Interlaced to Progressive...Good or Bad Idea?

[Leeray3]

Hi there,

An interesting point was made to me the other day and I think before I proceed further with any video conversions I should get my facts right.

Basically I capture all of my VHS tapes onto DVD. The format is Interlaced which is fine, However I have on occassions edited the capture as old tapes are sometimes oversaturated etc.

My question is should I output the file as Interlace or Progressive?

I have read that doing this is fine as long as its interlace to progressive and not the other way round. When ever I edited (and I have a few to do) I always output to progressive however it has been brought to my attention that this is not the best thing to do and can lead to a choppy video.

Does anyone have any opinions/facts about this. I would really appreciate some help with this.

Thanks.

 

[Stephen Neal]

It depends what the tapes are of, and what frame rate of progressive output you are talking about.

Interlaced content carries 50 independent images (at half vertical resolution) per second, which gives 50Hz motion. 25Hz progressive only carries 25 independent images per second, but with full vertical resolution, where as 50Hz progressive carries 50 independent images per second with full vertical resolution.

If your VHSs are of 25Hz native progressive content (films, tv series shot on film) then there is no real difference in quality between 50Hz interlaced and 25Hz progressive - so you can take a punt (in these cases - assuming the phase of the film transfer is correct - the 50Hz interlaced signal contains a 25Hz progressive source).

If the VHSs are of stuff shot native video (i.e. entertainment, sit com or drama in a studio or on location shot on video cameras) then 50Hz interlaced stuff would need to be converted to 50Hz progressive to fully retain the motion in the source, conversion to 25Hz progressive would make the motion juddery.

NB This is why DVD players with progressive outputs replay DVDs at 576/50p rather than 576/25p (as to preserve the motion in 576/50i interlaced video sourced content, you have to run at 50Hz progressive not 25Hz progressive)

Personally, I'd keep stuff shot natively interlaced as interlaced through the editing process if possible, it should make things quicker and should preserve quality if the editing software is able to cope with interlaced stuff (Decent software should be as most SD content is still interlaced).