ELI5: Why are CMYK conversions different using Pantones new Lab colors

[gordo]

Back in the steam-powered days when I dealt with print buyers/specifiers we tried to get our sales reps to ask what the target was when the client specified a PMS color to be printed as a spot ink. Pantone's recipe? The hue in our swatch book? The hue in the client's swatch book? The L*a*b value?
The client's technical response was usually a confident "Huh?"
That's when draw-downs on the customer's chosen substrate really helped.

When print buyers/specifiers used Pantone's spot colors to specify colors in CMYK our technical response was usually a confident "Huh?"
That's when a color atlas printed on a substrate with similar OBA content and absorbency really helped.

It's all about effective communication and setting realistic expectations.

 

[Correct Color]

It's all about effective communication and setting realistic expectations.

Ain't that the truth. Sometimes I think teaching that very concept to my clients, and giving them the confidence in their processes to be able to communicate effectively -- and fearlessly -- is really the most important thing I have to sell.

Mike

 

[marc3llo]

Hi all,*

I'm bringing back this post because it's such an amazing one but also because I am trying to print as many Pantone colours as I can with a CMYK colour strategy in a flexo press.

Question is... what can I do to expand my gamut while trying to match the Pantone colours? I read another great post about expanding gamut/hifi-printing and they mentioned that using FM screening can expand your gamut.
What about Lpi's? Is it better 110, 133 or 150?. Since I can't change the CMYK inks (for expanded gamut ones),* what else can I do to produce the most percentage of "accurate"* pantone colours simulation? Swinging process colours will do the trick?
All of the above?

Finally, the end of this is to match pantone colours, not to print more vibrant images.

Thanks a lot for your help!
Marcelo

 

[Stephen Marsh]

Try these past topic threads:

http://printplanet.com/forums/flexo/30486-simulating-spot-colors-flexo

http://printplanet.com/forums/prepress-workflow-discussion/28598-extended-gamut-line-colours

http://printplanet.com/forums/esko/27015-stochastic-flexo

http://printplanet.com/forums/prepress-workflow-discussion/26876-eskoartworks-equinox


Stephen Marsh

 

[marc3llo]

Thanks a lot Stephen, I'll read them.

Regards,
Marcelo

 

[mastegman]

I have been following this very informative thread for some time. I haven't had the time to read all of the posts or to confirm what I am about to offer so forgive me if it has been said already.

I have the 3rd Edition of the Pantone Color Bridge swatch books in front of me in which the reference printing conditions for the CMYK equivalents of spot colours are specified. At the time of publication this was ISO 12647-2 (Offset printing) and ISO 2846-1 (Printing Inks). It goes on to define the workflow (digital) using CTP and a Euclidean dot, screen angles, ink densities (including measurement - Status T), paper stock, screen ruling and target dot gain using linear plates and a negative plate workflow as well as expected Grey Balance for quarter, mid and three-quarter tones.

These specification describe the process control parameters which should produce a colour space that conforms to the ISO standard. This colour space is always defined in Lab values because different combinations of CMYK can reproduce the same colour space (even for the same printing conditions if Grey Component Replacement [GCR]) is used. If your printing conditions do not match those specified in the standard you will need different CMYK values to match the targeted spot colours. ISO 12647-2 has been revised several times, the most recent of which was in 2013 when the color space was affected by adjustment to new printing parameters.

In short, the CMYK values provided by Pantone Color Bridge are 'best estimate' with a load of qualifications. You need to understand these qualifications in order to produce the desired result. The bottom line is that without spectral data the Lab values are your best 'estimate' of the targeted colour. The part I have not confirmed is whether the latest editions of Pantone Color Bridge has been updated with Lab values that reflect these revised printing conditions.

 

[Stephen Marsh]

That is a good summary mastegman [P.S. I think that I know who you are! :]

However, when I measured my First Edition Third Printing Color Bridge book, I was surprised at the results for solid primaries, which then of course led me to doubt the rest of the book…


Stephen Marsh

I have been following this very informative thread for some time. I haven't had the time to read all of the posts or to confirm what I am about to offer so forgive me if it has been said already.

I have the 3rd Edition of the Pantone Color Bridge swatch books in front of me in which the reference printing conditions for the CMYK equivalents of spot colours are specified. At the time of publication this was ISO 12647-2 (Offset printing) and ISO 2846-1 (Printing Inks). It goes on to define the workflow (digital) using CTP and a Euclidean dot, screen angles, ink densities (including measurement - Status T), paper stock, screen ruling and target dot gain using linear plates and a negative plate workflow as well as expected Grey Balance for quarter, mid and three-quarter tones.

These specification describe the process control parameters which should produce a colour space that conforms to the ISO standard. This colour space is always defined in Lab values because different combinations of CMYK can reproduce the same colour space (even for the same printing conditions if Grey Component Replacement [GCR]) is used. If your printing conditions do not match those specified in the standard you will need different CMYK values to match the targeted spot colours. ISO 12647-2 has been revised several times, the most recent of which was in 2013 when the color space was affected by adjustment to new printing parameters.

In short, the CMYK values provided by Pantone Color Bridge are 'best estimate' with a load of qualifications. You need to understand these qualifications in order to produce the desired result. The bottom line is that without spectral data the Lab values are your best 'estimate' of the targeted colour. The part I have not confirmed is whether the latest editions of Pantone Color Bridge has been updated with Lab values that reflect these revised printing conditions.

 

[gordo]

That is a good summary mastegman [P.S. I think that I know who you are! :]

However, when I measured my First Edition Third Printing Color Bridge book, I was surprised at the results for solid primaries, which then of course led me to doubt the rest of the book…


Stephen Marsh

You beat me to it! LOL


mastegman could you provide the exact wording of the reference printing conditions that Pantone states? Maybe a scan?

If Pantone actually printed CMYK to ISO 12647-2 it would be the first time in the company's history that they actually met an industry print standard.

 

[mastegman]

Stephen, yes, it is me, Mark. We have to stop meeting like this.

Knowing you to be a very meticulous person I assume you were measuring a NEW swatch book. Being a 1st Edition this must have been some time ago as I am sure you are aware that measuring an old swatch book is fraught with danger for the same reason that using it for visual comparison is: stocks and inks change over time and cannot be relied upon for accurate color assessment. This is why we keep them in a cool, dark and dry place, and replace them after a time (depending on budget and critical nature of the work in question). Apart from that we have the compounding effects of the variability of measuring instruments which is far more significant than I ever imagined. My recommendation is to 'archive' the 1st edition and update to the current one.

I am in no doubt that this variability in instruments, in combination with the inherent instability of the print production process, is at the heart of the tolerances built into ISO standards. In short, printing is an imprecise science that still relies on many of 'crafty' skills of the operator to achieve the desired result however, without the necessary underpinning knowledge they are 'flying blind'. It is unfortunate that a lot of this knowledge that was once taught in the colleges does not seem to be apparent in the trouble shooting skills of many who resort to forums like this. It is a Just-In-Time strategy. I hope our contributions go some way to arresting that. I know you and Gordo and certainly doing your bit. I digress.

Gordo, I have attached images of the first leaf of the swatch book as well as the leaf with the Technical Notes from my 3rd Edition of Color Bridge. Not sure what the current edition is.

 

[gordo]

Gordo, I have attached images of the first leaf of the swatch book as well as the leaf with the Technical Notes from my 3rd Edition of Color Bridge. Not sure what the current edition is.

Interesting...
Looking at it with steam-powered eyes...

IMG_0434.JPG - "Brighter, more durable paper" this refers to them using papers which have more OBAs than past swatch books.

IMG_0435.JPG - "sRGB and HTML values for solid colors" - that's the web not print. No CIE L*a*b* values

IMG_0435.JPG - To conform to the ISO 2846-1 specification, inks must meet the specifications for color at some ink film thickness within the specified range (0.7-1.3 microns for yellow, magenta, and cyan and for black 0.9-1.3 microns) while also meeting the specification for transparency. Stephen would measure best on that point.

IMG_0437.JPG - SIDs are within norms. Non-polarized Status T is North America standard.

IMG_0439.JPG - If Yellow has the lowest SID, and the plates as stated are linear, then how come its dot gain at 50% is just below K and higher than C and M whose SIDs are 40 points higher? Hmmmm? And it's the same as C and M at 75%? Something's wrong.

The "gray balance combinations" are just targets - not what happened.

 

[Stephen Marsh]

Hi Mark, good to see you over here!

I made the measurements when the book was new, however that was a good three years ago now.

I could be incorrect, however I still consider the color bridge to be a mystery target condition that does not conform to standard ISO Coated v2 or GRACoL C1 type conditions (although it may be closer than in previous editions).


Stephen Marsh

 

[marc3llo]

Hi, Thanks for all your replies.

This ISO 12647-2 is for offset and ink densities are also offset ones.. So if I am going to print the pantone swatches in flexo.. How can I transfer all these parameters /standardisation into the flexo arena? Mind you that we don't print to any iso standard.. But having said that I don't even want to hit any targets/pantone colours at the moment, I want to be able to expand the gamut of regular CMYK flexo inks (not specifically dedicated for expanded gamut) and once I have a bigger gamut I could run another linearisation and fingerprint to put the new "right" values to create pantone colours. Is this process correct? As I mentioned in my original post, I planning to run fm screen, high lpi's, trying to push the densities up and also looking at swapping magenta for a red and cyan for p300.
What do you reckon about all this process? How can I make it better (or right for the case)

Thanks a lot guys
Marcelo

 

[marc3llo]

Anyone has any idea whether I can improve my gamut with these changes or not?
Thank you guys
Marcelo

 

[Stephen Marsh]

Anyone has any idea whether I can improve my gamut with these changes or not?
Thank you guys
Marcelo

Flexo makes use of spots instead of process colours on a job by job basis as the brand, converter, design, budget and process dictates, there is nothing new there.

Simply increase density and you get a larger gamut. Throw in FM screening and the gamut is extended again (I think more in highlights to quartertones than elsewhere, but I may be wrong). This is of course not so easy to do in flexo on various films and substrates often using a print white.

What is “new” is creating an alternative set of process inks as a standard to replace CMYK, using say a red and a light blue + YK.

Yes, you will get better solid light blues and reds, that is a given.

But will the overall gamut be better?

But what about ink traps/overprints? What about gray balance? What about the extra complexity of preparing work? What about the complexity introduced in proofing? What happens when things go wrong?

We all know of the failings of standard CMYK, but it is also helpful to think on the benefits and why it works so well and why it is such a standard way of producing full colour. Are you attempting to create a solution that is looking for a problem?

If this is so “easy” or “beneficial”, why is this not the “standard” way of doing things?

Why have different vendors slightly reformulated CMYK and added orange, green and or violet when looking to expand gamut?

If you are a member of linkedin you could join this group:

https://au.linkedin.com/grp/home?gid=8239205


Stephen Marsh

 

[gordo]

Simply increase density and you get a larger gamut. Throw in FM screening and the gamut is extended again (I think more in highlights to quartertones than elsewhere, but I may be wrong). This is of course not so easy to do in flexo on various films and substrates often using a print white.

FM provides the increased gamut from about the 20% to the 75% tones.

On a sidebar. Strictly speaking FM screening does not increase the gamut. Instead, it does not decrease the gamut as much as AM screening does. The effect is an increase in gamut. Also, it's not really the fact that it's an FM screen - i.e. how the halftone dots are organized - that creates the extra gamut. Instead it is the smaller size of the halftone dots of an FM screen relative to a typical AM screen. Increase the lpi of the AM screen to about 350 lpi and it will have a similar gamut to a 20 micron FM screen.

 

[Deleted member 16349]

FM provides the increased gamut from about the 20% to the 75% tones.

On a sidebar. Strictly speaking FM screening does not increase the gamut. Instead, it does not decrease the gamut as much as AM screening does. The effect is an increase in gamut. Also, it's not really the fact that it's an FM screen - i.e. how the halftone dots are organized - that creates the extra gamut. Instead it is the smaller size of the halftone dots of an FM screen relative to a typical AM screen. Increase the lpi of the AM screen to about 350 lpi and it will have a similar gamut to a 20 micron FM screen.

I am a bit confused about the increase in gamut issue. In my view it must be a vertical increase in the gamut but no so much an extent to more saturated colour which I think needs more of a lateral increase in gamut. The smaller dots I have expected (commented on this in my 1997 TAGA paper) would have thinner ink films and therefore would be lighter (dot density) and have a slightly different hue.

What I am wondering, how much of this increase in gamut is useful?

Is it also possible that with FM one gets different colours but also lose some other colours. If you remember the samples you gave me a long time ago, a single ink would not always print the same hue when printed with AM and FM screens. This implies that even with printing all the CMYK inks, one might not to be able to reproduce all the colours that are supposed to be within the gamut of both systems.



Gordon, do you know of any studies that clarify the issue of increased gamut for FM?

 

[marc3llo]

Thanks Stephen and Gordo for your replies. Yes I agree with you that swapping red and blue for magenta and cyan will add extra complexity to the job, but this is a trial at this stage and as trial I can allow to do this and as you mentioned, higher lpi's and higher density. I'll promise to bring some feedback in a couple of weeks when this goes to press. Thanks again,
Marcelo

 

[gordo]

I am a bit confused about the increase in gamut issue. In my view it must be a vertical increase in the gamut but no so much an extent to more saturated colour which I think needs more of a lateral increase in gamut. The smaller dots I have expected (commented on this in my 1997 TAGA paper) would have thinner ink films and therefore would be lighter (dot density) and have a slightly different hue.

What I am wondering, how much of this increase in gamut is useful?

Is it also possible that with FM one gets different colours but also lose some other colours. If you remember the samples you gave me a long time ago, a single ink would not always print the same hue when printed with AM and FM screens. This implies that even with printing all the CMYK inks, one might not to be able to reproduce all the colours that are supposed to be within the gamut of both systems.

Gordon, do you know of any studies that clarify the issue of increased gamut for FM?

Erik is referring to a Creo marketing piece that compared side by side single and two color process screen tint builds in AM and FM.

If you want a detailed description of gamut comparison go here:
The Print Guide: AM and FM gamuts compared

There have been many studies comparing AM and FM gamuts - although they are unanimous in concluding that FM has a larger gamut they, unfortunately, very often show the lack of rigorous testing procedures and correct use of terminology.

Here are two references:
Color Gamut Improvement when Using FM-Screening The abstract states: "Colours printed with non-periodic (FM) screening produce a higher colour gamut as compared to dot centered printing with periodic screening."

and:

http://cias.rit.edu/~gravure/tt/pdf/pc/TT4_Wiphut01.pdf

FM screening can simulate the hues of AM screening in one and two color screen tint builds by adding a third process color but AM at typical lpis cannot simulate one and two color FM screen tint builds. They are out of gamut for the AM screening.

How much of the extra gamut is useful is difficult to quantify.
For spot colors, based on tests done at Creo, FM enables about 10% more of the Pantone library to be simulated than an AM screen.
For 4/C images there's not a real noticeable difference. That's because the extra chroma only occurs with one and two color screen tint builds which rarely happens in today's GCR'd separations. Also, you only see the difference when making a direct visual comparison between the two which doesn't normally happen in production printing. Sometimes it does happen. One example was a double page spread of a single image in Vanity Fair magazine. Due to the magazine's page imposition the left side was AM and the right was FM and the difference was very clear. We used that to great marketing effect.