Re: Dancing in the minefield....
Re: Dancing in the minefield....
- Subject: Re: Dancing in the minefield....
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Tue, 17 Dec 2002 15:05:39 -0600
Dan Husted wrote:
>
I am relativly new to the color management minefield and am looking for a
>
little direction so I don't lose a limb.
You have brought up many important topics in your message. I will express my
opinions, but I know ahead of time that there are many experts on this list
who will strongly disagree with me on some issues (and I'm sure I'll hear
from them). So you might want to consider a variety of opinions before
making your final decisions. Good news: my opinions are free. Bad news:
sometimes you get what you pay for.
Working Spaces:
--------------
Choose a working space whose gamma is 2.2 -- see the bottom half of this
page for my reasons: <
http://www.brucelindbloom.com/CompandCalcHelp.html>.
The gamma values of many common working spaces are tabulated here:
<
http://www.brucelindbloom.com/WorkingSpaceInfo.html>.
>
I started using Adobe98 but I feel I am losing some data,
Instead of "feeling," you can try to actually find out if this is happening.
After converting an image into the working space, use your eyedropper to
examine the RGB values of non-neutral colors. If any of the R, G or B
components are at (or very close to) zero or 255, then clipping against the
working space is likely to have occurred. You cannot make this determination
by visual inspection of the monitor, since most working spaces extend beyond
the gamut of your monitor, and apparent color clipping may actually be
clipping against the monitor gamut instead of the working space gamut.
>
Also, should the monitor and working space be the same gamma ?
These two gammas are independent of each other.
Monitors:
--------
Within a color managed environment like Photoshop: Load the video look up
tables (VLUTs) with ramps. Use the monitor's brightness and contrast knobs
(or whatever means are available to control the monitor's electronics) so
that you get as close as possible to your desired white point, a good black
and a gamma of 2.2. (It's not important that you actually achieve 2.2, it is
just a target goal.) Do not use VLUTs to do this. Then profile your monitor
while it is in this state. Do not make or use use monitor profiles with vcgt
tags. Leave your VLUTs with ramps in them. The reason for the ramped VLUTs
is that for any 8-bit to 8-bit LUT (like you'll find in most VLUTs), you
will lose levels by loading in a curved function. This is not a trade-off
situation where you give up something here to gain something there. When you
load a curve into a VLUT you give up levels and gain nothing (remember we're
in a color managed environment -- Photoshop will compensate for any
differences between the working space gamma and the monitor gamma). For
example, if your native monitor gamma is 2.5 and you use a vcgt tag to make
it appear as though it has a gamma 1.8, you have reduced the number of
levels driving the monitor from 256 down to 202. You can explore this
yourself here: <
http://www.brucelindbloom.com/LevelsCalculator.html>.
It's a different story when you are outside of a color managed environment.
You may want to "vcgt" your monitor into say 2.2 gamma so that it conforms
more closely to the sRGB standard (which is often the assumed RGB space in
such uncontrolled situations).
>
Is there a difference between 6500K and D65?
This has been recently discussed on this list, Go to the digest archives and
look (for example) at message 12 of Vol 3 #528.
Scanners:
--------
>
Also, should the scanner's gamma(1.8) be set to that of the monitor's(1.8),
>
(or 2.2 for that matter)?
I have recently expressed my opinion on scanner setup in message 8 of Vol 3
#502. The "gamma" of a scanner should be set in a way that best captures
visually significant information, without regard to either your monitor's
gamma or your working space gamma.
--
Bruce J. Lindbloom
email@hidden
http://www.brucelindbloom.com
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