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Old 12th May 2013, 17:48   #1  |  Link
D-Dave
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Aspect Ratios & Scaling Suggestions and Advice?

I've been reading through information concerning aspect ratios (Storage Aspect Ratio, Display Aspect Ratio, Pixel Aspect Ratio, etc.). Though the concept of aspect ratios makes sense for analog sources since analog dealt with samples rather than pixels, I'm not sure how to interpret this information for digital sources (DVD & HDV tapes). There are a few scenarios that I'm trying to figure out the appropriate way of dealing with odd pixels (as well as resolutions).

If I was working with footage from a DVD and my goal was to simply tidy up the footage and store the footage on a hard drive, would it be better to keep the SAR flags on the footage or to scale the footage to a square pixel resolution (720x480 to 853x480)? I'm not sure whether video players treat SAR flags any differently than video being scaled on a display. Now if I had footage (DVD, VHS, DV tapes) that will be upscaled to 1280x720, would it be a better decision to apply the filters before or after upscaling? In regards to the upscaling, would it be wise to use NNEDI3 to get the footage close to the desired resolution and then adjust with either Spline or Lanczos?

Moving onto HDV footage, if I was to edit my 1080i footage and keep it as 1080p (most likely deinterlaced at 60 fps), how should I deal with the SAR of my HDV footage? Would it be wise to upscale after deinterlacing but before applying filters? Lastly, if my output for the HDV footage was going to be in 1280x720, I was thinking of doing all my work at 1440x1080 then downscaling to 720p. Would this be better than correcting the odd pixel ratio by scaling to 1920x1080 before editing?
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Old 12th May 2013, 19:38   #2  |  Link
Sharc
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If the purpose is mainly to archive something: Why not just keep a copy of the original? Your opinion of "what is best" may change over time, so the best starting point for any future processing is always the original rather than some pre-processed version which you may find later that it has its own flaws which you cannot reverse.

Upscaling or resizing: Why do you want to upscale? Unless there is a technical need (e.g. standards compliance), keep in mind that upscaling does not add any real details to the footage. It rather blows up the width x height of the frame i.e. it is mainly a waste of storage capacity and/or bandwidth.

1080i conversion to 1080p: What is wrong with the 1080i format? Conversion to 1080p makes sense if you are sure that the original video is actually progressive and just encoded as interlaced for the sake of standards compliance. Otherwise, why giving up the double temporal resolution of the interlaced footage, or doubling the frame rate and file size with some kind of bobbing?
Again: for archiving, keep the original. Process the material for your actual use however you want, but don't "substitute" the original.

Just my 2 Cents
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Old 12th May 2013, 21:46   #3  |  Link
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Quote:
Originally Posted by Sharc View Post
Again: for archiving, keep the original. Process the material for your actual use however you want, but don't "substitute" the original.

Just my 2 Cents
Well said! I'll add my 2 cents to that as well.
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Old 13th May 2013, 22:39   #4  |  Link
D-Dave
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Apologies, let me rephrase my question: are SAR flags treated any different than video that is being scaled?
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Old 15th May 2013, 14:54   #5  |  Link
TheSkiller
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No, the PAR or DAR flags just tell the player to resize the video more in one direction than the other to give correct proportions.
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Old 15th May 2013, 18:04   #6  |  Link
D-Dave
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Thanks TheSkiller for the response. Now for my second question: would there be any benefits to applying filters after scaling rather than before?
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Old 15th May 2013, 20:00   #7  |  Link
Sharc
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If the footage is interlaced your first filter should be a deinterlacer, i.e. don't scale interlaced footage.
For other filters I am not sure if a general rule exists. The order may depend on the type of filter. I would for example apply a sharpening filter after scaling. A softening / noise reduction filter probably before scaling.
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Old 15th May 2013, 20:48   #8  |  Link
ps auxw
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Quote:
Originally Posted by D-Dave View Post
If I was working with footage from a DVD and my goal was to simply tidy up the footage and store the footage on a hard drive, would it be better to keep the SAR flags on the footage or to scale the footage to a square pixel resolution (720x480 to 853x480)? I'm not sure whether video players treat SAR flags any differently than video being scaled on a display. Now if I had footage (DVD, VHS, DV tapes) that will be upscaled to 1280x720, would it be a better decision to apply the filters before or after upscaling? In regards to the upscaling, would it be wise to use NNEDI3 to get the footage close to the desired resolution and then adjust with either Spline or Lanczos?
If your DVDs are mastered correctly, that number is actually not perfectly accurate. It's pretty close though. For detailed information on aspect ratios in the SD realm, I recommend taking a look at this site. As for the general question, I would just set the SAR flags and not scale the video to at all. If you are going to scale anyway, you could go either way though.

Quote:
Originally Posted by Sharc View Post
If the footage is interlaced your first filter should be a deinterlacer, i.e. don't scale interlaced footage.
Just make sure it isn't telecined before throwing a deinterlacer at it, as in that case you can actually restore the original progressive video by using an IVTC filter instead of having to use an interpolating deinterlacer.
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