2D plot of a matrix with colors like in a spectrogram
matplotlib, plot, python, spectrogram
Solution
Let `Z` be the array, here is what I finally use:
plt.imshow(np.transpose(Z), extent=[0,4.2,0,48000], cmap='jet',
vmin=-100, vmax=0, origin='lowest', aspect='auto')
plt.colorbar()
plt.show()
Notes:
`'jet'` is the colormap that is seen in the question's image, see also these colormaps
setting `origin='lowest'` has the same effect than replacing `np.transpose(Z)` by `np.transpose(Z)[::-1,]`
`vmin`, `vmax` give the scale (here from 0 to -100 dB in the example)
`extent` gives the limits of the x-axis (here 0 to 4.2 seconds) and y-axis (0 to 48000 Hz) (in this example I'm plotting the spectrogram of a 4.2 second-long audio file of samplerate 96Khz)
if `aspect='auto'` is not set, the plot would be very thin and very high (due to 4.2 vs. 48000 !)
Problem
How to plot, with Python, a 2D matrix `A[i,j]` like this: - `i` is the x-axis - `j` is the y-axis - `A[i,j]` is a value between 0 and 100 that has to be drawn by a colour (ex: 0=blue, 100=red) Is there a Python function for that? (NB: I don't want a function that does the spectrogram for me, such as `specgram`, because I want to compute the FFT of the signal myself; thus I only need a function that plots a matrix with colors)