Macbeth color chart question

[KenP]

Does anyone have the color density (CMYK) values for the 24 color
patches on the standard matte Macbeth color chart? I've got a listing
of the RGB values used to create the chart, but nothing on how a
printed chart should measure.

Thanks for any help,
KenP

[fnovau]

KenP <Ke...@nothome.net> wrote in message news:<qh9j009tkus7pk17e...@4ax.com>...

Here you will find a program that permits to compute CMYK to RGB and viceversa
http://www.mick.tilbury.btinternet.co.uk/index.htm?colcal.htm
-Francesc

[Paul Cooper]

You should be aware that there is no one to one mapping between RGB
and CMYK, and that RGB can represent colours not available in CMYK and
vice-versa. To give an example of the former, 10% grey in CMYK can be
represented by equal proportions of C, M and Y and a proportion of K
(black). There are literally hundreds of possibilities - and automatic
conversions don't always choose the "obvious" one of 10%K, 0% CMY!

If you are aiming for a CMYK device, it is better to work in CMYK
values all the way through the process.

Finally, CMYK has a well defined set of colour values for each ink -
defined by industry practise, if by nothing else. However, RGB is far
less well defined, varying with phosphors and LED emitters. So, RGB is
a far less constant thing than CMYK, which is itself less well defined
than more rigorous standards used in high precision colour systems..

Paul Cooper

[KenP]

Wheew - guess the answer is to buy a Macbeth chart and measure the
thing myself, doesn't look like there's any other way. I do see your
point, that the "K" term or black ink is used to tone down the other
colors as cheaply as possible-that's what it's for, right? My X-Rite
densitometer measures CMYV, where "V" represents visual density. I'm
not sure how that compares.

[Paul Cooper]

K is also used to provide a "pure" black - the black obtained by
mixing CMY tends not to be black. As you say, it is also cheaper!

Paul