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lower cyan without increasing magenta?

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  #11  
Old 03-07-2017, 01:01 PM
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andrewrodney andrewrodney is offline
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Re: lower cyan without increasing magenta?

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Originally Posted by Sabrina81 View Post
With this technique, CMYK isn't used for output. Just to clarify.
The scale of the numbers is always based on some specific output and that's the issue with using a silly color model based on many differing output devices and thus scale and ratio. Absolutely not the case with Lab.
These two sets of RGB values have four different CMYK equivalents due to four different CMYK profiles; which is correct?

http://digitaldog.net/files/CMYKs1.jpg
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  #12  
Old 03-07-2017, 01:28 PM
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Re: lower cyan without increasing magenta?

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Originally Posted by marameo View Post
Aside from this work do you think CMYK can still have a point when retouching for pre-press because of the density concept and the "Maximum Dot" and "Minimum Dot" in print specification?

I believe it's useful to take total ink readings in the palette just to see how the image will print. It's just one value (Σ) to assess the image.
CMYK changes are best reserved IMHO to deal directly with press variables and solving their specific problems.

RGB deals directly with our photographic variables and are usually the best for such problems.

I believe that anything that can be done in CMYK has at least an equal or even better alternative approach in RGB. Not everything that can be done in RGB can be repeated in CMYK

RGB is a wiser choice than editing based on the needs of one very specific CMYK output device - you are pretty much stuck as sending the data to any other (including CMYK devices) is likely to lead to a world of pain. Whereas work in RGB (preferably the wider spaces) and convert to virtually any output device know to man - providing you have the necessary profiles.

Of course just my opinion and I would be open to seeing objective testing to prove or disprove

EDIT

I knew I had seen something in the past - I think this fairly succinct

http://rgbcmyk.com.ar/en/rules-for-c...mages-to-cmyk/
  • Rule 1: DO NOT convert to CMYK.
  • Rule 2: If it is not possible to apply Rule 1, then DO NOT convert to CMYK yet!

Last edited by Tony W; 03-07-2017 at 02:02 PM. Reason: Subjective rather than objective
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  #13  
Old 03-07-2017, 03:49 PM
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Re: lower cyan without increasing magenta?

I'd love to understand if being aware of Ink limit (Total Area Coverage) is part of a retoucher "best practise" or if this is just a subject that the prepress people must face.

What if the retoucher is being informed by the publication or the photographer that the Ink limit should be under 260?

Should the retoucher convert to a custom CMYK profile (GCR, Medium, 260%) and then assign a known working profile (swop)?

Last edited by marameo; 03-07-2017 at 05:07 PM.
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  #14  
Old 03-07-2017, 05:24 PM
Shoku Shoku is offline
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Re: lower cyan without increasing magenta?

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Originally Posted by Tony W View Post
Not everything that can be done in RGB can be repeated in CMYK
True. And it is also true that every color space has it's limitations. That's why we use CMYK, RGB, and LAB. We use what works, and that can vary from image to image.
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  #15  
Old 03-07-2017, 05:44 PM
anderson234 anderson234 is offline
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Re: lower cyan without increasing magenta?

I could learn a lot from your discussion. I appreciate it.
But at this point, I care most about the numbers/pattern that Lee Varis's CMYK method showed us, which directly helpes me quickly adjust skin tone to normal. Maybe RGB or LAB is better, but I need that pattern, too. I'll try to find it within RGB and LAB.
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  #16  
Old 03-07-2017, 05:52 PM
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Re: lower cyan without increasing magenta?

Quote:
Originally Posted by marameo View Post
I'd love to understand if being aware of Ink limit (Total Area Coverage) is part of a retoucher "best practise" or if this is just a subject that the prepress people must face.

What if the retoucher is being informed by the publication or the photographer that the Ink limit should be under 260?

Should the retoucher convert to a custom CMYK profile (GCR, Medium, 260%) and then assign a known working profile (swop)?
CMYK is device dependent, so for the average retoucher who is sending files back to a photographer, or to a marketing firm, not knowing where the final output may be, and in some cases multiple outputs, then color managed RGB is your best choice.

However, if you know the final output will be printed offset, either standard (analog) Offset, or Digital Offset, knowing how that press handles files, and what paper type will be used, is important to ensure consistent results. So if you know a file will print at a particular printer, find out all the info you can:

1. Do they have their own printer profiles?
2. if not, which profile do they recommend based on the paper to be used?

Once you have the info you need, just convert from RGB to the chosen CMYK. I would do this yourself to identify if there will be any problems due to out of gamut RGB.

Knowing dot limit can prevent a lot of headaches. Example: our standard offset had a total ink limit of 350 - very high. Our digital offset has a total ink limit of 290, so files prepared for our standard offset would lose detail in the shadows on the digital press if we didn't compensate. Compensation is done via color management.

1. Each press is profiled - we use a hybrid G7 process - and printer profiles are created for each paper type we use.

2. In Photoshop we convert to the printer profile for the press and paper that will be used so what we see is a very close approximation of what we expect will print.

4. For Standard offset, curves are also created for the printing plates to adjust dot size for best reproduction. This is also based on the press profile.

5. For the digital press the RIP is set up to convert by either device link or straight conversion based on that press's profile. Device link is used to maintain GCR for images with mostly black.

We also use GCR for the standard offset to maintain neutrality in B&W images, or color images with a lot of neutrals. Device link is not needed.
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  #17  
Old 03-07-2017, 06:40 PM
klev klev is offline
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Re: lower cyan without increasing magenta?

Quote:
Originally Posted by marameo View Post
I'd love to understand if being aware of Ink limit (Total Area Coverage) is part of a retoucher "best practise" or if this is just a subject that the prepress people must face.

What if the retoucher is being informed by the publication or the photographer that the Ink limit should be under 260?

Should the retoucher convert to a custom CMYK profile (GCR, Medium, 260%) and then assign a known working profile (swop)?
You typically know the required submission spec, and it will specify things like ink limits.

Something like a magazine would typically be around 300% - 350%. Why would you assign a working profile? The whole purpose of the profile is to constrain things during conversion. Assigning it after the fact doesn't do anything. The percentages are already defined. You might confuse someone, but it wouldn't change your numbers.
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  #18  
Old 03-07-2017, 06:53 PM
Sabrina81 Sabrina81 is online now
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Re: lower cyan without increasing magenta?

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Originally Posted by andrewrodney View Post
These two sets of RGB values have four different CMYK equivalents due to four different CMYK profiles; which is correct?
None are "correct." You and I have been around this track before, so let's just agree to disagree. I find the CMYK method useful. But it isn't a method to find "correct" skin tone values. So let's not thrash that straw man yet again.

In your Lab method, your rule is to keep the a and b values "numerically close, not more than 15 positive values." Is there a "correct" numerical difference? No, because it's a method that offers a rough guide to getting skin tones "correct." That's all that the CMYK method offers, no less and no more.

I find the CMYK method more useful than your Lab method. Others may find yours more useful. Try them both. Use what works best for you. But let's not go off into the weeds about "correct" values.
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  #19  
Old 03-07-2017, 06:56 PM
Sabrina81 Sabrina81 is online now
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Re: lower cyan without increasing magenta?

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Originally Posted by Shoku View Post
CMYK is device dependent, so for the average retoucher who is sending files back to a photographer, or to a marketing firm, not knowing where the final output may be, and in some cases multiple outputs, then color managed RGB is your best choice.
As I tried to point out earlier, the CMYK method for adjusting skin tones does not comvert the image to CMYK. It just uses CMYK values to get a rough idea which colors to adjust. It does not assume that the output will go to a CMYK printer. Rather, the assumption is that the image will remain in RGB.
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  #20  
Old 03-07-2017, 07:01 PM
Sabrina81 Sabrina81 is online now
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Re: lower cyan without increasing magenta?

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Originally Posted by Tony W View Post
CMYK changes are best reserved IMHO to deal directly with press variables and solving their specific problems.

RGB deals directly with our photographic variables and are usually the best for such problems.
The Lee Varis CMYK method for adjusting skin tones does not involve converting an RGB image to CMYK. The image remains in RGB. A sample point is set to read out CMYK values, which are used as a rough reference guide to determine which colors to adjust.
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