Learning OpenCV

Creating a Window

First, we want to show an image on the screen using HighGUI. The function that does this for us is cvNamedWindow(). The function expects a name for the new window and one flag. The name appears at the top of the window, and the name is also used as a handle for the window that can be passed to other HighGUI functions. The flag indicates if the window should autosize itself to fit an image we put into it. Here is the full prototype:

int cvNamedWindow(
    const char* name,
    int         flags = CV_WINDOW_AUTOSIZE
);

Notice the parameter flags. For now, the only valid options available are to set flags to 0 or to use the default setting, CV_WINDOW_AUTOSIZE. If CV_WINDOW_AUTOSIZE is set, then HighGUI resizes the window to fit the image. Thereafter, the window will automatically resize itself if a new image is loaded into the window but cannot be resized by the user. If you don't want autosizing, you can set this argument to 0; then users can resize the window as they wish.

Once we create a window, we usually want to put something into it. But before we do that, let's see how to get rid of the window when it is no longer needed. For this we use cvDestroyWindow(), a function whose argument is a string: the name given to the window when it was created. In OpenCV, windows are referenced by name instead of by some unfriendly (and invariably OS-dependent) "handle". Conversion between handles and names happens under the hood of HighGUI, so you needn't worry about it.

Having said that, some ...