Issues related with the switch from FOGRA39/47 to FOGRA51/52
by Refik Telhan
Dear Colleagues,
It all started with a question raised by Mr. Martin Orpen in his mail dated 22.08.2018 on the colorsync-users list. There was then almost a week long discussion with an open end.
>From that point on, I have made several conversions using FOGRA39, FOGRA47, FOGRA51 and FOGRA52 based profiles. At some point I have started generating profiles with the FOGRA51 and FOGRA52 datasets in multiple profiling software applications with different settings to have a better understanding on what is going on.
Mr. Orpen’s original complaint was the lack of yellow in skin tones with conversions made with PSO Coated v3. But when I started doing conversions using this profile, I have ended seeing that that deficiency ih yellow is widespread. Furthermore, what was true for FOGRA51 was also true for FOGRA52-based profiles.
To simplify the matter, I have created a Photoshop file in L*a*b* color mode that contained a linear gradient from L*=0 – a*=0 – b*=0 to L*=100 – a*=0 – b*=0. I have placed 10 color sampler points to L*= 5, 15, 25, 35, 45, 55, 65, 75, 85 and 95, to keep track of their changes. I then converted this file into “eciRGB v2” color space. The RGB values at these points came out to be R=G=B=13, 37, 64, 90, 114, 140, 165, 190, 216 and 242, respectively.
Starting with this neutral gray RGB gradient, I have done (relative colorimetric with black point compensation) conversions into FOGRA39 using ISO Coated v2 (ECI), into FOGRA51 using PSO Coated v3, into FOGRA47 using PSO Uncoated 12647 (ECI) and into FOGRA52 using PSO Uncoated v3. Below are the CMYK percentages for each of the 10 spots.
FOGRA39 conversion:
#01 / L*=05 a*=0 b*=0 / C=81 M=72 Y=65 K=85
#02 / L*=15 a*=0 b*=0 / C=75 M=65 Y=61 K=73
#03 / L*=25 a*=0 b*=0 / C=67 M=57 Y=55 K=58
#04 / L*=35 a*=0 b*=0 / C=60 M=50 Y=49 K=44
#05 / L*=45 a*=0 b*=0 / C=53 M=44 Y=43 K=33
#06 / L*=55 a*=0 b*=0 / C=46 M=37 Y=36 K=22
#07 / L*=65 a*=0 b*=0 / C=38 M=29 Y=30 K=13
#08 / L*=75 a*=0 b*=0 / C=29 M=22 Y=23 K=06
#09 / L*=85 a*=0 b*=0 / C=19 M=13 Y=13 K=02
#10 / L*=95 a*=0 b*=0 / C=07 M=05 Y=05 K=00
FOGRA51 conversion:
#01 / L*=05 a*=0 b*=0 / C=75 M=63 Y=50 K=89
#02 / L*=15 a*=0 b*=0 / C=67 M=57 Y=47 K=77
#03 / L*=25 a*=0 b*=0 / C=61 M=51 Y=44 K=62
#04 / L*=35 a*=0 b*=0 / C=55 M=46 Y=40 K=48
#05 / L*=45 a*=0 b*=0 / C=50 M=42 Y=37 K=35
#06 / L*=55 a*=0 b*=0 / C=43 M=35 Y=32 K=22
#07 / L*=65 a*=0 b*=0 / C=36 M=28 Y=26 K=12
#08 / L*=75 a*=0 b*=0 / C=27 M=21 Y=20 K=05
#09 / L*=85 a*=0 b*=0 / C=18 M=13 Y=13 K=01
#10 / L*=95 a*=0 b*=0 / C=06 M=05 Y=04 K=00
As you can see, the same color is converted into a different C-M-Y balance as the L* value goes lower with the FOGRA51 conversion. On the other hand, the C-M-Y balance is kept steady till the very dark shadows in FOGRA39. As the CMYK primaries are pretty much the same on both sides and the TVI curves, though different by about 1.7%, have the same C-M-Y balance, I cannot see any reason for the drop in Y as we go down the L* axis.
The situation is almost the same with FOGRA47 and FOGRA52.
FOGRA47 conversion:
#01 / L*=05 a*=0 b*=0 / C=81 M=62 Y=54 K=90
#02 / L*=15 a*=0 b*=0 / C=75 M=59 Y=52 K=80
#03 / L*=25 a*=0 b*=0 / C=65 M=53 Y=47 K=64
#04 / L*=35 a*=0 b*=0 / C=58 M=48 Y=44 K=46
#05 / L*=45 a*=0 b*=0 / C=49 M=40 Y=36 K=36
#06 / L*=55 a*=0 b*=0 / C=38 M=30 Y=28 K=27
#07 / L*=65 a*=0 b*=0 / C=29 M=21 Y=20 K=20
#08 / L*=75 a*=0 b*=0 / C=20 M=15 Y=14 K=14
#09 / L*=85 a*=0 b*=0 / C=12 M=08 Y=08 K=08
#10 / L*=95 a*=0 b*=0 / C=04 M=03 Y=03 K=02
FOGRA52 conversion:
#01 / L*=05 a*=0 b*=0 / C=85 M=62 Y=42 K=88
#02 / L*=15 a*=0 b*=0 / C=76 M=58 Y=43 K=78
#03 / L*=25 a*=0 b*=0 / C=66 M=54 Y=39 K=61
#04 / L*=35 a*=0 b*=0 / C=58 M=47 Y=36 K=43
#05 / L*=45 a*=0 b*=0 / C=49 M=40 Y=33 K=28
#06 / L*=55 a*=0 b*=0 / C=40 M=32 Y=28 K=16
#07 / L*=65 a*=0 b*=0 / C=33 M=25 Y=22 K=08
#08 / L*=75 a*=0 b*=0 / C=24 M=17 Y=16 K=03
#09 / L*=85 a*=0 b*=0 / C=15 M=10 Y=10 K=01
#10 / L*=95 a*=0 b*=0 / C=05 M=03 Y=03 K=00
To approach the situation from another angle, I have also converted the same neutral gray RGB file into GRACoL2006 and GRACoL 2013 to see have how they perform under the same conditions. Here are the results:
GRACoL2006_Coated1v2 conversion:
#01 / L*=05 a*=0 b*=0 / C=83 M=75 Y=71 K=87
#02 / L*=15 a*=0 b*=0 / C=80 M=73 Y=70 K=69
#03 / L*=25 a*=0 b*=0 / C=73 M=65 Y=64 K=49
#04 / L*=35 a*=0 b*=0 / C=64 M=55 Y=55 K=34
#05 / L*=45 a*=0 b*=0 / C=56 M=47 Y=47 K=23
#06 / L*=55 a*=0 b*=0 / C=49 M=40 Y=40 K=12
#07 / L*=65 a*=0 b*=0 / C=41 M=32 Y=33 K=04
#08 / L*=75 a*=0 b*=0 / C=31 M=24 Y=24 K=00
#09 / L*=85 a*=0 b*=0 / C=19 M=13 Y=14 K=00
#10 / L*=95 a*=0 b*=0 / C=06 M=04 Y=05 K=00
GRACoL20013_CRPC6 conversion:
#01 / L*=05 a*=0 b*=0 / C=80 M=71 Y=62 K=90
#02 / L*=15 a*=0 b*=0 / C=75 M=67 Y=62 K=75
#03 / L*=25 a*=0 b*=0 / C=69 M=60 Y=57 K=55
#04 / L*=35 a*=0 b*=0 / C=62 M=53 Y=51 K=38
#05 / L*=45 a*=0 b*=0 / C=55 M=46 Y=44 K=25
#06 / L*=55 a*=0 b*=0 / C=46 M=38 Y=37 K=16
#07 / L*=65 a*=0 b*=0 / C=39 M=30 Y=29 K=07
#08 / L*=75 a*=0 b*=0 / C=30 M=23 Y=22 K=02
#09 / L*=85 a*=0 b*=0 / C=18 M=13 Y=13 K=00
#10 / L*=95 a*=0 b*=0 / C=06 M=04 Y=04 K=00
Although the paper white of GRACoL2013 is now in line with 12647-2:2013, it does separate RGB into a C-M-Y balance very similar to GRACoL2006.
Extreme loss of yellow ink in areas mid-tone and upwards has many negative side effects. Rich blacks are bluish/purplish and many clients do not like that. Yellow ink typically prints last for a good reason. It contains varnishes that give the image extra gloss and rub resistance. It is also the least tacky of the inks. Hence, by reducing its amount in the separation causes even less yellow ink being transferred to paper. Wet on wet printing sometimes requires more of the final ink to be properly transferred not less.
To get round this problem I have tried recalculating the profiles to get some gray axis correction when converting with perceptual rendering intent. The old ProfileMaker v5, CoPrA v4 and Color Toolbox v18 (with incremental control) all have the tools to compensate for the color of paper. Interestingly this feature does help in the highlight to mid-tone range but not in the mid-tone to shadow range.
On a recent occasion, I have also witnessed the fact that inkjet contract proofs are not good in simulating the inherent shift towards blue/purple in the shadows. What may appear as a neutral shadow on a certified proof is printed with a blue/purple cast, which may not be visually acceptable the client.
This problem needs to be addressed. Doing a conversion in Photoshop using a relative colorimetric or a perceptual rendering intent is quite misleading without switching on the Proof Color View with paper white simulation. You can only see the overall loss of yellow when you activate soft proofing. Given that Photoshop still leaves much to be desired in terms of soft proofing, especially with uncoated papers, you can only use verified/certified inkjet proofs to see the actual result of your RGB to CMYK conversion.
While FOGRA39 and FOGRA47 do share an imaginary paper white (95,0,2), being close to a*=0 + b*=0, the conversions made by both profiles maintain some kind of paper relative neutrality. Even if the paper white simulated absolute colorimetric proofs are not precisely matching any real print substrate, we had over the years developed chromatic adaptation skills that would bridge the gap. While the prepress process is rather smooth with FOGRA39, bridging the gap between the contract proof and the real substrate has always been the problematic side.
But with FOGRA51 (and as a matter of fact, for the same reason, with FOGRA52) prepress and proofing needs heavy tweaking after RGB to CMYK conversion to introduce some of the lost yellow back to the scene. If not done properly, a proof to print match is tricky especially if you have heavy areas in the image. Hence, the process as a whole became problematic.
Dear colleagues, I invite you to shed some light on this in mystery.
Best regards,
Refik Telhan, EE B.Sc.
Light and Color Management Consultancy
Aydogdu Sokak 12A, Tarabya Mahallesi
Sariyer, 34457, Istanbul, Turkey
Mobile: + (90) (532) 426 21 87
e-Mail: rtelhan(a)ofset.com rtelhan(a)icloud.com
P.S. The following link will let you download a PDF that contains screen shots of the above conversions. There are also four screen shots from the interface of CoPra 5, showing that the problem is related with the measurement data sets and not with the profiles calculated by Color Toolbox.
https://www.dropbox.com/s/vqdjezncf8l60cq/FOGRA_Conversions.pdf?dl=0
5 years, 1 month
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Question about GWG2.0 Spot to CMYK Overprint (also FOGRA and PDF/X-Ready certification)
by Jan-Peter Homann
Hello to the PDF specialists,
I have a customer, who wants to be ISO 12647-8 certified by FOGRA with a
high end CMYK Inkjet solution.
The certification includes the PDF/X-Ready output suite 3.02 which
contains the patch GWG2.0 Spot to CMYK overprint.
With the current RIP version this patch shows crosses in a different
green, than the rectangles.
/The GWG readme for this patch states://
//A faint ‘X’ in slightly darker green may show in all of the tests;
this is acceptable behavior in this patch. Only a clearly visible X
indicates an incorrectly rendered patch. Please see example on the first
page of this README file.//
//This patch appears to be a simple patch, and should be rendered
without fail on its own. It is, however, possible that the amalgamation
of this patch with other patches may very well lead to problems. There
are several cases in which objects set to overprint using Spot colors
can prove to create some advanced problems. For example, If you simulate
Spot colors for proofing or commonly convert Spot colors to CMYK this
patch can be used to highlight potential errors in your working
practices. Use this patch along with patch 10 —Spot to CMYK conversions
for testing Spot color simulation./
If I open the patch in Acrobat Professional and activate overprint
simulation I don´t see any crosses (expected behavior). In output
preview (german Ausgabevorschau) I measure, that the overprinting
objects have only a tone value of 1% (in the top row CMYK overprints
spot, in the bottom row spot overprints CMYK). The object inspector does
not show an alternate colorspace for the spot color objects in GWG green.
The standard output intent for the patch is ISOcoatedv3_300_eci.icc If I
change the simulation profile in Acrobat Pro to quite different printing
conditions like e.g. newspaper or Epson inkjet profiles, all patches
stay perfect green - no crosses.
I talked with the RIP vendor for the solution and also they are
surprised. In 2016 internal test showed perfect patches with no visible
crosses. Now we see two different greens. Concerning the GWG readme,
this is an acceptable behavior.
Both the customer, the RIP vendor and I want to understand, what is
happening here. Between 2016 and today, the RIP solution got an update
of the Adobe PDF Print Engine (APPE). As the printer uses only CMYK for
printing, the RIP must convert overprints between spot and CMYK to CMYK
only.
I have following questions to the PDF-specialists in this list:
1) Is it possible, that an APPE update changes the behaviour how
overprints between spot and CMYK are rendered to CMYK only ?
2) Why i don´t see an alternate colorspace for GWG green in the object
inspector of Acrobat Pro ?
3) Why I don´t see slight crosses in Acrobat Pro, when I change the
simulated print condition ?
4) Does GWG has an mailinglist to aks such questions ? (I didn´t found
it on the GWG website...)
Thank you for any hints
Jan-Peter
--
Homann colormanagement tel: +49 30 611 075 18
Jan-Peter Homann mob: +49 171 54 70 358
Herzbergstr. 55 www.colormanagement.de
10365 Berlin mailto:homann@colormanagement.de
5 years, 1 month
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