Dual ISO - massive dynamic range improvement (dual_iso.mo)

[a1ex]

Here's an experimental cr2hdr that solves the second picture.

It also fixes some dark spots that sometimes appeared in noisy areas.

Problems (this is why I didn't update it on the first page):

- you can see more aliasing on resolution charts, and in IMG_6706 from Danne (maybe others too).
- noise pattern is also different; visible on IMG_8485 from naturalsound, for example.

So, if you find a situation where you get noticeable shadow aliasing (more than with cr2hdr from first post), upload a CR2 and a side-by-side comparison.

Next time try exposing with ETTR. The second picture was really underexposed (and in this case it's better to simply shoot at ISO 1600).

[akumiszcza]

Both photos were made with AETTR+Dual-ISO, but on AutoSnap mode and both, I think, were not the final, settled, photos.

[a1ex]

Got it. If it's the one after a overexposed attempt, this explains it.

When ETTR looks at something underexposed, it knows exactly how much to adjust, but if it looks at something overexposed, it has no idea. It tries to use some heuristics from previous photos; sometimes works, sometimes not. If you know this, you should be able to predict what it's going to do.

[djronbxs]

shoudl I use dual iso when taking a bracketed hdr ?

[Walter Schulz]

Dual-ISO is meant for situations where HDR is not possible. Dynamic scenes vs. static scenes (with a grain of salt). If you are able to use HDR in a given situation you won't need Dual-ISO.

Ciao
Walter

[Marsu42]

If you are able to use HDR in a given situation you won't need Dual-ISO.

... unless you haven't won in the lottery lately and would like to use 1 shutter cycle instead of 3, extending the camera's lifetime. Also using dual_iso will save you a lot of postprocessing time as it's "sooc", esp. the 6d benefits because unlike the 5d3 it doesn't do raw in-camera hdr.

[1%]

Only problem is the 1/2 res shadows.

[a1ex]

Do you have an example where this is noticeable?

[1%]

Somewhere, its not that bad. The only real issues I've had were when I did dual ISO 800/100 and the image comes out completely black and then is a bit noisy when its brought up. I'm not a fan of using it in reverse, is this even proper?

I think this one the ISO 100 was just too far under. I have to look for or make some reversed ones where similar things happen.

http://www.filedropper.com/dual0955

[SpcCb]

I use Dual ISO in reverse (ie. 800/100 || 400/100) most of time, without any problem [5D2].
It's very useful to recover hight lights and/or to get max dynamic.

[a1ex]

Okay, found the bug that was causing noisy shadows in the forest shot.

Before and after:


Also it fixes some black spots and banding, visible in the shot from 1% (which was also extremely underexposed; both test shots were developed at +6 EV in ufraw):


This one passed all my pixel peeping tests, so you can download it from the first post. There's some small color fringing in the resolution charts, but I highly doubt you'll notice it in practice (all my other test shots look the same or better). If anything is rendered worse than with previous version, upload a CR2 and a side-by-side comparison.

[1%]

Looks good, now have to see if I have any more @ rerun what I did already.

[akumiszcza]

Thank you, a1ex – works great! As far as it's possible for these bad and unexposed photos

BTW, I've found a quick way of checking if a given .cr2 is Dual-ISO, or not (I get quite many Dual-ISO photos without the prefix and some non-Dual-ISO with the prefix – I guess it's some kind of racing condition while having Auto Snap or Always On and shooting in quick series?). By turning small image previews in additional panel of Bridge (smaller than thumbnails for me at least) I see the stripes quite clearly – Moire effect. It's much faster than opening 100% previews at least. It should work with other software I guess, but you need to find the proper preview size.

[a1ex]

I simply run cr2hdr on all files (usually, more than half of them are dual ISO, and the ones that are not are skipped quickly). Then, my raw processing script picks the DNG if there's one, or the CR2 otherwise.

The file prefix is not quite synced in burst mode, so I'm not sure whether to keep it or not. I don't think I can make it reliable in the near future.

[akumiszcza]

I simply run cr2hdr on all files (usually, more than half of them are dual ISO, and the ones that are not are skipped quickly). Then, my raw processing script picks the DNG if there's one, or the CR2 otherwise.

I do the same way — see the scripts here: http://www.magiclantern.fm/forum/index.php?topic=8738.msg81768#msg81768
I've just noticed the moire in small previews and thought it might be useful for some people.

The file prefix is not quite synced in burst mode, so I'm not sure whether to keep it or not. I don't think I can make it reliable in the near future.

I would opt for removing it — it's unreliable and might leave some photos processed wrongly (it's not visible at first glance sometimes if photos are dual-iso and somebody might batch process them without using cr2hdr first, which can give unpredictable results).

[Audionut]

The file prefix is very handy.  Sure it doesn't work in burst mode but that's what warnings are for.
Processing 2000+ wedding photos, it's much easier to pick out the dual ISO shots with the prefix then to wait hours batch processing the lot of them.

It's only a problem where you have alternate shooting enabled.  I'd settle for reduced capture rate where file prefix is not default and alternate capture is enabled.

[Danne]

Dual iso prefix. How do I enable this? Tried to in dual iso menu but there was no difference in prefix? I, m not in burst mode.

[1%]

I just do the prefix + check the photos in FS viewer when moving them... has worked for like 400-500 pics.

[akumiszcza]

The file prefix is very handy.  Sure it doesn't work in burst mode but that's what warnings are for.
Processing 2000+ wedding photos, it's much easier to pick out the dual ISO shots with the prefix then to wait hours batch processing the lot of them.

It's only a problem where you have alternate shooting enabled.  I'd settle for reduced capture rate where file prefix is not default and alternate capture is enabled.

I've made a short benchmark for 20 non-dual-iso cr2 files using cr2hdr alone and scripts I have there: http://www.magiclantern.fm/forum/index.php?topic=8738.msg81768#msg81768
cr2hdr alone (drag&drop) = 1:46.52
No renaming of files, just many processes of cr2hdr:
timer cmd /c dualisonorename.vbs = 48.391 (maxprocs=4) 40.902 (maxprocs=8 ) 41.252 (maxprocs=16)
Many processes of cr2hdr + renaming using exiftools:
timer cmd /c dualiso.vbs = 59.851 (maxprocs=4) 62.404 (maxprocs=8 )

So for 2000 photos it would take 1 hour 8 minutes on my old computer (Core2 Q6600). Less than that, because the program takes some time to start and stop (less processes at once then). Of course, for Dual-ISO files the time will increase, but so as with your method.

And I think I have some photos with wrongly assinged prefix that were not made by burst but by Always On AETTR. Probably ML finished calculations of new exposure at the exact moment I took the photo?

[a1ex]

It's possible; when ETTR switches from dual to non-dual ISO, the change may not be applied right away; so if you catch the wrong timing, you are out of luck.

I've added a warning for now. Having a file list (like with intervalometer) may be easier to sync.

[djronbxs]

what do we need to download now from your first post ? cr2hdr or the dual iso module ?

[Audionut]

Having a separate log of which files are dual ISO would make it easy for a post application.

[a1ex]

Small cr2hdr update for video guys: better guess of black level in the absence of optical black bars.

Before:


After:


There may be subtle differences in photo mode too, in shadows (since this guess is used during blending).

[tron]

@alex: Can you please check:

https://www.dropbox.com/s/cvdz6nz2t0rvnxy/DUAL0650.CR2

I converted it with the Oct-10 version (latest I guess) and at 100% (and more) patterns are visible.
(Shot at ISO 100/1600. The resultant DNG was set as: Exposure +3.2 Highlights -100 Shadows +100 Temperature: 3200)

[tron]

@alex again. I had a problem with the dcraw (continuous error messages about not being valid win32 application if I recall correctly) from the latest .zip (Oct 10) I have overridden it with the dcraw from Sep 20.