Resizing HD to SD 720 or 1080

[Chris Harding]

Hi Adam

Quite correct.. the wrapper doesn't make it an interlaced file at all..it's progressive all the way so importing it into Vegas, one would leave Project Properties de-interlace box at none..which I tend to leave at default!

If I do shoot at 1080 50i I usually use VAAST's Upshift to transcode down to HDV (MPEG2) and then also tell Upshift to make the output file progressive so I always have progressive files in my project media. The end result from Upshift certainly seems to give a pretty sharp and pristine image but I have no idea what method NewBlue use (they make the software) to de-interlace. I wonder if V10 would de-interlace better than Upshift but I'm always in a quandry whether to use interpolate or blend...it's mainly weddings so there isn't really any high motion involved ... the help says use "blend" for high motion...do they consider high motion someone walking or more a Nascar race????

Yes, I know I should be shooting progressive but in PAL we only have 25P not 30P so you tend to get motion problems on frames unless you drop to 720 and use a double frame rate...with weddings I don't take the chance so they get done interlaced!!

Chris

[Peter Manojlovic]

Originally Posted by Adam Stanislav

If you have 30p wrapped in 60i, then it still is progressive, so what is there to de-interlace? De-interlacing only makes sense with true interlaced footage.

Yes Adam...
That's the problem. Some people actually DO deinterlace PsF footage.
Some softwares interperate PsF footage as interlaced, and process as such..

[Adam Stanislav]

I see what you mean now. And I agree, deinterlacing PsF is a no-no.

[Eric Olson]

Originally Posted by Chris Harding

the help says use "blend" for high motion...do they consider high motion someone walking or more a Nascar race????

Typically blend fields is only used when high motion is combined with a fast shutter. Even in these situations many people would prefer the stop-action strobing-effect caused by interpolate fields to the blurry double-exposures caused by blend fields. To deinterlace a wedding recorded at 50i with a shutter speed of 1/50 second, I would use interpolate fields.

[Frans Meijer]

Originally Posted by Adam Stanislav

And I agree, deinterlacing PsF is a no-no.

You basically would have to de-interlace before rescaling because in interlaced material the fields are incomplete images, they're missing every other line and regular rescaling algorithms can not cope with that (they assume an image with a homogeneous pattern of pixels).

From what I gather from the help, Blend fields would combine the lines of the two fields while interpolate drops one field then interpolates the missing lines in the remaining field. For 'PSF' material blend should be used. For rescaling PsF you'd de-interlace using blending.

[Peter Manojlovic]

Frans...

As far as the frame is concerned, it is considered progressive, regardless of what the sensors or internal mechanisms of the camera output...Deinterlacing the PsF frame should be avoided, since it is, in essence, a fully displayed frame, and not a frame consisting of two separate fields..

[Frans Meijer]

Afaik PsF is in interlaced format, each frame is split in two fields each with half of the lines missing. At least that is what I always believed interlace means.

From Wikipedia, the article Progressive segmented frame states

With PsF, a progressive frame is divided into two segments, with the odd lines in one segment and the even lines in the other segment. Technically, the segments are equivalent to interlaced fields, but unlike native interlaced video, there is no motion between the two fields that make up the video frame

For an optimal resizing of such a frame, the software (or other equipment) will have to combine the two segments or fields (whichever word you prefer), into one frame before resizing. The recombination is the same operation as de-interlacing, although given the progressive origin of the segmented (or interlaced) frame that operation is pretty straightforward.

[David Jimerson]

Actually, "blend" is what you should NOT use if you have a lot of motion, because it'll be blending two fields, and in those two fields, moving objects will be far apart. This will require a lot of blurring, and you're almost certainly going to be seeing quite a bit of ghosting.

"Interpolate" is better because it works with single fields. It may end up having slightly lower resolution, but the other kinds of artifacts will be far less.

[Chris Harding]

Many thanks guys

That's a neat summary and I can really see the sense in de-interlacing with interpolate as a wedding is fairly slow moving.

I was transcoding with Upshift as mentioned and looking at the final SD DVD you can pick up ghosting here and there occasionally so I guess Upshift uses the blend method. What seems strange is you have 3 de-interlace options... "copy from input", "progressive", and "interpolate"

To me the 2nd and 3rd options both deinterlace!! but it seems one uses blend. The next batch I'll skip using Upshift and just transcode the clips to CanopusHQ and use Vegas to do the interlacing!!

Chris

[Phil Lee]

Hi

Originally Posted by Chris Harding

Hi Peter and Eric

That sounds like perfect sense...I assume it would also work well for PAL where we are resizing to 576/50i???
Based on your assumption then guys, would it be an advantage to NOT shoot interlaced 1080 but in fact shoot (in my case) 1080 50P which should mean that the NLE already has de-interlaced double frame rate footage to resize???

If I look at project properties with 720 50P Vegas does show it at double frame rate. Sadly my cams don't shoot 1080 50P only 25P and according to the specs the 25P is over a 50i wrapper. If the NLE doesn't have the first step to worry about then this is probably why people are saying that 720 does a better resize as plenty of cameras can shoot 720 50 or 60P without any issues.

Chris

I found 1080/50p looks even worse resized to DVD than starting with 1080i, it was a shock.

The main problem seems too be there is too much detail, when you start with 1080i and de-interlace and bob up to 50p, in the process you are approximating the image and essentially this removes detail. When it resizes down to 576i, the interlaced lines smudge up against each other and jaggies are less of a problem, and on de-interlacing the interlaced lines merge and knit together better. With 1080/50p straight down 576i those interlace lines sharply meet each other and you get jagged lines and it looks rough.

I think this is why 1080->720->576 is consider better looking, the extra resizing is helping remove detail.

I found better methods using AVISynth and a script, this works great on 1080i without having to de-interlace it, and does a good job with 1080p.

If you can, 1080p to 576p looks fantastic, like a good commercial film transfer if your footage can withstand being 25p.

I have tried resizing from 1080/50p to 576p at 50fps and it looks great, so you think just take odd lines from one frame and even lines from the other to get 50i and it should look equally great but interlaced, wrong, it looks horrendous, just too much detail in each interlaced frame.

Regards

Phil

[Eric Olson]

Originally Posted by Phil Lee

so you think just take odd lines from one frame and even lines from the other to get 50i and it should look equally great but interlaced, wrong, it looks horrendous

Taking the "odd lines from one frame and even lines from the other" is not a good way to weave 50p into 50i. The usual method is

1. average line 1 and line 2 of frame 1 to obtain line 1 of field 1,
2. average line 2 and line 3 of frame 2 to obtain line 1 of field 2,
3. average line 3 and line 4 of frame 1 to obtain line 2 of field 1,
4. average line 4 and line 5 of frame 2 to obtain line 2 of field 2,
5. average line 5 and line 6 of frame 1 to obtain line 3 of field 1,
6. average line 6 and line 7 of frame 2 to obtain line 3 of field 2,
7. and so on

which has the advantage of being simple without introducing unacceptable aliasing or interline twitter.

What either Vegas or DVD Architect actually do to weave 50p to 50i is beyond me; however, there are reports that DVD Architect is better at such conversions than Vegas.

http://www.dvinfo.net/forum/what-hap...itect-5-a.html