GCR - Friend or Foe?

[JudP]

As part of a major color management program we are currently implementing I am testing Alwan's Optimizer ECO software. I know that there has been a lot of discussion on the subject of GCR but I wanted to get some input on this from those who have seen what I am seeing.

I have a 38" six unit Goss Sunday 2000, a Heidelberg XL 105 and an HP Indigo 7200 and am finger printing, profiling and developing plate curves for each. I've been told that GCR is the way to go to gain better stability on press however our flesh tones, with GCR applied, have a muddy, greyish look. If anyone is familiar with Alwan's ECO Optimizer we currently use a GCR setting of 7 and I've tested several different settings an am almost tempted to do away with GCR all together.

Any input?

 

[gordo]

As part of a major color management program we are currently implementing I am testing Alwan's Optimizer ECO software. I know that there has been a lot of discussion on the subject of GCR but I wanted to get some input on this from those who have seen what I am seeing.

I have a 38" six unit Goss Sunday 2000, a Heidelberg XL 105 and an HP Indigo 7200 and am finger printing, profiling and developing plate curves for each. I've been told that GCR is the way to go to gain better stability on press however our flesh tones, with GCR applied, have a muddy, greyish look. If anyone is familiar with Alwan's ECO Optimizer we currently use a GCR setting of 7 and I've tested several different settings an am almost tempted to do away with GCR all together.

Any input?

Pretty much all the separations done since the 1990s are GCR separations because that is the default in PhotoShop and it is how the industry supplied ICC separation profiles are created. The GCR may not be as aggressive as what you can achieve with Alwan.

Because GCR makes the black printer such a large part of the image separation, success is very dependent on the quality of the black printer on your press in terms of ink quality and transfer. Also, with aggressive GCR, because there's so much more ink on the first unit, there is a greater possibility that the black will be affected by the next three units which can cause a muddy look. This problem first showed up when GCR was introduced in the 1970s/80s and caused magazine publishers to reject GCR separations for ad submissions. Modern presses and inks make this less problematic but the potential for problems remain in a KCMY sequence.

best, gordo

 

[JudP]

Thanks Gordo and I can totally see why GCR separations were rejected in the beginning. I am definitely not pleased with the results but don't know if I am in the "minority". Cost of ink is another "benefit" advertised with GCR however this is such a secondary issue to print quality that it really is a non-issue for us.

Have you seen what I am describing with optimized files coming from Alwan?

Best, Jud

 

[Lukas Engqvist]

I think you have to be clear on what stability GCR offers. GCR doesn't make a system more stable, in fact it requires the black to be more stable than UCR, what it does give is less variation in grey, because neutrals are mostly in K. Also see the discussion about narrow and wide black that we had recently.

 

[Magnus]

Alwan

Alwan

Jud, we are using a similar solution (Binuscan CMS server) and we doesn't have any problems with greyish skin tones. Our GCR is very aggressive and K starts at 5%. We print on KBA sheet fed presses with KCMY sequence.

Do you convert from 'profile A' to 'profile a' with Alwan GCR or do you convert from profile a (standard) to b (press)?

If you convert from A to B, is the profile newly updated?

We've seen grey skintone problems when we tried to use only plate curves to print accordingly to Fogra39 and then did a Fogra39 to Fogra39 Device Link conversion.

 

[JudP]

Thanks Magnus,

They muddy greyish look we are seeing on press is specifically in the 3/4 tones and shadows.

We use Alwan to handle not only our GCR but the file is also gamut mapped and optimized for the presses. Alwan then sends this file into Apogee (Agfa's prepress workflow) which applies the plate curve. I think I will try a lower K start. As I said above, we are using 7 and not too happy with it.

Jud

 

[Stephen Marsh]

Just curious, have you tried different (finer) screen rulings, angles, dot shapes etc?

Stephen Marsh

 

[Alois Senefelder]

Inputs

Inputs

JudP

The symptoms you describe, Muddy Greys 3/4 tones and Poor Shadows, in my opinion indicate - Poor Control of Press Inking Inputs , emulsified ink and poor ink trapping. I also suggest you read the Post from "Otherthoughts" Thread: Automatic GCR software page 7 --- Date Posted : 12-31-2008



Regards, Alois

 

[Alois Senefelder]

Gcr

Gcr

Gentlemen,

GCR PDFs - I hope you will find of interest and value.



Regards, Alois

 

[JudP]

Stephan - We were earlier printing Sublima 240 on the web however we found that this was more difficult to color manage so we have been running at 200 conventional. I have not tried any other line screens with our GCR settings but I think I will. Have you tried this?

Thanks Alois! I will look over that thread you recommended and see if that is our problem. I'm also downloading the PDFs that you attached.

Jud

 

[Stephen Marsh]

200 should be fine, I just thought that you might be using a chunky screen and that the dot structure/rosette was more visible.

Stephen Marsh

 

[gordo]

Stephan - We were earlier printing Sublima 240 on the web however we found that this was more difficult to color manage so we have been running at 200 conventional. I have not tried any other line screens with our GCR settings but I think I will. Have you tried this?

Just for clarification, other than not having any halftone dots smaller than 4%, Sublima and "conventional" are exactly the same. From a press point of view there's virtually no difference as far as the impact of lpi is concerned.

Are you printing to an industry standard? What color management difficulties did you have with 240 lpi?
What is the quality of your ink transfer. How do the dots look under magnification. It would be great if you could post microphotos of your presswork's halftone dots.

best, gordo

 

[JudP]

Hey Gordo, we have our own density targets which we came up with as a standard. K = 1.60/C = 1.43/M = 1.32/Y = .92.

I would love to post microphotos of the dots of my press sheet but how do I do this? I have taken a digital camera on its macro setting and held this against a loupe on press and taken some photos. Will this work? I would really appreciate a critique on our dots!

Jud

 

[gordo]

Hey Gordo, we have our own density targets which we came up with as a standard. K = 1.60/C = 1.43/M = 1.32/Y = .92.

I would love to post microphotos of the dots of my press sheet but how do I do this? I have taken a digital camera on its macro setting and held this against a loupe on press and taken some photos. Will this work? I would really appreciate a critique on our dots!

Jud

All things considered, your SIDs are not too far away from the typical. That being said, I would be concerned about the Magenta. Typically Magenta is higher (or equal to) than Cyan. Your Magenta is 11 points lower. I would try to understand why.

All print shops should own a usb digital microscope as part of their quality control kit. They cost much less than $100. Here's a sampling from ebay: usb digital microscope | eBay

The one I own is a 20x-200x which cost me $75 in a brick and mortar store. Attached is a snap of halftone dots to give you an idea as to the quality (click to enlarge).

best, gordo

 

[Lukas Engqvist]

Sublima is definately not in 3/4 tones, but sublima (and agfas hybrid for lower lpi) are there to help you avoid banding eg you fade out to paper.

 

[Hopkins Printing]

Hi JudP,

We have been an Alwan user for almost a year and are quite pleased with its performance. In the beginning, there were a few settings "bugs" we had to work out for our workflow needs but are now enjoying the benefits of the software.

Best regards,
Jon Morgan
Hopkins Printing

 

[rich apollo]

I, too, am running Alwan with Apogee. What you're describing sounds like an issue with the plate curve, not a problem stemming from GCR. I've run CMYK Optimizer off and on since '05 or '06. I've never had any degradation of imagery. The thing that I've found is that you can exacerbate piling on the black unit, and you can possibly decrease the ink take-off of the CMY to a degree that makes those units difficult to control.

Do you have a way to see what kind of dot gains you're getting? Depending on the paper type, to me it looks like your black is low, your cyan is high, and your yellow is low.

Is there something that's keeping you from simply opening up the black 3/4 tone?

And, are you certain that Apogee isn't set to perform a color transform somewhere in the workflow?

How are you determining what your plate curves should be?

Feel free to PM me. I'd be happy to help you work through this, if I can.

 

[danremaley]

Gcr

Gcr

With GCR, the Black becomes the most important color, dot gain is critical, as well as the 'print contrast' number. You could also move the Black to the last print unit. Color variation is noticed in "hue shifts" warm grays, magenta purples. With GCR you only get differences in 'lightness' / 'darkness'. Much more acceptable. I have a printed reference piece that show this, email me and I'll send you one. [email protected]
Dan

 

[JudP]

Hi Jon!

Thanks for responding. Are you using the GCR functionality in Alwan? Do you mind sharing what settings you are using?

Jud

 

[Hopkins Printing]

Indeed we are. We have the ECO flavor of CMYK Optimizer.

I will export my Alwan settings and send them to you. Please email off forum at jmorgan<at> hopkinsprinting <dot> com.

Jon