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dreifish

Member Since 25 Oct 2013
Offline Last Active Feb 15 2017 07:53 PM
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Posts I've Made

In Topic: Panasonic GH5 Photos / Specs

19 January 2017 - 04:53 AM

725 grams? That's a hefty body indeed!


In Topic: GoPro Karma v. DJI Mavic - opinions from the perspective of the underwater ph...

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. 


In Topic: Custom white balance and noise

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. 


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.