Is there any loss of quality in a Dual-ISO image vs a normal exposure?

[Chele]

I use ML every time I use my cameras (70D & 6D).  I have been using it for several months on the 70D and just few weeks on the 6D(just bought it).  The cameras are used strictly for photography in manual mode and am a big fan of ETTR.  With that said, I just started playing with Dual-ISO (had not been able to get it to work before ).  I took several landscape photos this week, I would take two shots of every scene with the 6D, one with Dual ISO turned on and another with it off ---- no other difference -- manual mode and camera set on tripod --- ISO 100/800 F16, SS from 1/8" to 1.5", Canon 70-200L F4 IS(is disabled), circular polarizer.

The shots taken with Dual ISO have more "snap" to them, I can't get the other shots to match that "snap".  I'm using LR v5.7 and the monitor has been calibrated. 

https://flic.kr/s/aHskpS5oMp  (images are labeled as Std and Dual ISO)

SO, the question: What are the disadvantages to using Dual ISO(quality, resolution, etc)?  So far I really like Dual ISO!

Thanks,

[mothaibaphoto]

Read this thread

[Levas]

Good way too know if dual iso could be of any use is to enable the magic lantern raw histogram.
You can see a raw histogram while in live view, one of the best futures for exposure tweaking.
If your shadows aren't touching the left side of the histogram and your highlights aren't touching the right side, then there is no use of dual iso.

And your 6d doesn't suffer that much of ugly pattern noise in the shadows as some other canons do.
So lifting non clipped shadows 2 stops with the 6d isn't a problem.

[Guillermo Luijk]

Could you please show 100% crops of the shadows and the highlights in exactly the same area for dual and std ISO?.

At web picture sizes dual iso will always produce cleaner images, while 100% crops are more representative of what you would achieve printing large.

Regards

[Chele]

Thanks for the histogram tip and the link to the article.  I'll post the samples later on today or tomorrow.


Trying to back off on ML, becoming too much of a fanboy:(

[Chele]

The two crops have been added as requested. 

Levas,
I think the histogram does not really help in this case:(, the images shown here don't really reach the full DR of regular RAW images.  I think that in this case, unless there is a down side, Dual ISO gives better images even when within the camera's (6D) DR.  Of course, this is in my taste, or lack of!

Here is the link for the two full images as well as the cropped snapshots.

https://www.flickr.com/gp/76233298@N02/7705c2

[Levas]

You can't discuss about taste and I definitely see difference between the two shots.
I downloaded the full resolution images and the dual iso image is brighter overall I guess. Or at least brighter in the shadows and midtones.
That's probably the snap you talk about.

But if you zoom in to 100% and look at the plain field in the middle of the photo, you can see there is less detail, less rocks in the field, the field overall looks a little smudged or so.
And if you look at the top of the hills against the sky, you see some thick lining, with some green and some purple colors (aliasing)

I don't know if you did much post processing, but I'd definitely think you could achieve the same 'snap' with the standard exposure image.

[dfort]

Is there any loss of quality in a Dual-ISO image vs a normal exposure?

If you call this loss of quality then yes:

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

Taken from the first post in the Dual ISO - massive dynamic range improvement (dual_iso.mo) discussion.

The sample posted on flickr isn't a subject that has a very wide dynamic range so there doesn't seem to be much in the way of resolution loss. However, you get some more exposure in both the highlights and shadows in dual iso so you're probably getting some extra color saturation and thus your perceived "snap" to the image.