GH2 banding when shooting LCD monitors

[Gareth]

Hello all

I've got my hands on a GH2 and I was planning on shooting some footage of various LCD screens. This will be custom software in use at specific locations so I can't use Camtasia or similar.

Whilst running some tests, I've noticed some severe banding on certain screens. All the screens so far have been 60hz. I've shot in PAL 25fps and NTSC 30fps at both 1/50 and 1/60 (and other shutter speeds) but I can't lose the banding. The frequency of the bands changes but no shutter speed loses it completely. All other settings are either neutral or off i.e. standard mode flat and no ExT, no Digital Zoom etc.

The same screens shot on my point and shoot Lumix DMC-TZ10 show no banding at all. It seems strange that a budget camera doesn't show banding but the GH2 does regardless of the settings.

I believe I understand the sync differences that cause the banding but don't understand why I can't get rid of it on the GH2.

Example footage here:

GH2 banding: [media]http://www.youtube.com/watch?v=v1Q1D1QDMdk[/media]
DMC no banding: [media]http://www.youtube.com/watch?v=ehLH82zGYXM[/media]

So my question is, does anyone have experience of successfully shooting LCD screens on a GH2 or other DSLR type camera? Am I expecting too much or perhaps doing something wrong - maybe there's something I haven't tried? Thanks for any advice.

Gareth

[Gareth]

Looking at those example videos again I should probably explain... The DMC video shows pulsing but I'm not concerned about that - there is no banding. The GH2 video shows four monitors, the first two are a pair in a dual monitor setup, they show the worst banding. The third, smallest monitor also shows banding but not as severe. The fourth doesn't show any banding. The footage is PAL 25 fps with the shutter at 50. I'm rotating the camera to show how the bands don't remain vertical, they follow the angle of the camera.

[Axel]

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You mix up terms. Banding is only visible (and very prominent) in the TZ-10 footage. Both videos show occasional moire, which has nothing to do with frame rates or the so-called 'clear scan' at all. Moire occurs, when the resolution is not exactly 'true', then fine patterns (the screen pixel pattern) will overlay. With the GH2, this has more to do with the system lenses (Panasonic, Olympus), which, in order to provide outlines for fast AF, sharpen the image, overriding your settings in filmmodes.
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[quote name='Gareth' timestamp='1353927468' post='22305']The frequency of the bands changes but no shutter speed loses it completely.[/quote]

What you call banding are frequency interferences (darker bars that run over the screen). They will be completely eliminated only if monitor frequency, framerate and shutter speed all fit. So for example with 50Hz, 1/50 and 25fps. The moire that then is still visible once you pan diagonally has another reason, as described above.

[Gareth]

Thanks Axel. I understand moire and I'm not concerned about that - I should have made that clear. I'm referring to the rolling dark bars you call frequency interference. My understanding was exactly as you suggested, that if I matched monitor refresh rate with camera frame rate and shutter speed I would eliminate the bars but that's not the case. Here's some 30fps (29.97) 1/60 of the same 60hz monitor. The bars are different but still very obvious.

http://youtu.be/RUS6K7AhzNo

[Axel]

Indeed. Now, I can't explain that. All I can say is, that I eliminated the bars with my (european current) 50Hz @ 25p. I sometimes film my editing monitors, just because they are there, for tests, there is no other reason. They look as clear and motionless as paper sheets.

[Gareth]

Very odd. A friend sent me some footage taken of their monitor with their GF1 and it too is completely motionless. I really don't understand it. I'd appreciate anyone else sharing their experience so I can start to get a feel for if this is specific to my camera. Thanks again Axel.

[nahua]

You do understand that not all monitors refresh at 50 or 60hz. Some monitors refresh at 55hz and 65hz or even 80 hz. I get the same results as you do. I think the resolution on the GH2 is so great that it shows up. I can shoot the same screen with a 5dmkIII and GH2, the GH2 shows the "banding" while the 5dmkIII doesn't. I recommend trying to find another monitor to shoot, one that does do a true 50hz. I hope this helps.

[Gareth]

It does help, thanks nahua. Yes, I understand monitors use different refresh rates. The majority of my test monitors are fixed at 60hz and not all show the rolling bars. The iPad2 for example (60hz refresh I believe) does not show them regardless of shutter speed. It's interesting that you get bars using the GH2 and not the MkIII.

If any other GH2 owners could shoot a couple of seconds of an LCD monitor (with a matching refresh/shutter speed) it would still really help me gauge if the rolling bars are more of an issue with my setup or the GH2 in general. Many thanks.

[Drew Lahat]

A bit late to the party, but the issue is as relevant as ever.

 

We shoot a lot of high-end corporate videos and online commercials using GH2's and Sony EX1/EX3's. They almost always involve shots of people operating computers, tablets, smartphones etc.

 

The "fault" is the monitor's. It's often not the LCD panel itself, but the backlight that drives it. These are often CCFL (fluorescent tubes), and while you can adjust the LCD refresh frequency, the CCFL frequency might be fixed. If the backlight has aged or is off for some reason, or the power supply that drives it is off, the frequency won't match any standard and you'll have to either replace the monitor or use a camera that lets you dial the shutter speed / scan frequency (= not a DSLR).

 

For example, we've never had issues with Apple monitors, they look fine with our GH2's at 1/50 and 1/60 speeds. But our Dell U2410 LCD's (all of them) will flicker no matter what. With the EX1 we were able to dial custom shutter angles to cancel it out.

 

PS I see refresh issues with all the videos you posted - the good monitor looks good on all cameras, and the problem monitors have problems on all cameras - the artifacts look different but they're there.