PDA

View Full Version : DV = Interlaced !? Why?


mkanar
19th November 2001, 19:19
Experts skip below to my question that starts with *****. The preceeding information is simply a fast run-through of video technology as I understand it.

DV = Digital Video, not Digital Video in general but the codec used in today's Digital8 (D8) and MiniDV camcorders.

Okay, so for a long while (years back) I couldn't understand what all the fuss was about interlaced video....so every odd line gets drawn on the screen and then every even line, which makes up a complete frame; so what's the problem? Ah-ha! I finally realized that the odd and even lines where being captured at different times (in the case of NTSC, I "think" that there is about 0.016683016022368587882791802633247 seconds between each even and odd line capture.

Of course, movies that are *filmed* are captured as complete frames; only 24 of them each second. In the case of NTSC, some of the frames of course have their even or odd lines duplicated and interlaced with the next frame so that it comes out as about 29.9706fps or whatever. However, my point here is that these full (progressive) frames are sent to the TV as interlaced video, but television audiences are generally satisfied with the smoothness of the output even though the source has only 24 full-frames/second rather than almost 60 half-frames per second.

***** My question:

After moving some video from my DV (D8) camcorder to my computer via IEEE 1394 AKA FiREWiRE, I was actually kind of surprised not that the frames were interlaced, but that my digital camcorder continues the legacy method of capturing the even and odd frames at different points in time. To me, it seems as if it would have made more sense to capture both the even and odd lines at the same time. Then, when viewing the video on a computer or non-interlaced display, the video would look good. In the case of outputting this video data to the TV, the even and odd lines would be output to the television as interlaced video, much like a 24fps film, except no need for pulldown since the source would already be 29.9706fps or whatever. It seems to me that compressing progressive frames would be easier than compressing interlaced frames since there are more differences due to the time differential. Furthermore, some of us hope that someday, video will be predominently progressive rather than interlaced. With LCD screens continuously becoming cheaper to produce, and since LCD screens prefer non-interlaced video anyway, I would think that the industry would also be pushing away from interlaced video.

Anyhow, I appreciate corrections/clarifications and/or explainations!

Thanks!

Milos
19th November 2001, 20:04
As I understand myself video standards, you're completly right.

But, in case of DV, one advantage of interlaced video is smoothness (60 fields/s is smoother than 24 frames/s)

What would be great is progressive 60 frames /s (or 50 frames/s for PAL) and that would be also "down" compatible with TV diplay...

Cart
20th November 2001, 00:17
Some DV camcorders have a progressive mode, although I hear that some of them just deinterlace the video. Have you checked to see if yours has that option?

But as Milos said, the reason the video is interlaced is because it looks much smoother when viewed on a TV, which is still the predominant video medium.

-Cart
http://www.geocities.com/lukesvideo/index.html

mkanar
8th February 2002, 06:49
I have a Sony TRV-310 (NTCS, version 1). Using a home-built parallel printer port<=>LANC cable that I built, I believe that I can change a bit in memory that was discovered by some of the people over in Europe while working to modify the camcorder to do all of the firewire stuff that it should do but that europoean law doesn't allow.

Anyone around here have a camcorder with a progressive scan option that is a little-bit more friendly to access?

Thanks

bb
9th February 2002, 18:44
I have a Canon MV3 MC with real progressive scan. As far as I know, Sony doesn't sell progressive scan camcorders. Unfortunately most camcorders don't have progressive scan, although I wouldn't recommend anything else. No need for deinterlacing.

The firewire stuff you're talking about is needed to enable DV-in for camcorders having it disabled because of the stupid European laws. You cannot enable progressive scan similarly.

bb

ztv
12th February 2002, 15:13
use interlaced fields, specialy when making svcd, the quality is better!

mkanar
13th February 2002, 05:49
bb: the european 'fix' to get dv-in on the trv-310 is to modify a byte in the nvram. According to some foreign reverse-engineered data, there is another byte in nvram that determines if the camera should capture interlaced or progressive. thanks though. :)

bb
13th February 2002, 06:18
@mkanar:
Do you know if that nvram byte switches the camcorder to real progressive mode, or will it deinterlace only?

bb

avih
15th February 2002, 14:04
There's a fascinating arcticle about subjective preffered viewing method 50HZ-100HZ progressive or interlaced in different resolution, on tv or computer screen.

if u'll take one directory up, you'll find many more very interesting arcticles about interlaced video, deinterlacing methods, video formats and more video issues concerning percieved visual quality. VERY VERY professional. the [co-]author of these arcticles works for philips.

i do not have any affiliation with him and bumped into the pages when searching some info.

check it out:
http://www.ics.ele.tue.nl/~dehaan/pdf/69_ICCE01_formats.pdf

regards
avi