Python / matplotlib: print to resolution and without white space / borders / margins

Question

I have time series data (signal) of different length that I would like to plot without any margins between scale and signal.

Goal: plot each signal so (physical) printing of the plot will show every single data point. The plot shall be saved to a file.

Given:

1. printer with 600 dpi maximum printing resolution.
2. signals with different number of data points (from 30000 to 100000).

example of signal:

import numpy as np
Fs = 512
# Create random signal
np.random.seed(1)
data = [np.random.uniform(-10000, 20000) for i in range(5*Fs)]

If I just plot it with matplotlib:

import matplotlib.pyplot as plt
plt.figure(figsize=(len(data)/600,2)) # divide by 600 which is dpi resolution of printer
plt.plot(data, color = "black", linewidth = 1.0)
plt.show()

I do not want any white space between the first data point and the Y axis or between the last data point and the right border. The label of the Y axis should also not interfere with the plot's size, so its width should also be considered.

How do I accomplish to have every single point printed?

Answer 1

I will neglect the point about more than 30000 points as this is nonsense for printing. So assuming a configuration as implied by the code of some 3000 points or so, you can calculate the figure size needed to show the plot with one point per printable point. You would also need to make sure that the linewidth is actually one dot wide.

import numpy as np
Fs = 512
# Create random signal
np.random.seed(1)
data = [np.random.uniform(-10000, 20000) for i in range(5*Fs)]

import matplotlib.pyplot as plt

dpi = 600
figheight = 4 # inch, some constant number

margin_left  = 1.0  # inch
margin_right = 0.4 # inch

figwidth = (len(data)/float(dpi)) + margin_left + margin_right # inch


plt.figure(figsize=(figwidth,figheight), dpi=dpi) 
plt.margins(x=0) # remove inner-axis padding of data
plt.subplots_adjust(left=margin_left/float(figwidth),
                    right=1.-margin_right/float(figwidth))
 # use 72/dpi for linewidth such that one point is one dot
plt.plot(data, color = "black", linewidth = 72./dpi)
plt.savefig("output.png", dpi="figure")
# note that show() may not make sense, 
# since it readjusts the figure size to maximum screen size
plt.show()