Transparency Over PMS Spot Colors

[jethrodesign]

Hi, need some advice on the most fool-proof way to accomplish what we're trying to do. We are creating some candy packaging that will be printed rotogravure using CMYK + 3-4 PMS + Spot Varnish. It is being printed overseas, so communication with pre-press department will be challenging at best (if at all). 

The bulk solid background color for the package will be a PMS spot color. Then we will have a 'fake window' showing bulk product, which is an Adobe RGB photo with a circular Illustrator clipping mask. This, so far, is pretty straight-forward.

Where we are a bit concenred is we will also have a few random individual 'pieces' of the product floating around the package front (e.g,. bursting from the fake window photo). For this, we've taken a photograph of the various individual pieces, and silhouetted them out (using a layer mask) in Photoshop, so that they have nice anti-aliased edges (softer and more natural than a hard vector clipping path). They are very rough-edged shapes (not smooth round shapes, for instance). This master Photoshop file is saved as an Adobe RGB PSD with transparency.

We place these individual pieces in Illustrator, using a rough clipping path to separate each piece from the others. Then, on these individual pieces, we create a Drop Shadow using Illustrator FX. The drop shadow is set to 100%K only and 'Multiply' mode. We would like this black shadow to overprint anything below it. These individual 'pieces' are placed on top of the flat PMS spot color areas in some places, however.

When inspecting in Illustrator, or saving as a PDF/X-4 and inspecting in Acrobat, everything looks perfect. When we use Overprint Preview in Acrobat, we can inspect where the shadows are and there is just an increasing amount of black added to the 100% PMS color, just as we would expect.

HOWEVER, when we print to our local printer (Xerox C60 with Fiery RIP), any areas of the solid background that are interacting in any way with any transparency in Illustrator show up as a different color (more muted). So large chunks of the background don't appear to be the right color. Only a few small slices where there must not be any transparency interaction show up nice & vibrant as expected. We've tried different transparency flattening settings and print settings to no avail.

-- Could this just be an issue with our printer or RIP, since it is just a CMYK printer?

-- Are there any dangers these days with transparency flattening issues over PMS colors?

-- If what we're doing is not proper, what would be a better workflow for creating these? The pieces need to be able to be freely placed & adjusted over the solid background color.

Thanks for any insight. We just don't do a lot of work with spot colors these days. If this was process only, it would be easy-peasy and done. Just don't want the printer to run into similar issues to what we're seeing on our local printer, espeically if they're not paying attention and let it run...

[meganchi]

The Photoshop images that you are placing should be CMYK profile, not RGB. This might possibly be the issue when you are printing to the CMYK printer because it doesn't know how to interpret RGB. Everything else you setup should be fine, but remember if you are printing anything CMYK, then the images in Photoshop need to be converted to CMYK prior to saving as a layered photoshop file that is placed into Illustrator.

[carlosgarro]

Hi.

Why don't you use CMYK in the photos? In this way, you maintain the consistency of color according to the parameters of your print provider. 

First set your color settings in Adobe Bridge:

Convert your images to this color space and apply the shadow in Illustrator:

For this sample I use 100% Black with Multiply

Here's the file in Acrobat

[jethrodesign]

Hi, thanks for the replies. Sorry, we keep everything in Adobe RGB for the sake of editing, then 'generally' convert to final output space on creating final PDFs for the printer once we know the final output intent (e.g., GRACoL, SWOP, Custom Profile from the printer, etc.). This is a pretty standard workflow for print jobs, since we'll lose a lot of color data once we make the conversion to CMYK (and hopefully to the proper CMYK output intent).

For this, we do have a profile for the printer, which is assigned to the Illustrator file. I suppose we could do a test where we manually convert to this output space in Photoshop and see if it helps at all. It won't be the output intent for our local printer, but should be close enough for testing. 

But just so you know, we see the exact same thing when inspecting in Acrobat as what you're showing in your example (Note that the images are converted to CMYK during the PDF creation). It's only when we output to our local printer that we see the issue. So we just weren't sure if it was an issue with our Fiery RIP, and if there was any potential of the final printer experiencing the same thing.

[Ton Frederiks]

Since you will be using Rotogravure printing, and I suppose use separate inks for the spot colors, the sparations are the ones to look at, not the simulation of you Fiery CMYK printer.

If the file separates as expected, you can feel (a kind of) comfortable.

Just to make sure provide the composite file as well as examples of the separated plates to the printer.

[Scott Pagan]

i suspect it's your printer (copier) advanced settings, the rendering intents do not match.  you're outputting RGB and CMYK and i'd bet your rendering output profiles are set to maximize color for each seperately.  example: rgb = adobeRGB1998, cmyk = relative colormetric, throw in a RIP that honors pms spot colors (and possible spot color replacement), the overlaying areas will have conflicting rendering giving you the muted effect.  see if you can match both rendering intents to same profile and disable spot color replacements and see if your cmyk copier print looks correct.  not sure how the production gravure RIP will handle since it is a cmyk+ printing process.  good luck!

[jason_imagicla]

I work in the pre-press department for a large format printer and this has been an ongoing problem for many years. The problem occurs when the artwork is rasterized using our RIP software. The RIP is a constant variable so file format or color space make zero difference. It call comes down to choosing one option over the other.

As a general rule, we advise our clients to only use process colors when placing objects that contain transparency. However, we still run into this problem at least once a month. There are plenty of solutions available but it is all dependent on the artwork and our client's expectations. Good communication is crucial to meeting those demands.

[jethrodesign]

Thanks for all of the replies here, much appreciated! 

Since a lot of people were concerned about the use of RGB images, we did a test where we first converted all images to CMYK now that we have a proper output profile from the printer (we didn't have this prior). When printing, while the variation in the soild colors aren't as pronounced now, the issue is still there.

So we then tried printing separations to see if there was an actual issue (using the original RGB images). Interestingly, when we set Illustrator to 'In-RIP Separations', we get a composite single print with NO transparency issues and the color looking most accurate. When we set it to 'Separations (Host Based)', we don't see any variations in the solid PMS background color channel (which prints as black). 

So I'm hopeful that the way we've set things up is proper and it was just an issue with our RIP properly compositing the colors where there was transparency effects over the PMS color (flattening those areas to CMYK, but leaving other areas original). 

Our main reason for concern in all this is that the printer may require our original Illustrator files. In all other jobs we do, we send a proper print-ready PDF/X file (converting all RGB images to the proper output intent at this point) so we have more control over making sure things are done properly and can't be modified.

Thanks again!