Because we only have 3 color detector cells in our eyes we can imitate
any color with various combinations of red, green, and blue lights mixed
together in varying amounts. Most animals (lizards, fish, birds) can see
an additional color, ultraviolet, which mammals lost when our forbears
were nocturnal. Color receiving cells, "cones" don't work very well in
low light levels so nocturnal animals tend to have eyes populated mostly
by "rod" cells, which are much more sensitive to low light levels (why
you don't see colors at night). Apes have evolved back into daytime
lifestyle and repopulated our eyes with color cells, which hadn't been
completely lost, unlike ultraviolet which had been.
If you add red, green, and blue light it stimulates all our color
receptors and it looks like white light. This is called additive mixing.
A talking bird would say, "What? You're crazy. That's not white. There's
no ultraviolet in it." A hypothetical alien who had dozens of different
types of color receptor would be able to see clearly that it was just a
mix of red light and green light and blue light.
Mixing red and green lights looks like "yellow" to us, but is still just
red+green light. It just stimulates our receptors the same way a single
yellow light would. You can prove this to yourself by looking at the
faked yellow through a narrow band yellow filter and both the parts are
blocked.
Painters make colors by mixing pigments. They work slightly differently
to mixing lights. Pigments get their color by absorbing light of most
colors and reflecting only some. This is subtractive mixing. Because of
this the colors used to fake all the other colors are different. They
are red, yellow and blue. They are actually a slightly different "red"
and "blue" so are often called magenta and cyan to avoid confusion. If
you add red and yellow pigments they produce the appearance of green
because each subtracts colors from the available light.
red+green+blue - red - blue = green
white
If you mix all the pigments together it approaches black because it
filters more and more light out, but because it always reflects some
light in reality you end up with a dark color that is tinted slightly
with color so looks some shade of brown. This is why printing uses an
additional ink that is black. That divides color up into CMYK (cyan,
magenta, yellow, black) tones.
Cheers,
- Miriam
Russell Jones wrote:
Great news :) I liked IYOCGwP and have mentioned it here before now.
BTW, on page 34 of the new book you write "(Red, blue, and yellow are
the primary colors for paints and pigments, but the computer monitor
uses light, not paint.)"
The primary colours for pigment and paint are cyan, yellow and magenta, no?
Russell
On 10 February 2012 21:04, Al Sweigart <a...@inventwithpython.com
<mailto:a...@inventwithpython.com>> wrote:
Hey everyone, I'm the author of "Invent Your Own Computer Games with
Python". I've written a new book that focuses more on Pygame titled,
"Making Games with Python & Pygame". You can download it for free from:
http://inventwithpython.com/pygame
Feel free to email me any questions. Thanks!
-Al
--
If you don't have any failures then you're not trying hard enough.
- Dr. Charles Elachi, director of NASA's Jet Propulsion Laboratory
-----
Website: http://miriam-english.org
Blogs: http://miriam-e.dreamwidth.org
http://miriam-e.livejournal.com
