Yes, I think color conversions are that complex. RGB was designed for monitors allowing a broad range of additive colors in the form of light (i.e. lit pixels). CMYK was designed for subtractive printing to paper offering a restricted range of those colors; many of the RGB colors being "out of gamut" for CMYK, meaning there is no formula to convert them. Nobody serious is printing high-quality hardcopy using R, G, and B inks. And I'm not sure why one would want to use CMYK to print to the screen.
Craig > From: david.da...@non.schneider-electric.com > To: framers@lists.frameusers.com > Date: Wed, 22 Oct 2014 03:34:52 -0500 > Subject: RE: CMYK vs RGB RE: PDF query > > Are colour conversions really that "complex"? > They're just converting colour coordinates in one colour-space to those in > another, using some straightforward formulae that are hidden under the hood. > (The choice of formula, and what to do if a colour is 'out of gamut', depends > on the 'rendering intent', of which we usually have a choice of four). > The conversions will give 'round-tripping' errors if they're out of gamut. > This is why better Adobe software (Illustrator, Photoshop, InDesign) maps RGB > and CMYK via a device-independent ("LaB") representation, rather than > straight from one to the other. > The problem with FrameMaker is that the conversion algorithms it uses are > crude rubbish. This is why they frequently give such awful results, not > because it's "complex". > > From previous threads on the Adobe Forums, it seems that the conversion > formula Frame uses is: > > RGB to CMYK: > C = max(R, G, B) - R > M = max(R, G, B) - G > Y = max(R, G, B) - B > K = 100 - max(R, G, B) > > CMYK to RGB: > R = min(100 - K - C, 0) > G = min(100 - K - M, 0) > B = min(100 - K - Y, 0) > > ...which gives rubbish results. > > David > > ____ > > From: Jacob Sch?ffer (Grafikhuset) <j...@grafikhuset.dk> > To: <i...@heiko-haida.de>, "'Craig Ede'" <craig...@hotmail.com> > Cc: 'framers' <framers@lists.frameusers.com> > Subject: RE: CMYK vs RGB RE: PDF query > Message-ID: <00a601cfec93$39b38e10$ad1aaa30$@grafikhuset.dk> > Content-Type: text/plain; charset="utf-8" > > It?s definitely NOT easy to explain this. Color conversions are COMPLEX. > Anyway, RGB -> CMYK conversion is lossy, and CMYK -> RGB is also lossy. > > > > What is the point of the RGB switch afterall? Why not just pass through > what?s input and remove this switch? > > *** Confidentiality Notice: This e-mail, including any associated or attached > files, is intended solely for the individual or entity to which it is > addressed. This e-mail is confidential and may well also be legally > privileged. If you have received it in error, you are on notice of its > status. Please notify the sender immediately by reply e-mail and then delete > this message from your system. Please do not copy it or use it for any > purposes, or disclose its contents to any other person. This email comes from > a division of the Invensys Group, owned by Invensys Limited, which is a > company registered in England and Wales with its registered office at 3rd > Floor, 40 Grosvenor Place, London, SW1X 7AW (Registered number 166023). For a > list of European legal entities within the Invensys Group, please select the > Legal Entities link at invensys.com. Invensys Limited is owned by the > Schneider-Electric Group. > > You may contact Invensys Limited on +44 (0)20 3155 1200 or e-mail > recept...@invensys.com. This e-mail and any attachments thereto may be > subject to the terms of any agreements between Invensys (and/or its > subsidiaries and affiliates) and the recipient (and/or its subsidiaries and > affiliates). > _______________________________________________ > > > You are currently subscribed to framers as craig...@hotmail.com. > > Send list messages to framers@lists.frameusers.com. > > To unsubscribe send a blank email to > framers-unsubscr...@lists.frameusers.com > or visit > http://lists.frameusers.com/mailman/options/framers/craigede%40hotmail.com > > Send administrative questions to listad...@frameusers.com. Visit > http://www.frameusers.com/ for more resources and info.
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