qimage2ndarray | small python extension

My compliments on such an extensive report. Your issue lies probably in this weird setup you've got going on.

In your first example it works because label is a global variable, so displayFrame can access it as such. In the other case, label is only declared in the scope of the __init__ of the basicWindow instance, so displayFrame knows nothing about it.

Make label a member of the instance (self.label = QLabel()), displayFrame a method of the basicWindow class (def displayFrame(self):) and then access the label correctly; note that you also need to make both cap and timer member of the instance (self), otherwise their objects will be immediately "garbage collected" after __init__ returns.

Finally I reduce my exe file size from 233MB to 64MB by solution provided here :

1. Create a new conda environment pyinstaller-env
2. install numpy with conda install conda-forge::numpy "blas=*=openblas"
3. Switch environment to pyinstaller-env and packaging my QT application.

n Python, all numbers are considered "True" except for the 0 that is "False", so when you convert a Boolean to "alpha" if a pixel of 10 is a black color in the gray scale, it becomes 1 that is white in the boolean scale so that it generates the change, so to convert to boolean using astype(np.bool) is not the best option but to establish a more suitable threshold, for example 127:

To be able to make an item visible, the first task we must do is to identify it, for that we could establish an id for each item. We use the setData() and data() method, then we use the fitInView() method to scale the window to the item, this does not make the item totally visible because if there is another item on it we will get an unwanted output, for that we use setZValue(), the higher the value of Z will be on top of another item, your code will not provide an example that can be tested correctly so create my own example:

When you use QtGui.QCursor.pos() is getting the coordinates of the cursor with respect to the screen, but when you want to paint a widget you must be in the coordinates of the widget, for it the widget has the mapToGlobal() method: