TMPGEnc Inverse Telecine and Deinterlace question

[sdo]

I'm capturing some of my laserdiscs to burn to svcd. In messing with Raiders of the Lost Ark, I've come across a problem with TMPGEnc that seems to be a deinterlacing / inverse telecine artifact. On some scenes where there is alot of heavy horizontal lines, the video goes crazy for a few seconds then settles out. A good frame looks like this:

http://www.downtowncomputing.com/good_frame_01.jpg

Note the windows, particularly the cross pieces (muntins is the technical term I'm told).

Now look at a couple of bad frames:

http://www.downtowncomputing.com/bad_frame_01.jpg
http://www.downtowncomputing.com/bad_frame_02.jpg

Note again the windows and also the new jaggies on the desks and other straight edges. It looks nasty when playing the video in real time. It jumps in and out between good and bad.

The original .avi files (captured with VirtualDub using Huffyuv v2.1.1 compression at 640x480) show no signs of problems.

I've found that I can eliminate the problem by changing a TMPGEnc Inverse Telecine setting. Under Setting, Advanced, Inverse Telecine, Auto-Setting, the default "deinterlace set threshold" is 300 for deinterlace method of Even-Odd field (field). If I change it to 400, everything seems OK.

Any idea what's going on and why changing that setting seemed to fix the problem? Will changing that cause me any problems down the road?

Thanks,
Steve

[anticowboyism]

Look at the movie frame by frame. You should start to see a pattern of progressive and interlaced frames. A normal Telecined video will show 3 progressive then 2 interlaced frames. If that is what you have, then a normal IVTC will do the trick. Realize that no IVTC algorithm will be 100% accurate. There are some advanced techniques in TMPGEnc to correct these misses, you can read about. Examining the progressive/interlaced pattern frame by frame will reveal the exact field setup, and your necissary countermeasures. If you haven't already, also try to set the Field order to Bottom first.

[sdo]

Look at the movie frame by frame. You should start to see a pattern of progressive and interlaced frames. A normal Telecined video will show 3 progressive then 2 interlaced frames. If that is what you have, then a normal IVTC will do the trick.

Yes, that is indeed what I have. The video is captured at 30 fps from the laserdisc player but the "movie" itself is 24 fps. The normal inverse telecine with Even-Odd Field (field) deinterlacing worked just fine for all other parts of the avi file.

But in this one scene that the screen captures show, TMPGEnc went crazy. Even after I "fixed" it by increasing the "deinterlace set threshold" setting, it still looks really bad in that one scene because those window cross hatches are, about 1 pixel high and they're against a solid white background. This causes another problem in that frame after frame, parts of those lines dissapear and reappear, presumably as part of the mpeg2 compression. I've been trying all kinds of things to fix that. I'm starting to appreciate what it means to do a good mastering job on a DVD. I'm sure these are the same types of issues that the "pros" deal with.

There are some advanced techniques in TMPGEnc to correct these misses, you can read about. Examining the progressive/interlaced pattern frame by frame will reveal the exact field setup, and your necissary countermeasures.

I've searched all over the place. The TMPGEnc documentation is fairly sparse in this area and the websites I've found don't go into a lot of detail on what the settings actually do.

If you haven't already, also try to set the Field order to Bottom first.

That was the first thing I tried. I've definatly got it right with Top First (checked by selecting deinterlace, then Even-Odd Field (field) and looking at the output. Bottom First jumps back and forth between frames and is jittery. Top First is fine.

Like I said, it's just in this one scene that there was a problem. The rest of the video came out fine.

-Steve

[anticowboyism]

You could just be experiencing your CRT monitor's inability to display interlaced signal. If your final product is meant for TV playback, try watching it on the TV. Make sure you are encoding as interlaced after the IVTC, then watching on the TV.

[anticowboyism]

Now that I think of it, you really shouldn't be using IVTC at all if your final product is to be played on an interlaced device. IVTC will restore the progressive 24fps, and you still want 30fps interlaced for TV display. Maybe I'm just confusing myself...

Look at the bottom of this page for a little about correcting misjudged frames. http://arbor.ee.ntu.edu.tw/~jackei/dvd2avi/ivtc/

[sdo]

Make sure you are encoding as interlaced after the IVTC, then watching on the TV.

I'll give that a shot. I'm using the SVCD (NTSC Film) setting as a baseline. In TMPGEnc, that locks out the frame rate and "encode as" options. (in grey it says encode as "3/2 pulldown when playback")

Now that I think of it, you really shouldn't be using IVTC at all if your final product is to be played on an interlaced device. IVTC will restore the progressive 24fps, and you still want 30fps interlaced for TV display. Maybe I'm just confusing myself...

I don't think that's the case. The DVD player that I'm playing it on will do the telecine (3/2 pulldown?) and output at 30 fps just like it should. The method I'm using worked great on the other laserdiscs that I did (Empire Strikes Back), though I've had a lot of issues with merging and cutting the svcd compliant mpeg2 files (but that's another issue).

I'm trying a few other things, including not saying that it's film, and I'll report back on how this works.

Thanks folks... this board has been INVALUABLE (!!!) as a resource in this project.

-Steve