c – OpenCV：处理每一帧

IplImage* custom_callback(IplImage* frame);

此签名表示将在系统检索的每个帧上执行回调.在我的例子中,make_it_gray()分配一个新图像以保存灰度转换的结果并返回它.这意味着您必须稍后在代码中释放此框架.我添加了关于它的代码的评论.

请注意,如果您的回调需要大量处理,系统可能会跳过相机中的几帧.考虑Paul R和diverscuba23的建议.

#include <stdio.h>
#include "cv.h"
#include "highgui.h"


typedef IplImage* (*callback_prototype)(IplImage*);


/* 
 * make_it_gray: our custom callback to convert a colored frame to its grayscale version.
 * Remember that you must deallocate the returned IplImage* yourself after calling this function.
 */
IplImage* make_it_gray(IplImage* frame)
{
    // Allocate space for a new image
    IplImage* gray_frame = 0;
    gray_frame = cvCreateImage(cvSize(frame->width,frame->height),frame->depth,1);
    if (!gray_frame)
    {
      fprintf(stderr,"!!! cvCreateImage failed!n" );
      return NULL;
    }

    cvCvtColor(frame,gray_frame,CV_RGB2GRAY);
    return gray_frame; 
}

/*
 * process_video: retrieves frames from camera and executes a callback to do individual frame processing.
 * Keep in mind that if your callback takes too much time to execute,you might loose a few frames from 
 * the camera.
 */
void process_video(callback_prototype custom_cb)
{           
    // Initialize camera
    CvCapture *capture = 0;
    capture = cvCaptureFromCAM(-1);
    if (!capture) 
    {
      fprintf(stderr,"!!! Cannot open initialize webcam!n" );
      return;
    }

    // Create a window for the video 
    cvNamedWindow("result",CV_WINDOW_AUTOSIZE);

    IplImage* frame = 0;
    char key = 0;
    while (key != 27) // ESC
    {    
      frame = cvQueryFrame(capture);
      if(!frame) 
      {
          fprintf( stderr,"!!! cvQueryFrame failed!n" );
          break;
      }

      // Execute callback on each frame
      IplImage* processed_frame = (*custom_cb)(frame);

      // Display processed frame
      cvShowImage("result",processed_frame);

      // Release resources
      cvReleaseImage(&processed_frame);

      // Exit when user press ESC
      key = cvWaitKey(10);
    }

    // Free memory
    cvDestroyWindow("result");
    cvReleaseCapture(&capture);
}

int main( int argc,char **argv )
{
    process_video(make_it_gray);

    return 0;
}

编辑：

我更改了上面的代码,因此它打印当前帧速率并执行手动灰度转换.它们是对代码的小调整,我是出于教育目的而做的,所以我们知道如何在像素级执行操作.

#include <stdio.h>
#include <time.h>

#include "cv.h"
#include "highgui.h"


typedef IplImage* (*callback_prototype)(IplImage*);


/* 
 * make_it_gray: our custom callback to convert a colored frame to its grayscale version.
 * Remember that you must deallocate the returned IplImage* yourself after calling this function.
 */
IplImage* make_it_gray(IplImage* frame)
{
    // New IplImage* to store the processed image
    IplImage* gray_frame = 0; 

    // Manual grayscale conversion: ugly,but shows how to access each channel of the pixels individually
    gray_frame = cvCreateImage(cvSize(frame->width,frame->nChannels);
    if (!gray_frame)
    {
      fprintf(stderr,"!!! cvCreateImage failed!n" );
      return NULL;
    }

    for (int i = 0; i < frame->width * frame->height * frame->nChannels; i += frame->nChannels)
    {
        gray_frame->imageData[i] = (frame->imageData[i] + frame->imageData[i+1] + frame->imageData[i+2])/3;   //B
        gray_frame->imageData[i+1] = (frame->imageData[i] + frame->imageData[i+1] + frame->imageData[i+2])/3; //G
        gray_frame->imageData[i+2] = (frame->imageData[i] + frame->imageData[i+1] + frame->imageData[i+2])/3; //R
    }

    return gray_frame; 
}

/*
 * process_video: retrieves frames from camera and executes a callback to do individual frame processing.
 * Keep in mind that if your callback takes too much time to execute,CV_WINDOW_AUTOSIZE);    

    double elapsed = 0;
    int last_time = 0;
    int num_frames = 0;

    IplImage* frame = 0;
    char key = 0;
    while (key != 27) // ESC
    {    
      frame = cvQueryFrame(capture);
      if(!frame) 
      {
          fprintf( stderr,"!!! cvQueryFrame failed!n" );
          break;
      }

      // Calculating framerate
      num_frames++;
      elapsed = clock() - last_time;
      int fps = 0;
      if (elapsed > 1)
      {
          fps = floor(num_frames / (float)(1 + (float)elapsed / (float)CLOCKS_PER_SEC));
          num_frames = 0;
          last_time = clock() + 1 * CLOCKS_PER_SEC;
          printf("FPS: %dn",fps);
      }

      // Execute callback on each frame
      IplImage* processed_frame = (*custom_cb)(frame);  

      // Display processed frame
      cvShowImage("result",char **argv )
{
    process_video(make_it_gray);

    return 0;
}