Ursa Mini - true RAW histogram?

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Emilian Dechev

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Ursa Mini - true RAW histogram?

PostThu Apr 20, 2017 5:31 am

A topic about ISO matters in RAW.

Correct me if I am wrong, but as far as my knowledge goes, the ISO when shooting RAW is purely meta-data. That is because, no matter what ISO you set 200 or 1600 - the amount of light hitting the sensor is the SAME. Right? But the thing is, that the histogram is not the same!

Of course, the histogram is a function of the display, and the display shows that perceived difference in brightness. But then, how is the DP going to know, how each element of the scene is truly exposed?

Of course, light meter. But its not the same, sometimes you really need that histogram to give you an overview, to get the highlights and shadows just right.

So a technical question: is it possible for the Ursa Mini, to show a "true histogram" - one that measures the light hitting the sensor, no matter what is the ISO?

And another question: as we all know, the "native ISO" of the UM46 is ISO 800. Does that mean, that "ISO 800" is actually showing that "true histogram" I am talking about?
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roger.magnusson

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Re: Ursa Mini - true RAW histogram?

PostThu Apr 20, 2017 3:36 pm

The histogram is correct in all ISO settings as I understand it. Changing ISO in the Ursa Mini changes the latitude you have above and below middle grey. This post explains it well: viewtopic.php?f=2&t=51260#p297150

Also, the histogram is not comparable to a light meter, it's probably based on the sensor data after debayering.
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Emilian Dechev

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Re: Ursa Mini - true RAW histogram?

PostThu Apr 20, 2017 7:10 pm

Ah alright, so ISO in RAW is NOT just metadata?

And then, if all settings equal the same amount of DR, what is the purpose of shooting at the "native ISO" anyway?
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roger.magnusson

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Re: Ursa Mini - true RAW histogram?

PostThu Apr 20, 2017 7:34 pm

Yes, it's just metadata. Selecting different ISO:s in Resolve applies different curves that changes the number of usable stops below or above middle grey. Even if it's the same DR, it's still useful to be able to control where you want the most DR, in the highs or the lows.
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Emilian Dechev

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Re: Ursa Mini - true RAW histogram?

PostFri Apr 21, 2017 4:26 am

Alright then it is metadata. So there should be a way to get a "histogram" which is not affected by that metadata. It will be useful, when one want to expose the scene without bothering about the ISO at all.
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Dan Shay

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Re: Ursa Mini - true RAW histogram?

PostFri Apr 21, 2017 1:05 pm

Emilian Dechev wrote:A topic about ISO matters in RAW.

Correct me if I am wrong, but as far as my knowledge goes, the ISO when shooting RAW is purely meta-data. That is because, no matter what ISO you set 200 or 1600 - the amount of light hitting the sensor is the SAME. Right? But the thing is, that the histogram is not the same!


If you just switch ISOs the light hitting the sensor is the same. But each ISO requires a different amount of light. ISO 200 needs twice the amount of light as ISO 400, which needs twice ISO 800. There is no absolute setting for a histogram, you have to choose an ISO. Just like you have to choose an ISO for a light meter to get a f-stop.
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Emilian Dechev

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Re: Ursa Mini - true RAW histogram?

PostFri Apr 21, 2017 1:31 pm

Makes sense, thanks!
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Mihail Moskov

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Re: Ursa Mini - true RAW histogram?

PostFri Apr 21, 2017 8:22 pm

It is possible to have a raw histogram. Magic Lantern has one. It is mostly useful for ETTR shooting though, cause linear values aren't well suited for judging the tonal distribution (on a histogram). Also, Canon cameras change gain when ISO is changed, so ISO is not an exposure multiplier for post in that case.

You could also have one on a BM camera, but it would be of even more limited utility. The most useful exposure tools for raw shooting would probably be a digital spotmeter (likely the most useful -- and simple -- display exposure tool anyway) and a raw clipping zebra which indicates photosites saturated with light.

If you want to get fancy, then a false color extension which actually uses the raw values (instead of IRE levels/tone mapped values) could be invaluable. This would allow for differentiating tonal zones in the extreme highlights and shadows (an HDR friendly feature too), which are otherwise either clipped or highly compressed after tone mapping.
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Emilian Dechev

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Re: Ursa Mini - true RAW histogram?

PostFri Apr 21, 2017 10:17 pm

Alright I am getting more confused now ;)

Well the whole reason I was asking for the "RAW histogram" is that, when I shoot RAW, I can bring back 2 or 3 stops of highlights - this is information that was displayed as "clipped" at the histogram at the time of the shoot. But that is not the case with Prores. When I shoot Prores I should watch the histogram strictly, because if I over-expose, there is no way to bring it back.

In other words, I have a "true histogram" only in Prores.

When I switch to RAW and I look at the histogram, there is an "invisible range" still available for the highlights. Its like the RAW histogram should be extended to the right with 2 or 3 stops more. And I need to do a guesswork.

That leads me to another question. If the camera has "15 stops" , why I cant bring back highlights from Prores? Isnt the DR of a camera, the same, no matter the recording codec? I know Prores is 10-bit and RAW is 12-bit, but the DR of the sensor should be the same.
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Uli Plank

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Re: Ursa Mini - true RAW histogram?

PostSat Apr 22, 2017 6:38 am

Are you using ProRes in "Film" or "Video" mode? If I shoot ProRes "Film", I can recover nearly as much as in RAW, maybe half or two thirds of a stop less of dynamic range.

But 15 stops? That's marketing BS, just like with RED cameras. Maybe I'm too critical, but I'd say about 12-13 useable stops.

That's still as good as analog film, where Kodak themselves are claiming 12 stops in their white papers.
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Emilian Dechev

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Re: Ursa Mini - true RAW histogram?

PostSat Apr 22, 2017 10:52 am

I dont care if the stops of DR are 12 or 15. I just want to know, why I can recover highlights that were marked as "blown" in the histogram?

So I should expose "ETTR" and magically assume, that the histogram is wider than it seems and can go 2 more stops to the right ;)

Maybe it is a hardware limitation, because the histogram reads from the display, not the sensor data. Not sure how that goes...

About the test - yes the Prores was in "film".

The test is fairly simple. Just point the camera to a bright scene, which is clearly over-exposed. ISO 800, as in "native". Then I make 1 shot in RAW (film), then I make the same shot in Prores 422 (film).

Then in Premiere, I use the "lumetri color" effect. With the RAW shot, I can recover 2-3 stops. With the Prores shot, I can recover about 0.5 stops.

Well maybe it is a Premiere drawback, I should repeat the test with Davinci.
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John Brawley

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Re: Ursa Mini - true RAW histogram?

PostSat Apr 22, 2017 4:02 pm

In ProRes the DR is baked in. All the DR is there and it's up your skill as the colourist to bring that out.

In RAW, you're generally seeing a representation of an exposure, but you can slide the exposure tab around and it APPEARS to recover more DR, but it's going to be pretty much the same total DR you have with RAW.

RAW gives you a different workflow to get to the DR by rolling it off (default look) some to show you a "nice" image from the start that you can then "recover" more highlights and shadows into. It's basically showing you what VIDEO would do to that image in camera, BUT you can change your mind (and you should).

ProRes means you're forced to put ALL the DR into the one image, so they do it using a very flat boring looking LOG curve that you need to grade, but the preview gives you NO IDEA of how the image might look.

Maybe try shooting some tests for yourself ?

Show us your tests. For example, how do you know that it's "clearly" over exposed ?

I personally find histograms to be a pretty useless tool for judging exposure. They're very much a post / DSLR tool.

Zebras and False colour will show you what's happening much more accurately.

Also, ProRes 444 is 12 bit if you want all your DR in ProRes.

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Uli Plank

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Re: Ursa Mini - true RAW histogram?

PostSat Apr 22, 2017 4:44 pm

Just that!

But even ProRes 422 contains the full DR, it only has less discrete values to distribute your tonal values. It will be less robust in extreme grading, but the DR is still there.
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John Brawley

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Re: Ursa Mini - true RAW histogram?

PostSat Apr 22, 2017 4:47 pm

Uli Plank wrote:Just that!

But even ProRes 422 contains the full DR, it only has less discrete values to distribute your tonal values. It will be less robust in extreme grading, but the DR is still there.


Of course you're correct ! Even ProRes PR contains all the DR, it's just a LOT less robust once you try to grade with it.

For me, 12 bit is the BIGGEST advantage of these cameras, because 12 bits in ProRes (or RAW) means you have an amazing amount of power to grade and bend the look to your will. This is the real reason I believe these cameras perform so well. But bit depth is an often overlooked feature.

JB
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Uli Plank

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Re: Ursa Mini - true RAW histogram?

PostSat Apr 22, 2017 6:42 pm

So true.
We all need to keep in mind that bit depth is a multiplier, so 12 bit is not 20% more than 10, but 300%.

BTW, I just made a short test, since we have a beautiful sunset here right now. Set the zebra to 100% and tuned the iris for clipping in ProRes "Film" and in RAW, both at 800 ISO. They clip at exactly the same point.

Yes, the log curve get's adjusted slightly with different ISO, but clipping is still the same. So, if you want to expose to the right for "Film" mode, just use zebra. If you are filming in "Video" mode, it's a different story.
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Ursa Mini - true RAW histogram?

PostSat Apr 22, 2017 9:31 pm

Whether you are shooting 10bit or 12bit log, in Resolve both are unpacked to 16bit linear, per colour channel which is 48bits of 'sparse' data. Obviously beginning with the 12bit log rather than 10bit, you can accurately represent more values in the scene since you have 64x more RGB values, 2 to the power of 6.


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John Brawley

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Re: Ursa Mini - true RAW histogram?

PostSun Apr 23, 2017 3:49 am

Uli Plank wrote:So true.
We all need to keep in mind that bit depth is a multiplier, so 12 bit is not 20% more than 10, but 300%.

BTW, I just made a short test, since we have a beautiful sunset here right now. Set the zebra to 100% and tuned the iris for clipping in ProRes "Film" and in RAW, both at 800 ISO. They clip at exactly the same point.



Zebra's at 100% or False colour (red @ 100%) are the ways I like to expose. If I know what's clipping then everything else is easy.

Even better would be a second zebra for black clipping but False colour does that too.

JB
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Adam Silver

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Re: Ursa Mini - true RAW histogram?

PostSun Apr 23, 2017 7:37 am

John Brawley wrote:
Uli Plank wrote:So true.
We all need to keep in mind that bit depth is a multiplier, so 12 bit is not 20% more than 10, but 300%.

BTW, I just made a short test, since we have a beautiful sunset here right now. Set the zebra to 100% and tuned the iris for clipping in ProRes "Film" and in RAW, both at 800 ISO. They clip at exactly the same point.



Zebra's at 100% or False colour (red @ 100%) are the ways I like to expose. If I know what's clipping then everything else is easy.

Even better would be a second zebra for black clipping but False colour does that too.

JB


Hey John,

If I remember correctly, I believe you shoot mostly ProRes. Are you using ProRes in "Film" or "Video" mode? If you're using Film mode, are you also using a LUT to monitor while shooting?

Adam
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John Brawley

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Re: Ursa Mini - true RAW histogram?

PostSun Apr 23, 2017 3:31 pm

Adam Silver wrote:
Hey John,

If I remember correctly, I believe you shoot mostly ProRes. Are you using ProRes in "Film" or "Video" mode? If you're using Film mode, are you also using a LUT to monitor while shooting?

Adam



Most of my work is TV drama.

Most TV drama is shot 1920 ProRes.

Most of what I shoot is 1920 444 in film mode. I usually have a show LUT and that tends to be loaded into the Ursa and I tend to shoot and monitor with it on.

Jb
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Adam Silver

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Re: Ursa Mini - true RAW histogram?

PostSun Apr 23, 2017 6:16 pm

John Brawley wrote:
Adam Silver wrote:
Hey John,

If I remember correctly, I believe you shoot mostly ProRes. Are you using ProRes in "Film" or "Video" mode? If you're using Film mode, are you also using a LUT to monitor while shooting?

Adam



Most of my work is TV drama.

Most TV drama is shot 1920 ProRes.

Most of what I shoot is 1920 444 in film mode. I usually have a show LUT and that tends to be loaded into the Ursa and I tend to shoot and monitor with it on.

Jb


Thanks so much, John! :)

Adam


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