Author Topic: 6D Dual Iso and more DR hack?  (Read 18773 times)

a1ex

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Re: 6D Dual Iso and more DR hack?
« Reply #75 on: January 21, 2014, 07:46:10 PM »
Right, only the last photo was with 1100D. Details here: http://www.magiclantern.fm/forum/index.php?topic=9923.msg95567#msg95567

Levas

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Re: 6D Dual Iso and more DR hack?
« Reply #76 on: January 21, 2014, 09:50:14 PM »
Code: [Select]
enabled = 1
calibrated.gain.100 = -37
calibrated.gain.200 = -34
calibrated.gain.400 = -39
calibrated.gain.800 = -41
calibrated.gain.1600 = -43
calibrated.gain.3200 = -52
calibrated.gain.6400 = -56
calibrated.gain.12800 = -156

This is how it did through a dumb extender tube. It does seem to be lowering the stdev and increasing DR if you take 1 pic with mini ISO and one without.

Quote from the link a1ex posted:
http://www.clarkvision.com/articles/evaluation-canon-6d/index.html
" The constant dark level with long exposure time indicates the camera has on-sensor dark current suppression. This, however, does not suppress noise from dark current. But it results in a uniformly dark level that needs no post processing correction. No long exposure dark frames are needed when making long exposures if recording raw. "

Can this also mess up the numbers found by 1% for the 6d ?

ayshih

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Re: 6D Dual Iso and more DR hack?
« Reply #77 on: January 21, 2014, 10:50:25 PM »
If that last 0.1-0.2 EV of shadow detail is more important then 1EV of highlight detail, you may benefit from ISO 6400 vs ISO 3200. ...

Thanks, Audionut, for that detailed explanation.  I was getting a bit confused by the discussion of noise and the claim of "fake" ISOs, and your explanation (as well as one of your links) helped greatly to straighten me out.  In essence, going to higher ISOs reduces the read noise as measured in equivalent electrons, but once the read noise is much smaller than the photon shot noise, the SNR will improve only slightly at best.  Thus, ISOs >~ 6400 can appear to be "fake" even if they are real analog gain, simply because you're already dominated throughout the image by photon shot noise.
Canon EOS 50D | 17–40mm f/4L & 70–300mm f/4.5–5.6 DO IS | Lexar 1066x

Audionut

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Re: 6D Dual Iso and more DR hack?
« Reply #78 on: January 22, 2014, 04:21:17 AM »
In essence, going to higher ISOs reduces the read noise as measured in equivalent electrons, but once the read noise is much smaller than the photon shot noise, the SNR will improve only slightly at best.  Thus, ISOs >~ 6400 can appear to be "fake" even if they are real analog gain, simply because you're already dominated throughout the image by photon shot noise.

That's correct.  I took some sample images before bed last night, but I missed a couple of wanted sample points, stay tuned!

Here's a sneak peak of what to expect though.  ISO 800 vs ISO 12800 (5D3)



And ISO 800 vs ISO 12800 where the samples were brightness corrected in camera (shot noise effected).

Levas

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Re: 6D Dual Iso and more DR hack?
« Reply #79 on: January 22, 2014, 10:29:45 AM »
read the article mentioned by Audionut, learned some new things there.

From what I read in the article, the only way to know/see if an iso is "real" or digitally pushed is to look at the highlights.
If iso 25600 is derived from iso 6400 pushed by 2 stops, it should loose 2 stops of highlight data.
Shadows and midtones show no visible difference.


Audionut

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Re: 6D Dual Iso and more DR hack?
« Reply #80 on: January 22, 2014, 10:44:18 AM »
Wrong way around.  The highlights will always move +/- 1EV for a 1 stop ISO adjustment.  The secret is in the shadows. 

We know we lose 1EV of highlight data between ISO 3200 and ISO 6400, but what do we gain in the shadows!

But it results in a uniformly dark level that needs no post processing correction. No long exposure dark frames are needed when making long exposures if recording raw. "

Can this also mess up the numbers found by 1% for the 6d ?

No.  ISO calibration is done on the white level.

a1ex

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Re: 6D Dual Iso and more DR hack?
« Reply #81 on: January 22, 2014, 10:52:54 AM »
your explanation (as well as one of your links) helped greatly

The whole article is very well written and informative: http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/index.html

FYI, Emil Martinec (the author of this article) is the author of the AMaZE demosaic algorithm (one of the best ones) and he also pointed out the theory behind Dual ISO 5 years ago: http://www.luminous-landscape.com/forum/index.php?topic=26838

Levas

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Re: 6D Dual Iso and more DR hack?
« Reply #82 on: January 22, 2014, 11:48:24 AM »
another approach, raw_diag used on iso 12800, 25600, 51200 and 102400

The gaps in the data in 51200 and even wider gaps in the 102400 say's it all.
No extra gaps in the data going from 12800 to 25600.






Hmm, these links don't work the way I want it.
4 graphs can be found here:
https://drive.google.com/folderview?id=0B1BxGc3dfMDaZFp6bDdmc2ZLSk0&usp=sharing

Marsu42

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Re: 6D Dual Iso and more DR hack?
« Reply #83 on: February 02, 2014, 09:46:27 PM »
let me translate that for you: it doesn't work on the 6D

It does by now, but help is required - see here: http://www.magiclantern.fm/forum/index.php?topic=10292