mathplotlib imshow complex 2D array

Question

Is there any good way how to plot 2D array of complex numbers as image in mathplotlib ?

It makes very much sense to map magnitude of complex number as \"brightness\" or

Answer 1

You can use matplotlib.colors.hsv_to_rgb instead of colorsys.hls_to_rgb. The matplotlib function is about 10 times faster! See the results below:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import hsv_to_rgb
import time

def Complex2HSV(z, rmin, rmax, hue_start=90):
    # get amplidude of z and limit to [rmin, rmax]
    amp = np.abs(z)
    amp = np.where(amp < rmin, rmin, amp)
    amp = np.where(amp > rmax, rmax, amp)
    ph = np.angle(z, deg=1) + hue_start
    # HSV are values in range [0,1]
    h = (ph % 360) / 360
    s = 0.85 * np.ones_like(h)
    v = (amp -rmin) / (rmax - rmin)
    return hsv_to_rgb(np.dstack((h,s,v)))

here is the method of picked answer by @nadapez:

from colorsys import hls_to_rgb
def colorize(z):
    r = np.abs(z)
    arg = np.angle(z) 

    h = (arg + np.pi)  / (2 * np.pi) + 0.5
    l = 1.0 - 1.0/(1.0 + r**0.3)
    s = 0.8

    c = np.vectorize(hls_to_rgb) (h,l,s) # --> tuple
    c = np.array(c)  # -->  array of (3,n,m) shape, but need (n,m,3)
    c = c.swapaxes(0,2) 
    return c

Testing the results from the two method with 1024*1024 2darray:

N=1024
x, y = np.ogrid[-4:4:N*1j, -4:4:N*1j]
z = x + 1j*y

t0 = time.time()
img = Complex2HSV(z, 0, 4)
t1 = time.time()
print "Complex2HSV method: "+ str (t1 - t0) +" s"

t0 = time.time()
img = colorize(z)
t1 = time.time()
print "colorize method: "+ str (t1 - t0) +" s"

This result on my old laptop:

Complex2HSV method: 0.250999927521 s
colorize method: 2.03200006485 s