deinterlacing

[asdf1]

One quick question, If i'm using a pvr-150 and i am outputing to a sdtv, which is interlaced picture, why do i need to deinterlace it. I mean right now i have it set to bob deinterlacing, i think but why not just forget the deinterlacing, since the tv is interlaced. right? Oh and i am not using a monitor at all, the tv is the primary output (only output). thanks in advanced, i know you guys have the answer.

[stefan]

This might explain it, if you're up for some reading. Especially the part "is interlacing a bug?" a fair bit down.
http://www.100fps.com/

[McBainUK]

Thanks for the link stefan, lots of interesting info there, well written too

[dvasco]

http://www.100fps.com/video_resolution_vs_fluidity.htm
4) If you have interlaced material (like DV from your camcorder) and want to display it on TV sets (with a SVCD for example) instead of computer screens, then you don't need to deinterlace. If you wanted to play deinterlaced material, your TV screen would not be able to display it OR it would have to interlace it and you will lose quality.

So, the OP was right. As I felt. There is no need to deintelerace if played back on a SDTV. I will have the same setup.

[csy]

IMO deinterlacing is a very very bad thing. It takes a pure picture (interlaced) and modifies (distorts and adds artifacts) to make it presentable on a progressive-format screen. Additionally it halves the temporal sampling rate. The picture quality without deinterlacing is much sharper and clear compared to deinterlacing and does equal the the same quality as a standalone TV. So it makes sence not to deinterlace if you don't have to.

There are several steps you must follow to ensure the captured interlaced raster lines are exactly 1-for-1 mapped to the same raster lines on your SDTV. By default the mapping is not 1:1. If they do not map 1:1 then some raster lines will be presented in reverse interlace-field order resulting in double-difference interlacing jaggies seen on the TV when motion occurs.
Starting from the source capture resolution which is nominally 720x480 for NTSC and 720x576 for PAL.
1) Set the screen resolution to be the same as the capture resolution.
2) Disable any aspect ratio correction (use stretch to full screen) (not applicable for "none" mode and the Intervideo decoder does not have this setting when used in GBPVR).
3) Disable video card scaling/overscan correction on the TV-out. On ATI cards enable TV "video mode" (no action required for Nvidia cards).
4) Disable (meaning zero) GBPVR scaling and overscan correction in config.xml
Note: GBPVR appears to have a scaling issue requiring a tweak to correct this as per thread:
http://forums.nextpvr.com/showthread.php?t=14475

The next problem is to get the interlaced field order presented in the correct order to the SDTV. This is where everything starts falling apart. Interlaced video has 2 fields, one containing the odd numbered raster lines (odd-field), and the other containing the even raster lines (even-field), with the fields running at double frame-rate but only half the vertical resolution. For broadcast TV the odd-field is recorded and played-back first, but Digital Video (eg handycams) has the even-field first. In my experience you have a 50/50 chance of striking the correct field order (with either raw-YUV or MPEG2), resulting in double-difference interlacing jaggies seen on the TV when motion occurs.

Finally the last problem is the field-rate synchronisation. What should happen is the broadcast frame-rate should be used to clock all the downstream frame-rate generators, and therefore it is all synchronisted and no field slips (drops or gains) occur. For the most part this all works correctly, however in my experience the TV-out encoder chips on Nvidia and ATI video cards appear to free-run, resulting in periodic dropping or gaining a field. The problem is each field slip results in swapping the field order presentation to the SDTV, therefore resulting in double-difference interlacing jaggies seen on the TV when motion occurs. So this shows up as say 2 minutes of smooth motion then 2 minutes of juddering motion, repeating.

One thing to be cautious of when experimenting with transparent interlacing (no deinterlacing) is that the broadcast TV may be transmitting progressive-format programmes/shows in the interlaced signal. This can trick you into thinking that your "no deinterlacing" is working fine when it actually isn't. You need to view interlaced-recorded shows, eg live sports and lookout for the jaggied edges (jaggies). Interlaced-recorded ticker tapes are also a good source to view how well it is working. As a double-check, deliberately try watching on a computer monitor, - you should see all the interlace jaggies as movement occurs (if you don't then deinterlacing is occuring or the programme/show is progressive format).

So in conclusion it hit the too-hard basket for me and I am now deinterlacing.

[dvasco]

So in conclusion it hit the too-hard basket for me and I am now deinterlacing.

Thanks for the info. I'll compare.

[malgernon]

Just wanted to say thanks to Csy for this list.

Artefacts had made me avoid interlaced output in favour of de-interlaced. Strictly speaking this was inappropriate for my Standard Definition TV.

Going with these recommendations I found I got sharper picture quality.

My Epia-M TV-Out doesn't support 720x576, to match PAL. (I wonder if any graphics cards do?)

But - specifically - taking my resolution down to the next nearest, which is 800x600, got rid of the "jaggies" on interlaced content when there was movement.

Overall its been a noticeable improvement on the picture quality- good news since my Epia doesn't have room for a graphics card.

Cheers,

Malgernon