How to Remove Interlace Artifacts at Slow Shutter Speeds - GH2

R

Ralph B

Well-known member
If you're shooting in 60i (50i PAL) and you set the shutter speed slower than 1/60 (1/50 PAL), you would expect to get a progessive looking frame. But the GH2 produces a picture that still looks interlaced. How is this possible?

Well, there actually is a progessive looking picture lurking in there, but the GH2 is jumbling the fields around between adjacent frames to make it look interlaced. Here's a fix for that. It's an AviSynth script.

directshowsource("Your_movie.MTS")
ComplementParity()
separatefields()
Trim(1,0)
weave()

This will produce a correct looking picture without any interlace artifacts.

Now the question is, is this really a progressive picture? The answer is, not exactly, but close. It has the same vertical resolution of an interlaced picture - definitely more than a single field being interpolated. It might be something akin to Canon's Frame mode on their old XL cameras. Bottom line - it looks good. Not as good as progressive, but still good.

So, why would you shoot in this mode when you can shoot in 1080P at the same slow shutter speed? There are two reasons I can think of.

1) When you're in really low light, shooting 1080i will produce significantly less noise than 1080P at the same shutter speed. Try it and see for yourself.

2) For people in PAL land, this is a way to get a 25P look.

Hope you find this useful.
 
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Ralph,
thank you for this script.
Forgive my ignorance on this matter (I'm relatively new to video), but do you think the theory behind this script may be applied to files recorded over hdmi as well? I've been reading the long threads on HDMI recording and I still hope to get rid of avchd on my GH2 PAL with an external recorder.
Cheers
 
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diegocervo said:
Ralph,
thank you for this script.
Forgive my ignorance on this matter (I'm relatively new to video), but do you think the theory behind this script may be applied to files recorded over hdmi as well? I've been reading the long threads on HDMI recording and I still hope to get rid of avchd on my GH2 PAL with an external recorder.
Cheers
Click to expand...

Good question. Unfortunately, the answer is no. But, I'm working on it. I have an Intensity Pro board and like you, I want to get the absolute best out of the camera. This script was a little success story along the way.

BTW, does the script actually work with a PAL GH2 when you shoot 1080 50i with a shutter slower than 1/50? I have no way of testing that.
 
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Ralph B said:
Good question. Unfortunately, the answer is no. But, I'm working on it. I have an Intensity Pro board and like you, I want to get the absolute best out of the camera. This script was a little success story along the way.

BTW, does the script actually work with a PAL GH2 when you shoot 1080 50i with a shutter slower than 1/50? I have no way of testing that.
Click to expand...


As i realy miss 25P this is interesting to me but i dont understand this directshowsource("Your_movie.MTS")
ComplementParity()
separatefields()
Trim(1,0)
weave()
i am afraid.
 
just out of curiosity, are you experiencing any chroma issues with the Intensity pro? Sandbox noticed that red and blue channels look like they were interlaced with jaggy edges (http://www.dvxuser.com/V6/showthread.php?233386-GH2-HDMI-Discoveries)

The weird thing is that I get the same result that sandbox is talking about when I convert mts files to prores with either media encoder or a couple of other tools that work "fast". 5DtoRGB (which is really sloooooow) gives me a perfect conversion instead.
I downloaded the trial version of neoscene and played with cineform just to see how it performs and it outputs a file with about the same quality as 5DtoRGB.

Now, I'm wondering if the chroma issue is something more related to the way that external recorders handle the conversion to prores or to the HDMI on GH2. Did you try other codecs?
Thanks
 
flinty said:
As i realy miss 25P this is interesting to me but i dont understand this directshowsource("Your_movie.MTS")
ComplementParity()
separatefields()
Trim(1,0)
weave()
i am afraid.
Click to expand...


You need to learn how to use AviSynth. Here are some links to get started:

http://www.animemusicvideos.org/guides/avtech3/amvapp-avisynth.html

http://sourceforge.net/projects/avisynth2/

http://avisynth.org/mediawiki/Main_Page


You will also need VirtualDub.

http://www.animemusicvideos.org/guides/avtech3/amvapp-vdub.html

http://virtualdub.sourceforge.net/


AviSynth and VirtualDub work together. It will take some time to learn them, but it's worth it. AviSynth is very powerful and will give you capabilities for processing video that are unavailable anywhere else.
 
Ralph B said:
You need to learn how to use AviSynth. Here are some links to get started:

http://www.animemusicvideos.org/guides/avtech3/amvapp-avisynth.html

http://sourceforge.net/projects/avisynth2/

http://avisynth.org/mediawiki/Main_Page


You will also need VirtualDub.

http://www.animemusicvideos.org/guides/avtech3/amvapp-vdub.html

http://virtualdub.sourceforge.net/


AviSynth and VirtualDub work together. It will take some time to learn them, but it's worth it. AviSynth is very powerful and will give you capabilities for processing video that are unavailable anywhere else.
Click to expand...

Thanks i might be a bit old for it now but i will look into it.
 
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