Explanation of IplImage* img

Question

I just started learning OpenCV with "Learning OpenCV Computer Vision with the OpenCV Library".

In the first example which demonstrates how to display a picture, it has a line

IplImage* img = cvLoadImage("name.type")

Although the book explains it, I still do not fully know what exactly IplImage* img does.

Does cvLoadImage loads the image to img which IplImage is pointing to? Can anyone explain this to me please? Thank you

Answer 1

• img is the name of the variable, might as well be blahblahblah;

• IplImage is the type of the variable, it's just a struct that contains the image data itself plus some info (size, color depth, etc.) on the image;

  typedef struct _IplImage {
  int                  nSize;
  int                  ID;
  int                  nChannels;
  int                  alphaChannel;
  int                  depth;
  char                 colorModel[4];
  char                 channelSeq[4];
  int                  dataOrder;
  int                  origin;
  int                  align;
  int                  width;
  int                  height;
  struct _IplROI*      roi;
  struct _IplImage*    maskROI;
  void*                imageId;
  struct _IplTileInfo* tileInfo;
  int                  imageSize;
  char*                imageData;
  int                  widthStep;
  int                  BorderMode[4];
  int                  BorderConst[4];
  char*                imageDataOrigin;
  } IplImage;
  

For more info on IplImage: Other question about IplImage

• cvLoadImage provides a pointer to an IplImage, which means it creates an IplImage when it loads it and returns you it's emplacement.

Do not forget to do cvReleaseImage(&img) when you are finished with it, if you do not want to have memory leaks.