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dreifish

Member Since 25 Oct 2013
Offline Last Active Jan 14 2017 10:47 PM
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Posts I've Made

In Topic: High ISO Pana GH4 clip to share

13 January 2017 - 01:34 AM

 

 

This really demonstrate how much these things are subjective.  :lol2:  It's perfect to my eyes.

 

For my type of diving I never worked at less than ISO 1000 with my old GH2 and GH3. I know they are noisy but when you are there you have to bite the bullet.

I was curious to understand if there is a real improvement with the now obsolete GH4 and I could serenely work at ISO 1250.  :mocking:

 

Thank you for your example.

 

I think it depends on what size you're viewing the footage in -- and I suggest downloading the original rather than looking at the Vimeo stream, as the Vimeo compression may be smoothing out some of the noise. On a phone or laptop display, the noise might not be obvious, but once blown up to HDTV size, it's pretty obvious (to me anyway). 

 

Also, add color correction to try to adjust the purple water column for example, and the noise becomes considerably worse. That can be counteracted to some extent by using noise reduction in post, of course.


In Topic: Custom white balance and noise

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. 


In Topic: TTL flash trigger for M43 Panasonic/Olympus cameras?

12 January 2017 - 12:14 AM

Hahaha, quite creative solution there, Pseudonym! 

 

With the GH5 apparently forgoing the built-in flash, I'm thinking the value of the GH4 flash trigger just went up. Perhaps I should've kept mine :D


In Topic: High ISO Pana GH4 clip to share

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:

 


In Topic: LOG Footage - Opinions on Underwater Use?

10 January 2017 - 05:51 AM

In my opinion, the use-case for log gammas is weak underwater. LOG gammas are there to allow you to squeeze a wider dynamic range into a smaller 8 or 10 (or sometimes 12) bit container. Whereas regular rec709 only lets you record around 7-8 stops of dynamic range, a log profile gets you closer to the 12-14 stops a camera's sensor might actually be capable of discerning.

 

However, in my experience, not that many underwater scene actually require such a dynamic range. All those particles in the water already sap the contrast, so most of the time you'll find your scene if you're shooting with the sun behind you has way less than 7 or 8 stops of dynamic range anyway. Same goes if you're using artificial light -- you should be able to light your scene so that it all fits into 7 stops of dynamic range. So the only time you really might appreciate the extra dynamic range of a log profile is if you're shooting into the sun or out through the opening of a cave or something like that. Not your typical use case..