# Inverse Discrete Wavelet transform

Started by July 7, 2008
```Below is a reply by Jani Huhtanen in another old thread...

>Below is a diagram of the synthesis part of the wavelet transform (one
>level):
>
>y0[n]--UpSample--x0[n]--G0(z)--z0[n]--
>                                     + ---> z[n]
>y1[n]--UpSample--x1[n]--G1(z)--z1[n]--
>
>Say that y0[n] and y1[n] are defined for n=1..8 (i.e. 8 samples). After
>UpSample x0[n] and x1[n] are defined for n=1..16 (i.e. 16 samples), where

>
>        x0[2*n] = y0[n],
>        x0[2*n+1] = 0,
>
>and
>
>        x1[2*n] = y1[n],
>        x1[2*n+1] = 0.
>
>At this point the sample count has doubled from 8 to 16 for both detail
and
>approximation parts. Next these upsampled signals x0 and x1 are filtered
by
>G0 and G1 respectively. This does not increase the sample count.
>
>
>Jani Huhtanen
>Tampere University of Technology, Pori
>

In regards to this topic, I am still trying to understand DWT.
After upsampling is done, Zeros are inserted between the coefficents(8
samples becomes 16 samples). After filtering/convolution is done, does the
zeros change to some other value(ie. IDWT change the zero to a non-zero
value)?

```