【求助】代码运行后，摄像头启动，但窗口是黑的

大神求助啊 程序没有报错 代码如下
#include "cv.h"
#include "highgui.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <math.h>
#include <float.h>
#include <limits.h>
#include <time.h>
#include <ctype.h>
#include "cxcore.h"
#include <iostream>
#ifdef _EiC
#define WIN32
#endif
static CvMemStorage* storage = 0;
static CvHaarClassifierCascade* cascade = 0;
void detect_and_draw( IplImage* image );
const char* cascade_name = "haarcascade_frontalface_alt.xml";
/* "haarcascade_profileface.xml";*/
int main( int argc, char** argv )
{
cvNamedWindow( "capture", 1 );
cascade_name = "haarcascade_frontalface_alt2.xml";
cascade = (CvHaarClassifierCascade*)cvLoad( cascade_name, 0, 0, 0 );
if( !cascade )
{
fprintf( stderr, "ERROR: Could not load classifier cascade\n" );
return -1;
}
storage = cvCreateMemStorage(0);
cvNamedWindow( "result", 1 );
IplImage* frame=NULL;
IplImage* image=NULL;
int j=0;
CvCapture* capture=cvCaptureFromCAM(0);
if(!capture) //警告
{
printf("不能打开摄像头！\n");
return -1;
}
else
{
while(j<= 300)
{
frame=cvQueryFrame(capture);
cvShowImage("capture",frame);
image = frame;
if( image )
{
detect_and_draw( image );
}
j++;
if(cvWaitKey(2)>0)
break;
}
}
cvReleaseImage( &image );
cvDestroyWindow("result");
cvDestroyWindow("capture");
return 0;
}
void detect_and_draw(IplImage* img )
{ double scale=1.2;
static CvScalar colors[] = {
{0, 0, 255}, {0, 128, 255 }, { 0, 255, 255 }, { 0, 255, 0 },
{ 255, 128, 0 }, { 255, 255, 0}, { 255, 0, 0 }, { 255, 0, 255 }//去掉了旁边的中括号；
};//Just some pretty colors to draw with
IplImage* gray = cvCreateImage(cvSize(img->width,img->height),8,1);
IplImage* small_img=cvCreateImage(cvSize(cvRound(img->width/scale),cvRound(img->height/scale)),8,1);
cvCvtColor(img,gray, CV_BGR2GRAY);
cvResize(gray, small_img, CV_INTER_LINEAR);
cvEqualizeHist(small_img,small_img); //直方图均衡
//Detect objects if any
//
cvClearMemStorage(storage);
double t = (double)cvGetTickCount();
CvSeq* objects = cvHaarDetectObjects(small_img, cascade, storage, 1.1, 2, 0/*CV_HAAR_DO_CANNY_PRUNING*/,cvSize(30,30)) ;
t = (double)cvGetTickCount() - t;
printf( "detection number = %d detection time = %gms\n",objects->total,t/((double)cvGetTickFrequency()*1000.) );
//Loop through found objects and draw boxes around them
for(int i=0;i<(objects? objects->total:0);++i)
{
CvRect* r=(CvRect*)cvGetSeqElem(objects,i);
cvRectangle(img, cvPoint(r->x*scale,r->y*scale), cvPoint((r->x+r->width)*scale,(r->y+r->height)*scale), colors[i%8]);
}
for( int i = 0; i < (objects? objects->total : 0); i++ )
{
CvRect* r = (CvRect*)cvGetSeqElem( objects, i );
CvPoint center;
int radius;
center.x = cvRound((r->x + r->width*0.5)*scale);
center.y = cvRound((r->y + r->height*0.5)*scale);
radius = cvRound((r->width + r->height)*0.25*scale);
cvCircle( img, center, radius, colors[i%8], 3, 8, 0 );
}
cvShowImage( "result", img );
cvReleaseImage(&gray);
cvReleaseImage(&small_img);
}