Any Dermatologists Here Who Can Address Skin Tone?

[TheUnblinkingEye]

Reading academic articles on skin tone the consensus seems to be that the color of humans is depends partly on the ratio of brownish black eumelanin and the reddish yellow pheomelanin.*

But are those accurate descriptions of the pigments? Does the pigment produced by the melanocytes have a consistent and invariable color or does the color range depending on genetics, biology, and health?

*The other main determinants of skin tone are usually listed as hemoglobin in capillaries and various reflective effects of the skin layers.

 

[The Ghost of Caravaggio]

Skin tone can be affected by the sensor IR filter characteristics.

The sensor IR filter's spectral transmittance properties dominates how skin IR affects skin tone. There are other several variables.

• Lens IR hot spots
• Temperature of tendons and muscles just below the skin. I often saw this on sports photo gigs (Nikon D300) where the knees of people finishing a 10K amateur race would render various shades of red I didn't see with my eyes. I assumed the red knees did not bode well for future knee health.
• Blood flow differences between skin regions - how close the vessels are to the skin, the flow rate and the blood vessel density.
• Environment temperature
• How the subject is lit.

As I am not a dermatologist, I don't know if the eumelaninheomelanin ratio affects IR transmission from the body through the skin.

During the 2007 Leica M8 IR filter debacle there were examples of IR contamination in portraits due to blood flow near the facial skin surfaces.

A strong lens IR filter would eliminate IR contamination as a variable in skin tone.
_____________________
“…the mathematical rules of probability theory are not merely rules for calculating frequencies of random variables; they are also the unique consistent rules for conducting inference (i.e., plausible reasoning)”
E.T Jaynes, Probability Theory: The Logic of Science

 

[Bernard Delley]

this is photographic science: some of us color geeks own and can handle a reflectance photo-spectrometer like XRite Studio1 .

It would be interesting to see some examples of skin reflectance spectra.

I will have a go once i find time for this. Not to be forgotten, but far back in my queue.

 

[Mark S Abeln]

Reading academic articles on skin tone the consensus seems to be that the color of humans is depends partly on the ratio of brownish black eumelanin and the reddish yellow pheomelanin.*

As I understand it, there is brown eumelanin—a dark yellow, actually—and black eumelanin, which is colorless, as well as the reddish pheomelanin. Apparently there are other melanins, but they aren't in the skin and hair.

But are those accurate descriptions of the pigments? Does the pigment produced by the melanocytes have a consistent and invariable color or does the color range depending on genetics, biology, and health?

Good question, but I hadn't read anything about varying chemical compositions of these. Most importantly, the basic coloring in all humans can be accurately described by different quantities of these three, along with the other basic factors listed below.

*The other main determinants of skin tone are usually listed as hemoglobin in capillaries and various reflective effects of the skin layers.

Based on reading I did some years ago, here are the main factors that go into skin color:

• The base connective tissue, which is slightly bluish pink. This contributes to the skin coloring of the very palest individuals, including albinism, where melanins are absent.
• Blood, which usually gives a red hue due to the capillaries near the skin surface; this can be variable — less in the cold or during fright, and prominent during exercise. Anemia can change blood color, giving pale individuals an ashen appearance.
• Pheomelanin is reddish in color and is the main component in the coloring of redheads. It is found in larger quantities in most females, and is found in greater concentration in the lips, nipples, and sex organs.
• Brown eumelanin — a dark yellow color, actually —leads to blonde hair and yellow and olive skin. When coupled with pheomelanin, it gives brown hair.
• Black eumelanin which is colorless and is present in dark skin and in black and grey hair.
• Eumelanins are typically found in lesser quantities in females than in males.
• The relative proportions of the melanins changes with age, and may be blotchy, enhanced due to sun exposure. Some diseases may also change skin color beyond the normal range determined by the factors listed above, making nontypical skin color a good indicator of illness.

[Source]

Healthy human skin and hair color only appear within a 30-40 degree angle of the HSB hue circle, and this same range is often found in ripened fruit. Human vision tends to be very sensitive to changes in hue here, thanks to the strong overlap and fast rate of change in sensitivity with light frequency of the L and M cones in the eye in that region.

Photographically, the main factors in getting good skin color is to first have a neutral white balance, and then avoiding blowing or plugging each of the three color channels.

--
http://therefractedlight.blogspot.com

 

[Tristimulus]

this is photographic science: some of us color geeks own and can handle a reflectance photo-spectrometer like XRite Studio1 .

It would be interesting to see some examples of skin reflectance spectra.

Skin tones vary all around the globe.

My skin vary from ordinary to pale (sick), motteled (after beeing outdoors in harsh weather), spotted (after beeing outdoors in -30 C), and reddish (sunburnt), and so on.

Guess different skin tones of others vary a lot like my skin tone does.Yes - it would be interesting to see some examples of skin reflectance spectra (preferably without makeup for a shooting session).

I will have a go once i find time for this. Not to be forgotten, but far back in my queue.

 

[D Cox]

The background colour comes of course from haemoglobin in the red blood cells. This is bright saturated red when freshly oxidized, and a darker red when it's lost its oxygen and is travelling through the veins to the lungs to get more.

Fine white fibres or particles over a dark background scatter blue light (the Tyndall effect). This shows up most where the fibres lie over veins, which contain darker blood. The blueish colour of veins comes partly from the Tyndall effect and to a smaller extent from visual colour contrast of the blueish against the pink.

Haem is a pigment that contains Iron, and its spectrum is similar to those of Iron-based artists' pigment such as Venetian Red or Indian Red. A thin layer of white pigment over these reds can simulate the Tyndall effect in skin.

The melanin in skin is near the surface (where it needs to be to block UV light), and as people have already said, varies in concentration.

The colours of skin are quite easily simulated by a trained painter, especially by using oil paints. A visit to a national gallery that contains plenty of paintings from around 1500 to 1830 will show you good examples.

Skin colours are not easily simulated by three-primary photographic and printing technology.

Don Cox

 

[JimKasson]

It would be interesting to see some examples of skin reflectance spectra.

These are all from me:









--

the last word the last word - Photography meets digital computer technology. Photography wins -- most of the time.

Photography meets digital computer technology. Photography wins -- most of the time.

blog.kasson.com

 

[Sympa]

It seems hue actually is not that different between skin types, at least when color grading. See Captain Disillusion's great video on color. The vectorscope part starts here:

Great video to watch right from the start, btw.

 

[cameronrad]

Could probably find some good information about this stuff in the 3D/VFX/CGI community. Subsurface scattering is something that comes to mind.

• http://graphics.ucsd.edu/~henrik/papers/skin_bssrdf/skin_bssrdf.pdf
• https://developer.nvidia.com/gpugem...-advanced-techniques-realistic-real-time-skin
• https://vcg.seas.harvard.edu/public...ng-a-measurement-based-skin-reflectance-model
• https://eprints.whiterose.ac.uk/163976/1/v39i4pp075_089.pdf
• https://vgl.ict.usc.edu/research_FC.php
• https://renderman.pixar.com/louise

 

[D Cox]

Good spectrum curves. I have a couple from way back, but yours are better.

Those bumpy curves are just asking for metameric failure. You could perhaps make a curve of the spectrum of an area of skin in a colour print, and compare that to the curve of the real skin area.

Don

 

[JimKasson]

Good spectrum curves. I have a couple from way back, but yours are better.

Those bumpy curves are just asking for metameric failure. You could perhaps make a curve of the spectrum of an area of skin in a colour print, and compare that to the curve of the real skin area.

In general, process color spectra are going to be wildly different from object spectra, even if the colors are perfectly matched.

 

[D Cox]

Good spectrum curves. I have a couple from way back, but yours are better.

Those bumpy curves are just asking for metameric failure. You could perhaps make a curve of the spectrum of an area of skin in a colour print, and compare that to the curve of the real skin area.

In general, process color spectra are going to be wildly different from object spectra, even if the colors are perfectly matched.

Perfectly matched for one observer under a specified light.

Don

 

[JimKasson]

Good spectrum curves. I have a couple from way back, but yours are better.

Those bumpy curves are just asking for metameric failure. You could perhaps make a curve of the spectrum of an area of skin in a colour print, and compare that to the curve of the real skin area.

In general, process color spectra are going to be wildly different from object spectra, even if the colors are perfectly matched.

Perfectly matched for one observer under a specified light.

Don

If you’re arguing that we should have spectral reproduction, I don’t disagree with you, but that’s not happening in my lifetime.

 

[Mark S Abeln]

In general, process color spectra are going to be wildly different from object spectra, even if the colors are perfectly matched.

Perfectly matched for one observer under a specified light.

If you’re arguing that we should have spectral reproduction, I don’t disagree with you, but that’s not happening in my lifetime.

Approximate spectral reproduction would be a great industrial research project.

 

[JimKasson]

In general, process color spectra are going to be wildly different from object spectra, even if the colors are perfectly matched.

Perfectly matched for one observer under a specified light.

If you’re arguing that we should have spectral reproduction, I don’t disagree with you, but that’s not happening in my lifetime.

Approximate spectral reproduction would be a great industrial research project.

I can think of several ways to do such a self-luminous display, but none of them have any commercial possibilities whatsoever.

However, mixing of basis function filtered light for each pixel seems like a display possibility, and a complicated filter wheel in front of a monochrome sensor might serve as a capture device.

 

[TheUnblinkingEye]

Thank you all. Great info.

 

[TheUnblinkingEye]

Epson sells a white ink cartridge, do you think it would be worth experimenting with overprinting a 1 or 2 percent layer of white on top of the skin layer to see if it would create the same effect?



"A thin layer of white pigment over these reds can simulate the Tyndall effect in skin."

Haem is a pigment that contains Iron, and its spectrum is similar to those of Iron-based artists' pigment such as Venetian Red or Indian Red. A thin layer of white pigment over these reds can simulate the Tyndall effect in skin.

The melanin in skin is near the surface (where it needs to be to block UV light), and as people have already said, varies in concentration.

The colours of skin are quite easily simulated by a trained painter, especially by using oil paints. A visit to a national gallery that contains plenty of paintings from around 1500 to 1830 will show you good examples.

Skin colours are not easily simulated by three-primary photographic and printing technology.

Don Cox

 

[D Cox]

Epson sells a white ink cartridge, do you think it would be worth experimenting with overprinting a 1 or 2 percent layer of white on top of the skin layer to see if it would create the same effect?

"A thin layer of white pigment over these reds can simulate the Tyndall effect in skin."

Worth trying if you have a suitable printer.

 

[xpatUSA]

Skin tone [in an image] can be affected by the sensor IR filter characteristics.

My understanding is that the wavelength of any IR radiated by skin is well above that detectable by:

1) a normal sensor with it's associated UV/IR blocking filter, say 450-650nm.

and even

2) silicon with it's upper limit of c. 1150nm.

On the other hand:

"The infra-red emissions from human skin at 27 °C lie within the wavelength range of 2–20 μm, and they peak around 10 μm."

https://mdpi-res.com/d_attachment/applsci/applsci-12-04302/article_deploy/applsci-12-04302.pdf

--
what you got is not what you saw ...

 

[JimKasson]

Skin tone [in an image] can be affected by the sensor IR filter characteristics.

My understanding is that the wavelength of any IR radiated by skin is well above that detectable by:

See the reflectance spectra I posted in this thread, showing strong reflectance in the very near IR.

1) a normal sensor with it's associated UV/IR blocking filter, say 450-650nm.

and even

2) silicon with it's upper limit of c. 1150nm.

On the other hand:

"The infra-red emissions from human skin at 27 °C lie within the wavelength range of 2–20 μm, and they peak around 10 μm."

https://mdpi-res.com/d_attachment/applsci/applsci-12-04302/article_deploy/applsci-12-04302.pdf