diff options
Diffstat (limited to 'Lib/colorsys.py')
| -rw-r--r-- | Lib/colorsys.py | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/Lib/colorsys.py b/Lib/colorsys.py index a6c0cf6a46..b93e384406 100644 --- a/Lib/colorsys.py +++ b/Lib/colorsys.py @@ -33,17 +33,25 @@ 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 +# +# There are a great many versions of the constants used in these formulae. +# The ones in this library uses constants from the FCC version of NTSC. 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 + i = 0.74*(r-y) - 0.27*(b-y) + q = 0.48*(r-y) + 0.41*(b-y) 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 + # r = y + (0.27*q + 0.41*i) / (0.74*0.41 + 0.27*0.48) + # b = y + (0.74*q - 0.48*i) / (0.74*0.41 + 0.27*0.48) + # g = y - (0.30*(r-y) + 0.11*(b-y)) / 0.59 + + r = y + 0.9468822170900693*i + 0.6235565819861433*q + g = y - 0.27478764629897834*i - 0.6356910791873801*q + b = y - 1.1085450346420322*i + 1.7090069284064666*q + if r < 0.0: r = 0.0 if g < 0.0: |