Exposure vs. ISO

[Micheal Del Castillo]

hello,

I'm shooting my first short on Scarlet next week and have a technical question regarding the "Exposure" slider in Settings>Look>Color menu.

When I slide it to the right for a brighter picture it does not effect the ISO rating, or the shutter speed reading and seems to work independently of
those.

What is the advantage/disadvantage to using it instead of the ISO, and/or is there a difference?

Thanks.

 

[Gunleik Groven]

Short answer:
There is no real good argument for using exposure vs ISO.
Exposure +1 = ISO 400 --> 800 and the same noise.

FLUT +1 gives the same effect as ISO + 1 stop.

Not sure if Exposure is now "reset" to push the highlights over the top.

Main thing is:

Only light actually affect the physical exposure.

 

[Paul Russell]

The amount of light hitting the sensor is what counts. ISO/FLUT etc are just interpretations of RAW.

 

[Micheal Del Castillo]

Thank you guys for the response. That makes sense.

 

[Daniel Reed]

Unless its a dragon sensor if i recall correctly...

in which case, to double the light one needs to use the exposure setting

Short answer:
There is no real good argument for using exposure vs ISO.
Exposure +1 = ISO 400 --> 800 and the same noise...

 

[Gunleik Groven]

Unless its a dragon sensor if i recall correctly...

in which case, to double the light one needs to use the exposure setting

I used to be a lot more tongue-in-cheek here than I have become, until I realised that people actually do what you write "because they found the info on reduser".

So just as a humourless nit-picky Viking:

Amount of light hitting the sensor, is the only thing that will ever change the actual exposure

 

[Adrian Jebef]

Amount of light hitting the sensor, is the only thing that will ever change the actual exposure

This is the correct answer.

If your scene "looks" too dark add more light don't change your metadata settings (exposure, ISO, FLUT, etc).

 

[David Battistella]

Raw view
histogram
goal posts
exposure tool

become best friends with these four things and you dramatically increase the quality and elasticity of the images you make.
Learn what each does intimately. Test them. These four things in that order will tell you how much light is hitting the sensor.

Oh, don't forget your light meter either.

Battistella

 

[Gary Paul Walker]

Raw view
histogram
goal posts
exposure tool

become best friends with these four things and you dramatically increase the quality and elasticity of the images you make.
Learn what each does intimately. Test them. These four things in that order will tell you how much light is hitting the sensor.

Oh, don't forget your light meter either.

Battistella

When you pick up a camera for the first time, I do believe this should be taped on top of it for reference.

 

[Micheal Del Castillo]

Yes, more light for the sensor. The rest is just metadata. That part is understood.

What else I would like to know is why have an "exposure" tab in the menu, when you already have ISO to adjust "meta." If there is no advantage to it than it just confuses the process. Sorry to nit pick it, but there has to be a point for it, no?

 

[D Fuller]

This from Graeme:

Exposure can force clipping. FLUT and ISO gently bend the tones in the image to avoid clipping. A FLUT of +1 is the same as doubling ISO, but with FLUT you have a nice fine control over the over-all image brightness.

Yes, Exposure is utterly linear. It's in there should you need that, whereas for normal use the FLUT curves are much more appropriate.

So the behavior is different. Exposure increases the apparent exposure linearly, without applying any curve to roll off the highlights, but with greater risk of clipping. ISO and FLUT increase the apparent exposure using a curve that protects the highlights to some degree.

 

[D Fuller]

And if you want the really detailed answer:

FLUT is a name we are giving to a new set of image processing features in post and in camera. As Jim mentions, along with it comes new histograms, new false color, and new camera settings. The work done on FLUT has helped to enable these functions in camera.

But let's talk about how FLUT works with image processing, and how specifically it deals with the concept of "gain".

Gain is a necessary part of image processing and it's simplest to think of it as the most basic way to brighten an image. Traditionally, gain in camera was done in the analogue domain. The downside to this is that as the image is gained up, it causes bright highlights to clip, and indeed it will loose one stop of highlights to clipping for every stop of gain applied. Originally in our camera and software, we applied gain (under the controls ISO and exposure) in a way that worked just as analogue gain does.

Although it sounds simple enough to just adjust the gain so that it does not clip the highlights, like a traditional video "knee", the devil is always in the details. Instead of a gamma option, which is what a traditional knee is, it was decided to build the smooth roll-off and non-clipping gain properties into a complete system, which much more suits the RAW development nature of working with the R3D files.

This means that while all RAW development controls benefit from the underlying FLUT math, the main controls that directly effect it are ISO and the new FLUT Control. ISO and FLUT Control work together and produce exactly the same results, but FLUT control is calibrated in stops and has a fine degree of control, whereas ISO is labeled in traditional units and 1/3 stops. They work together, so if you gain up on ISO and back down the same amount on FLUT, they cancel each other out. If you gain up on ISO and add more gain on FLUT, you can get an awful lot of gain. You can use ISO, or you can use FLUT and get to exactly the same point. You can roughly gain up the image with ISO and fine-tune with FLUT control. The choice is yours. I love FLUT control as it's in stops, and to me, that's a more natural way of thinking than the ISO numbers.

Sometimes, however, you may wish to have absolutely linear gain and clip those highlights, so "exposure" control works just as it did before - it's pure linear gain and it will hard clip. However, because FLUT is an underlying system - all is not lost...

Take the user curve controls for example, they'll allow you to "pull back" a highlight you've forced to clip through use of the "exposure" control. Or the new Lift/Gamma/Gain controls will also allow you to do the same and pull back highlights you've clipped earlier in the image processing chain.

So, to put it all together simply:

FLUT is an underlying technology, designed to help you avoid clipping unnecessarily.
It works primarily through ISO and FLUT Control, but helps all RAW development controls.
Exposure works just as it's always done if you need it.
The ISO and FLUT controls work together - think of them as "better gain"

Graeme

From this thread.

With Dragon, there is less danger of clipping highlights, of course, but I believe the differences described here are still true. Graeme has said recently that "Exposure" is an utterly linear manipulation of gain.

 

[Mikael Lubtchansky]

Amount of light hitting the sensor, is the only thing that will ever change the actual exposure

to be absolutely nit-picking : the only camera parameter (excepting the lens aperture, filters... all before the light hits the sensor) that IS affecting the RAW exposure is the shutter speed/angle which in case of a non-mechanical shutter happens 'after' the photons hit the sensor (or rather prevents them from being used in the image)...

 

[Daniel Reed]

Yeah, haha, absolutely :beer:

I was just reiterating a post Graeme made about the ISO vs Exposure setting in redcine for Dragon.

I used to be a lot more tongue-in-cheek here than I have become, until I realised that people actually do what you write "because they found the info on reduser".

So just as a humourless nit-picky Viking:

Amount of light hitting the sensor, is the only thing that will ever change the actual exposure

 

[Gunleik Groven]

to be absolutely nit-picking : the only camera parameter (excepting the lens aperture, filters... all before the light hits the sensor) that IS affecting the RAW exposure is the shutter speed/angle which in case of a non-mechanical shutter happens 'after' the photons hit the sensor (or rather prevents them from being used in the image)...

True!

THX.
Shutter still affects how many photons are READ into an exposure, as time-axis x photons = exposure ('ish)
Shutter still is part of what determines how many photons are counted...

But I stand corrected!