Does Deinterlacing then Reinterlacing lose quality?

[Edwin Street]

I'm editing a show for a tv network that still broadcast in miniDV.

The footage I'm getting to edit is all sorts of random footage such as youtube videos, 1080i footage and minidv footage.

At this stage I'm converting all footage to ProRes 422 720p because some parts of the show I have to upload to YouTube. However at the end I have to export it all back to miniDV to go onto the channel.

My question is, will I lose any quality de-interlacing and upscaling miniDV to 720p, then once it's edited exporting back to miniDV (therefore re-interlacing it)?

Can you de-interlace, then re-interlace without losing quality?

I'm using MPEG Streamclip for all the converting if that helps.

[David Stoneburner]

I can't see how you won't lose some quality. You're just changing the files too many times. You might save some quality by editing in SD then take your final edit back to tape for the broadcast and for YouTube up convert to 720p. What ever is the majority of your footage should help keep quality. So if you have more SD footage, down convert your HD footage. That way when you up convert for YouTube again the HD will be a little closer in quality to the SD. You won't have a final edit with major shot quality differences. Just my 2 cents.

[Cole McDonald]

Yes, you'll lose quality... at its worst, deinterlacing throws away 50% of your image (every other line)... at its best, it guesses at the pixels based on the information around them.

Re-interlacing works by duplicating the lines of the fields to fill in every other field, giving you 2 copies of the same image for each separate pass of the CRT's scanline... my question is... do you need to re-interlace for a CRT based audience (the only real reason for interlacing at all)?

[Eric Olson]

Originally Posted by Edwin Street

At this stage I'm converting all footage to ProRes 422 720p because some parts of the show I have to upload to YouTube. However at the end I have to export it all back to miniDV to go onto the channel.

Assuming you mean ProRes 422 720p60, this sounds like a reasonable workflow: You can easily skip print 720p60 to 720p30 for web delivery and just as easily convert 720p60 to 480i30 for DV delivery.

As others have mentioned, 480i30->720p30->480i30 is a bad idea.

Even 480i30->720p60->480i30 can result in quality loss. In particular, shifting a 720p60 intermediate on the timeline by an odd number of frames during editing will result in a slight loss of resolution because what started out as a top field in the 480i30 source would be rendered as a bottom field in the master. I wouldn't worry about this unless you have a lot of DV source.

[Geoffrey Cox]

Given that miniDV plays interlaced footage perfectly well I would have thought that if most of the footage is interlaced then you should avoid having to process this at all. I would make two versions - one for the web and one for the tv. When I have had problems like this and wanted to keep things interlaced (for DVD) I de-interlaced the problem footage and re-imported this back into the editor and then exported the whole lot as interlaced.

If that all sounds like too much hassle / takes too long then clearly Eric knows what he's talking about! One thing though - not sure why folk here have assumed you are using SD material.

[Edwin Street]

Thanks for all the help and I understand now that de-interlacing then reinterlacing (or reinterleaving- whatever is the right way of saying it) takes away a huge amount of quality.

I've decided to edit in HDV 1080i50 (I'm in PAL land) because the director is using Sony HVR V1P. Even though there is a lot of other formats to convert, at this stage I'm converting all DVD footage and YouTube footage into HDV 1080i50.

I understand that HDV 1080i is actually 1440x1080 resolution but this way I can easily print to miniDV tape at 576i or deinterlace for upload to YouTube.

I noticed Geoffrey that you mentioned keeping things interlaced for DVD. But I've found that for all the movies that I've bought on DVD, I can't tell if they're interlaced or not. It appears, if I look closely on my LCD monitor, (making sure I'm not using a program that automatically deinterlaces like Windows Media Player. But instead using VLC with deinterlacing turned off) it appears that DVDs are progressive. But I'm guessing that it comes down to how it was filmed- interlaced or progressive?

One question I can't seem to find the answer to is this:
Does enlarging an interlaced video image (say 1080i) in software such as FCP7 or AMC, does this enlarge the interlacing so that it becomes distinguishable? I've had to enlarge the HDV footage but I'm unsure as to whether or not it will make the interlacing noticeable. By enlarging the footage, I mean to click the Motion tab in FCP7 and zoom in closer to the picture. I don't mean increase the resolution of the video. I hope you understand what I'm trying to say.

[Eric Olson]

Originally Posted by Edwin Street

I've decided to edit in HDV 1080i50 (I'm in PAL land) because the director is using Sony HVR V1P.

When mixing 1080i50 TFF with 576i50 BFF source the resulting DVD should be 576i50 BFF. This is because downsampling HDV to SD with either field dominance results in identical quality, whereas the field dominance of interlaced SD source needs to be preserved. 1080i50 is a reasonable choice to use on the timeline when editing. If none of the source is 576i50, then your original choice of 720p25 may have been fine. This is because HDV often looks better on DVD deinterlaced to 576p25 anyway.

[Geoffrey Cox]

Originally Posted by Edwin Street

I noticed Geoffrey that you mentioned keeping things interlaced for DVD. But I've found that for all the movies that I've bought on DVD, I can't tell if they're interlaced or not. It appears, if I look closely on my LCD monitor, (making sure I'm not using a program that automatically deinterlaces like Windows Media Player. But instead using VLC with deinterlacing turned off) it appears that DVDs are progressive. But I'm guessing that it comes down to how it was filmed- interlaced or progressive?

My understanding is that DVD is a natively interlaced medium and proper DVD players communicate with an LCD screen correctly so you should not see any interlacing artifacts. Certainly that is my experience. Software DVD players, VLC player etc have settings to de-interlace the material but don't do it that well which is why it is better to de-interlace for computer only / web based delivery. I never de-interlace for DVD and it always looks fine if played using a hardware DVD. I've no idea what the commercial DVD authoring process involves however. A good example is if when using an editor like FCP you simply monitor it on your LCD out of the display port, interlaced material can look really bad because the LCD sees it as progressive but if you use a hardware video interface like the Matrox mini it deals with it, and the screen sees the material as interlaced and hey presto it looks great (on my LCD screen it flashes up 1080i showing the recognition).

With regards to your final question I'm not really sure what you mean but I can say that when viewing the timeline in FCP through the viewer screen then if it is set to 'fit to screen' then it throws half the resolution away, so interlacing artifacts are not visible but if you expand it to 100% then it displays at full resolution and they become all too obvious.

Though Eric is surely far more knowledgeable than me, I can say that by using Compressor properly I have found HDV 1080i down-converted to SD DVD looks fine.

Having said all that though you can see why keeping everything progressive from the start is the way to go but until full 50p becomes the norm I'll stick with 50i as I don't like shooting 25p at all (motion is horrible).

[Edwin Street]

Originally Posted by Eric Olson

When mixing 1080i50 TFF with 576i50 BFF source the resulting DVD should be 576i50 BFF.

What does TFF and BFF mean?

[Eric Olson]

Originally Posted by Edwin Street

What does TFF and BFF mean?

TFF means top field first and BFF means bottom field first. An interlaced frame consists of two fields: the top field and the bottom field. When the frame is played, the video player needs to know which field should be displayed first and which second. The terms TFF and BFF specify this convention, which depends on the video source.

[Edwin Street]

The director of the show wanted me to do a test Print to Video before going to air. So I did in FinalCutPro7 and printed the entire 24 mins to miniDV tape through my MiniDV Panasonic NV-GS180, then watched it back on my TVs through the composite cable from the camera. On the plasma you can see each interlaced line really clearly, and on the CRT it flickers really badly.

I'm editing in HDV 1080i25. Do I have to deinterlace the entire show before I print to video? Doesn't Printing to Video interlace it again anyway?

Do I have to do something called pull down before I print it to tape?

Please help, I don't want it to look like this on air.

[Cole McDonald]

Test all the possible options, then pick the one that looks the best on the output devices you've got access to.

De-Interlaced TFF, BFF, straight interlaced, then see which looks the best... use that.

[Eric Olson]

Originally Posted by Edwin Street

On the plasma you can see each interlaced line really clearly, and on the CRT it flickers really badly/

It sounds like the 1080i25 source is being misinterpreted as 1080p25 during downscaling. To isolate the problem, check that the ProRes 422 source files made by MPEG Streamclip are properly tagged as 1080i25 using MediaInfo.

MediaInfo - Download

The output should contain lines like

Chroma subsampling               : 4:2:2
Bit depth                        : 8 bits
Scan type                        : Interlaced
Scan order                       : Top Field First

If the scan order of your source is tagged as progressive, then you did something wrong with MPEG Streamclip. Otherwise, you are doing something wrong with FCP7. Here is a related thread from the Vegas forum.

http://www.dvinfo.net/forum/what-hap...ml#post1728277

In Vegas, the problem is cured by a single project setting. It should be possible to track down which option is wrong in your workflow, however, I'm not experienced enough with Macintosh to offer sure guidance. Another way to guarantee this sort of thing doesn't happen is to convert all interlaced footage to 720p50 before editing.

[Edwin Street]

Thanks Eric for telling me about Media Info, it's a very handy piece of software and only cost me $0.99 from the MacApp Store.

I figured out the problem and this is what I did.

Exported my HDV 1080i video from the timeline. Opened up a new Easy Setup project in Final Cut Pro 7 (Easy Setup DV-PAL Anamorphic 25.000fps), imported the 1080i video then dropped in onto the new DV-PAL timeline, when it asked me to change sequence settings to match the clip settings I clicked 'no'

Then rendered the new timeline and printed it to tape and it's perfect DV PAL 16:9 576i. When I play it back on the plasma I can't see any interlacing and when I play it back on the CRT tv it doesn't flicker. Win!