Dan Margulis Applied Color Theory
Achieving Neutrality with Mixed Lighting
Date: Sat, 03 Apr 2004 10:47:44 -0000
From: “lwb_guitar”
Subject: Acheiving neutrals with mixed lighting etc.
Hi,
OK, been reading for a while and have managed to work
up the courage to make my first post ...
I’m a graphic designer, working mainly with
artists and arts organisations. My main line of work is producing
publications which document gallery exhibitions, and thus most of the
images I deal with feature a lot of white wall space.
Of course, a lot of the time the white isn’t
white. A lot of otherwise respectable and venerable institutions have no
clue how to light exhibits properly for photographic documentation, and a
lot of otherwise excellent photographers have no clue how to measure the
colour temperature of the lights in the space, or deal with daylight
creeping into a tungsten-lit space or the three different types of
fluorescent strip that have gotten mixed in with the lighting over the
years.
I’d be interested to hear any strategies people
on the list have for dealing with this kind of situation. I’ll detail
one that’s been successful for me recently (after years of
painstakingly painting between differently colour balanced adjustment
layers):
First I get a rough neutral using a curve adjustment
layer — i.e., kind of ‘splitting the difference’ between
the various shades of white. Then I flatten and convert to Lab and make a
Hue/Saturation adjustment layer and entirely desaturate the image.
The trick then is to blend that desaturated layer into
the background layer using the advanced layer blending options: basically
blending if the a or b channels of the background layer contain a certain
amount of chromacity, and splitting the sliders to create a smooth
transition. In plain words, whatever’s _close_ to neutral is replaced
with the entirely neutral desaturated layer, and whatever’s more
saturated shows through.
It occurs to me that this is a long winded way of doing
something that could be done with one simple move in the saturation curve
of the HSB mode that PS no longer supports (I looked into Curvemeister for
this reason, but I’m not keen on the interface. Still making the
decision whether to shell out for it). My method is a little more powerful,
though, as it allows me to neutralise the a and b channels separately, so I
can tailor my blending to where the colour casts lie.
Anyone have to deal with this type of images regularly?
Comments, suggestions?
Be gentle with me!
Robert Johnston
___________________________________________________________________________
Date: Sat, 03 Apr 2004 11:41:06 -0000
From: Stephen Marsh
Subject: Re: Acheiving neutrals with mixed lighting
etc.
OK, been reading for a while and have managed to work
up the courage
to make my first post ...
Hi Robert, yes the list can be daunting at first, but
it soon feels like a comfortable, favourite old piece of clothing after a
short while. <g>
I’m a graphic designer, working mainly with
artists and arts
organisations. My main line of work is producing
publications which
document gallery exhibitions, and thus most of the
images I deal
with feature a lot of white wall space.
This is an easy problem to solve, compared to many
other common edits that are required when colour correcting.
Of course, a lot of the time the white isn’t
white.
As this list’s focus is on what happens after an
image is captured - we only have to explore correction methods in this
thread and do not need to stray into the image capture. I am a firm
believer in the person upstream knowing the next stages requirements and
taking them into concern, and that getting the initial photography correct
is usually better than post processing (but this all depends of course).
It occurs to me that this is a long winded way of doing
something
that could be done with one simple move in the
saturation curve of
the HSB mode that PS no longer supports
Robert, in some ways our different approaches are
similar - but I think the one that I often use may be of some help in that
it is perhaps less complex. See below...
(I looked into Curvemeister
for this reason, but I’m not keen on the
interface. Still making the
decision whether to shell out for it).
As a beta tester on this product - I can say that the
author is very receptive and responsive to suggestions (Mike beat Adobe to
the punch in incorporating some of my curves ‘wish list
items’).
Anyone have to deal with this type of images regularly?
Comments,
suggestions?
My method goes something like this, if after a fairly
fast but accurate cleanup of these areas (large flat areas like walls):
Sometimes I may use a duped layer, but this can also be
done with adjustment layers. One thing I like with de-saturating the duped
layer is that it is often more ‘tactile’ and one can easily see
what one is doing to the data when blending.
In RGB, one needs to add a hue/sat adj. layer - or in
CMYK one will also need a channel mixer (and curves if being really
‘accurate’ in forming a neutral ratio). This is blended in
color blend mode. One simply de-saturates the entire image - but we only
really care about the near white walls, which should vary greatly in tone
from the other areas of the image.
I often find that a true de-saturation looks too
artificial, one ‘expects’ to see some colour variation and
transition of hue - but not to any real ‘perceptual’ degree, it
is often more a ‘hint’ than a more noticeable hue
variation...hope this makes sense. So the adjustment layer may only be
blended at 70% or whatever to retain some small degree of hue variation in
the mostly neutral scene.
It is then a simple case of using the layer option
blend if sliders to only contribute this de-saturation of the lighter tones
of the de-
saturation data to the lighter tones of the underlying
layer. One can also add a ‘density mask’ (based off the 10
channel content or ~ selections etc) as a layer mask to this layer or
adjustment layer data if not happy with the sliders or if one needs to
quickly paint out the effect or lessen it in some spot areas.
One has to pay attention that coloured areas of a
similar luminance range to the ‘near white walls’ will become
desaturated, but it is easy to overcome this with the various commands and
tools in Photoshop to mask out these areas.
This obviously presumes that you are working in a safe
editing space RGB and you know the destination CMYK so that you can supply
a neutral file...or that if in CMYK you have the right profile or
‘magic numbers written down on paper’ for neutral CMY values at
various % points from white to black.
Be gentle with me!
No need Robert, you have asked a very on topic question
and have demonstrated that you are more than capable of coming up with a
very flexible and powerful solution on your own.
I look forward to your future posts.
Stephen Marsh.
___________________________________________________________________________
Date: Sat, 3 Apr 2004 09:44:52 -0500
From: Dragonfly Imaging & Printing
Subject: Re: Re: Acheiving neutrals with mixed lighting
etc.
On Apr 3, 2004, at 6:41 AM, Stephen Marsh wrote:
I am a firm believer in the
person upstream knowing the next stages requirements
and taking them
into concern, and that getting the initial photography
correct is
usually better than post processing (but this all
depends of course).
Absolutely Stephen. Those were my first thoughts as
well.
With digital capture and RAW post-processing, many
common problems will be a thing of the past. Exciting times!
It might also be possible to use a Gretag Eye-One
device and their Share software to read the actual Lab values “in
situ”.
John Toles
Dragonfly Imaging & Printing
http://www.dragonflyprinting.com/
http://www.dragonflygallery.ca/
___________________________________________________________________________
Date: Sat, 03 Apr 2004 15:43:59 -0000
From: “lwb_guitar”
Subject: Re: Acheiving neutrals with mixed lighting
etc.
—- In colortheory@yahoogroups.com, “Stephen
Marsh” wrote:
... This is blended in color blend mode.
That’s a really helpful tip. It hadn’t
occurred to me that the overall luminosity can change when desaturating an
image ... I was just using ‘normal’.
I often find that a true de-saturation looks too
artificial,
one ‘expects’ to see some colour variation
and transition of hue -
but not to any real ‘perceptual’ degree, it
is often more a ‘hint’
than a more noticeable hue variation...hope this makes
sense. So
the adjustment layer may only be blended at 70% or
whatever to
retain some small degree of hue variation in the mostly
neutral
scene.
Absolutely. If you have obvious signs of artificial
lighting (spots on walls etc.) then the viewer _knows_ that it’s a
tungsten-lit image and expects to see a little red/yellow casting. In a way
it’s the viewer’s preconception that you need to match, and not
the ‘actual’ scene if that makes sense. I often take the
opacity of the desaturated layer down to 70% or so. Other times, when casts
are really severe, I’ll keep it all the way up at 100% and then,
after the fact, warm up the entire image with a small move toward
red/yellow. Warm is always more palatable than cold, anyway.
One can also add a ‘density mask’ (based
off the 10 channel content or ~
selections etc)
Can you explain what you mean by 10 channel content or
~ selections? I’m ashamed to say I haven’t bought any of Mr
Margulis’ books yet otherwise I’m sure I’d be familiar
with these terms ...
This obviously presumes that you are working in a safe
editing space
RGB and you know the destination CMYK so that you can
supply a
neutral file...or that if in CMYK you have the right
profile
or ‘magic numbers written down on paper’
for neutral CMY values at
various % points from white to black.
I’m working in RGB (Colormatch), so it’s
easy to gauge neutrality with the info panel.
Thanks a lot for your informative reply Stephen,
Robert
___________________________________________________________________________
Date: Sat, 03 Apr 2004 09:33:48 -0700
From: Andrew Rodney
Subject: Re: Re: Acheiving neutrals with mixed lighting
etc.
on 4/3/04 7:44 AM, Dragonfly Imaging & Printing
wrote:
It might also be possible to use a Gretag Eye-One
device and their
Share software to read the actual Lab values “in
situ”.
With a dot release of Match coming very soon, you1ll be
able to read strobe with the Eyeone.
Andrew Rodney
http://www.digitaldog.net
___________________________________________________________________________
Date: Sat, 03 Apr 2004 09:39:36 -0700
From: Andrew Rodney
Subject: Re: Acheiving neutrals with mixed lighting
etc.
on 4/3/04 3:47 AM, lwb_guitar wrote:
I’d be interested to hear any strategies people
on the list have for
dealing with this kind of situation. I’ll detail
one that’s been
successful for me recently (after years of
painstakingly painting
between differently colour balanced adjustment layers):
The right numbers in your file can be output with
regard to light by tweaking the output profile. That is, measure and build
a profile for the output device with the light in which the print will be
viewed. If you have say an Epson for this output you profile the paper but
measure the light under which the print will be viewed with the EyeOne from
GretagMacbeth using the ambient head and EyeOne Share. That can be built
into an existing profile for the printer IF it was made using ProfileMaker
Pro, also from GretagMacbeth. One profile from one set of measured data
from the Epson can be built and updated in a minute or two (load the Light
source from EyeOne Share as a .CFX file and click on the build profile
button).
Makes a lot more sense to alter the output based on
it1s eventual appearance than try and adjust the file which will likely
need all kinds of tweaks per device.
Andrew Rodney
http://www.digitaldog.net
___________________________________________________________________________
Date: Sat, 03 Apr 2004 23:35:52 -0000
From: Stephen Marsh
Subject: Re: Acheiving neutrals with mixed lighting
etc.
Can you explain what you mean by 10 channel content or
~ selections?
I’m ashamed to say I haven’t bought any of
Mr Margulis’ books yet
otherwise I’m sure I’d be familiar with
these terms ...
Perhaps more commonly known as a luminosity mask or
luminance mask - but I like density mask as a term as the mask content may
not be starting out from luminosity data.
The ‘mistermed’ luminosity mask is often
generated via and cmd/ctrl + opt/alk + ~tilde key keycut to load a
selection based off the composite channel of the image (one can also
opt/alt click the comp. channel icon too). As Dan describes this data - it
is a greyscale version of the images tones, it has less contrast than the
L channel of LAB.
The 10 channel concept for masking (Dan has an even
more powerful 10 channel concept for colour correction which is more
complex) is simply using the channels of LAB/RGB/CMYK as a source for
starting a mask, if appropriate. If starting with a RGB orginal, the CMY
plates may not help too much - but the K from CMYK and the AB of LAB are
very different to the more similar RGB/CMY channels and may be more useful.
The CMY channels will be slightly different, but generally speaking they
will also have ink limiting and dot gain applied to them which may be less
than useful in all cases...it all depends.
I may find myself using apply image to mix a mask from
image channel
data from duped files in other modes, using blend
modes, opacity,
fades to blend modes after the apply image step, curves
etc.
The layer option blend if sliders in luminosity
blending ranges are often doing the same thing - so the
‘density’ mask added to the layer or layer
set in question is often only used to fine tune what
the sliders (which
are often opt/alt key split to perform smooth
transitions in the blend if).
I’m working in RGB (Colormatch), so it’s
easy to gauge neutrality
with the info panel.
So all you need is to convert to the correct output
profile, and that the output device performs as per the profile
description.
Dan has a lot of freely available information even if
you do not have his book/s or been to his colour class:
http://www.ledet.com/margulis/PP7_Ch02_ByTheNumbers.pdf (this sample chapter should ‘sell’ you the book, beware it is advanced and things are taken for granted such as how to create a great mask, in the rare cases that Dan uses a mask/selection)
http://ep.pennnet.com/ (Dan’s Make Ready column,
soon in the NAPP Photoshop User mag!)
Stephen Marsh.
Adobe Photoshop training classes are taught in the US by Sterling Ledet & Associates, Inc.