ISO vs Exposure?

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Nick Heydon

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ISO vs Exposure?

PostThu Oct 08, 2020 9:15 am

Hey all,

If I've shot something at 400ISO on the P4k in Braw, but it's under exposed, is it best to up the ISO to say 640, or leave the ISO at 400 and bump the exposure slider?

Similarly, if something is over exposed, is it best to lower the ISO to 200 or use the slider to bring it down?

Is there even any difference in regards to noise being introduced etc?

I'm using the Autokroma BRAW Studio Panel in Premiere if that makes any difference.
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Robert Niessner

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Re: ISO vs Exposure?

PostThu Oct 08, 2020 9:40 am

Those settings are mostly interchangeable. I haven't found any differences between the usage of them. Maybe in very extrem settings which I didn't try, but those wouldn't have made sense anyway.
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ttakala

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Re: ISO vs Exposure?

PostThu Oct 08, 2020 9:48 am

ISO is like a gamma correction, exposure is closer to offset correction.

I tend to use the exposure slider in the raw tab in Resolve. I found that it gives more natural results, but have to admit, I haven't done side by side comparisons in a long time. So could be just a habit at this point.

In terms of noise, I don't think there is much difference.
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Dmitry Shijan

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Re: ISO vs Exposure?

PostThu Oct 08, 2020 9:58 am

In BM cameras ISO is same as Exposure in RAW tab and same as Gain in Linear gamma viewtopic.php?f=21&t=65149&p=543725#p537852

Gain in linear gamma corresponds to Expose F-Stops in RAW tab like this:
linear gain 2 = expose 1
linear gain 4 = expose 2
linear gain 8 = expose 3
linear gain 16 = expose 4
and so on...
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Nick Heydon

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Re: ISO vs Exposure?

PostThu Oct 08, 2020 10:06 am

Thanks for the quick responses guys. It's kind of what I thought, but wanted to be sure before I adjust too much footage the 'wrong' way.
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Robert Niessner

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Re: ISO vs Exposure?

PostThu Oct 08, 2020 10:44 am

I did try it out with CDNG from a BMCC shot in 2014, color science set to Gen 4,
white balance = 4800, shadows = +25, contrast = +25
and my LBK neutral LUT applied.

Then just played with ISO and exposure settings:

ISO200 EXP 0_1.3.5.jpg
ISO 200 / Exposure 0
ISO200 EXP 0_1.3.5.jpg (503.77 KiB) Viewed 646 times


ISO800 EXP -2_1.3.6.jpg
ISO 800 / Exposure -2
ISO800 EXP -2_1.3.6.jpg (484.78 KiB) Viewed 646 times


ISO400 EXP 0_1.3.3.jpg
ISO 400 / Exposure 0
ISO400 EXP 0_1.3.3.jpg (576.47 KiB) Viewed 646 times
Saying "Thx for help!" is not a crime.
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Robert Niessner
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Robert Niessner

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Re: ISO vs Exposure?

PostThu Oct 08, 2020 10:46 am

ISO800 EXP -1_1.3.4.jpg
ISO 800 / Exposure -1
ISO800 EXP -1_1.3.4.jpg (557.17 KiB) Viewed 646 times


ISO800 EXP +1_1.3.1.jpg
ISO 800 / Exposure +1
ISO800 EXP +1_1.3.1.jpg (558.62 KiB) Viewed 646 times


ISO1600 EXP 0_1.3.2.jpg
ISO 1600 / Exposure 0
ISO1600 EXP 0_1.3.2.jpg (544.26 KiB) Viewed 646 times


You can see that there is a subtle difference.
Saying "Thx for help!" is not a crime.
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Robert Niessner
LAUFBILDkommission
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Blackmagic Camera Blog (German):
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CaptainHook

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Re: ISO vs Exposure?

PostFri Oct 09, 2020 6:44 am

In Gen 4 ISO adjustments in the RAW tab apply different log curves that also shift middle grey by reference to scene linear in terms of stops (or 1/3 stops etc). This means contrast will change for the different ISO curves where as the exposure slider will not.

In Gen5 ISO and exposure are essentially the same thing in that its a fixed log curve and changing either ISO or exposure acts as a multiplier/scaling in linear.
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CaptainHook

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Re: ISO vs Exposure?

PostFri Oct 09, 2020 7:03 am

@Robert - if you try the same thing with a 4.6K/G2 and compare say ISO200 versus 3200 the contrast difference will be even more noticeable. :)
**Any post by me prior to Aug 2014 was before i started working for Blackmagic**
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antoine

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Re: ISO vs Exposure?

PostFri Oct 09, 2020 7:17 am

It shouldn't change anything that you are using Autokroma BRAW Studio Source Settings Panel to color grade inside Premiere Pro, behind the hood it's still using the same official BRAW API :)

CaptainHook wrote:In Gen5 ISO and exposure are essentially the same thing in that its a fixed log curve and changing either ISO or exposure acts as a multiplier/scaling in linear.


Thanks for this information, very important to tell users about it !
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rick.lang

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Re: ISO vs Exposure?

PostFri Oct 09, 2020 9:40 pm

On the BMPCC4K, I religiously try to shoot at ISO 400 or 3200 and use Colour Science 5 and usually adjust the exposure slider in the Camera raw tab of Davini Resolve 16.
Rick Lang
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Robert Castiglione

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Re: ISO vs Exposure?

PostSat Oct 10, 2020 5:47 am

By the way.

That is a very nice shot.

Rob

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