GH2 in 50Hz countries ? Is there a workaround for 25 FPS ?

J

John Brawley

Well-known member
It seems confusing still, but just wanting to confirm that the GH2 is only doing 25P derived from 50p 1080, but only at 17mbs ?

Or I can shoot 24 FPS at a higher data rate but then have to re-time everything ?
 
It seems like the PAL model actually is proper 1080i50 (not 25p in a 50i wrapper) at 17bmps or 1080p24 at 24mbps - no 25p

so yeah, you gotta use cinematools to conform 24-25p speeding everything up by 4%

I'm hanging out for a firmware update. Or hack

In the meantime us Ausies will just have to suffer the moire and aliasing of the canons if we want 25p.

BTW John, I'm the dude who got you coffee last year at the IF awards voting thing in Melbourne!! :)
 
auzgc said:
In theory, 1080 25p can be extracted from 50i footage with shutter speeds 1/40 and under, but it offsets the video by one field requiring some post processing.
See http://www.dvxuser.com/V6/showthread.php?231315-Any-GH2-news-on-the-HDMI-output-front/page25
Click to expand...

I'm confused by the 1/40th shutter speed requirement. Why would I need to shoot with a lower than optimal shutter speed ? And lowering the shutter speed then offsets the field order ? Can't i just drop a 50i clip shot at 1/50th on a 25P timeline ?

I have a series coming up that I want to intercut GH2 and RED footage with. 1/40th of a second shutter speeds won't match.

jb
 
jenningsp said:
It seems like the PAL model actually is proper 1080i50 (not 25p in a 50i wrapper) at 17bmps or 1080p24 at 24mbps - no 25p

so yeah, you gotta use cinematools to conform 24-25p speeding everything up by 4%

I'm hanging out for a firmware update. Or hack

In the meantime us Ausies will just have to suffer the moire and aliasing of the canons if we want 25p.

BTW John, I'm the dude who got you coffee last year at the IF awards voting thing in Melbourne!! :)
Click to expand...

Hi Patrick. Nice to hear from you.

So 50i is true interlace ? Is this idea behind the 1/40th shutter speed ?

jb
 
Yes, it is proper 50i interlaced at 1080.
The 1/40 shutter speed is just a hacky way of getting 25p out of the 50i feed without deinterlacing. It is obviously not an optimal solution.
 
I've looked at two clips from a GH2 in 50i mode. One was true 50i. One had progressive frames interlaced into consecutive pseudo-interlaced frames. Apparently the latter behaviour is what you get when you shoot 50i at shutter speeds under 1/50 - presumably some obscure timing characteristic of the electronics that has to be satisfied.

In either case it's only 17mbps and that ain't enough. On the upside, it rather invalidates the idea that AVCHD doesn't have a mode for 25p video. If they were worried about that, well, they're not really doing 50i anyway.
 
yep true interlaced

The 1/40th shutter speed thing is trying to force the camera into a pseudo 25p mode. Where you tell the sensor to use a more than 360 degree shutter (because the sensor is actually 50p but the camera only records every odd/even line), so it resets it's scan rate out of sync with 50fps. so it gives you proper 25p , but apparently the camera doesn't record it properly... so you have to do some offsetting of fields in post.

but yeah, your stuck with 1/40th shutter... so your motion blur will look a bit off

is the series by any chance offspring season 2? why not go with the 7D or 5D? i've been using them for the past two years and the texture of the image matches the RED better than the panasonics. they're not as sharp and they moire and alias all over the place, but the texture!!! i'm actually about to order a whole bunch of different grades of diffusion filters to experiment with, to try and get rid of the aliasing.

pat
 
jenningsp said:
yep true interlaced

but yeah, your stuck with 1/40th shutter... so your motion blur will look a bit off
Click to expand...

Hi again Pat..

That pretty much rules out that workaround. The motion blur and field re-timing would make it unworkable for the amount we shoot.

jenningsp said:
is the series by any chance offspring season 2? why not go with the 7D or 5D? i've been using them for the past two years and the texture of the image matches the RED better than the panasonics. they're not as sharp and they moire and alias all over the place, but the texture!!! i'm actually about to order a whole bunch of different grades of diffusion filters to experiment with, to try and get rid of the aliasing.
Click to expand...

I don't think diffusion is the answer. The problem isn't so much aliasing, and moire, but just the lack of resolution. So many of the lines are skipped that there just isn't the picture information in the image. I don't find they intercut with RED very well at all. We had the most success with them when using them by themselves in a scene rather than intercutting with RED.

I'm shooting a series entirely on 7d's and 1D's right now. I don't want to use canon's ever again !

The main reason I like the GH2 is because it's even smaller than the EOS, they can take all my SHG olympus and PanaLeica 4/3 lenses and they have an articulated screen for operating. I might just have to go for AF102's instead though I don't like the size of them.

Im interested in what you describe as *texture*. What do you think is making this so inherent to the canon X/D series cameras ?

jb
 
Unless someone can show otherwise, it would be best to assume that the 1/40th 'hack' to achieve 25P is generating half-vertical resolution footage. In other words, that it takes a single 540x1920 field and expands it to a 1080x1920 frame.

In which case the best options will be either to retime the 24P to 25P, or use a smart adaptive deinterlacer on the 50i.
 
I dont really understand why Pana stopped 25p in full HD on the GH2. Nevertheless if your shots are supposed to go on TV in PAL you can shoot in 50i or 720p and not worry. In case I would have to shoot for TV I would go 720p or 50i and not go below 50fps. Lets hope some FW upgrade comes soon!
 
GrahamH said:
Unless someone can show otherwise, it would be best to assume that the 1/40th 'hack' to achieve 25P is generating half-vertical resolution footage. In other words, that it takes a single 540x1920 field and expands it to a 1080x1920 frame.

In which case the best options will be either to retime the 24P to 25P, or use a smart adaptive deinterlacer on the 50i.
Click to expand...

I am pretty sure the resolution is somewhere in between. See here for some frames I posted:

http://www.dvxuser.com/V6/showthrea...output-front&p=2198371&viewfull=1#post2198371

While the vertical resolution is not as high as the 24p mode it is significantly higher than 540. (perhaps closer to 720)
 
John Brawley said:
Im interested in what you describe as *texture*. What do you think is making this so inherent to the canon X/D series cameras ?

jb
Click to expand...

i completely understand not wanting to work with the canons ever again. i came to that point about 6 months ago, but unfortunately they fill a hole in the indie crowd and it's the cheapest "good enough" picture quality. so it's impossible to get away from them, at least for me :)

this "texture" idea is something i use to describe that missing element when talking about picture. it's basically how the image feels.

so there are some cameras that feel more "filmic" and it's not to do with dof or dynamic range or resolution. it's all in how the sensor renders the image and how it feels in motion - the texture :)

the panasonics are a bit videoy - they feel like video with shallow dof (like an F900). the canons are better but not great, i'd put them about the same as an F35. and then RED has probably the nicest texture.

but this all subjective of course :)
 
Last edited:
You must log in or register to reply here.
Back
Top