DV resizing/interlacing

[avin]

I've been try to resize my 720x576 DV source to something smaller. If I resize to 384x288 it seems to look fine. If I resize to something bigger such as 512x416, I start seeing interlacing effects I think. If I deinterlace and resize to the 512x416 resolution, you can see light horizontal lines across the video, but you can only detect it when the background is dark. Is that normal? I'm using the smart deinterlacer plugin for VitualDub and compressing to Divx.

I've read about DV having a rectangular pixel as opposed to square .. so does this mean my 720x576 is slightly stretched vertically? Is there a calculation I can perform to give me the width given the height or vice versa? Because the resolutions I used in the first paragraph were based simply on informed guesswork :).

[theReal]

You can use GordianKnot as a calculator for the correct 4:3 resolution. 512x416 is not right because 720x576 is indeed stretched. 4:3 would be 768x576 (and this is how it is shown on a tv screen).

Smart deinterlacer might leave some parts slightly interlaced, depending on the threshold. For a complete deinterlace of all fields in every frame just use deinterlace->blend.

[Hiei]

Because we must resize in blocks of 16 x 16 pixels, this makes following the closest sizes easier. Remember that the closer to 1.33:1 it is the more exact the aspect ratio to a 4:3 TV screen:

PAL/NTSC
(Size) 720 x 576 / 720 x 480
(Ratio)
720 x 544 1.32:1
640 x 480 1.33:1
592 x 448 1.32:1
544 x 416 1.30:1
512 x 384 1.33:1
448 x 336 1.33:1
400 x 304 1.32:1
384 x 288 1.33:1
336 x 256 1:31:1
320 x 240 1.33:1


For DivX, we recommend something like 640 x 480 or even 512 x 384. For PAL and for NTSC you can go as low as 336 x 256 since you're used to 20% less TV resolution than the rest of the world! Also, full DVD resolutions will very often cause jerky playback. This will happen each time the DivX video hits a keyframe. For my 500 MHz CPU, the DivX codec gives optimum smooth playback with under 1000 blocks of 16 x 16 pixels before problems. Therefore a full 720 x 576 resolution DivX with 1620 blocks is no good. If you intend to make a DivX video that will play on anyone's machine, then we suggest you consider the following:

[igor140]

The horizontal lines you are getting are remaining interlacing artifacts. You can do the following:

Don't use Avisynth / Directshow for decoding your DV video. Using the Mainconcept VfW Codec is a little slower, but gives much better results, and - for some reason - makes deinterlacing much easier.

Use smart deinterlacer as the first filter before anything else. If the default settings don't do the job try the following:
- compare color channels instead of luma
- lower the motion threshold - you can go well below the recommended settings
-depending on your source it might be necessary to "phase shift" AND "field swap after phase shift"

As theReal said above, Gordian Knot is the dream-tool of all resizers.

[Wilbert]

@theReal

720 x 576 is displayed on your TV as 786.6 x 576 (720*59/54=786.7)
with a real aspect ratio of 1.3657 : 1

@Hiei

Thus if you are resizing in blocks of 16 x 16 pixels, you have:

PAL
(Size) 720 x 576
(Ratio)
720 x 528 1.3636:1
640 x 464 1.3793:1
592 x 432 1.3704:1
544 x 400 1.3600:1
512 x 368 1.3913:1
448 x 320/336 1.4000/1.3333 : 1
400 x 288 1.3889:1
384 x 288 1.3333:1
336 x 240 1:4000:1
320 x 240 1.3333:1

Concluding that the first four resolutions are accurate ?

[theReal]

720 x 576 is displayed on your TV as 786.6 x 576 (720*59/54=786.7)You are right. I wasn't thinking about pixels not being square on the TV.
The fullsize picture of a TV tuner card is 768x576 pixels, that's what I was thinking about.