GCR color shifts

[Ptheobald1]

Hi Group,

I work in Prepress for a packaging printer and one of our press divisions is requesting pretty significant GCR conversion be applied to their client supplied CMYK images. I have been experimenting with using Edit/Convert to Profile/GCR/Heavy with an 85% Black Ink Limit, 300 Total Ink Amount using Photoshop CS5.
This is introducing some unwanted color shifts, especially in the magenta and yellow channels. I have also experimented with doing a LAB mode conversion then going to GCR/CMYK but it does not seem to make much difference....I'm pretty sure Photoshop goes to LAB as a conversion color space when using the Convert To Profile move.

Has anyone come up with a better way to to apply GCR to supplied CMYK without having to go back and do adjustment curves to get the appearance close to the original supplied images? The images are mostly food products, cookies, snacks, chips etc...
Thanks in advance for any suggestions,
Pat

[Greg_Firestone]

Have you looked into doing device link color conversions? You'd need additional software to do it but the results are better than standard GCR using traditional ICC color conversions (at least in my opinion).

Greg

[mglouis]

Not using Photoshop's custom ink but with ICC profiles then color shifts are negligible. For this you need an icc profile that represents your print specification and has relatively aggressive GCR. If printing to Swop or Gracol then you could play with the K generation settings in Monaco Profiler or similar program until you get the black length and width where you want it. If you like what you are getting from Photoshop, minus the color shift, then you would tweak Monaco's K-plate settings until the K-to-CMY ratio in your grayscale is similar to what you are getting out of Photoshop. Now use this profile for both source and destination with absolute colorimetric rendering.

If Gracol is appropriate for your needs then PM me your email and I'll send you a copy of our production profile.

Matt Louis

[Lukas Engqvist]

Try using the colour profiles at colormanagement there are alternate ink limit profile for standard colour spaces.

[Ptheobald1]

]Have you looked into doing device link color conversions? You'd need additional software to do it but the results are better than standard GCR using traditional ICC color conversions (at least in my opinion).

Greg

Hi Greg,
I am certainly going to look into device link conversion. I have started doing some research into it, it looks pretty promising.
Thank you,
Pat

[Ptheobald1]

"Try using the colour profiles at colormanagement there are alternate ink limit profile for standard colour spaces."

Lukas,
This is great, I am going to get in there and do some testing today.
Many thanks,
Pat

[Stephen Marsh]

"Try using the colour profiles at colormanagement there are alternate ink limit profile for standard colour spaces."

Lukas,
This is great, I am going to get in there and do some testing today.
Many thanks,
Pat

Pat, there are also higher GCR versions of standard profiles which you may also wish to test (I am sure that Lukas was referring to these as they also have reduced ink limits).

There are folks on the forum that can convert a file for you using device links, as DVL are not usually available for test installation due to license conditions. You may also be able to purchase a DVL profile rather than the software used to create the profiles if budget is a concern.


Regards,

Stephen Marsh

[Ptheobald1]

Hi Stephen,
When using an ICC profile approach for GCR conversion do users Mode Convert from CMYK to LAB then back to CMYK using (for example) the SWOP2006_Coated3_GCR_bas.icc I downloaded from the site Lukas referred me to?
Is this one of the higher GCR versions of standard profiles you mean?

Budget is (of course) always a concern, it's the new normal we all live with : )
Pat


Pat, there are also higher GCR versions of standard profiles which you may also wish to test (I am sure that Lukas was referring to these as they also have reduced ink limits).

There are folks on the forum that can convert a file for you using device links, as DVL are not usually available for test installation due to license conditions. You may also be able to purchase a DVL profile rather than the software used to create the profiles if budget is a concern.


Regards,

Stephen Marsh

[Lukas Engqvist]

I normally convert to RGB (ECI-RGB, AdobeRGB would also work if you do not have very intense yellows) and then to the desired CMYK profile. Why I don't go via Lab is that then I would need to go 16 bit, using relative conversion with BCP this approach is fairly painless.
Device link works too, and we use that in our RIP, but some times I want to be able to do the colour reduction, and teach clients how they themselves can solve ink limit issues.

If there are areas that for some reason are negatively affected, if you do CMYK RGB CMYK in PS you can "paint with history" in any area that you want to restore to original, provided you don't have too much ink there… use a soft brush and it should be seamless. (this is still using tools you have paid for).

PS does support device link in current version, but wish there was a "GCR brush tool in CMYK mode" a brush that could paint + or - GCR, have wished for it every time a new version of PS comes out.

[meddington]

I normally convert to RGB (ECI-RGB, AdobeRGB would also work if you do not have very intense yellows) and then to the desired CMYK profile. Why I don't go via Lab is that then I would need to go 16 bit, using relative conversion with BCP this approach is fairly painless.

Are you inferring a CMYK conversion to Lab, then convert to CMYK, of just referring to the profile connection space (Lab)? Not sure I see the benefit of adding a conversion to RGB first.