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) <[email protected]>
To: <[email protected]>, "'Craig Ede'" <[email protected]>
Cc: 'framers' <[email protected]>
Subject: RE: CMYK vs RGB RE: PDF query
Message-ID: <[email protected]>
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
[email protected]. 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 [email protected].
Send list messages to [email protected].
To unsubscribe send a blank email to
[email protected]
or visit
http://lists.frameusers.com/mailman/options/framers/archive%40mail-archive.com
Send administrative questions to [email protected]. Visit
http://www.frameusers.com/ for more resources and info.
