OpenCV中获取图像某一像素值

IplImage
  |-- int  nChannels;     // Number of color channels (1,2,3,4)
  |-- int  depth;         // Pixel depth in bits: 
  |                       //   IPL_DEPTH_8U, IPL_DEPTH_8S, 
  |                       //   IPL_DEPTH_16U,IPL_DEPTH_16S, 
  |                       //   IPL_DEPTH_32S,IPL_DEPTH_32F, 
  |                       //   IPL_DEPTH_64F
  |-- int  width;         // image width in pixels
  |-- int  height;        // image height in pixels
  |-- char* imageData;    // pointer to aligned image data
  |                       // Note that color images are stored in BGR order
  |-- int  dataOrder;     // 0 - interleaved color channels, 
  |                       // 1 - separate color channels
  |                       // cvCreateImage can only create interleaved images
  |-- int  origin;        // 0 - top-left origin,
  |                       // 1 - bottom-left origin (Windows bitmaps style)
  |-- int  widthStep;     // size of aligned image row in bytes
  |-- int  imageSize;     // image data size in bytes = height*widthStep
  |-- struct _IplROI *roi;// image ROI. when not NULL specifies image
  |                       // region  to be processed.
  |-- char *imageDataOrigin; // pointer to the unaligned origin of image data
  |                          // (needed for correct image deallocation)
  |
  |-- int  align;         // Alignment of image rows: 4 or 8 byte alignment
  |                       // OpenCV ignores this and uses widthStep instead
  |-- char colorModel[4]; // Color model - ignored by OpenCV
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