Dan Margulis Applied Color Theory
Natural Greens
Date: Wed, 1 Jun 2005 20:17:28 EDT
From: Dan Margulis
Subject: Natural Greens
*********FORWARDED MESSAGE**********
Subj: Natural greens
Date: Wednesday, June 1, 2005 2:31:26 PM
From: yelis@jet.msk.su
To: Dan Margulis
Dan,
Sorry for sending message directly - I am not sure that
my question is of
interest to the colortheory list.
In your book (4th edition) you say that greenish yellow
is impossible for
natural greens (pg.27 and elsewhere). On the other hand
on pg.216 (fig.
11.8) you discuss artichoke color - 74L (8)A 17B - and
say that it is green
and could be right. Am I missing something - because I
think that color is
greenish yellow and you say so in the table on pg.100?
Does that mean that
greenish yellows are acceptable?
It is not a theoretical question for me - I was working
on a file with lots
of greenish yellows (G slightly above R, B almost two
times less) and good
neutrals (rocks, birch trunks, etc.) All my attempts to
make greens green
rather than yellow made image significantly less
believable.
Best regards,
Vladimir Yelisseyev
___________________________________________________________________________
Date: Wed, 1 Jun 2005 22:12:47 -0400
From: "Michael Demyan"
Subject: RE: Natural Greens
Hi Vlad:
Did you try using the Hue/Saturation tool? Select
Greens from the drop down and then use the color picker+ to select a few of
your "yellow-greens" and then adjust the hue slider to just
affect the greens you selected. This approach has worked for me for other
color adjustments.
Michael Demyan
Fine Photography & Digital Graphic Design
www.mikedemyan.com
___________________________________________________________________________
Date: Thu, 02 Jun 2005 08:50:31 -0000
From: "v_yelis"
Subject: Re: Natural Greens
First part of my question was to clarify - are such
colors Ok? Because in Dan's book in some places (pg.27, etc.) they are
stated as impossible, but then on pg.216 as Ok (and even after correction
they remain yellow-greens).
Vladimir
___________________________________________________________________________
Date: Thu, 2 Jun 2005 09:30:29 EDT
From: Dan Margulis
Subject: Re: Natural Greens
Vladimir writes,
In your book (4th edition) you say that greenish
yellow is impossible for
natural greens (pg.27 and elsewhere). On the other
hand on pg.216 (fig.
11.8) you discuss artichoke color - 74L (8)A 17B - and
say that it is green
and could be right. Am I missing something - because I
think that color is
greenish yellow and you say so in the table on pg.100?
Does that mean that
greenish yellows are acceptable?
In the LAB definition, yes, in the CMYK definition, no.
When working with green colors in LAB, I recommend that you set the right
half of the Info palette to read CMYK equivalents, because the rule is
simpler to understand.
In CMYK, Photoshop defines "green" as cyan=
yellow. This color is too blue for almost all plant life. Instead, the
yellow must be higher, but not so much higher as to make the plant a
greenish yellow rather than a yellowish green. The most extreme values
normally found would be Y=C for a very blue green and Y=2C for a very
yellow one.
In LAB, "green" (meaning A is negative, B is
zero) is a much bluer color than CMYK "green". It is almost
halfway to cyan. So the "green" in LAB is the color referred to
in English as "teal."
No plant life can possibly have 0b, because that would
convert to CMYK as Y<C. Even a very blue plant probably has a=2*(-b).
Because the range begins so far away from the
"green" point, it goes well beyond the midpoint between
"green" (A negative, B zero) and "yellow" (A zero, B
positive). It is even possible to find a plant that is 3a=(-b).
The artichoke color, 74L(8)a17b, is therefore
acceptable. It converts to CMYK as 33C18M46Y, a dull, yellowish green.
Dan Margulis
___________________________________________________________________________
Date: Thu, 02 Jun 2005 19:36:48 -0000
From: "v_yelis"
Subject: Re: Natural Greens
Thanks, Dan.
Vladimir
___________________________________________________________________________
Date: Fri, 24 Jun 2005 14:43:02 -0500
From: Jerry Sedgewick
Subject: Pure color green
Hello everyone,
I'm a newbie to this group and a scientist/imaging
specialist who works almost exclusively with colorized grayscale images.
In this world I belong to, detectors (primarily photomultiplier tubes:
PMTs) collect photons and then these are mapped to grayscale LUTs (Look Up
Tables) or to colorized LUTs for display. The user can acquire these
images as TIFF files, with some manufacturers allowing the "save"
to include the color LUT overlay (often a screen capture) as an indexed
color image; or as an indexed color image with a grayscale LUT.
In all instances, the LUTs are set by default to
colorize one channel only, either in red, green or blue. When a mode
change is done to RGB Color, the channel of interest is colorized and the
other two channels are completely black.
You can imagine the nightmare, then, of printing these
images while maintaining brightness in the green, red and (especially) blue
channels because of gamut issues.
I have been able to change the RGB colors for the red
and blue so that these are not pure and so that these colors reproduce in
print. The green, however, is elusive. In some images, a
yellow-green easily makes the transition from RGB to CMYK without
highlights getting squashed into large pools of flat green. In other
instances, however, it is near impossible to create a yellow-green and one
is only left with a green-blue (with 100% yellow and 100% cyan) that looks
more like seaweed in a dank pond.
I have tried several things
1. Returning the colorized image to grayscale
(using Channel Mixer to preserve luminance) and then colorizing in CMYK.
I can't seem to colorize to green-yellow leading me to believe it
doesn't dispay: but I've seen the color reproduced in publication, so I
know it exists in the CMYK gamut.
2. Pasting the RGB channels into CMY sans the K
channel and then gradually adding some incremental image details borrowed
from the magenta channel to the K channel (with the idea that little K
value would lead to a brighter image, anyway, even if the color is off).
3. Using the Magenta channel to affect contrast.
I still get seaweed at best.
Any suggestions? If interested, the images can be
viewed and downloaded from rawlight.com/CMYKgreen.html. Any help with
this procedure would lead to helping thousands of scientists around the
world!
Jerry
________________________________________________________________________
Date: Fri, 24 Jun 2005 16:08:27 -0700
From: Marco Ugolini
Subject: Re: Pure color green
Jerry,
I downloaded both of your images (RGB and CMYK) and
right off the bat I need to ask you what profiles are supposed to be
associated with each. That would give me a better idea of how to handle the
color conversion, given that my system is color-managed and my monitor is
calibrated and profiled.
Please let me know what profiles you are using.
By the way, even without knowing the exact profile
associated with your files, I seem to be getting results that are slightly
better than what you have in your CMYK file (if viewed through a "US
Web Coated (SWOP) v2" profile).
Assuming that your original RGB file is in sRGB, if I
convert to Euroscale Coated v2 using a Relative Colorimetric intent with
Black Point Compensation (RelCol + BPC), the results are quite good:
slightly cooler than the original RGB, but much yellower and brighter than
what you get converting to US Web Coated (SWOP) v2 (still using RelCol +
BPC).
I know, Euroscale Coated v2 is not a standard in this
country, but my point is that by changing the target space for your
conversion, you get different results. Also, if you convert from Euroscale
Coated v2 to US Web Coated (SWOP) v2, again the colors go bluish and flat,
which would indicate that there is a problem with how those bright
yellow-greens are rendered within the color space of US Web Coated (SWOP)
v2.
I am as puzzled as you are as to why those bright
yellow-green colors should become so blue-green and dull instead: like you,
I would tend to think that there should be a better match for them in the
color space of the US Web Coated (SWOP) v2 profile. And things don't get
much better if I convert to the US Sheetfed Coated v2 profile either.
This is all the more of a head-scratcher if you compare
the gamuts of these profiles using the Grapher tool in Chromix's ColorThink
2.1.2. (Besides profiles, you can also map the colors of your color image
file inside Grapher, which gives a graphic representation of where that
file's colors lie within the CIELAB space.) In particular, Euroscale Coated
v2 and US Sheetfed Coated v2 have an almost identical reach into the
yellow-green range of colors. And yet, Euroscale Coated v2 renders those
colors as much more yellow-green and vivid than does US Sheetfed Coated v2
using the same exact conversion parameters. This makes very little sense,
since, if anything, US Sheetfed Coated v2 has an even BETTER reach than
Euroscale Coated v2 as colors go darker.
Who can shed light on this puzzle?
--------------
Marco Ugolini
Mill Valley, CA
___________________________________________________________________________
Date: Fri, 24 Jun 2005 19:15:57 -0500
From: Jerry Sedgewick
Subject: Re: Pure color green
Thanks for your quick response, Marco.
On this particular image, the input profile is probably
no better than sRGB, as each value in the 8-bit grayscale range is assigned
the color green with a 255 G, 0 Red and 0 blue at the brightest end and 0
G, 0 R, and 0 blue at the black end. If one were to take a 0 - 255
grayscale gradient and apply a pure green using color table in the indexed
color mode, then that's about what you get. Manufacturers do not supply
profiles, and the assumption is that one only needs to get appropriate
color on the monitor for immediate viewing and visual satisfaction.
I have my output profile set on "U.S. Web Coated
SWOP V2" because I am in the position of having to put up a fight to
get calibrations/profiles from publishers. It's an oddity in my line
of work to have a scientist ask for such a thing even though many
publications are changing to policies in which all authors must submit
publication-ready, CMYK files. Therefore, all I can do is set the
profile generically.
I do own a Barco Monitor that is calibrated, but awaits
output profiles from at least one willing publisher. But, given the
nature of this indexed-green-color-to-CMYK problem, my hope is to create
some standardized approach for scientists, and let the cards fall where
they may when the image is a little odd. I guess it would be a
by-the-numbers approach.
I did do some further work on this image. It
appears that in the green color, whether it leans toward yellow or toward
blue, the uppermost workable value lies at about 200 G. As long as
all colors lie under that (between 0 and 200 on an 8-bit scale), then
everything is right with the world. Greater than that value, and the
highlights get filled in with a lifeless grayish-green, and some detail
blooms in the highlights.
Perhaps I should view this problem as a kind of NTSC
video-world issue where the gamut is really tight. As long as
contrast can be bumped up within the limitations of dynamic range, then the
image can still have enough pep to look right.
Still, I wonder if something fancy can't be done with
channel blending or by ramping the K in CMYK or luminance channel in LAB.
Any thoughts would be appreciated...
Jerry Sedgewick
University of Minnesota
___________________________________________________________________________
Date: Fri, 24 Jun 2005 22:17:30 -0400
From: "Michael Demyan"
Subject: RE: Pure color green
Hi Sege:
In CMYK (U.S. Web coated (SWOP) v2 try these curve
adjustments. My curves are with white on the left and black on the right
(opposite PS defaults) Double click on the bottom shade bar below the graph
to flip it of yours is the default with the black on the left. All curves
are straight lines with two points.
Channel Input Output - Input Output
Black 0 0 82 95
Magenta 0 54 85 100
Cyan 0 25 100 80
Yellow 0 0 25 100
I got a yellow green that is close, while still
preserving the shadows.
Let me know how it works for you.
Michael Demyan
Fine Photography & Digital Graphic Design
www.mikedemyan.com
___________________________________________________________________________
Date: Sat, 25 Jun 2005 06:16:01 -0000
From: Stephen Marsh
Subject: Re: Pure color green
Any suggestions? If interested, the images can
be viewed and downloaded
from rawlight.com/CMYKgreen.html. Any help with
this procedure would lead
to helping thousands of scientists around the world!
Jerry, some quick thoughts after playing for 5min or
so.
You seem to understand the limits of CMYK and that
100CY is as pure green as you get - but this may not be the green you wish
so the most saturated point may be 80c100y or whatever. As you know, you
are working with a much more limited hue range and a lesser contrast range
in print.
In general, no matter the final approach used, would
aim for a very snappy, strong, contrasty black plate, with enhanced tonal
separation that may depart a bit from the original for
artistic/reproduction purposes (if acceptable, I presume you also publish
the actual figures or data or whatever rather than rely only on images).
There may be less than CMY ink in the shadows of such a
separation than a standard one.
A couple of quick things to try:
Starting with a great grayscale image, go to
multichannel mode. dupe the black channel once, invert the tones, then dupe
it again. Then add a white fourth channel. The inverted black channels will
be stacked into the CY channel positions, with the blank white channel in
the magenta position. The original grayscale or black channel is at the
bottom. Then use mode/cmyk to change swap over from multichannel to true
CMYK mode. Then assign the appropriate profile that provides a good
softproof. You may need to boost the CY channels. The image will not have
any CMY in the shadows though...so add a channel mixer adjustment layer: C
channel = 60% of the K, M50% Y50%.
Another option may be to add any adjustment layer to
the best raw conversion to CMYK that you can make. Go to layer options and
uncheck the blending of the MK plates so that only CY are added. Change to
multiply blending mode. One can also use blend if sliders to limit the
effect to the lighter tones and not the shadows.
Another option could be to make the best conversion
that you can to CMYK. Then go back to the original RGB and convert again,
this time using ABSCOL rendering. Then layer this over the good CMYK in
multiply mode and enter layer options to un-check the addition of the MK
plates and or use blend if sliders etc.
Stephen Marsh.
___________________________________________________________________________
Date: Sat, 25 Jun 2005 11:42:44 -0500
From: "R. Lutz"
Subject: Re: Pure color green
Welcome to the forum Jerry. If I understood your
problem I posted a possible solution in the file section of this forum:
http://groups.yahoo.com/group/colortheory/files/
Here is a summary if you don't want to use the file section.
Procedure:
1. Use the out of gamut warning to show which colors in
the RGB image will not print in CMYK.
2. assign each RGB profile you have available to the
RGB image and see which has the least out of gamut colors --for me it was
Apple RGB.
3. Use the hue/saturation control (cmd U) to reduce the
out of gamut colors while retaining something similar to the original
colors.
4. Convert the RGB image to CMYK.
5. Use CMD U again and adj the sliders to get the
closest color to the original RGB image.
6. Sharpen to taste
Good luck!
Dick Lutz
