Hi Matthias, List People,
Exact color replication is pretty much in one league with voodoo and other forms of black magic. Trust me - you will always get close easily, but exact replication is ludicrous unless you have a really big budget.
To get back to some of the questions raised in your email:
Pantone: This is a proprietary (ring a bell?) color system based on using exact physical colors. So as it was pointed out, most do emulate Pantone with CMYK, but what is normally done is to use the physical pantone bucket of color for the one referenced in the data used for print. http://en.wikipedia.org/wiki/Pantone
RGB->CMYK: What RGB? ProPhoto RGB, Adobe RGB or maybe sRGB? Strange Insider-jokes aside, there is no perfect mapping as they represent different color spaces: http://en.wikipedia.org/wiki/Color_space
GIMP&CMYK: The GIMP only uses an immediate mapping to simulate CMYK to RGB conversion which is of course lossy as demonstrated above.
The bottom line is that I would avoid trying to overachieve on color management. A lot of people just emulate Pantone in CMYK anyways and nobody notices anyhoo. Making an exact match from CMYK to RGB is pointless as they are used in two completely different types of application - one for the three colored computer screen, the other for four colored print.
It should be much more helpful to make a small set of reference colors for the programs we know are used. So you would define a set of RGB colors for usage with the GIMP and Inkscape and then maybe use the provided CMYK colors for scribus and alike.
But to stress this point again: If this is about materials and brochures that will be printed in limited numbers, the time you put into all the color management (not to mention that most of the proprietary color spaces are not supported in most Free Software) is wasted. There are good and reasonably priced online-printing services (like flyeralarm.de for Germany) who can handle even RGB pdfs very well and the difference in color is negligible. Unless of course you suddenly feel we are Deutsche Telekom and WE NEED EXACTLY THIS TONE OF PINK!
take care, David
Matthias Kirschner wrote:
Hi all,
three years ago we got the following data from the people who did the Fellowship layout:
- SmartCard bright green: 50,0,100,0 (CMYK), or Pantone: 376C
- SmartCard dark green & logo: 70,0,100,0 (CMYK), or Pantone: 361C
- RGB logo color: 99,152,41 (Web only)
Now we have some problems with that. We want to use the same color for all websites and website buttons, etc. and also consistent in all printed forms. We know that we can never be consistent across different mediums, at least not 100%. But we would like to aim to be consistent within the same medium, so all web pages using the fellowship greens should have the same colour of green, and so on.
Gimp said that 70/0/100/0 is 6bb340. But how can it at the same time be 639829 as they claim for the fellowship logo??
Is this statement true:
I don't think you should stare yourself blind at that :-) According to this page for instance, http://blog.indika.net.id/html-color-codes-matching-chart-pantone-cmyk-rgb-hex/ 7489 C is not 70/0/100/0 but 60/0/80/7 :-) There's no one true perfect answer for either, since even saying that 7489 C is 70/0/100/0 is a conversion from the Pantone scale to the CMYK scale. It's a lossy conversation if you will ;-)
Is there a perfect mathematically strict conversion between RGB and CMYK? Or is it dependant on a lot of things? Does it depend which printer you are using when using CMYK?
Reinhard found this one and said that it is perhaps what we need:
http://www.publisher.ch/heft/056/Pantone.php3 Wie erscheint eine Pantone-Sonderfarbe, wenn sie im Vierfarbendruck mit Cyan, Magenta, Yellow und Schwarz simuliert wird? Die Color Bridge gibt darauf eine optische Antwort. Mit diesem Werkzeug können Sonderfarben direkt mit den entsprechenden und neu bestimmten Prozessfarben verglichen werden. Zudem erhält der Anwender der Color Bridge die sRGB- und HTML-Farbwerte der jeweiligen Pantone-Farbe.
Can someone here help us what we have to do to be consitent in differnt media (web, print)? We do not have much clue about that.
Thanks, Matthias