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Grain in underwater footage

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dave emery
Grain in underwater footage
on Apr 26, 2010 at 4:02:02 am

A friend only shoots underwater with his EX1 and Gates housing. He has tried almost every setting that makes sense and continues to have a lot of grain in the dark blue areas of the frame.
His primary settings are, -3 gain, 180 shutter, 720/50p over cranked to 60 fps. No PP. His aperture is auto and sits around 4 to 5.6.
I suggested to shoot for all round brighter shot by turning the gain to 0, shutter off and not over crank. When he tried this it made no difference to the grain and created bad motion blur.
The following is his last email to me, could there be something in this?
"I discussed it w a pro & he told me it may be the compression which may be working in variable rate.
Depending on plug-in, what I get is either MP4 or MP2 format & the compression may look at the blue expanse & decide to compress it more as it’s all looking alike.
Trust me it’s NOT the exposure – I have footage of a very dark reef and it shows no grain – but the blue background does! Also, when I point the camcorder upwards towards the sun and thus have a lot more light, it still looks grainy!"

Thoughts please!! As this really is a concerning issue.

Cheers
Dave.


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Don Greening
Re: Grain in underwater footage
on Apr 26, 2010 at 4:36:03 am

Ask you friend to turn off edge detail and do another test. If the noise goes away then the edge detail is set too high and the crispening setting is also triggering the detail setting to engage too soon. These settings, if they're too sensitive would probably act on stuff in the water or the water itself to put edge detail on any "noise" in the water with an undesirable effect.

Turning off edge detail entirely is not generally recommended either, because other needed settings get turned off as well with the EX series of cameras. You can keep crispening and edge detail on but severely limit their settings so that they're effectively off. Your friend needs to do some research to better understand how the EX cameras operate.

Perhaps Alister Chapman will see this post an add his considerable knowledge to this answer.

- Don


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dave emery
Re: Grain in underwater footage
on Apr 26, 2010 at 5:05:52 am

Hi Don, thanks for your reply.
He has not got a PP turned on so shouldn't the edge detail and crispening be neutral?
However I think from what u say he may get better results setting up a PP with with massively reduced detail. But wouldn't it be better to + the crispening as it would delete fine detail and leave high level elements?
Thanks again, as i too have some underwater jobs lined up with my EX1.


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Don Greening
Re: Grain in underwater footage
on Apr 26, 2010 at 5:15:40 am

If he doesn't have a PP setting active then the edge detail etc. will be set for full on detail. Not good for shooting in an environment that has lots of crap floating around.

[dave emery] "But wouldn't it be better to + the crispening as it would delete fine detail and leave high level elements? "

Yeah, start with a crispening setting of at least +10 as this "raises the threshold at which detail is applied to the image" (thanks to Alister Chapman).

- Don



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Noah Kadner
Re: Grain in underwater footage
on Apr 26, 2010 at 4:08:58 pm

At a 180 degree shutter and -3 gain I'd guess he's underexposing. Grain will appear on shots that are more than a stop underexposed no matter how low you set the gain and detail settings. Is this near the surface during the day? If it's more than a few meters underwater I'd suggest an on camera light and a slower shutter speed/frame rate. The moment you go underwater you lose a couple of stops, compounded by shooting through the window of an underwater housing. An underwater light meter would also be a solid investment.

Noah

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Mike Neumann
Re: Grain in underwater footage
on Apr 30, 2010 at 12:54:04 am

Hi, I'm the shooter David talks about - thanks to everybody for their comments.

I shoot Sharks and my primary aim is to capture fast action with a minimum of motion blur, hence the 720/50 overcranked to 60, 180 shutter. I also under-expose by 1/2 as in my experience, all camcorders over-expose when UW, and the exposure is spot on.

This is however not an issue of exposure.
I operate on auto iris (can't be fiddling around) and the aperture sits comfortably at around 4. I get grain on sunny and cloudy days and whether I aim against the surface or against the bottom, meaning regardless of available light.

The grain appears in large uniformly colored areas of blue water as opposed to images where there's a lot of different elements. One friend suggested that this may be the result of variable rate compression when writing to the SS card.

Went diving yesterday with a PP with detail set at -20, crisp at +50: no notable improvement!

Any UW shooters who could give me some additional tips?


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