這是我在本站看到的一階FFT程式 請教一下 剛接觸影像處理 有人知道這個副程式中的 ar與ai與n,isign代表什麼嗎? 能否給與指教 或是能提供小弟有關一階FFT,IFFT的程式範例? 感激..... void FFT1D(double* ar, double* ai,int n,int isign) { double u_r,u_i,w_r,w_i,t_r,t_i; int i,j,k,m,ip; int ln,n2,stepN,stepN2; //resort n2 = n / 2; j = 1; for (i = 1; i < n; i ) { if (i < j) { t_r = ar[i - 1]; t_i = ai[i - 1]; ar[i - 1] = ar[j - 1]; ai[i - 1] = ai[j - 1]; ar[j - 1] = t_r; ai[j - 1] = t_i; } k = n2; while (k < j) { j = j - k; k = k / 2; } j = j k; } // ln = log(n)/log(2); stepN=1; for (k = 1; k <= ln; k ) /* loops thru stages */ { stepN*= 2; stepN2=stepN / 2; w_r = cos(Pi/(double)stepN2 ); w_i = isign*sin(Pi/(double)stepN2 ); u_r = 1.0; u_i = 0.0; for (m = 1; m <= stepN2; m ) /* loops thru 1/2 twiddle values per stage */ { for (i = m; i <= n; i = stepN) /* loops thru points per 1/2 twiddle */ { ip = i stepN2; t_r = ar[ip - 1] * u_r - u_i * ai[ip - 1]; t_i = ai[ip - 1] * u_r u_i * ar[ip - 1]; ar[ip - 1] = ar[i - 1] - t_r; ai[ip - 1] = ai[i - 1] - t_i; ar[i - 1] = ar[i - 1] t_r; ai[i - 1] = ai[i - 1] t_i; } t_r = u_r * w_r - w_i * u_i; u_i = w_r * u_i w_i * u_r; u_r = t_r; } } if(isign==-1) { for (i = 0; i < n; i ) { ar[i]/=n; ai[i]/=n; } } }

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