/***************************************************************************
 * Func: inv_dct                                                           *
 *                                                                         *
 * Desc: performs an inverse Discrete Cosine Transform on an MxN array     *
 *                                                                         *
 * Params: DCT - MxN array of data for inverse transform                   *
 *         inverse - MxN array of inverse transformed data                 *
 ***************************************************************************/
void inv_dct(double DCT[M][N], double inverse[M][N])
    {
    int u, v;             /* frequency domain variables */
    int x, y;             /* spatial domain variables */
    double accum;         /* accumulator */
    double twoN;          /* 2 times N */
    double twoM;          /* 2 times M */
    double scale;         /* 2 / square_root(MN) */
    double Cu, Cv;        /* C(u) and C(v) */

    twoN = 2.0 * N;
    twoM = 2.0 * M;
    scale = 2.0 / sqrt((double)N*M);

    for(x=0; x<M; x++)
	for(y=0; y<N; y++)
	    {
	    accum = 0.0;
	    for(u=0; u<M; u++)
		for(v=0; v<N; v++)
		    {
		    if(u == 0)
			Cu = COEFF;
		    else
			Cu = 1.0;
		    if(v == 0)
			Cv = COEFF;
		    else
			Cv = 1.0;
		    accum += (Cu * Cv * cos((PI*u*(2*x+1))/twoM) *
			       cos((PI*v*(2*y+1))/twoN) * DCT[u][v]);

		    }
	    inverse[x][y] = accum * scale;
	    }
    }