LAB values in ink manager

[DavidT]

Hi

My CS 'help centre' doesn't seem to be working correctly at the moment so could I trouble the gurus with a question or two, please?

Can someone explain in simple terms what 'Use LAB values for spots' in the ink manager does and how it would affect, say, imagesetter or digital results, were it to be selected? Why would you use the option and, I suppose, why would you not use the option?

I have never used the option and found no need to until this morning when, on a particular job, a printer said the dots on cmyk separations of spots simply weren't strong enough. This is the first time this has happened. Clicking the option before outputting to film whumps up the ink coverage.

[tman@adobeforums.com]

The intention of LAB color spaces is to produce a color space that is more perceptually linear than other color spaces. Perceptually linear means that a change of the same amount in a color value should produce a change of about the same visual importance. When storing colors in limited precision values, this can improve the reproduction of tones. Both are also absolute color spaces, so they define colors exactly, unlike (for example) RGB or CMYK which do not exactly define color, only a mixing recipe for light or ink (respectively).

see this link for MORE information

<http://en.wikipedia.org/wiki/Lab_color_model>

[Gerald_Singelmann@adobeforums.com]

Take a look at this:
<http://www.adobeforums.com/cgi-bin/webx/.3bbfd51e/10>

[rob_day@adobeforums.com]

how it would affect, say, imagesetter or digital results, were it to be
selected?




If you check use the Lab values for a process color job, the CMYK values you will get at output or export will depend on your color management settings, so if you have an accurate CMYK profile, the color on press will probably be more accurate.

Your case is an example of why Pantone's CMYK mixes don't really work. Because CMYK is device dependent, their recipes only work for one press profile and in this case your printer is not printing to that profile.

Also, check this:
<http://www.adobeforums.com/cgi-bin/webx?128@@.3bc183bf>

Rob

[DavidT]

Thanks, Gerald. I read that but it doesn't really answer my post. Well, it does and it doesn't, particularly the part about why you should use one option over the other. I'm looking for an idiot's guide to the two options - use lab or not use lab - to explain to the other operators here.

I recall I never got an answer to my question

DavidT, "Spot color changes to l-a-b" #4, 10 May 2006 4:47 am </cgi-bin/webx?14@@.3bbfd51e/3>

so I suppose the answer is 'yes, it is document level'. In ID, it can be set at default level.

Mike Witherall's questions further on in the thread

Should we all operate our Indy and Illy softwares this way? I suppose
I am better coordinated with the way Photoshop thinks about color?




were not answered with 'yes' or 'no' either. I thought only politicians avoided those words...

If 'yes' is the answer, how come it cannot be set by Illustrator as a default?

EDIT: Rob just answered the part of my query.

[Gerald_Singelmann@adobeforums.com]

I thought only politicians avoided those words...




Your question is comparable to the question "Should I set my text in Times or some other font?"
There is no Yes or No to that question.

Some basic facts.

- when you use a spot colour in InDesign I assume you did do so on purpose and at some stage actually want to have a fifth film/plate

- if you do not want a fifth film at any stage in the printing process but instead want to print on some colour printer, do not use spot colours

- every spot colour has a so called alternate colour that is only used to display the spot on devices that don't separate. The alternate colour can be defined in RGB, CMYK or Lab and is usually not colour managed.

To make this clear: if your final output is printed by separation (i.e. five films) you don't care tuppence about the alternate colour. The alternate colour is only relevant on composite devices (monitor, colour printer)

Why would you choose CMYK?
For example: you create a document and are as yet unsure if it is to be printed 4C or 5C. The spot colour is to be pure yellow even when printed in 4C.
If the alternate colour were defined in Lab you would not have control over the exact mix of the 4C version. If you defined it in CMYK you could use 0-0-100-0 which would result in your spot-objects either being on the spot film or (exclusively) on your yellow film.

Why would you choose Lab?
For example: you create a document and you know it will be printed 5C. But you want all colour prints done previously to the final output to be as accurate as possible. Defining the alternate colour as CMYK would give you different results on every printer you print on. Using Lab gives you the chance to get correctly colourmanaged results even in those preliminary prints.

Life is not easy. :(

HTH
Gerald

[DavidT]

Thanks Gerald. In the case which brought up this problem this morning, the file was created elsewhere. Designers! I only have the job of outputting. In other words, the designer has specified four spot colours but the client has told us to print cmyk because of price.

By not using the lab option, the cmyk films are all very weak and the pressperson can't get even an approximation of the spots.

By using the lab option, an almost exact cmyk match is obtainable.

It's the first time I've used that option. Now, I know some spots are easier to match than others but I've never come across such a variance - on the film - as happened today. I'm less confused than I was, just more puzzled, if you see what I mean.

[Gerald_Singelmann@adobeforums.com]

David,

Everytime a printer talks about designers and vice versa I remember fondly a Calvin & Hobbes strip, where Calvin tries to sell "swift kicks in the butt". Business is slow which is all the more surprising since Calvin is convinced that everyone he knows needs what he is selling.
;)
Gerald

[Michael_Trout@adobeforums.com]

A bit Off topic, but:

As a designer, not a press person, I would appreciate an explanation how a 4 spot color job is more or less exepensive than a 4 process color (CMYK) job?

Although I am not in the habit of developing a 4 spot color design (once it surpasses 3 spots, I go with CMYK), it could be useful to understand why it might be costlier to produce. From my limited POV, both a four spot color and a four process color piece use the same number of plates, the same amount of film, RIP time, etc.

-mt

[Bob Levine]

Presses are always ready with CMYK inks. With spots, you have to pay for
the custom inks as well as the get ready and the clean up.

Bob

[DavidT]

Well, I can only speak from our point of view, naturally. Apart from the possibility of buying tins of ready-made pantone inks, as opposed to mixing our own, yes, it's nominally the same cost in materials.

The problem occurs when you're actually geared up for cmyk, as we are and our larger-format buddies up the road are. With the need to keep these machines in full swing, washing up for spot colours and adjusting ink density, blanket pressure and all the rest of the gubbins associated with changing inks can really slow things down. Labout costs are thus pushed onto the customer.

Then of course you have digital printing, some of which is perfect for spot colour matching: our Canon is pretty good. Thus, spot colour can be cheaper! But plastic toner (as used by Xerox) can't then be put through a another laser, say by the customer printing onto letterheads.

Swungs and roondaboots.

[rob_day@adobeforums.com]

I'm less confused than I was, just more puzzled, if you see what I mean.




Using a solid ink system as a reference point for a CMYK job is a questionable practice—the two have little in common. There may be cases where you are forced to try and match a solid ink with CMYK—as in David's where the client has no budget for a 5th color, has no color management, and wants a specific color.

Assuming there is good color management at output, the only situation where the Pantone CMYK builds would be equal to (not better than) the Lab values would be if the target press conditions exactly matched the press conditions Pantone used to come up with the builds.

[Peter_Truskier@adobeforums.com]

Also, it's worth mentioning that Photoshop (at least CS2) defaults to using lab for spot colors, whereas InDesign and Illustrator default to NOT using lab. This can be responsible for the "Why don't my spot colors match between apps?" question.

[DavidT]

So again, it looks like I should default my copy of ID to lab and remember to change my Illustrator documents to lab, no?

[rob_day@adobeforums.com]

Also, it's worth mentioning that Photoshop (at least CS2) defaults to
using lab for spot colors




If you choose from a solid ink library Lab is your only choice, it's been that way since at least version 7.

So again, it looks like I should default my copy of ID to lab and remember
to change my Illustrator documents to lab, no?




As long as you have decent color management.

[rob_day@adobeforums.com]

So again, it looks like I should default my copy of ID to lab and remember
to change my Illustrator documents to lab, no?




One other thing to consider is ID and Illustrator have no color management for spot color while PS does, so while using Lab values for spot color jobs is far better than CMYK definitions, there is still the issue of tints, which may or may not display or print to composite printers accurately because there's no spot working space.