3.8

FFTSmooth v1

../_images/FFTSmooth-v1_dlg.png

FFTSmooth dialog.

Summary

Performs smoothing of a spectrum using various filters.

Properties

Name Direction Type Default Description
InputWorkspace Input MatrixWorkspace Mandatory The name of the input workspace.
OutputWorkspace Output MatrixWorkspace Mandatory The name of the output workspace.
WorkspaceIndex Input number 0 Workspace index for smoothing
Filter Input string Zeroing The type of the applied filter. Allowed values: [‘Zeroing’]
Params Input string   The filter parameters

Description

FFTSmooth uses the FFT algorithm to create a Fourier transform of a spectrum, applies a filter to it and transforms it back. The filters remove higher frequencies from the spectrum which reduces the noise.

This version of the FFTSmooth algorithm has one filter:

Zeroing

  • Filter: “Zeroing”
  • Params: “n” - an integer greater than 1 meaning that the Fourier coefficients with frequencies outside the 1/n of the original range will be set to zero.

Usage

Example: Zeroing with Params=2

ws = CreateSampleWorkspace(function="Multiple Peaks",XMax=20,BinWidth=0.2,BankPixelWidth=1,NumBanks=1)

#add a bit of predictable noise
noiseAmp=0.1
noiseArray= []
for i in range(ws.blocksize()):
    noiseAmp = -noiseAmp
    noiseArray.append(noiseAmp)

for j in range(ws.getNumberHistograms()):
    ws.setY(j,ws.readY(j)+noiseArray)


wsSmooth = FFTSmooth(ws, Params='2', Version=1)

print "bin Orig  Smoothed"
for i in range (0,100,10):
    print "%i  %.2f  %.2f" % (i, ws.readY(0)[i], wsSmooth.readY(0)[i])
../_images/FFTSmoothZeroing.png

Output:

bin Orig  Smoothed
0  0.20  0.30
10  0.20  0.30
20  0.37  0.47
30  10.20  10.30
40  0.37  0.47
50  0.20  0.30
60  8.20  8.30
70  0.20  0.30
80  0.20  0.30
90  0.20  0.30

Categories: Algorithms | Arithmetic\FFT | Transforms\Smoothing

Source

C++ source: FFTSmooth.cpp

C++ header: FFTSmooth.h