Date   

Re: Seeing Green.....

Michael Jahn
 

On Sat, Feb 20, 2016 at 9:29 AM, Martin g33kthug@... [COLORTHEORY] <COLORTHEORY@...> wrote:
 
To ensure your neutrals stay neutral you should provide something like c27 m24 y25 k70 for your darker neutral.


Hi Martin,

Being a G7 kinda guy, I admit I am quite biased and find myself blurting things like "your fancy CMYK values for neutral grey may be quite pointless in my press environment"

and then share this chart to help explain "why"

https://flic.kr/p/aeMtiT

without **knowing the Lab values is of the substrate
without **knowing the Lab values solid primarys ( 100% C, 100% M 100% Y and 100% Y )
without **knowing the Lab values of the solid overprints ( 100%Y+M, 100%Y+C and 100%C+M )

Point being - it is difficult to 'predict' what the actually on press recipe to achieve a neutral grey using CMYK values.

As a designer, all one needs to do is create a tint that is 50C, 38Y and 38Y and place it next to a 50K tint, then tell the separator or printer to 'make them the same grey" - how they do that is entirely up to them I am afraid.

- and if you can't make a proof of what i just described above where they visually are neutral, then your proof is meaningless.

I have been sharing an example CMYK PDF that has SWOP tints since I made this PDF in 1997;

https://drive.google.com/file/d/0B7MTaA9sxe4xMjBjOThjYzUtOTg0My00YjQyLWE0MmItOTk4MzM5OGIxNWRl/view?usp=sharing


** knowing = measuring on the press sheet with a spectrophotometer and reading the Lab values 
for the few that are unfamiliar with the G7 Method - here is a link to a document that might help ( not the latest version, but online and downloadable;

http://files.idealliance.org/G7/PressOpGuide/Sheetfed_Offset/G7_Press_Guide.pdf

Hope this helps !

Respectfully,

Michael Jahn
1824 Garvin Avenue
Simi Valley, CA 93065
(805) 416 6946


Re: Seeing Green.....

Martin
 

On 19 Feb 2016, at 15:24, Jim Donovan jim@harrispublishing.com [COLORTHEORY] <COLORTHEORY@yahoogroups.com> wrote:

I knew my values were fine. Some cmyk values were around 64c 54m 57y 32k, 39c 33m 32y 19k

From a printer's POV I don't think these values are "fine".

They are neutrals that are entirely dependent on the printer maintaining perfect grey balance.

To ensure your neutrals stay neutral you should provide something like c27 m24 y25 k70 for your darker neutral.

A magazine's own repro dept would more than likely use even more aggressive GCR to save ink (and money) by using cmy values around 10% and nearer 80% k :)

--
Martin Orpen
Idea Digital Imaging Ltd


Re: Seeing Green.....

Dan Margulis
 

Jim Donovan writes,

 Amazing that your eye can pick up -1a in a neutral Rick! I would guess you are the exception! 

I suspect not. We are a lot more sensitive to things that are disagreeable. Color science alleges that a neutral that is (2)a0b (bluish green) is just as perceptibly non-gray as would be 0a(2)b (blue) or 1a1b (red). That may be true as a matter of optics but a greenish gray is much more “noticeable” because we dislike it. Warm grays and blue-grays are more to our liking

Similarly, Jim raised such a big issue with the printer because he was unhappy with the way the cover looked. If the printer had erred by printing the job too warm instead of too green, according to print specifications one error is as bad as the other, but I am sure Jim would not have been nearly as upset.

Ogden Rood wrote in the late nineteenth century: "The presence in a picture of a very moderate amount of a colour approaching bluish-green or emerald-green excites in most persons a feeling of disgust, and causes a work otherwise good to appear cold and hard--very cold and hard.”

Dan Margulis


Re: Seeing Green.....

Jim Donovan
 

Good separations have worked for ages and should always work. However,
there have been situations where good separations have been ruined by
bad color management. The color management era has offered more
opportunities for color problems - an irony.

AMEN HENRY!!!! It was a magenta ink density problem on press. Jim Donovan

On Fri, Feb 19, 2016 at 9:37 AM, Henry Davis davishr@... [COLORTHEORY] <COLORTHEORY@...> wrote:
 

Great Jim! I wish there were more specifics about the cause - was the
SID wrong or the plate curve or was there some color management
snafu. The slug color bar might be telling. Whichever, I'm glad that
it's all working out and that the relationship is still good.

In spite of other opinions, I think your procedures are fine. Good
separations have worked for ages and should always work. However,
there have been situations where good separations have been ruined by
bad color management. The color management era has offered more
opportunities for color problems - an irony.

Henry Davis

On Feb 19, 2016, at 10:24 AM, Jim Donovan jim@...
[COLORTHEORY] wrote:


>
> Sorry for the delayed response, just now heard back from the
> printer. Long and short of it is after pulling their copies to
> inspect, with the head pressman, plant manager and pressman who ran
> the signature they flat out said and I quote "We blew it!" This was
> an isolated incident, they do an outstanding job for us and have for
> the 20 years I have worked with them printing our publications. So
> this matter has been addressed and taken care of.
>
> Our procedures are fine. We provide hi-res cmyk pdf's to the two
> different print shops we use and they send them to press. Every
> photo that prints in our magazines(Unless it is a provided ad that
> is just a plug and play) is checked, corrected and processed by
> me.It's on me to make sure the cmyk files are solid. I know this
> will raise hackles and some will think it's not possible but the
> reality is you provide a good cmyk separations they are going to
> print good,even without tagged and profiled images,a proof, or
> ripped bullet proof files, unless there is an issue after we hand
> the file off somehow with the plate setter of press problems.We do
> it everyday. Anyone can always find something wrong with any proof
> vs the actual print job regardless of how careful the procedures.
> Thanx again for the input, Jim Donovan



Re: Seeing Green.....

Henry Davis
 

Great Jim! I wish there were more specifics about the cause - was the SID wrong or the plate curve or was there some color management snafu. The slug color bar might be telling. Whichever, I'm glad that it's all working out and that the relationship is still good.

In spite of other opinions, I think your procedures are fine. Good separations have worked for ages and should always work. However, there have been situations where good separations have been ruined by bad color management. The color management era has offered more opportunities for color problems - an irony.

Henry Davis

On Feb 19, 2016, at 10:24 AM, Jim Donovan jim@harrispublishing.com [COLORTHEORY] wrote:
<Snip>


Sorry for the delayed response, just now heard back from the printer. Long and short of it is after pulling their copies to inspect, with the head pressman, plant manager and pressman who ran the signature they flat out said and I quote "We blew it!" This was an isolated incident, they do an outstanding job for us and have for the 20 years I have worked with them printing our publications. So this matter has been addressed and taken care of.

Our procedures are fine. We provide hi-res cmyk pdf's to the two different print shops we use and they send them to press. Every photo that prints in our magazines(Unless it is a provided ad that is just a plug and play) is checked, corrected and processed by me.It's on me to make sure the cmyk files are solid. I know this will raise hackles and some will think it's not possible but the reality is you provide a good cmyk separations they are going to print good,even without tagged and profiled images,a proof, or ripped bullet proof files, unless there is an issue after we hand the file off somehow with the plate setter of press problems.We do it everyday. Anyone can always find something wrong with any proof vs the actual print job regardless of how careful the procedures. Thanx again for the input, Jim Donovan


Re: Seeing Green.....

Jim Donovan
 

 Sorry for the delayed response, just now heard back from the printer. Long and short of it is after pulling their copies to inspect, with the head pressman, plant manager and pressman who ran the signature they flat out said and I quote "We blew it!" This was an isolated incident, they do an outstanding job for us and have for the 20 years I have worked with them printing our publications. So this matter has been addressed and taken care of. I was just looking for opinions on when a green cast would start to really be evident, I knew my values were fine. Some cmyk values were around 64c 54m 57y 32k, 39c 33m 32y 19k and add or subtract 3,4 points in any number of ink combinations, the cover was a photo of a rock wall with values constantly changing with cracks, ledges and crevices. Nothing justified the green cast that was reproduced. Their magenta was off, it's the strongest ink and will make the biggest difference when off in my experience. It has happened to anyone who has sent 10's of thousands of pages to press and 100's of thousands of images to press as I have for our company over the last 20 years. If it hasn't it will.

 Would love to say we have a rip, are profiled, tagged, bagged and provide bullet-proof proofs, but the reality of the world I live in is that we are not, we don't and never will with the company I work for. We are not printing art repo, coffee table, fashion product matching publications were those procedures would be needed. We do eye pleasing nice solid niche publications that do just fine and we have lots of happy customers.They just blew this one, that simple, I'm sure they will not blow another. They will satisfy any issues should there be a complaint from an advertiser.

 Our procedures are fine. We provide hi-res cmyk pdf's to the two different print shops we use and they send them to press. Every photo that prints in our magazines(Unless it is a provided ad that is just a plug and play) is checked, corrected and processed by me.It's on me to make sure the cmyk files are solid. I know this will raise hackles and some will think it's not possible but the reality is you provide a good cmyk separations they are going to print good,even without tagged and profiled images,a proof, or ripped bullet proof files, unless there is an issue after we hand the file off somehow with the plate setter of press problems.We do it everyday. Anyone can always find something wrong with any proof vs the actual print job regardless of how careful the procedures. Thanx again for the input, Jim Donovan

On Tue, Feb 16, 2016 at 7:13 PM, Rick Gordon lists@... [COLORTHEORY] <COLORTHEORY@...> wrote:
 

It's also amazing to me what I DON'T pick up sometimes. I think that when I see that, it's because I'm specifically looking for it.

So when I compare a 1-unit nudge to the a curve (or in the tint bar of ACR), I definitely find the difference noticeable, and tend to prefer the warmer one.

If it were without a comparative reference, I probably couldn't tell absolutely.

Rick Gordon

---------------------
On 2/16/16, 7:18 AM, Jim Donovan jim@... [COLORTHEORY] wrote:

Amazing that your eye can pick up -1a in a neutral Rick! I would guess you are the exception! Jim Donovan

___________________________________________
RICK GORDON
EMERALD VALLEY GRAPHICS AND CONSULTING
___________________________________________
WWW: http://www.shelterpub.com



Re: Seeing Green.....

Rick Gordon
 

It's also amazing to me what I DON'T pick up sometimes. I think that when I see that, it's because I'm specifically looking for it.

So when I compare a 1-unit nudge to the a curve (or in the tint bar of ACR), I definitely find the difference noticeable, and tend to prefer the warmer one.

If it were without a comparative reference, I probably couldn't tell absolutely.

Rick Gordon

---------------------
On 2/16/16, 7:18 AM, Jim Donovan jim@... [COLORTHEORY] wrote:
Amazing that your eye can pick up -1a in a neutral Rick! I would guess you are the exception! Jim Donovan

___________________________________________
RICK GORDON
EMERALD VALLEY GRAPHICS AND CONSULTING
___________________________________________
WWW: http://www.shelterpub.com


Re: Seeing Green.....

Henry Davis
 

It would still be interesting if you could post some of the CMYK builds that turned out green.  The printer should have some interest in these values as well.  I couldn't tell from the posts if the cast was in a delicate pastel - but the previous Black area that went green suggests a problem with solid ink density on press (or a Black build that would tend Green).

There was no mention of any proofs supplied by the printer and it's not clear if the printer got a copy of the Epson prints that you made.  I would hesitate calling them "proofs" (especially at this point) as this puts a bad light on the printer that is possibly undeserved.  Had the printer provided proofs that had the unwanted green cast on the cover it would be a different story.

It might benefit others on the list if you tell how your Epson prints are made: direct from application to Epson printer or from application to RIP) and if profile conversions were made.

Again, original CMYK values along with a discussion of the workflow might help to discover whether the ball was dropped in the pressroom or prepress.  Preventing future problems will depend on an understanding and agreement about workflow and press procedures.  You seem to enjoy a good relationship with the printer and a friendly discussion about this run might result in an even better relationship - and better looking jobs.

Henry Davis

On Feb 16, 2016, at 10:18 AM, Jim Donovan jim@... [COLORTHEORY] wrote:

 

 Thanks for the reply's. Yes they were given cmyk files and no the values do not justify the amount green cast that was produced.Had five different sets of eyes look at it, and 6 other pages we proofed and all of them agree, it's much greener than it should be. Did espon proofs of of 6 other pix in the same magazine from interior signatures and all are acceptable when compared to the print job. The epson proof varies noticeably from the cover that was printed. Also compared an ad that ran in the previous issue and this current issue that we are discussing on the cover signature that had a vehicle that had a black roof. It clearly has shifted toward green were it was previously a neutral black.

 Will speak with the printer today. They run all issues of this publication and will see when they compare that previous issue something( magenta is my guess)is amiss. They do a great job for us, this one just got away from them a bit.


Re: Seeing Green.....

Jim Donovan
 

 Thanks for the reply's. Yes they were given cmyk files and no the values do not justify the amount green cast that was produced.Had five different sets of eyes look at it, and 6 other pages we proofed and all of them agree, it's much greener than it should be. Did espon proofs of of 6 other pix in the same magazine from interior signatures and all are acceptable when compared to the print job. The epson proof varies noticeably from the cover that was printed. Also compared an ad that ran in the previous issue and this current issue that we are discussing on the cover signature that had a vehicle that had a black roof. It clearly has shifted toward green were it was previously a neutral black.

 Will speak with the printer today. They run all issues of this publication and will see when they compare that previous issue something( magenta is my guess)is amiss. They do a great job for us, this one just got away from them a bit.

 Amazing that your eye can pick up -1a in a neutral Rick! I would guess you are the exception! Jim Donovan



On Mon, Feb 15, 2016 at 10:29 PM, Rick Gordon lists@... [COLORTHEORY] <COLORTHEORY@...> wrote:
 

I find that, to my eye, a green cast in neutrals can be perceived at very low (even -1 or -2 a values, with b positive or negative). I personally seem to be able to tolerate a notch too much a+ than a slightly a-negative value, particularly if the b value is positive, and sometimes have targeted a-negative/b-positive neutrals to set slightly a-negative values to 0.

Also, a touch too much a-negative can be blown further in the wrong direction by MMM, and I've sometimes had to resort to blocking that area of the spectrum from MMM when neutrals may be affected. I understand that MMM is supposed to minimize changes in neutrals, but a situation like an off-white wall where the warmth is not uniform due to natural lighting conditions (particularly with higher-ISO images) can be problematical.

Rick Gordon

---------------------


On 2/15/16, 2:38 PM, Jim Donovan jim@... [COLORTHEORY] wrote:
Hello, Long story short. I had a cover signature offset print with a greenish cast to it that I know is incorrect,shifted on press for sure. Rest of the magazine looked acceptable. Did some epson proofs of interior pages and they were acceptable, the print result of the cover is quite a bit off from my epsons. We just look for eye pleasing color, not color matching and we do not have everything profiled and will not be doing so. I know it's not proper but it's the world I have to live in.

 My question is very general. Obviously you need a -a value for green. I would like some opinions on how negative a must be to start showing a  greenish cast? -1a 1b? -2a 5b? -3a 3b? Seems to me that you need -3/-4 and up(more negative) to really start seeing a noticeable greenish cast?

 I fully realize all the variables and the amount of them that contribute to a color shift in offset printing, again just a general opinion is all I am seeking. Will speak with the printer tomorrow about the cover sig, always happy with their work, this one just slipped on them. Thank You, Jim Donovan

___________________________________________
RICK GORDON
EMERALD VALLEY GRAPHICS AND CONSULTING
___________________________________________
WWW: http://www.shelterpub.com



Re: Adobe Light Room Vs Photoshop?

tropevp
 

Thank you for your opinions.

I do see a need for image management for images, and to that I see a need for another program like Lightroom.

Thanks to all who shared their LR/PS workflow or their workflow. I always saw PS through different eyes than that of a photographer.

I just ordered copies of Dan's updated LAB book (it took me long enough) and I am very excited to read it!

Thank you again,
Ted Moon


Re: Seeing Green.....

Rick Gordon
 

I find that, to my eye, a green cast in neutrals can be perceived at very low (even -1 or -2 a values, with b positive or negative). I personally seem to be able to tolerate a notch too much a+ than a slightly a-negative value, particularly if the b value is positive, and sometimes have targeted a-negative/b-positive neutrals to set slightly a-negative values to 0.

Also, a touch too much a-negative can be blown further in the wrong direction by MMM, and I've sometimes had to resort to blocking that area of the spectrum from MMM when neutrals may be affected. I understand that MMM is supposed to minimize changes in neutrals, but a situation like an off-white wall where the warmth is not uniform due to natural lighting conditions (particularly with higher-ISO images) can be problematical.

Rick Gordon

---------------------

On 2/15/16, 2:38 PM, Jim Donovan jim@... [COLORTHEORY] wrote:
Hello, Long story short. I had a cover signature offset print with a greenish cast to it that I know is incorrect,shifted on press for sure. Rest of the magazine looked acceptable. Did some epson proofs of interior pages and they were acceptable, the print result of the cover is quite a bit off from my epsons. We just look for eye pleasing color, not color matching and we do not have everything profiled and will not be doing so. I know it's not proper but it's the world I have to live in.

 My question is very general. Obviously you need a -a value for green. I would like some opinions on how negative a must be to start showing a  greenish cast? -1a 1b? -2a 5b? -3a 3b? Seems to me that you need -3/-4 and up(more negative) to really start seeing a noticeable greenish cast?

 I fully realize all the variables and the amount of them that contribute to a color shift in offset printing, again just a general opinion is all I am seeking. Will speak with the printer tomorrow about the cover sig, always happy with their work, this one just slipped on them. Thank You, Jim Donovan

___________________________________________
RICK GORDON
EMERALD VALLEY GRAPHICS AND CONSULTING
___________________________________________
WWW: http://www.shelterpub.com


Re: Seeing Green.....

Henry Davis
 

Was the printer given CMYK files?
Would a green cast be expected from the CMYK build(s) found in the cover?

Some specific values from the file given to the printer might be helpful.

Henry Davis

On Feb 15, 2016, at 5:38 PM, Jim Donovan jim@harrispublishing.com [COLORTHEORY] wrote:
<Snip>


Hello, Long story short. I had a cover signature offset print with a greenish cast to it that I know is incorrect,shifted on press for sure. Rest of the magazine looked acceptable. Did some epson proofs of interior pages and they were acceptable, the print result of the cover is quite a bit off from my epsons. We just look for eye pleasing color, not color matching and we do not have everything profiled and will not be doing so. I know it's not proper but it's the world I have to live in.


Seeing Green.....

Jim Donovan
 

Hello, Long story short. I had a cover signature offset print with a greenish cast to it that I know is incorrect,shifted on press for sure. Rest of the magazine looked acceptable. Did some epson proofs of interior pages and they were acceptable, the print result of the cover is quite a bit off from my epsons. We just look for eye pleasing color, not color matching and we do not have everything profiled and will not be doing so. I know it's not proper but it's the world I have to live in.

 My question is very general. Obviously you need a -a value for green. I would like some opinions on how negative a must be to start showing a  greenish cast? -1a 1b? -2a 5b? -3a 3b? Seems to me that you need -3/-4 and up(more negative) to really start seeing a noticeable greenish cast?

 I fully realize all the variables and the amount of them that contribute to a color shift in offset printing, again just a general opinion is all I am seeking. Will speak with the printer tomorrow about the cover sig, always happy with their work, this one just slipped on them. Thank You, Jim Donovan

 


Re: What color is flesh?

Sef McCullough
 

Nice Jacek, that direction is really useful - I basically keep that same script (pulled from Dan's books) on hand just to remind myself if I ever forget. It's very easy while we are working on an image to lose that anchor of accurate skin numbers while adjusting color overall.

And really nice photos thanks for posting.

Sef McCullough
retouchist.org


Re: Adobe Light Room Vs Photoshop?

James Gray
 

I basically agree with John.  The one powerful thing that Lightroom has is the database management system for managing, storing, and organizing your images.  To the best of my knowledge everything else you can do with Lightroom you can do in Adobe Camera Raw (ACR).  Using Lightroom or ACR with their sliders can be a lot easier than learning to use adjustment layers and masks based on channels.  BTW, I do not use Lightroom to manage my photos.  I prefer my own system for managing, storing, and organizing my photos.

James Gray

On Mon, Feb 15, 2016 at 11:51 AM, john.isner@... [COLORTHEORY] <COLORTHEORY@...> wrote:
 

No one, should be pushing Lightroom as an alternative to Photoshop.  Lightroom is meant to be used in conjunction with Photoshop.  Use Lightroom for what it is good for (raw processing, workflow management) and use Photoshop for what it is good for (channels, layers, color spaces, PPW, etc.).


When you hear some  brag that they have abandoned Photoshop and are doing everything in Lightroom, you should immediately recognize that you are talking to a Photoshop amateur. They are using the 1% of features in Photoshop that are indeed done better in Lightroom.



Re: Adobe Light Room Vs Photoshop?

Michael Demyan <mdemyan@...>
 

Hi Ted,

As a professional photographer, I photograph in RAW using Auto color correction in the cameras. My workflow starts with BreezeBrowser Pro to consolidate images from multiple cameras from my assistant and myself. I arrange all images according to the timestamp and then dump any obvious mistakes. I then batch rename them in consecutive order. Second step it to take all images into Lightroom to rapidly color correct the temperature and tint, adjust the exposure where necessary and make a few general tweaks. The images are then saved as jpegs, and brought into Photoshop where the final adjustments such as straightening, cropping, and image tweaking using Dan's Modern Photoshop Color Workflow techniques.
Lightroom has a place in image processing, but it cannot possibly do all that Photoshop offers. It does not have layers or the ability to switch between color spaces. Lightroom is a tool that allows compiling and cataloging images along with some manipulation.
Personally, I strive for the most beautiful photograph that represents what I saw when I took the photograph, and sometimes more.

Mike Demyan
www.mikedemyan.com

On 2/15/2016 1:18 PM, tropevp@... [COLORTHEORY] wrote:
 



So why the push for Lightroom? I am not trying to start a flame/war but other than, say batch pre-processing and the catalogue, what does Lightroom have that Photoshop doesn't, that schools of Photography push Lightroom unto its students?

Thank you,
Ted Moon.



--
Mike Demyan 610-730-6456


Re: Adobe Light Room Vs Photoshop?

john.isner@...
 

No one, should be pushing Lightroom as an alternative to Photoshop.  Lightroom is meant to be used in conjunction with Photoshop.  Use Lightroom for what it is good for (raw processing, workflow management) and use Photoshop for what it is good for (channels, layers, color spaces, PPW, etc.).

When you hear some  brag that they have abandoned Photoshop and are doing everything in Lightroom, you should immediately recognize that you are talking to a Photoshop amateur. They are using the 1% of features in Photoshop that are indeed done better in Lightroom.

It may be helpful to think of Lightroom as a replacement for Bridge, not Photoshop.


Re: What color is flesh?

Jacek Poplawski
 

Just my two cents... :)

According to Dan Margulis rules flesh tone should be A positive and B positive, and B is usually higher than A. After some experiments I found that it is also very important for L to be high. When L is low skin color looks off, disgusting, too saturated. Of course some areas of skin will be dark, but there is a huge different when there are bright areas with gradations than flat not-bright skin.

With more liberal approach to colors, one can accept high B values on skin hightlights and negative B values in shadows. It is typical fashion color grading, and I was warned it is not popular on this group :)

When we look at full photo we don't read pixel values with our eyes. We see composition. So same skin color will look good on one photo and terrible on another. It is color harmony what matters. 

Color harmony and color contrast are reasons why Man from Mars and Modern Man from Mars are so effective. Unfortunately, I was never able to success with MMM on skin tone. I know all three Dan books, I read them many many times, and I understand MMM is very useful when dealing with other colors the skin tone. With background, clothes, jewelry or even makeup. But I never was able to direct MMM correctly to increase quality of skin tone itself. To my surprise I can make skin tone better by old Man from Mars method (well it was based on man portrait so it should work on skin tones)

BTW this is my first post here, so hello everyone :) I am reading this group for a while and I am really enjoying exploring color theory. You can find my works on 500px.com/darkelf and @darkelfphoto on Instagram. I hope it is allowed to post links to of here :)



On wtorek, lutego 9, 2016, 05:34, Hector_APR amerphoto@... [COLORTHEORY] wrote:

 

When making color corrections
and you're unsure what the
person's flesh color is...
which way to go?

Now, it is my understanding
that everyone in the world
is one color...Brown.

Different shades,
but different shades of
Brown.

So, do you shoot
for brownish beige
yellowish,
or...reddish?

I know, when I try to
adjust the TV set colors,
so that everyone is close
to beige,

In the end,
you want
realistic flesh color.

What I mean is, I want
realistic flesh colors regardless
the color of the person.

You can take a good photo
of a person with two different
cameras and on paper you
get two different flesh colors.

Hector Davila


Re: Understanding A Complex Layer Stack - Waterfowl Lakes

Michael Jahn
 

Not that it matters much, but I have worked for several color scientist and have a degree in Medical Illustration, so, I have a few years of working with color, working for pantone, working with color measuring system, working with ink companies and working for print manufacturing companies.

Humans normally have three types of cones.

They are not actually yellow seeing or green seeing cones, so, yes, some folks say things like red cones, but it is really not correct.

The first responds the most to light of long wavelengths, peaking at about 560 nm ; this type is sometimes designated L for long.

560 nm is a green.

The second type responds the most to light of medium-wavelength, peaking at 530 nm, and is abbreviated M for medium.

530 nm is also a green

The third type responds the most to short-wavelength light, peaking at 420 nm, and is designated S for short.

420 nm is indigo

The difference in the signals received from the three cone types allows the brain to perceive a continuous range of colours, through the opponent process of color vision.

The colour yellow, for example, is perceived when the L cones are stimulated slightly more than the M cones, and the colour red is perceived when the L cones are stimulated significantly more than the M cones. Similarly, blue and violet hues are perceived when the S receptor is stimulated more than the other two.

It is complicated. we see Purple when we detect short light waves and long light waves simultaneously. interesting to note, we can detect very small differences in purples, but have a hard time detecting very large differences in yellows.

if you notice - that is kinda why they use most blueish purplish color chips in the Farnsworth-Munsell 100 Hue Color Vision test.

http://www.color-blindness.com/farnsworth-munsell-100-hue-color-vision-test/#prettyPhoto/2/





Re: Understanding A Complex Layer Stack - Waterfowl Lakes

James Gray
 

Michael,
I have to throw a fly in the ointment.  I have some graphs that I have collected on color vision.  The so called "red" cones are maximally sensitive at about 564 nm.  That is in the yellow part of the spectrum, not in the red part of the spectrum.  So if you want to be really technical, the youtube video you posted is mistaken in saying we do not have yellow cones.  However we see red when red light falls on the retina because the so called "red" cones are more sensitive to red light than to green light.  The sensation of color is caused by opponent processes in the cells of the retina.  The "green" cones are maximally sensitive at about 534 nm.  When photons concentrated at about 620 nm falls on the retina, opponent processes "measure" the difference in the firing of the "red" and "green" cones and see a larger difference than when the light is about 564 nm.  So the so called "red" cones are good at detecting light in the red part of the spectrum when connected through an opponent process with the green cones.  However, there is also a blue-yellow opponent process in the retina.  Where does the yellow come from?  Most of what I have read indicates that the output from the red and green cones is combined in an additive process that is then compared to the blue cone output in an opponent process.  This would explain why we see four unique colors: red, yellow, green, and blue.  Other colors appear phenomenologically to be a blend or mixture of these four colors.  The absorption curves plotted as a function of wavelength of the three kinds of cones in the eye are not symmetrical.  In fact the curves for the red and green cones are not even monotonically decreasing from the peak as wavelength gets shorter.  For the red cones the lowest absorption seems to be at about 450 nm.  There is a noticeable increase (around 10%) in absorption at about 410 nm.  Could this feature of the absorption curve of the red cones be the reason why violet looks like a mixture of blue and red?  It is the only explanation I have come across and I have been puzzled by this phenomenon for 40 years or more.  I will add one more thing.  I do not go along with the terminology that purple is not a color.  The light waves in the visible spectrum are not colored.  Color is a property attributed by the human (and animals with trichromatic vision) visual system to light waves and mixtures of lightwaves.  It is based on the absorption spectrum of three different kinds of cones in the retina.  Any light source that is made up of a single wavelength will appear to have color and we refer to the light as monochromatic.  However the perceived color of such monochromatic light can be matched using a mixture of other wavelengths.  I believe it is still the same color if it looks the same to an observer.  We know that we can produce non-spectral colors by mixtures of spectral colors.  On that basis I think that purple is a color even though there no such thing as a single wavelength of light that will be seen as purple.

Respectfully,
James Gray

On Wed, Feb 10, 2016 at 8:57 PM, Michael Jahn michaelejahn@... [COLORTHEORY] <COLORTHEORY@...> wrote:
 


On Wed, Feb 10, 2016 at 7:09 PM, James Gray James@... [COLORTHEORY] 
 

"Isn't it curious that the light at the violet end of the spectrum looks phenomenologically like a mixture of blue and red."

no, actually, it is not at all curious- it is flat is out weird !



The fact is that purple ( https://en.wikipedia.org/wiki/Line_of_purples ) is NOT a real color.

Magenta isn't a color either, but I digress. The next time you see a rainbow, look carefully, - magenta ( or purple )  is missing. 

Rainbows have all colors of the spectrum: red, orange, yellow, green, blue and violet.



Cones. We don't have yellows cones.

- but we can see yellow.


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