GH1 sky "skipping/ breathing" on static shot, why??

L

LittleTreeMedia

Active member
Hi All, so I shot some test video last night at of the Brooklyn Bridge, GH1 with the Lumix 20mm f1.7, iso 1600, FHD, locked off on a tripod. It looked all good as i was recording, shot a few different clips with different lenses, and when I got home I noticed that on all the clips shot with the 20mm lens the sky was skipping/ breathing. Its happening when it bring it in through FCP and when I use ClipWrap which leads me to believe its in the raw footage.

Its the weirdest thing and its only in the sky (see video in link below, you may need to go to full screen to see it since its a lo res render).

http://www.youtube.com/watch?v=xU_YV6EGwMo

I know what the banding looks like, unfortunatley i have seen it before in my footage, and this doesnt look the same. Any ideas on what caused it and what i can do to prevent it from happening again? Thanks!

Dave
LTM
 
I can't be sure and maybe someone could confirm but would I think that with the low light and the Camera's predictive capabilities that it could be related to the water movement. Maybe the cam was anticipateing more movement in under exposed areas because of the dark fast moving, partially exposed water. I see thses kinds of things in darks a lot. Even on my HMC150 with its CCDs.
 
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It might help if you posted a native clip, because all I see is the youtube compression and long gop issues (keyframe popping)
 
That's very likely what it is, "keyframe popping". The GH1 compression isn't good enough, this is why people use the GH13 hack, or GH2

To be sure, a native clip (native as in straight from the camera) would prove/disprove this
 
LittleTreeMedia said:
PDR, let me know what you think, here is the MTS file, but you will need ClipWrap or another program to convert. In all my years, i have never seen keyframe popping. Do you know any way around it besides not shooting what i was?

https://rcpt.yousendit.com/1150681023/a207b3e771062de4d38bdaa0d935f1ac
Click to expand...

You probably haven't shot with such poor compression in your other cameras. Back in the old days DV-AVI is intraframe (I-frame only) , so there is no quality difference between frames

The "popping" occurs at every P=>I transition, the quality difference between them is percieved as "popping" . If compression is good enough (more efficient, uses b-frames, or perhaps higher bitrates to compensate) , then the popping wouldn't be noticable. You wouldn't see this on the high bitrate GH13 for example.

Did you notice the "mud" as well? This is a static picture, yet the image isn't very crisp. The reason is the compression is so poor that it cannot hold the details. If there was any motion, it would fall apart even more

The GH1 compression is probably the worst out there, even some camera phones have better compression. The GH1 compression was discussed thoroughly when it first came out. Search for "GH1 mud" and similar threads if you want more details

Is there any way around it? yes, hack it or use a different camera. Darker scenes are more predisposed to this because of the way this brand of AVC allocates macroblock quantizers to dark areas. What's putting it over the top and stressing the codec is the movement in the water. If it was a completely static scene (no moving water) I doubt you would see this artifact
 
Thanks PDR. I have noticed the mud before, and I have been thinking about upgrading to GH13 (at least i think I can). But since i'm in the middle of another project I have shied away from it, but now maybe a good time to do it.... Thanks for your help.
 
LittleTreeMedia said:
Thanks PDR. I have noticed the mud before, and I have been thinking about upgrading to GH13 (at least i think I can). But since i'm in the middle of another project I have shied away from it, but now maybe a good time to do it.... Thanks for your help.
Click to expand...

You absolutely have to hack it. The difference is night and day - it's incredible. The hack is not hard, takes 20 minutes tops, and will improve the quality by a million times. I've never seen that I-frame popping on either of my hacked GH1s.
 
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