How to create and save a matplotlib figure without frame and labels ?

This article will show you how to create an image using matplotlib without any outlines or labels.

Removing frame and labels of a matplotlib figure

Let's look at this example of using matplotlib

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

def bivariate_normal(X, Y, sigmax=1.0, sigmay=1.0, mux=0.0, muy=0.0, sigmaxy=0.0):
    Xmu = X-mux
    Ymu = Y-muy
    rho = sigmaxy/(sigmax*sigmay)
    z = Xmu**2/sigmax**2 + Ymu**2/sigmay**2 - 2*rho*Xmu*Ymu/(sigmax*sigmay)
    denom = 2*np.pi*sigmax*sigmay*np.sqrt(1-rho**2)
    return np.exp(-z/(2*(1-rho**2))) / denom

delta = 0.025
x = y = np.arange(-3.0, 3.0, delta)
X, Y = np.meshgrid(x, y)
Z1 = bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
Z2 = bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
Z = Z2-Z1  # difference of Gaussians

my_dpi=100

Shape = Z.shape

fig = plt.figure(figsize=(Shape[1]/my_dpi, Shape[0]/my_dpi), dpi=my_dpi)

im = plt.imshow(Z, interpolation='bilinear', cmap=cm.RdYlGn,
                origin='lower', extent=[-3,3,-3,3],
                vmax=abs(Z).max(), vmin=-abs(Z).max())

fig.savefig('MatplotlibImageNoFrame01.png', dpi=my_dpi)
plt.show()

You can then remove the frame or outline of an image by adding the set_axis_off() command:

ax = plt.Axes(fig, [0., 0., 1., 1.])
ax.set_axis_off()
fig.add_axes(ax)

Example

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

def bivariate_normal(X, Y, sigmax=1.0, sigmay=1.0, mux=0.0, muy=0.0, sigmaxy=0.0):
    Xmu = X-mux
    Ymu = Y-muy
    rho = sigmaxy/(sigmax*sigmay)
    z = Xmu**2/sigmax**2 + Ymu**2/sigmay**2 - 2*rho*Xmu*Ymu/(sigmax*sigmay)
    denom = 2*np.pi*sigmax*sigmay*np.sqrt(1-rho**2)
    return np.exp(-z/(2*(1-rho**2))) / denom

delta = 0.025
x = y = np.arange(-3.0, 3.0, delta)
X, Y = np.meshgrid(x, y)
Z1 = bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
Z2 = bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
Z = Z2-Z1  # difference of Gaussians

my_dpi=100

Shape = Z.shape

fig = plt.figure(figsize=(Shape[1]/my_dpi, Shape[0]/my_dpi), dpi=my_dpi)

ax = plt.Axes(fig, [0., 0., 1., 1.])
ax.set_axis_off()
fig.add_axes(ax)

im = plt.imshow(Z, interpolation='bilinear', cmap=cm.RdYlGn,
                origin='lower', extent=[-3,3,-3,3],
                vmax=abs(Z).max(), vmin=-abs(Z).max())

fig.savefig('MatplotlibImageNoFrame02.png', dpi=my_dpi)

plt.savefig("test.png", bbox_inches='tight', dpi=200, facecolor='red', pad_inches = 0)

plt.show()

Saving matplotlib figure

Once you have created your matplotlib figure, you can save it as an image file for use in other applications. To have the figure fit perfectly, include the parameters "bbox_inches='tight'" and "pad_inches=0" in save():

plt.savefig("MatplotlibImageNoFrame02.png", bbox_inches='tight', dpi=200, facecolor='red', pad_inches = 0)

Example of use

Create an interactive map using Folium and add a Cartopy-created image as an overlay to the map. Step1: create a mercator map with cartopy:

import cartopy.crs as ccrs
import matplotlib.cm as cm
import matplotlib.pyplot as plt
import matplotlib as mpl

plt.figure(figsize=(16,9))

ax = plt.axes(projection=ccrs.Mercator(min_latitude=-85.0, max_latitude=85.0, globe=None, latitude_true_scale=1))

ax.set_axis_off()

ax.coastlines(resolution='110m')

plt.savefig("cartopy_mercator.png", bbox_inches='tight', dpi=200, pad_inches = 0)

plt.show()

Step2: overlay image

import os
import folium

from folium.raster_layers import ImageOverlay

m = folium.Map([0,0], zoom_start=1, crs='EPSG3857')
merc = "cartopy_mercator.png"

folium.TileLayer(
        tiles = 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}',
        attr = 'Esri',
        name = 'Esri Satellite',
        overlay = False,
        control = True
       ).add_to(m)

if not os.path.isfile(merc):
    print(f"Could not find {merc}")
else:
    img = folium.raster_layers.ImageOverlay(
        name="Mercator projection SW",
        image=merc,
        bounds=[[[-85,-180]],[85,180]],
        opacity=0.5,
        interactive=True,
        cross_origin=False,
        zindex=1,
    )

    folium.Popup("I am an image").add_to(img)

    img.add_to(m)
    folium.LayerControl().add_to(m)

m

References