How to obtain a fixed height in pixels, fixed data x/y aspect ratio and automatically remove remove horizontal whitespace margin in Matplotlib?

Question

Let\'s take this as a starting point based on: Specifying and saving a figure with exact size in pixels

#!/usr/bin/env python3

import sys

import numpy as np         


        

Answer 1

I don't know if I understood your question, but if you want to limit the whitespace in a figure with a 1x2 subplot layout, you simply have to create a figure with a width that's half the height:

h = 400
nrows = 2
w = h/nrows
dpi = 100

fig, ax = plt.subplots(nrows=nrows, ncols=1, figsize=(w/dpi, h/dpi), dpi=dpi)

t = np.arange(-10., 10., 1.)
a = ax[0]
a.set_aspect(1)
a.plot(t, t, '.')
a = ax[1]
a.plot(t, -t, '.')
a.set_aspect(1)
plt.tight_layout(pad=1)
plt.savefig(
    'main.png',
    format='png',
    dpi=dpi,
    facecolor='y',
)

>> identify main.png

main.png PNG 200x400 200x400+0+0 8-bit sRGB 6048B 0.000u 0:00.000

Answer 2

SVG output + plt.savefig(bbox_inches='tight' + Inkscape convert

This is terrible, but it does what I want without a lot of extra boilerplate, so here we go:

#!/usr/bin/env python3

import sys

import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl

h = int(sys.argv[1])
fig, ax = plt.subplots(nrows=2, ncols=1)
t = np.arange(-10., 10., 1.)
a = ax[0]
a.set_aspect(1)
a.plot(t, t, '.')
a = ax[1]
a.plot(t, -t, '.')
a.set_aspect(1)
plt.savefig(
    'main.svg',
    format='svg',
    dpi=h/fig.get_size_inches()[1],
    facecolor='y',
    bbox_inches='tight',
)

and then:

inkscape -b FFF -e main.png -h 400 main.svg

output:

bbox_inches='tight' gives a decent looking image without too much borders, but makes me lose the exact size, so we use the SVG output as a way to work around that.

This should work well since SVG is a vector format, and therefore should scale to any size seamlessly.

I use Inkscape for the conversion because Imagemagick requires you to manually calculate the resolution:

• https://superuser.com/questions/598849/imagemagick-convert-how-to-produce-sharp-resized-png-files-from-svg-files/1602059#1602059
• How to convert a SVG to a PNG with ImageMagick?

Tested on Inkscape 0.92.5.