HDMI output on g7 and g85 is quite noisy

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HDMI output on g7 and g85 is quite noisy

ClunktheBand

Earlier today I was trying out my g85 and I noticed that the HDMI image looks quite noisy unless you start recording. Here is a video from a few years ago where someone else noticed this as well - The signal looks noisy, but it cleans up as soon as you press record. Now I'm worried because I'm buying cameras specifically for external recording over HDMI... Lots of times when this camera and the g7 are recommended (including by this site) it's partly because of the 4:2:2 over HDMI, but if it turns out the HDMI is noisy like this, then it's not really delivering on that selling point.

Or is this normal? I've never used a gh4 or gh5, maybe HDMI always looks noisy?

Anyway, I'm bummed ever since noticing this, and I figured I'd make a post about it here since in general it seems like if there's anyone who understands this stuff, they would be here.

Potential workarounds -

Record internally whenever recording externally. Drawback to this is an annoying workflow, exponentially so if you're running a multi-cam setup. And you would need big SD cards if you're doing a long shoot.
Rig some sort of dummy SD card that tricks the camera into thinking it's recording.
Set up an SD card to automatically delete files when it's full so you never need to stop recording.
Find some menu setting or firmware adjustment to force the camera to act like it's recording.

On the other hand, could this actually be a good thing?

It's possible that what might actually be happening, is that once you press record, you stop getting a live view and it's instead playing back what is being written to the card (lagging a frame or two behind.) If that's how it works, then the image would only be less noisy because it's already gone through the h.264 codec and had a lot of the image data thrown out. In that case, it would actually be better to start off with an uncompressed noisy image.

If anyone has any advice or anything, let me know. Currently I'm trying to stomach having to spend another $300/400 per camera (I'm buying eight cameras) for gh4 (which doesn't have in-body stabilization or as good of autofocus) all to get rid of some noise on the HDMI signal.

joelwsmith

ClunktheBand

Thanks for reaching out and welcome to the community!

I've been using Panasonic G7, G85, GX85, GH4, GH5, and GH5S cameras for the last 7 years, including on hundreds of hours of multicam shoots through a switcher where HDMI outputs are used. The G85 was actually my go-to for about 3 years for recording 6-8 hour days in a 3 camera multicam setup for one of my clients. I also used the G7 a lot before the G85 and never noticed noisy HDMI output (the G7 can't record and output HDMI simultaneously). From my experiences I have never encountered this issue before. Images are always clean for me whether the camera is currently recording or not. So, this is interesting for sure.

It's possible that what might actually be happening, is that once you press record, you stop getting a live view and it's instead playing back what is being written to the card (lagging a frame or two behind.) If that's how it works, then the image would only be less noisy because it's already gone through the h.264 codec and had a lot of the image data thrown out. In that case, it would actually be better to start off with an uncompressed noisy image.

This is almost definitely not the case. The live view on the LCD is routed separately from the encoding/recording portion of the camera.

What might be happening is some noise reduction is only turned on when recording. That would be the most likely scenario, IMO.

Just to make sure, are you using ISO 800 or lower?

Is the noise you're seeing related to ISO/gain or is it some other kind of noise?

ClunktheBand

Hey there, sorry it took so long to respond!

The noise level is about the same on both the g7 and the g85, but it's only really noticable on the g85 because (like you pointed out) the g7 doesn't display over HDMI while you're recording. But they are about the same. Also I have an update. Later that day I was testing this out again, and I noticed that when I zoomed in a flat color surface there was visible artifacting. Artifcacting could only be from codec compression, as far as I know. So I think it's safe to say the noise is being reduced because the image is being compressed - not a good thing.

The artificating stopped when I stopped recording. And the noise also returned. But if I pressed record, the noise would clean up and there was visible artifcacting.

My plan is to improve my lighting so that I can lower the ISO. And then also I noticed that the g7 and g85 have noise reduction as one of the slider settings in the color profiles. So I'll be sure to turn those down if it's bothering me. But overall I think this is a case of pixel peeping...yes, the image is noticably less noisy if I press record, but it also introduces artifacting. That's not an improvement - it's a tradeoff.

When it comes to recording externally, I'd rather start with a somewhat noisy image that I can clean in post, rather than starting with an image that's already been run through the internal compression.