Suppose that \(\begin{array}{@{}c@{\;}c@{}c@{}c} && &P_b \\ & \times & & P_b \\ \ = & & Q & P_b, \\ \end{array}\)where \(P\), \(Q\), and \(b\) represent three distinct digits 1-9. If \(Q=\frac{P}{2}\) and \(P\) is two less than \(b\), what is the value of the digit \(P\) ?
