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Author Topic: Colour Vision  (Read 7906 times)
Chris_T
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« Reply #20 on: July 07, 2007, 08:42:54 AM »
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I should clarify that my working space is rgb and not cmyk. But I often check both the rgb as well as the cmyk values in the Info palette. My assumption is that they are "equivalent".

Learning from Margulis, I have become more used to the relative cmyk values for different skin tones. If there are better sources on this topic, I would be glad to look into them. I also find the k channel can be a good hint for skin tones, which I don't know of a way to extract from rgb.

The numbers often get me within the ballpark. The ultimate adjustments are based on what I see on the monitor and in prints.

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Why CMYK which is a device dependant color space, will produce vastly different values based on your color settings and isn't the color space you're sending the final numbers to? Makes no sense to me (and an on going debate on another fourm). LAB, OK, its device independent. RGB or CMYK based on the actual output device (or better, your own RGB working space), makes sense.
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Eric Myrvaagnes
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« Reply #21 on: July 07, 2007, 12:37:37 PM »
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I should clarify that my working space is rgb and not cmyk. But I often check both the rgb as well as the cmyk values in the Info palette. My assumption is that they are "equivalent".

Learning from Margulis, I have become more used to the relative cmyk values for different skin tones. If there are better sources on this topic, I would be glad to look into them. I also find the k channel can be a good hint for skin tones, which I don't know of a way to extract from rgb.

The numbers often get me within the ballpark. The ultimate adjustments are based on what I see on the monitor and in prints.
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OK, Chris, I guess I'll have to read Margulis!

Eric
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digitaldog
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« Reply #22 on: July 07, 2007, 12:44:28 PM »
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I should clarify that my working space is rgb and not cmyk. But I often check both the rgb as well as the cmyk values in the Info palette. My assumption is that they are "equivalent".

They are not! I think this idea of using a specific CMYK output color space based on something you're not printing to, to look at numbers is super silly. You can just as easily use the source color space upon which ALL other output color spaces will be based.

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The numbers often get me within the ballpark. The ultimate adjustments are based on what I see on the monitor and in prints.
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Leading me to wonder what Dan would say about this based on his dismissive attitude about display calibration or so many useful RGB working spaces (ProPhoto for one).

The discussion of using CMYK values for skin tones or other by the numbers operation is on going here:

[a href=\"http://dgrin.com/showthread.php?t=65450]http://dgrin.com/showthread.php?t=65450[/url]

Then there's the question of how this all falls apart in so many raw converters, where you want to do all the heavy lifting (color and tone corrections globally) that don't support nor should, CMYK.

Of course, in Dan's world, you don't use raw files, JPEGs are better. Yes, he said that.
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Andrew Rodney
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Mark D Segal
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« Reply #23 on: July 07, 2007, 10:48:26 PM »
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Learning from Margulis, I have become more used to the relative cmyk values for different skin tones. If there are better sources on this topic, I would be glad to look into them. I also find the k channel can be a good hint for skin tones, which I don't know of a way to extract from rgb.

The numbers often get me within the ballpark. The ultimate adjustments are based on what I see on the monitor and in prints.
[a href=\"index.php?act=findpost&pid=126983\"][{POST_SNAPBACK}][/a]

Check Ben Willmore's stuff - written up in his Adobe Photoshop CS Studio Techniques. The first thing he pointed out is the huge variability of skin tones. You can't lump them into simple ethnic categories. Come to a city like Toronto, spend 15 minutes on a downtown street people-watching and you'll see why. Ben recommended getting ahold of stock photo catalogue thumbnails from the internet or the catalogue CD, (some of which are free on request)) and download a huge number of thumbnails (don't need resolution for this) of people with various skin hues. That becomes your skin reference library. Then when you need to colour correct a particular individual's skin tone, find the closest memory match from your thumbnail library, measure its colour values (in RGB or Lab) and substitute those colours in Photoshop using the Color Range tool. Use ordinary RGB working spaces to do this. You don't even need to think about CMYK anything for this, unless you are outputting to a CMYK press and you want to double check that the numbers are in gamut.
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Mark D Segal (formerly MarkDS)
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Chris_T
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« Reply #24 on: July 08, 2007, 07:22:44 AM »
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They are not! I think this idea of using a specific CMYK output color space based on something you're not printing to, to look at numbers is super silly. You can just as easily use the source color space upon which ALL other output color spaces will be based.

Some colors' numbers are easier to remember in rgb, and some in cmyk. For example, neutral is r=g=b, and "brown" is r~=g and >b, etc. In the vast majority of skin tones, m shoud be <y, and c (and k) increases as the skin tones get darker, etc. [All from Margulis' book.] I therefore use rgb for some colors and cmyk for others, at least to get within the ballpark. Until I find a way to stay with only rgb, I guess I'll settle for being "silly".

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The discussion of using CMYK values for skin tones or other by the numbers operation is on going here:

http://dgrin.com/showthread.php?t=65450

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An interesting and lengthy thread. I'll find the skin tones discussion sometime. Thanks.
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Chris_T
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« Reply #25 on: July 08, 2007, 07:28:51 AM »
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Check Ben Willmore's stuff - written up in his Adobe Photoshop CS Studio Techniques. The first thing he pointed out is the huge variability of skin tones. You can't lump them into simple ethnic categories. Come to a city like Toronto, spend 15 minutes on a downtown street people-watching and you'll see why.

Agreed and understood. This is mentioned in books by Margulis and Eismann. As mentioned earlier, I use the numbers method to get within the ballpark.

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Ben recommended getting ahold of stock photo catalogue thumbnails from the internet or the catalogue CD, (some of which are free on request)) and download a huge number of thumbnails (don't need resolution for this) of people with various skin hues. That becomes your skin reference library. Then when you need to colour correct a particular individual's skin tone, find the closest memory match from your thumbnail library, measure its colour values (in RGB or Lab) and substitute those colours in Photoshop using the Color Range tool. Use ordinary RGB working spaces to do this. You don't even need to think about CMYK anything for this, unless you are outputting to a CMYK press and you want to double check that the numbers are in gamut.
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A good suggestion, thanks. There are also a couple of skin tone and hair color charts with numbers floating around online.
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Mark D Segal
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« Reply #26 on: July 08, 2007, 07:47:41 AM »
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Some colors' numbers are easier to remember in rgb, and some in cmyk. For example, neutral is r=g=b, and "brown" is r~=g and >b, etc. In the vast majority of skin tones, m shoud be <y, and c (and k) increases as the skin tones get darker, etc. [All from Margulis' book.] I therefore use rgb for some colors and cmyk for others, at least to get within the ballpark. Until I find a way to stay with only rgb, I guess I'll settle for being "silly".
An interesting and lengthy thread. I'll find the skin tones discussion sometime. Thanks.
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Chris, there is strong support for using CMYK as a metric but not as a working space when it comes to skin tones, because as Katrin Eismann explained, most of these color values are based on prepress experience. Katrin explains this on pages 124 to 127 of her Photoshop Restoration and Retouching Third Edition, where she also quotes an explanation from Dan Margulis, Applied Color THeory List, and provides a fair bit of her own detailed guidance.

Do check Ben Willmore's approach to skin tones. It's truly a practical and realistic way of going about such corrections when you'd prefer to depend less on estimating and numbers for translating those estimates.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
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« Reply #27 on: July 08, 2007, 08:03:42 AM »
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Hi Chris,

Looks like you were posting while I was writing! Seems we're on similar wave length.

Mark
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Mark D Segal (formerly MarkDS)
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Chris_T
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« Reply #28 on: July 08, 2007, 08:03:44 AM »
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There are several Margulis books. I must have read his Professional Photoshop 4th edition several times, but can only digest parts of it. It is not a book for everyone. Many do not like his writing style, including myself. There are no click by click tutorials. Some consider his opinions utter hogwash. I don't understand or follow everything he says, but find some of his writing and suggestions very valueable and not found elsewhere. Unlike the numerous PS authors who simply regurgitate the Adobe manuals or provide tutorials without explaining what is happening under the hood, Margulis stands out by himself. He takes the time to first identify and diagnose a problem before offering a solution. The short chapter on how to identify and evaluate an image's true neutral areas has saved me mucho time and effort. Worth the price of the book by itself.

Margulis may be opinionated, but people like him is just what we need at this stage of digital technology. A different voice in a world dominated by a single product and its supporters cannot hurt. BTW, he is the first inductee to the PS Hall of Fame.

http://www.photoshophalloffame.com/2001winners.html

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OK, Chris, I guess I'll have to read Margulis!

Eric
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« Last Edit: July 08, 2007, 08:09:37 AM by Chris_T » Logged
Chris_T
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« Reply #29 on: July 08, 2007, 08:15:33 AM »
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Do check Ben Willmore's approach to skin tones. It's truly a practical and realistic way of going about such corrections when you'd prefer to depend less on estimating and numbers for translating those estimates.
[a href=\"index.php?act=findpost&pid=127104\"][{POST_SNAPBACK}][/a]

OK, I'll check it out. Yes, we seem to be on the same wavelength on cmyk for skin tones.
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digitaldog
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« Reply #30 on: July 08, 2007, 10:05:48 AM »
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Ben recommended getting ahold of stock photo catalogue thumbnails from the internet or the catalogue CD, (some of which are free on request)) and download a huge number of thumbnails (don't need resolution for this) of people with various skin hues. That becomes your skin reference library.


Yup, an excellent idea, one I've suggested (although the bit about using the stock photo thumbnails is a good one). Having a visual reference (and possibility numeric reference depending on working space) is the way to go here, instead of using some arbitrary CMYK space that you're not using. After you yourself output files you like, you can begin to build your own skintone library. Learn to understand the numbers either in LAB which is a universal numbering system or your working space (which I think is more intuitive).
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Andrew Rodney
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« Reply #31 on: July 08, 2007, 01:09:15 PM »
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Read Andrew's linked dgrin thread-(where do you get the energy, Andrew?). Anyway my question concerns the posted image samples in that thread and the familiar appearance of overly neutralized or desaturated feel to the overall image giving a kind of charcoal underbase feel whenever images are edited in LAB or CMYK.

I've noticed this in the "after" images in some of Dan's channel mixing tutorials I've read in past issues of PEI magazine. I thought at first it was from CMYK press drift but when I saw it in the images in that thread, it confirmed my suspicions. Is this something inherent editing in those color spaces or is it user's taste in color?

I've actually experienced this odd color anomoly using LAB's selective hue/saturation using curves to push the gamut of intensely colored flowers. It looks correct but something is off. I've come to realize that neutralizing shadows and midtones is influenced greatly by surround color and WB color cast. For example shadows on beige color rocks often appear bluish viewed on a 6500K calibrated display even though the data reads R=G=B. This is because the sun casts a warm light on the opposite side. I wonder if this gets messed up when editing in LAB or CMYK.
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wesley
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« Reply #32 on: July 16, 2007, 04:16:01 AM »
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This may or may not be the space to fly this one, but it struck me some long time ago that with all the technical chat about systems, calibration, Photoshop tweaking and so forth, not a lot - nothing, in fact - seems to have been mentioned about the photographer/printer´s own colour vision.

This was always a huge stumbling block for workers in the wet darkroom; I can remember having a ´boss?´ at one time who had the problem of sussing out whether a cyan tinge was tending more to blue or towards green, whether either of these two, in fact, was one or the other and not cyan...
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If I may stir the discussion slightly off topic. There's a photographer in the Art & Commerce [a href=\"http://www.artandcommerce.com]http://www.artandcommerce.com[/url] agency in NY who is colorblind. His name is John Clang and his personal site is http://www.johnclang.com

His color tones are unique and interesting, I think it's largely due to his color blindness. Perhaps photographers who are color blind could use their personal color palette to their advantage and present a unique look to their work?

Best regards
Wesley
« Last Edit: July 16, 2007, 12:01:44 PM by wesley » Logged

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