Picking random colors in RGB space and outer rim of top of the HSV cone

random_colors.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Random colors for RGB LEDs

Random RGB (R=U[0,1), G=U[0,1), B=U[0,1)) can lead to dark and light colors 
which may not be goal when picking a random color for a RGB LED

This shows how to pick a color in the HSV space (H=U[0,1), S=U[0.8,1), V=1])
and convert it to RGB. Note that the Saturation is sampled such that colors
are picked from the rim of the Value=1 disk in the HSV space, this to say,
close-to-white colors are avoided.

@author: rcassani
"""

from matplotlib import pyplot as plt
import matplotlib.patches as mpatch
import numpy as np


def hsv_to_rgb(h, s, v):
    # HSV (1.0, 1.0, 1.0) to RGB (1.0, 1.0, 1.0)
    # See matplotlib.colors import hsv_to_rgb
    i = (h * 6.0).astype(int)
    f = (h * 6.0) - i
    p = v * (1.0 - s)
    q = v * (1.0 - s * f)
    t = v * (1.0 - s * (1.0 - f))
    i = i % 6
    if i == 0: return (v, t, p)
    if i == 1: return (q, v, p)
    if i == 2: return (p, v, t)
    if i == 3: return (p, q, v)
    if i == 4: return (t, p, v)
    if i == 5: return (v, p, q)
    
# Create figure and subplots
plt.close('all')
fig = plt.figure()
ax_rgb = plt.subplot(1,2,1)
ax_hsv = plt.subplot(1,2,2)

# Number of colors (n_cols × n_rows)
n_cols  = 25
n_rows  = 25

np.random.seed(10)
rng = np.random.default_rng()

for i_col in range(n_cols):
    for i_row in range(n_cols):
        # Random RGB        
        rgb_rnd = rng.random(3) # U[0.0, 1.0)
        # Random HSV to RGB
        rgb_hsv = hsv_to_rgb(rng.random(1)[0],      # h
                             rng.uniform(0.7, 1.0), # s
                             1)                     # v  
                        
        # Position of patches
        x_pos = i_col * 2
        y_pos = i_row * 2
        # Add patches
        ax_rgb.add_patch(mpatch.Rectangle((x_pos, y_pos), 2, 2, color=rgb_rnd))
        ax_hsv.add_patch(mpatch.Rectangle((x_pos, y_pos), 2, 2, color=rgb_hsv))
        
# Configure axes        
ax_rgb.title.set_text('Random RGB color: (R=U[0,1), G=U[0,1), B=U[0,1))')
ax_rgb.set_xlim(0, 2 * n_cols)
ax_rgb.set_ylim(2 * n_rows, 0)
ax_rgb.set_aspect('equal')
ax_rgb.axis('off')

ax_hsv.title.set_text('Random HSV color: (H=U[0,1), S=U[0.8,1), V=1])')
ax_hsv.set_xlim(0, 2 * n_cols)
ax_hsv.set_ylim(2 * n_rows, 0)
ax_hsv.set_aspect('equal')
ax_hsv.axis('off')

plt.show()