opencv 从摄像头获取图片并显示灰度图

opencv关于摄像头的几个api

/* start capturing frames from camera: index = camera_index + domain_offset (CV_CAP_*) */
CVAPI(CvCapture*) cvCreateCameraCapture( int index );

/* grab a frame, return 1 on success, 0 on fail.
  this function is thought to be fast               */
CVAPI(int) cvGrabFrame( CvCapture* capture );

/* get the frame grabbed with cvGrabFrame(..)
  This function may apply some frame processing like
  frame decompression, flipping etc.
  !!!DO NOT RELEASE or MODIFY the retrieved frame!!! */
CVAPI(IplImage*) cvRetrieveFrame( CvCapture* capture, int streamIdx CV_DEFAULT(0) );

/* Just a combination of cvGrabFrame and cvRetrieveFrame
   !!!DO NOT RELEASE or MODIFY the retrieved frame!!!      */
CVAPI(IplImage*) cvQueryFrame( CvCapture* capture );

/* stop capturing/reading and free resources */
CVAPI(void) cvReleaseCapture( CvCapture** capture );

很简单一个流程就是

1.cvCreateCameraCapture//获取捕捉器

2.cvQueryFrame//抓取一帧

3.cvReleaseCapture//释放捕捉器

灰度图

将一幅彩色图转换成灰度图 参见说明文档

（1） 字节型图像的灰度-彩色转换:
cvConvertImage(src, dst, flags=0);
 src = float/byte grayscale/color image
 dst = byte grayscale/color image
 flags = CV_CVTIMG_FLIP     (垂直翻转图像)
         CV_CVTIMG_SWAP_RB  (置换 R 和 B 通道)
（2） 彩色图像->灰度图像:
// Using the OpenCV conversion: 
cvCvtColor(cimg,gimg,CV_BGR2GRAY); // cimg -> gimg 
 
// Using a direct conversion: 
for(i=0;i<cimg->height;i++) for(j=0;j<cimg->width;j++) 
  gimgA[i][j]= (uchar)(cimgA[i][j].b*0.114 + 
                       cimgA[i][j].g*0.587 + 
                       cimgA[i][j].r*0.299);
（3） 不同彩色空间之间的转换:
cvCvtColor(src,dst,code); // src -> dst
 code    = CV_<X>2<Y>
 <X>/<Y> = RGB, BGR, GRAY, HSV, YCrCb, XYZ, Lab, Luv, HLS 
e.g.: CV_BGR2GRAY, CV_BGR2HSV, CV_BGR2Lab

上代码 比较清晰

#include <stdlib.h>
#include <opencv2/opencv.hpp>
using namespace std;
using namespace cv;


int main(int argc, _TCHAR* argv[])
{
    IplImage * tmpImg = 0;
    IplImage * grayImg = 0;    

    //初始化一个摄像头捕捉器
    CvCapture* capture = cvCreateCameraCapture(1);
    int num = 0;
    cvNamedWindow("camera");
    cvNamedWindow("gray");

    //取背景
    while( (tmpImg = cvQueryFrame(capture))!= NULL)
    {
        if(tmpImg == NULL)
            break;
        // Using the OpenCV conversion: 
        CvSize dst_size; //get the tmpImg's size
        dst_size.width = tmpImg->width;
        dst_size.height = tmpImg->height;
        grayImg = cvCreateImage(dst_size,tmpImg->depth,1);//create gray image
        cvCvtColor(tmpImg,grayImg,CV_BGR2GRAY); // tmpImg -> grayImg
 
        cvShowImage("camera",tmpImg);
        cvShowImage("gray",grayImg);

        if(grayImg != NULL)
            cvShowImage("gray",grayImg);
        waitKey(1000);
//        if(num>10)
//            imwrite(getImageName(num),Mat(tmpImg));
        if(++num == 120)
            break;
    }
    if(capture!=NULL)
        cvReleaseCapture(&capture);

    //销毁窗口
    cvDestroyWindow("camera");
    cvDestroyWindow("灰度图");
    //此函数等待按键，按键盘任意键就返回
    waitKey();
 
    return 0;
}