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From: "lea murphy"
:color space questions
: First of all, thank you to those who responded to my color
management
: question a couple weeks ago, especially karl shah-jenner, as your
: info was most helpful.
glad to hear it :-)
:If you don't mind bearing with me, I have at
: least a couple more questions before I get going as I should.
: Let me come clean. I don't really 'get' color management. I'm not
: clear on how all the different 'spaces' and 'profiles' work together
: (is a space the same thing as a profile? See, I really don't get
it.)
: and when to apply one.
It's important to understand this stuff now that many are work
digitally to
some extent. Just as it was important for *some* of us to understand
colour processes when we worked with film. Admittedly a lot of
processing
steps were handled by specialised pros in the field - film
chemists, lab
staff who really needed to understand all the intricacies of the
medium,
leaving we photographers to just shoot our film safe knowing the
rest would
be handled properly. Now days you're on your own, there are no
chemists
running monitoring processes so the whole colour monitoring and
control
process is in your hands, and is something each individual must learn.
Don't forget that this fact alone was something people yearned for
- the
ability to control every step themselves without the risk of
someone else
making a mistake somewhere - now we all get to make our OWN
mistakes ;-)
Onto colour space or Gamut
Colour space / gamut is the limit of colours a device can represent
- a
monitor can make very deep rich colours with very high contrasts, a
printer
has a lot less colours and a lot less contrast.
Think of it as similar to slides V prints - slides like monitors
show you
the image by transmitted light and subsequently have a huge contrast
(contrast being the difference between black and white) while a
print is
viewed by reflected light and has a heck of a lot less contrast.
you know
this from whenever you have a side printed on cibachrome - the
richness,
the depth of tones is lost - you can only make a print so black and so
white..
Each device has it's own colour space or gamut - it's limit to the
range
and depth of colours it can make.
Speaking of monitors for a bit, each monitor will have an upper
limit to
the amount of colour it can produce - you can't go beyond these
colours
however there are a number of ways to modify the displayed colours.
You can't set the monitor contrast, gamma and colour balance
directly from
the monitor internal electronics, but these are done at the factory -
nonetheless if you imagine for a moment that someone has turned
down the
green gun in the CRT a bit, then to obtain neutral tones you'd have to
adjust the red and blue guns down too (using monitor controls)-
effectively
lowering your brightness and thus contrast.. and thus your colour
range and
contrast will be lower than were that green gun turned up.
You can however adjust the monitor directly using the
colour/contrast/brightness/other settings built into your monitor by
twiddling the monitor switches and menus and this can be done
independent
of the computer. When setting up through adobe gamma for example, the
first thing the program asks you to do is "first set the contrast
to it's
highest level" and gives you a grey/black box to examine while you are
doing this.. you use the monitor controls to perform this task.
Another way to modify the perceived colours is through the video
card -
what info this squirts out to the monitor in the form of colour
depth. Is
the monitor set to 256 colours, 16 bit, 24 bit or 32 bit? (Is
there a 48
bit yet?) Each will produce not just the various levels of banding
you
will or will not see, but obviously also the range of colours.
Assuming so far that all are set to maximise the depth of colour
and range
of contrast, you will have the best colour space possible from this
particular monitor :-) but we're not done yet
Next we have to make sure those colours render in as *matched* a
fashion as
possible. Harking back to film again for a clue - if our
processing was
off or if we excessively pushed or pulled a film we'd find the curves
shifted out of alignment and behaved weirdly - the most extreme
example of
this was cross processing when the red, green and blue layer curves
move so
wildly away from one another that it's simply not possible to bring
them
back to true, so the colours will be wrong. We might achieve a
neutral
grey in the mid tones, but the blue and yellow will be skewed so that
highlights will be yellow, and shadows blue. If we get the shadows
neutral
the rest of the tones shift to yellow, if we get the highlights
neutral the
darker tones shift blue. nasty.
Fortunately when we buy a monitor it's close to right and we don't
have a
lot to do, but because we are trying to work as close as possible
to true
we will still need to get these colours *more* right. So we fire
up some
sort of calibration software or we adjust by eye for the fine
tuning and we
start to move from the realm of 'colour space' into 'profile'.
The software and bits of hardware around for calibrating monitors all
perform various functions designed to render colours as correctly as
possible, some like the Spyder thing work by using colour analysers
work
toward colour accuracy based on certain standards (whatever these
standards
may be - and these are the magic 'profiles') while some others use
your
personal perception of colour, such as Adobe Gamma.
They are not however interchangeable - each profile is designed to
function
is a certain environment and there's no cure-all that makes
everything work
all of the time! Each profile will chance the gamut of your monitor,
shrinking the colour space to a certain degree.
Leaving this part of monitors aside for a while, we'll consider the
monitor
profile and how it ties to output.
Ultimately you will have different intents for each image, and
different
profiles will need to be applied for each final step. An example I
used
before was the CMYK approach. Most print presses have 4 colour
inks and
they frequently work with the Pantone colour range (there are
others, and
many other colour standards but lets work theoretically with one
and hope
we never have to deal with it, or others like it ;). This standard
has
been set to allow graphic designers to design stuff up on their
computers
profiled to this limited colour range so they know when it's sent
to print
the colours will reproduce VERY closely to the gamut the printers are
capable of printing. Their output and workflow is NOT based on
perception
of colour, but rather colourimetric values. What this means in a
simple
sense is that the light source by which the final images are viewed is
immaterial - the colours may look *quite* wrong to our eye, but
under a
colour analyser they will match a set of standard colours like a
swatch
from a pantone chart. They will use a Spyder and set up the
computer to
the standardized gamut of the 4 colour printer and match their
monitors,
software and input devices to this standard, the standard being
limited to
the output device.
Thus when they load a colour into a block of text or a background
they will
see on their monitor what that colour will look like in relation to
others
once it rolls off the press, and were they to lay the original colour
swatch beside the print the two should match precisely.
However anyone who's had the pleasure of seeing their work in print
will
have discovered that many graphic designers have a bit of a problem
with
photographs. You see there are no standard colours in a photo
image, there
is nothing they can lay a swatch against to check the colour and to
top it
off, there's no way a 4 colour printer can reproduce the colours we
get out
of an RA4 machine or a slide anyway! They will run an eyedropper
tool over
a photo and guess the colours, then maybe make a slight tweak (or not)
before dropping it into their publication. (fight ensues between
graphic
designer and irate photographer, each accusing one another of not
understanding colour!)
A case of different intents..
So we need a profile set up for our monitor which matches the gamut
of the
4 colour printer which we can load* when we want to do work for
magazine
printing.
(* by 'load' I mean we 'apply' this monitor profile, which will
proceed to
alter the colours on our monitor to match those that this 4 colour
printer
can produce - we then need to 'tweak' those colours to make them look
acceptable to us and to how we'd like it to reproduce)
Of course we also use a mates 6 colour wide format printer, and our
own 8
colour printers from time to time too - so we really need profiles for
these as well! We should be loading each of these profiles while
working
our image so the 'profile' (colour modification) shows us the
colours on
the monitor such that they match the colours our chosen printer can
produce.
..and there's the Frontier we send images to from time to time, and
they
use different paper stocks as well, so yet more profiles are needed.
Each image NEEDS to be modified and manipulated within the colour
space
profile of the intended output device otherwise the colours or
contrast
will be wrong, so we really do need a fair few profiles tucked
away. Of
course they need to be backed up too, and we need to be able to
check to
see if the correct profile is actually loading when we attempt to
load it,
and then there's the issue of the colour drift in a CRT as it heats
up,
cools down, starts, wanders with shifts in power etc etc etc..
<groan!>
It is a lot less trouble for the graphic designers though, once a
profile
is set they tend to work pretty exclusively with it and it alone,
aside
from maybe the proofing they do with a single printer who's gamut
will be
crippled down to closely match the gamut of the big 4 colour printer.
now here's the BIG difference, unlike the graphic designer who's
workflow
is geared toward a single output device with a limited gamut, we
often want
to get the BEST colours we can out of a printer to make our images
as rich
as possible!
At present we can get our biggest gamuts, the most colours, in
diminishing
order from:
1. Film output devices - like the Polaroid propalette 8000
2. Frontier printers and other laser/led devices that image to RA4
3. 8 colour (or better) dye ink printers
4. 6 colour dye ink printers
5. 4 colour dye sub printers
6. 8 colour (or better) pigment printers
7. 4 colour dye ink printers
8. 6 colour pigment printers
9. 4 colour pigment printers
Obviously changing inks, manufacturers etc will change our colours,
as will
to a lesser extent changing the media on which we print. Oh yeah, the
varying papers will all need different profiles too :-/
So rounding up, we build ourselves all the profiles (colour
modifiers if
you like) that we need, and we apply each one as needed to our
monitors to
allow us to see the colours that our printer can produce.
It's actually a lot more complicated than this and the steps folks
take to
get their profiles can be many and varied, some quite expensive -
most are
time consuming, all are frustrating and the results are often wrong
:-(
Colour management is a massive headache to everyone who delves into
the
subject and it's applications, and as I said before every year some
company
or consortium invests millions coming up with new standards that will
hopefully simplify things and next year the process gets repeated
all over
again.
The best I can suggest is to latch onto something, ANYTHING that
gets you
close to what you want then 'tweak' until you get closer.
Lastly, if you're working toward web images use the broadest gamut you
can - adobe rgb or, NO profile and work with your histogram tool to
make
sure you have your tones distributed as appropriately as possible.
Most
browsers ignore profiles anyway so if you've attached something it
will
just be ignored and the simple RGB values will be displayed to the
viewer -
who invariably has a cheap, 10 year old monitor.. out of alignment,
with
moiré issues.. and a collapsed red gun set to 256 colours :-P
: I know my lab's Noritsu is set to print in sRGB (as are almost all
: lab printers if I'm not mistaken). In PS should I be converting
to sRGB?
yes :)
: Also, I have downloaded my lab's printer profile and can set that as
: my color space in PS. Should I be doing that?
it's a good start!
: I am so confused.
we all are!
: Any suggestions?
fiddle, tweak and muddle until you get closer to what looks good to
you
:)
k
