about the artifacts problem in 1080p24

[DrBlaz]

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

[Ian-T]

That is exactly what I was proposing when I posted this yesterday:

http://www.dvxuser.com/V6/showthread.php?t=172228

Go for it DrBlaz.

[Kholi]

http://www.dvxuser.com/V6/showthread...wpost&t=172228

[DrBlaz]

it seems to be the ISO changing automatically, I posted it here

http://www.dvxuser.com/V6/showthread.php?t=172323

[SLoNiCK]

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/

[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 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..

[John Caballero]

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.

How do you know exactly that this is happening?

[Isaac_Brody]

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.

[joe 1008]

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.

[Kholi]

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.