Exposing + Native ISO

[Nick Morrison]

That said - I think we can squeeze that RANGE down a bit - make it more narrow. Right now - I'm gonna say Dragon it's between 800 and 950 - and again, in MOST situations - my preference will be to rate it at 640 - but I will wait until I get a new OLPF and then I will re-test EVERYTHING and I will tell you what the smallest RANGE I feel comfortable defining as "NATIVE ISO" - specifically for 4K finishing.

Good thread, huh

I love Reduser. I'm glad to be back.

This thread is sort of blowing my mind. I actually feel like I'm struggling to keep up at times, which I know is a good thing.

Mark, your ISO "range" for Dragon is really helpful. Thanks as always for your informative, well reasoned, and well written posts. Dragon is still wrapped in a veil of mystery, and your insight - and questions - are helping to lay down a much clearer floor of what we can expect to do, and need to be aware of, when we eventually start shooting with Dragon.

thx

 

[Nick Morrison]

I think the graph that Adrian posted - (ironically pulled from the Alexa website) - really helps people understand how the dynamic range shifts relative to 18% grey. And yeah ... it's a bit counter to think that you might want to increase your ISO when you go outside

WOW. I was actually thinking the same thing!!!! That ironically, it may be better to shoot at 320 iso at night...as so much if your usable "range" could be donated to blacks and shadows. And that in incredibly bright sunlight...maybe shooting at 2000 iso could donate more range to your highlights, especially if there are limited to no shadows in your shoot.

Counter-intuitive. But addictingly interesting.

 

[Scott Crawley]

I'm down with all of this... Except the bits part. The number of bits makes all of the difference. It is a huge part of the reason why Dragon footage is more pliable in post. (As long as you don't throw those bits away.) They are the reason why you can dig more out of those shadows with less noise. They are part of the reason why Evin's JPEG doesn't do justice to the print.

Edit

ISO value has been inherited from film realm to give a point of reference to cinematographers used to working with film. Using the similar methodology helps their accustomed workflow.

Experienced cinematographer is aware of effects and repercussions of "pushing" ISO. Shooters not familiar with same concepts may easily see it as just another setting unaware of the repercussions.

Red has chosen to cater different market segments where expectations and user experience greatly differ. Kowledgeable shooter knows exactly what ISO push does. Less experienced people can perceive ISO as "this setting gives me more light wih less lighting and with WYSIWYG it looks okay."

Mental process: "I increased the sensitivity, no biggie, NR is going to cover the cost"
Reality: sensitivity is the same, you just re-distributed the density to upper parts of the histogram, reducing it in lower parts and NR is covering just one part of the cost

And it may look okay right there until the material gets to a post room with controlled light conditons and image is shaped closer to desired outcome by manipulating contrast hue and saturation values, when shadows start to reveal goblins in a rave party and little Mary turns to a plastic puppet.

Underexposing a skintone for 2 stops may seem as "not a big deal" on a slider scale but many are not aware of (or are just taking too lightly) the fact that 2 stops difference is 4 times amount of light. In cases where particular camera issues like usable DR are debated there seems to be a lack of comprehension of exponential scaling which a human brain compensates by default to allow the perception of vast range of information which surrounds it. I have seen many examples proving that and attempts of digging out the detail from highly underexposed footage. Talking just about the relatively solvable noise issue with color quality and lack of data being disregarded.

No matter how much cleaner shadows are, and regardless of RAW or bits used or available DR, if partocular part of the image is greatly underexposed the usable data is not there, the well is not filled enough. Skintones turn to butterfly's wings, shadow work turns to shoveling gravel and post work is a mess.

OT side note: who noticed that Geoff is back?

 

[Mark L. Pederson]

WOW. I was actually thinking the same thing!!!! That ironically, it may be better to shoot at 320 iso at night...as so much if your usable "range" could be donated to blacks and shadows. And that in incredibly bright sunlight...maybe shooting at 2000 iso could donate more range to your highlights, especially if there are limited to no shadows in your shoot.

Counter-intuitive. But addictingly interesting.

Right - but remember - you still need the light hitting the sensor - so, if you rate your light meter at 320 - or the camera at 320 and look at the histogram and go outside at night and you got nothing - well ... you are not going to exploit those nice stops of DR. What it does do - is push you to get more light to the sensor to get to a workable stop. And I personally will forgo some DR on the top, since I have a LOT with Dragon - in favor of cleaner images. Again, depends on what you are shooting and what you want to achieve.

 

[D Fuller]

No. ISO is a technical, fixed value. Exposure is a creative choice. If you change your development ISO in Post it would be an intentional creative choice. One that you hopefully thought of in advance when you were on-set setting your scene referenced exposure. ISO tells you how to expose for an equal distribution of dynamic range both above and below middle-grey. Where you actually set your exposure defines what you find important in the scene.

Exposure has everything to do with ISO. How can you make a confident creative choice if you don't know the middle and limits of your exposure range (DR)?


Again, I highly recommend Ansel Adams' books on this subject. I have yet to come across a more elegant explanation of the technical and creative process than that which is found within the pages of his books.

One of the problems we struggle with constantly here is that terms get re-invented, and then don't necessarily have the same meaning for everybody. once upon a time, a film stock's ASA was written on the can, and the term ISO referred to the number you were using for exposure. It helped to clarify. It'd be great if we could somehow get the terms to differentiate those two things.

 

[Nick Morrison]

Right - but remember - you still need the light hitting the sensor - so, if you rate your light meter at 320 - or the camera at 320 and look at the histogram and go outside at night and you got nothing - well ... you are not going to exploit those nice stops of DR.

I love that you say that. Yes, I've learned from experience (and from these boards) that a digital sensor - even one as modern and hungry as Dragon - is not the Holy Grail and it still NEEDS LIGHT, it needs to CONSUME ENERGY OF SOME KIND, in order to properly perform. You need to FEED THE BEAST, FEED IT LIGHT (of some kind), otherwise it will go very hungry and spit out lots of noise and crap.

Even Dragon needs to be fed.

That being said, as you say, shifting your range DOWN to donate more DR to shadows (ie shooting at LOWER ISO) could be very useful in lowlight as you are catering your DR to your NEEDS. Your creative needs. Which in that moment is mostly about range in blacks.

Love this thread.

 

[Mark L. Pederson]

Love this thread.

What if I told you this whole thread was really just one big, huge practical joke ... and all you need to know is "ISO is JUST meta-data"

 

[Nick Morrison]

What if I told you this whole thread was really just one big, huge practical joke ... and all you need to know is "ISO is JUST meta-data"

I'd throw my laptop out the window and ask to take the BLUE PILL instead. Come on NEO! Don't tell me it's all fake!

 

[David Battistella]

David, just for clarity's sake I was using the TMax-100 story to illustrate that Red's use of ISO was more accurate than Kodaks. I have used ISO 800 on the MX as my base exposure for the entire time I had that sensor. The only time I intentionally reduced ISO was when shooting VFX plates and green screen that I knew would benefit from the cleaner shadows. Specifically though the rated 800 ISO on the MX has been totally accurate to my meters since day one. I never tested to see if this was the mid point of the DR, but then that never seemed to matter to those that insisted that it was a 320-500 ISO sensor even though that was definitely not the mid point of the DR, which would have been closer to EI 1600 for 6.5 stops even distribution.

Oh and I used about 10 rolls for testing, the 100 rolls was for the entire class

Thanks evin,

Maybe the point I was more trying to illustrate is that in both cases, Tmax or RED a reference ISO was provided as a starting point of where to place middle grey.

I get that there is a RANGE but I feel a reference sensitivity that balances many factors should be given by RED. Maybe it will be left for each user to "discover"? I don't know. All you guys have your cameras and I don't yet, I'm going off r3ds and my knowledge and experience with RED images to try to wade through some of this stuff.

The wait is killing me.

Battistella

 

[Mark L. Pederson]

I'd throw my laptop out the window and ask to take the BLUE PILL instead. Come on NEO! Don't tell me it's all fake!

Don't take the Blue Pill. It's all good Nick.

 

[Terry VerHaar]

One "rule" I try to follow - above all else - is that I try never to have either goal post lit up, if at all possible. This gives me a "thick" negative and I can always lose detail (push things into black) in post, if desired. I also get all the detail in the highlights. It seems safe to assume that none of the discussion in this thread would negate this approach; if I am capturing the entire dynamic range of the scene, nothing is lost. Right?

I guess the question that is on the table for me, then, is how the thoughtful use of the ISO (to put more levels of gradation above or below middle grey, as needed) will improve this approach. Stated another way, if you are capturing a 10-stop scene (complete DR coverage) will my "negative" be improved by "tweaking" the ISO to get middle grey in the "zone" where I want it? Or, is this discussion really all about those situations where you have to decide between clipping highlights or risking noise?

Again, thanks to all for this great educational discussion!

 

[David Battistella]

Semi quoting Zappa.

"The crux of the biscuit is light."


This is the other major thing, I think many people are using ISO as gain instead of as a basis for measuring light.

In video terms +3, +6, +9, +12 db, how much noise can you tolerate? Vs. how much picture you want to see?

So some of what is creeping in now is the merging of video and film. Traditional Film guys work in one way, video guys work in "boost and gain" to make a brighter picture. I think that this creates some real problems when ISO is viewed as gain.

Instead of reaching for the gain, people should be reaching for more lights, but video made it all a bit lazy.


Battistella

 

[D Fuller]

Well ... I am pretty sure that Kodak and Fuji took post processing into their ISO determination for film stocks.

You say "I want RED to determine that" - can you tell me, technically and subjectively, how you want them to "determine that"?

So ... RED picks a number - Phil picks a different number - and I pick a different number - they are all close - but all different.

Sounds like a RANGE to me.

But okay - since it's the manufacturer declaring it - it's "right" then?

I'm NOT saying RED should not just pick a number in the RANGE. But if you are gonna use that as your BASE ISO - then please enlighten me, and RED, how they should determine that number so that guys like me won't say - that's not the right number - the REAL number is XYZ Because THAT is exactly what is going to happen.

IMO - threads like this - and teaching people that "Native ISO" is really a RANGE not an exact number - is better for everyone.

But Adrian's comments and arguments are awesome and valid.

That said - I think we can squeeze that RANGE down a bit - make it more narrow. Right now - I'm gonna say Dragon it's between 800 and 950 - and again, in MOST situations - my preference will be to rate it at 640 - but I will wait until I get a new OLPF and then I will re-test EVERYTHING and I will tell you what the smallest RANGE I feel comfortable defining as "NATIVE ISO" - specifically for 4K finishing.


Good thread, huh

I love Reduser. I'm glad to be back.

Good to have you back. Reduser is a better place with you here.

The thing is, that we all pick our own number is really no different that it was with film. I considered Tri-X base 320, not the 400 on the box. And then I did other stuff with it if I wanted different characteristics. But It took a while to learn how to do that predictably. And it turned out it took a while to learn that essentially the same idea was at play in an r3d.

 

[Terry VerHaar]

One of the problems we struggle with constantly here is that terms get re-invented, and then don't necessarily have the same meaning for everybody. once upon a time, a film stock's ASA was written on the can, and the term ISO referred to the number you were using for exposure. It helped to clarify. It'd be great if we could somehow get the terms to differentiate those two things.

ASA = American Standards Association
ISO = International Standards Organization

Aren't ASA and ISO essentially the same thing? Just terminology changing over time based on the "ruling" body?

 

[Nick Morrison]

One "rule" I try to follow - above all else - is that I try never to have either goal post lit up, if at all possible. This gives me a "thick" negative and I can always lose detail (push things into black) in post, if desired. I also get all the detail in the highlights. It seems safe to assume that none of the discussion in this thread would negate this approach; if I am capturing the entire dynamic range of the scene, nothing is lost. Right?

Agreed, I do much the same. Though sometimes clipping a tiny bit is pretty hard to avoid.

 

[Nick Morrison]

Instead of reaching for the gain, people should be reaching for more lights, but video made it all a bit lazy.
Battistella

Well said. Yeah with video some fundamentals went out the window...

 

[David Battistella]

I guess the question that is on the table for me, then, is how the thoughtful use of the ISO (to put more levels of gradation above or below middle grey, as needed) will improve this approach. Stated another way, if you are capturing a 10-stop scene (complete DR coverage) will my "negative" be improved by "tweaking" the ISO to get middle grey in the "zone" where I want it? Or, is this discussion really all about those situations where you have to decide between clipping highlights or risking noise?

Again, thanks to all for this great educational discussion!

Not every composition has absolute black and absolute white. But every scene has a "feels right" zone. And tweaking the ISO means you are rating and affecting how much light is hitting the sensor for any given scene. So, rating 1000 ISO outdoors is forcing you to stop down (close the aperture and let less light hit the sensor) to protect the highlight range, and rating at 320 indoors is forcing you to open up the aperture let more light in from the shadow areas of the scene.

But it comes down to which stops you want more of in the scene over or below middle grey, that is where the shift comes, along with the creative exposure choice. A fat histogram is part of it, but where the values are inside that histogram is the rest.

Battistella

 

[Nathaniel Kramer]

David, also to semi quote Frank -are you using zircon encrusted tweezers? I always set iso to 320 or 250 in low light situations and light to those numbers, but I always check my exposure, histo and goal posts in "raw" mode on the red monitor as there is no meta attached and it shows me where the non meta image starts at. when I have to choose between preserving darks or highlights, i will always choose the darks as thats where i will see noise if i have to push iso later. Thats not to say my way is the right way, its just the way that makes me feel comfortable my exposure is decent and will give me lattitude in post.

 

[Hrvoje Simic]

I'm down with all of this... Except the bits part. The number of bits makes all of the difference. It is a huge part of the reason why Dragon footage is more pliable in post. (As long as you don't throw those bits away.) They are the reason why you can dig more out of those shadows with less noise. They are part of the reason why Evin's JPEG doesn't do justice to the print.

Higher bit sampling gives:

- more precision/color accuracy potential
- "thicker negative" (post manipulation related, NOT general exposure related)
- finer transitions between color/luma tonalities and finer roll off to extreme values
> more natural looking material as a result

Additional bits are the reason the material is more "flexible". It is more densely sampled. That enables less falling apart in picture manipulation. Those bits do allow more usability of DR, but if light is missing, material is still underexposed and "too thin".

If the footage is underexposed those bits will NOT reduce the captured noise, noise is being sampled nevertheless, just more precisely. This is less of an issue with higher sensitivity, high resolution sensor such as this one, and as I said - noise can be removed to an extent, but color quality/precision/gradations of greatly underexposed then pushed image are a much larger issue. If someone is using that extended DR to capture more highlights while not exposing for the skintones, those extra bits and stops are used way up there and face is still a mess.

In order to avoid threads such as "I upgraded to a new sensor and my skintones look not as good as Alexa's in this unlit interior scene with nice clouds outside" it is very beneficial to stress that this DR increase should not be relied upon for salvage operations in post.

 

[Scott Crawley]

This is just the kind of clarification I was after, for everyone's benefit. ;-)

The more dense and accurate color sample means that you can push values in post further before the calculation goes wrong, delivering an incorrect color value to a pixel that is interpreted by the viewer as noise.

Right?

Deeper color sampling also means that you are more likely to get a correct color sample in the first place. More correct color samples means fewer pixels that have incorrect color, and that (it seems to me) equals less "noise" in the first place. Again, what is noise but a number of individual pixels dispersed throughout the frame that are displaying a color value that is both incorrect and drastically different from the pixels surrounding them?

Higher bit sampling gives:

- more precision/color accuracy potential
- "thicker negative" (post flexibility related, NOT general exposure related)
- finer transitions between color/luma tonalities and finer roll off to extreme values
> more natural looking material as a result

They are the reason the material is more "flexible". It is more densely sampled. That enables less falling apart in picture manipulation.

Those bits do allow more flexibility regarding the usability of DR, but if the material is underexposed beyond a certain point it is still underexposed and too thin.
If the footage is underexposed those bits will NOT reduce the captured noise, noise is being sampled nevertheless, just more precisely.
This is less of an issue with higher sensitivity high resolution sensor such as this one, and as I said - noise can be removed to an extent, but color quality/precision/gradations of greatly underexposed then pushed image are a much larger issue.

In order to avoid threads such as "I upgraded to a new sensor and in this unlit interior scene with clouds outside not clipping my skintones look not as good as Alexa's" it is very beneficial to stress that that DR should not be misused for salvage operations.