Visual C++ :: Get Cursor Position For Picture Control With Scroll Bar

I was loaded a bitmap using this code. I'm using mousemove method to known the Dialog's mouse move position & get the RGB pixel.

I want to get the picture contol's mouse move position & using this point (x,y) i will get the particular color ref value R, G, & B.

My picture control size is 256 * 256 & I was loaded an image 512 * 512.

Using scroll bar, I was view the image but can't get the particular pixel in the picture control.

The below code get the Dialog's mouse move cursor position & RGB Values only.

Code:
void CMyDlg::OnMouseMove(UINT nFlags, CPoint point) {
int R,G,B;
COLORREF ref;
ref = m_dcMem.GetPixel(point.x,point.y);
R = GetRValue(ref);
G = GetGValue(ref);
B = GetBValue(ref);
CButton::OnMouseMove(nFlags, point);
}

How can i get the picture contol position even use the scroll bar.