a question about subtractive color

[emanresu]

Hi Bob,

I just read your book review on the Speedliter's handbook.  From your review, I think it is a rather good book for me because I never fully grasp how to correctly use the flash.

However, I do have one question regarding the subtractive color.  In the review, you pointed out a mistake in the book (which is obviously incorrect), but then the review states that Cyan+Yellow=Blue...  I am not so sure about this.  I always thought in CYMK subtractive color, Magenta + Cyan = Blue, and Cyan + Yellow = Green (so the book once again is a bit off, but not entirely incorrect by saying yellow + blue = green because the three primary colors in CYMK subtractive scheme has no blue, only magenta, cyan, and yellow.   yellow + blue does yield a greenish color, but blue itself is the product of cyan + yellow.   Could you please verify this?  Thanks.

[klindup]

My understanding of the subtractive primaries is as follows:
magenta= white - green = red +blue
cyan = white - red = blue + green
yellow = white - blue = green + red.

The three additive primaries (red, green, blue) combine to give white whereas the three subtractive primaries (yellow, magenta, cyan) combine to give black.  In practice combining yellow, magenta and cyan gives a muddy brown and so a fourth colour black has to be used in all forms of printing.

[KeithB]

See here:
http://en.wikipedia.org/wiki/Subtractive_color

Don't you remember Kindergarten?  They did not call it "cyan" and "magenta" they called it "blue" and "red".

[emanresu]

Hi Keith,

in Kindergarten, we *were* using blue and red, not cyan and magenta.  RED/YELLOW/BLUE (RYB) is a different color model than CYMK.  According to the wikipedia article you referenced, RYB is what people used to think what primary colors were, and in art it is still being used.  But in any case, I don't think RYB and CYMK should be mixed because RED and BLUE would be secondary colors in the CYMK model.

In RYB, the secondary colors are:  ORANGE (red + yellow), GREEN (blue + yellow), and PURPLE (blue + red).  these happen to be the colors of the pencils/crayons kids usually get in kindergarten.

[klindup]

There are at least two sets of primary colours, additive and subtractive.  The additive primaries are red blue and green which if mixed give white.  The additive primaries are used when colour is generated by light such as in a colour television.  The subtractive primaries have been used for years by printers (letterpress, lithographic and gravure or intaglio) and are yellow magenta and cyan.  When mixed they give black. They are used when colour is produced by small dots of the subtractive primaries.  If you look at a a picture in a magzine under a magifying glass you nwill see the discrete dots of yellow magenta and cyan.

I guess that if you mix pigments as painters do then the set of primary colours is indeed red yellow and blue.  The primary colours depend on how you produce a particular hue.