Skin Tones (Sub Surface Scattering)
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Axel Gimenez
Skin Tones, rightly so, is a number one topic of discussion. But searching the forums, I haven't found a topic that discusses this aspect of skin tones. Did I just miss it?
For those that don't know, subsurface scattering is the phenomenon of light entering an object, bouncing around, and then coming back out. So, for skin, you get the reflectance plus a subtle glow from the sub-surface scattering effect. If you want to get an extreme example of this, turn on the flashlight on your cell phone and stick your finger over it. The red glow of your finger is subsurface scattering. Question: Because cameras are getting so sensitive to light that we can get a "proper" exposure with almost no light in the scene, does this limit the energy of the light so that the amount of "glow" of the subsurface scattering is ineffectual thus rendering unnatural skin tones even though they may be "exposed" properly? Does this make sense to anyone? I'm asking because I've noticed in my own footage that sometimes I love my skin tones and other times I don't even though I "exposed" them the same, essentially. The big differences was the power of the light source on set. Thus, when metering is it important not just to see what the T-Stop and shutter angle are but also the lux or fc? I think this also flips for day-for-night scenes. You can get too much "glow" from someone's skin because they're being lit by the sun while your shooting the night scene, for example. As an aside, I wonder if computational photography found in the new phones will generate a lot of plastic-looking people as we start to see dark scenes that get corrected to look like daylight scenes. Anyway, I know - test! I will but I can't wait to hear an answer :) Thanks, Axel
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Jan Klier
Axel,
Interesting question. On the post side (with footage I didn’t shoot) I frequently get client input regarding the glow of the talent’s skin, especially in beauty work.
But more to the point of your premise, maybe it’s also a matter of our reference. It is often the case these days that we use less light on set because cameras allow us to get away with, enabling speed and budget cuts. Maybe because of past sets being heavily lit we may be used to a high amount of glow whereas more ambient sets will produce more average amount of glow. Maybe our reference is not entirely accurate or the natural state of affairs – but we’ve gotten used to it for such a long time?
Jan Klier DP/Colorist NYC
From: cml-mentor@... <cml-mentor@...> On Behalf Of axeltg@...
Question: Because cameras are getting so sensitive to light that we can get a "proper" exposure with almost no light in the scene, does this limit the energy of the light so that the amount of "glow" of the subsurface scattering is ineffectual thus rendering unnatural skin tones even though they may be "exposed" properly? Does this make sense to anyone? ._,_
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Axel Gimenez
Hi Jan,
Thanks for your reply. I find it super interesting that you're getting clients who notice this as well. I think that confirms it :) Regarding reference, I'd think we're hard-wired for seeing humans under the sun, which a powerful light. So, naturally, a glow would be more present. Thus, I think it goes beyond just professionals who used powerful lights in the past. I'm thinking that understanding/measuring the intensity of the light, not just the exposure is an important thing we need to think about now but didn't in the past because all there was were powerful lights. Best, Axel
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Jonathon Sendall
I know that in 3D skin creation subsurface scattering is super important in creating realistic skin colour and lighting. In real life I would imagine the scattering is essentially a filter, the skin
filtering the light bouncing back out. What those values are though I'm not sure but I'm guessing someone here who has better knowledge of the filtered values and differences between skin emitters in 3D might reflect the reality in live shooting, especially of people of different skin tones and reflectance values, specular highlights and so on. Jonathon Sendall DP, London UK
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Mitch Gross
This has always been a huge issue to me, because it is one where I find different imaging devices and differ light sources react to it in various ways.
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LED lights with their non-continuous spectrums and their green/magenta spikes and troughs can appear to do a decent job on the surface of skin but then reveal blotches, veins and odd discolorations in the sun-surface scattering. The same goes for cameras with less-than-ideal CFAs and poor “color science” calculations (that term seems invented by RED, I always knew it as “colorimetry”). This is why it’s important to test using actual human beings with varying skin tones rather than just pointing at chip charts. In the end I can forgive so many color reproduction sins due to lighting and color timing conditions and choices, but bad skin rendition is just bad. BTW, Panasonic cinema cameras have great skin tone reproduction. :-) Mitch Gross Cinema Product Manager Panasonic System Solutions Company of North America New York
On Dec 16, 2019, at 9:56 AM, axeltg@... wrote:
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Axel Gimenez
Hi Mitch,
Thanks for this. I had a shoot last week where I used LEDs and in person, the subject looked fine but through the camera, he had red splotches all over his face. Very interesting. I just picked up a C-800 color meter and am excited to test various lights against the values I get from the sun and tungsten lights. On a side note, any chance I could test a Panasonic camera? :) I only have experience with ARRI Alexa Minis and RED. Wouldn't be until January. Best, Axel
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deanan@gmail.com
With all the makeup/foundation used on most shoots, subsurface scattering is mostly blocked. That combined with where the IR cut is on most camera systems. However, metamerism from foundation with spiky lightsources is something that needs more study. Deanan DaSilva Camera Development Consultant Playa del Rey, CA
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I’m glad to see this thread appear. I have always had an unfounded antipathy to florescent lights because I felt that even the corrected bulbs gave lousy skin tones. I finally heard that they have a high UV component and that while visible light reflects off the skin surface, UV penetrates and reflects off what is below the skin, giving a red-magenta cast, Mitch’s “sub-surface scattering.” Is this true?
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Merritt Mullen
You’d think the amount of subsurface scattering would be proportional to the amount of light hitting the skin so it wouldn’t matter if it was outdoors under the sun or at night under a streetlamp if you exposed the skin for the same brightness.
David Mullen, ASC Los Angeles
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Merritt Mullen
But more to the point of your premise, maybe it’s also a matter of our reference. It is often the case these days that we use less light on set because cameras allow us to get away with, enabling speed and budget cuts. Maybe because of past sets being heavily lit we may be used to a high amount of glow whereas more ambient sets will produce more average amount of glow. Maybe our reference is not entirely accurate or the natural state of affairs – but we’ve gotten used to it for such a long time?
Sign your message or it will probably bounce
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Merritt Mullen
Sorry for that post mistake I just made trying to quote the last post.
I was going to say again that surely this is relative to exposure, how much skin glows — if we are rating a camera at 3200 ASA in very low light and expose a face 1-stop over, surely it glows just as much as it would with a camera set to 100 ASA and exposed 1-stop over? I think today this issue is more aesthetic/stylistic — we tend to expose skin tones “down”, below key, for a more “realistic” effect, and for more mood. Anyone doing fashion photography knows the glamorized effect of overexposing skin tones... David Mullen, ASC Los Angeles
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Andy Jarosz
As someone who runs a practical effects shop that is fully geared up to produce photoreal silicone replicas of humans, does anyone see a value in the creation of a test "head" with accurately translucent flesh, for skintone testing? I want to be clear: it would be as expensive as it would be creepy. But it would provide an unchanging reference that people all over the world could use, unlike a real human. ---
On 12/16/2019 12:03 PM,
axeltg@... wrote:
Hi Mitch,
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https://cinematography.net/Skin%20Tungsten%20V%20LED.html
I’m not saying anything else about LED lights until the February tests 😊
From: cml-mentor@... <cml-mentor@...> On Behalf Of Mitch Gross
Sent: 16 December 2019 18:47 To: cml-mentor@... Subject: Re: [cml-mentor] Skin Tones (Sub Surface Scattering)
This has always been a huge issue to me, because it is one where I find different imaging devices and differ light sources react to it in various ways.
LED lights with their non-continuous spectrums and their green/magenta spikes and troughs can appear to do a decent job on the surface of skin but then reveal blotches, veins and odd discolorations in the sun-surface scattering. The same goes for cameras with less-than-ideal CFAs and poor “color science” calculations (that term seems invented by RED, I always knew it as “colorimetry”).
BTW, Panasonic cinema cameras have great skin tone reproduction. :-)
Mitch Gross Cinema Product Manager Panasonic System Solutions Company of North America New York
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Colin Elves
It’s not though because the wavelength of the light is also important - longer wavelengths penetrate into the skin deeper i.e. near infra red hits the blood vessels whereas blue light doesn’t.
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I suspect this is why you tend to get nicer results with tungsten, which produces a lot more long wavelength light, vs LEDs which often seem to struggle with producing the longer wavelengths. I noticed this on a shoot I did about a year ago where we lit everything with HMI except this one shot that had a litemat thrown in. The skin tones on that one shot were a nightmare. I’m hoping the newer LEDs with 5 or 7 different emitters will do a better job here. Colin Elves DP, Berlin
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Martyn James Bull
Well, this discussion is fantastic and of real value in everyday work. I’m also pleased to see it is grounded in facts coupled with experiences.
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Colin, do you have a link to the source for the image you supplied? It’s really great and I’d like to do further reading. Martyn J Bull Filmmaker Oxfordshire, UK
On 17 Dec 2019, at 09:13, Colin Elves <colin@...> wrote:
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Axel Gimenez
This is all fascinating. I've been shooting with LEDs recently at low-intensity levels. Thus, I thought the answer is to increase the intensity of the light to get the skin tones I'm looking for. But, if the wavelengths of light I need aren't there, then it wouldn't matter how intense the light was.
Then, to David's idea, perhaps intensity is not as important as I thought it was if you use a light that can represent all the important wavelengths. This is all so fascinating. Thanks for the graphic.
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Colin Elves
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Jonathan Gentry
A few thoughts on this study. So many factors to consider.
The effects of makeup on light reflection and penetration. Yellow, Red and NIR may penetrate deeper into the skin as compared to green, blue, but does that result in observable difference in reflection? How does skin complexion itself effect the depth of light penetration? I would think that very pale skin tones would allow deeper visibility while medium to darker complexions would not. In practical terms these interactions become so complex yet subtle that my mind goes back to the value of what looks good – is good.
Jonathan Gentry | Potomac Media DirDP, Washington D.C. Technical and Creative Services
From: <cml-mentor@...> on behalf of "Colin Elves via Cml.News" <colin=colinelves.com@...>
Here you go: https://link.springer.com/article/10.1007/s10103-017-2317-4
Colin Elves DP, Berlin
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Colin Elves
Yes, but it doesn’t make our lives any easier when there’s interactions between discontinuous sources and video camera CFAs. You want to know what you’re getting when you bring on a certain light.
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I suspect a large part of the much-maligned colour science of the Sony FS7 is down to problems it has with LEDs - it seems to perform well enough under sunlight and tungsten. And as Geoff’s video shows: different cameras react very differently to the same Led source but not to tungsten. I know the new Kinoflo units allow you to dial in the specific colour science of the camera you’re using (assuming it’s one of the ones they’ve built profiles for) so maybe that’s the way forward? Colin Elves Director of Photography Berlin
On 17 Dec 2019, at 18:14, Jonathan Gentry <jgentry@...> wrote:
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Jonathan Gentry
So regarding FS7 and skin tones vs Alexa…
I’ve seen that as ARRI Alexa math desaturating smoothing skin’s potential problem areas, where Sony A and FS series clearly show an LED’s various peaked response. Tungsten has a perfectly smooth response. Maybe there is more to it?
Results of this article were enlightening when it came to skin tone and lighting: https://nofilmschool.com/2017/04/2017-led-light-shootout
Jonathan Gentry | Potomac Media DirDP, Washington DC Technical and Creative Services Phone: 240.299.5460
From: <cml-mentor@...> on behalf of "Colin Elves via Cml.News" <colin=colinelves.com@...>
Yes, but it doesn’t make our lives any easier when there’s interactions between discontinuous sources and video camera CFAs. You want to know what you’re getting when you bring on a certain light.
I suspect a large part of the much-maligned colour science of the Sony FS7 is down to problems it has with LEDs - it seems to perform well enough under sunlight and tungsten.
And as Geoff’s video shows: different cameras react very differently to the same Led source but not to tungsten.
I know the new Kinoflo units allow you to dial in the specific colour science of the camera you’re using (assuming it’s one of the ones they’ve built profiles for) so maybe that’s the way forward? Colin Elves Director of Photography Berlin
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