“…In fact, although the theory of wavelet frames has been developed very fast in the past twenty years, e.g., see [1-4, 8, 11, 16-20] for an overview, it is still a hard work to find the dual frame for a given wavelet frame [5,6,14]. Motivated by [9,10,12,13,22,23], where the convergence of Riemannian sums of the inverse windowed Fourier transform was studied, the authors [15] studied the approximation of f with the Riemannian sums defined by (5). It was shown that under certain conditions, S a,b;ψ1,ψ2 f converges to f as (a, b) tends to (1,0).…”