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dreifish

Member Since 25 Oct 2013
Offline Last Active Feb 15 2017 07:53 PM
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#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.




#379729 Successor to the Sony AX100 ?

Posted by dreifish on 18 December 2016 - 05:02 PM

I, for one, am more optimistic.

 

First, plenty of cameras already offer 200mb/s+ recording onto sd cards. See, e.g. Panasonic GH4 (3 years old now), new Olympus EM-1 MK2. It's not a hardware limitation. SD cards exist now with write speeds approaching 90MB/s (that's 720mb/s). Plenty of headroom.

 

Furthermore, 4k60p can probably be done alright at 100mbps, especially if using h.265 rather than h.264 encoding (though obviously more is better). The Phantom 4 Pro from DJI records 4k60p at 100mb/s, for example.

 

So.. I don't think the bottleneck for 4k60p is necessarily storage. I think it's actually sensor read-out speed and the heat generated by current consumer-level sensors when called to read that pixels at such a high frequency. 

 

The GH5 is supposed to record 4k60p internally. The Phantom 4 pro already does, and the Inspire 2 from DJI with the X5S camera (another micro4/3 sensor) soon will. So I would say there's a real possibility the AX100's successor will do 4k60p. Whether that successor will be launched this year or not is anyone's guess, though.




#379587 Kal's Dream, Alor, Indonesia

Posted by dreifish on 13 December 2016 - 08:41 AM

Just a quick edit from some footage shot this morning in Alor, Indonesia. 

 




#379269 Sony a7s II underwater use -- All parameters

Posted by dreifish on 01 December 2016 - 02:18 AM

Hmm.. what? Nothing school-bus sized? Boring! :D




#379025 Underwater Colour Correction With The Sony AX100

Posted by dreifish on 23 November 2016 - 12:12 AM

If no one has, I have an RX100 mk1 that I can have a try on. Water here is just green rather than blue.

 

I'd be interested to hear also: how does the AX100 compare with the RX100 MK4 or (soon MK5) underwater?

It seems to be a clear win for UW video to buy the RX100 MK4/5 given same sensor, codec, bitrates etc. - camcorder ergonomics go out the window anyhow with UW housing.

 

The ergonomics of the Gates AX100 are going to be head-and-shoulders above a still housing for the RX100 line when filming video. Things like a flip-in-flip-out red filter, adjustable boyancy/trim characteristics and a 12x lens/Gates GP34A wet lens combo that lets you shoot everything from 100 degree wide angle to near macro without any lens swaps may seem like small differences, but they make a big difference if you're primarily a video shooter.




#379022 Sony a7s II underwater use -- All parameters

Posted by dreifish on 22 November 2016 - 05:06 PM

 

Thanks very much Andrei.  These are very helpful, for next time.  I was shooting at f8, and sometimes at f11.  I pretty much agree with everything you say here.  I am sure I can get better results and I wish I had used the zebras.  You suggested that last time and I did not implement it.

 

And I agree about not shooting into the sun.  Sometimes, however, the subject presents itself and if you want to film it, you just have to film it where you see it.  Here, I was not able to set up ideal conditions, but was pretty much scuba diving and looking after my girlfriend -- considering myself a documentarian while filming everything I could that looked photogenic.  I was eager to record things, in part to document the coral and fish species, and I am going back and attempting to identify as many of them that I can, so that I can become more knowledgeable about the ecology in the area.

 

Much room to improve.  Only wish I had more time to dive!

 

I was having a lot of trouble getting close enough to fish to get good portraits, with this wide angle set up.  Any suggestions on that?  I wonder what things would look like with just my 28mm on.  

 

In any event, the next challenge is setting up a new dive trip to try to continue to improve.  This last trip was expensive!  Am still looking at Indonesia.  We loved it.  

 

For anyone reading this, any suggestions?

 

Best, 

 

GLP

 

Depends how small of a fish you're talking about, but I find the 16-35F4 lens to be very versatile on the A7RII because you can film in either full frame or APS-C mode. Turn on APS-C mode, and you suddenly have a 24-50mm lens on. At the 50mm lens, it should be quite adequate for portraits of medium fish. For things that are smaller/more shy, you can use the 90mm macro (inside the same dome as the 16-35 or in its own macro port).

 

The 28mm by itself isn't a particularly versatile lens. The 16-35 does everything it can do and more.

 

It's going to be tough to find any place where the reefs are as vibrant as in Raja Ampat. Perhaps try Komodo between April-November. The reefs aren't quite Raja Ampat level and the biomass of fish is lower, but it's as good as it gets in Indonesia outside Raja Ampat. 




#378993 Sony a7s II underwater use -- All parameters

Posted by dreifish on 21 November 2016 - 05:41 PM

Ok guys.  I just posted the first little film from my Raja trip.  All this footage was shot at the same dive site -- the "Magic Mountain" that Ammar and I visited.  I was following the advice of several people on this topic.  I shot this exclusively with UAWB, and video lights when I could.

 

I started off using manual exposure control, and could get great results, but I was constantly having to adjust exposure.  When you are an ambient light photographer "running and gunning" on a dive like this, it really helps to use auto exposure, as every time you change the view, the exposure can change.  For example, capturing a scene shot into the light, or with the sun in the frame like many of these shots, is quite different from what you might do if you merely turned around and shot the other way.  Thus, I got passable results using auto ISO underexposed .7 stops, usually. 

 

This was shot with the a7s II.  I think the low light capability of the camera really makes it helpful in shooting ambient light.  Next, the waters varied from murky, to a little less murky, and were never anywhere as clear as either Grand Cayman, or Cozumel.  (This is one reason why there are 100 times more fish).  I think it also very much helped the white balance issues, which pop up when the water is too blue and clear.  Thus, AUWB works better in murky water, when you use video lights in particular. 

 

Nice footage and interesting observations, George. I'm not sure I agree that the low light capability of the camera is all that useful for underwater filming because the situation you're often dealing with with ambient light shots is too much light, not too little. I can't think of a situation where I've had to use an ISO higher than 1600 underwater, and, for all practical terms, I never go above ISO 800. 

 

I agree that fixed aperture, fixed shutter speed auto ISO gives the best flexibility for "run and gun" work with the least need to adapt to changing lighting conditions. But sometimes locking the ISO as well can have some advantages, as I'll discuss below.

 

As others have commented, some of your footage is over exposed, even at -0.7 ev. But if I'm correct about the cause, I don't think the solution is to go to -1.0EV. Rather, you need to be aware of your shooting conditions and start to get a feel for the ambient light. What do I mean by this?

 

First, a number of the shots are into the sun. When shooting ambient light video, it's usually best practice to try to keep the sun behind you to reduce the dynamic range of the scene, reduce lens flaring effects, and get the best mid-tone contrast. This is true even when shooting with lights, because video lights aren't as powerful as strobes, so they can't light the foreground properly if you're underexposing to keep the sun from clipping half of your scene.  Keeping the sun behind you can be tricky with a really wide lens, but start to develop the habit of looking around for where the sun is and anticipating the action so you can position yourself in the best place to film it while keeping the sun behind your shoulder. In the long run, this will help you get much more vibrant footage.

 

Second, what aperture setting were you using? One of the dangers of going with auto ISO is that you lose awareness of what ISO the camera is actually using. So, for example, if you're shooting in very shallow water in bright conditions, the camera will be using its lowest ISO (ISO 100). It will do so whether you have your EV set at 0, -0.7, -1, or -2 for that matter, because it can't go any lower. And the results will always be overexposed because your combination of shutter speed and aperture are simply letting too much light in. I've noticed this is a common problem in shallow water during mid-day dives if shooting at 1/50 or 1/60 with the aperture at F8 or sometimes even at F11. This is why I keep the zebras (100+IRE) on to stay vigilant for overexposure. So remember, when shooting in the shallows, check to see what kind of aperture and shutter speed combination you need to get proper exposure at ISO 100 rather then just relying entirely on auto-ISO to do the trick. Odds are you might have to bump your aperture up to F16 and/or even double your shutter speed to 1/100 or 1/120 to limit the ambient light. This is not optimal as it may soften your image a bit because of diffraction (narrower apertures) or create less inter-frame blurring than would be ideal (higher shutter speed), but, in practice, I haven't noticed perceptible degradation in quality in the resulting video. If it's really a concern for you, use a 2-stop neutral density filter or orange/magneta filter which will also block 1-2 stops of incoming light and allow you to keep the aperture at F11 and shutter speed at 1/50 or 1/60.

 

It's interesting to hear that you think the murkier Indonesian waters are helping with the white balance problems of the Sony cameras. I need to get myself in the water somewhere with 50+ meters of visibility to see if that kind of blue water breaks the white balancing algorithms :)




#378961 Sony a7s II underwater use -- All parameters

Posted by dreifish on 21 November 2016 - 01:46 AM

Hehe, looks nice. What monitor is that?




#378775 Sony a7s II underwater use -- All parameters

Posted by dreifish on 14 November 2016 - 10:48 PM

I would like to download this test and study it with the vectorscope. At this depth I will go with lights no doubt.
I like the 9900K, but I would touch de BIAS somthing like A5 M4 or A6 M5...
Will try next week at red sea Magic filter is AWB ans UAWB mode to see....

 

Hmm.. you might want to be careful with pushing the bias towards magenta to that extent to counteract the cooler ambient light, especially when shooting with video lights. It may result in the illuminated subjects being a bit too purple. For example, at 3:24 in your Similans film, the fan coral and the water color strike me as a bit too purple (though it's subtle). It does render the sand and rocky reef a nice color, though.

 

Unfortunately, the A7RII (and other Sony cameras) do seem to have a tendency to push towards green a bit too much, especially in UAWB mode. The white balance bias is one method to try to correct that. I wonder though if we couldn't achieve a better result by shooting in a custom picture profile (could be based on Gamma ITU709  & Color Mode ITU709) with a negative Color Depth for green/yellow or by changing the Color Phase. So many things to experiment with -- this would obviously best be tested using an waterproof color chart. 




#378770 Sony a7s II underwater use -- All parameters

Posted by dreifish on 14 November 2016 - 09:39 PM

Here is the A7R II different WB modes test video at 20m depth, ambient light.

 

<iframe width="640" height="390" src="https://youtu.be/--4pRdwSNYQ"frameborder="0" allowfullscreen></iframe>

 

https://youtu.be/--4pRdwSNYQ

 

Not sure how to embed a YouTube video :)

 

I think it's fair to say none of the white balance settings you tested do much to restore the warmer colors (including Underwater Auto White Balance) in the foreground subject (though it's a bit hard to tell -- ideally need to test with something in the foreground that's red/yellow under torches). This accords to my own testing. I'm not really surprised -- Sony's white balance system caps out at 9900k, and to execute an accurate white balance (e.i. to make a white/grey object record equal levels across the red, green and blue channels) you'd need something closer to 20000-50k at that depth, plus a strong magneta push.

 

If you have lights and the ambient light isn't too powerful, the best approach obviously is to just set the white balance to something that gives you nice blues in the water column (4300k-4800kl usually works quite well) and use the lights to illuminate the foreground once you're below 10 meters. You can use some warming gels on your lights if the light they produce is significantly cooler than 5000k. 

 

But if you need to work with ambient light for some reason, the obvious solution is to add a orange/magneta filter to the lens to supplement the camera's custom white balance abilities. It's more inconvenient because you have to commit to using it for the whole dive. The results may also not be to everyone's taste. Here's some screen grabs from test footage shot at 15m and 18m with an orange magic filter, both with UAWB and with a custom white balance done off my palm:

 

http://www.andreiv.c...ilter/n-WRgsbH/

 

Unfortunately, I don't have any footage shot at the same locations without the magic filter to compare, but you can look at the test footage Ammar shared from 20m to see how much of a difference the orange filter makes.

 

Note that the SLOG2 images are actually graded (just to boost the contrast so they don't look quite as flat).

 

I think it's interesting to note that the UAWB algorithm does not really push the reds as much as a CWB does. This has the advantage of preserving a nice blue water column, but the foreground reef and sand isn't quite as vibrant and remains a bit too greenish for my taste. On the other hand, with the custom white balance, I feel like the reds are pushed to the point where it's unnatural, and the water column becomes muddy, with a hint of magenta.

 

I can't say I really like either result.




#378724 Keldan 8x - flux or CRI?

Posted by dreifish on 12 November 2016 - 11:17 PM

I think part of the answer will turn on what sort of camera you'll be filming with.

 

Inside a cave, you have no ambient light to outcompete, so the strength of your lights is less crucial if you have a camera that can film clean video in low light (e.g. ISO 3200, 6400 or even 12800 if filming with something like the Sony A7S/A7SII). This is great, because it means you can run your lights at lower power and still get nice footage. For reef shots, a camera with high sensitivity won't help much because it'll be equally sensitive to the ambient light, and what you want to do is have your torches brighter than the ambient light in order to bring back the full spectrum of colors. So, for reef scenes, the more powerful your lights, the better. 

 

Also keep in mind the inverse square law of illumination -- light intensity decreases proportionately with the square of the distance from the light source. What this means, in practice, is that no light will strongly illuminate objects very far away. Importantly, it also means that varying the distance to the object you're trying to illuminate will be more effective than increasing the power of the light source. 12k lumens may be 50% brighter than 8k lumens, but in terms of reach, you're only increasing the light's reach by around 22%. (In other words, the 12k lumen light will produce the same illumination at 1.22m away as the 8k light would produce at 1m away). I don't don't dive in caves, so I can't really opine about how much of a difference the stronger light would make from experience, but, based on the above, I would say there's diminishing returns to increasing light intensity if your goal is to illuminate more of the cave. 

 

Regarding 82CRI vs 96CRI -- I haven't seen any specific tests done underwater. I've used some 70CRI lights in the past and use 90CRI lights currently. My impression is that the higher CRI lights tend to produce richer shades of red and yellow. Is it a major difference? I doubt someone could look at footage blindly and tell you if it was filmed with 82CRI lights or 96CRI lights, because there's so many other variables confounding the final result (strength of the lights relative to the strength of the ambient light, etc)  Now, if you were comparing them side by side, you'd probably see a difference. Maybe. But even then you'd be confounding it because one light is stronger.

 

Once you add cyan filters, CRI goes out the window since by definition the cyan filters are stripping out the reds and the yellows. With cyan filters, neither light is going to have a particularly good CRI. 

 

If you're still confused, to what I did -- get the Gates GT14 lights. 90CRI and 14000 lumens -- best of both worlds :)