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Author Topic: Study about CMYK Profile compare to RGB Profile  (Read 543 times)

aaronchan

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Study about CMYK Profile compare to RGB Profile
« on: December 09, 2017, 08:25:31 AM »

Dear All,

In this thread, I would like to study and discuss about CMYK profile VS RGB profile.
I've attached here a link with my ICC profiles, which is based on Epson P6000 with OEM ink and a cheap no brand RC satin paper.
https://drive.google.com/drive/folders/1Gog9rZtcH9wmdU_85o1YfrETmibUnkkE?usp=sharing

The RGB ICC was made in i1Profiler with a 3075 patches target which is custom designed by myself.
I had been using this target to profile all of my paper which produce very good color and neutral black and white print.

For the CMYK Profile,
I was using Ergosoft Poster Print and linearized the 3 times from 18 steps -> 36 steps -> 54 steps.
Then use ColorThink Pro 3 to plug in the number to try to find the optimal individual ink limit for each channel.
With the printed ink limit test chart, I chose 220% as the total ink limit for this combination.
After that, I used i1P to generate a target which has 2568 patches target.
Measured with i1P2 and i1IO2
The setting of the black separation ramian as default, but I chose "heavy" for the black curve.
Perceptual table I chose Colorful.
Table section is Optimized Quality.
In the Advanced setting, I picked Version 2 as the ICC Version.
And for the smoothness I slided all up to 100.
And the rest remain as default.

The outcome is quite interesting.
When I compare both ICC,
The RGB has much larger color gamut than the CMYK.
Specially in the Green and Blue area.

I've used Bill's 28 balls to do a softproof.
Which the cmyk one is actually "not that bad".
You can see a bit dull in the outer side of the color balls.
But the smoothness and the trasistion are very close to the RGB Profile already.

So now I have 2 questions here:
1.
When I compare a RGB profile to CMYK profile, am I doing a wrong thing already since this is more like comparing an apple to and orange?
2.
I've tried a lot of different combination of individual ink limit already, but I still couldn't even get close in the Green and Blue area comparing to the RGB profile.
Is that me or this is supposed to be like this?

I hope we can have a happy discussion here since I believe most of us use RGB printing workflow to print our works or client's job.

Best Regard,
Aaron Chan

arobinson7547

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Re: Study about CMYK Profile compare to RGB Profile
« Reply #1 on: December 10, 2017, 04:51:55 PM »

RGB can be WAY easier and a bit less work; certainly when printed on top of the already ink limited presets tied to a Paper selection.
But when doing CMYK and especially CMYK of a non-htm driver (usually within a Rip), then you get do to a LOT more work (Manualy determining the Ink Limits Per Channel for Colors and Black (Max Chroma/Lowest L*), Determining how you what to Linearize those channels (Density, DotArea Chroma, Lab, dE-P, %dE-SP).

You get to choose if you'd like to gray balance your printer/paper/print setting combination BEFORE printing out your Profile Target, by Gray Balancing CMY from 0 thru 100%. This is a great thing to do if you'd like to take out all color cast which would naturally exist. Then sometimes there is what I call Advanced Ink Limiting where you can limit 2 channels (like Red (MY) Green (CY) Blue (CM) separately and 300% Combinations (CMY, CMK, CYK, MYK from The Total Ink Limit of 400% combinations.

My personal favorite is manually setting Channel ink limits, Linearizing those channels multiple times using a linearization chart that uses 12345 percents in the Highlights and then uses 1% increments after 83% ( so 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100). I think if you can take care to ensure ALL your channels are not necessarily PERFECTLY linear but certainly monotonous so that 97% may not be smack dab in the middle of   96 and 98 but as long as it is 'in between' and not higher, lower, or occupying the same space as the preceding or following steps.

The sum of all the [not so] little things that can be done BEFORE ever even printing a Profiling Target can go a long way in squeezing the last bit of Quality out of this part of the Process.

When you hear of people talking about sections of there profile colorspace closing up, where there is no separation or detail; They never had the chance to optimize those regions. And you need to be on the per channel level to do that.

That's a CMYK think.

I would not be fair if I did not mention that I also have seen RGB profiles give more Gamut (not everwhere or overall but in certain regions. I guess it's trade-offs.
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