numpy RGB to HSV

rgb_to_hsv_np.py

#
# Copyright (c) 2016, Nikolay Polyarnyi
# All rights reserved.
#

import numpy as np


def rgb_to_hsv(rgb):
    """
    >>> from colorsys import rgb_to_hsv as rgb_to_hsv_single
    >>> 'h={:.2f} s={:.2f} v={:.2f}'.format(*rgb_to_hsv_single(50, 120, 239))
    'h=0.60 s=0.79 v=239.00'
    >>> 'h={:.2f} s={:.2f} v={:.2f}'.format(*rgb_to_hsv_single(163, 200, 130))
    'h=0.25 s=0.35 v=200.00'
    >>> np.set_printoptions(2)
    >>> rgb_to_hsv(np.array([[[50, 120, 239], [163, 200, 130]]]))
    array([[[   0.6 ,    0.79,  239.  ],
            [   0.25,    0.35,  200.  ]]])
    >>> 'h={:.2f} s={:.2f} v={:.2f}'.format(*rgb_to_hsv_single(100, 100, 100))
    'h=0.00 s=0.00 v=100.00'
    >>> rgb_to_hsv(np.array([[50, 120, 239], [100, 100, 100]]))
    array([[   0.6 ,    0.79,  239.  ],
           [   0.  ,    0.  ,  100.  ]])
    """
    input_shape = rgb.shape
    rgb = rgb.reshape(-1, 3)
    r, g, b = rgb[:, 0], rgb[:, 1], rgb[:, 2]

    maxc = np.maximum(np.maximum(r, g), b)
    minc = np.minimum(np.minimum(r, g), b)
    v = maxc

    deltac = maxc - minc
    s = deltac / maxc
    deltac[deltac == 0] = 1  # to not divide by zero (those results in any way would be overridden in next lines)
    rc = (maxc - r) / deltac
    gc = (maxc - g) / deltac
    bc = (maxc - b) / deltac

    h = 4.0 + gc - rc
    h[g == maxc] = 2.0 + rc[g == maxc] - bc[g == maxc]
    h[r == maxc] = bc[r == maxc] - gc[r == maxc]
    h[minc == maxc] = 0.0

    h = (h / 6.0) % 1.0
    res = np.dstack([h, s, v])
    return res.reshape(input_shape)


def hsv_to_rgb(hsv):
    """
    >>> from colorsys import hsv_to_rgb as hsv_to_rgb_single
    >>> 'r={:.0f} g={:.0f} b={:.0f}'.format(*hsv_to_rgb_single(0.60, 0.79, 239))
    'r=50 g=126 b=239'
    >>> 'r={:.0f} g={:.0f} b={:.0f}'.format(*hsv_to_rgb_single(0.25, 0.35, 200.0))
    'r=165 g=200 b=130'
    >>> np.set_printoptions(0)
    >>> hsv_to_rgb(np.array([[[0.60, 0.79, 239], [0.25, 0.35, 200.0]]]))
    array([[[  50.,  126.,  239.],
            [ 165.,  200.,  130.]]])
    >>> 'r={:.0f} g={:.0f} b={:.0f}'.format(*hsv_to_rgb_single(0.60, 0.0, 239))
    'r=239 g=239 b=239'
    >>> hsv_to_rgb(np.array([[0.60, 0.79, 239], [0.60, 0.0, 239]]))
    array([[  50.,  126.,  239.],
           [ 239.,  239.,  239.]])
    """
    input_shape = hsv.shape
    hsv = hsv.reshape(-1, 3)
    h, s, v = hsv[:, 0], hsv[:, 1], hsv[:, 2]

    i = np.int32(h * 6.0)
    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

    rgb = np.zeros_like(hsv)
    v, t, p, q = v.reshape(-1, 1), t.reshape(-1, 1), p.reshape(-1, 1), q.reshape(-1, 1)
    rgb[i == 0] = np.hstack([v, t, p])[i == 0]
    rgb[i == 1] = np.hstack([q, v, p])[i == 1]
    rgb[i == 2] = np.hstack([p, v, t])[i == 2]
    rgb[i == 3] = np.hstack([p, q, v])[i == 3]
    rgb[i == 4] = np.hstack([t, p, v])[i == 4]
    rgb[i == 5] = np.hstack([v, p, q])[i == 5]
    rgb[s == 0.0] = np.hstack([v, v, v])[s == 0.0]

    return rgb.reshape(input_shape)

RuntimeWarning: invalid value encountered in true_divide
s = deltac / maxc