遍历图片所有像素

 	// 载入图像  
  	img=cvLoadImage("lena.jpg",-1);
  	if(!img)
       {
   		printf("Could not load image file: %s\n",argv[1]);
    	exit(0);
  	}
  	// 获取图像信息	
  	height    = img->height;  
  	width     = img->width;	
  	step      = img->widthStep;	
  	channels  = img->nChannels;
  	data      = (uchar *)img->imageData;
  	
  	// 反转图像
  	for(i=0;i<height;i++) for(j=0;j<width;j++) for(k=0;k<channels;k++)
    	data[i*step+j*channels+k]=255-data[i*step+j*channels+k];