How to plot a point or a line in front of a imshow figure in matplotlib ?

Examples of how to plot a point or a line in front of a imshow figure in matplotlib

Superimpose a point and imshow

Goal: find and plot a point corresponding to a global minima

import numpy as np
import matplotlib.pyplot as plt

def f(x,y):
    return (x+y)*np.exp(-5.0*(x**2+y**2))

x,y = np.mgrid[-1:1:100j, -1:1:100j]

z = f(x,y)

plt.imshow(z,origin='lower')
plt.colorbar()

i,j = np.unravel_index(z.argmin(), z.shape)

plt.scatter(i,j,color='r')

plt.xlim(0,100)
plt.ylim(0,100)
plt.title('Draw a point on an image with matplotlib (2/2)')

plt.savefig("draw_on_image_01.png")
plt.show()
plt.close()

Superimpose a point and imshow using the option extent

Example of how to superimpose a point and imshow using matpllotlib

import numpy as np
import matplotlib.pyplot as plt

def f(x,y):
    return (x+y)*np.exp(-5.0*(x**2+y**2))

x,y = np.mgrid[-1:1:100j, -1:1:100j]

z = f(x,y)

plt.imshow(z,extent=[-1,1,-1,1],origin='lower')
plt.colorbar()

i,j = np.unravel_index(z.argmin(), z.shape)

x = ( i * 2.0 ) / 100.0 - 1.0
y = ( j * 2.0 ) / 100.0 - 1.0

plt.scatter(x,y,color='r')

plt.xlim(-1.0,1.0)
plt.ylim(-1.0,1.0)
plt.title('Draw a point on an image with matplotlib \n (case 2 with extent)')

plt.savefig("draw_on_image_03.png")
plt.show()

Superimpose a line and imshow

Example of how to superimpose a line and imshow using matpllotlib

import numpy as np
import matplotlib.pyplot as plt

def f(x,y):
    return (x+y)*np.exp(-5.0*(x**2+y**2))

x,y = np.mgrid[-1:1:100j, -1:1:100j]

z = f(x,y)

plt.imshow(z,extent=[-1,1,-1,1],origin='lower')
plt.colorbar()

i,j = np.unravel_index(z.argmin(), z.shape)

x = ( i * 2.0 ) / 100.0 - 1.0
y = ( j * 2.0 ) / 100.0 - 1.0

plt.axvline(x=x,color='red')
plt.axhline(y=y,color='red')

plt.xlim(-1.0,1.0)
plt.ylim(-1.0,1.0)
plt.title('Draw a line on an image with matplotlib')

plt.savefig("draw_on_image_04.png")
plt.show()

References