Untitled Document

Dear Group

In general, how does a rip that doesn't have a Pantone library determine what cmyk to print if an Illustrator file has a pantone spot color (solid coated)in the file? File saved as an eps.

Pete Merck

___________________________________________________________________________

It's hard to comment in general on something like this, but I'd say there'd have to be a default color it applies to unknown spot colors. I've seen black as that default, and I've also seen a bright purple.

I don't know that this will help answer your question, but you can in Illustrator define a spot as a CMYK tint. I've seen the RIP correctly convert a color like "Really Dark Green Spot Color" to the correct CMYK number even though there's no way it has a library callout for that name.

-----

J Walton

___________________________________________________________________________

Hard to comment, RIP's mean different things to different people. The RIP that a printer uses for CTP may be different to the RIP that a Photographer uses for inkjet printing (or sometimes the same/similar).

I would presume that most RIP's would use the embedded colour build for the spot colour that is contained in the EPS file. Pantone defaults to CMYK builds, but one can also select to have the build described as RGB or LAB values - but I am unsure of what happens in these more 'complex' spaces that require conversion.

Does the EPS have PostScript colour management enabled (not to be confused with ICC colour management)?

Stephen Marsh.

___________________________________________________________________________

A little too general a question, I suspect you need to be a bit more specific to get a meaningful answer. That said:

In general an image setter RIP (eg CTP) would output the file strictly as presented and perform the Illustrator Pantone spot as per Adobe colour tables (what you see on screen for CMYK values for the spot colour in question). Once you go to ink jets and laser printers the water is muddied somewhat because they don't give a linear output and this is corrected (by the RIP). Most RIPs, certainly everyone I have ever used, have pantone colour tables embedded which give a fair representation of spot colours - not tints however that really is pushing things to totally impractical limits. To go further many on the laser printer front also have the means to measure a patch and define it as a spot colour which can be addressed by most applications (including Illustrator).

Peter Leyland

PDQ Print Services

___________________________________________________________________________

The application that generates the EPS file includes both the named color as well as a CMYK equivalent which comes from the palette used for building the document. If the RIP hasn't licensed Pantone spot colors, usually referred to as Pantone Calibrated or something like that, then the RIP simply uses the CMYK builds for those objects.

This is why it's possible to get different colors for the same named colors. The application/palette responsible for defining those CMYK equivalents can be different.

Chris Murphy

Color Remedies (TM)

www.colorremedies.com/realworldcolor

___________________________________________________________________________

The company I work for makes a rip but doesn't license Pantone, so I have to tell customers we don't match Pantone (we use trumatch).

I usually advise people that they convert pantone colors to CMYK before sending the file to the rip. But from what I gather in your explaination is that the same color either leaving the pantone color intact or changing it to CMYK would result in the same printed color. Illustrator is the usual program used.

Pete Merck

___________________________________________________________________________

Chris Murphy wrote:

Agreed, Chris - but can you shed light on what happens if one builds the Spot colour in another space, say RGB or LAB?

I think it was in 2000 that Pantone changed the default CMYK builds for spot colours, and this issue is common for mixes of older and newer apps that differ in their library build.

This also commonly happens in Photoshop, if one does not select the Process library which has the same hard-wired values as say InDesign or the Pantone CMYK guide and uses the library tied to the CMYK working space.

It is always wise to double check that all illustration/layout/raster files haves synced CMYK values.

Pete Merck wrote:

We use a Cyclone front end to drive our HP5500 large format inkjet, it too did not come with any Pantone lookup tables, but spot colour substitution is enabled by default. The named colours in the lookup table appear to be optimised for MS Office. So at least you offer Trumatch.

It is easy enough for me to manually create the named colours in the RIP based on the LAB values from Pantone in Photoshop, if required.

This came up in a recent job. We were told that matching Pantone 021 (orange) was important. The file was vector and had a spot colour, named Pantone 021 C. But the CMYK colour build for this spot ink was around 30points higher in the magenta than the 'Pantone CMYK' default build. We informed them that it was not possible to match PMS 021 exactly, so were they after a clean, if not *bright* 'orange' hue - but lighter than 021...or something similar in darkness to 021 but more toward red, rather than orange (as per their supplied CMYK build running 30% high in the magenta). They said orange, not what their CMYK build would print as supplied.

As we do not usually spot colour match at the inkjet, we would have used their supplied values and they would have probably complained, even though they supplied the colour build.

I ran tests with the spot colour printed as CMYK values as per the Pantone 'bible' (which is no bible) with colour matching off at the RIP. I ran tests with a CMYK and a LAB based EPS with RIP colour lookup for Pantone 021 C. I also ran tests with an EPS with LAB based colour build with colour matching off at the RIP. The CMYK build was considered best, over both LAB methods (in-house assesment). No complaint from the client. Pantone 021 is a tough test, even for a 6 colour dye inkjet on photogloss. I have yet to test with reds, greens, blues, pastels etc. I expect in some cases the default Pantone CMYK build to be better than LAB, while in other cases LAB will be better. In other cases, a human mixing the CMYK build may be best.

A very good piece of advice if dealing with Fiery or Xerox type RIPs in colour copier settings. Avoid spot colours and named colours among mixed objects/files (if you don't like nasty surprises), convert all vector and layout colours to CMYK from Spot. Also ensure that colour builds are consistent.

This brings me to a mini rant - even though a composite RIP in a copier may use Adobe PS v3, it does not behave the same as a RIP that is producing separations for film/plate - even if it too is an Adobe PS v3 device. Evem more so using transparency features of later Adobe products that require flattening as in Illus and InDesign (but not Photoshop). Digital composite printing is a whole new learning curve for those used to dealing with film/plate/press. File prep is similar, but different and ofen specific to the shop in question and the unique issues that that shop faces with it's RIPs and RIP settings etc.

I would agree, presuming that the RIP and the desktop application are both delivering the same CMYK values.

For composite printing, if mixing spot colours as CMYK builds, it seems best to just make them process and not spot, at the end of the project (it is good to keep them spot so that layout apps import the colour from vector files, earlier in the process before print).

If you really need to keep the spot colours as spot when printing composite, then it may pay to do a test and to perhaps request that a test also be done with RIP spot colour matching off if it did produce undesired results (even more so if vector/raster and layout all should have seamless blends of the same CMYK colour).

Replacing named colours at the RIP with a better composite build is a great theory - that sometimes falls down in application.

Regards,

Stephen Marsh.

___________________________________________________________________________

On Jul 3, 2006, at 7:51 AM, Stephen Marsh wrote:

RGB, LAB or CMYK are just the alternate builds that an application uses for a spot color in case the receiving RIP has no idea what the named spot color is.

I haven't tested odd combinations, such as Document space not being the same as print space to see if it's doing more than one conversion or if it's smart enough to convert directly to print space as it should without first going through or getting stuck at Document CMYK. That would also test if Illustrator prevents the production of a PostScript file using a color mode other than the preferred one for the output device. i.e. I don't think you're going to get LAB or RGB PostScript, but rather CMYK PostScript.

At least in the case where Document space is CMYK, and the same profile is used for Print Space, even though the spot color is LAB based in the document, in the PostScript file it is CMYK and has been converted from LAB to the Document/Print Space profile.

It happened again last year too when they switched from the Solid to Process Guide to the Bridge (yes they actually call the guide Bridge).

Chris Murphy

Color Remedies (TM)

www.colorremedies.com/realworldcolor

___________________________________________________________________________

If the Illustrator CS2 is used, it's possible to have it use LAB values for spot colors instead. Using a custom profile at print time, the LAB values are converted to custom values for the printer. If you export the file as PDF from Illustrator, the spot areas contain both the Pantone named color reference and LAB values.

Chris Murphy

Color Remedies (TM)

www.colorremedies.com/realworldcolor

___________________________________________________________________________