "## 3. 模型如何使用\n",
    "\n",
    "### 3.1 模型推理\n",
    "* 安装PaddleOCR whl包"
   ]
  },
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   "source": [
    "! pip install paddleocr --user"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "* 快速体验"
   ]
  },
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   "source": [
    "# 命令行使用\n",
    "! wget https://raw.githubusercontent.com/PaddlePaddle/PaddleOCR/dygraph/doc/imgs/11.jpg\n",
    "! paddleocr --image_dir 11.jpg --use_angle_cls true --ocr_version PP-OCRv2"
   ]
  },
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   "source": [
    "运行完成后，会在终端输出如下结果：\n",
    "```log\n",
    "[[[24.0, 36.0], [304.0, 34.0], [304.0, 72.0], [24.0, 74.0]], ['纯臻营养护发素', 0.964739]]\n",
    "[[[24.0, 80.0], [172.0, 80.0], [172.0, 104.0], [24.0, 104.0]], ['产品信息/参数', 0.98069626]]\n",
    "[[[24.0, 109.0], [333.0, 109.0], [333.0, 136.0], [24.0, 136.0]], ['（45元/每公斤，100公斤起订）', 0.9676722]]\n",
    "......\n",
    "```\n",
    "\n",
    "\n"
   ]
  },
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   "metadata": {},
   "source": [
    "### 3.2 模型训练\n",
    "PP-OCR系统由文本检测模型、方向分类器和文本识别模型构成，三个模型训练教程可参考如下文档:\n",
    "1. 文本检测模型：[文本检测训练教程](https://github.com/PaddlePaddle/PaddleOCR/blob/release%2F2.6/doc/doc_ch/detection.md)\n",
    "1. 方向分类器: [方向分类器训练教程](https://github.com/PaddlePaddle/PaddleOCR/blob/release%2F2.6/doc/doc_ch/angle_class.md)\n",
    "1. 文本识别模型：[文本识别训练教程](https://github.com/PaddlePaddle/PaddleOCR/blob/release%2F2.6/doc/doc_ch/recognition.md)\n",
    "\n",
    "模型训练完成后，可以通过指定模型路径的方式串联使用\n",
    "命令参考如下：\n",
    "```python\n",
    "paddleocr --image_dir 11.jpg --use_angle_cls true --ocr_version PP-OCRv2 --det_model_dir=/path/to/det_inference_model --cls_model_dir=/path/to/cls_inference_model --rec_model_dir=/path/to/rec_inference_model\n",
    "```"
   ]
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   "source": [
    "## 4. 原理\n",
    "\n",
    "优化思路具体如下\n",
    "\n",
    "1. 检测模型优化\n",
    "- 采用 CML (Collaborative Mutual Learning) 协同互学习知识蒸馏策略。\n",
    "     <div align=\"center\">\n",
    "   <img src=\"https://pic4.zhimg.com/80/v2-05f12bcd1784993edabdadbc89b5e9e7_720w.webp\"  width = \"60%\"  />\n",
    "   </div>\n",
    "\n",
    "如上图所示，CML 的核心思想结合了①传统的 Teacher 指导 Student 的标准蒸馏与 ② Students 网络直接的 DML 互学习，可以让 Students 网络互学习的同时，Teacher 网络予以指导。对应的，精心设计关键的三个 Loss 损失函数：GT Loss、DML Loss 和 Distill Loss，在 Teacher 网络 Backbone 为 ResNet18 的条件下，对 Student 的 MobileNetV3 起到了良好的提升效果。\n",
    "\n",
    "   - CopyPaste 数据增广策略\n",
    "   <div align=\"center\">\n",
    "   <img src=\"https://pic1.zhimg.com/80/v2-90239608c554972ac307be07f487f254_720w.webp\"  width = \"60%\"  />\n",
    "   </div>\n",
    "\n",
    "数据增广是提升模型泛化能力重要的手段之一，CopyPaste 是一种新颖的数据增强技巧，已经在目标检测和实例分割任务中验证了有效性。利用 CopyPaste，可以合成文本实例来平衡训练图像中的正负样本之间的比例。相比而言，传统图像旋转、随机翻转和随机裁剪是无法做到的。\n",
    "\n",
    "CopyPaste 主要步骤包括：①随机选择两幅训练图像，②随机尺度抖动缩放，③随机水平翻转，④随机选择一幅图像中的目标子集，⑤粘贴在另一幅图像中随机的位置。这样，就比较好的提升了样本丰富度，同时也增加了模型对环境鲁棒性。\n",
    "\n",
    "2. 识别模型优化\n",
    "- PP-LCNet 轻量级骨干网络\n",
    "  \n",
    "采用速度和精度均衡的PP-LCNet，有效提升精度的同时减少网络推理时间。\n",
    "\n",
    "- UDML 知识蒸馏策略\n",
    "   <div align=\"center\">\n",
    "   <img src=\"https://pic1.zhimg.com/80/v2-642d94e092c7d5f90bedbd7c7511636c_720w.webp\"  width = \"60%\"  />\n",
    "   </div>\n",
    "   在标准的 DML 知识蒸馏的基础上，新增引入了对于 Feature Map 的监督机制，新增 Feature Loss，增加迭代次数，在 Head 部分增加额外的 FC 网络，最终加快蒸馏的速度同时提升效果。\n",
    "\n",
    "- Enhanced CTC loss 改进\n",
    "   <div align=\"center\">\n",
    "   <img src=\"https://pic3.zhimg.com/80/v2-864d255454b5196e0a2a916d81ff92c6_720w.webp\"  width = \"40%\"  />\n",
    "   </div>\n",
    "   中文文字识别任务中，经常遇到相似字符数误识别的问题，这里借鉴 Metric Learning，引入 Center Loss，进一步增大类间距离来增强模型对相似字符的区分能力，核心思路如上图公式所示。"
   ]
  },
  {
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   "metadata": {},
   "source": [
    "## 5. 注意事项\n",
    "\n",
    "PP-OCR系列模型训练过程中均使用通用数据，如在实际场景中表现不满意，可标注少量数据进行finetune。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 6. 相关论文以及引用信息\n",
    "```\n",
    "@article{du2021pp,\n",
    "  title={PP-OCRv2: bag of tricks for ultra lightweight OCR system},\n",
    "  author={Du, Yuning and Li, Chenxia and Guo, Ruoyu and Cui, Cheng and Liu, Weiwei and Zhou, Jun and Lu, Bin and Yang, Yehua and Liu, Qiwen and Hu, Xiaoguang and others},\n",
    "  journal={arXiv preprint arXiv:2109.03144},\n",
    "  year={2021}\n",
    "}\n",
    "```\n"
   ]
  }
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