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问题描述

我要编写使用OpenCV进行视频捕捉一个跨平台的应用程序。在所有的例子中,我发现从相机帧用抓功能,并等待一段时间处理。我想处理序列中的每一帧。我想定义自己的回调函数,这将在每次执行,当一个新的帧准备处理(如在的的DirectShow 的适用于Windows,当你定义和投入图自己的过滤对于这样的目的)。

I want to write a cross-platform application using OpenCV for video capture. In all the examples, i've found frames from the camera are processed using the grab function and waiting for a while. And i want to process every frame in a sequence. I want to define my own callback function, which will be executed every time, when a new frame is ready to be processed (like in directshow for Windows, when you defining and putting into the graph your own filter for such purposes).

所以现在的问题是:我怎么能做到这一点。

So the question is: how can i do this?

推荐答案

据低于code,所有的回调,就必须遵循这样的定义:

According to the code below, all callbacks would have to follow this definition:

IplImage* custom_callback(IplImage* frame);

此签名意味着回调将要由系统检索的各帧上执行。在我的例子,make_it_gray()分配一个新的形象来保存灰度转换的结果并返回。这意味着你以后必须释放此框架上的code。我补上了code注释一下吧。

This signature means the callback is going to be executed on each frame retrieved by the system. On my example, make_it_gray() allocates a new image to save the result of the grayscale conversion and returns it. This means you must free this frame later on your code. I added comments on the code about it.

请注意,如果你的回调需要大量的处理,系统可能会跳过从相机几帧。考虑建议的保罗 - [R 的和的 diverscuba23 的那样。

Note that if your callback demands a lot of processing, the system might skip a few frames from the camera. Consider the suggestions Paul R and diverscuba23 did.

#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:

我改变了code以上所以它的显示当前帧率的并执行的手动灰度转换的。他们是在code小的调整,我这么做是为了教育目的,所以一个人知道如何在像素级别执行操作。

I changed the code above so it prints the current framerate and performs a manual grayscale conversion. They are small tweaks on the code and I did it for education purposes so one knows how to perform operations at pixel level.

#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->height), frame->depth, 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, 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);

    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: %d\n", fps);
      }

      // 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;
}

这篇关于OpenCV的:过程的每一帧的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

08-23 13:59