梳理caffe代码data_transformer（十二）

梳理caffe代码data_transformer（十二）

data_transformer详细注释看头文件和实现部分：

头文件：

 

/////////////////TransformationParameter的caffe消息定义
/*
// Message that stores parameters used to apply transformation
// to the data layer's data
message TransformationParameter {
  // For data pre-processing, we can do simple scaling and subtracting the
  // data mean, if provided. Note that the mean subtraction is always carried
  // out before scaling.
  optional float scale = 1 [default = 1];
  // Specify if we want to randomly mirror data.
  optional bool mirror = 2 [default = false];
  // Specify if we would like to randomly crop an image.
  optional uint32 crop_size = 3 [default = 0];
  // mean_file and mean_value cannot be specified at the same time
  optional string mean_file = 4;
  // if specified can be repeated once (would substract it from all the channels)
  // or can be repeated the same number of times as channels
  // (would subtract them from the corresponding channel)
  repeated float mean_value = 5;
  // Force the decoded image to have 3 color channels.
  optional bool force_color = 6 [default = false];
  // Force the decoded image to have 1 color channels.
  optional bool force_gray = 7 [default = false];
}
*/
/*
DataTransformer类主要负责对数据进行预处理， 比如减去均值、进行crop，镜像，强制设置为彩色强制设置为灰度图像以及像素值的缩放，此外该类还将Datum、const vector<Datum>、cv::Mat&、vector<cv::Mat> 、Blob<Dtype>*类型的数据变换到目标大小的blob。负责对上述类型的数据推断其shape。
*/
#ifndef CAFFE_DATA_TRANSFORMER_HPP
#define CAFFE_DATA_TRANSFORMER_HPP
#include <vector>
#include "caffe/blob.hpp"
#include "caffe/common.hpp"
#include "caffe/proto/caffe.pb.h"

namespace caffe {

/**
 * @brief Applies common transformations to the input data, such as
 * scaling, mirroring, substracting the image mean...
 */
template <typename Dtype>
class DataTransformer {
 public:
  explicit DataTransformer(const TransformationParameter& param, Phase phase);
  virtual ~DataTransformer() {}

  /**
   * @brief Initialize the Random number generations if needed by the
   *    transformation.
   */
// 初始化随机数生成器，因为在对数据进行变换的时候有可能用到，比如说打乱数据的输入顺序
  void InitRand();

  /**
   * @brief Applies the transformation defined in the data layer's
   * transform_param block to the data.
   *
   * @param datum
   *    Datum containing the data to be transformed.
   * @param transformed_blob
   *    This is destination blob. It can be part of top blob's data if
   *    set_cpu_data() is used. See data_layer.cpp for an example.
   */
// 对Datum的数据进行变换，放入到transformed_blob中
  void Transform(const Datum& datum, Blob<Dtype>* transformed_blob);

  /**
   * @brief Applies the transformation defined in the data layer's
   * transform_param block to a vector of Datum.
   *
   * @param datum_vector
   *    A vector of Datum containing the data to be transformed.
   * @param transformed_blob
   *    This is destination blob. It can be part of top blob's data if
   *    set_cpu_data() is used. See memory_layer.cpp for an example.
   */
// 对Datum容器的数据进行变换翻入到transformed_blob
  void Transform(const vector<Datum> & datum_vector,
                Blob<Dtype>* transformed_blob);

#ifdef USE_OPENCV
  /**
   * @brief Applies the transformation defined in the data layer's
   * transform_param block to a vector of Mat.
   *
   * @param mat_vector
   *    A vector of Mat containing the data to be transformed.
   * @param transformed_blob
   *    This is destination blob. It can be part of top blob's data if
   *    set_cpu_data() is used. See memory_layer.cpp for an example.
   */
// 如果定义OpenCV还可能对mat容器数据类型的数据进行变换
  void Transform(const vector<cv::Mat> & mat_vector,
                Blob<Dtype>* transformed_blob);

  /**
   * @brief Applies the transformation defined in the data layer's
   * transform_param block to a cv::Mat
   *
   * @param cv_img
   *    cv::Mat containing the data to be transformed.
   * @param transformed_blob
   *    This is destination blob. It can be part of top blob's data if
   *    set_cpu_data() is used. See image_data_layer.cpp for an example.
   */
// 将opencv读取的单个图像转换到blob中去
  void Transform(const cv::Mat& cv_img, Blob<Dtype>* transformed_blob);
#endif  // USE_OPENCV

  /**
   * @brief Applies the same transformation defined in the data layer's
   * transform_param block to all the num images in a input_blob.
   *
   * @param input_blob
   *    A Blob containing the data to be transformed. It applies the same
   *    transformation to all the num images in the blob.
   * @param transformed_blob
   *    This is destination blob, it will contain as many images as the
   *    input blob. It can be part of top blob's data.
   */
// 将输入的blob进行变换，可能是取出blob的中的一部分数据到新的blob
  void Transform(Blob<Dtype>* input_blob, Blob<Dtype>* transformed_blob);

  /**
   * @brief Infers the shape of transformed_blob will have when
   *    the transformation is applied to the data.
   *
   * @param datum
   *    Datum containing the data to be transformed.
   */
// 根据Datum获取blob的形状
  vector<int> InferBlobShape(const Datum& datum);
  /**
   * @brief Infers the shape of transformed_blob will have when
   *    the transformation is applied to the data.
   *    It uses the first element to infer the shape of the blob.
   *
   * @param datum_vector
   *    A vector of Datum containing the data to be transformed.
   */
// 根据Datum容器获取blob的形状
  vector<int> InferBlobShape(const vector<Datum> & datum_vector);
  /**
   * @brief Infers the shape of transformed_blob will have when
   *    the transformation is applied to the data.
   *    It uses the first element to infer the shape of the blob.
   *
   * @param mat_vector
   *    A vector of Mat containing the data to be transformed.
   */
#ifdef USE_OPENCV
// 根据Mat容器获取blob的形状
  vector<int> InferBlobShape(const vector<cv::Mat> & mat_vector);
  /**
   * @brief Infers the shape of transformed_blob will have when
   *    the transformation is applied to the data.
   *
   * @param cv_img
   *    cv::Mat containing the data to be transformed.
   */
// 根据Mat获取blob的形状
  vector<int> InferBlobShape(const cv::Mat& cv_img);
#endif  // USE_OPENCV

 protected:
   /**
   * @brief Generates a random integer from Uniform({0, 1, ..., n-1}).
   *
   * @param n
   *    The upperbound (exclusive) value of the random number.
   * @return
   *    A uniformly random integer value from ({0, 1, ..., n-1}).
   */
// 生成从0到n-1的服从均匀分布的随机数,要求继承他的都必须实现如何生成随机数
  virtual int Rand(int n);
// 将给定的Datum进行转换
  void Transform(const Datum& datum, Dtype* transformed_data);

  // 变换所使用的参数
  TransformationParameter param_;
  // 随机数生成器的种子
  shared_ptr<Caffe::RNG> rng_;
  // 是训练还是测试？
  Phase phase_;
  // 数据均值 blob
  Blob<Dtype> data_mean_;
  // 数据均值blob的容器
  vector<Dtype> mean_values_;
};

}  // namespace caffe

#endif  // CAFFE_DATA_TRANSFORMER_HPP_

实现：

 

 

//DataTransformer需要输入的是blob，所以需要看一下里面的参数，因此再把这一部分内容的proto贴出来，这是新版的caffe
/*
// Specifies the shape (dimensions) of a Blob.
message BlobShape {
  repeated int64 dim = 1 [packed = true];
}

message BlobProto {
  optional BlobShape shape = 7;
  repeated float data = 5 [packed = true];
  repeated float diff = 6 [packed = true];
  repeated double double_data = 8 [packed = true];
  repeated double double_diff = 9 [packed = true];

  // 4D dimensions -- deprecated.  Use "shape" instead.
  optional int32 num = 1 [default = 0];
  optional int32 channels = 2 [default = 0];
  optional int32 height = 3 [default = 0];
  optional int32 width = 4 [default = 0];
}
*/
/////////////////TransformationParameter的caffe消息定义
/*
// Message that stores parameters used to apply transformation
// to the data layer's data
message TransformationParameter {
  // For data pre-processing, we can do simple scaling and subtracting the
  // data mean, if provided. Note that the mean subtraction is always carried
  // out before scaling.
  optional float scale = 1 [default = 1];
  // Specify if we want to randomly mirror data.
  optional bool mirror = 2 [default = false];
  // Specify if we would like to randomly crop an image.
  optional uint32 crop_size = 3 [default = 0];
  // mean_file and mean_value cannot be specified at the same time
  optional string mean_file = 4;
  // if specified can be repeated once (would substract it from all the channels)
  // or can be repeated the same number of times as channels
  // (would subtract them from the corresponding channel)
  repeated float mean_value = 5;
  // Force the decoded image to have 3 color channels.
  optional bool force_color = 6 [default = false];
  // Force the decoded image to have 1 color channels.
  optional bool force_gray = 7 [default = false];
}
*/
#ifdef USE_OPENCV
#include <opencv2/core/core.hpp>
#endif  // USE_OPENCV

#include <string>
#include <vector>

#include "caffe/data_transformer.hpp"
#include "caffe/util/io.hpp"
#include "caffe/util/math_functions.hpp"
#include "caffe/util/rng.hpp"

namespace caffe {
// 构造函数
template<typename Dtype>
DataTransformer<Dtype>::DataTransformer(const TransformationParameter& param,
    Phase phase)
    : param_(param), phase_(phase) {
  // check if we want to use mean_file
  // 判断是否有平均值文件
  if (param_.has_mean_file()) {
    CHECK_EQ(param_.mean_value_size(), 0) <<
      "Cannot specify mean_file and mean_value at the same time";
    // 平均值文件的路径
    const string& mean_file = param.mean_file();
    if (Caffe::root_solver()) {
      LOG(INFO) << "Loading mean file from: " << mean_file;
    }
    BlobProto blob_proto;// 调用google/protobuf?? ,用于加速运算的数据接口，有时间再详细了解其应用方法
//这个函数是实现了从二进制文件中读取数据到blob_proto中,猜测函数来自第3方库的google/protobuf模块
    ReadProtoFromBinaryFileOrDie(mean_file.c_str(), &blob_proto);
    data_mean_.FromProto(blob_proto);// 调用Blob类的成员函数FromRroto从BlobProto中加载数据
  }
  // check if we want to use mean_value
  if (param_.mean_value_size() > 0) {
    CHECK(param_.has_mean_file() == false) <<
      "Cannot specify mean_file and mean_value at the same time";
    for (int c = 0; c < param_.mean_value_size(); ++c) {
      mean_values_.push_back(param_.mean_value(c));//将元素param_.mean_value(c)加入到mean_values_容器的最后一位
    }
  }
}

/*提前先描述一下数据层的Datum，
Datum数据结构,Caffe并不是把向量和矩阵直接放进数据库的，而是将数据通过caffe.proto里定义的一个datum类来封装。数据库里放的是一个个的datum序列化成的字符串。Datum的定义摘录如下：
message Datum {
  optional int32 channels = 1;
  optional int32 height = 2;
  optional int32 width = 3;
  // the actual image data, in bytes
  optional bytes data = 4;
  optional int32 label = 5;
  // Optionally, the datum could also hold float data.
  repeated float float_data = 6;
  // If true data contains an encoded image that need to be decoded
  optional bool encoded = 7 [default = false];
}
一个Datum有三个维度，channels, height,和width，可以看做是少了num维度的Blob。存放数据的地方有两个：byte_data和float_data，分别存放整数型和浮点型数据。图像数据一般是整形，放在byte_data里，特征向量一般是浮点型，放在float_data里。label存放数据的类别标签，是整数型。encoded标识数据是否需要被解码（里面有可能放的是JPEG或者PNG之类经过编码的数据）。Datum这个数据结构将数据和标签封装在一起，兼容整形和浮点型数据。经过Protobuf编译后，可以在Python和C++中都提供高效的访问。同时Protubuf还为它提供了序列化与反序列化的功能。存放进LMDB的就是Datum序列化生成的字符串。
Caffe中关于LMDB的代码有三类：生成数据集、读取数据集、生成特征向量。接下来就分别针对三者进行分析。
生成数据集:
生成数据集的代码在examples，随数据集提供，比如MNIST。
首先，创建访问LMDB所需的一些变量：
MDB_env *mdb_env;
MDB_dbi mdb_dbi;
MDB_val mdb_key, mdb_data;
MDB_txn *mdb_txn;
...
mdb_env是整个数据库环境的句柄，mdb_dbi是环境中一个数据库的句柄，mdb_key和mdb_data用来存放向数据库中输入数据的“值”。mdb_txn是数据库事物操作的句柄，”txn”是”transaction”的缩写。
然后，创建数据库环境，创建并打开数据库：
if (db_backend == "lmdb") {  // lmdb
  LOG(INFO) << "Opening lmdb " << db_path;
  CHECK_EQ(mkdir(db_path, 0744), 0)
      << "mkdir " << db_path << "failed";
  CHECK_EQ(mdb_env_create(&mdb_env), MDB_SUCCESS) << "mdb_env_create failed";
  CHECK_EQ(mdb_env_set_mapsize(mdb_env, 1099511627776), MDB_SUCCESS)  // 1TB
      << "mdb_env_set_mapsize failed";
  CHECK_EQ(mdb_env_open(mdb_env, db_path, 0, 0664), MDB_SUCCESS)
      << "mdb_env_open failed";
  CHECK_EQ(mdb_txn_begin(mdb_env, NULL, 0, &mdb_txn), MDB_SUCCESS)
      << "mdb_txn_begin failed";
  CHECK_EQ(mdb_open(mdb_txn, NULL, 0, &mdb_dbi), MDB_SUCCESS)
      << "mdb_open failed. Does the lmdb already exist? ";
} else {
  LOG(FATAL) << "Unknown db backend " << db_backend;
}
mkdir(db_path, 0744)为数据库创建文件夹，如果文件夹已经存在，程序会报错退出。也就是说，程序不会覆盖已有的数据库。已有的数据库如果不要了，需要手动删除。需要注意的是，LMDB的一个环境中是可以有多个数据库的，数据库之间以名字区分。mdb_open()的第二个参数实际上就是数据库的名称(char *)。当一个环境中只有一个数据库的时候，这个参数可以给NULL。最后，为每一个图像创建Datum对象，向对象内写入数据，然后将其序列化成字符串，将字符串放入数据库中：
Datum datum;
datum.set_channels(1);
datum.set_height(rows);
datum.set_width(cols);
for (int item_id = 0; item_id < num_items; ++item_id) {
  image_file.read(pixels, rows * cols);
  label_file.read(&label, 1);
  datum.set_data(pixels, rows*cols);
  datum.set_label(label);
  snprintf(key_cstr, kMaxKeyLength, "%08d", item_id);
  datum.SerializeToString(&value);
  string keystr(key_cstr);

  // Put in db
  if (db_backend == "lmdb") {  // lmdb
    mdb_data.mv_size = value.size();
    mdb_data.mv_data = reinterpret_cast<void*>(&value[0]);
    mdb_key.mv_size = keystr.size();
    mdb_key.mv_data = reinterpret_cast<void*>(&keystr[0]);
    CHECK_EQ(mdb_put(mdb_txn, mdb_dbi, &mdb_key, &mdb_data, 0), MDB_SUCCESS)
        << "mdb_put failed";
  } else {
    LOG(FATAL) << "Unknown db backend " << db_backend;
  }

  if (++count % 1000 == 0) {
    // Commit txn
    if (db_backend == "lmdb") {  // lmdb
      CHECK_EQ(mdb_txn_commit(mdb_txn), MDB_SUCCESS)
          << "mdb_txn_commit failed";
      CHECK_EQ(mdb_txn_begin(mdb_env, NULL, 0, &mdb_txn), MDB_SUCCESS)
          << "mdb_txn_begin failed";
    } else {
      LOG(FATAL) << "Unknown db backend " << db_backend;
    }
  }
}
放入数据的Key是图像的编号，前面补0至8位。MDB_val类型的mdb_data和mdb_key中存放的是数据来源的指针，以及数据的长度。mdb_put()函数将数据存入数据库。每隔1000个图像commit一次数据库。只有commit之后，数据才真正写入磁盘。
读取数据集:
Caffe中读取LMDB数据集的代码是DataLayer，用在网络的最下层，提供数据。DataLayer采用顺序遍历的方式读取数据，不支持打乱数据顺序，只能随机跳过前若干个数据。
首先，在DataLayer的DataLayerSetUp方法中，打开数据库，并获取迭代器cursor_：
db_.reset(db::GetDB(this->layer_param_.data_param().backend()));
db_->Open(this->layer_param_.data_param().source(), db::READ);
cursor_.reset(db_->NewCursor());
然后，在每一次的数据预取时，InternalThreadEntry()方法中，从数据库中读取字符串，反序列化为Datum对象，再从Datum对象中取出数据：
Datum datum;
datum.ParseFromString(cursor_->value());
其中，cursor_->value()获取序列化后的字符串。datum.ParseFromString()方法对字符串进行反序列化。
最后，要将cursor_向前推进：
cursor_->Next();
if (!cursor_->valid()) {
  DLOG(INFO) << "Restarting data prefetching from start."
      cursor_->SeekToFirst();
}
如果cursor->valid()返回false，说明数据库已经遍历到头，这时需要将cursor_重置回数据库开头。不支持样本随机排序应该是DataLayer的致命弱点。如果数据库的key能够统一，其实可以通过对key随机枚举的方式实现。所以caffe定义了一个随机生成器RNG。
*/
template<typename Dtype>
void DataTransformer<Dtype>::Transform(const Datum& datum,
                                       Dtype* transformed_data) {
  // 参考TransformationParameter的定义
  const string& data = datum.data();
  const int datum_channels = datum.channels();//数据的channel
  const int datum_height = datum.height();//数据的行数
  const int datum_width = datum.width();// 数据的列数

  const int crop_size = param_.crop_size();// crop大小
  const Dtype scale = param_.scale();// 缩放比例
  const bool do_mirror = param_.mirror() && Rand(2);// 该参数用于在镜像位置对数据处理
  const bool has_mean_file = param_.has_mean_file();// 是否有均值文件
  const bool has_uint8 = data.size() > 0;// 数据是否为uint8还是float类型的
  const bool has_mean_values = mean_values_.size() > 0;// 是否有每个channel的均值

  // 检查合法性
  CHECK_GT(datum_channels, 0);
  CHECK_GE(datum_height, crop_size);
  CHECK_GE(datum_width, crop_size);

  Dtype* mean = NULL;
/*
前面有介绍这一部分CHECK内容，glog提供了多个便利的宏来处理特定关系的判定。具体有：
1,判定大小关系
CHECK_EQ, CHECK_NE, CHECK_LE, CHECK_LT, CHECK_GE, CHECK_GT，使用这些宏需要注意类型一致，如果出现类型不一致的，可使用static_cast转换。
2,判定指针是否为空
CHECK_NOTNULL（some_ptr），可用于对象初始化的时候。
3，判定字符串是否相等
CHECK_STREQ, CHECK_STRNE, CHECK_STRCASEEQ,CHECK_STRCASENE。可进行大小写敏感或不敏感字符串来分别判定。
4， 判定浮点是否相等或相近
CHECK_DOUBLE_EQ，CHECK_NEAR。这两个宏都需要指定一个可容忍的偏差上限。
*/
  if (has_mean_file) {// 检查mean_file是否与数据的参数一致
    CHECK_EQ(datum_channels, data_mean_.channels());
    CHECK_EQ(datum_height, data_mean_.height());
    CHECK_EQ(datum_width, data_mean_.width());
    mean = data_mean_.mutable_cpu_data();
  }
  if (has_mean_values) {
    CHECK(mean_values_.size() == 1 || mean_values_.size() == datum_channels) <<
     "Specify either 1 mean_value or as many as channels: " << datum_channels;
    if (datum_channels > 1 && mean_values_.size() == 1) {
      // Replicate the mean_value for simplicity
      for (int c = 1; c < datum_channels; ++c) {
        mean_values_.push_back(mean_values_[0]);
      }
    }
  }

  int height = datum_height;
  int width = datum_width;

  // 根据是否需要crop来生成h_off和w_off
  int h_off = 0;
  int w_off = 0;
  if (crop_size) {// 如果crop_size不为0
    height = crop_size;
    width = crop_size;
    // We only do random crop when we do training.
    // 在训练的时候随机crop图像块,这里需要自己实现Rand这个函数来确定是如何随机的
    if (phase_ == TRAIN) {
      h_off = Rand(datum_height - crop_size + 1);// 产生从0到datum_height - crop_size的随机数
      w_off = Rand(datum_width - crop_size + 1);
    } else {// 测试的时候不用随机，取图像的中心
      h_off = (datum_height - crop_size) / 2;
      w_off = (datum_width - crop_size) / 2;
    }
  }

  // 对数据进行变换，主要是将原来的像素值减去均值，然后乘以scale这么一个操作
  // 如果需要crop则最终转换的Blob的大小即为crop*crop
  // 如果不是，则最终的Blob大小即为datum_height*datum_width
  Dtype datum_element;
  int top_index, data_index;
  for (int c = 0; c < datum_channels; ++c) {
    for (int h = 0; h < height; ++h) {
      for (int w = 0; w < width; ++w) {
        data_index = (c * datum_height + h_off + h) * datum_width + w_off + w;// 获取数据的索引，我不是很明白怎么计算的？
        if (do_mirror) {// 是否需要在镜像位置转换
          top_index = (c * height + h) * width + (width - 1 - w);//在宽这个坐标上做文章，来实现镜像
        } else {//
          top_index = (c * height + h) * width + w;
        }
        if (has_uint8) {// 数据如果是uint8则进行转换
          datum_element =
            static_cast<Dtype>(static_cast<uint8_t>(data[data_index]));
        } else {// 否则就是float
          datum_element = datum.float_data(data_index);
        }
        if (has_mean_file) {// 如果有mean_file,则原来的像素值减去均值，然后乘以scale
          transformed_data[top_index] =
            (datum_element - mean[data_index]) * scale;
        } else {
          if (has_mean_values) {// 否则减去该channel的均值（每个channel有其一个均值），然后乘以scale
            transformed_data[top_index] =
              (datum_element - mean_values_[c]) * scale;
          } else {// 否则如果没有均值那么就直接乘以scale即可
            transformed_data[top_index] = datum_element * scale;
          }
        }
      }
    }
  }
}


template<typename Dtype>
void DataTransformer<Dtype>::Transform(const Datum& datum,
                                       Blob<Dtype>* transformed_blob) {
  // If datum is encoded, decoded and transform the cv::image.
  if (datum.encoded()) {//  检查是否编码了，如果是则解码
#ifdef USE_OPENCV
    // 先检查是不是两个属性都设置， 如果是则说明参数设置有误
    CHECK(!(param_.force_color() && param_.force_gray()))
        << "cannot set both force_color and force_gray";
    cv::Mat cv_img;
    if (param_.force_color() || param_.force_gray()) {
        // 如果强制彩色或者强制灰度图像一个成立则使用DecodeDatumToCVMat解码
    // If force_color then decode in color otherwise decode in gray.
      cv_img = DecodeDatumToCVMat(datum, param_.force_color());
    } else {// 否则使用DecodeDatumToCVMatNative解码
      cv_img = DecodeDatumToCVMatNative(datum);
    }
    // Transform the cv::image into blob.
    // 变换
    return Transform(cv_img, transformed_blob);
#else
    LOG(FATAL) << "Encoded datum requires OpenCV; compile with USE_OPENCV.";
#endif  // USE_OPENCV
  } else {// 如果没有编码则，检查force_color和force_gray是否设置，如果设置则不合法，因为该选项只适合于编码后的数据
    if (param_.force_color() || param_.force_gray()) {
      LOG(ERROR) << "force_color and force_gray only for encoded datum";
    }
  }

  const int crop_size = param_.crop_size();
  const int datum_channels = datum.channels();
  const int datum_height = datum.height();
  const int datum_width = datum.width();

  // Check dimensions.
  const int channels = transformed_blob->channels();
  const int height = transformed_blob->height();
  const int width = transformed_blob->width();
  const int num = transformed_blob->num();

  CHECK_EQ(channels, datum_channels);
  CHECK_LE(height, datum_height);
  CHECK_LE(width, datum_width);
  CHECK_GE(num, 1);

  if (crop_size) {
    CHECK_EQ(crop_size, height);
    CHECK_EQ(crop_size, width);
  } else {
    CHECK_EQ(datum_height, height);
    CHECK_EQ(datum_width, width);
  }
  // 继续变换数据
  Dtype* transformed_data = transformed_blob->mutable_cpu_data();
  Transform(datum, transformed_data);
}

template<typename Dtype>
void DataTransformer<Dtype>::Transform(const vector<Datum> & datum_vector,
                                       Blob<Dtype>* transformed_blob) {
  const int datum_num = datum_vector.size();
  // 变换到的目标blob的形状
  const int num = transformed_blob->num();
  const int channels = transformed_blob->channels();
  const int height = transformed_blob->height();
  const int width = transformed_blob->width();

  CHECK_GT(datum_num, 0) << "There is no datum to add";
  CHECK_LE(datum_num, num) <<
    "The size of datum_vector must be no greater than transformed_blob->num()";
  // 新建一个uni_blob,里面只有一个batch
  Blob<Dtype> uni_blob(1, channels, height, width);
  for (int item_id = 0; item_id < datum_num; ++item_id) {
    int offset = transformed_blob->offset(item_id);
    uni_blob.set_cpu_data(transformed_blob->mutable_cpu_data() + offset);
    Transform(datum_vector[item_id], &uni_blob);
  }
}

#ifdef USE_OPENCV
template<typename Dtype>
void DataTransformer<Dtype>::Transform(const vector<cv::Mat> & mat_vector,
                                       Blob<Dtype>* transformed_blob) {
  // 获取mat的参数
  const int mat_num = mat_vector.size();
  const int num = transformed_blob->num();
  const int channels = transformed_blob->channels();
  const int height = transformed_blob->height();
  const int width = transformed_blob->width();

  CHECK_GT(mat_num, 0) << "There is no MAT to add";
  CHECK_EQ(mat_num, num) <<
    "The size of mat_vector must be equals to transformed_blob->num()";
  //  同上
  Blob<Dtype> uni_blob(1, channels, height, width);
  for (int item_id = 0; item_id < mat_num; ++item_id) {
    int offset = transformed_blob->offset(item_id);
    uni_blob.set_cpu_data(transformed_blob->mutable_cpu_data() + offset);
    Transform(mat_vector[item_id], &uni_blob);
  }
}

// 如果是图像的话，需要减去均值乘以scale，判断是不是需要做镜像处理
// 逻辑与前面类似
template<typename Dtype>
void DataTransformer<Dtype>::Transform(const cv::Mat& cv_img,
                                       Blob<Dtype>* transformed_blob) {
  const int crop_size = param_.crop_size();
  const int img_channels = cv_img.channels();
  const int img_height = cv_img.rows;
  const int img_width = cv_img.cols;

  // Check dimensions.
  const int channels = transformed_blob->channels();
  const int height = transformed_blob->height();
  const int width = transformed_blob->width();
  const int num = transformed_blob->num();

  CHECK_EQ(channels, img_channels);
  CHECK_LE(height, img_height);
  CHECK_LE(width, img_width);
  CHECK_GE(num, 1);

  CHECK(cv_img.depth() == CV_8U) << "Image data type must be unsigned byte";

  const Dtype scale = param_.scale();
  const bool do_mirror = param_.mirror() && Rand(2);
  const bool has_mean_file = param_.has_mean_file();
  const bool has_mean_values = mean_values_.size() > 0;

  CHECK_GT(img_channels, 0);
  CHECK_GE(img_height, crop_size);
  CHECK_GE(img_width, crop_size);

  Dtype* mean = NULL;
  if (has_mean_file) {
    CHECK_EQ(img_channels, data_mean_.channels());
    CHECK_EQ(img_height, data_mean_.height());
    CHECK_EQ(img_width, data_mean_.width());
    mean = data_mean_.mutable_cpu_data();
  }
  if (has_mean_values) {
    CHECK(mean_values_.size() == 1 || mean_values_.size() == img_channels) <<
     "Specify either 1 mean_value or as many as channels: " << img_channels;
    if (img_channels > 1 && mean_values_.size() == 1) {
      // Replicate the mean_value for simplicity
      for (int c = 1; c < img_channels; ++c) {
        mean_values_.push_back(mean_values_[0]);
      }
    }
  }

  int h_off = 0;
  int w_off = 0;
  cv::Mat cv_cropped_img = cv_img;
  if (crop_size) {
    CHECK_EQ(crop_size, height);
    CHECK_EQ(crop_size, width);
    // We only do random crop when we do training.
    if (phase_ == TRAIN) {
      h_off = Rand(img_height - crop_size + 1);
      w_off = Rand(img_width - crop_size + 1);
    } else {
      h_off = (img_height - crop_size) / 2;
      w_off = (img_width - crop_size) / 2;
    }
    cv::Rect roi(w_off, h_off, crop_size, crop_size);
    cv_cropped_img = cv_img(roi);
  } else {
    CHECK_EQ(img_height, height);
    CHECK_EQ(img_width, width);
  }

  CHECK(cv_cropped_img.data);

  Dtype* transformed_data = transformed_blob->mutable_cpu_data();
  int top_index;
  for (int h = 0; h < height; ++h) {
    const uchar* ptr = cv_cropped_img.ptr<uchar>(h);
    int img_index = 0;
    for (int w = 0; w < width; ++w) {
      for (int c = 0; c < img_channels; ++c) {
        if (do_mirror) {
          top_index = (c * height + h) * width + (width - 1 - w);
        } else {
          top_index = (c * height + h) * width + w;
        }
        // int top_index = (c * height + h) * width + w;
        Dtype pixel = static_cast<Dtype>(ptr[img_index++]);
        if (has_mean_file) {
          int mean_index = (c * img_height + h_off + h) * img_width + w_off + w;
          transformed_data[top_index] =
            (pixel - mean[mean_index]) * scale;
        } else {
          if (has_mean_values) {
            transformed_data[top_index] =
              (pixel - mean_values_[c]) * scale;
          } else {
            transformed_data[top_index] = pixel * scale;
          }
        }
      }
    }
  }
}
#endif  // USE_OPENCV

template<typename Dtype>
void DataTransformer<Dtype>::Transform(Blob<Dtype>* input_blob,
                                       Blob<Dtype>* transformed_blob) {
  const int crop_size = param_.crop_size();
  const int input_num = input_blob->num();
  const int input_channels = input_blob->channels();
  const int input_height = input_blob->height();
  const int input_width = input_blob->width();

  if (transformed_blob->count() == 0) {
    // Initialize transformed_blob with the right shape.
    if (crop_size) {
      transformed_blob->Reshape(input_num, input_channels,
                                crop_size, crop_size);
    } else {
      transformed_blob->Reshape(input_num, input_channels,
                                input_height, input_width);
    }
  }

  const int num = transformed_blob->num();
  const int channels = transformed_blob->channels();
  const int height = transformed_blob->height();
  const int width = transformed_blob->width();
  const int size = transformed_blob->count();

  CHECK_LE(input_num, num);
  CHECK_EQ(input_channels, channels);
  CHECK_GE(input_height, height);
  CHECK_GE(input_width, width);


  const Dtype scale = param_.scale();
  const bool do_mirror = param_.mirror() && Rand(2);
  const bool has_mean_file = param_.has_mean_file();
  const bool has_mean_values = mean_values_.size() > 0;

  int h_off = 0;
  int w_off = 0;
  if (crop_size) {
    CHECK_EQ(crop_size, height);
    CHECK_EQ(crop_size, width);
    // We only do random crop when we do training.
    if (phase_ == TRAIN) {
      h_off = Rand(input_height - crop_size + 1);
      w_off = Rand(input_width - crop_size + 1);
    } else {
      h_off = (input_height - crop_size) / 2;
      w_off = (input_width - crop_size) / 2;
    }
  } else {
    CHECK_EQ(input_height, height);
    CHECK_EQ(input_width, width);
  }

  // 如果有均值文件则
  Dtype* input_data = input_blob->mutable_cpu_data();
  if (has_mean_file) {
    CHECK_EQ(input_channels, data_mean_.channels());
    CHECK_EQ(input_height, data_mean_.height());
    CHECK_EQ(input_width, data_mean_.width());
    for (int n = 0; n < input_num; ++n) {
      int offset = input_blob->offset(n);
      /*
         template <typename Dtype>
       void caffe_sub(const int N, const Dtype* a, const Dtype* b, Dtype* y);
       math_function中定义的caffe_sub目的是矩阵相减input_data（以offset开始的矩阵） = input_data（以offset开始的矩阵） - data_mean_
    */
      caffe_sub(data_mean_.count(), input_data + offset,
            data_mean_.cpu_data(), input_data + offset);
    }
  }
  // 如果每个channel有均值则
  if (has_mean_values) {
    CHECK(mean_values_.size() == 1 || mean_values_.size() == input_channels) <<
     "Specify either 1 mean_value or as many as channels: " << input_channels;
    if (mean_values_.size() == 1) {
      caffe_add_scalar(input_blob->count(), -(mean_values_[0]), input_data);
    } else {
      for (int n = 0; n < input_num; ++n) {
        for (int c = 0; c < input_channels; ++c) {
          int offset = input_blob->offset(n, c);
          // 给nput_data[offset]地址开始的每一个元素加上一个-mean_values_[c]
          caffe_add_scalar(input_height * input_width, -(mean_values_[c]),
            input_data + offset);
        }
      }
    }
  }

  // 如果啥均值都没有则直接复制
  Dtype* transformed_data = transformed_blob->mutable_cpu_data();

  for (int n = 0; n < input_num; ++n) {
    int top_index_n = n * channels;
    int data_index_n = n * channels;
    for (int c = 0; c < channels; ++c) {
      int top_index_c = (top_index_n + c) * height;
      int data_index_c = (data_index_n + c) * input_height + h_off;
      for (int h = 0; h < height; ++h) {
        int top_index_h = (top_index_c + h) * width;
        int data_index_h = (data_index_c + h) * input_width + w_off;
        if (do_mirror) {
          int top_index_w = top_index_h + width - 1;
          for (int w = 0; w < width; ++w) {
            transformed_data[top_index_w-w] = input_data[data_index_h + w];
          }
        } else {
          for (int w = 0; w < width; ++w) {
            transformed_data[top_index_h + w] = input_data[data_index_h + w];
          }
        }
      }
    }
  }
  if (scale != Dtype(1)) {
    DLOG(INFO) << "Scale: " << scale;
    caffe_scal(size, scale, transformed_data);
  }
}

template<typename Dtype>
vector<int> DataTransformer<Dtype>::InferBlobShape(const Datum& datum) {
  if (datum.encoded()) {
#ifdef USE_OPENCV // 如果使用OpenCV则可以用先转换为CVMat，然后在推断blob的形状
    CHECK(!(param_.force_color() && param_.force_gray()))
        << "cannot set both force_color and force_gray";
    cv::Mat cv_img;
    if (param_.force_color() || param_.force_gray()) {
    // If force_color then decode in color otherwise decode in gray.
      cv_img = DecodeDatumToCVMat(datum, param_.force_color());
    } else {
      cv_img = DecodeDatumToCVMatNative(datum);
    }
    // InferBlobShape using the cv::image.
    return InferBlobShape(cv_img);
#else
    LOG(FATAL) << "Encoded datum requires OpenCV; compile with USE_OPENCV.";
#endif  // USE_OPENCV
  }

  // 否则直接粗暴地从datum里面获取形状的数据
  const int crop_size = param_.crop_size();
  const int datum_channels = datum.channels();
  const int datum_height = datum.height();
  const int datum_width = datum.width();
  // Check dimensions.
  CHECK_GT(datum_channels, 0);
  CHECK_GE(datum_height, crop_size);
  CHECK_GE(datum_width, crop_size);
  // Build BlobShape.
  vector<int> shape(4);
  shape[0] = 1;
  shape[1] = datum_channels;
  shape[2] = (crop_size)? crop_size: datum_height;
  shape[3] = (crop_size)? crop_size: datum_width;
  return shape;
}

template<typename Dtype>
vector<int> DataTransformer<Dtype>::InferBlobShape(
    const vector<Datum> & datum_vector) {
  const int num = datum_vector.size();
  CHECK_GT(num, 0) << "There is no datum to in the vector";
  // Use first datum in the vector to InferBlobShape.
  // 使用第一个来进行推断
  vector<int> shape = InferBlobShape(datum_vector[0]);
  // Adjust num to the size of the vector.
  shape[0] = num;
  return shape;
}

#ifdef USE_OPENCV
// 如果使用OpenCV
// 使用CVMat中的信息来推断形状
template<typename Dtype>
vector<int> DataTransformer<Dtype>::InferBlobShape(const cv::Mat& cv_img) {
  const int crop_size = param_.crop_size();
  const int img_channels = cv_img.channels();
  const int img_height = cv_img.rows;
  const int img_width = cv_img.cols;
  // Check dimensions.
  CHECK_GT(img_channels, 0);
  CHECK_GE(img_height, crop_size);
  CHECK_GE(img_width, crop_size);
  // Build BlobShape.
  vector<int> shape(4);
  shape[0] = 1;
  shape[1] = img_channels;
  shape[2] = (crop_size)? crop_size: img_height;
  shape[3] = (crop_size)? crop_size: img_width;
  return shape;
}

template<typename Dtype>
vector<int> DataTransformer<Dtype>::InferBlobShape(
    const vector<cv::Mat> & mat_vector) {
  const int num = mat_vector.size();
  CHECK_GT(num, 0) << "There is no cv_img to in the vector";
  // Use first cv_img in the vector to InferBlobShape.
  // 使用第一个来推断
  vector<int> shape = InferBlobShape(mat_vector[0]);
  // Adjust num to the size of the vector.
  shape[0] = num;
  return shape;
}
#endif  // USE_OPENCV

// 初始化随机数种子
template <typename Dtype>
void DataTransformer<Dtype>::InitRand() {
  // 要么需要镜像要么训练阶段和需要crop同时满足的情况下才初始化随机数种子
  const bool needs_rand = param_.mirror() ||
      (phase_ == TRAIN && param_.crop_size());
  if (needs_rand) {
    const unsigned int rng_seed = caffe_rng_rand();// 获得随机数种子（通过熵池或者时间生成种子）
    rng_.reset(new Caffe::RNG(rng_seed));//初始化随机数种子并实例化随机数生成器
  } else {
    rng_.reset();//否则随机数生成器设置为空
  }
}

// 产生从0到n的随机数
template <typename Dtype>
int DataTransformer<Dtype>::Rand(int n) {
  CHECK(rng_);
  CHECK_GT(n, 0);
  caffe::rng_t* rng =
      static_cast<caffe::rng_t*>(rng_->generator());
  return ((*rng)() % n);
}

INSTANTIATE_CLASS(DataTransformer);
/*
初始化类的宏定义是这样的，前面有讲过，这里再给出来
#define INSTANTIATE_CLASS(classname) \
  char gInstantiationGuard##classname; \
  template class classname<float>; \
  template class classname<double>
*/

}  // namespace caffe