"The following expression defines the length of the delay line vector of the low frequency component filter in terms of the C language (integer division by two is used here for simplicity):
dlyLowLen= (lenLow+offsLow- 1) / 2,
wherelenLowandoffsLoware respectively the length and additional delay of the low frequency component filter."
The way I understand it, to set the delay line is similar to setting some border extensions. If, for example, we have some approximation and detail coefficient, both of length 15, and our low and high pass filters have length 4, the convolution of the 4-element filter with a signal of length 30 (signal of length 15 after upsampling) will give us an output of length 30-4+1=27. In order to get an output of length 30, we need a border extension of length 3. Now according to the above, the delay line has length 1 (if we set the offset to be 0, as in the IPP manual example). Assuming that it is upsampled as well, we get a border extension of 2, which is still not enough. How do we get to a signal of the right length in the end?!?!?!?!?
2) I cannot understand if the delay line is added at the beginning or at the end of the signal.
3) In the documentation (WTInv), there is a nice figure of the one dimensional inverse transform. The delay line seems to be added AFTER upsampling and filtering... how is this possible? What does this means?
I'm trying to play with the parameters and to understand how do I get to the results I see, but I really cannot figure it out.... if I cannot even get this, I don't think I have any chance of setting the parameters correctly for any input slightly different from the examples in the IPP manual.
Could someone please help me? I feel a bit desperate...