"""Conversion functions between RGB and other color systems.

This modules provides two functions for each color system ABC:

  rgb_to_abc(r, g, b) --> a, b, c

  abc_to_rgb(a, b, c) --> r, g, b

All inputs and outputs are triples of floats in the range [0.0...1.0]

(with the exception of I and Q, which covers a slightly larger range).

Inputs outside the valid range may cause exceptions or invalid outputs.

Supported color systems:

RGB: Red, Green, Blue components

YIQ: Luminance, Chrominance (used by composite video signals)

HLS: Hue, Luminance, Saturation

HSV: Hue, Saturation, Value

"""

# References:

# http://en.wikipedia.org/wiki/YIQ

# http://en.wikipedia.org/wiki/HLS_color_space

# http://en.wikipedia.org/wiki/HSV_color_space

__all__ = ["rgb_to_yiq","yiq_to_rgb","rgb_to_hls","hls_to_rgb",

           "rgb_to_hsv","hsv_to_rgb"]

# Some floating point constants

ONE_THIRD = 1.0/3.0

ONE_SIXTH = 1.0/6.0

TWO_THIRD = 2.0/3.0

# YIQ: used by composite video signals (linear combinations of RGB)

# Y: perceived grey level (0.0 == black, 1.0 == white)

# I, Q: color components

def rgb_to_yiq(r, g, b):

    y = 0.30*r + 0.59*g + 0.11*b

    i = 0.60*r - 0.28*g - 0.32*b

    q = 0.21*r - 0.52*g + 0.31*b

    return (y, i, q)

def yiq_to_rgb(y, i, q):

    r = y + 0.948262*i + 0.624013*q

    g = y - 0.276066*i - 0.639810*q

    b = y - 1.105450*i + 1.729860*q

    if r < 0.0: r = 0.0

    if g < 0.0: g = 0.0

    if b < 0.0: b = 0.0

    if r > 1.0: r = 1.0

    if g > 1.0: g = 1.0

    if b > 1.0: b = 1.0

    return (r, g, b)

# HLS: Hue, Luminance, Saturation

# H: position in the spectrum

# L: color lightness

# S: color saturation

def rgb_to_hls(r, g, b):

    maxc = max(r, g, b)

    minc = min(r, g, b)

    # XXX Can optimize (maxc+minc) and (maxc-minc)

    l = (minc+maxc)/2.0

    if minc == maxc: return 0.0, l, 0.0

    if l <= 0.5: s = (maxc-minc) / (maxc+minc)

    else: s = (maxc-minc) / (2.0-maxc-minc)

    rc = (maxc-r) / (maxc-minc)

    gc = (maxc-g) / (maxc-minc)

    bc = (maxc-b) / (maxc-minc)

    if r == maxc: h = bc-gc

    elif g == maxc: h = 2.0+rc-bc

    else: h = 4.0+gc-rc

    h = (h/6.0) % 1.0

    return h, l, s

def hls_to_rgb(h, l, s):

    if s == 0.0: return l, l, l

    if l <= 0.5: m2 = l * (1.0+s)

    else: m2 = l+s-(l*s)

    m1 = 2.0*l - m2

    return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD))

def _v(m1, m2, hue):

    hue = hue % 1.0

    if hue < ONE_SIXTH: return m1 + (m2-m1)*hue*6.0

    if hue < 0.5: return m2

    if hue < TWO_THIRD: return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0

    return m1

# HSV: Hue, Saturation, Value

# H: position in the spectrum

# S: color saturation ("purity")

# V: color brightness

def rgb_to_hsv(r, g, b):

    maxc = max(r, g, b)

    minc = min(r, g, b)

    v = maxc

    if minc == maxc: return 0.0, 0.0, v

    s = (maxc-minc) / maxc

    rc = (maxc-r) / (maxc-minc)

    gc = (maxc-g) / (maxc-minc)

    bc = (maxc-b) / (maxc-minc)

    if r == maxc: h = bc-gc

    elif g == maxc: h = 2.0+rc-bc

    else: h = 4.0+gc-rc

    h = (h/6.0) % 1.0

    return h, s, v

def hsv_to_rgb(h, s, v):

    if s == 0.0: return v, v, v

    i = int(h*6.0) # XXX assume int() truncates!

    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

    # Cannot get here