The 25p / 50i debate

E

eggmedia

Member
I know this has been discussed ad nausem but I'd like to throw something in to the ring and see what everyone thinks. I've been shooting with my GH2 in FSH 50i mode and then de-interlacing the footage using Re-Vision Fields Kit and grading with Magic Bullet. I'm very happy with the results I'm getting. The footage is pretty sharp before being processed but comes out looking quite 'filmic' in the end. At least to my eye it does ; )

I came across a review page for the GH2 which states that the sensor is capturing 50p and then writing it as a 50i stream. So does this mean that there are 50 progressive frames written in the 50i stream and is any information actually lost?

Here's a screenshot of the sensor info:

GH2%20sensor%20output.png
 
No expert here but if the sensor was reading at 25p the you would get a progressive image spread over two frames. You could then de-interlace to get 25 true images at full resolution. This is what the NTSC version does but at 24 fps in a 60i container. Pulldown removal can then regain the progressive output. With the PAL version I believe that as it is reading at 50 frames per second and then sending that down the pipe as 50 'fields per second', my reasoning is that you are losing half your vertical resolution per frame.

If they sent down 50 full progressive frames per second then you would not lose anything but we know it doesn't record that although the upstream sensor data is at 50 progressive frames per second. But due to the processing where interlacing is added some information must be discarded to get 50i. If one was to do a quick pan you may discover that each field shows a unique interlaced frame. My two cents. The general consensus as far as the majority of threads I have read is that there is no way as of now to get progressive images out of the PAL GH2 easily. A hack may help and the HDMI capture worka round may help but I suspect it is a true interlaced file being recording in spite of the sensor readout.

To add another rabbit trail -- Dpreview suggest that the sensor is capable of 120 fps. NTSC version I presume - I don't think it actually reads at that speed but the chapter concerning that gives you insight. I wonder why they mentioned it after all........read below.

http://www.dpreview.com/reviews/panasonicdmcgh2/

It may also explain why it is not so easy to get the nice motion blur form the NTSC GH2.
 
I would interpret that as meaning the sensor is 'capturing' 50 progressive frames per second. The camera's electronics are throwing out half of each frame to turn it into a field. So the first progressive frame throws out all the even lines, the second throws out all the odd lines, the third throws out all the even lines again, etc.

That is just a guess, though.
 
It is actually very easy to get 1080p @ 25 FPS straight out of the GH2. Just lower your shutter speed below 1/50th of a second and record in 1080i. It will record 1080p @ 25 FPS embedded in 1080i. Also known as 1080i/25 PSF. It will have a slightly lower overall shutter speed than ideal but you probably won't notice it in most scenes.
 
I would interpret that as meaning the sensor is 'capturing' 50 progressive frames per second. The camera's electronics are throwing out half of each frame to turn it into a field. So the first progressive frame throws out all the even lines, the second throws out all the odd lines, the third throws out all the even lines again, etc.

That is just a guess, though.
Click to expand...
A correct guess. That's how it works.

The sensor is capturing 50 progressive frames. The recording format is 50 fields. So it splits each frame up into fields and records one field per frame -- which results in a loss of half the potential vertical resolution.

If it was true 25p mode, the sensor would be running at half speed, and each frame would be recorded across two fields, resulting in full resolution.
 
The general consensus as far as the majority of threads I have read is that there is no way as of now to get progressive images out of the PAL GH2 easily. A hack may help and the HDMI capture worka round may help but I suspect it is a true interlaced file being recording in spite of the sensor readout.


720P is progressive even in pal land,as sharp as 50i as well,a true 25P option would be nice, by the way 24P H is 24 Mbps
 
i dont have this camera yet - waiting for a 25 p / 24mbs firmware tweak - or i am going with a 60 d and canon glass-

but i wonder what would happen if:

shoot in 720 / 50p mode at 17mbs

bring the footage into final cut through magic bullet grinder - which upscales 720p to 1080p by default

voila 1080p 25fps - i am sure the scaling will mess something up - and we are still stuck with the 17mbs rate - the 24mbs would be so much better)

how much worse is the 17mbs vs the 24 mbs ? is it even noticeable ?
 
grinder is a really good app - it beats the hell out of waiting for compressor to consistently crash when converting more than 4 clips at once

Grinder supports my go pro hd stuff - i didnt think about the compatibility issues with avchd - another headache to consider ?
 
Red Giant are talking about widening the compatibility. It's coming I think. Although Panasonic GH may not be a priority.
 
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