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Archive 2014 · DualISO vs Exmor

whumber
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p.1 #1 · p.1 #1 · DualISO vs Exmor

Note: This was a two part article previously posted elsewhere that I've merged together, so I may have missed some things and there may be sections where the writing doesn't flow properly.

I've already posted this on another website but thought people here might be intersted as well. I've noticed there's a feeling that MagicLantern's DualISO for the 5D3 is nothing more than a gimmick and that it's too flawed to actual be useful.I've been using it for over a year now and while there were some major tradeoffs to using it in the beginning, the MagicLantern guys (i.e. mostly A1ex) have made enormous steps towards making it a genuinely useful tool for high dynamic range shooting on Canon DSLRs.

When the A7R was first released I bought one because I wanted to see what it was like shooting on the same sensor as the D800E, but after a couple days I returned it because I just could not get over the terrible ergonomics and poor battery life of the camera. I did do some very rough comparisons between DualISO and the A7R at the time so I had some sense then of how they compared. Anway, fast forward to a couple weeks ago; like always happen someone was complaining that their 5D3 didn't give enough dynamic range, so I recommended DualISO and then a bunch of people started claiming that you lose half your resolution, get horrible aliasing and artifacts, it was completely unsuitable for printing, and still didn't get rid of the pattern noise or bring the DR anywhere close to an Exmor sensor camera. I wanted to create some kind of controlled experiment to compare a DualISO 5D3 with an Exmor sensor, as I hadn't seen anything like that online, so I bought an A7 and EF adapter to perform the test.

The first shot shows the two shots pictures with no post-processing exposure adjustments (Note: Please forgive the terrible picture, I was cleaning up my bike while I was doing this.) Exposure was set so that the sky was as exposed as possible without clipping and I turned off all the lights in my garage so that the interior was much darker. Focus is on the rectangular object in the lower left corner, which is a Risk box, and is ~5 stops underexposed. Both pictures were taken with a 70-200ii.


	http://i.imgur.com/2AKkFhHh.jpg

The second shot shows the result of a 5-stop push in LR to the entire exposure for each shot. The 5D3 shot was scaled to match the resolution of the A7 so there was no obvious difference due to resolution. Also, for these shots there's no luminance noise reduction applied but I did apply +25 of chrominance noise reduction; I'll show a shot with zero noise reduction in the full writeup.


	http://i.imgur.com/vGG80jFh.jpg

Finally the meat of what I wanted to know, in a severely underexposed area of the frame where I pushed the shadows an ungodly amount how well does the 5D3 with DualISO compare.


	http://i.imgur.com/yNClqunh.jpg

The 5D3, left, shows a bit more noise and less detail but actually maintains more accurate colors than the A7 which seems to desaturate the shadows significantly. But compared to the difference between a vanilla 5D3 and the A7 and this becomes a pretty amazing result.

For fun, here's the vanilla 5D3 and the 1Ds3 for comparison.


	http://i.imgur.com/RUWzOO9h.jpg

Also, the X-T1 vs the A7.


	http://i.imgur.com/ZtYVTGsh.jpg

Sep 05, 2014 at 07:34 AM

whumber
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p.1 #2 · p.1 #2 · DualISO vs Exmor

I then took both cameras hiking to get some more real world type pictures as well as to show one of the weaknesses that I know still exists with DualISO. For all of the following pictures I metered so that the highlights were just clipping (based on the A7 zebras) and then dialed it down 1/3rd a stop. ISO, aperture, and shutter speed are identical for each scene, although the light was changing quite a bit so not all shots are exposed identically but I'd say they're all within 1/3rd stop. For the first shot I was using a 40mm STM on the 5D3 and a 16-35 F4 IS on the A7 (made the weight distribution fairly even and meant I didn't have to constantly swap lenses), while on the last shot I used the 16-35 at 16mm for both cameras. Both shots were done at ISO 100 while the secondary ISO for the DualISO shots was 1600 for the first shot and 3200 for the last shot were I wanted to show a specific type of artifacting that can occur.

The first is a tree that had a nice dark shadow down the middle from a branch hanging just right with a bright blue sky in the background.


	http://i.imgur.com/YSDXNvXh.jpg

Zooming in we can see that the shadow from the branch is almost completely black near the branch and then gradually lightens a bit.


	http://i.imgur.com/olGOKQVh.jpg

First, comparing the vanilla 5D3 and A7 I pushed the exposure by 2 stops and set the shadows slider to +100 in Lightroom.


	http://i.imgur.com/1cccrUxh.jpg

We can already see that the vanilla 5D3 is falling apart in the shadows with tons of color noise and mush for detail in the particularly dark regions while the A7 still looks fine. This was were the overall exposure looked fine but I decided to push two more stops just to see how the A7 did.


	http://i.imgur.com/5kSC6gQh.jpg

By this point the 5D3 shadows are unuseable garbage but the A7 is still looking respectable, very impressive and this is the primary reason why landscape photographers have been ditching Canon for Nikon over the past two years. Well that and the 14-24. And 36MP, but I digress.

So now that we've shown the A7 rules and vanilla 5D3 drools, how did magic lantern do? Again, we start off with +2 stop exposure and +100 shadows.


	http://i.imgur.com/eFjyzXgh.jpg

Whoa, huge difference compared to the vanilla 5D3. At this point I'll say the DualISO 5D3 and A7 are doing equally well, but what happens if we push another stop?


	http://i.imgur.com/c9aaLWbh.jpg

The two are still very close but I think the noise in the A7 has a slightly higher quality to it, still extremely close but I'll give it to the A7 at this point. How about one more stop.


	http://i.imgur.com/4b1cedXh.jpg

Again, still close but I think the A7 is starting to pull away from the DualISO 5D3 now. The 5D3 seems a bit more exposed than the A7, probably from the changing light conditions, and the interpolation scheme seems to be showing some flaws at the edges of where the bark becomes washed out. Conveniently, Lightroom's moire removal tool works extremely well to get rid of these, but they can still show up if you push the files very hard. A win for the A7, but not by a large margin. Below, I'm showing the dualISO 5D3 next to the vanilla 5D3 to show what an insane difference dualISO makes for the 5D3.


	http://i.imgur.com/dgpT65eh.jpg

Edited on Sep 05, 2014 at 07:37 AM · View previous versions

Sep 05, 2014 at 07:34 AM

whumber
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p.1 #3 · p.1 #3 · DualISO vs Exmor

The last thing I want to show is that there is another type of artifacting that can occur in situations where you push the secondary ISO very high, for this example 3200, and you have thin lines (i.e. small branches or wires) running almost parallel to the sensor rows. On the left hand side of the frame in the shots below you can see a tree with some bare branches sticking out.


	http://i.imgur.com/uj44YAmh.jpg

If we zoom in, we can see some places where the tree branches seem to vanish and reappear. This can happen in a very specific scenario where you are :

Using a very high secondary ISO. This usually only happens over ISO 3200, and MagicLantern will warn you about using these settings.

You have a very thin object. Thin as in less than ~2 pixel in width.

That thin object is at an angle of less than ~15 degrees to the long-axis row of pixels.


	http://i.imgur.com/e0kLtoqh.jpg

If you run into this scenario you will probably see this issue. Whether or not you'll see it in a print is another issue entirely. I made a 13x19 print of this exact shot and it's pretty much impossible to see but if you print larger then it could certainly be an issue. Most scenes don't require the secondary ISO to be set any higher than ISO 800 though as you really get diminishing returns for each additional stop of secondary ISO, but in cases where you absolutely need to push higher then be careful.

So who wins? Clearly the A7. It's simply the better tool for this kind of shooting. The workflow is way easier, you don't have to fiddle with installing MagicLantern, turning on DualISO, fiddling with the secondary ISO, or worrying about factors that might leading to artifacting. Plus it retains resolution better when pushed. That said, unlike with the vanilla 5D3 where the difference in image quality in these types of adverse situations is enormous, we're really nitpicking minor differences here. The fact that the guys from MagicLantern have extracted so much extra dynamic range from the Canon sensor is pretty amazing. Additionally, there's a yet to be released update for magic lantern that adds ~0.8 stops of highlight headroom for the 5D3 just using some of the pixel capacity that Canon decided to keep in reserve for whatever reason (i.e. when the 5D3 sensors clips to white, it's not actually clipped. There's at least another 0.8 stops available before it really clips.)

So is DualISO great for people who only shoot landscapes and run into DR issues all the time? I'd call it good but not great, if you're this kind of shooter you're crazy for not moving to Nikon or at least picking up an A7R. Is it great for people who normally shoot lower contrast scenes but get frustrated when they occasionally do run into a DR limited scenario? Definitely, this is pretty much the category that I fall into and DualISO has pretty much eliminated any temptations to move over to Nikon.

As a final thought, about a week after I initially wrote and posted this I was really interested how these results translated to prints. I had made prints of the shot with the branch aliasing issue and was surprised how little of that actually showed up in prints so I decided to make 13x19 prints of all the shots I took. I feel pretty safe in saying that if you're printing at 13x19 or smaller and keep secondary ISO at or below 1600, the A7 has no real advantage over the DualISO 5D3. When A1ex releases the the ADTG update I'll have to rent a D810 and do another comparison.

Sep 05, 2014 at 07:35 AM

jcolwell
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p.1 #4 · p.1 #4 · DualISO vs Exmor

Thanks for sharing your tests.

Dual ISO looks pretty good. Maybe it's time to try ML on one of my 6D.

Sep 05, 2014 at 07:53 AM

PhilDrinkwater
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p.1 #5 · p.1 #5 · DualISO vs Exmor

Really good writeup. Thanks!

Sep 05, 2014 at 07:58 AM

AGeoJO
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p.1 #6 · p.1 #6 · DualISO vs Exmor

Thanks for doing the test and comparison. So, it looks like more could be extracted from the dated Canon sensor, huh?

Sep 05, 2014 at 08:49 AM

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p.1 #7 · p.1 #7 · DualISO vs Exmor

That's amazing work. Thanks for sharing. Could you summarize the positives and negatives of dual iso in your experience?
Thanks
Derrick

Sep 05, 2014 at 11:13 AM

snapsy
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p.1 #8 · p.1 #8 · DualISO vs Exmor

Very nice comparison. The resolution loss with dual ISO is a function of the sensor not being able to read all lines for the secondary ISO read path. That is something Canon should be able to solve in a new sensor if they're motivated enough. It might be the very solution they have planned for increasing low ISO dynamic range, vs switching to a parallel digital ADC readout architecture like Sony uses.

Sep 05, 2014 at 11:35 AM

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p.1 #9 · p.1 #9 · DualISO vs Exmor

Great way to work around the canon shadows noise issues. Beside the auto iso, most sony cam have multiple iso sequence option to lower the noise in low light. Actually, this multiple iso option works great in any light condition. It is the same approach like ML application. I am wonder why canon has not done this yet. Thank for sharing.

Sep 05, 2014 at 11:40 AM

Fred Miranda
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p.1 #10 · p.1 #10 · DualISO vs Exmor

Great post. I have tried it when it was first released and it was just ok. It seems they improved this function greatly now.

What happens to the current DualISO highlights? Does it get clipped earlier?

Sep 05, 2014 at 11:57 AM

whumber
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p.1 #11 · p.1 #11 · DualISO vs Exmor

mttran wrote:
Great way to work around the canon shadows noise issues. Beside the auto iso, most sony cam have multiple iso sequence option to lower the noise in low light. Actually, this multiple iso option works great in any light condition. It is the same approach like ML application. I am wonder why canon has not done this yet. Thank for sharing.

DualISO uses a single exposure with alternating ISO values applied to each bayer line pair.

Sep 05, 2014 at 12:01 PM

whumber
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p.1 #12 · p.1 #12 · DualISO vs Exmor

Fred Miranda wrote:
Great post. I have tried it when it was first released and it was just ok. It seems they improved this function greatly now.

What happens to the current DualISO highlights? Does it get clipped earlier?

With the current builds of ML the highlights behave exactly as they do with a vanilla sensor, although if you push the secondary ISO to a crazy value you can get some strange aliasing-like artifacts like I showed with the branches. With the experimental builds they've tweaked the ADC registers so that you can get a true lower ISO, something like ISO 64, which gives you another 0.8 stops of highlight headroom.

Sep 05, 2014 at 12:04 PM

mttran
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p.1 #13 · p.1 #13 · DualISO vs Exmor

whumber wrote:
DualISO uses a single exposure with alternating ISO values applied to each bayer line pair.

Sony multiple iso option is also a single output exposure with an average auto iso.

Sep 05, 2014 at 12:10 PM

whumber
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p.1 #14 · p.1 #14 · DualISO vs Exmor

snapsy wrote:
Very nice comparison. The resolution loss with dual ISO is a function of the sensor not being able to read all lines for the secondary ISO read path. That is something Canon should be able to solve in a new sensor if they're motivated enough. It might be the very solution they have planned for increasing low ISO dynamic range, vs switching to a parallel digital ADC readout architecture like Sony uses.

If they've setup their dual pixel sensors in a way that would allow separate amplifier gains for each sub-pixel then you should be able to avoid the minor resolution loss and other potential artifacts completely. I know that the research builds of ML are reported to have slightly more DR than the D810 when pushing the secondary ISO to 800 it will be really interesting to see what can be done when they get ML running on the 70D.

Sep 05, 2014 at 12:31 PM

whumber
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p.1 #15 · p.1 #15 · DualISO vs Exmor

mttran wrote:
Sony multiple iso option is also a single output exposure with an average auto iso.

Are you thinking of multiexposure noise reduction? That's completely different from DualISO. DualISO only takes one exposure so that moving objects are a non-issue. Multi-exposure noise reduction is a nice feature but only works for completely static scenes unless you're trying to simulate a ND filter.

Sep 05, 2014 at 12:35 PM

Access
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p.1 #16 · p.1 #16 · DualISO vs Exmor

All I can say is this: It's too bad the guys from Canon aren't able to / can't / won't hire the ML team to do the job that their own programmers evidently can't do.

Edited on Sep 05, 2014 at 12:47 PM · View previous versions

Sep 05, 2014 at 12:46 PM

whumber
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p.1 #17 · p.1 #17 · DualISO vs Exmor

dakel wrote:
That's amazing work. Thanks for sharing. Could you summarize the positives and negatives of dual iso in your experience?
Thanks
Derrick

Good idea.

Pros

Read noise issue eliminated

Dynamic range brought up to Exmor level (or even higher for research builds)

Completely free

Along with DualISO, ML also offers features like focus peaking, RAW histograms, and amazing intervalometer and bracketing capabilities for still photographers

Cons

Adds an extra step to your workflow (although this has largely been mitigated by the MagicLantern DualISO LR plugin)

More to think about when shooting, should I use DualISO or not, what should my secondary ISO be (here you can set ML to automatically calculate these things for you based on the RAW histogram)

Some minor resolution loss in non-overlapping regions (resolution loss is very small using latest interpolation schemes and if keeping secondary ISO at or below 1600)

Quality of shadow noise is not quite as nice as non-DualISO shots (only shows up on computer screens, I've never actually seen this translate into prints)

Potential for artifacts in extreme situations (Keep secondary ISO at or below 1600 and you should be fine)

Just to reiterate though, if you're primarily a landscape shooter I think that a D810, A7R, or MF is still the way to go. But for people like me who don't print larger than 13x19 and for whom DR limited landscape shots are a small subset of a portfolio, then DualISO is a fantastic tool to have in the arsenal.

Sep 05, 2014 at 12:47 PM

mttran
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p.1 #18 · p.1 #18 · DualISO vs Exmor

whumber wrote:
Multi-exposure noise reduction is a nice feature but only works for completely static scenes unless you're trying to simulate a ND filter.

It works with hand held & moving subject. Try it, your A7 should has this option.

Sep 05, 2014 at 01:05 PM

whumber
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p.1 #19 · p.1 #19 · DualISO vs Exmor

mttran wrote:
It works with hand held & moving subject. Try it, your A7 should has this option.

I'm guessing it's either the handheld twilight or anti-motion blur scenes modes you're referring to. From what I can tell they don't actually work with moving subjects, they try to match the frames and if a frame doesn't match the initial frame then it's just thrown away.

Sep 05, 2014 at 01:17 PM

kezeka
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p.1 #20 · p.1 #20 · DualISO vs Exmor

Where can we find a link to the latest ML 5D3 firmware? This is pretty nifty. Also, is there a way to revert back to the stock firmware?

Sep 05, 2014 at 01:49 PM

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