Dan Margulis Applied Color Theory
Best Practice for RGB Stock Images
From: James Stuart Johnson
Date: Thu, Jan 23, 2003 3:18 pm
Subject: Best practice for RGB stock images?
Hi, all
I have been lurking here for ages. I finally have a
quick question.
I am working on a project-involving image for sale as
stock, i.e. Photos and hand generated Textures and Illustrations. I wish to
make them available for the widest possible usage while keeping them
accessible to software without profiling. I intend to use RGB TIFFs and
those using Photoshop or profile aware software I intend to embed a
profile, but which provides the possible range in RGB?
What I was able to gather so far form books and
manuals: Wide RGB looks like the way to go, I also noticed Pro Photo RGB I
have no idea of it's intended target.
Is there a good way of comparing profiles or website
comparing various spaces and recommending best practices? I would like some
kind of chart or histogram.
Basically is Wide RGB the best option or should I look
at other profiles?
Thanks,
James Stuart Johnson
J. Stuart J. Production Art & Imaging
________________________________________________________________________
From: Stephen Marsh
Date: Thu, Jan. 23, 2003 7:38 pm
Subject: Re: Best practice for RGB stock images?
James writes:
I have been lurking here for ages. I finally have a
quick question.
I doubt the thread answering the question will be
short or quick though. <g>
I am working on a project-involving image for sale as
stock, i.e.
Photos and hand generated Textures and Illustrations.
I wish to make
them available for the widest possible usage while
keeping them
accessible to software without profiling. I intend to
use RGB TIFFs
and those using Photoshop or profile aware software I
intend to embed
a profile, but which provides the possible range in
RGB?
With the above criteria, it would seem like ColorMatch
or Apple RGB for Mac clients and sRGB for PC clients. That is if you want a
problem free image for non ICC savvy users.
If you care more about the gamut and the profile -
then Adobe RGB 1998 would probably be the widest space I would use for 8
bpc RGB data. Just beware that non ICC savvy people or those who do not use
CM and A98 will often get the wrong result from the space (which is not
like a monitor or their default WS).
Do you know your client base, what they do and how
they do it?
Have you considered just one profile on the CD that
points to all images, or is tagging each one acceptable (for most RGB
profiles this should not add that much to the file size).
Are you considering value added metadata such as thumb
icons, previews, IPTC keywords etc (again considering file size additions
to the entire archive if this an issue. There was an old thread about
tagging 30,000 images with the same profile, but it escapes me).
What I was able to gather so far form books and
manuals: Wide RGB
looks like the way to go, I also noticed Pro Photo RGB
I have no idea
of it's intended target.
Well, it depends on where you read your stuff.
<g> There is the theory and the actual application of the theory -
often the two are not the same.
Is there a good way of comparing profiles or website
comparing
various spaces and recommending best practices? I
would like some
kind of chart or histogram.
The histogram would not have much meaning without
understanding the source image and the transforms.
Basically is Wide RGB the best option or should I look
at other
profiles?
Try these links, similar topics are mentioned and it
should give you some more defined points to consider and then you can ask
more targeted questions.
http:
//www.ledet.com/margulis/ACT_postings/ProfilingandProofing/ACT-I-
Switched.htm
http:
//www.ledet.com/margulis/ACT_postings/ProfilingandProofing/ACT-
profiles-who-what.htm
http:
//www.ledet.com/margulis/ACT_postings/ProfilingandProofing/ACT-
sRGB-vs-Adobe.htm
http://www.brucelindbloom.com/WorkingSpaceInfo.html
http://www.creativepro.com/story/feature/8582.html
http://www.creativepro.com/story/feature/6541.html
Hope this helps,
Stephen Marsh.
________________________________________________________________________
From: Terry Wyse
Date: Thu, Jan23, 2003 9:16 pm
Subject: Re: [colortheory] Best practice for RGB stock
images?
OK, I'll bite! :-)
I would have to say that Wide Gamut RGB and/or Pro
Photo RGB would probably hose the images for 95% or your
"audience". For those who treat the image correctly (preserve the
profile), both of those spaces are so "far out" that I consider
them of little use for general editing on a monitor (you won't see what
you're doing unless you scruntch it done to something reasonable like A98,
Colormatch or sRGB). I won't even say the "16-bit" word. ;-)
I'd probably go with Adobe98 but as Steve mentioned,
ColorMatchRGB and sRGB are not unreasonable choices for a non-ICC audience.
Maybe offer Mac/PC images tagged with these respective profiles. If the
user recognizes the profile, fine, if not, they're probably still going to
be OK.
I'd consider all the big, wide and loud spaces ( you
know who you are!) useful only as an archiving space from a high-end
scanner or digital camera capture where you need to store all the available
color for eons to come in hopes that the Ultra-Wide-Super-Chroma
offset/inkjet/photographic output device gets invented. And hope that your
image archive hasn't devolved into bits of noise on whatever medium you
stored it on.
Or I could be wrong.
Terry
--
__________________________________
WyseConsul
Color Management Consulting
v 704.843.0858
__________________________________
________________________________________________________________________
Date: Thu, 30 Jan 2003 20:14:14 -0500
From: Deb Koons
Subject: RE: Best practice for RGB stock images?
Hi James,
You can find out more info about Kodak's ProPhotoRGB
working-color-space at Kodak's ColorFlow website:
http://www.kodak.com/go/colorflow/
There are a couple of whitepapers there, and a
download of the actual profile.
I also found good info about color spaces in my copy
of "Real World Photoshop 7" and I suspect there is a lot of
discussion of this subject in the new "Real World Color
Management" (mine is on order).
HTH, Deb Koons
____________________________________________________________________________
Date: Sat, 1 Feb 2003 19:54:08 -0500
From: John Castronovo
Subject: Re: Best practice for RGB stock images?
ProPhotoRGB is intended to be a retouching space and a
speculative one at that as it allows one to describe colors beyond
theoretical limits. Some software can interpret these 'colors' as black! I
certainly wouldn't suggest using it to share files with anyone let alone
someone who might ignore the embedded profiles.
For the maximum compatibility, convert to sRGB after
doing your edits in a larger space. The result will look and print pretty
well on just about anyone's equipment even if they're not icc aware,
however, sRGB is certainly more gamut limited than some would like for very
saturated colors. In this regard, you're doomed either way.
Have a look at http:
//www.hutchcolor.com/Spreadsheets_to_go/RGB_coords.xls
if you'd like to compare these spaces with one
another.
john castronovo
____________________________________________________________________________
Date: Wed, 5 Feb 2003 15:36:40 -0700
From: Chris Murphy
Subject: Re: Best practice for RGB stock images?
On Saturday, February 1, 2003, at 05:54 ÊPM, john c.
wrote:
For the maximum compatibility, convert to sRGB after
doing your edits in a
larger space. The result will look and print pretty
well on just about
anyone's equipment even if they're not icc aware,
however, sRGB is certainly
more gamut limited than some would like for very
saturated colors. In this
regard, you're doomed either way.
I would not recommend converting images of any
importance to sRGB without consideration for where it will end up. If it's
likely it will be viewed on-screen or printed to an inkjet printer *on
Windows* this is not unreasonable. It's unfortunate, but that's another
discussion. For inkjet destinations on Mac OS, a gamma 1.8 space is still
assumed as source for many printer drivers, including all of Epson's that
I've seen.
If you have no choice but to go for "one size
fits all" then expect those kind of results as well.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
Date: Sat, 8 Feb 2003 18:59:51 -0500
From: John Castronovo
Subject: Re: Best practice for RGB stock images?
From: "Chris Murphy"
I would not recommend converting images of any
importance to sRGB
without consideration for where it will end up. If
it's likely it will
be viewed on-screen or printed to an inkjet printer
*on Windows* this
is not unreasonable. It's unfortunate, but that's
another discussion.
For inkjet destinations on Mac OS, a gamma 1.8 space
is still assumed
as source for many printer drivers, including all of
Epson's that I've
seen.
Agreed. I'm no fan of sRGB, but if one had to choose
just one space for an image to look best for most people who aren't icc
aware, it would have to be that. It's not good, just safe. BTW, which Mac
profile do you think is most common or safest? AppleRGB, Colormatch?
john castronovo
____________________________________________________________________________
Date: Sat, 8 Feb 2003 18:12:31 -0700
From: Chris Murphy
Subject: Re: Best practice for RGB stock images?
On Saturday, February 8, 2003, at 04:59 PM, john c.
wrote:
Agreed. I'm no fan of sRGB, but if one had to choose
just one space for an
image to look best for most people who aren't icc
aware, it would have to be
that. It's not good, just safe.
You still need to ask the question about the target
market. There are people who specifically target Mac users, and they are
absolutely in a good position to target ColorMatch RGB and not sRGB. If
your target is unknown, and the color sophistication is presumed to be
better on a Macintosh, then again it's not unreasonable to target
ColorMatch RGB. If your target is unknown, and you want the best possible
result for the largest market, then yes you would target sRGB because there
are a lot of Windows users on the planet. What to pick depends on the
situation - on the target market.
BTW, which Mac profile do you think is most
common or safest? AppleRGB, Colormatch?
If you or your customers have an Apple 13"
display, then Apple RGB is a reasonable choice. Otherwise, ColorMatch RGB
is the better choice.
I'm actually curious if sRGB actually still reflects
the behavior of the average CRT display still. And what of higher qualify
CRTs? What is the deviation? And also, what about the average LCD compared
to sRGB. And still further what about high quality LCDs? I have no data to
back up this supposition, but I wonder if sRGB is about to become
antiquated.
Along the lines of antiquity, I feel like the legacy
gamma of 1.8 on the Macintosh should be abandoned. The original reason we
have it is no longer applicable, and it just makes things a pain in the ass
for everyone. I feel it hurts us a lot more than it helps. It's a pain to
web developers. It's a pain to the online experience of Mac users. It's
also possibly a pain to print driver vendors, and display adapter vendors.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
Date: Sun, 09 Feb 2003 03:00:26 -0000
From: "Stephen Marsh
Subject: Re: Best practice for RGB stock images?
--- "john c." wrote:
Agreed. I'm no fan of sRGB, but if one had to choose
just one space for an
image to look best for most people who aren't icc
aware, it would have to be
that. It's not good, just safe. BTW, which Mac profile
do you think is most
common or safest? AppleRGB, Colormatch?
John, if we are talking about non ICC savvy users -
then it makes little difference.
Test it yourself. Assign ColorMatch RGB to a Apple RGB
file, or vice versa. Minor saturation loss/gain in some cases - much more
minor than possible monitor differences between users. I would just run
with CM RGB.
Not the same sort of thing as getting sRGB and A98
mixed up.
Stephen Marsh.
____________________________________________________________________________
Date: Sun, 9 Feb 2003 12:01:21 -0000
From: "Bob Frost"
Subject: Re: Best practice for RGB stock images?
Chris,
The new version, to complement the existing sRGB, is
already on its way -sRGB64.
www.microsoft.com/hwdev/tech/color/sRGB64.asp
Bob Frost.
____________________________________________________________________________
Date: Sun, 9 Feb 2003 08:30:10 -0600
From: "John"
Subject: Re: Best practice for RGB stock images?
Good Morning,
I wish someone could answer this sRGB question for me.
I use one of the largest color labs in the USA, they
were one of the first if not the first pro lab to offer digital imaging and
they have always used sRGB. I have asked people in their customer service
departments and they don't know either, but will try to get back to me.
They are mainly a "portrait" lab, but I'm
sure there is some commercial work, I use a local lab for my commercial
assignments.
Best,
John Douglas
____________________________________________________________________________
Date: Sun, 9 Feb 2003 11:02:25 -0500
From: "john c."
Subject: Re: Best practice for RGB stock images?
Along the lines of antiquity, I feel like the legacy
gamma of 1.8 on
the Macintosh should be abandoned. The original reason
we have it is no
longer applicable, and it just makes things a pain in
the ass for
everyone. I feel it hurts us a lot more than it helps.
It's a pain to
web developers. It's a pain to the online experience
of Mac users. It's
also possibly a pain to print driver vendors, and
display adapter
vendors.
Chris,
I agree that it would be good for Macs to abandon the
1.8 standard. It makes it really tough for everyone. Of course, the real
problem is that people still refuse to embed and use profiles.
If we only knew that an image was prepared for viewing
with one profile or another, none of this would be a problem. Yet, people
who should know better like printers and pre-press folks still yell at me
when I ask them for a source profile. I get responses like, "What's a
profile" or "How come YOU need a profile and I don't?" Who
has the power to change an industry so rigidly stuck in stupidity?
john castronovo
____________________________________________________________________________
Date: Sun, 9 Feb 2003 13:11:59 -0700
From: Chris Murphy
Subject: Re: Best practice for RGB stock images?
On Sunday, February 9, 2003, at 05:01 AM, Bob
Frost wrote:
The new version, to complement the existing sRGB, is
already on its
way -- sRGB64.
From what I can tell, this is more of a
competitor to Adobe RGB (1998) (in concept), than it is an update to sRGB.
sRGB was based on average CRT behavior, with presumably some modifications
to make it gray balanced and behave well. What I'm looking for is an
updated profile that describes the average display. If that's still sRGB,
fine. I don't find yet another RGB space for editing images to be very
compelling by itself. But if Microsoft allows a mechanism to use sRGB64
instead of sRGB for prosumers, I can see why it's being suggested. However,
I think it would be easier to create a UI for the end user to select their
own assumed space on a system wide basis, instead of creating yet another
color space for us to debate about. And 64-bits? What's that mean? How is
64-bits total divisible by three channels? And what CMMs are doing
computations with more than 16-bits? I know of only Adobe ACE (which uses
20-bits per channel).
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
Date: Sun, 9 Feb 2003 13:13:37 -0700
From: Chris Murphy
Subject: Re: Best practice for RGB stock images?
On Sunday, February 9, 2003, at 07:30 AM, John
wrote:
I use one of the largest color labs in the USA, they
were one of the first if
not the first pro lab to offer digital imaging and
they have always used sRGB.
I have asked people in their customer service
departments and they don't know
either, but will try to get back to me.
So what's the question? :) Why does this lab use sRGB?
I have no idea. You'd have to ask them. And there is a really good chance
they aren't going to have a compelling answer.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
Date: Sun, 9 Feb 2003 13:30:43 -0700
From: Chris Murphy
Subject: Re: Best practice for RGB stock images?
On Sunday, February 9, 2003, at 09:02 AM, john
c. wrote:
I agree that it would be good for Macs to abandon the
1.8 standard. It makes
it really tough for everyone. Of course, the real
problem is that people
still refuse to embed and use profiles.
Not everything needs them. For example, web content is
already based on sRGB for all practical purposes. And since most people
using a computer are viewing web pages and email (with increasing amounts
of HTML content), it makes sense to me to dump the legacy 1.8 gamma in
favor of the more common media. People who really think they need gamma 1.8
for some reason can use Display Calibrator or buy a 3rd party instrument
and calibrate to 1.8. I use 2.2, and incidentally all three authors of Real
World Color Management use and recommend 2.2.
We should be in a position to make reasonable
assumptions about average display behavior, be it a CRT, LCD, movies from
digital camcorders (which don't use profiles), and other media sources. I
just think it would be easier if the legacy 1.8 gamma wasn't in the way.
The reason for its existence is no longer in existence (unless you have an
original Apple Laserwriter in production use).
If we only knew that an image was prepared for viewing
with one profile or
another, none of this would be a problem. Yet, people
who should know better
like printers and pre-press folks still yell at me
when I ask them for a
source profile. I get responses like, "What's a
profile" or "How come YOU
need a profile and I don't?" Who has the power to
change an industry so
rigidly stuck in stupidity?
They probably don't need a profile because they're so
used to their closed-loop system that the profile is actually in their
heads. They just don't see it that way. You need that mental profile put
into a physical file - an ICC profile - because you don't work with their
equipment day in and day out.
Years after saying it, I'm still of the opinion that
printers' responsibility is to:
1. Provide consistent and stable press conditions; and
2. The press behavior should be based on a standard
(GRACoL, SWOP, ISO 12647, whatever) *OR*
3. They need to supply a profile for their unique
press condition *OR*
4. They need to accept jobs with tagged images, honor
the tag, and separate the job properly
And print buyers' responsibility is to:
1. Prepare properly separated files (per printer's
requirements, either standardized or based on their profile) *OR*
2. Supply jobs with properly tagged files.
On top of that - both parties need to agree on a
contract proofing system and produce contract proofs before going to press.
That is the last line of "defense" to protect both parties and
finalize expectations.
It's pretty simple if everyone agrees on what their
role is going to be. Clearly defined roles sets up acceptable expectations
on both sides, and makes it clear which party isn't holding up their end of
the bargain. Most arrangements seem to deal with these issues after a
problem has already occurred.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
Date: Sun, 9 Feb 2003 23:23:08 -0500
From: John Castronovo
Subject: Re: Best practice for RGB stock images?
From: "Chris Murphy"
So what's the question? :) Why does this lab use sRGB?
I have no idea.
You'd have to ask them. And there is a really good
chance they aren't
going to have a compelling answer.
My guess is that they installed PhotoShop and never
knew enough to change
the default settings. <g>
john castronovo
____________________________________________________________________________
From: Ron Kelly
Date: Mon, Feb 10, 2003 12:50 am
Subject: Re: [colortheory] Best practice for RGB stock
images?
Chris Murphy wrote:
I just think it
would be easier if the legacy 1.8 gamma wasn't in the
way. The reason
for its existence is no longer in existence (unless
you have an
original Apple Laserwriter in production use).
Chris:
What is the reason for choosing one gamma over
another?
Is it anything more than simply a convention? Are you
asking that everyone switch to a common standard for convenience, or is
there more to it than that?
Ron Kelly
____________________________________________________________________________
From: Stephen Ray
Date: Mon, Feb 10, 2003 2:41 am
Subject: Re: [colortheory] Best practice for RGB stock
images?
On Sunday, February 9, 2003, at 07:30 AM, John wrote:
I use one of the largest color labs in the USA, they
were one of the first if
not the first pro lab to offer digital imaging and
they have always used sRGB.
I have asked people in their customer service
departments and they don't know
either, but will try to get back to me.
I can offer an educated guess at this one.
Probably because sRGB is
1.) ubiquitous and
2.) it happens to (somewhat) represent photographic
paper from scanned photos, and
3.) sRGB can often make scanned film's flesh tones
more realistic than if the film were scanned using a larger gamut color
space.
I'm currently imaging a client's photo tests comparing
Adobe 98 and sRGB and, at first blush, the sRGB is clearly the better photo
rendition in regards to saturation and neutrality, as is usually the case.
Stephen Ray
____________________________________________________________________________
From: Chris Murphy
Date: Mon, Feb 10, 2003 12:29 pm
Subject: Re: [colortheory] Best practice for RGB stock
images?
sRGB doesn't inherently represent photographic paper
from scanned photos. That is occurs is probably because the scanner is
specifically targeting sRGB behavior. This would also explain the results
you get in #3 above. If the scanner targets sRGB, then of course sRGB
should be the assigned profile and that will make the image look correct,
Adobe RGB won't. If the scanner is placed into a raw scanning mode,
profiled, then scan an image, use the profile to convert the image from raw
scanner RGB to Adobe RGB, I think you will see noticeably better results.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
From: Chris Murphy
Date: Mon, Feb 10, 2003 12:25 pm
Subject: Re: [colortheory] Best practice for RGB stock
images?
On Sunday, February 9, 2003, at 10:50 PM, Ron Kelly
wrote:
What is the reason for choosing one gamma over
another?
Gamma is by far not the biggest issue or debate we
have in color management, or operating systems. BUT, if it's the topic of
the hour, there are a number of reasons why I don't think gamma 1.8 is
appropriate anymore:
a.) Monitors have a natural gamma of around 2.2 to
2.4. Calibration results will be better (reduced potential for calibration
induced posterization/banding) the less we change the monitor.
b.) Gamma 2.2 is more perceptually uniform. It's not
exactly the same thing as what we get with LAB, which has something more
complex than just a gamma curve, but a gamma just over 2.3 is a close
approximation.
c.) The reason why we used gamma 1.8 to begin with, to
simulate the mid-tone gain of a particular output device, no longer exists
and is no longer needed. Using gamma was a form of hardware grayscale
management. This is now performed by the CMS using profiles and it's not
something that can be turned off. So gamma 1.8 is simply antiquated.
d.) Most of the things consumers do on a computer is
browse the web, email, use a digital camera, and maybe print some images
every now and then. All of these things would benefit if the platforms
didn't have different gammas. That's the main reason for color matching
problems - gamma discrepencies. The phosphors in CRTs aren't drastically
different, but their tone reproduction can be.
The bottom line is that more people are aided by the
dumping of the legacy 1.8 gamma than are hurt by it.
Now as for the gamma of an editing space - that's a
different debate. I still think a gamma 2.2 space is better, especially if
we're working in an 8-bits/channel space. But some have claimed better
reversibility (going into and out of a space) with a gamma 1.8 based color
space. I haven't seen compelling real world examples of this yet, however.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
From: Jono Moore
Date: Date: Mon, Feb 10, 2003 8:16 pm
Subject: Re: [colortheory] Best practice for RGB stock
images?
on 9.2.03 8:02 AM, john c. at wrote:
If we only knew that an image was prepared for viewing
with one profile or
another, none of this would be a problem. Yet, people
who should know better
like printers and pre-press folks still yell at me
when I ask them for a
source profile. I get responses like, "What's a
profile" or "How come YOU
need a profile and I don't?" Who has the power to
change an industry so
rigidly stuck in stupidity?
How about "rigidly stuck with what works"?
If you are going to be happy with "good
enough" colour, sure. If you really want your pictures to look their
best are you going to want to rely on profiles?
Not to mention all the variables involved in profiling
a print shop...
I mean, isn't this what Dan's book is all about?
We just produced an art book for our local museum,
which went to a very high-end shop for printing. They're all over
profiling, direct to plate, digital proofing, etc. The proofs did not look
like the printed piece, thankfully, but we were trying to make colour
decisions based on those proofs. The project was behind schedule so we just
had to cross our fingers and hope for the best. Luckily it turned out the
way it was supposed to, not how the proofs looked.
Part of the problem as I see it:
Say we have a profiled shop. You give us a bunch of
RGB files with profiles attached. We print the job and there are complaints
about the colour. Part of _my_ problem with this is that I can not go back
and check the colour of the picture (vs. what came out on the press/proof)
because it's in RGB! If it's in CMYK I can take the eye dropper to it and
say, beyond a reasonable doubt, if the colour is accurate or not. If this
was to happen, and everyone says they are profiled properly, who is to
blame?
--
Jono Moore
udoprinting.com
____________________________________________________________________________
From: "Stephen Marsh
Date: Date: Mon, Feb 10, 2003 11:01 pm
Subject: Re: Best practice for RGB stock images?
Chris Murphy wrote:
b.) Gamma 2.2 is more perceptually uniform. It's not
exactly the same
thing as what we get with LAB, which has something
more complex than
just a gamma curve, but a gamma just over 2.3 is a
close approximation.
Ah, I have not heard of this before Chris - not just a
simple gamma curve? Do you mean that there are more than one control point
on the curve in addition to the midtone, which affect the slope in other
areas? A bit like that other version of plain old sRGB that has a weird
gamma curve that is not standard? And now I hear of sRGB64, which is bound
to confuse things for some users or manufacturers by including sRGB in the
file name when it is apparently not like plain vanilla sRGB...why not
MSHP64 RGB?. Or is that HPMS64 RGB? <g>
Is there a definitive published source ANYWHERE on
this? 2.5 or 3 is the closest thing I have read in print, and quick tests
seem to back this up whe examing USM, but I have not compared luminance
levels lost in various RGB gammas to LAB to try to see which RGB looses the
same amount of unique levels (as a rough indication of the approx gamma,
not that I know if this is an accurate way to establish gamma of L of LAB,
I am just running with what I think I know! <g>).
Now as for the gamma of an editing space - that's a
different debate. I
still think a gamma 2.2 space is better, especially if
we're working in
an 8-bits/channel space. But some have claimed better
reversibility
(going into and out of a space) with a gamma 1.8 based
color space. I
haven't seen compelling real world examples of this
yet, however.
Chris, you probably ignored the recent thread which
was about sharpening,
linear colour blending option and gaussian blurs in
gamma1 vs. gamma compensated spaces, due to your keyword filter excluding
the terms TIMO or AIM etc. <g>
At first blush it seems that 2.2 gamma RGB is the only
common one which stuffs up the colour of a large blur which averages two
unique unblurred colours. 1.8 RGB, LAB and CMYK do not desaturate, they
still keep some degree of colour, although the end hue does vary between
spaces. This was in reference to a section of Timos site that someone
recently asked about, he has a blue and red chessboard pattern gaussian
blur demo. I did not test higher than A98 which uses 2.2, perhaps I should
have (or tested other phosphor primaries at 2.2 gamma etc) - but I was just
attempting to add to the original question by saying that 1.8 gamma RGB,
LAB and CMYK edits should not be forgotten in the whole debate about the
relative merits of some specific edits in gamma1 or 2.2 spaces (I get the
feeling that for some there are no other spaces except 1 or 2.2 gamma RGB -
when for me serious editing is never that bland).
Stephen Marsh.
____________________________________________________________________________
From: Terry Wyse
Date: Date: Mon, Feb 10, 2003 10:43 pm
Subject: Re: [colortheory] Best practice for RGB stock
images?
on 2/10/03 8:16 PM, Jono Moore wrote:
How about "rigidly stuck with what works"?
If you are going to be happy with "good
enough" colour, sure. If you really
want your pictures to look their best are you going to
want to rely on
profiles?
I don't know what this comment has to do with
profiles. Profiles are a TOOL to help you achieve more predictable color,
nothing more, nothing less. I'd argue that using profiles will get you to
GOOD color quicker than almost anything else. It will always take a good
operator to get to GREAT color from that point.
Not to mention all the variables involved in profiling
a print shop...
Yes, that's the "problem" with profiles:
they actually make a prepress/print shop responsible for the color they
produce and "force" them to use some measure of process control.
Yes, that's a bad thing.
I mean, isn't this what Dan's book is all about?
Uh, no. Dan, in fact, uses profiles to his advantage
when called for and ignores profiles when he feels they get in his way. At
least that's my take.
We just produced an art book for our local museum,
which went to a very
high-end shop for printing. They're all over
profiling, direct to plate,
digital proofing, etc. The proofs did not look like
the printed piece,
thankfully, but we were trying to make colour
decisions based on those
proofs. The project was behind schedule so we just had
to cross our fingers
and hope for the best. Luckily it turned out the way
it was supposed to, not
how the proofs looked.
They had proofs that didn't reflect what they printed?
What does this have to do with profiles? If they we're using profiles in
proofing to simulate their press, they OBVIOUSLY had bad profiles or at the
very least had profiles that no longer represented what they are printing
today. Again, lack of process control could be the culprit assuming they
had accurate profiles at one time.
Say we have a profiled shop. You give us a bunch of
RGB files with profiles
attached. We print the job and there are complaints
about the colour. Part
of _my_ problem with this is that I can not go back
and check the colour of
the picture (vs. what came out on the press/proof)
because it's in RGB! If
it's in CMYK I can take the eye dropper to it and say,
beyond a reasonable
doubt, if the colour is accurate or not. If this was
to happen, and everyone
says they are profiled properly, who is to blame?
#1: Using profiles does NOT force one into an RGB
workflow.
#2: Let's see, you can put an eyedropper on any CMYK
value and KNOW if the color is accurate or not? And what if I told you
these CMYK values were going to a sheetfed offset press? A web press? How
about if it's going to be printed flexo? The final product is going to an
inkjet printer? Do these all mean the same thing to you as far as CMYK?
This whole notion that if you have RGB images you
CAN'T know what the color is vs. having CMYK images you can ALWAYS
accurately predict what the color is is simply nonsense.
Terry "rigidly stuck in ignorance" Wyse
--
__________________________________
WyseConsul
Color Management Consulting
v 704.843.0858
__________________________________
____________________________________________________________________________
From: J Walton
Date: Tue, Feb 11, 2003 12:37 am
Subject: Best RGB space for CMYK output
I know that this general issue has been discussed
before, but I haven't seen this specific question asked. If it has been,
you have my apologies.
I work for a prepress company which has moved to an
RGB workflow. We scan and retouch in DonRGB, but all of our output is CMYK.
We never have a use for RGB as a final product. I wonder if we've chosen
the wrong working space.
Question 1 - If you did not have to worry about RGB
output and could focus on making CMYK images look good, what RGB working
space would you use?
Question 2 - If you chose sRGB or Colormatch, how
would you avoid clipping on pure cyans and yellows?
Thanks,
J Walton
____________________________________________________________________________
From: "Stephen Marsh
Date: Tue, Feb 11, 2003 4:33 am
Subject: Re: Best RGB space for CMYK output
J Walton wrote:
I work for a prepress company which has moved to an
RGB workflow. We scan
and retouch in DonRGB, but all of our output is CMYK.
We never have a use
for RGB as a final product. I wonder if we've chosen
the wrong working
space.
You mean CMYK should have been chosen?
Question 1 - If you did not have to worry about RGB
output and could focus
on making CMYK images look good, what RGB working
space would you use?
Sounds like CMYK and not RGB?
Question 2 - If you chose sRGB or Colormatch, how
would you avoid clipping
on pure cyans and yellows?
Cyan would not be clipped, as it is possible to reach
100C in CMYK.
<g>
Sorry J - I could not resist.
There should be no reason why these issues could not
be addressed in post separation edits (or has everyone there forgotten how
to directly edit CMYK now that they use RGB?).
Unless you move to a wider gamut RGB space, there is
no way around the maximum cyan generation - but this may not always be
needed for all images, and if it is required and you do have to use a more
narrow RGB, then you will either have to introduce post sep edits or accept
the limitations of the chosen RGB space.
I have worked in RGB workflows for press (that always
sounds like an oxymoron to my ears <g>) - and I have worked in other
situations where RGB is alien and a rare site...or mixes of both. You
eventually adapt in either case.
Stephen Marsh
____________________________________________________________________________
From: Chris Murphy
Date: Tue, Feb 11, 2003 12:54 am
Subject: Re: [colortheory] Best practice for RGB stock
images?
On Monday, February 10, 2003, at 06:16 PM, Jono Moore
wrote:
If you are going to be happy with "good
enough" colour, sure. If you really
want your pictures to look their best are you going to
want to rely on
profiles?
If you change this to: "If you really want your
pictures to look their best, are you going to want to rely *only* on
profiles?" then my answer is "no." You can't automate all
aspects of getting the best possible color reproduction - yet. But as
written above, I'd disagree. Yes you must rely, to a fair degree, on
profiles. But not just any kind of profile - high quality production
profiles.
I mean, isn't this what Dan's book is all about?
Dan's book is about image enhancement. It's important
to realize the limitations of color management, not getting so totally
wrapped up in it that you spend all or most of your energy there instead of
on your images. At the same time, it's possible to spend all or most of
your energy on your images, and end up chasing your tail as you try to
output from device to device. What's necessary is to find the right
balance.
We just produced an art book for our local museum,
which went to a very
high-end shop for printing. They're all over
profiling, direct to
plate, digital proofing, etc. The proofs did not look
like the printed piece,
OK, I've cut the quote right there because a huge
contradiction has occurred. First, they can't be that high-end, let alone
all over profiling, if the proofs don't look like the printed piece.
PERIOD. That's a serious breach of what contract proofs are all about. No
one expects proofs to be identical to the printed piece, but they expect
them to be reasonably representative within limits agreed upon by customer
and printer in advance.
Say we have a profiled shop. You give us a bunch of
RGB files with profiles
attached. We print the job and there are complaints
about the colour.
Again - stop right there. You've left out the proof!
Who is suggesting that printers should receive RGB files, with (or without
profiles), and immediately print the job? You *PROOF* first and then you
get the complaint. You don't go to press and get a complaint. That's
seriously anachronistic! OK...continuing:
Part
of _my_ problem with this is that I can not go back
and check the colour of
the picture (vs. what came out on the press/proof)
because it's in RGB!
No offense, but that's not at all compelling. If you
don't want to accept RGB jobs that might be OK, as it depends on your
company's business model. I'd suggest that as time goes forward there is an
increasing likelihood you will need to have an effective means of dealing
with RGB jobs because they are increasingly common. Those who figure out
how to deal with them effectively will get those kinds of jobs, and make
money servicing those customers.
Regardless, you do need to give the customer a
mechanism by which their jobs can be properly separated. Who does the
separation is an important, but secondary consideration.
If you're going to accept RGB jobs, then you need to
have the right tools. Various prepress systems will accept RGB PostScript
or PDF jobs, convert the entire document using either embedded or assumed
profiles as sources, to a destination profile you specify and boom - it's a
CMYK job - and you can check CMYK values. That's the file that the proof is
produced from and plates are produced from for printing on press.
If you don't have such a system, you can take the
PostScript file from the page layout application (which converts the
document to CMYK at print time), make a PDF of it, and bring it into
Acrobat running Pitstop Pro and it will let you poke around with an
eyedropper tool on any object you want, and see its CMYK values.
If it's in CMYK I can take the eye dropper to it and
say, beyond a reasonable
doubt, if the colour is accurate or not. If this was
to happen, and everyone
says they are profiled properly, who is to blame?
These things should be dealt with at the proofing
stage. And it's not about blame. It's about a process. Who is responsible
for what? And determining if everyone did what they were supposed to. And
then proofing the job to make sure it looks the way it should.
If there are problems proofing, you troubleshoot it
with a similar mindset as you do font problems, or trapping problems.
Familiarity and experience with the process, and having the right tools to
aid in troubleshooting gives you the ability to find out where the problem
is, and what's going to be done to fix it.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
From: Chris Murphy
Date: TueÊFebÊ11,Ê2003 1:06 am
Subject: re: LAB's gamma curve
On Monday, February 10, 2003, at 09:01 PM, Stephen
Marsh wrote:
Ah, I have not heard of this before Chris - not just a
simple gamma
curve? Do you mean that there are more than one
control point on the
curve in addition to the midtone, which affect the
slope in other
areas?
Yes. I'll let Bruce Lindbloom answer this one in more
detail. All I know that a simple gamma curve doesn't describe L*, but is
closely approximated by a gamma curve just over 2.3. Bruce?
A bit like that other version of plain old sRGB that
has a
weird gamma curve that is not standard? And now I hear
of sRGB64,
which is bound to confuse things for some users or
manufacturers by
including sRGB in the file name when it is apparently
not like plain
vanilla sRGB...why not MSHP64 RGB?. Or is that HPMS64
RGB? <g>
sRGB is a familiar term. So it might be selected for
marketing reasons. I have no idea. I'm still not getting how it's 64-bit
based.
At first blush it seems that 2.2 gamma RGB is
the only common one
which stuffs up the colour of a large blur which
averages two unique
unblurred colours.
Blending is more colorimetrically accurate in gamma
1.0 spaces as far as I know. This is why Adobe stuck in that option in
Photoshop 6, with limitations: it doesn't affects all blends. I don't know
what the solution to the problem is ultimately, but what I can say is that
when it comes to editing spaces, there is still some room for debating
gamma 1.8 versus gamma 2.2. Why this isn't occurring in LAB, which has a
slightly higher gamma, I don't know either. Perhaps Bruce has an idea.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
Date: Tue, 11 Feb 2003 07:03:12 -0700
From: Andrew Rodney
Subject: Re: Best RGB space for CMYK output
on 2/10/03 10:37 PM, J Walton wrote:
I work for a prepress company which has moved to an
RGB workflow. We scan
and retouch in DonRGB, but all of our output is CMYK.
We never have a use
for RGB as a final product. I wonder if we've
chosen the wrong working
space.
Haven1t plotted it but I expect it1s a pretty large
space. I suspect it1s a lot larger than the display gamut which might be an
issue for you. Frankly, Adobe RGB 1998 sounds like it would work fine with
a CMYK only output workflow.
Question 1 - If you did not have to worry about RGB
output and could focus
on making CMYK images look good, what RGB working
space would you use?
Question 2 - If you chose sRGB or Colormatch, how
would you avoid clipping
on pure cyans and yellows?
It1s more likely you1re NOT clipping the colors in a
larger space because you were at least able to capture them. I1d stay away
from sRGB because it is certainly going to possibly have colors outside
(smaller in some cases) than 3CMYK gamut2 (notice the quote since that1s
saying a lot).
IF DonRGB is working for you, why mess with it?
Otherwise, Adobe RGB seems like a safe bet.
Andrew Rodney
____________________________________________________________________________
Date: Tue, 11 Feb 2003 09:42:52 -0500
From: Jim Rich
Subject: Re: Best practice for RGB stock images?
Jono wrote:
Say we have a profiled shop. You give us a bunch of
RGB files with profiles
attached. We print the job and there are complaints
about the colour. Part
of _my_ problem with this is that I can not go back
and check the colour of
the picture (vs. what came out on the press/proof)
because it's in RGB! If
it's in CMYK I can take the eye dropper to it and say,
beyond a reasonable
doubt, if the colour is accurate or not. If this was
to happen, and everyone
says they are profiled properly, who is to blame?
Jono,
I am not sure what your rant is here, but technically
speaking, why cant you go back and check the RGB file using the eyedropper
to check the CMYK values? The eyedroppers work in RGB so you can preview
the CMYK values as though the image was a CMYK file.
Profiles are just one part of the process that helps
businesses communicate color more efficiently. The process will work
without them it will just take longer to get it done. It sounds like want
is missing from your post is the part where you use common sense when
working with profiles and then some skill and to get the color correct.
Jim Rich
____________________________________________________________________________
Date: Tue, 11 Feb 2003 12:27:20 -0500
From: Terry Wyse
Subject: Re: Best RGB space for CMYK output
on 2/11/03 12:37 AM, J Walton wrote:
I work for a prepress company which has moved to an
RGB workflow. We scan
and retouch in DonRGB, but all of our output is CMYK.
We never have a use
for RGB as a final product. I wonder if we've
chosen the wrong working
space.
If you're coming off of a good drum scanner or
high-end flatbed, DonRGB or BestRGB are decent working spaces from which to
convert FROM your scanner profile. Whenever I setup a drum scanner, those
are my preferred spaces to convert to. BestRGB is preferred as it has a bit
more extension in the reds to accommodate Fuji transparence media. You can
go to Don's site (www.hutchcolor.com) to download BestRGB.
Question 1 - If you did not have to worry about RGB
output and could focus
on making CMYK images look good, what RGB working
space would you use?
Question 2 - If you chose sRGB or Colormatch, how
would you avoid clipping
on pure cyans and yellows?
If you've got some analysis tools (ICCToolBox or
ColorThink for example), you should be able to verify that your
"working space" is at least as large as your scanner profile.
Choose the smallest working space that still encompasses your scanner
profile's color gamut.
There's going to be a bazillion opinions on how to
answer your question(s) correctly and many of them will be
"correct" in their own way. Here's my two cents worth:
Personally, if I had a decent scanner, I'd want to
"keep" as much of the original scanner data as possible without
clipping or "throwing it away" by moving the data into a working
space that is too small. This means choosing the SMALLEST space that is
just LARGE enough to not clip any of the original scanner data. Since any
move (AFAIK) from a scanner/input space to a working space is going to be a
relative colorimetric conversion, it will CLIP any colors that our in the
scanner space but outside the working space. Once moving the image into
this "just right" working space, you then could consider this the
"RGB Master" or archive image.
In regards to moving from RGB to CMYK, you could then
make use of the various rendering intent choices (perceptual or relative
colorimetric w/ BPC on/off most likely) to CONTROL how the colors get
clipped or "scaled" into your CMYK space. You're going to
"lose" color data no matter what but I'd rather have a bit more
control of how that happens rather than simply throw it away up front when
moving from scanner space to working space where it WILL clip the data if
you've chosen a working space that is too small.
Again, careful analysis of your scanner profile(s)
compared to the various standard working spaces will give you the
information you need to make the correct choice.
Terry
__________________________________
WyseConsul
Color Management Consulting
v 704.843.0858
__________________________________
____________________________________________________________________________
Date: Tue, 11 Feb 2003 16:08:25 -0500
From: Terry Wyse
Subject: Re: Best RGB space for CMYK output
What I MEANT to simply say but didn't explain very
eloquently:
You DO NOT have control over the clipping of colors
when moving from a scanner input profile to a RGB working space profile.
There's no option for rendering intent. All conversions from scanner to
working space RGB will be relative colorimetric. Thus, you'd want to use
the smallest working space that encompasses the scanner profile.
You DO have control when performing a RGB-to-CMYK
conversion over HOW the out of gamut colors get handled.
SO....start with a RGB working space that
doesn't throw away colors right from the start and use a combination of
rendering intent and your skill as an operator to decide WHICH color(s) get
clipped in the final CMYK conversion.
Terry
____________________________________________________________________________
Date: Tue, 11 Feb 2003 13:31:19 -0700
From: Chris Murphy
Subject: Fwd: LAB's gamma curve
Here we go:
> The equation for converting luminance, Y, into L*
is shown here:
> <http:
//www.brucelindbloom.com/Eqn_XYZ_to_Lab.html>
>
> The equation for converting L* to Y is shown here:
> <http:
//www.brucelindbloom.com/Eqn_Lab_to_XYZ.html>
>
> An interactive companding calculator for viewing
gamma, L*, density, > etc.
> may be found here:
> <http:
//www.brucelindbloom.com/CompandCalculator.html>
>
> My analysis of the gamma function that
"best" fits L* may be found > here:
> <http:
//www.brucelindbloom.com/CompandCalcHelp.html#BestGammaForLab>
>
> Finally, I have a deeper analysis of the L*
function (actually a > grafting
> together of two functions) which may be found
here:
> <http:
//www.brucelindbloom.com/LContinuity.html>
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
Date: Tue, 11 Feb 2003 23:35:27 EST
From: Stephen Ray
Subject: Re: Best RGB space for CMYK output
on 2/11/03 12:37 AM, J Walton wrote:
I work for a prepress company which has moved to an
RGB workflow. We scan
and retouch in DonRGB, but all of our output is CMYK.
We never have a use
for RGB as a final product. I wonder if we've
chosen the wrong working
space.
If there is no surprising contrast or color shift,
then DonRGB could be fine but look closely at banding when moding to CMYK.
Different scan profiles, work spaces, output profiles, and their
combinations, exhibit better or worse banding. By the way, you're not going
find banding problems by scanning an IT-8 Target. (There's no blends.)
And of course, never say never. If you don't have a
use for RGB scans I would venture to say your clients do, especially if
they know the milage they could get from them. Don't your clients have a
web site, publicity efforts, PowerPoint presentations, etc., anything other
than CMYK printing?
-Stephen Ray
____________________________________________________________________________
Date: Wed, 12 Feb 2003 07:26:11 -0500
From: John Castronovo
Subject: Re: Best RGB space for CMYK output
We've been converting all our work to DonRGB for
several years now with no ill effects seen or reported. The only concern is
that some people refuse to USE THE PROFILE when they open our work, even
though it's embedded.
john castronovo
tech photo & imaging
____________________________________________________________________________
Date: Wed, 12 Feb 2003 13:02:19 EST
From: Dan Margulis
Subject: Re: Gamma in LAB
Stephen writes,
Is there a definitive published source ANYWHERE on
this? 2.5 or 3 is
the closest thing I have read in print, and quick
tests seem to back
this up whe examing USM, but I have not compared
luminance levels
lost in various RGB gammas to LAB to try to see which
RGB looses the
same amount of unique levels (as a rough indication of
the approx
gamma, not that I know if this is an accurate way to
establish gamma
of L of LAB, I am just running with what I think I
know! <g>).
The L doesn't behave comparably to RGB channels. It
devotes relatively less space to extreme highlights and shadows, thus it
can be likened to a standard channel to which an S-curve has been applied.
This appears to be part of its effectiveness in sharpening.
Granted that a direct comparison has to be misleading,
if I'm forced to pick a number, I'd say that the L channel is very roughly
equivalent to RGB at a gamma of between 2.6 and 2.7.
Dan Margulis
____________________________________________________________________________
Date: Wed, 12 Feb 2003 15:51:10 -0800
From: J Walton
Subject: RE: Best RGB space for CMYK output...continued
Thanks to all for their replies, they were very
helpful.
Perhaps I should explain my reason for doubting
DonRGB. My concern is that using Perceptual rendering (which normally
looks best), going from a wide space to a small space (SWOP) will result in
banding. And we have had occasional problems with banding.
There is a limit to the total number of unique colors
in an 8-bit RGB file. Since I only care about SWOP output, then I want my
bits focused on the smallest possible area while containing the SWOP gamut.
If I use Wide Gamut RGB I am intentionally limiting the total number
of usable (CMYK) numbers in the file, am I not?
I'm not sure I understand why I need to choose my
working RGB space based on my scanner's space. The final CMYK output
is the ONLY thing I sell my clients, so it's the ONLY thing that matters to
me. Shouldn't I choose a working space based on the final output?
Theoretically I can see a benefit to having a working
or archive file in a large space, but I don't work in Theory Land, and my
clients don't buy theoretical images. If DonRGB is causing or
emphasizing banding, and it's bigger than I need for SWOP output, why
shouldn't I switch?
J Walton
____________________________________________________________________________
Date: Wed, 12 Feb 2003 17:19:22 -0700
From: Chris Murphy
Subject: Re: Best RGB space for CMYK output...continued
On Wednesday, February 12, 2003, at 04:51 PM, J Walton
wrote:
If DonRGB is causing or emphasizing banding, and it's
bigger than I need for SWOP output, why shouldn't I
switch?
I'd be suspicious that there is banding already in the
file, and a larger space like DonRGB may be exacerbating a preexisting
problem. If you have such a problem in the future, I would reassign a
profile such as Adobe RGB and reseparate. While the color will be a little
different due to just reassigning the profile, you will be making an
apples-apples comparison with this method: the point is to see if a
different source profile associated with the original numeric values
eliminates the posterization problem.
I have yet to see matrix based source profiles CAUSE
posterization/banding. But I have seen larger space source profiles
exacerbate posterization that was already in the file. And really, this
problem is more commonly caused by a problematic destination profile. That
is, perhaps a smoother destination profile could be used with the same data
and the wider space source profile.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
____________________________________________________________________________
Date: Wed, 12 Feb 2003 20:50:59 EST
From: Dan Margulis
Subject: Re: Best practice for RGB stock images?
Jim Rich writes,
Profiles are just one part of the process that helps
businesses communicate
color more efficiently. The process will work without
them it will just take
longer to get it done. It sounds like want is missing
from your post is the
part where you use common sense when working with
profiles and then some
skill and to get the color correct.
Right on target, just as the other replies from Terry
and Chris were. However, lest it seem that we're ganging up on Jono, let me
point out that he was responding to considerable provocation and may have
overstepped somewhat in his reply.
What Jim, Terry, Chris and I say is typical of what
those knowledgeable in the field believe here in the year 2003. What Jono
responded to was more typical of 1998 or early 1999: "Of course, the
real problem is that people still refuse to embed and use profiles...Who
has the power to change an industry so rigidly stuck in stupidity?"
The statement pointed the usual fingers at the stupid printers and stupid
service bureaus. All that was missing was the usual "you have to
understand the technology is in its infancy" and "what you really
should be doing is educating your clients rather than putting your head in
the sand."
Jono wasn't talking about his own personal settings or
how to calibrate his own devices. He was speaking of the viability of using
profiles to interchange documents with total strangers. In that limited
area, he's right: printers and SBs have concluded, quite rightly in
my view, that this is an ineffective, costly, and error-prone way to do
things. And in any event there are so few clients who know what they're
doing with embedded profiles that the printers feel little need to pay
attention.
Speaking as one of the persons so rigidly stuck in
stupidity that I ordinarily refuse to embed profiles, however, let me
reiterate that there *are* many good uses for the technology and those who
don't understand what profiles do are unnecessarily limiting their options.
Dan Margulis
____________________________________________________________________________
Date: Wed, 12 Feb 2003 21:06:09 EST
From: Dan Margulis
Subject: Re: Best RGB space for CMYK output...continued
J writes,
I'm not sure I understand why I need to choose my
working RGB space based on
my scanner's space. The final CMYK output is the
ONLY thing I sell my
clients, so it's the ONLY thing that matters to me.
Shouldn't I choose a
working space based on the final output?
Yes, which is why this thread is so mystifying. It
strikes me as like saying that your company has decided that you should
drive while upside down and you need our advice as to what brand of socks
will give your toes the best hold of the steering wheel.
If you own a printer that wants RGB input, you want to
work in RGB unless there's some image-specific reason to go elsewhere. The
same applies here. Why on earth would you want to make *any* RGB your
primary workspace, if you are *only* concerned with output in CMYK?
The first choice, therefore, is to work mostly in
CMYK, reserving the option of RGB and/or LAB where appropriate. The second
choice would be some RGB that bears some relation to the CMYK gamut: sRGB,
Apple RGB, or ColorMatch RGB. The third choice would be something wider
gamut like Adobe RGB, which introduces a lot of gamut problems but makes it
somewhat easier to get "acceptable" color. The fourth choice is
LAB, which is even harder to work with but offers certain unique
advantages.
If CMYK is your only concern, the eighty-sixth choice
is to work in some ultra-wide-gamut RGB, which combines all of the
disadvantages of 2 through 4 in one colorful package.
Dan Margulis
____________________________________________________________________________
Date: Wed, 12 Feb 2003 19:56:53 -0800
From: J Walton
Subject: RE: Best RGB space for CMYK output...continued
I think Dan's argument makes a lot of sense (except
for the sock thing ;-), especially since until now I haven't explained the
use of RGB.
We quite frequently need to repurpose the same image
for a variety of different CMYK outputs. We retouch the image and it
goes first to Time magazine, later on it goes to USA Today, and later still
it prints sheetfed on glossy stock. We want the advantage of using
one worker file and easily moving to 300 DMAX, 240 DMAX, and 340 DMAX.
We also like the advantage of being able to automatically compensate
for diffe