analyze_lpf Method (AnWTFilter)

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Filters the input signal by this analysis filter, decomposing it in a low-pass and a high-pass signal. This method performs the filtering and the subsampling with the low pass first filtering convention.

The input signal resides in the inSig array. The index of the first sample to filter (i.e. that will generate the first low-pass output sample) is given by inOff. The number of samples to filter is given by inLen. This array must be of the same type as the one for which the particular implementation works with (which is returned by the getDataType() method).

The input signal can be interleaved with other signals in the same inSig array, and this is determined by the inStep argument. This means that the first sample of the input signal is inSig[inOff], the second is inSig[inOff+inStep], the third is inSig[inOff+2*inStep], and so on. Therefore if inStep is 1 there is no interleaving. This feature allows to filter columns of a 2-D signal, when it is stored in a line by line order in inSig, without having to copy the data, in this case the inStep argument should be the line width.

This method also allows to apply the analysis wavelet filter by parts in the input signal using an overlap and thus producing the same coefficients at the output. The tailOvrlp argument specifies how many samples in the input signal, before the first one to be filtered, can be used for overlap. Then, the filter instead of extending the input signal will use those samples to calculate the first output samples. The argument tailOvrlp can be 0 for no overlap, or some value that provides partial or full overlap. There should be enough samples in the input signal, before the first sample to be filtered, to support the overlap. The headOvrlp provides the same functionality but at the end of the input signal. The inStep argument also applies to samples used for overlap. This overlap feature can be used for line-based wavelet transforms (in which case it will only be used when filtering the columns) or for overlapping block-based wavelet transforms (in which case it will be used when filtering lines and columns).

The low-pass output signal is placed in the lowSig array. The lowOff and lowStep arguments are analogous to the inOff and inStep ones, but they apply to the lowSig array. The lowSig array must be long enough to hold the low-pass output signal.

The high-pass output signal is placed in the highSig array. The highOff and highStep arguments are analogous to the inOff and inStep ones, but they apply to the highSig array. The highSig array must be long enough to hold the high-pass output signal.

Syntax

Visual Basic
C#

'Declaration
 
Public MustOverride Sub analyze_lpf( _
   ByVal inSig As Object, _
   ByVal inOff As Integer, _
   ByVal inLen As Integer, _
   ByVal inStep As Integer, _
   ByVal lowSig As Object, _
   ByVal lowOff As Integer, _
   ByVal lowStep As Integer, _
   ByVal highSig As Object, _
   ByVal highOff As Integer, _
   ByVal highStep As Integer _
)

public abstract void analyze_lpf( 
   object inSig,
   int inOff,
   int inLen,
   int inStep,
   object lowSig,
   int lowOff,
   int lowStep,
   object highSig,
   int highOff,
   int highStep
)

Parameters

inSig: This is the array that contains the input signal. It must be of the correct type (e.g., it must be int[] if getDataType() returns TYPE_INT).
inOff: This is the index in inSig of the first sample to filter.
inLen: This is the number of samples in the input signal to filter.
inStep: This is the step, or interleave factor, of the input signal samples in the inSig array. See above.
lowSig: This is the array where the low-pass output signal is placed. It must be of the same type as inSig and it should be long enough to contain the output signal.
lowOff: This is the index in lowSig of the element where to put the first low-pass output sample.
lowStep: This is the step, or interleave factor, of the low-pass output samples in the lowSig array. See above.
highSig: This is the array where the high-pass output signal is placed. It must be of the same type as inSig and it should be long enough to contain the output signal.
highOff: This is the index in highSig of the element where to put the first high-pass output sample.
highStep: This is the step, or interleave factor, of the high-pass output samples in the highSig array. See above.

Reference

AnWTFilter Class
AnWTFilter Members
GrapeCity.Documents.Imaging.jpeg.jj2000.j2k.wavelet.IWaveletFilter.getDataType