I'm unclear on how to use Dual-ISO to best advantage. I think I may be close to a good workflow, but I wanted to check for sure, and also learn about "the error of my ways" from others on this forum with more experience and expertise.
- Appropriate for scene with high contrast, where HDR would help.
- Even with RAW histogram, there is "valuable content" on the left and/or right side.
- Otherwise, "why bother?" if the levels fit within the histogram ok (low to moderate contrast)
- For an example using ISO 100/1600:
- Dual-ISO starts at OFF
- (but does Auto-ETTR take Dual-ISO into account, so this isn't necessary or appropriate?)
- Or does the camera's normal metering end up being appropriate?
- Determine best exposure for bright areas at ISO 100, perhaps with ETTR, trial-n-error, etc.
- ...
- The RAW histogram would tend to look like it was ETTL (exposed to the LEFT)
- Exposure will tend to be underexposed, with few if any blown highlights, but will probably appear to have "blocked shadows" on the LCD.
- Enable Dual-ISO (this example uses 100/1600)
- Take picture(s)
- Process with cr2hdr.exe
- Open with ACR, LR, or other
- Expect to see an image that looks rather underexposed
- Image should have quite a bit more usable dynamic range, so the exposure/shadows/blacks can be increased significantly without as much noise happening
Or not?
Am I "unclear on the concept"? Do I have a flawed understanding of how Dual-ISO is supposed to work?
Is my workflow more or less ok, but sub-optimal? Would a different technique work better? Am I leaving something out? I haven't really been following the progress on ETTR and Auto-ETTR, but my guess is that those capabilities are now somewhat integrated.
My speculation is that once you "get the hang of it", you don't have to disable Dual-ISO, but can more go by the metering and/or Auto-ETTR.
ETTR with default settings should be a good starting point. If it enables dual ISO, it's likely to get noticeable improvements. Indeed, your best bet is an image that looks very dark if you expose it to the right (because in this case you will probably want to raise the shadows).
It also depends heavily on how are you going to color grade your pictures, and how good is your denoising software. If you raise the shadows a lot, it will help. If not, the improvement may not be noticeable.
If you use DxO PRIME for denoising, you probably won't see any improvement except for really extreme cases. For me, 45 minutes for denoising a single image is a bit too much (but the results are fantastic IMO). With a GPU, I think it only takes a few minutes from what I've read.
QuoteAppropriate for scene with high contrast, where HDR would help.
Correct.
QuoteEven with RAW histogram, there is "valuable content" on the left and/or right side.
The RAW histogram is just giving you a correct representation of the captured detail. The content would only be "valuable" if it falls outside the bounds of what the camera can capture in a single exposure, and you decide you don't want it blown to white (overexposed), or to far in the shadows (underexposed).
QuoteOtherwise, "why bother?" if the levels fit within the histogram ok (low to moderate contrast)
Exactly. Unfortunately, dual-ISO doesn't come for free. It has limitations that must be considered.
QuoteFor an example using ISO 100/1600:
Dual-ISO starts at OFF
(but does Auto-ETTR take Dual-ISO into account, so this isn't necessary or appropriate?)
Or does the camera's normal metering end up being appropriate?
Determine best exposure for bright areas at ISO 100, perhaps with ETTR, trial-n-error, etc.
There are 2 exposures with dual-ISO. In simplest terms, the lower ISO captures the highlight detail and the higher ISO captures the shadow detail. Where
both ISOs capture detail, full resolution is retained. Where only the lower ISO captures highlight detail (higher ISO becomes overexposed), then you suffer reduced resolution (aliasing).
QuoteThe RAW histogram would tend to look like it was ETTL (exposed to the LEFT)
Generally yes.
QuoteExposure will tend to be underexposed, with few if any blown highlights, but will probably appear to have "blocked shadows" on the LCD.
The only blown highlights will be those that you choose to blow. You retain control over exposure with dual-ISO.
It will tend to look very dark though due to the way cr2hdr (correctly) merges both exposures.
QuoteTake picture(s)
Process with cr2hdr.exe
Open with ACR, LR, or other
Expect to see an image that looks rather underexposed
Image should have quite a bit more usable dynamic range, so the exposure/shadows/blacks can be increased significantly without as much noise happening
Correct.
There are some tutorials here (http://www.magiclantern.fm/forum/index.php?topic=8322.0) and here (http://www.magiclantern.fm/forum/index.php?topic=8443.0) which may be useful.
Thanks for the input. Whew. It seems like I am not too far off.
Quote from: a1ex on December 05, 2013, 03:26:38 AM
It also depends heavily on how are you going to color grade your pictures
I've seen "color grade" mentioned, but I am ignorant about what that means. I did find the post on "Auto Color Grading", but it was mostly over my head. Also, it seemed dependent on quite a few tools that I'm unfamiliar with.
Is this a valid summary: gets all pictures "in the ballpark" as a starting point.
Quote from: l_d_allan on December 05, 2013, 04:07:10 AM
I've seen "color grade" mentioned, but I am ignorant about what that means.
In a nut shell, adjusting the image in post. Exposure, contrast, highlights, shadows, saturation, etc, etc.
When you take a dual-ISO image and raise the shadows, that's grading.
Quote from: Audionut on December 05, 2013, 03:38:35 AM
Exactly. Unfortunately, dual-ISO doesn't come for free. It has limitations that must be considered.
I wonder if my list of limitations is correct: complicates and slows down workflow, some loss of resolution .... others?
QuoteThere are 2 exposures with dual-ISO.
Now that's different from my newbie understanding. I had thought that during a single exposure, different scan lines of sensor pixels had different tone curve characteristics (i.e., ISO).
Are there two actual exposures? Is the sensor turned on and back off twice? I suppose that happens quite quickly, but with a moving target, could you get some ghosting? For a 5d2 with Digic-4, any idea of the time delay between the exposures?
QuoteWhere both ISOs capture detail, full resolution is retained. Where only the lower ISO captures highlight detail (higher ISO becomes overexposed), then you suffer reduced resolution (aliasing).
I recall the original post describing Dual-ISO mentioned resolution loss, but I thought it was more straightforward than what you describe. Your explanation fills in some gaps.
So .... if you had Dual-ISO enabled with a relatively low contrast scene with no blown highlights and no blocked shadows, then the "ON" and "OFF" files would be very, very similar? Little or no loss of resolution?
Quote from: Audionut on December 05, 2013, 04:19:05 AM
In a nut shell, adjusting the image in post. Exposure, contrast, highlights, shadows, saturation, etc, etc.
So, the "Auto Grading Script" seems like it might be a smarter "Auto button" than ACR and LR have? Or more flexible with more user control?
Quote from: l_d_allan on December 05, 2013, 04:35:24 AM
I wonder if my list of limitations is correct: complicates and slows down workflow, some loss of resolution .... others?
I only consider the resolution problems as a limitation. Increased workflow is just that, it doesn't
limit the rendering capability of the scene.
Quote from: l_d_allan on December 05, 2013, 04:35:24 AM
Now that's different from my newbie understanding. I had thought that during a single exposure, different scan lines of sensor pixels had different tone curve characteristics (i.e., ISO).
Are there two actual exposures? Is the sensor turned on and back off twice? I suppose that happens quite quickly, but with a moving target, could you get some ghosting? For a 5d2 with Digic-4, any idea of the time delay between the exposures?
My apologies. There aren't 2 exposures as in the shutter actuates twice. There are 2 exposures as in you should consider both ISO's when determining
correct exposure.
For instance you might use ISO 100 for the highlights, but you have to consider what your other ISO is doing to wanted detail. The higher ISO controls shadow detail, but it also determines where aliasing becomes a problem in the highlights.
Quote from: l_d_allan on December 05, 2013, 04:35:24 AM
I recall the original post describing Dual-ISO mentioned resolution loss, but I thought it was more straightforward than what you describe. Your explanation fills in some gaps.
Resolution loss will occur where either ISO is overexposed, since there is no longer full detail from both exposures.
Quote from: l_d_allan on December 05, 2013, 04:35:24 AM
So .... if you had Dual-ISO enabled with a relatively low contrast scene with no blown highlights and no blocked shadows, then the "ON" and "OFF" files would be very, very similar? Little or no loss of resolution?
I would expect the dual-ISO shot to be a touch better. Because you clearly haven't ETTR the lower ISO and the higher ISO will now be ETTR. Of course, you could have just ETTR the low ISO and called it a day :)
Quote from: Audionut on December 05, 2013, 04:51:16 AM
Resolution loss will occur where either ISO is overexposed, since there is no longer full detail from both exposures.
The resolution loss comes from the line skipping. Where the higher ISO is overexposed, you have half the lines with detail (the lower ISO) and half the lines with no detail (overexposed, the higher ISO).
Just like video, the actual amount of aliasing is determined by the detail of the scene. Flat textures are easy to fill in, sharp detail is harder.
Quote from: l_d_allan on December 05, 2013, 04:38:05 AM
So, the "Auto Grading Script" seems like it might be a smarter "Auto button" than ACR and LR have? Or more flexible with more user control?
Yes. I don't use ACR or LR though, so I have no idea how smart they are (though I could try a demo). I've compared my script against rawtherapee's auto: https://www.dropbox.com/sh/013ewzjdjtj7p55/rBM16yO5Rh
Quote from: Audionut on December 05, 2013, 04:51:16 AMI would expect the dual-ISO shot to be a touch better. Because you clearly haven't ETTR the lower ISO and the higher ISO will now be ETTR. Of course, you could have just ETTR the low ISO and called it a day :)
Thanks for your patience on providing a number of clarifications.
Based on what you've written, there doesn't seem to be much, if any, downside to having Dual-ISO enabled all the time. With static images, you'd take the time to get ETTR at a good setting.
If I understand what you've written, with a low to moderate contrast scene (as evidenced by fitting within the histogram), most or all of the information would come from the low ISO part of the exposure. The high ISO info wouldn't apply.
But when you did need the expanded DR of Dual-ISO, it would be there.
Somehow, I think that conclusion reflects a simplistic understanding on my part.
And to me, a more complicated and slower workflow is a liability (not a limitation, as you point out).
Some geek speculation:
The impression I have is that during the actual exposure, a ML routine is invoked that examines a pair (or quadruple?) of scan lines. In real time during the exposure, it is deciding whether to used just the low ISO pixels, or to merge the high and low ISO info. It almost seems like that would be on a pixel by pixel basis.
But I have my doubts that is really going on.
Also, I'm unclear how "aliasing" comes into it? Do you have a situation were two (or four?) pixels are averaged and/or interpolated? I observe that the thumbnails have a huge amount of moiré, but that's gone after cr2hdr.exe works its magic.
But I guess I don't have to understand how it works to be able to use. Whew.
Quote from: l_d_allan on December 05, 2013, 05:09:16 AM
If I understand what you've written, with a low to moderate contrast scene (as evidenced by fitting within the histogram), most or all of the information would come from the low ISO part of the exposure. The high ISO info wouldn't apply.
It would where the higher ISO becomes overexposed. And this is determined by the low ISO exposure and what higher ISO setting you have.
A low contrast scene that has been ETTR with the lower ISO, is going to overexpose the higher ISO (lose detail).
Quote from: l_d_allan on December 05, 2013, 05:09:16 AM
Also, I'm unclear how "aliasing" comes into it? Do you have a situation were two (or four?) pixels are averaged and/or interpolated? I observe that the thumbnails have a huge amount of moiré, but that's gone after cr2hdr.exe works its magic.
The lines you seen in a thumbnail are different to actual aliasing that may or may not be present.
Consider a very early example here (http://www.magiclantern.fm/forum/index.php?topic=7139.msg59876#msg59876).
Those lines all through the photo are aliasing. Dual-ISO scans 2 lines at 1 ISO and the next 2 lines at the other ISO. In the example linked, every other 2 lines of detail was overexposed. Because those every other 2 lines where overexposed, there was no detail to fill in the gaps. a1ex has made leaps and bounds in the processing since that early example, but the issue will still be there in limited situations.
Quote from: l_d_allan on December 05, 2013, 05:09:16 AM
But I guess I don't have to understand how it works to be able to use. Whew.
A better understanding of how it works, leads to a better ability to use it! It has limitations, and these need to be considered.
Follow the tutorial here (http://www.magiclantern.fm/forum/index.php?topic=8322.0) and the links there. With Auto ETTR + dual ISO + SNR limits set, this becomes a set and forget affair for probably 99% of all situations.
Quote from: a1ex on December 05, 2013, 03:26:38 AM
If you use DxO PRIME for denoising, you probably won't see any improvement except for really extreme cases. For me, 45 minutes for denoising a single image is a bit too much (but the results are fantastic IMO). With a GPU, I think it only takes a few minutes from what I've read.
Unfortunately, denoising cannot capture more detail, and is bound to destroy fine details Dual-ISO can capture extra detail without the noise. ;D
The detail is already there, just that noise is stronger. A good denoising algorithm will try hard to keep the detail; the non-local algorithms won't averae the neighbours of each pixel, like traditional algorithms do; they will find patches that look similar and will average those.
Here's an animation: http://www.cs.tut.fi/~foi/3D-DFT/
A similar algorithm can be used for super-resolution (that is, do a really good guess of missing pixels).
A comparison would be nice. My subjective impression is that DxO reveals roughly 1 stop of shadow detail, and noise is reduced by roughly 3-4 stops.
I regard detail as the highest priority, fine detail especially. I very rarely apply any luma denoising on my images.
There are denoising algorithms that work well, but they come at the expense of to much fine detail loss for myself. I also prefer to use the subjective increase in detail that noise produces where possible. I also very rarely view my content at a 1:1 ratio. It's either resized for web (averaging), or printed as such that the noise is not visible when viewed at reasonable viewing distances.
edit: At the noise levels present in the first 2 images in the PDF you linked, denoising would be preferred.
Got a little test for DxO PRIME:
original raw from Greg (http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5828.CR2)
dxo output (dng) (http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5828_DxO.dng)
a raw with shutter speed slower 2 stops (http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5829.CR2)
and jpeg files developed with ufraw from the above files (click for full-res images):
(http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5828_crop.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5828.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5828_DxO_crop.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5828_DxO.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5829_crop.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/dxo/IMG_5829.jpg)
Forgot a small detail: here's how fast is DxO without a GPU:
(http://a1ex.magiclantern.fm/bleeding-edge/dxo/prime-crop.png) (http://a1ex.magiclantern.fm/bleeding-edge/dxo/prime.png)
It would be great if you or anyone else can do a similar test with dual ISO vs DxO.
As expected, DxO has destroyed fine (and medium IMO) detail.
Above that AC control knob but below the radio there is a band of textured fabric/plastic.
In the 2 stop slower shutter shot, detail is present. In the DxO sample, it's been destroyed. Not to mention all of the artifacts in the DxO sample. :o
I'll run some tests myself, but don't expect them until Sat/Sun GMT+10.
Yeah, this is why I said it only brings back roughly 1 stop of detail. Still, I find it much cleaner than any other denoiser I've seen.
Dual ISO also removes some fine shadow detail in deep shadows (but it still does well on test charts, where noise gets hidden by strong detail). Not sure how it compares; the theory says 3 stops, but I didn't actually compare it with a 2x3EV bracketed shot.
Regarding combined DxO and dual ISO, I've noticed we have almost reached the limits of the 16-bit DNG format. That is, I've experimented with some highlight recovery algorithms, and if I reserve two bits for recovered highlights, the deep shadows (where the noise is strong enough to benefit from DxO) will get destroyed.
So, if we ever manage to implement dual shutter or a denoiser comparable to DxO, we should look at some file format that handles HDR better. I've looked at OpenEXR and floating point DNG, but both of them would require a major change in my workflow.
Quote from: a1ex on December 13, 2013, 09:05:09 AMI've looked at OpenEXR and floating point DNG, but both of them would require a major change in my workflow.
... but no doubt this is the way to go, I'm processing all my HDR as EXR recently in apps and then convert to floating point DNG in Lightroom. This is a major quality boost when doing further postprocessing over 16 bit, and the EXR-based floating point hasn't got an as hilarious filesize as floating point TIFF:
I can create floating point DNGs, but none of the open source programs I've tried could open them. Of course, I could convert them back to plain DNG with Adobe converter. Also, dcraw & friends do their internal processing as 16-bit, so even if I patch them to read floating DNGs, it wouldn't solve anything.
RawTherapee has a floating point pipeline, and I think darktable too.
Quote from: a1ex on December 13, 2013, 09:24:01 AM
Also, dcraw & friends do their internal processing as 16-bit, so even if I patch them to read floating DNGs, it wouldn't solve anything.
Indeed, and since traditional raw has only 14bit there's probably little reason for them for change this anytime soon. But maybe it's feasible to update the dcraw code to floating point yourself as you already know about the floating point dng format?
Quote from: a1ex on December 05, 2013, 05:02:50 AM
Yes. I don't use ACR or LR though, so I have no idea how smart they are (though I could try a demo). I've compared my script against rawtherapee's auto: https://www.dropbox.com/sh/013ewzjdjtj7p55/rBM16yO5Rh
Btw the ACR/LR "auto tone" is a complete catastrophe since they switched to pv2012, they silently keep tuning it with every update, but it still looks awful with every shot I've done. The only usable "auto" of ACR is auto exposure (double click the ev slider), if you really want working "auto" use DxO as they've got many good and actually working presets.
There is already a dcraw-float version, will look into that. If I can mod it to use Kelvin WB and the soft film curve from ufraw, that's pretty much all I need for my scripted workflow.
Quote from: Marsu42 on December 13, 2013, 09:34:46 AM
Btw the ACR/LR "auto tone" is a complete catastrophe since they switched to pv2012,
Agreed, I pushed the auto button once and couldn't believe what had happened :o Luckily I prefer to shoot manual and can mostly batch process a bunch of shots with the same settings. Also, the highlight recovery of pv2012 is excellent.
Quote from: Audionut on December 13, 2013, 04:55:30 PM
Also, the highlight recovery of pv2012 is excellent.
Let's see:
Original raw (http://a1ex.magiclantern.fm/bleeding-edge/hilite/3U3B3866.CR2) (blue channel is not clipped at all, red clipped a little, green clipped a lot)
ACR 8.3, -3EV, developed by Greg:
(http://a1ex.magiclantern.fm/bleeding-edge/hilite/small/3U3B3866.jpg) (http://greg.orimega.com/upload/ml/3U3B3866.jpg)
LR 5.3 demo, -3EV, developed by me (side question: why it's everything green at 5000K and zero tint?!)
(http://a1ex.magiclantern.fm/bleeding-edge/hilite/small/3U3B3866lr.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/hilite/3U3B3866lr.jpg)
A dumb algorithm I'm experimenting with (jpeg from ufraw):
(http://a1ex.magiclantern.fm/bleeding-edge/hilite/small/ettr.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/hilite/ettr.jpg)
DNG created by my algorithm (http://a1ex.magiclantern.fm/hdr/ufraw%20bug/ettr.dng%5B/url) (yep, same as the one from ufraw bug)
That's a good test case. Normally ACR/LR will recover detail if only one channel is blown. In Adobe applications you should use the highlight slider first to recover highlight detail, although in this case it makes no difference.
Have you made further changes to ufraw? How does it fair now on this (http://www.magiclantern.fm/forum/index.php?topic=5197.msg31367#msg31367)?
edit: I should have probably read more of that thread ::) ;)
This is how I found the bug. With the original ufraw, you need to change the white level in the DNG to 1-2 stops above what is now in order to get a correct rendering.
Just for fun:
Canon JPEG (extracted from the CR2):
(http://a1ex.magiclantern.fm/bleeding-edge/hilite/small/3U3B3866.thumb.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/hilite/3U3B3866.thumb.jpg)
dcraw -H 9:
(http://a1ex.magiclantern.fm/bleeding-edge/hilite/small/3U3B3866.dcraw.jpg) (http://a1ex.magiclantern.fm/bleeding-edge/hilite/3U3B3866.dcraw.jpg)
Quote from: a1ex on December 13, 2013, 06:31:28 PM
LR 5.3 demo, -3EV, developed by me (side question: why it's everything green at 5000K and zero tint?!)
That's why I was talking about when describing my wb/tint problems with LR, and even when you copy/past a valid wb setting from a non-dual iso shot it's not the same (I want to give you a proper report on this & that's why I didn't report back yet, but everything I tried results in a wb shift in LR). Is it really different with the standalone ACR converter?! They are supposed to use the exact same algorithms, just like ACR in PS.
As for highlight recovery in LR: Yes, it's good, but it's too weak for many dual_iso shots because even recovery -100 has still blown whites but if you add some -ev there still appears data out of nowhere. The only solutions are either to use tone curves or do a "one-shot hdr" assembly in enfuse or similar.
Also note that highlight recovery in LR is very different for crop & ff sensors; on crop it's stronger but tends to introduce real clipping, on ff it's weaker but never loses the natural roll-off into clipped areas.
a1ex, the RT team develop a algorithm with similar result: http://rawtherapee.com/forum/viewtopic.php?f=7&t=4500
Very good results! ;D
The actual RT
'color propagation' algorithm is good, but create much chroma artefact and is very [very] slow...
Quote from: Audionut on December 05, 2013, 06:25:50 AM
There are denoising algorithms that work well, but they come at the expense of to much fine detail loss for myself.
Any news about
RawImageCleaner by Reiner Wittmann (aka
kassandro)?
I test this, many times, and the results is incredible... really.
The stratagy of using the RemoveGrainHD on non-interpolate mosaiced data is really genial.
I really want to see that, one day, implemented and working 'smooth'.
[just idea]Maybe this could be implemented in the future at some command line tool for processing
.MLV:
MLV2DNG > DNGRecoverEdges (don't make difference?)> Fix possible vertical banding> Fix possible dead pixels> RawImageClearer> CR2HDR> Demosaicing (AMaZE, IGV or AHD)> Compile to some format (like Prores or Cineform 444).
Quote from: Audionut on December 05, 2013, 06:25:50 AM[...] much fine detail loss [...]
Do you try deconvolution algorithms? The Lucy-Richardson make a good job to 'recover' it.
Quote from: a1ex on December 13, 2013, 09:05:09 AM
So, if we ever manage to implement dual shutter
I'm curious what "dual shutter" is.
5d2 and Dec 14th Nightly Build.
ISO 100 seems to be the only usable "base ISO". With 1600 as the "Recovery" ISO, it shows an estimated 2.8 EV of dynamic range (DR) gained. Super!
But ... if I select ISO 400 as the "base" ISO, and attempt to use 6400 as the "Recovery" ISO, it doesn't seem to be working as expected. When I "Q" into the details of Dual-ISO, 6400 is shown as "Recovery" but there is only an estimated 1.1 EV gained.
When I get back to the Main "Expo" tab, the info for Dual-ISO shows 400/1600, with estimated 1.1 EV gain. I was expecting to see 400/6400 and closer to 2 to 2.5 EV of DR gained.
Am I doing something wrong? Is this "as expected" and I have a flawed understanding of Dual_ISO?
Are others seeing this behavior?
Quote from: Luiz Roberto dos Santos on December 14, 2013, 05:55:51 AM
Any news about RawImageCleaner by Reiner Wittmann (aka kassandro)?
No idea.
Removegrain was/is excellent, and was used in many avisynth scripts. I used it frequently to reduce the bitrate requirements without visual difference.
I don't keep up with denoisers, I really do not like to use them. Everyone I have seen so far has either blurred detail, and/or produced artifacting. I make sure to ETTR and crush blacks as needed.
Quote from: l_d_allan on December 14, 2013, 01:54:15 PM
I'm curious what "dual shutter" is.
Double shutter actuation for single photo. Note that it wouldn't even need the shutter to actuate twice for a large benefit. Being able to scan the entire frame at different ISOs before flush would be rather excellent.
Quote from: l_d_allan on December 14, 2013, 02:12:59 PM
Are others seeing this behavior?
I've had a few drinks, so not keen on being able to explain things in a manner than anyone could understand :o
Check this link: http://www.magiclantern.fm/forum/index.php?topic=7139.msg59971#msg59971
Notice how the DR gain reduces with increasing ISO.
Max real ISO on 5D2 is 1600.
Thanks!
That clarifies some fuzziness in my head.
BTW: Canon should have you on their payroll, and paying you Big Bucks.
Hmmmm ... wonder if "Auto-ISO" should be smart enough to take this into account? But that's another OP for another day.
Quote from: Audionut on December 14, 2013, 02:13:28 PM
Double (dual) shutter actuation for single photo. Note that it wouldn't even need the shutter to actuate twice for a large benefit. Being able to scan the entire frame at different ISOs before flush would be rather excellent.
Now THAT sounds interesting. Almost beyond "rather excellent".
With the power of the DIGIC-5 and 5+ cpu, I would speculate that the time between read-outs of the sensor values would be in the range of milliseconds ... or possibly even milliseconds?
So ... is this more or less how it would work? ML would scan the sensor at ISO 100, and "tuck the values away somewhere". Then re-scan a millisecond later at ISO 400 and get a second set of values? And then a third at ISO 1600? On newer cameras with "Real" ISO 3200 or ISO 6400, maybe rescan at highest ISO? Or not?
But as far as how much processing this would take, the "pipeline" for prep of JPEG's would seem at least as involved. Or not?
Potentially, there might essentially be No Ghosting. DR as good as the human eye?
Quote from: Marsu42 on December 13, 2013, 08:43:11 PM
As for highlight recovery in LR: Yes, it's good, but it's too weak for many dual_iso shots because even recovery -100 has still blown whites but if you add some -ev there still appears data out of nowhere. The only solutions are either to use tone curves or do a "one-shot hdr" assembly in enfuse or similar.
As I use Dual-ISO more, I'm encountering what you describe ... need the sliders to go past +/- 100 ... "twist those dials to 11"
In ACR, Auto-Exposure seems to only go to +/- 50, and after 50, it becomes less and less linear.
I used Dual-ISO with my 5d2 and T3i last night at a Christmas concert with Very contrasty interior lighting. HDR wasn't an option (too much movement). Dual-ISO was much more able to handle the contrast compared to non-Dual-ISO.
I'm still unclear on "Best Practice" for such a situation. Sorry for being slow. I started with ISO 100, and did some trial-and-error to get a best guess. I wonder if I should have started with ISO 1600, and done ETTR?
Or start with ISO 100, and do ETT-Left?
Is this a situation where Auto-ETTR and Dual-ISO work well together? I'm aware they can be used together, but am otherwise ignorant about how these ML capabilities combine.
BTW: are you familiar with Datacolor's SpyderCube? Interesting gadget, especially the "black trap" and "chrome ball" for the potential of "by the numbers" dynamic range.
I rigged up a DIY black trap (hole in 55-250 box with old black sock inside it) to go along with my SpyderCube to simulate a spotlight situation. The SpyderCube was in the spotlight, and the DIY black trap was partially in the shade from the tripod leg.
http://berean.zenfolio.com/misc/hC87E705#hc87e705
The ACR eyedropper can actually see the differences:
- DIY black-trap in shade from tripod leg = RGB(0,0,0)
- Unshaded DIY black-trap = RGB(1,1,1)
- SpyderCube black-trap in spotlight = RGB(5,6,5)
- Chrome ball in spotlight = RGB(255,255,255)
I'm hoping it will help clarify "best practice" between my ears.
Quote from: l_d_allan on December 14, 2013, 05:56:55 PM
So ... is this more or less how it would work?
No idea, I was dreaming :P a1ex is using existing Canon functionality for dual-ISO, so unless the option to scan the sensor twice before flushing the data is present in the Canon code, I doubt it would ever be possible.
Quote from: l_d_allan on December 14, 2013, 10:24:06 PM
I'm still unclear on "Best Practice" for such a situation.
There are 2 exposures. Base ISO exposure and recovery ISO exposure. You need to meter for both.
For your highlights, you meter off the lower ISO. For your shadows, you meter off the higher ISO. I personally always meter the highlights first. So ISO 100 and check histogram for over exposure. Then enable dual-ISO with a recovery ISO as needed. You can use zebras to check what the recovery ISO is doing. Where colored zebras appear, the recovery ISO is overexposed and you lose resolution. Where grey zebras remain, shadows are still in the noise floor.
Quote from: Audionut on December 13, 2013, 08:48:49 AM
I'll run some tests myself, but don't expect them until Sat/Sun GMT+10.
Power supply died last night. Will be a couple of days before I get a replacement.
Quote from: Marsu42 on December 13, 2013, 09:17:14 AM
... but no doubt this is the way to go, I'm processing all my HDR as EXR recently in apps and then convert to floating point DNG in Lightroom. This is a major quality boost when doing further postprocessing over 16 bit, and the EXR-based floating point hasn't got an as hilarious filesize as floating point TIFF:
Got it working (my first experiment on 32-bit float DNG here (http://www.magiclantern.fm/forum/index.php?topic=9285.msg91867#msg91867)). Can you share how you are processing the floating point DNG in Lightroom?
I've opened my DNGs in LR 5.3, boosted exposure to +5, shadows to max, and it seems their internal processing is on 16-bit integer. So right now, the only tool that can process 32-bit DNGs properly seems to be Adobe's dng_validate.exe from the DNG SDK.
Quote from: a1ex on December 15, 2013, 05:30:00 PM
I've opened my DNGs in LR 5.3, boosted exposure to +5, shadows to max, and it seems their internal processing is on 16-bit integer.
Unfortunately you seem to be correct, your fp raw dng is limted to -5....+5 ev exposure correction, while my non-raw demosaiced hdr dng files are -10....+10. Interesting the Adobe sdk supports it, I guess they didn't add it to ACR/LR yet simply because there aren't any cameras known to them that output that format yet :-(
The only solutions I can think of is to either ask an Adobe dev to add this format (that non-oss for you...) or convert the fp raw dng to non-raw, ACR/LR is able to deal with the latter, though it probably increases the flle size and you lose the ability for lossless wb correction.
Quote from: a1ex on December 14, 2013, 02:22:27 PM
Max real ISO on 5D2 is 1600.
Anyone happen to know the max "real" ISO on the 6d?
5d3?
T3i/600d?
5DIII - 128k
6D - 6400
others - 3200
gen 1 like 500D/50D/5DII are 1600
Quote from: 1% on December 17, 2013, 12:16:34 AM
5DIII - 128k
6D - 6400
Are you sure?! The code in lens.h only makes a difference between digic4 (3200) and digic5 (12800), if you're correct and the 6d is also "only" 6400 this should be changed in the code.
There seems to be 4 categories of ISOs (according to how they behave internally):
a) the ones that can be configured via CMOS[0] (on 5D2: 100-1600; they may be different in photo vs lv; the dual iso module uses this one as max iso)
b) the ones that use digital gain, and you can undo that gain via ML digital ISO controls (on 5D2: 6400); this is used for tricks like gradual exposure, hdr video...
c) in-between (maybe this is also hardware but it has some secondary amplifier path)
d) max ISO that can be applied via exposure override in LiveView
So it's quite complex, and the numbers from lens.h may not be 100% correct.
For practical purposes, I consider the max useful ISO to be 1600. The higher ones are not any cleaner (maybe up to 0.5 stops), and the price to pay is a large amount of clipped highlights.
I don't really like the results I get from isos above A in general, especially when its dark. For both CR2 and raw wouldn't they be equivalent to photoshop?
Well, if you compare 1600 untouched with 6400 darkened in post by 2 stops (all other variables being equal), you may see that 6400 is a tiny bit cleaner on 5D3 (maybe also on 6D).
But for that tiny bit, you lose 2 stops of highlights.
Anyway, if ETTR chooses ISO 1600 or more, it probably is the least noisy option (of course, assuming you have already maxed out shutter and aperture).
ETTR usually makes good choices, I don't really set much anymore. Only have to override or turn it off when I just want the highlights in the dark and can't have a long exposure.
But my 128K iso is not so useable. The 6400 is still in the A range. So 5DIII has 1 "analog" iso above what 6D has.
Here's some data:
5D3:
Quote
Table 1
-------------------------------------------------
Apparent Maximum Measured
ISO Gain Read Noise signal Dynamic range
e/DN (electrons) (electrons) stops
100 5.04 34.9 68900 10.9
200 2.52 18.3 32400 10.8
400 1.26 9.8 16200 10.7
800 0.63 5.6 8100 10.5
1600 0.315 3.6 4050 10.1
3200 0.157 2.7 2030 9.6
6400 0.079 2.5 1000 8.6
12800 0.039 2.1 500 7.9
25600 0.0197 2.05 250 6.9
maximum DN: ISO 100 = 15331 (includes offset)
DN offset = 2048
Pixel pitch= 6.25 microns.
22.3 megapixels.
-------------------------------------------------
src: http://clarkvision.com/articles/evaluation-canon-5diii/index.html
5D2:
Quote
Table 1
-------------------------------------------------
Apparent Maximum Measured
ISO Gain Read Noise signal Dynamic range
e/DN (electrons) (electrons) stops
50 4.2 24.2 65700 11.41
100 4.1 23.5 59400 11.30
200 2.03 11.9 29700 11.20
400 1.01 6.4 14800 11.18
800 0.51 3.7 7425 10.97
1600 0.25 2.5 3710 10.54
3200 0.127 2.5 1860 9.54
6400 0.063 2.5 930 8.54
12800 0.032 2.5 460 7.54
25600 0.016 230
Pixel pitch: 6.4 microns.
S/N on 18% gray card, ISO 100 = 103.
Sensor Full Well Capacity at lowest ISO: 65,700 electrons.
Sensor dynamic range = 65700/2.5 = 26,280 = 14.7 stops.
ISO at unity gain (scaled to 12 bit) = 1600 (14-bit unity gain = ISO 404).
Low Light sensitivity Factor: 640.
Apparent Image Quality, AIQ = 109
All data derived by R. Clark, December, 2008.
src: http://clarkvision.com/articles/evaluation-canon-5dii/index.html
Quote from: a1ex on December 17, 2013, 04:59:25 PM
Well, if you compare 1600 untouched with 6400 darkened in post by 2 stops (all other variables being equal), you may see that 6400 is a tiny bit cleaner on 5D3 (maybe also on 6D).
But for that tiny bit, you lose 2 stops of highlights.
Soooooo ... is it a valid interpretation that on my DSLR's (5d2, T3i/600d, and 6d), it is "best practice" to limit ISO to 1600 max? Even on the 6d? Then lighten in pp? I use ACR and LR.
That's what I do.