Plot smooth line with PyPlot

Question

I've got the following simple script that plots a graph:

import matplotlib.pyplot as plt
import numpy as np

T = np.array([6, 7, 8, 9, 10, 11, 12])
power = np.array([1.53E+03, 5.92E+02, 2.04E+02, 7.24E+01, 2.72E+01, 1.10E+01, 4.70E+00])

plt.plot(T,power)
plt.show()

As it is now, the line goes straight from point to point which looks ok, but could be better in my opinion. What I want is to smooth the line between the points. In Gnuplot I would have plotted with smooth cplines.

Is there an easy way to do this in PyPlot? I've found some tutorials, but they all seem rather complex.

Answer 1

You could use scipy.interpolate.spline to smooth out your data yourself:

from scipy.interpolate import spline

xnew = np.linspace(T.min(),T.max(),300) #300 represents number of points to make between T.min and T.max

power_smooth = spline(T,power,xnew)

plt.plot(xnew,power_smooth)
plt.show()

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spline is deprecated in scipy 0.19.0, use Bspline class instead.

Switching from spline to Bspline isn't a straightforward copy/paste and requires a little tweaking:

from scipy.interpolate import make_interp_spline, BSpline

xnew = np.linspace(T.min(),T.max(),300) #300 represents number of points to make between T.min and T.max

spl = make_interp_spline(T, power, k=3) #BSpline object
power_smooth = spl(xnew)

plt.plot(xnew,power_smooth)
plt.show()

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Before:

After:

Answer 2

I presume you mean curve-fitting and not anti-aliasing from the context of your question. PyPlot doesn't have any built-in support for this, but you can easily implement some basic curve-fitting yourself, like the code seen here, or if you're using GuiQwt it has a curve fitting module. (You could probably also steal the code from SciPy to do this as well).

Answer 3

For this example spline works well, but if the function is not smooth inherently and you want to have smoothed version you can also try:

from scipy.ndimage.filters import gaussian_filter1d

ysmoothed = gaussian_filter1d(y, sigma=2)
plt.plot(x, ysmoothed)
plt.show()

if you increase sigma you can get a more smoothed function.