MEK: Add references and links re: color spaces and color conversions.

1 files changed, 38 insertions, 0 deletions

diff --git a/hsv2rgb.cpp b/hsv2rgb.cpp
index 45cf326b..3d5c3d62 100644
--- a/hsv2rgb.cpp
+++ b/hsv2rgb.cpp
@@ -364,5 +364,43 @@ void rainbow2rgb( const CHSV& hsv, CRGB& rgb)
 }
 
 
+// References:
+//  Spectra and rainbows are not the same thing.  Wikipedia has a good
+//  illustration here
+//   http://upload.wikimedia.org/wikipedia/commons/f/f6/Prism_compare_rainbow_01.png
+//  from this article
+//   http://en.wikipedia.org/wiki/Rainbow#Number_of_colours_in_spectrum_or_rainbow
+//  that shows a 'spectrum' and a 'rainbow' side by side.  Among other
+//  differences, you'll see that a 'rainbow' has much more yellow than
+//  a plain spectrum.  "Classic" LED color washes are spectrum based, and
+//  usually show very little yellow.  
+//
+//  Wikipedia's page on HSV color space, with pseudocode for conversion
+//  to RGB color space
+//   http://en.wikipedia.org/wiki/HSL_and_HSV
+//  Note that their conversion algorithm, which is (naturally) very popular
+//  is in the "maximum brightness at any given hue" style, vs the "uniform
+//  brightness for all hues" style.
+//
+//  You can't have both; either purple is the same brightness as red, e.g
+//    red = #FF0000 and purple = #800080 -> same "total light" output
+//  OR purple is 'as bright as it can be', e.g.
+//    red = #FF0000 and purple = #FF00FF -> purple is much brighter than red.
+//  The colorspace conversions here try to keep the apparent brightness
+//  constant even as the hue varies.
+//
+//  Adafruit's "Wheel" function, discussed here
+//   http://forums.adafruit.com/viewtopic.php?f=47&t=22483
+//  is also of the "constant apparent brightness" variety.
+//
+//  TODO: provide the 'maximum brightness no matter what' variation.
+//
+//  See also some good, clear Arduino C code from Kasper Kamperman
+//   http://www.kasperkamperman.com/blog/arduino/arduino-programming-hsb-to-rgb/
+//  which in turn was was based on Windows C code from "nico80"
+//   http://www.codeproject.com/Articles/9207/An-HSB-RGBA-colour-picker
+
+
+
 #endif