Why does deinterlace look better on my TV?

[Graham Meredith]

Hi, I'm using the TV tuner of my Matrox G400TV capture card to record TV shows, then I use VirtualDub and TMPGEnc to capture and encode my footage. I then use DVDAuthor and DVD decrypter to burn it to DVD, and watch it on my Akai DVD player and Magnavox TV.

Whenever I follow some of the suggestions to encode the footage as "INTERLACED" because I'm watching it on a standard TV, the results turn out worse than when I deinterlace. If I leave it interlaced, the picture "vibrates" up and down slightly. Selecting the deinterlace option "even field" in TMPGEnc gives the sharpest steadyest, smoothest picture, both on computer and TV, and looks great.

This brings me to the issue that maybe I might not be using the options correctly.

Firstly, I thought that TV footage captured through a TV tuner card on a computer was automatically non-interlaced ("progressive" so to speak). I capture in Virtual Dub, then frameserve to TMPGEnc, with no filters or deinterlace features active in Vdub - I just use it to cut out the ads. I set my "Video source type" in TMPGEnc to "non interlaced". I set the field order to "B" - because that's what my Matrox card uses, according to Matrox.

If that's the case, why does it look better when I use the de-interlace function, as opposed to not using it, in TMPGEnc?

When I deinterlace, the "even field" option gives the sharpest picture. "Blend" looks good also, but slightly blurrier. "Even/odd 2xfps" causes it to "vibrate" slightly, the same as when I don't de-interlace"

So what setting should I be using? The obvious answer is "whichever looks the best", but this isn't helping me to understand what's going on. I get good results, but I don't technically know why. If I'm using "Even field" deinterlacing, what's actually happening? Am I only encoding 1 field, and losing half my picture and resolution in the process? Should be using "blend" instead?

Cheers, Graham

[lordsmurf]

"Vibrates"??
Can you upload a sample clip somewhere?

Did you by chance CROP the video?

There is no way a deinterlace can give a "smooth" picture, it'll jerk around on pans and movements. There will also be nasty jaggy lines everywhere. And a blend will create ghosts everywhere.

[edDV]

Usually a tuner outputs interlaced but that depends on the card and settings. At the tuner level, "deinterlaced" usually means single field ( i.e tossing half the vertical resolution). I'm not familiar with the G400TV but someone here probably is.

[gadgetguy]

It sounds like when you encoded interlaced you reversed the field order, giving that "vibrating" effect. When you de-interlace using even field or odd field you are indeed eliminating half your picture.
Personally, I would encode interlaced material as interlaced. When done properly it gives the best results when watched on TV and using decent software (PowerDVD) it looks good on the PC too.

[Graham Meredith]

Lordsmurf,
Hi, no, I didn't do any cropping or any resizing, filtering, etc. As for "smooth picture" when panning - yes, surprisingly, it is smooth, no jagged lines.


Gadgetguy,
I'll try reversing the field order. Should I set the "video source type" to "Interlaced" in TMPGEnc, under the presumption that it IS interlaced (re: edDV's post)?

So in any circumstance where I DO want to de-interlace, should I be using the "blend" option?

Thanks for all your advice!

Cheers, Graham

[gadgetguy]

Sorry, I don't use TMPGEnc so I'm not sure what settings should be, but I would presume that the source is interlaced.

[edDV]

...

So in any circumstance where I DO want to de-interlace, should I be using the "blend" option?

Thanks for all your advice!

Cheers, Graham

If your goal is to play it back on a normal TV, try to keep it interlaced. Deinterlace (the type you describe) is used when you want extreme compression and computer viewing. Blend will create "double-vision" type blurs during motion. Give it a test and see if you can live with it.

[junkmalle]

I have an old Matrox G450 eTV card so I know exactly what your problem is. They have a bug where they save pairs of scanlines reversed. This is NOT the usual field order issue that people here are used to dealting with. Since you are using VirtualDub you can fix this problem with the Field Swap filter. Or better yet (to avoid YUV to RGB conversion), use HuffYUV when you capture and then use its "Swap fields on decomress" option. Both of those are designed specifically to fix that flaw.

[Graham Meredith]

Junkmalle,

Ahh! Thanks for that tip. I'll give that a go, like I said before, I know my card uses field order B (bottom field first), but wasn't sure if that was the norm, or how to use that fact. I found the filter in Vdub. Will give it a try when I get home tonight, on my matrox card computer.

I presume now that this means I untick all options of de-interlacing in TMPGEnc, as I frameserve from Vdub with the reverse field filter enabled.

Cheers, Graham

[FulciLives]

Also as you asked before be sure to set up the encode in TMPGEnc as "interlaced".

A red flag went off when I read your first post and you mentioned setting it up as "non-interlaced" in TMPGEnc. If the source is interlaced and you set up TMGPEnc for a non-interlaced source ... well ... that is asking for trouble!

- John "FulciLives" Coleman

[Graham Meredith]

FulciLives,
Yes, I guess that was part of the whole issue that I wasn't sure of in the first place - is my source from my matrox card interlaced or non-interlaced. I'll presume interlaced, unless anyone here knows otherwise.

Graham

[FulciLives]

FulciLives,
Yes, I guess that was part of the whole issue that I wasn't sure of in the first place - is my source from my matrox card interlaced or non-interlaced. I'll presume interlaced, unless anyone here knows otherwise.

Graham

Well based on what junkmalle said, it sounds as though the card does capture interlaced ... but incorrectly.

He already gave you two ways of fixing it though

Just be sure you use a "good" resolution. That always means 480 height for NTSC or 576 height for PAL. The width can vary from capture card to capture card but usually should be either 720 or 704.

One last thing ... I wouldn't be surprised that either of the two interlaced fixes that junkmalle mentions end up changing the field order to TOP instead of BOTTOM. I could be wrong about that but if you try one way and get bad quality try the other way. Keep it in the back of your mind

- John "FulciLives" Coleman

[SatStorm]

Just for the info, I know who has this card...
Sefy

[junkmalle]

One last thing ... I wouldn't be surprised that either of the two interlaced fixes that junkmalle mentions end up changing the field order to TOP instead of BOTTOM. I could be wrong about that but if you try one way and get bad quality try the other way. Keep it in the back of your mind

I use the card only as a display device now and don't have the capture drivers installed. But I think the "swap fields" fix does reverse the temporal field order.

[Graham Meredith]

Hi, Sefy
Any tips on what you do with the G400TV in this case?

Cheers, Graham

[junkmalle]

Here's what's wrong with the eTV captures:

Other cards save scanlines in order when they capture. So a video with 480 scanlines (interlaced or not) appear in order in the image:

1
2
3
4
...
477
478
479
480

The usual temporal field order setting controls which of the fields to display first when sending the fields to an interlaced TV. Either the top field (1,3,5...479) will be sent first followed 1/30th second later by the bottom field (2,4,6...480), or the other way around.

When saving with the eTV card it saves the fields in the wrong order. Each pair of scanlines is reversed:

2
1
4
3
...
478
477
480
479

As you can see, this is the equivalent of placing the top field physically below the bottom field. So when this is displayed on an interlaced television the image bounces up and down by a scanline 30 times a second.

The "Swap Fields" options in VirtualDub and HUFFYuv are designed to fix this problem and restore the order of the scanlines. This eliminates the bounce. You still have to get the temporal field order correct or you will get fast-jerky motions.

You do not need to deinterlace.

[SatStorm]

@Graham Meredith: Since you are a sooo old member and you know who Sefy is, you could easily search the archives of our forum back on 2000 - 2002 and get all the info about this card you want to know....
That's why I mention Sefy