View Full Version : avi & mpg & fielding & stereo viewing & line blanking

10-13-2003, 08:17 AM
After several months trying to get VREX to take an order over the phone for a couple of pairs of shutter glasses, they're finally on the way (touch wood). ( their website only takes US cards as payment)
So now I need to prepare some stuff to try on them.
The basic theory is simple, just have one eye view on the even scan lines and the other on the odd scanlines, the glasses switch eyes on and off at the right frequency, you see 3D.
The glasses are attatched to a 'dongle' that goes between the PC and the monitor, and extracts the scan information from the signal in order to synchronise the glasses.
So I obviously have to be looking at an output on my PC monitor rather than the output from my VT on the video monitor.
The 'stereo mpg' output from lw seems to produce something completely different, so I am rendering L & R image sequences then combining them in LW by loading them as foreground and background images with an alternate blackline & whiteline alpha image.
This produces an image which seems to fulfill the requirements - and when I use photoshop's de-interlace filter on it I can 'recover' either L or R image by selecting odd or even lines.

Now, can any of you experts predict which of avi or mpg codecs are going to preserve that fielding for me?

10-13-2003, 05:59 PM
No expert here ;)

Doesn't MPEG-1 have that type of information... I think I saw this related to Video CDs... From that you would suppose MPEG-2 (used with DVD) would support the same...

10-15-2003, 05:31 AM
Well, I've got my shutter glasses, and they work - within limitations. At first they appear not to work - that's untill you realise that the 'mode' button on the control actually has to be jammed down as if it was broken.


1) Should have been obvious, each image (L or R) occupies only alternate lines & therefor has only half the vertical resolution of a full frame image. So it's not really as clear as one hopes.
Simple fact, one video chanel does not contain enough data for a 'good' stereo video image.

2) How to view it. - I was hoping to be able to store line-blanked video on my VT and view/edit it using the 'Toaster vision' to see what I was doing, but unfortunately whover wrote the code that powers TV has set it up so that even when you set it to show fields - and hence 'see double' the actual fielding is not preserved in the monitor scan, so no 3D.

Exporting to DivX 5.02 does work though, at which point I discovered Limitation 1 !

I am now going to explore rendering at higher resolution - 1280x960 I think, and I hope I am going to be able to halve my render time by rendering pixels that are 'double height' - i.e. set the camera for 1280x480 with a pixel ratio of 0.5 in order to render my L&R sequence, then combine them by compositing in LW (Scene/Effects/Compositing) with L image as background and R image as foreground and a 'line mask' image of 1280x960 as Foreground Alpha (this needs Foreground Fader ticked) - with camera set at 1280x960. In theory this will men that either the even or odd scan lines will be 'higher' than they ought to be, but I don't think that eyes will notice.
Troble is I think DivX will refuse the resolution, But who knows.

I'll try anything twice!