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Andrew Ko

What is Color Separation? - "Once Upon a Time in Hollywood"

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In the latest edition of American Cinematographer, colorist Yvan Lucas says that the amazing saturation achieved in Tarantino's latest film "Once Upon a Time in Hollywood" comes: "partly from the print stock, 2383. Kodak came out with it about 20 years ago. This film print is very colorful, and the primary colors are really separated and very pronounced. It's almost astounding. You get true red, green, and blue - and Quentin told me 'When I see those colors, that's when I know it's film.'"

My question is, what exactly is meant by "separation" on a technical level? Is this not possible on digital? What qualities would this film stock have that simply shooting with 4:4:4 or 4:2:2 video wouldn't be able to achieve? I've also felt that color is what separated film from digital, but I can't seem to understand why.

Does anyone have any insight into this? Would be very much appreciated!

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Modern digital cameras often do not see saturated colour very clearly, and there isn't a very good solution to it.

The problem is that, instinctively, one would assume that the RGB filters on a Bayer-patterned sensor would be bright, saturated, primary colours. They're not. Often they're pretty desaturated, which helps with sensitivity (by not filtering out too much light). It also helps with sharpness, because the RGB images from the Bayer sensor are not as different as we'd expect; it's easier to infer where sharp edges are in the image since all of the pixels can see most of them.

The result is a picture with rather reduced saturation. This can be corrected with what a specialist might generally call "matrixing," but which basically means "winding the saturation up." This works to a degree, but subtle distinctions between colours can be reduced; for instance, a lot of Bayer cameras can have trouble telling purple from blue, and it can introduce chroma noise if people try too hard to tease out the colorimetry.

There are a lot of caveats to all of this. Higher end cameras are more likely to use more saturated filters, accept the sensitivity and sharpness hit, and achieve better colorimetry as a result. An Alexa is not a great example because it's far from the latest technology, but it was never a design which targeted massive sharpness or huge sensitivity. It does, though, have a nice colour response. Also, the human eye works very much in the same way; it does have red, green and blue-sensitive cells, perhaps better described as long-wavelength, medium-wavelength and short-wavelength because they have a very broad sensitivity that overlaps a lot, much like a camera sensor.

I don't know if what you're describing is caused by all this, but it's likely it has at least some impact.

P

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Posted (edited)
2 hours ago, Phil Rhodes said:

Modern digital cameras often do not see saturated colour very clearly, and there isn't a very good solution to it.

The problem is that, instinctively, one would assume that the RGB filters on a Bayer-patterned sensor would be bright, saturated, primary colours. They're not. Often they're pretty desaturated, which helps with sensitivity (by not filtering out too much light). It also helps with sharpness, because the RGB images from the Bayer sensor are not as different as we'd expect; it's easier to infer where sharp edges are in the image since all of the pixels can see most of them.

The result is a picture with rather reduced saturation. This can be corrected with what a specialist might generally call "matrixing," but which basically means "winding the saturation up." This works to a degree, but subtle distinctions between colours can be reduced; for instance, a lot of Bayer cameras can have trouble telling purple from blue, and it can introduce chroma noise if people try too hard to tease out the colorimetry.

There are a lot of caveats to all of this. Higher end cameras are more likely to use more saturated filters, accept the sensitivity and sharpness hit, and achieve better colorimetry as a result. An Alexa is not a great example because it's far from the latest technology, but it was never a design which targeted massive sharpness or huge sensitivity. It does, though, have a nice colour response. Also, the human eye works very much in the same way; it does have red, green and blue-sensitive cells, perhaps better described as long-wavelength, medium-wavelength and short-wavelength because they have a very broad sensitivity that overlaps a lot, much like a camera sensor.

I don't know if what you're describing is caused by all this, but it's likely it has at least some impact.

P

Wow! A very interesting answer, one that I've never heard before as far as the digital debate goes. Thank you for taking the time to write this, it certainly seems like insight with a deeper understanding of the systems at play.

P.S. How do you even get to know this stuff?

Edited by Andrew Ko

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9 hours ago, Andrew Ko said:

In the latest edition of American Cinematographer, colorist Yvan Lucas says that the amazing saturation achieved in Tarantino's latest film "Once Upon a Time in Hollywood" comes: "partly from the print stock, 2383. Kodak came out with it about 20 years ago. This film print is very colorful, and the primary colors are really separated and very pronounced. It's almost astounding. You get true red, green, and blue - and Quentin told me 'When I see those colors, that's when I know it's film.'"

My question is, what exactly is meant by "separation" on a technical level? Is this not possible on digital? What qualities would this film stock have that simply shooting with 4:4:4 or 4:2:2 video wouldn't be able to achieve? I've also felt that color is what separated film from digital, but I can't seem to understand why.

Does anyone have any insight into this? Would be very much appreciated!

I really suspect this is a bit of marketing BS.  2383 and vision camera original stocks to handle some colors "better" than digital workflows, but also handle some colors much worse.  Film has it's own "look", yes, but "color separation"?  I'm not sure this is really one of them...

It's been my observation that film tends to force near flesh tones towards a "standard" flesh tone, removing variations of skin tones in a "pleasing" way.  And this seems the opposite of "color separation".  One of the first things I notice about a digital capture, vs a film capture is that the digital image shows more distinctly colored reflections/variations in the skin tones that don't usually present themselves as strongly on film.

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8 hours ago, Bruce Greene said:

I really suspect this is a bit of marketing BS.  2383 and vision camera original stocks to handle some colors "better" than digital workflows, but also handle some colors much worse.  Film has it's own "look", yes, but "color separation"?  I'm not sure this is really one of them...

It's been my observation that film tends to force near flesh tones towards a "standard" flesh tone, removing variations of skin tones in a "pleasing" way.  And this seems the opposite of "color separation".  One of the first things I notice about a digital capture, vs a film capture is that the digital image shows more distinctly colored reflections/variations in the skin tones that don't usually present themselves as strongly on film.

I see, interesting. They did mention in the article a lot of bout skin tones in reference to film and digital, something about "letting it go red," but I forget the details. Thanks for your insight!

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I think color is slowly getting better on digital. The color I see from Panasonic's S series cameras is the best Ive seen from digital yet. Very pure clean color. That said film has its own look.

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I once graded film to match digital and paid special attention to vectorscope peaks.

Even when the chroma and saturation matched, the digital vectorscope had a more diffuse point cloud, as if blur had been applied to the image. (It hadn't.)

Subjectively, the film looked more saturated to me.

This is just one camera and one film stock and one person's experience. But I noticed... something.

2383 is a print stock, for which there are emulation LUTs. Never had the fortune to finish on film (well, except when I shot reversal) so I can't speak to how saturated it is or isn't compared with scanned film, an emulation LUT, and digital projection. Guessing the real thing looks better still, but I do post digitally so I may never know.

There are other differences, too. Reversal/digital vs color negative film. Look up the "Linny LUT" for an interesting take on that.

The spectral acceptance curves for some very saturated films (Velvia, etc.) are quite narrow compared with what I believe a Bayer pattern filter achieves. The "trichromatic" digital medium format back is similar in this regard, though the marketing is misleading and there is still a lot of overlap between filter acceptance curves despite what they imply. Regardless, look at images from it and compare with the standard back. The "colorspace" etc. is all the same. Just different dyes in the Bayer pattern and a slightly slower (ISO) sensor as a result.

Could you just grade one to match the other with a LUT? I couldn't say.

I've read a lot of information indicating a lot of contradictory things about this topic. I think you just need to trust your eyes. I think another part of it is that everyone is drawn to video or film for a different reason. If you like shooting in one format or another, embrace it, I guess. Or maybe not. I thought Michael Mann's style or Fincher's in Zodiac would be the future of digital cinematography, but instead the Alexa and a "film look" seems more popular now..

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DCI tried to match the colors of Vision print stock when developing the standards for theatrical digital projection, but perhaps one fundamental issue beyond film vs digital is color reproduction using additive or subtractive display technology.

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Not a very technical answer and a completely different stock, but I can tell you recently seeing 16mm Ektachrome projected made my jaw drop in the color rendition. It was more than just slightly more saturated...it had colors that I just didn't see after working with scanned film for years.

And don't get me started on 16mm Kodachrome...that was another world projected. 

I've made prints from Vision stocks look great but never seem to have that overwhelming beauty that reversal stocks give me when projected. I realize this is due to the higher contrast and color saturation but it is something everyone should see while they can.

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On 9/4/2019 at 3:41 PM, M Joel W said:

I once graded film to match digital and paid special attention to vectorscope peaks.

Even when the chroma and saturation matched, the digital vectorscope had a more diffuse point cloud, as if blur had been applied to the image. (It hadn't.)

Subjectively, the film looked more saturated to me.

This is just one camera and one film stock and one person's experience. But I noticed... something.

2383 is a print stock, for which there are emulation LUTs. Never had the fortune to finish on film (well, except when I shot reversal) so I can't speak to how saturated it is or isn't compared with scanned film, an emulation LUT, and digital projection. Guessing the real thing looks better still, but I do post digitally so I may never know.

There are other differences, too. Reversal/digital vs color negative film. Look up the "Linny LUT" for an interesting take on that.

The spectral acceptance curves for some very saturated films (Velvia, etc.) are quite narrow compared with what I believe a Bayer pattern filter achieves. The "trichromatic" digital medium format back is similar in this regard, though the marketing is misleading and there is still a lot of overlap between filter acceptance curves despite what they imply. Regardless, look at images from it and compare with the standard back. The "colorspace" etc. is all the same. Just different dyes in the Bayer pattern and a slightly slower (ISO) sensor as a result.

Could you just grade one to match the other with a LUT? I couldn't say.

I've read a lot of information indicating a lot of contradictory things about this topic. I think you just need to trust your eyes. I think another part of it is that everyone is drawn to video or film for a different reason. If you like shooting in one format or another, embrace it, I guess. Or maybe not. I thought Michael Mann's style or Fincher's in Zodiac would be the future of digital cinematography, but instead the Alexa and a "film look" seems more popular now..

Very interesting observation. The idea of the digital vectorscope having a more diffuse point cloud somehow rings true for me thinking about a certain flatness to digital compared to film that I notice.

Thank you for your response, and everyone else as well.

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