RGB to CMYK Conversion

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GaryT
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RGB to CMYK Conversion

Post by GaryT » Mon Mar 09, 2015 9:11 pm

So i use Pitstop Server and Enfocus Switch to convert all RGB images to CMYK. I have recently started to notice issues with the conversion. Sometimes the conversion is just too red. I know the reason, Its because the conversion of RGB to CMYK takes a Source profile and a Target Profile. The times it comes out too red, its converting the wrong source file. I have my settings set up to convert Adobe RGB 1998 as the source, and when somebody turns in a sRGB image the conversion is too red.

So my question is how would i go about building a hotfolder that could figure out if the source RGB image is sRGB or Adobe 1998 and then move the file into the correct Pitstop conversion to convert it to CMYK?

mattbeals
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Re: RGB to CMYK Conversion

Post by mattbeals » Tue Mar 10, 2015 1:53 am

PitStop uses the default RGB/CMYK/LAB/Gray ICC profiles in the preferences ONLY IF there is no profile attached to the object(s).

IF the object is tagged with an ICC profile, THEN that profile is used no matter what your preferences are set to.

IF you want to always convert using Adobe RGB 1998 vs. sRGB, THEN you must first select objects tagged with sRGB, retag them Adobe RGB 1998, THEN convert them to CMYK.

You could select sRGB tagged objects, and NOT convert those. That would leave sRGB objects unconverted which you could then manually handle.

What CMM, rendering intent and destination ICC profile are you using?

It's an old and very ugly site, but the info is still relevant. http://www.automatetheworkflow.com/cms/
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GaryT
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Re: RGB to CMYK Conversion

Post by GaryT » Thu Mar 12, 2015 4:38 pm

The intended ICC profile is GRACoL2006_coated1v2.icc

Rendering Intent im using is Absolute Colorimetric.

The CMM i am using is System CMM.

mattbeals
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Re: RGB to CMYK Conversion

Post by mattbeals » Fri Mar 13, 2015 8:57 am

Should be perceptual or relative. Usually RGB to CMYK is perceptual, CMYK to CMYK or RGB to rgb. Use the lCMS engine. You get better results than ColorSync or the Windows CMM. Also, the lCMS engine is cross platform so results are the same between platforms.
I'm just a dude. Anything I say has nothing to do with any other person or company.

GaryT
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Re: RGB to CMYK Conversion

Post by GaryT » Fri Mar 13, 2015 5:17 pm

Thanks for the help so far, Im definitely going to use lCMS. I have like five problem files that would convert and a couple images were never close to the correct color. Using lCMS has got that color closer then any other setting i have used.

I tried using perceptual and just think that it lightens up the images too much. Im definitely going to keep it in mind for the future, but i have decided that relative rendering intent is the way we will go.

Going back to my first question do, do you think its a good idea to tag sRGB images as Adobe 1998 images before conversions?

Gary

mattbeals
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Re: RGB to CMYK Conversion

Post by mattbeals » Fri Mar 13, 2015 8:10 pm

Is it a good or bad idea? That's debatable. It can work either way. I think the more "technically correct" was would be to convert from one RGB to the other, then RGB to cmyk. If you re-tag an image the color *can* shift noticeably. Your mileage may vary.

Does re-tagging work? Yes, much of the time. The rest of the times? Not so much...

My preference? Don't re-tag. There's a reason the images were created in the space they are tagged with.
I'm just a dude. Anything I say has nothing to do with any other person or company.

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