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dreifish

Member Since 25 Oct 2013
Offline Last Active Yesterday, 06:54 AM
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#386012 Panasonic LUMIX GH5 for underwater video

Posted by dreifish on 20 July 2017 - 01:50 AM

I'm not a technical expert by any means but the way I understand it, is that any white balancing at depth, whether manual or automatic, will introduce a certain amount of noise, because effctively you are 'artificially' inreasing the red channel - and that will add more noise to that channel, because by white balancing you are not adding any more information to that channel. Things should be better in 10bit because of the addl. color info compared to 8bit, so I am having good hopes in the GH5 in that respect

Whether there is more noise introduced on a Panasonic compared to lets say Sony I dont know. But I can tell you from my time with the Sony AX100 camcorder it was introducing plenty of noise if you where below 15 meters on ambient light only. I guess thats just a critical depth fo most cameras where they start to struggle.

 

Right -- what you're essentially doing when you're white balancing at depth is telling the camera to apply gain to the brightness levels recorded by the "red" photoreceptors. So it's equivalent to boosting the ISO, and will make any existing noise in the red channel more apparent. With the GH4, the noise was quite visible/distracting when trying to white balance around 20 meters (especially if your base ISO was already 400 or 800 to account for the lower light). 

 

This step happens before any of the data is encoded into an 8 bit or 10 bit video file-- white balance is processing applied to the 12 bit data coming right off the sensor. So the final recording format isn't going to make a difference to the amount of noise. The GH5 should still be better overall then the GH4 simply on account of newer sensor technology, using a larger area of the sensor for video and better noise reduction, but the differences are probably similar to the overall improvement in low light performance. DXOMark rates the GH4 and GH5 as essentially identical in terms of noise performance, so I wouldn't expect the GH5 to be significantly better than the GH4 in terms of noise when white balancing. A full frame camera like the 1DX Mark II should be 1-2 stops better, which is what the Backscatter guys seem to report as well.

 

As to whether a 10-bit 4:2:2 h.264 file will make it easier to correct a bad white balance in post than an 8-bit 4:2:0 file h.264, it might make a bit of a difference, but it won't be night and day like you would get if you were recording raw. During the encoding process that creates the h.264 file, the 12 bit data in the red channel is going to first get confounded with the signal from adjacent blue and green pixels as part of debayering. Then it's going to get compressed from a 12-bit space where 4096 gradations of brightness can be represented to a 10-bit space that only supports 1024 gradation. That alone throws away 75% of your data. Then you end up throwing away the color data for half the pixels when you go from 4:4:4 to 4:2:2 color. So you're already down to 12.5% of the original data (not accounting for errors introduced by debayering based on the wrong white balance) before you even get to the compression stage. Then you add the fact that h.264 compression tends to preferentially eliminate data in the shadows. Your red channel underwater is mostly going to contain data in the shadows if it's not pre-boosted by a "proper" white balance before this stage is reached.

 

So yeah. If you want to retain information in the red channel when shooting in a compressed video format, you need to make sure that the data is properly baked in by a good in-camera white balance. Since the red channel signal is going to be very weak coming right off the sensor, if you don't boost it significantly before recording it (and more importantly, compressing it substantially using h.264 compression), you'll end up trying to reconstruct what should be dozens of shades of red of various brightness from very little data indeed. 

 

All of which is to say that, when recording to any sort of compressed RGB or YUV codec underwater using only ambient light, the camera's ability to do a proper white balance in the 40000-50000 kalvin range with significant magenta push is far more important to the final result than the bit depth or color depth of the recording codec.  Good white balance flexibility will get you nice colors even in a 8-bit, 4:2:0, low bitrate codec. Case-in-point: canon dslrs. Whereas if your camera won't let you set a white balance higher than 9900 kalvins (e.g. all Sony mirrorless cameras that, and maybe some of their cinema cameras too), the codec won't matter. At least, not unless you can record the raw sensor data before debayering and compression.




#386006 Panasonic LUMIX GH5 for underwater video

Posted by dreifish on 19 July 2017 - 11:05 PM

Interes

 

Andrei, this is the the link to the 7'' equivalent: http://www.diveandse...nitors/dnc-7ah1

 

The 7'' sells for USD 2650 incl. bulkhead, cables etc.  The new 5.5'' is less - but not by much.  As I have a pre-release version I don't want to talk about my price as I dont want to preempt what they may later put on their webpage as official price. Not a super bargain but you get an extremely solid and rugged piece of gear.

 

The 5.5'' is already a HUGE screen compared to the build-in 3.2'' of the GH5. If there would have been a lighter 5' version, I might have even taken that.  Its not just the size itself, it's the much better viewing position having a monitor on top rather than that build-in LCD at the lower end of the camera housing.

 

7'' would be too big for me (and I am wearing optical glasses in my mask), but thats why there are different sizes :)

 

NB: Whether they make a new 7'' version you'd have to ask. I think the 7A is actually pretty new and may have the same specs inside (apart from screen size) The layout of the buttons and the menu operation (press-and-turn-wheel) has changed somewhat on the new smaller version.

Ah.. the 7A has definitely been around for a few years now. I remember looking at it at Backscatter maybe 3-4 years back now. Was hoping they'd updated it.

 

Still, the price seems to have gone down a little bit. All things considered, it's probably about half what you'd have to pay for a housed Atomos Shogun, so it's tempting. Just not sure about the quality of the display and tools available on it compared to more standard offerings from Atomos or SmallHD. But definitely a win when it comes to bulk, it seems! Part of me wants to go with the Atomos/Nauticam housing to also get the option of 10bit 4k60p recording in a slightly more robust prores codec, as well as the brighter screen and ability to use it on land. 

 

I agree with you that a 5.5" monitor that you can position is already a great improvement over using the internal screen, but for critical focus and framing at 4k+ resolutions, I've never heard anyone complaining that a monitor was too big :) I suppose a lot depends on the boyancy and trim characteristics though. If the Atomos makes the Gh5 really negative or back heavy or impossible to operate well, then I guess it's a no-go.




#385872 Bigblue lights feedback

Posted by dreifish on 16 July 2017 - 01:00 AM

Nothing wrong with them from what I've seen. Only limitation is that it uses cree less, which don't have a very high cri -- 70 or 80 at best.

I live in Shenzhen now and I've recently been in contact with a local manufacturer that is now producing 8000 lumen 95cri video lights that, from what I can tell, use the same leds used in the gates gt14 lights. I haven't been able to get my hands on a unit yet, but hope to do so soon to test them out. Should be able to get them for under $500 a piece


#385259 Sony a7s II underwater use -- All parameters

Posted by dreifish on 22 June 2017 - 12:31 PM

Great summary!  I think this will help those who are new to this page.  Query:  Do you just set the WB to 5.2K, or whatever the temp of your lights are?  What does this do to the color of the water, at a distance, where the light is not illuminating it?  How does this compare to underwater WB using basically the same technique?

 

Thanks for this distillation of wisdom.

 

GLP

 

 

 

Yes, correct. I usually set the white balance to 5200k because that's the temperature of the lights I'm using.  In general, the cooler the white balance (i.e. the lower the kalvin temperature), the more blue the water will look. Alex Mustard wrote a nice article about it some years back now. At 5200k clear tropical water already takes on a nice blue color. A less saturated blue near the surface and a more saturated blue the deeper you go. This is because what you're recording is the color of the sunlight being filtered through all the water between you and the surface. The more water, the more the reds and yellows get filtered out, and thus the more richly saturated the blue. For photography, I usually try to set my white balance even lower (around 4500k) to shift the color of the water column further towards true blue and away from aqua. I then light up the foreground using strobes that have warming gels attached so the foreground subjects render the 'correct' color rather than coming off as too blue.

 

Conversely, setting the white balance to warmer temperatures (say, 10000k) will produce muddier, more aqua/green/grey water backgrounds. It's not a great look in tropical water, IMO. This is essentially what happens when you use the Underwater Auto White Balance mode or try to custom white balance off a white/grey card at depth with or without a red filter. The warmer white balance reintroduces some reds and yellows to your foreground subjects, but turns the water column a desaturated magneta-grey.

 

In temperate waters, a color temperature slightly warmer than daylight like 6000-6500k can make the water column more richly green (emerald) rather than aqua-grey, so that actually can be a stylistic choice.  

 

All of the above is true whether you're shooting with lights or without, as the lights don't illuminate the water, they pass though it. 




#385005 Panasonic LUMIX GH5 for underwater video

Posted by dreifish on 13 June 2017 - 01:34 AM

An u/w pro shooter friend of mine switched from GH4 to Canon 1DXii and says he's now able to leave AF on for most stuff.

 

Sounds nice. Canon seems like the the best option for underwater work, but the 1DXII is ultimately unappealing given the price. Since white balancing seems to work well on the GH5, I feel like autofocus is a small enough thing to sacrifice in return for the $7000 when you add up the body and housing.

 

Maybe Nauticam will come out with a (well-priced) housing for the new Canon C200. That camera seems to tick a lot of boxes for both topside and underwater shooting.




#384973 Panasonic LUMIX GH5 for underwater video

Posted by dreifish on 12 June 2017 - 04:56 AM

Etc, the continuos autofocus is contrast detect based, so probably no more usable in video on the GH5 than it was on the GH4, or, for that matter, pretty much every other large sensor camera out there other then a few Canon offerings with dual-pixel autofocus. CDAF is always going to hunt a bit when shifting focus, which looks terrible in video. Even the Sony cameras which have PDAF don't really do that great if you leave continuous autofocus on for underwater video -- they'll often shift focus from your main subject to particles or small fish closer to the lens, ruining your shot. So I'm rather distrustful in any sort of continuous autofocus for wide angle underwater video. There's simply to many things that can distract the focus from your main subject and no good way to tell the camera what your main subject is.

 

But honesty, shooting wide lenses and with narrow apertures as is normally the case with wide angle video, you can just pre-focus and lock focus before filming and be ok in the vast majority of cases. Now for macro, I would love to have a good continuous autofocus system since critters are always moving and your depth of field is miniscule. But I don't know of any such systems out there. Perhaps the Canon 70d/80d/7dII/1dxii/5d4 or their cinema-line cameras can pull it off. I've never tried them or seen underwater footage from them shot with continuous autofocus, so I can't really comment.




#384972 Anyone happy with their TriPod?

Posted by dreifish on 12 June 2017 - 04:43 AM

I believe the new Nauticam GH5 housing incorporates just that kind of base, for what it's worth. 

 

http://www.nauticam....od-legs-na-gh5/




#384969 Sony a7s II underwater use -- All parameters

Posted by dreifish on 12 June 2017 - 04:19 AM

FCPX, Davinci Resolve and Premiere don't display that kind of data as far as I know.

 

For those coming late to this thread, let me attempt a short summary:

 

For great colors using the Sony cameras (A7, A7II, A6300/6500 line), you really need to shoot with powerful video lights (WB manually set based on the color of your lights). To allow the lights to compete with the ambient light, you're best off shooting early in the morning or in the last hours before sunset when there is less overall ambient light or at depth (30+ meters) where again there is less ambient light to outcompete. Under these circumstances, it helps to underexpose the background around -0.7 to -1.3 EV to get nice richly saturated blues while adjusting the strength of your lights to avoid overexposing the subjects (use the zebras to check for overexposure.)

 

There's no need to shoot in SLOG or any of the cinegammas if you apply the above exposure principles, as the dynamic range of your scene will fit well within the 7-8 stops of exposure you get under standard picture modes or REC709. 

 

Forget about trying to shoot without lights and doing a manual white balance. Your results will be disappointing unless you're in very clear water and very shallow (5-10m max). In those circumstances, the Underwater Auto White Balance mode can work ok.

 

My experiments using red filters and manual white balance have been pretty frustrating and disappointing overall, so it's not an option I would recommend.




#383030 C300 mk2 for underwater

Posted by dreifish on 10 April 2017 - 11:12 PM

I wonder if the absence of any footage is not more a product of the segmentation of the market. It seems to me that the c300II and other similar cameras (sony fs7, panasonic varicam) in the 5-20k price range are addressing a non-existing market, especially when it comes to underwater footage.

 

On one hand, regular hobby users probably can't justify the price of a full package once you factor in housings, external monitors/recorders, ports, lenses, etc. when compared to DSLR type cameras (or ever action cameras) that are perfectly adequate for their use. On the other hand, professionals that actually need (read, can sell) raw 4k footage are selling to blue-chip natural history or hollywood-type productions productions that turn their noses at anything that isn't a 50k+ Red or Arri...




#380766 GoPro Karma v. DJI Mavic - opinions from the perspective of the underwater ph...

Posted by dreifish on 19 January 2017 - 04:37 AM

Hmm.. interesting. Looks like a similar concept to the now-defunct Karma. 

 

However, two things severely limit it's usefulness as a drone imo, based on the footage in the video. First, the camera has the same fisheye angle of view as a gopro, which doesn't work well for a drone. Second, the stabilization seems quite bad compared to DJI drones.

 

Not really sure why they went with just three propellers. 




#380764 Custom white balance and noise

Posted by dreifish on 19 January 2017 - 04:28 AM

Why not just custom white balance whilst descending to target depth? E.g. white balance at say 20 meters and then continue to 40 meters. This way you eliminate some of the blue or green color cast, but are not yet boosting red to extremely noisy levels.

You can certainly experiment with this.

 

With cameras that have a limited range for white balance adjustment (e.g. Sony cameras), this is more or less what you are forced to do since trying to set white balance too deep will likely result in an error.

 

Still, for my tastes, the results of white balancing at a shallower depth and then filming deeper are a bit too greenish-blue. It's not just the color itself, either. A large part of the contrast we perceive in an image comes from color contrast. For example, reds are much more noticeable when placed against green, blue against yellow, etc. So, images that include the warmer tones tend to have more contrast and are more "poppy" than ones that are all just shades of blue and green. 

 

My preference is to use artificial light (strobes or video lights) when filming below 10 meters, and keeping the white balance set to the temperature of the lights. I find that it producing much more pleasing results than trying to shoot with only natural light.

 

Does it accurately reflect what I saw on the dive? No. But for me, photography isn't about striving for the most accurate version of reality. It's about producing beautiful images. Accurately capturing reality is not as straightforward as you might think, anyway, since cameras see the world very differently than our visual system processes the world. Physiologically, most of what you "see" is actually a very detailed model constructed by your brain based on your past experience, based only partially on the limited, low bandwidth real-time input from your eyes. 




#380564 Custom white balance and noise

Posted by dreifish on 13 January 2017 - 01:28 AM

When you set a custom white balance underwater, the camera is forced to boost (or apply gain to) the red channel in order bring the signal level closer to the green and blue channels so that white appears to be white (even though in reality a white object at depth will reflect a lot more green and blue wavelength light than red wavelength light). So, imagine your ISO is set to 100 for simplicity's sake -- the red and green signal may be treated as iso 100, whereas the red signal will be treated at a higher iso -- let's say ISO 1600. Whether this is done at the hardware analog-to-digital converter level or as a pure mathematical signal multiplication probably differs from camera to camera (though I suspect it's generally done as a digital multiplication of the red channel signal after analog-to-digital conversion).

 

So, short answer -- yes. White balancing at depth will result in noise, especially in the red channel. And that noise will increase the deeper you go. Incidentally, the exact same thing will happen if you shoot in RAW and white balance in post -- the post-processing software is boosting the red signal in the RAW data, leading to increased noise. The increase in noise will be proportional to the severity of the white color correction. 

 

And there's no way around it really. Using a red filter to try to balance the amount of red/blue/green light that reaches the sensor results in less overall light reaching the sensor and a higher ISO (thus noise) as well. I suppose you could compensate by using a slower shutter speed in that scenario, assuming you composition allows for a slower shutter speed. 




#380515 High ISO Pana GH4 clip to share

Posted by dreifish on 11 January 2017 - 04:50 PM

Eh.. things already start to get quite noisy at ISO 800 with significant white balance adjustments at depth.

 

The reef shark footage below was shot at ISO800 with custom white balance off my palm at 20-25m:

 




#379817 Sony a7s II underwater use -- All parameters

Posted by dreifish on 21 December 2016 - 05:46 PM

Well I looked at this again Andrei, and again I am intrigued that the color of the water (water column?) in the background of your video lit shots is so naturally blue.  It seems that it is very clear there. I had not thought about setting the color temperature to be the color of the lights.  My little Sola 3000s are nowhere near that powerful.  It really constrains what type of shot you can take.  I will be posting some more from the Raja trip.  The water was much cloudier than what is conveyed in your videos.  Than you again for all your contributions.

 

GLP

 

The deep blue of the water column is a combination of things, George. First, water clarity -- we had 20m+ visibility, which definitely helps. Add to that underexposure to bring out more saturated blues, a relatively low fixed 5200k white balance (if you go even lower, like 4800k or 4300k you'll get even richer blues for the water column, but at the expense of a foreground that's too cool unless you shoot with warming filters for your lights). And finally, the Autumn leaves creative style adds punchiness and saturation to the blues (and the reds, and the yellows..)

 

Even with weaker lights you'll be able to achieve a similar result if the ambient illumination is low. Shoot on cloudy days, early morning or late afternoon, and at depth where less ambient light penetrates.




#379731 Sony a7s II underwater use -- All parameters

Posted by dreifish on 18 December 2016 - 07:59 PM

Very nice.  I am amazed that you were able to get this with 5200K fixed white balance.  I have been wedded to the UAWB, which of course switches back and forth.  I was told by guy at Backscatter that fixing termperature like this would not work. 

 

If you were not using lights, would this work?

 

Where were you staying at Alor.  My fiance and I are planning our next trip and are investigating things.  And generally, where would people on this page recommend we go?  We might want to try a nice liveaboard.

 

GLP

 

George -- UAWB works fine, within a given range of parameters (i.e. clear water, lots of light, 10m or shallower, sun behind your back preferably).  I think it's probably the best option on the A7 cameras within those conditions.

 

Here however, most of the shots were below 20m on a cloudy day early in the morning -- in other words, low ambient light, where my Gates GT14 lights were easily able to overpower the ambient light and bring back rich, warm colors to the reef.  5200k is the white balance of the GT14s -- that's why I used it. This type of shooting would absolutely not work without strong video lights. Everything would just be greenish/blue. 

 

So.. shoot UAWB in the shallows when there is strong ambient light, and a fixed or AWB with strong video lights when deeper/with less ambient light. I've been experimenting some more with red filters, but have yet to come up with any formula that I find gives acceptable results. Custom white balance underwater always ends up pushing the red channel far too much, leading to a muddy, magenta water column. This sadly happens even when taking a white balance reading off something pink like my hand or a brown patch of coral. It can probably be fixed with post-processing, but I prefer skipping the filter altogether and just relying on video lights at depth. 

 

I was in Alor as part of the crossing trip for a new liveaboard. There are a number of land-based resorts in the area. I've generally only heard good things about Le Petite Keppa, but never stayed with them myself.