about the artifacts problem in 1080p24

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DrBlaz

Active member
hello, like probably many people here, I'm very excited about this cam and awaiting the moment I have the gh1 in my hands, I plan to shoot as soon as possible and the time I will have to test the cam will be very short. So I would like to learn as much as possible about the problems and limitations.


I'm concerned about the artifatcs in 24p, and after testing all m2ts I downloaded, it seems more a software or hardware problem than a bitrate problem. why not a bitrate problem? other avchd cams at similar bitrates can do fast pannings without any artifact, only the normal motion blur. Also, I don't know how avchd codecs work, but 720p60 store more pixels than 1080p24.


The artifatcs seem to appear only when motion blur is present, or, also when the cam is focusing and the image blurs for a moment. I have a lot of samples, will upload to megaupload if anyone is interested. May be it can be minimized with different shutter speeds, or even better, if we spread the problem over the internet and panasonic gives us a firmware update.


May be a proud GH1 owner could do a simple test, just in 1080p24 a fast panning at at least 1/50 and at 1/120 , better also at 1/30 and 1/60 !! and give us the original m2ts


regards :beer:
 
Look at pic I've attached. There are crops form interlaced clip compressed in 2 ways with XviD. The very only difference between these crops is that in left case "interlaced" option was not set in coder settings. I think that the main problem with pans on GH1 is based on coder ignorance of interlaced video structure. IMHO, teaching the coder to compress video respecting fields may improve the performance on pans even better than simple bitrate boosting to 24Mbps. Of course, both tricks will make image much more crisp and clean/
 

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as said before, the AVCHD codec comes originally from sony and panasonic, so it is hard to believe its a codec implementation problem. The bitrate is also ok.


I think the problem is simply the camera adjusting the ISO automatically, this is, when changing the ISO to adjust it when recordind, it causes the mod in a few frames.

The GH1 manual says that in several recording modes, the camera can change the ISO when recording in small changes, in the auto ISO mode or another mode called "intelligent ISO"

I wish I have my GH1 to test it, but In all the m2ts I have downloaded, the mod frames appear except in the videos recorded in full manual or ISO locked.

Even in some videos, the artifatcs appear exactly in this conditions:
- shutter speed locked
- user changing aperture manually
AND THEN the image sensivity do an auto-adjust!! this can only be caused by ISO changes, and this is exactly when the artifacts appear.


So the anwer is simply, please GH1 owners, do that test:

lock the iso and do a fast paning, and then set the auto ISO or intelligent ISO mode and do a fast paning

lets see..
 
I think I've mentioned this already but not removing pulldown properly exacerbates the artifact problem. Though once cameras start shipping we'll know more for sure.
 
Not sure if the codec is strong enough. Recently a friend of mine showed some shots he did with one of those Panasonic 17MB/sec. AVCHD consumer cameras. He shot all at 1080i and even on a SD monitor the slightest pan (an he knows to pan smooth an slowly) produced a smeary image, much worse than normal motion blur.

Not only there is an enormous amount of pixels to compress, the interlaced mode of 1080i makes it even worse for the compression. Interlaced should dissappear into the annals of TV tecnology ASAP. The 720p mode shines IMO, because it's progressive. Also, as the codec mostly defines the difference between frames, he has less work to do with 50p or 60p images: There is simply less difference from frame to frame.
 
Already posted, in the other thread, exactly what's happening. Isaac also clarified that it will all hinge on how you remove pulldown. That interlace residue goes away with Cineform Neoscene.

Do yourself a favor if you have windows, get the Neoscene demo and grab some raw clips, do pulldown.

Compare.
 
Bad luck for me, I work with mac. But I have to update and I am seriously considering going windows with Cineform & Vegas. (Please don't let this become a mac vs. windows or a vegas vs. final cut threat, now ;))

And I'm still considering the european version, already contacted a dealer over there. Both, 50i and 50p should be better than 60i and 60p, I'm specially keen on that probably quite sturdy 50p mode: 50p to 25p to 24p is so easy to get and should look perfect. I mean, all the HVX and the lower HPX models up to the 500 are basically 720p cameras - so why do I need perfect 1080p from a 1500$ cam all in a sudden?
 
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sure, once cameras start shipping we will do our tests, lets hope its at beggining of june!!!

Sorry, but the artifacts I'm talking about have nothing to do with pulldown, I've tried neoscene but I prefer avisynth/virtualdub, its lot better, its free, the pulldown is perfectly removed plus I can program some top quality filters like accurate noise reduction, chroma upsampling to 4:2:2, etc, all with the flexibitity of adapting it for each particular video.

I think the "mud artifacts" are the BIG flaw of GH1, I can stand 17mbs and no HDMI, but don't want to see a ruined scene after filming. The "mud artifacts" do appear when panning, but also sometimes when not paning. And this is the problem, you can avoid the paning artifacts just adding some blur, but the non-paning are impossible to avoid. I've downloaded lot of m2ts from 17mbps video cameras, including panasonic sd9 , and no one has this kind of problem.

The mud seems to appear very reduced in 720p mode, but anyway it appears, and I dont want to use 720p , this codec is 4:2:0, so 1080p24 has 50% more chroma info, it makes a difference to get the best image before editing.

The idea of GH1 "intelligent ISO" generating the problem, is just a perception from the few m2ts I've downloaded, lets see...

this rar has a sequence of mud frames when not paning:

http://www.megaupload.com/?d=K543N3RF




joe: estoy tambien en santo domingo , ¿tu tambien esperando por la gh1? saludos!
 
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SLoNiCK said:
Look at pic I've attached. There are crops form interlaced clip compressed in 2 ways with XviD. The very only difference between these crops is that in left case "interlaced" option was not set in coder settings. I think that the main problem with pans on GH1 is based on coder ignorance of interlaced video structure. IMHO, teaching the coder to compress video respecting fields may improve the performance on pans even better than simple bitrate boosting to 24Mbps. Of course, both tricks will make image much more crisp and clean/
Click to expand...

I wonder if making it native 24p would solve some of those issues then. It sure would clear up the headaches of pulldown removal and de-interlacing.
 
DrBlaz

as said before, the AVCHD codec comes originally from sony and panasonic, so it is hard to believe its a codec implementation problem. The bitrate is also ok.

I bet GH1 and (let's say) HMC150 have different processing engines. GH1 AVC stream lacks some features important for quality like b-frames, CABAC. Looks like Panasonic guys just put together 2 VenusHD chips (720p AVCHD Lite capable) to process fullHD video but didn't enchanced them.

The idea of GH1 "intelligent ISO" generating the problem, is just a perception from the few m2ts I've downloaded, lets see...

It shurely can spoil the show. If luma intensity changes fast between fields it generates same "ladder" as panning - just remember how photo flash looks on iterlaced video.

killacam

I wonder if making it native 24p would solve some of those issues then. It sure would clear up the headaches of pulldown removal and de-interlacing.

Of course it will be the best way for both mac and win NTSC users. It's even easier to produce for Panasonic. But they wanted to keep it compatible with existing AVCHD specs and (what is more serious) their TV-sets and players.
 
SLoNiCK said:
Looks like Panasonic guys just put together 2 VenusHD chips (720p AVCHD Lite capable) to process fullHD video but didn't enchanced them.
Click to expand...
I think the two chips were introduced to accelerate the readout from the sensor and therefore reduce the jello.
 
stav1606

I think the two chips were introduced to accelerate the readout from the sensor and therefore reduce the jello.

From one side it's too generous to add a whole processing unit to increase the readout speed cause it more rational to add just 2 more ADC writing to the same frame buffer. But from the other side it may be cheaper to double the existing solution in mass production unit rather than design a new chip. All in all, it seems to be definitely not the case when quantity easily turns into quality.
 
stav1606 said:
I think the two chips were introduced to accelerate the readout from the sensor and therefore reduce the jello.
Click to expand...

the Venus Engines were also implemented to conserve power...
they are one of the reasons the GH1 is so good on battery power.
i also read somewhere that the engines aid in NR for stills, which seems to have
worked as the GH1 handles low light better than the G1 (from examples iv seen so far)
 
As a comparision I'm wondering what you guys think of this one. Hidden away on the page linked to here is a 1080/25P raw mts clip:

http://www.dvxuser.com/V6/showthread.php?t=172094

Look for "Download the Movie". From a aesthetic view it's horrible as it's handheld by somebody overdosed on caffeine with high aperture and high shutter speed but that makes it a bit of acid test for artefacts. Looking frame-by-frame one can see edges pixeling here and there but but when played it doesn't display any obvious breaks of the codec to me. There are some jello occurrences too but again I didn't see them until I stepped through the frames. Although I might be too old for this sh*t :)
 
Martti Ekstrand

God saves the Queen and the whole PAL land! If Panasonic will turn bitrate to 24 Mbps it will look... It will LOOK, if you know what I mean :)
 
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