Interlacing Question?

me · Post by me » Mon Jun 15, 2009 5:33 pm

hello-

I am curious--

Is video produced on HD discs (Blu-ray and AVCHD) usually interlaced?

If so, why?

From what I understood (and I could well be wrong) the original reason for interlacing had something to do with a quirk of the old CRT TVs.

Now, with most new TVs being LCD or plasma, in fact all HD TVs are AFAIK (not CRT), not so different from the LCD computer monitors, why would interlacing continue for new HD video discs?

When interlaced discs (both DVD and AVCHD, BD) are played back on a computer, does the computer software automatically deinterlace the video on playback?

If so, why when one exports a video file to be played back on computer, should one deinterlace? Is it that discs are automatically deinterlaced on playback, but a file on the HDD would not be?

DVDDoug · Post by **DVDDoug** » Mon Jun 15, 2009 8:40 pm

I don't know what's 'usual', but Wikipedia shows both interlaced (i) and progressive (p) formats for Blu-Ray.

From what I understood (and I could well be wrong) the original reason for interlacing had something to do with a quirk of the old CRT TVs.

I think so. It allows a refresh/flicker rate of twice the actual framerate. With a digital system (even with a CRT on your computer), you can have a refresh rate that's independent of the framerate. (It's not just the framerate, because movies are 24FPS. I think it has something to do with the way the image is "drawn" on the screen, and the "persistence" of the phosphor (which has to glow 'till it's refreshed, but it has to decay fast-enough that you don't get streaking/ghosting.)

But, I'm pretty sure I've seen HDTVs rated for 720p and 1080i... So, it must still be "easier" to build an interlaced display.

me · Post by me » Mon Jun 15, 2009 8:51 pm

DVDDoug wrote:I don't know what's 'usual', but Wikipedia shows both interlaced (i) and progressive (p) formats for Blu-Ray.

Well then, if one is creating a Blu-ray or AVCHD disk, and one does not know if it will play back on an interlaced or progressive TV, or on a computer, is it safest to encode interlaced? If played back on a progressive TV or computer, would that be recognized, and deinterlaced?

Post by **Ken Berry** » Mon Jun 15, 2009 10:16 pm

AFAIK, all plasma and LCD HDTVs, including ones rated 'p', contain a sort of decoder which allows them to play interlaced video. If you think about it, commercial DVDs are all interlaced, but when you play them on a standard definition DVD player connected to your HDTV, they play just fine...

sjj1805 · Post by **sjj1805** » Tue Jun 16, 2009 2:05 am

me wrote:Well then, if one is creating a Blu-ray or AVCHD disk, and one does not know if it will play back on an interlaced or progressive TV, or on a computer, is it safest to encode interlaced? If played back on a progressive TV or computer, would that be recognized, and deinterlaced?

Yes.