Need To Explain - Indesign Spot To CMYK screw up

[BigD]

I need to explain to a client why Indesign2 1.3 Pdf's with Spot Colour and Transparency have screwed up when converted to cmyk using Prinergy 2.3.1.4.

The objects have changed from a spot yellow colour to white boxes (the yellow has disappeared).

I know the issue has occurred because the customer did not tell Indesign to convert the spot colours when exporting the pdf files but what is the reason for the conversion not taking place properly in Prinergy from the pdf's like we could previously with Quark files distilled to pdf's?

Does anyone know what the reason is for the non conversion?

I couldn't find any documentation anywhere to back me up on this one.

Thanks, Dennis Wyers.

[adobewankenobe]

The short answer is, any spot colour subject to transparency, for example, a box shape with a spot colour fill, with a word over the top which has a dropshadow, will create a bitmap of the area covered by the transparency. When a process plan in prinergy is set to map colours to CMYK, all colours that are non CMYK will be mapped to CMYK. If the special colour was PMS 185 C, then most likely it would map to 100M, 100Y. In the case of the colour subject to transparency, InDesign lists the resulting colour as an Index colour, which by definition, does not have a specific CMYK equivalent, so it is converted to white by Prinergy. In areas where the transparency isn't present, the colour converts directly to the CMYK equivalent.

To help your client witness the effect prior to going anywhere near Prinergy, tell them to turn off Overprint preview under the advanced menu in Acrobat. The spot colour effected by transparency will display as white, which is exactly how it will look after going through Prinergy if ripped through the wrong process plan.

In Indesign, the client can select under Output Preview some preset transparency previews which displays where transparency will effect other objects. A nice feature.

[DCurry]

I'm not sure what it would be called on Prinergy (possibly the same thing), but on PSM and Brisque is a feature called PostScript Overprint, which forces the rip to honor all the overprints and other color settings from the incoming file. Whenever I have an InD file containing transparency that doesn't rip correctly, turning on PostScript Overprint is the very next step I take in troubleshooting it, and 9 times out of 10 it fixes the problem.

[BigD]

OK - Thanks for the replies people.

I have done some experimenting and found that if i want to overide spot colour and transparency in an indesign pdf file i can do it but i need to do it at imposition to plate stage.

If i try to change the pdf file to cmyk it will screw up no matter what.

If i leave the pdf files as spot colour and then select the imposition and instruct Prinergy to convert the spot colours to cmyk when ripping to plate - no issues. Definitely a workaround for a workaround.

BUT i don't want to run a spot colour workflow - so i have told the client to make sure they send us the files CMYK everytime no if's but's or maybe's.

Thanks for your input DCurry and adobewankenobe.