Resolution limit of underwater videos

I mainly use action cameras (Insta360 OneRS, ONE X2, Yi 4K+) but I also take videos with my Sony A6000 that I want to upgrade because of the lack of 4K. However, I recently read an interesting article about the underwater cinematography of the upcoming Avatar movie:

https://ymcinema.com/2022/10/24/the-underwater-cinematography-behind-avatar-2-3d-beam-splitter-and-nikonos-lenses/

The following quotes are from Pawel Achtel who developed the special camera system for the underwater work: 

“Dome ports, which are used for wide-angle lenses, produce image plane curvature combined with astigmatism when placed underwater. This causes extensive blurring of images. In ideal conditions, such systems are limited to approximately 2K equivalent sharpness (approximately 1000 line pairs per picture width). This falls far short of today’s high-resolution camera standards. Flat ports perform even worse. While having negligible effect out of the water, a flat port produces severe chromatic aberrations, pin-cushion distortions, astigmatism, and (often undesirable) image magnification. For wide-angle imaging, a flat port limits image sharpness to the equivalent of approximately 1K (standard definition) quality.  An example of a flat port can be a dive mask. Much of the underwater content that is claimed to be 4K or 8K is really limited to the approximately high-definition quality or less by its optics, even though it may be recorded on an 8K capable camera”.

The new GoPro Hero 11 has 5.3K and my Inst360 One RS can even record 6K (wide mode) but is it actually that high resolution or just a much lower resolution  artificially up-scaled? Few years and we will have 8K action cameras but do you need this when the optical quality is not there? Maybe the macro requires high resolution but considering the optical quality of the water going higher than 4K doesn't make sense.

What do you think about these limitations of resolution?

The benefits to 4k above full hd are already marginal. With my not perfect, but probably not below average vision, I can easily tell the difference between a 720p and 1080p signal on my tv, the difference for a 4k signal is not really obvious to me. 8k in my opinion is only sensible as a basis for further working with the files (ability to crop etc), which are of limited use underwater, because the further everything is away from the camera the worse it looks. Similar to the effect of downsampling from 4k to full hd and having an obviously better signal, 8k will probably good as a recording format, but not really as a distribution format. Obviously everything also depends on the format of delivery. My TV is not among the largest, and I assume that a larger TV will make the difference between 4k and HD much more obvious. With 8k I still have my doubts.

With regards to being limited by optics, I'm not so sure. I know there has been discussions about outresolving lenses with high mp sensors in still imagery for a long time, but so far, every increase in resolution (with now some MF bodies featuring over 100mp) seems to have been perceived as a real upgrade. On the other hand physics usually can't be cheated...

While all that is probably true, there is the real world benefit of using cropping in an 8k video to produce a motion-stabilized 4k video.

I'm guessing that new wet optics are going to be the answer here.

I think you are comparing apples and bananas here, the article is about producing IMAX footage for the big screen where you will likely see need the high resolutions.   It uses Nikonos lenses probably also because they are small which would reduce the size of the 3D beam splitters quite likely, also they used a pool of 100 Nikonos lenses and picked out two matched lenses, this seems to be important for the 3D work they are doing.  This is quite different to your computer monitor or a TV which have more limited resolution. 

One advantage of 4K screens for your PC is crisper text as the higher resolution is able to produce the rounded shapes of the characters much better without fuzzy edges from individual pixels.  The advantage of the 4K is more headroom when you are processing the images.

On the question of 4K for your go pro- I would say the main advantage is processing head room, quite likley the go-pro optics limit actual UW resolution to 1-2K as suggested in the article - you usually get what you pay for in optical quality.

I mainly use action cameras (Insta360 OneRS, ONE X2, Yi 4K+) but I also take videos with my Sony A6000 that I want to upgrade because of the lack of 4K. However, I recently read an interesting article about the underwater cinematography of the upcoming Avatar movie: https://ymcinema.com/2022/10/24/the-underwater-cinematography-behind-avatar-2-3d-beam-splitter-and-nikonos-lenses/

The following quotes are from Pawel Achtel who developed the special camera system for the underwater work: 

“Dome ports, which are used for wide-angle lenses, produce image plane curvature combined with astigmatism when placed underwater. This causes extensive blurring of images. In ideal conditions, such systems are limited to approximately 2K equivalent sharpness (approximately 1000 line pairs per picture width). This falls far short of today’s high-resolution camera standards. Flat ports perform even worse. While having negligible effect out of the water, a flat port produces severe chromatic aberrations, pin-cushion distortions, astigmatism, and (often undesirable) image magnification. For wide-angle imaging, a flat port limits image sharpness to the equivalent of approximately 1K (standard definition) quality.  An example of a flat port can be a dive mask. Much of the underwater content that is claimed to be 4K or 8K is really limited to the approximately high-definition quality or less by its optics, even though it may be recorded on an 8K capable camera”.

The new GoPro Hero 11 has 5.3K and my Inst360 One RS can even record 6K (wide mode) but is it actually that high resolution or just a much lower resolution  artificially up-scaled? Few years and we will have 8K action cameras but do you need this when the optical quality is not there? Maybe the macro requires high resolution but considering the optical quality of the water going higher than 4K doesn't make sense.

What do you think about these limitations of resolution?

 

 

 

In general based on practical experience there is benefit to shoot in 4K and it looks better than shooting in HD. This is because water has a degradation effect which reduces resolution and introduces other issues (I am not sure why a dome would have astigmatism but field of curvature, come and chromatic aberrations are clearly there to be seen).

This degradation effect reduces your 4K to say 2K however if you started from 2K you would end up in 1K.

So the whole argument that shooting higher resolution is not effective to improve image quality is flawed but what the writer said that the content made by an 8K camera underwater may not be 8k resolution is true.

There is however a situation of diminishing returns going higher with pixels as the maximum resolution of a camera is not in fact the claimed resolution and this is mostly dependand on the lens

So your GoPro 5.7K etc are probably not even resolving 2000 lppw of 4K and this is because they have a poor lens with lots of defect the sensor has those number of pixels but this does not mean at all that your gopro will prouduce 5.7k resolution is the lens that drives the resolution which is always lower than the sensor limit

And this is the reason why poor cheap system with poor lens look bad

So to answer your question you should upgrade your A6000 to a 4K capable camera but make sure you build a system not just buy a body and then use an average lens and port and no your gopro will always look crap no matter how many megapixels they have because they do not reach the theoretical limit even on land

Based on my experience the most important factor in resolution is water clarity unfortunately unless you do baited dives fish do not hang in clear water but love murky water with a lot of sediment which is the primary reason for loss of IQ let alone dome ports

This is shot in the mediterranean visiblity 10-15 meters

[/url] This is shot in the bahamas visibility 30 meters

It is the same set up though the level of sharpness is wildly different even at comparable distance

13 hours ago, phxazcraig said:

While all that is probably true, there is the real world benefit of using cropping in an 8k video to produce a motion-stabilized 4k video.

I'm guessing that new wet optics are going to be the answer here.

It's a good point but it also requires cropping

12 hours ago, ChrisRoss said:

I think you are comparing apples and bananas here, the article is about producing IMAX footage for the big screen where you will likely see need the high resolutions.   It uses Nikonos lenses probably also because they are small which would reduce the size of the 3D beam splitters quite likely, also they used a pool of 100 Nikonos lenses and picked out two matched lenses, this seems to be important for the 3D work they are doing.  This is quite different to your computer monitor or a TV which have more limited resolution. 

One advantage of 4K screens for your PC is crisper text as the higher resolution is able to produce the rounded shapes of the characters much better without fuzzy edges from individual pixels.  The advantage of the 4K is more headroom when you are processing the images.

On the question of 4K for your go pro- I would say the main advantage is processing head room, quite likley the go-pro optics limit actual UW resolution to 1-2K as suggested in the article - you usually get what you pay for in optical quality.

I think it's still avalid comparison since the physics applies not just for IMAX. Of course our work doesn't require the same quality as the new Avatar movie.I'm sure that in few generations we will have 8K GoPro but it won't make any sense with 1-2K underwater resolution.

10 hours ago, Interceptor121 said:

In cinematography you want straight lines distortion is a no go not allowed full stop. Which means lots of underwater productions are done with large dome ports. This is the reason a custom system has been developed as water contact optics would not fit the bill The referred example of 1000 lppw in a dome is difficult to understand as it does not say which system was used to measure it and the starting resolution.

In general based on practical experience there is benefit to shoot in 4K and it looks better than shooting in HD. This is because water has a degradation effect which reduces resolution and introduces other issues (I am not sure why a dome would have astigmatism but field of curvature, come and chromatic aberrations are clearly there to be seen).

This degradation effect reduces your 4K to say 2K however if you started from 2K you would end up in 1K.

So the whole argument that shooting higher resolution is not effective to improve image quality is flawed but what the writer said that the content made by an 8K camera underwater may not be 8k resolution is true.

There is however a situation of diminishing returns going higher with pixels as the maximum resolution of a camera is not in fact the claimed resolution and this is mostly dependand on the lens

So your GoPro 5.7K etc are probably not even resolving 2000 lppw of 4K and this is because they have a poor lens with lots of defect the sensor has those number of pixels but this does not mean at all that your gopro will prouduce 5.7k resolution is the lens that drives the resolution which is always lower than the sensor limit

And this is the reason why poor cheap system with poor lens look bad

So to answer your question you should upgrade your A6000 to a 4K capable camera but make sure you build a system not just buy a body and then use an average lens and port and no your gopro will always look crap no matter how many megapixels they have because they do not reach the theoretical limit even on land

Based on my experience the most important factor in resolution is water clarity unfortunately unless you do baited dives fish do not hang in clear water but love murky water with a lot of sediment which is the primary reason for loss of IQ let alone dome ports

This is shot in the mediterranean visiblity 10-15 meters

[/url] This is shot in the bahamas visibility 30 meters

 

 

It is the same set up though the level of sharpness is wildly different even at comparable distance

I think the most important point you made is the water clarity, which also influences the resolution (negatively) and is the main limiting factor. (but we know that we have to be as close as possible to our subject to reduce the amount of water between them)

2 minutes ago, gobiodon said:

I think the most important point you made is the water clarity, which also influences the resolution (negatively) and is the main limiting factor. (but we know that we have to be as close as possible to our subject to reduce the amount of water between them)

The most important point I make is that if resolution is maxed out at HD you need to use a 4K system to achieve it not one that produces HD or you will get 1 megapixel

Gopro etc are not resolving anywhere near the sensor megapixel count a gopro will do worse than a decent camera with 4K video in pretty much all conditions

Resolution drops with noise as well so a tiny sensor with a squashed lens and limited color correction is not the way forward

On 10/28/2022 at 8:49 AM, gobiodon said:

I think the most important point you made is the water clarity, which also influences the resolution (negatively) and is the main limiting factor. (but we know that we have to be as close as possible to our subject to reduce the amount of water between them)

I agree that water attenuation has greater effect on photography than the optical property of the lens. The clarity and particular matter are the most limiting factors.The have long solutions for quality underwater lens, Elcan, Rebikoff and of course the Nikkor UW for the nikonos. I think I read in the Mertens book, "In Water Photography -Theory and Practice"(a must read for serious underwater photographers) that the Elcan could resolve over 100 lines per millimeter(in 1970).

50 minutes ago, Davide DB said:

$20,000 hahahahah

2 hours ago, Interceptor121 said:

$20,000 hahahahah

But that's Australian dollars....

So.... that's $14k US or €13k.... cheap at half the price. Buy a piece of cinema history...... 

On 2/7/2023 at 3:57 PM, Davide DB said:

10% Valentine's Day discount. I'm not sure that my wife would be happy with this as a present (I stick to flower praline combo).

Guess this means no more UW Avatar movies in the future.

39 minutes ago, Alex_Mustard said:

Guess this means no more UW Avatar movies in the future.

Do you want another one??

If so much effort was put into matching the lens out of 100 lens, it is interesting that they are trying to sell.I would be skeptical that these are the same exact lens that was used on the split prism rig from Achtel. 

The seller is Achtel himself.

The third and final episode was already shot and now it is in editing phase.

You think there might be a future need for this rig as a whole system ?  I was wondering how they synchronized the focusing and f stop control of the two lens.

3 hours ago, tobyone said:

You think there might be a future need for this rig as a whole system ?

No idea. It's completely off from my scope.

Sawing that post I remembered this thread and I posted it for fun.

P.S.

San Valentine is here...