RYGCBM color space.

2011-07-12 16:15

Okay, so. Light lets you assemble colors from R/G/B. Ink uses C/M/Y. So, for instance, R+G light = yellow.

The thing is. I knew that red+blue was purple. And I knew that yellow+magenta yielded red. But I hadn’t realized that red+blue is actually magenta. And this means…

The primaries in each scheme, doubled up, produce the primaries in the other. Take two primaries from CMY and add them:

Cyan + Magenta: Blue.
Magenta + Yellow: Red.
Yellow + Cyan: Green.

Similarly, it works the other way:

Red + Blue: Magenta
Blue + Green: Cyan
Green + Red: Yellow

And if you think about WHY ink is subtractive and light is additive, this is even totally obvious. Yellow reflects red light and green light. Cyan reflects green light and blue light. Mix them, and the only thing still reflected is green light.

I knew every component of this, but I had not put it together until just yesterday.

Peter Seebach



  1. I though about what you wrote and…
    I guessed it could be modelled with bitwise OR (additive) and AND (subtractive) operations. So for RGB (light) you’d get:

    RED = ff0000; BLUE = 0000ff; MAGENTA == RED | BLUE;

    Looks OK so far. How about CMY (ink)?

    CYAN = 00ffff; MAGENTA = ff00ff; BLUE == CYAN & MAGENTA;

    :-) Happiness through simple things. Thanks!

    Ben Forshaw · 2011-07-15 04:02 · #

  2. Here’s an example, where you can see this relationship in action.

    (From an Inkscape tutorial )

    Dave Leppik · 2011-07-18 11:08 · #