`numpy:blackman`

source: /numpy/lib/_function_base_impl.py :3036

Signature

def blackman ( M )

Summary

Return the Blackman window.

Extended Summary

The Blackman window is a taper formed by using the first three terms of a summation of cosines. It was designed to have close to the minimal leakage possible. It is close to optimal, only slightly worse than a Kaiser window.

Parameters

M : int: Number of points in the output window. If zero or less, an empty array is returned.

Returns

out : ndarray: The window, with the maximum value normalized to one (the value one appears only if the number of samples is odd).

Notes

The Blackman window is defined as

w (n) = 0.42 - 0.5 cos (2 π n / M) + 0.08 cos (4 π n / M)

Most references to the Blackman window come from the signal processing literature, where it is used as one of many windowing functions for smoothing values. It is also known as an apodization (which means "removing the foot", i.e. smoothing discontinuities at the beginning and end of the sampled signal) or tapering function. It is known as a "near optimal" tapering function, almost as good (by some measures) as the kaiser window.

Examples

import numpy as np
import matplotlib.pyplot as plt

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np.blackman(12)

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Plot the window and the frequency response. .. plot:: :include-source: import matplotlib.pyplot as plt from numpy.fft import fft, fftshift window = np.blackman(51) plt.plot(window) plt.title("Blackman window") plt.ylabel("Amplitude") plt.xlabel("Sample") plt.show() # doctest: +SKIP plt.figure() A = fft(window, 2048) / 25.5 mag = np.abs(fftshift(A)) freq = np.linspace(-0.5, 0.5, len(A)) with np.errstate(divide='ignore', invalid='ignore'): response = 20 * np.log10(mag) response = np.clip(response, -100, 100) plt.plot(freq, response) plt.title("Frequency response of Blackman window") plt.ylabel("Magnitude [dB]") plt.xlabel("Normalized frequency [cycles per sample]") plt.axis('tight') plt.show()

Aliases

numpy.blackman