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Confusion about Format choice with HVX-200

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Tobias Lindner
Confusion about Format choice with HVX-200
on Nov 20, 2009 at 8:28:00 am

Dear Colleagues,

I am not sure if this has been discussed at length, however, I am a bit confused.

I will be shooting a documentary with the HVX-200.

Now, I am a bit confused about what format to use. Firstly, I really do not care about variable frame rates, since I am not going to use any overcranking. All will be normal speed, thus 25 frames.

So the choices are:
1080i/25p
720p/25p
720p/25pn

First of all, let's rule out the lower two:
Is there ANY benefit from shooting 720p/25p versus 720p/25pn? As far as I understood, 25p just records every frame twice. What is the point of that (except a post-decision to go slow-motion)? Is there any other benefit I am missing?

Secondly, the choice between 1080i and 720p:
I think I am missing something here, because I do not understand why 1080 is INTERLACED and yet 25P. Is it progressive or not? What is the difference between the 1080 progressive and the so-called TRUE PROGRESSIVE of 720p/25p? This is confusing me most.

The output resolution of 1080 is obviously higher thatn 720, but as I understand that is achieved by some algorithms in-camera. Is it possible to use a similar algorithm in post afterwards to up 720p to a 1080 resolution?

From image quality, I suspect the difference between 720 and 1080 is most evident in small-patterned images like wide shots. Is it possible to mix the two formats or will that be a mess? In the end, recording time is also a matter for me. 1080 has twice the data rate as 720p/25pn. Is it possible to mix the two formats or will that be a mess?

Thank you for your time!


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Michael Sacci
Re: Confusion about Format choice with HVX-200
on Nov 20, 2009 at 10:47:50 pm

720p/25p versus 720p/25pn - 25pN gives more runtime on card, this is the most people shoot the camera. 720p if you can matching other footage that was shoot or captured that way. Yes every frame is recorded twice,

I would also only use 1080i or 1080p if I was matching another source in a project. The camera is doing an upconvert to 1080 so most people shoot on 720p.

For me I want uniformity between cameras, frame rate and frame size so I choose the over all best for cameras that are being used on a project. If it is just a one or more HVX camera(s) shoot, I will shoot 720p@24pN.



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Tobias Lindner
Re: Confusion about Format choice with HVX-200
on Nov 21, 2009 at 2:19:52 am

Thank you for the quick answer.

I am shooting with only one camera.
Keep in mind I am aiming at cinematic release too. So I assume resolution IS indeed important. On the other hand, if the upconvert to 1080 decreases image purity, it is indeed worth thinking about sticking 720PN. Though I do not quite understand the argument for 720P EXCEPT recording time.

I still don't neccessarily get the format differences... But more importantly, how does the choice of 720 or 1080 affect image quality?

Would it be practical to mix 720P/25PN and 1080P/50i? I believe the problem is the 1080 is actually recording 50i while the 720 is recording 25p? And from a standpoint of looks? What would you think?

Cheers,

Tobias


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Kevin Randall
Re: Confusion about Format choice with HVX-200
on Nov 23, 2009 at 7:44:38 pm

Please resist repeating the misinformation about the resolution of the images created/recorded by the HVX200.

*Everything* output by the camera begins as a 1920 x 1080 progressive image. Doesn't matter if you are shooting progressive or interlaced, or at standard def, 720, or 1080. It all starts out at 1920 x 1080 progressive. The image is derived from a block of three CCD chips, each 960 x 540, with the green chip slightly offset in relation to the red and blue chips.

The image is derived from the chips as a 1920 x 1080 progressive image, and then is processed for recording according to the format chosen by the user. If the user is recording in 720, the image will be downrezzed to 720; if the user is recording standard def, the image will be downrezzed to the appropriate vertical resolution in NTSC or PAL. Some users have done tests comparing the 1080 and 720 recordings from the camera and found they were able to get slightly better 720 footage by recording 1080 and downconverting in other software, versus recording 720 in-camera.

(All of the above is totally separate from the question of how well the images from the HVX compare to images generated from other cameras, or whether the images from the HVX would be better if the chips had 1920 x 1080 photosites versus 960 x 540 photosites. The reality is, however one judges the quality of the images, for better or worse, when they begin their "lives" as digital images assembled from data coming off the chips inside the camera, they are 1920 x 1080 images. Any other resolution chosen by the user is a downrez.)

If the user has chosen to shoot interlaced, the images will be recorded as interlaced. If the user has chosen progressive, the images will be recorded as progressive, but in most formats laid out in an interlaced stream with pulldown. (They are true progressive images, "re-assembled" from the interlaced recording format, in the NLE.)

A detailed discussion of this matter can be found on the DVXUSER site: http://www.dvxuser.com/V6/showthread.php?t=96274


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