libfacedetection介绍

libfacedetection是一个开源的人脸检测库，使用C编写，将模型文件转化为C的静态变量，不依赖外部第三方库，使用时可以直接把源代码拷到自己的工程，也可以使用动态库(so)/静态库(a)的方式来调用，使用还是很方便的。

这里介绍基于该库的动态链接库编译及调用的demo.

2.下载及编译

git clone https://github.com/ShiqiYu/libfacedetection.git

cmake生成makefile，再make生成动态库和静态库

cmake -DCMAKE_INSTALL_PREFIX=/usr/local/libfacedetection -G "Unix Makefiles" ..

cmake之后会生成Makefile

查看动态库的依赖

进入example目录
由于linux没有可视化窗口，因此将imshow注释掉，再通过imwrite将结果保存下来

g++ libfacedetectcnn-example.cpp -o test `pkg-config --cflags --libs opencv` -I ../src/ -L ../build/ -lfacedetection

结果如下

3.代码分析

输入bgr格式数据，调用facedetect_cnn函数即可返回检测结果，再使用rectangle函数将矩阵画上去。

#include <stdio.h>
#include <opencv2/opencv.hpp>
#include "facedetectcnn.h"

//define the buffer size. Do not change the size!
#define DETECT_BUFFER_SIZE 0x20000
using namespace cv;

int main(int argc, char* argv[])
{
    if(argc != 2)
    {
        printf("Usage: %s <image_file_name>\n", argv[0]);
        return -1;
    }

    //load an image and convert it to gray (single-channel)
    Mat image = imread(argv[1]); 
    if(image.empty())
    {
      fprintf(stderr, "Can not load the image file %s.\n", argv[1]);
      return -1;
    }

    int * pResults = NULL; 
      //pBuffer is used in the detection functions.
      //If you call functions in multiple threads, please create one buffer for each thread!
      unsigned char * pBuffer = (unsigned char *)malloc(DETECT_BUFFER_SIZE);
      if(!pBuffer)
      {
          fprintf(stderr, "Can not alloc buffer.\n");
          return -1;
      }

    ///
    // CNN face detection 
    // Best detection rate
    //
    //!!! The input image must be a BGR one (three-channel) instead of RGB
    //!!! DO NOT RELEASE pResults !!!
    pResults = facedetect_cnn(pBuffer, (unsigned char*)(image.ptr(0)), image.cols, image.rows, (int)image.step);

      printf("%d faces detected.\n", (pResults ? *pResults : 0));
    Mat result_cnn = image.clone();
    //print the detection results
    for(int i = 0; i < (pResults ? *pResults : 0); i++)
    {
          short * p = ((short*)(pResults+1))+142*i;
      int x = p[0];
      int y = p[1];
      int w = p[2];
      int h = p[3];
      int confidence = p[4];
      int angle = p[5];

      printf("face_rect=[%d, %d, %d, %d], confidence=%d, angle=%d\n", x,y,w,h,confidence, angle);
      rectangle(result_cnn, Rect(x, y, w, h), Scalar(0, 255, 0), 2);
    }
    imshow("result_cnn", result_cnn);

    waitKey();

      //release the buffer
      free(pBuffer);

    return 0;
}

参考
[1] https://github.com/ShiqiYu/libfacedetection