Dual ISO Video - what are the advantages?

Started by Ballinger, May 16, 2019, 06:10:36 PM

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Ballinger

Hello,

Recently, a new module for ML appeared that facilitates RAW video recording at a dual ISO setting.  Along with a 1x3 sampling rate, among the features mentioned by the developer(s) of the module is the virtual elimination of both aliasing and moire' artifacts that have previously plagued ML RAW video recording at non 1x1 sampling rates (previously requiring crop mode recording).   My question is what ultimately is the advantage of dual ISO capability in the context of Magic Lantern use?  Is dual ISO required for the elmination of artificats and implementation of 1x3 sampling rates at non-crop modes or is dual ISO's main advantage increased dynamic range and reduction of noise in shadow detail? 


Thank you!   




Walter Schulz

Dual-ISO was introduced as a feature increasing DR. See https://www.magiclantern.fm/forum/index.php?topic=7139.msg59687#msg59687
Aliasing artifacts are listed as a trade-off.

Years later it came as a surprise that under certain circumstances Dual-ISO can reduce aliasing artifacts caused by other technique.*

I have no idea what is gained by a question "I used xy for abc and lately I learned xy can be used for def and I want to know which one is right". Tools may be versatile. So what?



* Disclaimer: Haven't tested it yet.

a1ex

Quote from: Walter Schulz on May 17, 2019, 10:27:42 AM
Years later it came as a surprise that under certain circumstances Dual-ISO can reduce aliasing artifacts caused by other technique.*

Wait, what?

What actually happened:

- 1x3 readout removed "line skipping" aliasing artifacts present on most Canon EOS models (by reading out every single line, at the expense of rolling shutter "delay" being 3 times higher)
- regular Dual ISO causes aliasing in under- and over-exposed areas (because of 2 lines read out + 2 lines missing, in areas covered by only one ISO, ON TOP of Canon's line skipping)
- with 1x3 readout - which is pretty much oversampling -  Dual ISO aliasing artifacts were minimized (i.e. video recorded with this technique no longer suffers from extreme aliasing)

So, it's not Dual ISO that reduces the aliasing artifacts. It's the 1x3 readout. It reduces the aliasing so well that Dual ISO video starts to be usable.

Ballinger

Quote from: Walter Schulz on May 17, 2019, 10:27:42 AM
Dual-ISO was introduced as a feature increasing DR. See https://www.magiclantern.fm/forum/index.php?topic=7139.msg59687#msg59687
Aliasing artifacts are listed as a trade-off.

Years later it came as a surprise that under certain circumstances Dual-ISO can reduce aliasing artifacts caused by other technique.*

I have no idea what is gained by a question "I used xy for abc and lately I learned xy can be used for def and I want to know which one is right". Tools may be versatile. So what?



* Disclaimer: Haven't tested it yet.


Thank you for the explanation.  I think I was mostly misunderstanding the fundamental purpose of dual ISO recording in the context of Magic Lantern features.  You're right of course in that one should use the right tool for the job.  Dual ISO ability makes filming more versatile and offer photographers more options to achieve the desired end result.   ;D

Ballinger

Quote from: a1ex on May 17, 2019, 10:59:03 AM
Wait, what?

What actually happened:

- 1x3 readout removed "line skipping" aliasing artifacts present on most Canon EOS models (by reading out every single line, at the expense of rolling shutter "delay" being 3 times higher)
- regular Dual ISO causes aliasing in under- and over-exposed areas (because of 2 lines read out + 2 lines missing, in areas covered by only one ISO, ON TOP of Canon's line skipping)
- with 1x3 readout - which is pretty much oversampling -  Dual ISO aliasing artifacts were minimized (i.e. video recorded with this technique no longer suffers from extreme aliasing)

So, it's not Dual ISO that reduces the aliasing artifacts. It's the 1x3 readout. It reduces the aliasing so well that Dual ISO video starts to be usable.

This makes perfect sense.  Thank you.