Magic Lantern "Dual ISO" Function

Stephen Mick

Stephen Mick

Totally Usable
Looks pretty cool…

http://www.magiclantern.fm/forum/index.php?topic=7139


(From ML Forum…)

Time for the first real image quality improvement in ML history :)


Here's a trick that samples half of the sensor at ISO 100 and the other half at ISO 1600, for example. If you mix these two, you can get almost the entire dynamic range the sensor is capable of (around 14 stops). 5D3/7D only.


There are no motion artifacts; not even a difference in motion blur for the two exposures. So, it works well for fast moving subjects.




Warning
This code changes low-level sensor parameters. In the technical doc you can see how this method messes with the feedback loop for optical black, for example. Therefore, it's safe to assume it can fry the sensor or do other nasty things. My 5D3 is still alive after roughly one week of playing with this, but that's not a guarantee.


We don't pay for repairs. Use it at your own risk.


Also, the 7D implementation seems quite buggy right now. Don't use it for serious stuff yet. Programming the dual DIGIC is not that easy for parallel computing noobs like me.


Usage
- 5D3: works for both raw photo and raw video. 7D: photo only.
- Select one ISO from Canon menu, the other from Dual ISO submenu.
- Expose to the right for the lower ISO (usually ISO 100). Maybe darken 1 stop from there.
- Start at ISO 100/1600.
- Try a larger gap for really extreme situations, or a smaller gap for better midtone detail (less aliasing).


Histograms, ETTR, playback tricks [5D3 only]
- Raw zebras will use the darker exposure for highlight warnings and the brighter one for shadow warnings.
- Raw histogram will use the darker exposure. Consider the brighter one as some sort of shadow recovery.
- JPEG zebras/histogram are totally unreliable.
- In photo LiveView you will see the ISO from Canon menu. In movie mode, you will see horizontal lines.
- ETTR will use the darker exposure.
- Playback in 1x will show some sort of HDR preview. At certain zoom levels, you'll be able to see only one of the two exposures, at very low resolution.
- The dynamic range indicator from the histogram is not accurate.


Postprocessing
- For CR2 files: cr2hdr.c (Windows: cr2hdr.exe). It requires dcraw and (optional) exiftool in your path.
- For RAW video files: latest raw2dng.exe.
- To get a natural HDR look: try my automatic color grading script.


Price to pay
- Half resolution in highlights and shadows
- Aliasing and moire - of course, in highlights and shadows
- You can no longer check critical focus when zooming in
 
Hehe.... And here I thought those guys were taking a summer vacation. Way to put me to shame!

This is exciting news. I know we gain some of the things that we cheared getting rid of from II > III, but I think we have to see what this kind of footage actually looks like. 14 stops of DR in a 14 bit file.... come on, that would be fun grading around if needed :D

And I can live with slates for now....
 
Hehe... I said something big was coming, right?

THIS IS AWESOME

The downsides are relatively minor, I don't think any sensor is going to get fried with this, and the aliasing/moire only appear in the recovered highlights and shadows, so it's a minor price to pay if you actually get to see something there, instead of pure white or pure noise!!

Now, let the real-world samples flow in


BTW: for anybody wanting to learn more, here http://www.magiclantern.fm/forum/index.php?topic=7139 they posted this (hugely impressive) pdf: http://acoutts.com/a1ex/dual_iso.pdf
 
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So, each dng has two different iso sensor reading? Or do I get two raw files when recording a scene?
 
While I think this is great. I would be awesome if they could make 220MB ProRes files.
 
I just ran a quick test and I am 99% sure I will stay away from dual ISO module. I prefer having moire/aliasing free 5D3 raw with better resolution to dealing with all these more/aliasing with less resolution in dual ISO mode.
 
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