CHROMiX

Evaluating ICC Profile w G7 Digital Press Evaluation Form

OK- I have built a profile for ColorBurst RIP (think its a good one). What do I use as an evaluation print and how do I set it up to insure I don’t mess up the evaluation print numbers (and resulting output.)

I downloaded the G7 Digital Prees Form 1- CMYK - to use as a test form. It has a section that uses CMY, K, and CMYK in to reproduce the same image- to eveluate grey balance for instance (all black, just CMY or cmy plus black.)

But I am perplexed about something- The G7 eval form is an untagged raw CMYK file- (without an icc profile.) The way ColorBurst is set-up- it always assumes an ICC profile for CMYK files if they aren’t tagged with one. In my case - ColorBurst assummes that untagged CMYK files are Gracol 2006 coated #1.

If I drop the untagged file in to the RIP - it will take the raw CMYK numbers and process them assuming they are Gracol Coated #1. Is that correct?

I tried assigning the Gracol Coated #1 to the CMYK file before sending it to ColorBurst - but that had undesirable consequences- The idnetical images made from CMY, K and CMYK that were to be used for greyscale evaluation were all converted into cmyk - all with equal values all with a overload of magenta.

I gather I am missing some fundamantal understanding here- can someone please hekp me out?

Thanks: Kirk

Hi Kirk,

I guess I have more questions for you before I can offer answers. Are you asking advice for what test print to use to verify that your RIP looks okay? Or are you asking what print to use to pass G7 certification?
The Digital Press Form 1 does not have any images on it that I can see - is that what you’re looking at?
Are you trying to do the G7 process in ColorBurst? The last I heard ColorBurst is not really setup to be able to do that easily.
You should be able to turn off color management in ColorBurst and print the untagged raw CMYK file without color management if that is what you’re trying to do.

I am not trying to G7 certify with this process. I am actually using forms 3 and 4 which include numerous color eval areas plus images (the wine, the bike, the fruit, the women.)

I am using the forms to evaluate (visually and measured) the quality of the color proofing process through the managed workflow (in this case in the ColorBurst Rip.) I have no requirement to use these forms.

Using the forms did bring to light my quandary and several questions. Hopefully I can express them clearly.

Part A: Tagged and untagged files- assigning profiles to test forms or not

  1. An untagged CMYK file has no specific LAB values associated with it until they are defined by a CMYK color space. -There are no reference LAB values to compare to once the form is printed and measured. (There may be LAB values provided for reference by Idealliance for printing these forms on GRACoL compliant Coated #1 stock- I need to recheck this- if so this could be part of my answer.)

  2. Assigning a CMYK color profile to the untagged CMYK file before sending it to the rip fundamentally changes the file in ways that are undesirable. For example, a swatch of 18% K only is transformed into CMYK values.

I want to evaluate the Colorburst process with the ICC profile I specifically created for the underlying paper, both visually and by measurement.

  1. After thinking about it, my conclusion is that assigning a profile to an untagged CMYK file (without retaining the original cmyk number) ruins the forms for testing. Assigning a profile retaining the files CMYK numbers may keep the forms good for visual evaluation but will not provide for reference LAB values (unless they were created elsewhere somehow.)

  2. In the ColorBurst workflow, assigning a GRACoL 2006 coated 1 profile to an untagged cmyk file while retaining the original cmyk numbers is the same as not assigning a profile and sending it to ColorBurst which in my setup assumes that untagged cmyk files are GRACoL 2006 coated 1.

  3. I dont see how ColorBurst is going to take the raw CMYK values pass them to the Profile Connection Space as GRACoL coated 1 and process them to the output profile for accurate color.

Can you help me here- or do I need a therapist at this point?

Thanks Patrick-
Kirk

Kirk and I talked about this situation outside of these forums.

These test images from IDEAlliance are in PDF form, which automatically get rasterized when you drop them into Photoshop. When you assign CMYK to these images they get assigned the working CMYK colorspace you have setup in color settings. In this case, it was SWOP. When this image is sent to the RIP to be printed using a GRACoL profile, it is necessarily re-separated and you lose the unique black generation in the process (and the color does not look so good either.)

Once the image is brought into Photoshop with the GRACoL profile as the default, the process runs smoothly and the image is printed with the K generation intact. Everything looks good.

A few more followup points from keconomos:

Regarding my #1 point. On further reflection- untagged cmyk values do not have associated LAB values. It is only after you assign a colorspace (working profile) to the cmyk values that they point to a specific LAB value. If you know both the cmyk values and the colorspace you can determine what the LAB values should be - and compare through Delta E against the measured proof print.

Regarding my #2 point. Assigning a working profile to an untagged cmyk file will not change the cmyk values in the file. These same cmyk values however will produce different LAB values depending on what profile you assign the untagged file.

My problem in #2 came about due to the process I was using:

To reiterate what Patrick touched upon- when you open a PDF in photoshop- Photoshop brings up a pdf raster menu. If the pdf you are opening is not tagged with a profile- Photoshop automatically assigns whatever working profile you have selected in your PhotoShop Color Settings. It doesn’t ask, it doesn’t warn- it just assigns the profile and opens.

Here is what happened to me- just as a warning. I had my CMYK working space set to SWOP. I intended to assign GRACoL coated #1 to the untagged CMYK PDF file. When I opened it in Photoshop the file appeared to be tagged with a SWOP profile (Photoshop assigned it automatically without warning)- so I converted the profile to GRACoL. The conversion changed the cmyk numbers.

In this circumstance- I would have to change my CMYK colorspace to GRACoL before opening the PDF or ignore the SWOP profile on the opened CMYK file and assign (not convert to) the GRACoL profile.

Hope that you find this info useful.


Kirk Economos
ManageColor.com