JVC manual focus & flicker problem

[Ronald Czarnecki]

I wanted some more opinions about a problem I am having on my JVC GY-HM170, I have new footage I shot with three of these cameras on this shoot. I took care to manual focus and lower the exposure to control flickering of the brights in the background.

As you can see in this test footage I had multiple problems on two cameras. Listen to the description and see if you ever had anything like this. What could be causing this?

JVC Test benches flicker_5000Kbps_1080p on Vimeo

[Noa Put]

To me it looks like the camera is hunting for focus which should not be the case if you say you where in manual focus. My guess is that there is a setting in the menu that still allows for the camera to refocus in manual mode.

[Duncan Craig]

Firstly, I'd suggest resetting the camera.

I know nothing about your model, but you need to check that it's in a standard video mode, stabilisation is off, AF and any wide latitude options are switched off too.

I wouldn't call the problems you are seeing 'flicker', more like an image processing error on high contrast areas. That's why you should try to discount any processing tricks that might be turned on in the camera.

[Ronald Czarnecki]

Thanks, I had the cameras check out at JVC in Long Beach CA. They reported no problems with the computer specs and they could not duplicate the problem (although they tried them outside in even daylight, not high contrast.

When I get the cameras back I will try to find out what I am doing wrong however the cameras were reset to factory original specs, I turned off Wide Dynamic Range (which helped), detail (however the image is fuzzy), and kept the exposure down. Still the brights flicker.

I will keep this thread updated.

[Ronald Czarnecki]

Update: JVC repair facility has gone over the cameras and found them to be within computer and scope specs. They could not duplicate the problem in their field test.

I took the first camera out of the box put my stripe shirt on the chair and again was able to duplicate the problem. Is this the way the cameras are to work? Can anyone duplicate this effect? All you have to do is make sure part of the object is overexposed, does not matter if your manual focus, shutter speed, detail, wide dynamic range set.

Is this common effect on JVC GY-HM 170u cameras?

JVC GY-HM170U Flicker After Repair on Vimeo

[Ronald Czarnecki]

UPDATE:
JVC was good enough to have my cameras returned to Long Beach for further investigation, however; the opinion came back that this was all operator error. In particular, the flickering was called MOIRE, I disagree because of this video.

Here in this video, there are no lines or stripes to affect the Bayer CMOS sensors of the camera. By the way, Canon Support just told me they have anti-aliasing filters on their Bayer sensors with the Canon XF-100 I had returned. I never had this problem with the Canon Cameras.

There are two clips here one is at the beginning where we see flickering on the pink shirt and one at 00:55 where the same camera, play, shirt, does not have flickering.

Vimeo

What do you think this is if it's not moire?

[Noa Put]

Operator error?? So jvc thinks it's your fault that the camera is not able to resolve the fine detail?
It could be moire but the camera displays it in the way that I have not seen before, especially the flashing that is very obvious.

[Ronald Czarnecki]

I talked to a former engineer representative of JVC and he feels the camera's sensor for 4k is being pushed. He suggested shooting lower on the iris then you normally would so that the camera is not overworked. Skin tones should be at 50% rather than the normal 70%.

I agree since shooting darker seem to avoid the flicker problem.

[William Hohauser]

That was some very strange stuff happening on his pink shirt. At least that's all I could see in the Vimeo file. Can you reproduce this artifact in controlled circumstances with professional video lights? There seems to be a few possibilities that are promoting this effect.

One: That area on his shirt is overexposed. Nothing much you can do about it, the faces are properly exposed and I assume that you are not in control of the stage lighting during the performance. Does this happen when exposure is optimal for the area? Can you change the knee settings on your camera? This might be an effect when the camera is trying to squash the overexposed area.

Two: Do you know if that particular stage was using multi-color LEDs? I filmed this summer at a place that just installed some very intense multi-color LED background stage lights replacing the old style wash lights I had filmed with before without a problem. I can tell you that whenever the lighting went to intense blue, my camera (a JVC HM600) at a 60th shutter recorded a distinct flicker that was barely noticeable to the audience. All the other colors were fine on camera. Not saying that this is your problem, just an experience I recently had.

Three: Is this moire effect visible when you connect the camera directly to a monitor? Does it go away if you change the sharpness settings in the camera? Does it happen with all shutter settings?

[Pete Cofrancesco]

I didn't watch the video but it's a well know fact that fine strips found on shirts can cause moire problems and some cameras are more susceptible. That's why you don't see newscasters wearing them. Video cameras also have difficulty with red.

[Ronald Czarnecki]

"It's a well know fact that fine strips found on shirts can cause moire problems and some cameras are more susceptible."
True but this is a plain pink shirt.

[Noa Put]

Originally Posted by Pete Cofrancesco

I didn't watch the video

If you don't watch it you don't know what the problem is :) This has been reported here before but couldn't find the video back but it had the same issue, it looked like a combination of overexposure and moire, it resulted in flashing overexposed areas when the camera moved a bit, nothing like "normal" moire" I have seen before.

[Ronald Czarnecki]

Can you reproduce this artifact in controlled circumstances with professional video lights?

Yes, you can see more video here, especially the rather plain chair that is flickering.
http://www.dvinfo.net/forum/jvc-4k-p...r-problem.html

“Does this happen when exposure is optimal for the area?”
Yes and No, if everything is dark then it works better, if you have some chrome or bright reflections off metal there is flickering. C stands, drum sets, mic stands.

“particular stage was using multi-color LEDs”

Perhaps not that stage but I have had shoots with those lights before the firmware was updated in the cameras and I did have loads of problems. These cameras are better with the latest updates.

“moire effect visible when you connect the camera directly to a monitor?”

Yes, I can see it on a monitor. Yes if you take all the detail off or turn it down it will go away but your image is blurry. Yes, different shutter settings and it will still happen depending on how bright or dark the image is.

[Ronald Czarnecki]

JVC is also looking at two other problems (also camera operator error according to the initial response)

1. Ghosting of background and foreground.

2. Focus lose on zooming or panning.

You can see some examples here:

Vimeo

[Pete Cofrancesco]

I'm browsing on my phone and it doesn't support the video.

To put it simply if you can't change your environment then you need to adjust your camera. There are camera settings people have suggested to reduce moire ie reduce sharpening and change the frame rate, change the resolution. Your response has been yeah but I don't want to... I'm not sure what else there is to say.

I recently posted a video where stage led lights were causing a strobbing effect . Seems these issues are cropping up more often.