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Old February 16th, 2008, 12:25 PM   #1
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Perfect downconvert to SD 50iPAL impossible?

I have been doing a lot of experiments downscaling EX1-material from HD to SD using various methods and my findings are that downscaling progressive material is easier and yields a better result. I don't know if this really is true or just coincidence. I have a theory however that I would love to have comments on.

Let me try to explain.

Downscaling progressive video would in theory be just like downscaling a digital still image. When changeing the image size all you have to do is scale down the image accordingly.

Now - downscaling an interlaced image adds a time factor. Since the image is made of two fields you can only downscale one field at the time without de-interlacing first. If you were to use information from the odd field to build the even field you would screw up the temporal factor, right?
So - that means that you only have half the resolution to work with when downscaling each field.

Now - here is where my mind gets stuck... How does this effect the result? I guess that if you are downscaling using factor 2:1 (going from 1080i to NTSC) this would not be a problem but going to PAL you wouldn't end up with even numbers would you?
Could that be the problems I am seing with flickering edges and strange moires? Could it be that the lines from different fields end up in the wrong order?

I am sorry for rambeling here. I am just trying to explain what I am trying to grasp...can someone who is better at this then me please help me understand?

If it is like I sense it is this might mean that it is not possible to make a perfect downconversion from 1080i to 50iPAL. Could this be true?

/ola
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Old February 16th, 2008, 12:47 PM   #2
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Hi

last week I had to deliver SD stuff which was supposed to be cut together with SD stuff already shoot in SD. So I did a test with all modes (PAL/I am in Germany). MY best result for material to be shown also on tubes and not only on PC or LCD monitors: Shooting in 1080/50i - putting all to an SD Timeline in Final Cut. The End. Of course with Avid and all other programms it could be a little bit more complicated...
I tried all modes - progressive, interlaced, 1080/720 etc. On a PC Monitor progressive looks much better but for tubes the best result was just 1080/50i > down to SD with an SD timeline/Final Cut.
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Old February 16th, 2008, 12:49 PM   #3
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By the way: The company was very much happy about the quality - they couldn't belive it was made by a "prosumer cam". Of course I told them "prosumer" is not the exact description for the EX1!!! ;-)
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Old February 16th, 2008, 01:02 PM   #4
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I tried the same thing.. Shooting 50i and importing to a DVCPRO50 timeline.. but it started to flicker and really screw up.. Can you please post your sequence preset for this downconversion?
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Old February 16th, 2008, 01:50 PM   #5
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It was "gerade Zeile" in german - should mean "even field" in english, compressor "DV Pal" (dvcpro should work, too), YUV "precision", filter quality "fastest". And: don't forget to render all !! I didn't do it it the first time and I got a bad picture when recording it to DV...
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Old February 16th, 2008, 02:15 PM   #6
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better than Compressor ?

It's also an issue with classical HDV. Don't u think compressor should do it better ?
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Old February 17th, 2008, 06:32 AM   #7
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Any thoughts on my field/frame theory? I would like to know if it is at all theoretically possible to make a perfect downconversion from 1080i to 50i PAL.
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Old February 17th, 2008, 01:05 PM   #8
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Ola, I'm getting desperate on this subject. I'm shooting 1080 50i and have not been able to get a decent SD DVD out of the HD timeline (using CS3 + Axio LE). The resulting SD DVD seems too soft - almost out of focus. Have applied sharpening prior to downconverting - resulting in a much better looking SD DVD but with an unacceptable flicker / shimmer at the letterbox edges! Apart from the horrendeous rendering time (even with the Axio LE).

I'm being tempted to switch to FCP. So Rainer, are you happy with the final SD DVD? Would you mind in giving me the exact step by step workflow (I'm not used to FCP) so that when I go to my local Mac reseller this week I re-create your workflow and will be able to assess the final DVD please?

Unless I find a solution I will be forced to revert back to my SD camera - as unfortunately it seems that I have stepped backwards instead of forwards.

Any help would be greatly appreciated.
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Old February 17th, 2008, 01:16 PM   #9
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Has anyone considered and / or is using anything such as Kona / Aja / Blackmagic hardware HD-Sd downconversion? Will these products produce very good quality SD picture. I know that they tend to be pricey, but if they do the job well and in real time, then they are worth every cent.

I'm trying to figure out whether it is possible to output from an HD timeline (whether CS3 or FCP) to an external HD-SD converter (anyone from the above) to either a recording deck (DVCAM or XDCAM) or to a second computer. If it is possible at all.....!
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Old February 17th, 2008, 01:19 PM   #10
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Anyone tried exporting your 1080p footage to tiffs, then batch resizing them to SD, importing them to SD timeline? in this way you'd be sure resizing is made with full resolution
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Old February 17th, 2008, 02:07 PM   #11
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If material is interlaced:
deinterlace(tdeint+edi=GREAT DEINTERLACER)>resize(Spline36 is best)

If material is progressive
resize (with spline36)


regards Dennis
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Old February 17th, 2008, 02:47 PM   #12
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Is Spline36 an application? or plugin?

EDIT:
Oh.. I guess it's an algorithm.. But do you know of any mac apps that has this? AVIsynth is PC-only.
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Old February 17th, 2008, 03:04 PM   #13
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oh my god - I am very sorry you are not working with Final Cut - really, I mean no offense to anyone here!! But when I am reading how complicated your way of downconverting seems to be, I am so happy about my change from Avid to FC last year! In FC I open an SD timeline, correct settings, importing the XDCAM EX files - let my Mac rendering the stuff, that's it. I am not at home right now but will let you know my settings tomorrow.
About the quality: I was told to shoot my stuff (interview) on Beta or Digibeta for a company. I spoke to a few friends and everyone told me to use my EX! I wasn't sure about, did a few tests and after my test settings, I took the risk and shoot the stuff with my EX at 1080/50i. My client got a DV tape - didn't knew it wasn't shoot on SD. Didn't say anything. I told him and he was surprised and pleased by the images! In fact, he asked me to send him an original EX file because now he was very much interested in the EX :-)
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Old February 17th, 2008, 04:23 PM   #14
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Quote:
Originally Posted by Rainer Mann View Post
oh my god - I am very sorry you are not working with Final Cut - really, I mean no offense to anyone here!! But when I am reading how complicated your way of downconverting seems to be, I am so happy about my change from Avid to FC last year!
Rainer, I am glad that you are happy with your editing software. However - it is not the workflow that concerns me. Downscaling in Avid is just as easy and progressive video looks great, but I am not 100% confident that the downscaling of interlaced material is perfect. That's why I started this thread and why I'd be very interested to hear if anybody using FCP conciders downscaled interlaced video to be inferior in any way to video originally shot in interlaced SD?
Mind you - I am talking interlaced HD source material downscaled to interlaced SD video. Not being deinterlaced, that is.
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Old February 17th, 2008, 05:36 PM   #15
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Hey,

I like the discussion, I am working in VEGAS and it does a great downscale job too.

For comparison, perhaps we should setup a testfile and have a try with avid, fcp, vegas etc.

Is anyone willing to offer a 10s xdcam ex file?

Lets stay in PAL for the beginning.

I could offer some webspace for the trial...

ULI
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