GH5 Aliasing in slow motion

L

Less_is_more

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I’m trying to decide which camera to get to dabble in video with more intent. So I’ve been looking at some footage online.

I found this video on YouTube shot at “120fps 1080p” with a Panasonic GH5.

It looks beautifully shot to my eye, but I hope the owner won’t mind if I point out aliasing in two shots around 30 seconds and 38 seconds in. Screenshots:

AudIjq.jpg




FE8wkc.jpg


Aliasing is bad enough in stills, but in video it really stabs you in the eye, I guess because the false colour or detail flickers. Watch the video itself rather than my screenshots to see what I mean.

Questions:

  1. Is aliasing generally a problem with the GH5 or just in slow motion?
  2. If only in slow motion, why?
  3. Does the GH5S, which has a lower resolution sensor and an optical low-pass filter (AA filter), eliminate this kind of aliasing?
  4. Does this happen with the GH4 (which also has an AA filter)?

Thanks!
 
1. 99% of cameras. Maybe 98%. [Per usual each camera handles what's in front of the sensor differently.]
2. Worse in slow-motion because the processing of the picture is not optimized for the best results (because of hardware and/or corporate).
3. Arguable, subjective. Conformed 4K/60p will always look nicer on either camera.
4. Worse quality, IMO. Old hardware - different world, expectations.
 
There are plugins that claim to treat or remove, but never tried any of them.

In the end, anything attempting to remove this would be performing some kind of blur or AI replacement.

Most people whom would like to combat aliasing/moire will look into third-party filters in front of the sensor. (Or even try softening filters in front of the lens, screw-on or via matte box.)
 
Thanks. A GH5S would already be at my absolute price limit, so sadly no cinema cameras for me (not that I’d know what to do with them anyway).

What did you mean by “Conformed 4K/60p” earlier?
 
Many people conform/slow down 4K/60p in a 4K/24p timeline for slow-motion (most NLEs have a button to do it instantly) because not many cameras have great 120p (only a handful, maybe 8-12). Some cameras do it internally too. (Over/under cranking.)

If you're not sure what that is in post...it's basically slow-motion that is created from more frames - 60 in this case - in a project that uses less frames to produces its motion of frames.

And the 4K/60p looks much better because it's not only of a higher resolution with more detail but because the camera produces a better IQ from this framerate versus the limited 120p in 1080p.

Check out the Blackmagic Pocket 4K/6K. More of a cinema tool than the GH5/S.
 
I think that aliasing is a by-product of the ultra high frame rate. I've never seen aliasing in GH5 footage at normal frame rates. I'd guess 60 fps is aliasing free too but I can't say for sure as I hardly ever use slo mo.
 
Is the GH5 skipping lines on the readout then? That’s the only explanation I can think of that would explain moiré at high frame rates but not low.

There’s no hint in the Panasonic specs that this happens.

How do the GH5 and GH5S compare in this regard? What’s the highest frame rates they each can do with full sensor readout?
 
Personally, IDK - but I don't think you really need to know, IMO.

An "eye-test" for all cameras is best. Exactly how you spotted it in the first place. And watch more videos of 120p footage from other cameras and you'll see more of it, again and again.

If you can't (meaning anyone) then standards are probably low to begin with (which is great too, makes life easier).
 
"How do the GH5 and GH5S compare in this regard?"

The GH5S, while actually better for 4K 60fps stuff, is worse for aliasing and artifacts at high HD frame rates. Both cameras are clean and have no aliasing or moire issues when shooting 4K. I use them both. I shoot a lot at 180 fps and while it's usually fine there are occasional shots that have problems. At those frame rates you're pushing the capabilities of the camera. I'm not aware of any camera in your stated budget that would do a better job. The new Sony A7SIII isn't any better, according to Bloom's review, when it comes to high 1080p frame rates, ie 240fps, though it will shoot beautiful 4K at up to 120fps.
 
There's a little in the opening shot on the bottom of the bird's wing, but no one will notice that besides crazy people.

For bird lovers/watchers, the shots are awesome.

(I remember originally commenting on this video - IIRC that it was posted here before at some point - thinking the Blue Jay had a lot of personality.)
 
markoconnell said:
The GH5S, while actually better for 4K 60fps stuff, is worse for aliasing and artifacts at high HD frame rates. Both cameras are clean and have no aliasing or moire issues when shooting 4K. I use them both. I shoot a lot at 180 fps and while it's usually fine there are occasional shots that have problems. At those frame rates you're pushing the capabilities of the camera. I'm not aware of any camera in your stated budget that would do a better job. The new Sony A7SIII isn't any better, according to Bloom's review, when it comes to high 1080p frame rates, ie 240fps, though it will shoot beautiful 4K at up to 120fps.
Click to expand...

That Sony α7S III looks great but is way outside my price range, and that’s before lenses. I already have Micro Four Thirds lenses for stills, so I’ll stick with that system.

I’m not even sure I need a GH-series camera. A G9 might do, but the GH5S in particular has several nice extras for video and audio (e.g. line-level audio-in to avoid the need to synch later. By the way, are the preamps different in the G9 / GH5 / GH5S? How useable are they for dynamic mics?). I also like the multi-aspect-ratio feature of the GH5S.

I’m still trying to understand this aliasing, though. Why would the GH5S produce significant aliasing if it has an AA filter and reads all the pixels? Therefore I presume it doesn’t read all the pixels above a certain frame rate.

But since the GH5S readout time is faster than the GH5 for regular frame rates (~11.5 ms versus 15 ms as listed here), I would have expected the GH5S to also do better at high frame rates. So it’s surprising to hear the opposite. Maybe the higher pixel count somehow works in favour of the GH5 while line-skipping?
 
BobKo said:
Here is some 180fps 1080p wildlife footage shot with a GH5. I particularly like the blue jay in the second segment: https://youtu.be/QKUiXIVuFAI. I don't notice any aliasing, but perhaps it's in there somewhere.
Click to expand...
Nice use of the camera! The subject is easier than an all-in-focus urban scene for aliasing, but how about the long tail feathers from about 6–28 seconds?

That’s not a real problem to me, though. It’s minor, a tiny area of the frame, and there is no lurid false colour.

The video that caught my eye is worse, with shimmering false colour on the footpath to the right of the white van from 28–31 seconds. I’d find that kind of artefact bothersome, but at least people are telling me it doesn’t happen at regular frame rates.
 
As mentioned, I haven't tested at what frame rate moire begins with GH5, but this review

https://photographypx.com/panasonic-lumix-gh5-review/

says:

"While the camera shoots 1080p up to 180 fps, shooting at frame rates above 60 fps eliminates both AF and audio recordings. Not only that, but image quality also suffers and is considerably softer with aliasing issues present,"

And I have never seen moire in 25p HD or 4k, including hours of urban architecture and interviews with patterned shirts etc. The shots are flawless when it comes to detail.

https://www.dpreview.com/reviews/im...&x=-0.10995411280361435&y=0.24519562792888713

This comparison shows fairly flawless detail for normal frame rate 4k and HD, but aliasing is clear in high frame rate.

So yes, at some point as frame rate inreases the camera starts line skipping or pixel binning and that's when moire starts.
 
Thanks, hyalinejim. That’s pretty definitive that not all pixels are read at high frame rates. And that would explain the aliasing.

Now I need to figure out when each camera starts skipping pixels as the frame rate increases.

hyalinejim said:
And I have never seen moire in 25p HD or 4k, including hours of urban architecture and interviews with patterned shirts etc. The shots are flawless when it comes to detail.
Click to expand...
Good to hear.

hyalinejim said:
https://www.dpreview.com/reviews/im...&x=-0.10995411280361435&y=0.24519562792888713

This comparison shows fairly flawless detail for normal frame rate 4k and HD, but aliasing is clear in high frame rate.
Click to expand...
Unfortunately they didn’t say what “High Frame Rate” means, nor did they shoot the GH5S at that frame rate for comparison. Still, it does show something is going on at higher frame rates.

I’m not so much complaining about this as trying to understand it so I can go in with my eyes open … and the right camera for me.
 
NorBro said:
There's a little in the opening shot on the bottom of the bird's wing, but no one will notice that besides crazy people.

For bird lovers/watchers, the shots are awesome.

(I remember originally commenting on this video - IIRC that it was posted here before at some point - thinking the Blue Jay had a lot of personality.)
Click to expand...

I can see a little stair-stepping on the feathers in that spot, now that you mention it.

And yes, I started a discussion on the GH5's image quality at higher frame rates, and linked this video as an example. Although it has not gone viral yet, the YouTube audience seems to like it.
 
hyalinejim said:
If I can find the time I'll do a little test for you on the GH5
Click to expand...
I’d certainly appreciate that if you get around to it, but I realise it’s a fair chore to do.

BobKo: I see from some other posts that you’re into audio. Do you have a feel for how clean the GH5’s preamps for external mics are? Any difference to the GH5S?
 
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