Problems with DCT and IDCT algorithm in java

Question

Here I have my DCT algorithm class with \"applyDCT\" and \"applyIDCT\" methods. Technically after doing a forward DCT (discrete cosine transform) on a 2x2 table of random intege

Answer 1

I have resolved this problem, I am sorry if my question was unclear but here is what was not right: The IDCT method had to have the coefficient inside the i and j for loops :

public double[][] applyIDCT(double[][] F) {
        double[][] f = new double[N][N];
        for (int i=0;i<N;i++) {
          for (int j=0;j<N;j++) {
            double sum = 0.0;
            for (int u=0;u<N;u++) {
              for (int v=0;v<N;v++) {
                sum+=(c[u]*c[v])/4.0*Math.cos(((2*i+1)/(2.0*N))*u*Math.PI)*Math.cos(((2*j+1)/(2.0*N))*v*Math.PI)*F[u][v];
              }
            }
            f[i][j]=Math.round(sum);
          }
        }
        return f;
    }

This only works for a 8x8 bloc of data, or else you would have to change this:

(c[u]*c[v])/4.0)

into something like this:

(2*c[u]*c[v])/Math.sqrt(M*N)

Where M and N are the dimentions of the table...

Here are the results with a 2x2 block of data:

Original values
---------------
54.0 => f[0][0]
35.0 => f[0][1]
128.0 => f[1][0]
185.0 => f[1][1]

From f to F
-----------
200.99999999999994 => F[0][0]
-18.99999999999997 => F[0][1]
-111.99999999999997 => F[1][0]
37.99999999999999 => F[1][1]

Back to f
---------
54.0 => f[0][0]
35.0 => f[0][1]
128.0 => f[1][0]
185.0 => f[1][1]