Best practice converting PANTONE Lab value spot colors to CMYK within a PDF?

[Jayhawkmike]

Specifically in Pitstop but any work-around you have will do. Example - you get a PDF with 5 spot colors. They didn't use Color Bridge and the PANTONE values are Lab NOT CMYK. Do you use a action lists?
We are retiring Neo (issues with support, lack of updates) and I'm just now getting back into relying on Pitstop for PDF editing, preflight, color, etc.

 

[Jayhawkmike]

Crickets. I'll ask Enfocus as well. I'm new to Pitstop 13, but I see that there is a SPOT to CMYK action list. Just would like to know HOW it's converting them. I don't think it's using Color Bridge formulas.

 

[Correct Color]

Jayhawk,

My understanding on this has always been that whenever a postscript file -- eps or pdf -- has a named spot color within, it also carries what is known as an "alternate description" of that color, which is -- as I remember it -- the CMYK value of the spot color in whatever color space your application was in when the file was made.

There is a way in Acrobat to access the alternate description and change it, but it's been awhile, and a few versions back.

As regards your second question, I'm not familiar with Pitstop at all, but any time you're going from spot to CMYK at print time, it'd better be to the destination printer profile. And keep in mind that bridge formulas aren't rendered exactly in any common working space, so as far as using them as actual printable CMYK values...

that's not too likely to ever happen.


Mike Adams
Correct Color

 

[abc]

It really depends on your expectation on how you want to handle this. The current way with Lab based Spot Colors is to convert to process using color management. The result will depend upon your color management settings and the destination profile/rendering intent etc. Color Bridge formulas do not apply in this situation.
If you want to discard the Lab alternate values and substitute for the 'old' CMYK alternate values as used in Indesign prior to CS6 then that's a different story.

PitStop does have the older Pantone libraries built-in (we are Pantone licensed so those are official numbers), so you can use those if you wish.
You can also export Pantone Swatches from layout applications (Indesign, Illustrator etc) and import those into PitStop as well if that's desired.

 

[Jayhawkmike]

Very good. My thoughts are it would be much easier to convert using the color management method rather than re-mapping the colors to the "old CMYK" numbers. If a job has lets say 10 spot colors, that could be a tedious process. Challenge would be matching older printed material where the client is relying on us to convert those colors for them.

 

[michaelejahn]

My thoughts are it would be much easier to convert using the color management method rather than re-mapping the colors to the "old CMYK" numbers. If a job has lets say 10 spot colors, that could be a tedious process. Challenge would be matching older printed material where the client is relying on us to convert those colors for them.

Hey Jayhawkmike - would like to add another thought. If you are making plates, and the RIP does not offer some library to convert, or, you have some fussy reason to take the spot color PDF and make a CMYK PDF, yous, I would be using Enfocus PitStop - although, would like to add something to that suggestion - Enfocused suggested - "You can also export Pantone Swatches from layout applications (Indesign, Illustrator etc) and import those into PitStop" - well, that SUGGESTS that the Pantone Swatches within Adobe apps are correct (?) or better said "desired" - they may not be, nor they might not be what YOU need. I would be really be voting for a PitStop Server set up or RIP set up where that all happens in one place.

When it comes to the several digital devices like the HP Indigo, i am all about "DO NOT CONVERT" - because they licence the Pantone Libraries, and they will apply the special recipies that enable that Pantone 151 ( saturated Orange ) to look like the swatch book (yipee ! ) and not the color bridge CMYK simulation (yuck)

So, sorry to say, there is no "best practice"

It really does bring a tear to my eye to see the praying hands.

I actually had an old EPROM board from a LINEART station that had the old blue "missed stitch" version

https://flic.kr/p/EWLF59

 

[abc]

Very good. My thoughts are it would be much easier to convert using the color management method rather than re-mapping the colors to the "old CMYK" numbers. If a job has lets say 10 spot colors, that could be a tedious process. Challenge would be matching older printed material where the client is relying on us to convert those colors for them.

You are correct here. I am not sure if it's even possible to match the 'old CMYK' numbers when converting via color management. That's why I mentioned it depends how you want to handle the situation.
I found this from Pantone.

“In general, if you are designing for spot color printing, you will use the PANTONE SOLID COATED or PANTONE SOLID UNCOATED libraries, depending on whether you are printing on coated or uncoated paper. The PANTONE COLOR BRIDGE libraries should be used IF AND ONLY IF you intend to output separations to simulate PANTONE colors, with values consistent with those published in the PANTONE COLOR BRIDGE guides.”

Just to clarify my point about importing libraries that Michael mentioned. We license the Pantone libraries within PitStop, but we deliberately have not yet moved to the Pantone Plus Lab based versions yet. It's easy to import a swatch, so I just wanted to mention it as I know it's a useful feature.

The Lab approach is a change in philosophy in my opinion and technically the best approach. The issue is matching previously printed jobs, as you correctly pointed out. I know of many people who have been caught by this with jobs on press.
One other point is this is a very easy preflight check in PitStop to identify Spot colors with Lab alternate values, but I assume these are now almost the norm?

​

 

[pacart]

Within Pitstop 13 I used 2 different methods depending on what I want to accomplish.

1. If I am trying to match already printed pieces or do reprints etc., I use the "Change Specific Color" feature within the "Global Changes", this allows you to select a specific color and change it to whatever you want.

2. If it is a new project I use "Convert to Color Space" and accept whatever it gives me.

I will say there is also a "Convert spot to CMYK" feature within the same menu, but I don't use it for some reason.

 

[abc]

Just be aware that the result of any of the 'Convert' Actions are based on your color management settings.
These can be found in the PitStop preferences if you want to check them.

 

[Stephen Marsh]

There is no easy answer…

As has been noted, for inkjet/toner based printing, generally spots are best converted at the RIP/DFE so that they can be converted directly to the often wider gamut device profile using a LUT, bypassing common CMYK press simulation. If the RIP/DFE can handle it, then Lab based spots *should* provide the best results.

For offset press conversions to CMYK, this is not as easy to answer.

The greater the difference between the press gamut and the Lab based spot, the more potential for unsatisfactory results. The closer the spot and press gamuts are to each other, Lab based spots *should* provide the best results.

So, if the spot is really out of gamut, then you may have a more pleasing conversion using a known “custom pre-baked” CMYK value, while for spots that are closer to press gamut, then an on the fly conversion from Lab to final press CMYK may result in a better match than using the “generic” Bridge CMYK recipe.

EDIT: An out of (press CMYK) gamut colour such as Orange 021 is a great example of what can go wrong with a Lab based source and a colour conversion:

http://printplanet.com/forum/prepre...iscussion/21977-spot-color-to-cmyk-conversion


Stephen Marsh

 

[Jayhawkmike]

Thanks for the responses. Ideally, if customers wanted their swatches represented as CMYK, they should design as CMYK, but that isn't happening no matter how much I wish it to be. I have as many as 14 spot colors (!) within a job supplied to us just last week. My old workflow would assign static "old" CMYK breakdowns for these colors, but these formulas and workflows are getting out of date and too tedious to re-map for every job.
So - What I'm concluding is unless a specific CMYK is given to us, we will use the color settings in Pitstop/InDesign using our choice of Coated GRACoL 2006 color space to convert these colors and either convert the colors with action lists (Pitstop) or export our the PDF with these settings in InDesign converting these colors as the PDF is written.