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How to apply Pantone skin tones

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  #91  
Old 02-23-2016, 02:51 PM
klev klev is offline
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Re: How to apply Pantone skin tones

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Originally Posted by marameo View Post
Is there more way to do it?

According to this video the channel mixer can be explained as this:

The output channel is red.

Green Slider: I drag it to the right it's going to put more red where the image has green. I drag it to the left it's going to put more cyan where the image has green.

Blue Slider: I drag it to the right it's going to put more red where the image has blue. I drag it to the left it's going to put more cyan where the image has blue.

Does it make sense?
That is consistent with my explanation. It makes more sense if you consider numbers rather than more green or less green.

If you have a pixel with value <80, 50, 90> and you apply channel mixer with the red channel set to 70%, 0%, 30% with no changes to green or blue channels, your new rgb coordinates should be approximately

< 0.7 * 80 + 0.3 * 90 , 50, 90>

This means a color adjustment applied to a given channel in channel mixer is

percentage_red * old_red + percentage_blue * old blue + percentage_green * old green.

If you apply adjustments to more than one channel using the same layer, each of those adjustments will use the old numbers to compute each new one.

I used this to make significant color adjustments at times. It's the same thing with CMYK. Your channels are different. You might use it there if you need to manually adjust black generation. It's not that uncommon to adjust black generation for a product shot on a white background with drop shadow. Sometimes that's an easy way to ensure the shadow has a neutral appearance, yet parts can be too light to otherwise include any black ink.

There are other ways to do the same thing, but I think this is often an expedient one once you build up some confidence with its behavior.

Last edited by klev; 02-24-2016 at 01:33 AM. Reason: clarification
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  #92  
Old 02-24-2016, 03:51 AM
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marameo marameo is offline
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Re: How to apply Pantone skin tones

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Originally Posted by klev View Post
You might use it there if you need to manually adjust black generation.
Would it help to set black generation curve to maximum to achieve better colour separation on the CMY channels?
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  #93  
Old 02-24-2016, 01:57 PM
klev klev is offline
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Re: How to apply Pantone skin tones

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Originally Posted by marameo View Post
Would it help to set black generation curve to maximum to achieve better colour separation on the CMY channels?
No. The black channel represents the use of black ink. Black ink is to ensure that darker colors don't look muddy or suffer from metamerism when printed on a 4 color press.

I'm not always sure what you're attempting, so sometimes it's difficult to provide a good answer on this stuff.
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  #94  
Old 02-24-2016, 01:57 PM
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marameo marameo is offline
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Re: How to apply Pantone skin tones

Anyway, back to my original post, I can now seem to at least match Pantone skin tones with Channel Mixer in CMYK mode far better then gradient maps or curves.
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  #95  
Old 02-24-2016, 02:03 PM
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Re: How to apply Pantone skin tones

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Originally Posted by klev View Post
No. The black channel represents the use of black ink. Black ink is to ensure that darker colors don't look muddy or suffer from metamerism when printed on a 4 color press.
OT but maybe worth mentioning. First, the alteration of that black will affect the other CMY colors. You can get an 'illustration' of this just using the old 'classic' CMYK engine in Photoshop. As you toggle the black gen, you'll see CMY affected too. Then never use that awful CMYK engine again.

Next, metamerism is a good thing! We'd never get two different devices to match without it. Metamerism is simple: two (2) samples with different spectra compared to each other with a given set of viewing conditions, produce a match. Metamerism only applies to two color patches when they are compared. It is not correct to refer to one color from a given ink or paper and say that it suffers from metamerism. A "meterameric pair of color patches" means that they appear to match under a given illuminate. However, they may not appear to match under another illuminate. Metamers ("metameric stimuli") by definition are two different spectrums that appear to be the same color. If they don't look the same color, they are not metamers.

If you are viewing a print (lots of colors) and within differing viewing conditions, and there is a mismatch, this could be called a metameric mismatch or metameric failure. But its not metamerism. One sample compared to itself in differing viewing conditions (the print), the proper term would be when they appear to match is color constancy and when they don't, color inconstancy.

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I'm not always sure what you're attempting, so sometimes it's difficult to provide a good answer on this stuff.
I completely agree!
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  #96  
Old 02-24-2016, 03:12 PM
klev klev is offline
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Re: How to apply Pantone skin tones

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Originally Posted by andrewrodney View Post
OT but maybe worth mentioning. First, the alteration of that black will affect the other CMY colors. You can get an 'illustration' of this just using the old 'classic' CMYK engine in Photoshop. As you toggle the black gen, you'll see CMY affected too. Then never use that awful CMYK engine again.
I prune my answers quite a bit for simplicity reasons. I find that if they're more complex they're likely to hide factual mistakes or technically correct but misleading information. I forgot about the old cmyk engine. I purchased a copy of photoshop around the start of cs6 and only used it a few times on other machines before that. This may have been before my time.

It's complicated to discuss colors, because they ultimately return to a reference to energy in watts/steradian or cone response as a physical metric. Both of those tend to be too far out of scope.


Quote:
Originally Posted by andrewrodney View Post
Next, metamerism is a good thing! We'd never get two different devices to match without it. Metamerism is simple: two (2) samples with different spectra compared to each other with a given set of viewing conditions, produce a match. Metamerism only applies to two color patches when they are compared. It is not correct to refer to one color from a given ink or paper and say that it suffers from metamerism. A "meterameric pair of color patches" means that they appear to match under a given illuminate. However, they may not appear to match under another illuminate. Metamers ("metameric stimuli") by definition are two different spectrums that appear to be the same color. If they don't look the same color, they are not metamers.

If you are viewing a print (lots of colors) and within differing viewing conditions, and there is a mismatch, this could be called a metameric mismatch or metameric failure. But its not metamerism. One sample compared to itself in differing viewing conditions (the print), the proper term would be when they appear to match is color constancy and when they don't, color inconstancy.
I don't use the term metamerism that often, so I forget that it's a misnomer. I wanted to point out that generation of "neutral" black ink doesn't have a precisely equivalent counterpart when you're referring to rgb.

Anyway it seems like he found a solution that makes him happy, which is good. I personally try to avoid solutions that involve a lot of conversion between color spaces, because I'll eventually turn up a number of limiting cases on that method.
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  #97  
Old 02-24-2016, 03:38 PM
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Re: How to apply Pantone skin tones

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Originally Posted by klev View Post
I forgot about the old cmyk engine. I purchased a copy of photoshop around the start of cs6 and only used it a few times on other machines before that. This may have been before my time.
The classic CMYK engine is worthless for creating CMYK conversions but it's still somewhat useful as a teaching tool; you can see the effect of CMY plus K by toggling the differing options. Black Gen, GCR/UCR etc. Point is, altering K does affect CMY which is what I think the OP was referring to.
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  #98  
Old 02-24-2016, 04:09 PM
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Re: How to apply Pantone skin tones

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Originally Posted by klev View Post
I personally try to avoid solutions that involve a lot of conversion between color spaces, because I'll eventually turn up a number of limiting cases on that method.
Well, so what does RGB give more then CMYK, as far as color correction is concerned at least? I understand the lower gamut issue. Yet, Channel Mixer seems more powerful in CMYK.
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  #99  
Old 02-24-2016, 04:42 PM
klev klev is offline
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Re: How to apply Pantone skin tones

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Originally Posted by andrewrodney View Post
The classic CMYK engine is worthless for creating CMYK conversions but it's still somewhat useful as a teaching tool; you can see the effect of CMY plus K by toggling the differing options. Black Gen, GCR/UCR etc. Point is, altering K does affect CMY which is what I think the OP was referring to.
I wasn't going to mention grey component replacement or undercolor removal (using expanded abbreviations for anyone unfamiliar with them). After conversion to cmyk, channel mixer can be applied to the black channel without affecting the others. If you used channel mixer on an image in an rgb color space, it would impact the values of cyan, magenta, and yellow generated during conversion. I don't think we're talking about anything outside of photoshop here.

Also I don't think he meant color separation in the typical pre-press sense here.

Also also if it did in fact change things back to cyan, magenta, and yellow, it would invalidate my prior example of a hack to avoid printing problems on product drop shadows.

Quote:
Originally Posted by marameo View Post
Well, so what does RGB give more then CMYK, as far as color correction is concerned at least? I understand the lower gamut issue. Yet, Channel Mixer seems more powerful in CMYK.
RGB has the advantage of being semi-generic, assuming you don't pick a bad profile (profiles act like constraints). It generates a smaller file, and it's generally easier to work with than cmyk. If you aren't careful you can introduce clipping when converting to cmyk, which I don't think you will notice right away. The inverse is also true but less likely. Some maroons and things can be described by certain ink combinations, yet aren't attainable in rgb. Ultimately your work is probably displayed in rgb. If you want to convert in between, you should look out for possible clipping on the conversion to cmyk and back to rgb. It can kill some of your detail in each case, which is why I suggest minimizing the number of unnecessary conversions. This won't happen in every image. It's just that sometimes values map out of range somewhere.

You haven't given any indication what you see as an advantage in cmyk, so it's hard to comment. What makes channel mixer seem powerful there? I've used it in both cases, and I still don't know your reasoning. I use it, because it's one of the easier ways to preserve local color differences when making significant alterations to the color of an object. In your case I haven't seen the way you use it, so it's difficult to comment.

Last edited by klev; 02-24-2016 at 04:52 PM.
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  #100  
Old 02-24-2016, 04:43 PM
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andrewrodney andrewrodney is offline
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Re: How to apply Pantone skin tones

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Originally Posted by marameo View Post
Well, so what does RGB give more then CMYK, as far as color correction is concerned at least? I understand the lower gamut issue. Yet, Channel Mixer seems more powerful in CMYK.
The ONLY reason to convert to CMYK is to send that document to some printing process that requires that exact recipe of CMYK! CMYK is an output color space.
RGB working space are Quasi-Device Independent. They are not based on any specific printed output device. They are based on theoretical display's. They are well behaved; when equal amounts of RG&B are provided, it's a neutral; always.

http://www.ppmag.com/reviews/200703_rodneycm.pdf
http://digitaldog.net/files/CMYKPart2.pdf
http://www.retouchpro.com/index.php?page=arrentals2
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