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！