OT: Clipped G&B channels

OldSmoke wrote on 12/12/2015, 8:58 AM

I hope all the wisdom of this forum can help me with this. Like every year, I am recording our Nutcracker On Ice show but I am facing a problem that I believe is a camera setup issue. The Green and Blue channels are both clipped in the brighter areas and I am not sure what is causing it.

I am using this year two HXR-NX3 and the rental shop recommended using PP4 which has a gamma setting of ITU709 and a color mode of ITU709MATRIX. I am wondering if that is causing the problem.

The other camera settings are a fixed shutter of 1/60, AGC limit of 18db and the Iris is on Auto.

If you look at the image, the clipping happens even with the chain LED lights which in general not warm white but the rather bluish cool white of "cheap" LEDs.
I know that this is something the best NLE cant recover but we got one more evening show to go and also one afternoon show at daylight so not all is lost.
I have not had this issues with the Z5U cameras but I had it about five years ago with a Z1U and also never figured out what caused it.

Comments

farss wrote on 12/12/2015, 2:47 PM

The cause of your problem is overexposure.

With these new light sources which produce light in a very narrow part of the spectrum the potential for overexposure using traditional ways of judging exposure is high. Obviously auto exposure is a fail but relying on zebras, histograms or even waveform monitoring can fool you into having parts of the image clipped i.e. over exposed. The only tool that'll save you is RGB parades. Even with those you need to use your eyeballs to observe that channel clipping is occurring because it happens at values below 255.

I don't have RGB parades in my camera so I just deliberately underexpose. The other thing that seems to help a bit is setting WB to daylight. Anything lit with tungsten is going to look warm to very warm if the lights are dimmed but I find that visually acceptable,

Bob.

OldSmoke wrote on 12/12/2015, 4:15 PM

I somewhat figured it out too. I did my usual WB setup with a test chart but that seemed to have fouled the camera last night. It was set at around 3500K but when I set it back to daylight today, 6500K it was ok again. Yes, some areas seem a bit too warm but that can be easier corrected then a clipped channel or two. What threw me off was that not all channels where over exposed when looking at the scopes in VP, just green and blue.

So the afternoon show went well, we had a bit of daylight at the rink too and that helped. Let's see if the evening show will be any better.

Thanks for giving it some thought too!

set wrote on 12/12/2015, 11:17 PM

I personally feel PP4 is a bit 'oversaturated' and the skin color a bit green under warm indoor / incandescent lighting. and same issue light yours.

I use PP3 at the moment (Sony A7s & PXW-X70), but love to know other people's opinion regarding to their preferred picture profile settings (other than s-log type PP)

Set