ICC Profile Evaluation Print ???

[keconomos@sbcglobal.net]

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 Press 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 in order to eveluate grey balance (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

[TerryWyse]

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 Press 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 in order to eveluate grey balance (all black, just CMY or cmy plus black.)

The G7 Digital Press Form....or any of the smaller G7 test forms....are good for evaluation, assuming G7 and GRACoL/SWOP colorimetry is your goal.

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?

That's correct. Untagged CMYK files will always get assigned the CMYK Input profile (should be called "Source" profile as ColorBurst continues to use incorrect terminology). If you have "Use Embedded Profiles" checked, untagged will still get assigned the source profile but tagged files will use their embedded profile as the source.

*Generally speaking*, when the application is CMYK press proofing, you do NOT want to use the "Use Embedded Profiles" checkbox as this could result in a completely different proof print than what you expect. This is NOT the case for RGB prints as you generally want ColorBurst to ALWAYS honor the embedded profile in this situation. The ideal workflow in my opinion would be to have a "Use Embedded Profiles" checkbox for each color space/model that way you could force the assignment of the CMYK source profile for proofing but honor embedded profiles for RGB printing.

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?

My guess is Kirk that you didn't *assign* the GRACoL profile but instead *converted* to it prior to dropping it in ColorBurst. In any case, those CMY, K and CMYK elements will ALL get converted to CMYK when passed through ColorBurst no matter if you assigned/embedded the GRACoL profile or not.....converting everything to the output/printer profile (in this case a CMYK printer profile) is how color-managed proofing works.

As far as the "overload of magenta", I'm not sure what you mean. Are you simply saying the gray balance appeared magenta-casted? If so, it could be a result of poor printer/output profile in your ColorBurst environment or it could be poor/incorrect viewing conditions. Inkjet proofs will often appear to have a color cast, especially in the neutrals, when viewed under incorrect viewing conditions.

Regards,
Terry

[Stephen Marsh]

OK- I have built a profile for ColorBurst RIP (think its a good one).

Kirk, I think that it would be good to go back to basics, before the water is muddied with custom profiles...

I think that it is helpful to have a "known state" to compare to. Your custom profile is unknown.

Load in standard Epson media, that is supported for your ColorBurst Environment (printer profile for the target resolution on the target printer with Epson ink and media). Run the proof using this default/canned environment setting.

Use this "default/canned" print as a visual reference.

Then move on and compare the results to your custom profile with the same RIP colour settings using the custom profile print settings.


Hope this helps,

Stephen Marsh

[keconomos@sbcglobal.net]

Terry- I want to be sure about your response to one of my burning questions. You wrote:

"My guess is Kirk that you didn't *assign* the GRACoL profile but instead *converted* to it prior to dropping it in ColorBurst. In any case, those CMY, K and CMYK elements will ALL get converted to CMYK when passed through ColorBurst no matter if you assigned/embedded the GRACoL profile or not.....converting everything to the output/printer profile (in this case a CMYK printer profile) is how color-managed proofing works."

I understand that when the LAB values go from the Profile Connection Space through the printer profile to the destination (printer) space they will be converted to CMYK values- However- what happens at the stage of assigning a source profile to the untagged cmyk values in the original file? I would think here that a value like 20 K (only black) would not be converted durring an assignment to a mix of cmyk. (Now that I have succinctly defined my question- it's pretty easy for me to check this out.)

[rich apollo]

what happens at the stage of assigning a source profile to the untagged cmyk values in the original file?

Nothing. The CMYK values are unchanged when an ICC profile is assigned. The ICC profile provides a context in which those values can be better understood.

The same CMYK values going down on cold-set newsprint, #1 grade coated paper (sheet-fed), and an Epson 9900 will yield different colors. The ICC profile assigned to a file tries to communicate the color associated with those CMYK values.

[keconomos@sbcglobal.net]

Thanks for the replies from everyone.

Rich- that us what I thought- assigning a profile will not change the cmyk values of the original file. However, the file will yield different LAB values in the PCS (Profile Connection Space) during the AtoB transform depending on the profile you assign it.

Terry- I am pretty sure I converted and not assigned the GRACoL #1 the first time I set up the test file for printing. I think that changed the cmyk values. I was working in Photoshop when I converted and although the original had no profile - I believe Photoshop assumed a profile and converted to GRACoL - remapping K values to cmyk values and more. I am going to check this again by test. If that is the case- sending these values in the AtoB transform would definetly chnage the LAB values.

[TerryWyse]

Thanks for the replies from everyone.

Rich- that us what I thought- assigning a profile will not change the cmyk values of the original file. However, the file will yield different LAB values in the PCS (Profile Connection Space) during the AtoB transform depending on the profile you assign it.

Exactly correct......at the moment you assign the profile, nothing at all happens but the moment you start talking about the PCS, things change....different profile assignments will not alter the CMYK values one bit but the conversion to the PCS is something else entirely....that depends on the profile that's being assigned.

Terry- I am pretty sure I converted and not assigned the GRACoL #1 the first time I set up the test file for printing. I think that changed the cmyk values. I was working in Photoshop when I converted and although the original had no profile - I believe Photoshop assumed a profile and converted to GRACoL - remapping K values to cmyk values and more. I am going to check this again by test. If that is the case- sending these values in the AtoB transform would definetly chnage the LAB values.

NOPE.....CMYK values will absolutely NOT change with a new or different profile *assignment*....if they changed then a *conversion* took place, whether it was intended or not. Again, we're just talking about assigning a profile at this point, not about the A2B/PCS conversion or anything else that might be happening downstream.

Terry

[keconomos@sbcglobal.net]

One thing I found out during testing yesterday is that Photoshop will always assign the working CMYK space to an untagged PDF file you are opening. Even if the Photoshop color settings are set to keep the existing color space when opening and ask if there is a mismatched or missing color profile.

When I opened the Digital Print Form PDF (non tagged)- Photoshop did not warn of a missing profile and did not ask if I wanted to apply a profile- it simply applied the working profile and opened the file. I confirmed with several tests. That was a surprise.

Terry- now the conversion instead of assignement becomes an issue. For example- my working color space in photoshop was set to SWOP coated when I opened the file. My erroneous conversion took the cmyk numbers assigned SWOP to the PCS and then out to GRACoL. The cmyk values of the file were altered during the conversion- and in fact represent different LAB values than if I had assigned GRACoL as the working space when opening.

Thanks for everyone's help- another piece of the puzzle and an educational process.

[meddington]

When I opened the Digital Print Form PDF (non tagged)- Photoshop did not warn of a missing profile and did not ask if I wanted to apply a profile- it simply applied the working profile and opened the file. I confirmed with several tests. That was a surprise.

if you're opening a PDf in Photoshop, your essentially rasterizing the file. you should have gotten an "Import PDF" dialog, and yes, if your mode was set to CMYKcolor, the working space is used by default and will be assigned.

[keconomos@sbcglobal.net]

reply to opening pdf- yes precisely- you get the "import pdf" dialog box and if you select CMYK as the colorspace for an untagged PDF you are opening, Photoshop assigns the working CMYK color space.