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Smoothing only a part of a Curve
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What functions/commands can I use to smooth only a part of my curve? Lets say I have data from x= 0 to x= 500 on the x-axis with corresponding y points. I would like to smooth only data between x= 200 to x= 400, and the rest to be the original data itself. So that sharp edges between x= 0 and x= 200 remains, and then between x= 200 to 400, I get a smooth curve part, and then beyond x= 400 it retains the original shape. There was nothing I could find that would let me smoothen only a part of my curve.
Could someone please help me on this one?
Best regards, Anirudh
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Answers (1)
Image Analyst
on 17 Feb 2014
Just smooth everything and replace the smoothed parts, like this code:
fontSize = 25;
% Make sample signal a noisy cosine
x = 1 : 500;
period = 70;
noisySignal = 3*cos(2*pi*x/period) + rand(1, length(x));
subplot(2,2,1);
plot(x, noisySignal, 'b.-');
title('Original Noisy Signal', 'FontSize', fontSize);
grid on;
yl = ylim();
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Apply the Savitzky-Golay filter.
k = 2; % Order of the polynomial
windowSize = 25;
smoothedSignal = sgolayfilt(noisySignal, k, windowSize);
subplot(2, 2, 2);
plot(x, smoothedSignal, 'b.-');
grid on;
title('Savitzky-Golay Filtered Signal', 'FontSize', fontSize);
% Make y limits be the same.
ylim(yl);
% Make a new signal with x=200 to 400 being smooth
newSignal = noisySignal; % Initialize.
newSignal(200:400) = smoothedSignal(200:400);
subplot(2, 2, 3:4);
plot(x, newSignal, 'b.-');
grid on;
title('Composite Signal', 'FontSize', fontSize);
% Make y limits be the same.
ylim(yl);
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/174357/image.jpeg)
You might also be interested in this from the Mathworks: http://www.mathworks.com/matlabcentral/answers/103916-how-can-i-smooth-a-signal-while-preserving-peaks-in-matlab-r2013a
3 Comments
Image Analyst
on 20 Feb 2014
It's virtually the same code. I don't really care WHERE you get noisy signal - I just made up the cosine curve because I needed some data. Of course you can get it however you need to , such as reading it in from a file, or whatever. After that the code is the same. Basically, filter it all and replace the chunk you want to with the filtered data.
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