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Photo Retouching "Improving" photos, post-production, correction, etc.

Skin Tone color corrections, CYMK or RGB?

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  #11  
Old 02-16-2005, 12:07 AM
charlotte charlotte is offline
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Skin tones and adjusting them . Sometimes I wonder if I will ever master it. I have no understanding of where to start. Usually I just use levels. But I know there are other ways and that you can watch the numbers in the info but I have no clue about all that. Would love to see more info on this topic . Maybe even a long ,slowwww, : ) in depth tutorial for us over 40 brains . I appreciate the info so far .Will read and reread it many many times . : /
Charlotte
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  #12  
Old 02-16-2005, 02:14 AM
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v.bampton v.bampton is offline
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Ok, nice and easy...

If you're working on a decently exposed image, then you shouldn't have a problem. Find the blackest point in the image (that's supposed to be black), and watch the info pallette as you adjust. Move the end point of your levels or curves individual channels that black point reads a neutral number, (ie. R5, G5, B5). The move to the highlights, find the lightest point that's supposed to be white (not a specular highlight) and make it, say R245, G245, B245. If you haven't got a true white and black point in the image then it's a bit more complicated, so practise on ones that do.

Once you've got a neutral white and black point, you're mostly corrected. See if there is anything else that's supposed to be a neutral midtone - maybe some ones suit, or church stonework. Beware that if the point you pick isn't actually supposed to be neutral, then your midtone colours will be thrown off. Again you're trying to get a neutral - where your R, G, and B number are all about the same.

Once your image looks (and is by the numbers) neutral, you can adjust for taste. I tend to add an additional adjustment layer on top for my personal adjustments, leaving the neutral adjustments as they are. That way if I don't like my adjustments I can always go back to neutral without having to start again.

I tend to add red and yellow to the highlights and midtones. Something like R 0, 1.05, 250, 0, 255. G 0, 1.0, 255, 0, 255. B 0, 0.93, 255, 0, 250. It's not exactly neutral, but adds a nice warm glow to the skin which for portraits is ideal.

Hope that helps a bit.
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  #13  
Old 02-20-2005, 09:38 AM
john_opitz john_opitz is offline
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If you want to go back and forth, from rgb to cmy and back to rgb again for editing. Try this profile. You can go back and forth with no/min. loss in gamut.
Caution: this profile is not for cmyk printing (output). This profile exceeds the TIL for printing.

Wide gamut cmyk profile
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  #14  
Old 02-21-2005, 12:31 AM
charlotte charlotte is offline
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Interesting v.bampton. Thanks for posting.
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  #15  
Old 03-07-2005, 08:04 AM
hpycmpr hpycmpr is offline
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Good thread

This is a great thread since it touches on a few topics I'm interested in. I'll try to respond separately on each topic to avoid confusion.

To provide some context to my posts, here's my PS experience so far. I've been teaching myself PS for two years, relying on books and tutorials. My favorite authors include Eismann, Haynes and Margulis. I rely heavily upon curves and by the numbers for my corrections, and not so much upon masks, painting, and channel mixing, all of which I'm now trying to get better at. So far I have been correcting my landscape photos from film scans, and now I'm beginning to correct portraits.
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  #16  
Old 03-07-2005, 08:13 AM
hpycmpr hpycmpr is offline
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More rgb than cmyk?

Quote:
Originally Posted by jayk2
Almost every tutorial and book says to edit skin tones using cymk and basically make sure the yellow reads 3-5% higher then Magenta. I work in Adobe RGB and wondering if that percentage rule applies only to CYMK? or can I apply that rule when using RGB?
With the exception of books by Eismann and Margulis, most of the books tend to teach correcting with rgb, skin tones or otherwise.

I almost use only rgb exclusively. One reason is my weakness in knowing how to mix channels, and another is the fear of losing data when changing modes between rgb and cmyk. Margulis goes into quite a bit of detail on channel mixing. I can follow his theory, but find it hard to put into practice without detailed tutorials.
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  #17  
Old 03-07-2005, 08:18 AM
hpycmpr hpycmpr is offline
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Mode conversion

Quote:
Originally Posted by Duv
I myself haven't a clue how to adjust skin tones using RGB. I've always converted to CMYK to do my skin correction and then back to RGB. There seems to be a lot more information on CMYK skin correction. Although I haven't noticed anything, I'm wondering if converting back and forth may introduce other subtle problems
I recall reading somewhere that the conversion to/from the LAB mode is lossless. Using LAB as an intermediate mode may be a solution. I haven't tried or tested this, so take this with a big grain of salt. <g>
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  #18  
Old 03-07-2005, 08:47 AM
hpycmpr hpycmpr is offline
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Curves

Quote:
Originally Posted by edgework
I do the same thing when I have to work in RGB. The rules are roughly similar, but keep in mind that Photoshop simulates the qualities of light in RGB, and ink on paper with CMYK. One significant difference is that in CMYK, applying a curve to any channel will affect both color and lightness in a very different way than with RGB. A rule of thumb is that you use the individual channel curves in RGB to adjust color, and you use the master curve to adjust contrast. Because Red, Green and Blue are all equal in intensity (equal values combine to produce dead neutral) the master curve can be used effectively to make lightness moves without altering the hue and saturation (although the lightness channel in lab mode is far more efficient). In CMYK, since cyan is such a crappy ink, it requires about 10% more than Magenta and Yellow to balance the other two and produce neutral. Using the master curve in CMYK is very dangerous, unless you are using it in luminosity mode.
Excellent points about the difference between rgb and cmyk. I also adjust individual curve channels first, and leave adjusting the composite at the end and only when necessary. Now that I'm beginning to correct portraits, it gives me motivation to try cmyk.
Quote:
Originally Posted by edgework
I was trained to use CURVES, and CURVES only, (and only in CMYK) since most of the other adjustment tools are more or less subsets of what curves are capable of doing. However, I've found that using selective color in the way previously mentioned, is a great quick fix. If, for example, a face has yellow highlights and hot red shadows, pulling magenta and adding yellow to the reds, and pulling yellow and adding magenta to the yellows brings the tones into balance, albeit a flat kind of balance.
Curves is my main tool. After that, I will use other tools to do whatever I cannot do with Curves.
Curves pros:
- They can do a whole lot of things.
- A steep portion of a curve boost contrast.
- I kind of feel like "knowing" what is being done to the pixels.

Curves cons:
- Needs patience.
- Steepening a portion of a curve flattens another (losing contrast). Can't have my cake and eat it too!
Quote:
Originally Posted by edgework
Another trick for skin (this is for CMYK corrections): I've never found a face that cannot be improved by making a contrast move to the magenta channel in luminosity mode. Flat skin tones are almost always the fault of the magenta plate, and even if the numbers are within a realistic range, the lack of contrast can make the skin appear too hot overall. Heightening the contrast in magenta, but keeping it in luminosity mode can open up detail in an instant, without messing up the color.
I'll definitely keep this in mind.
Quote:
Originally Posted by edgework
As for converting back and forth, the areas of RGB that extend beyond CMYK are far more extensive in the Greens and blues. The truth is, any colors in RGB that are outside the CMYK gamut aren't going to look all that appropriate in skin tones anyway--greens, blues, hot reds and day-glo oranges. If realism is the desired goal, moving into CMYK before correcting the color will weed out a lot of unrealistic tones. But if intensity and bright colors are the visual goal, and the target is RGB output, or the WEB, keep it in RGB.
Good point. For printing on a desktop inkjet, this may even be a less issue.
Quote:
Originally Posted by edgework
One problem with CMYK that is non-existent in RGB is ink density. Because there is a limit to the quantity of ink a press can handle without turning the result into mud, the CMY channels will usually flatten out to a single tone in the shadow range, shifting the detail information into the black plate. This can be a problem if you have shadows that carry a cast, either hot or cool. Moving an image into CMYK will usually turn the dark areas neutral, which will be a problem if the mood of the original art called for overall warmth or coolness. I often use selective color for these situations too, pulling cyan from black and adding magenta and yellow, or the other way around to cool them down. Pay attention to the darkest shadows as well as dark hair: it's easy for rich brunettes to become dingy blacks in the translation.
It took me a long time to figure out that the ink density is handled differently between a press printer (cmyk) and a desktop inkjet printer (rgb). On the inkjet, the ink density is NOT (solely?) controlled by rgb or cmyk values.
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  #19  
Old 03-07-2005, 09:10 AM
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Duv Duv is offline
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Quote:
Originally Posted by Duv
I myself haven't a clue how to adjust skin tones using RGB. I've always converted to CMYK to do my skin correction and then back to RGB. There seems to be a lot more information on CMYK skin correction. Although I haven't noticed anything, I'm wondering if converting back and forth may introduce other subtle problems. The tones you acheived are spot on. I never considered using Selective Colors to do my correction. I'll have to give it a try. Can I ask why you adjust yellow and red as opposed to magenta/yellow/cyan and black?

Cheers
Dave
Well now, don't I feel a bit silly quoting myself. I reread Eismann and realized I could have the best of both worlds.

Duplicate your RGB image
Convert to CMYK and make your adjustments
Drag it back onto the RGB layer and change blend to Color to bring back original RBG luminosity values

I've tried it quite a bit and it works like a charm.

Cheers

Dave
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  #20  
Old 03-07-2005, 09:13 AM
hpycmpr hpycmpr is offline
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Neutrals

Quote:
Originally Posted by v.bampton
Ok, nice and easy...

If you're working on a decently exposed image, then you shouldn't have a problem. Find the blackest point in the image (that's supposed to be black), and watch the info pallette as you adjust. Move the end point of your levels or curves individual channels that black point reads a neutral number, (ie. R5, G5, B5). The move to the highlights, find the lightest point that's supposed to be white (not a specular highlight) and make it, say R245, G245, B245. If you haven't got a true white and black point in the image then it's a bit more complicated, so practise on ones that do.

Once you've got a neutral white and black point, you're mostly corrected. See if there is anything else that's supposed to be a neutral midtone - maybe some ones suit, or church stonework. Beware that if the point you pick isn't actually supposed to be neutral, then your midtone colours will be thrown off. Again you're trying to get a neutral - where your R, G, and B number are all about the same.

Once your image looks (and is by the numbers) neutral, you can adjust for taste. I tend to add an additional adjustment layer on top for my personal adjustments, leaving the neutral adjustments as they are. That way if I don't like my adjustments I can always go back to neutral without having to start again.

I tend to add red and yellow to the highlights and midtones. Something like R 0, 1.05, 250, 0, 255. G 0, 1.0, 255, 0, 255. B 0, 0.93, 255, 0, 250. It's not exactly neutral, but adds a nice warm glow to the skin which for portraits is ideal.

Hope that helps a bit.
Correcting the neutrals is how I start with each image. An ideal image for this kind of correction is one with true neutrals at highlight, midtone and shadow. But as you pointed out, sometimes this is not as simple or even possible with some images. In order of difficulty, here are some examples:

Some images are shot in certain lighting conditions with a desireable color cast that should not be removed, such as landscape scenes at dusk or dawn. Whether these images have any true neutrals is irrelevant.

Some images do have true neutrals but they are difficult to identify, such as several statues with different shades of "gray" marble.

Some images do have true neutrals that are easy to identify, but are not at all three points of highlight, midtone and shadow.

An image shot in a studio under controlled lighting and the inclusion of a gray wedge will not have any of the above problems.
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