Multiply/overprint - TAC issue

[fredfish]

Hello

I've received print jobs from a client recently with multiply-effects; objects overprinting on images with darker areas. We get problems with ink coverage up to 370-380%, but we prefer 300%

The attached file is just a sample I made to generate the same issue.
The picture is aRGB placed in InDesign. The objects with the multiply effects are respectively 100% cyan and 100% mag+yellow. Converted to CMYK with ISO Coated 300% v2 when exported to PDF.

What would be a solution to get a ink limit to 300% in all areas, regardless of multiply/overprinting objects?

Thanks a lot

 

[lyzan]

Choose Convert to Destination, not Convert to Destination (Preserve Numbers). But watch out of color shifts that you may not wanted. I'm not sure if I will call this an Indesign problem or not. Even in safe CMYK workflow, you will get the same problem if you use effects like in your sample unless you do a re-separation by choosing Convert to Destination.

The best solution to this is use Device link color conversion application.

 

[Lukas Engqvist]

Yes this is a problem. (it is called colour management in after-blending in some circles) Device-link or Re-purposeing in the RIP to act as an Ink Limit goalie. (Here is where AGFA and other prepress flows have wrestled for some time. Some companies use an external 3rd party Colour Server / Ink Saver to cycle through in their workflow.

The thing is Colour management needs to occur in several places, once at the start to match colours, and then again to limit ink. It is a great shame that design software doesn't respect the ink limit of the profile that is used…*but to be totally honest transparency and blending modes work best in RGB anyway

 

[fredfish]

Hmmmm. I've also tried "Convert to Destination" with the same results.

 

[Greg_Firestone]

Hi Fredfish,

I don't think traditional ICC color management or device link conversions will work. You can adjust the TAC on the image, but if objects above it are overprinted, I don't think any software is smart enough to realize/understand this. I know that Inksaving will only function on flattened elements without transparency. I think it's a similar case for the overprints.

If the creator was to use a transparency versus overprint and this element was flattened (e.g. PDF/X-1a versus X4) you'd have better luck processing it. I did a test - two of the bars are overprinted while two are created using the multiply transparency feature.

Greg

 

[lyzan]

@Fredfish

yeah, that's strange. You will know if the colors will be converted to target destination if there is a yellow triangle with exclamation mark in "Color Conversion: Convert to Destination". Try ISO Coated V2 (has 330 TAC, BTW).

Otherwise, your option is Device Link Profile application.

@Greg

I don't have enough experience with X4 but I think APPE with third party workflow can handle that and my guess is @Fredfish has no APPE, but with X-1a, Device Link will definitely works. If you are familiar with PDF Toolbox, I think they have device link plug-in for Adobe Acrobat. I am using GMG ColorServer.

HTH
Lyzan

 

[rich apollo]

Hey fredfish,
Can you post the PDF with the RGB imagery and profiles?

 

[fredfish]

Here are the files

In "Multiply 5" the left bar is RGB multiply, and the right bar is CMYK 0-100-100-0 overprint
Background picture is sRGB.

In "Multiply 6" everything is converted to ISO Coated 300%

 

[Lukas Engqvist]

Why would you want to do that any way? I mean the blues go all grey when mixed with the overprinted red fields. This kind of design is best done in RGB in Photoshop (with gamut preview) and then placed in an InDesign file. In Photoshop, by all means use layers and transparency…*but just because you can do transparency in InDesign does not mean that in every circumstance you should.

CMYK colour were designed to lock out light, C is to block red, M is to block green and Y is to block blue… when you begin to mix CMYK with transparency you are really doing something that was never intended…*Ok it can be done…*we can work out the maths… but there really is no reason to it… other than doing a mathematical excercise.
Oh I know I done it too‚*I was there testing to understand, and found that the only sensible place to do it is in the RIP. I wish someone had explained these things to me before.

The appearance of the image you can get in Lab (or a specified RGB). It can be reproduced in CMYK using ICC profiles, but once you're doing colour by maths, in CMYK you have left the area of colour management and are into some abstract maths field.

Our job in prepress is taking the abstract image and nailing it down. In that way transparency is our friend it gives us access to abstract artwork… but we must not be afraid to nail it down once we promise to deliver the visual appearance of this work.

Please don't get me wrong… it's good for us to test the borders, and twiddle the knobs to find out how things work… but then we also have to know when too zoom out and ask what we are doing and why.

 

[fredfish]

Why would you want to do that any way?

Well, Lukas, I have ask myself the very same question. And I have to admit I don't know why. You're so right. We don't have to do it just because we can.

Well actually, you've answered my question, and next time I get a similar print job I would know what to tell the designer (client) to do.

Thanks for all replies