non square px ---> square px

[gizmo_1]

Hello!

I've captured some PAL clips via firewire.
Obviusly they are avi 720x576.

I need to convert them to a different format (*.flv Macromedia codec...) (http://www.macromedia.com/devnet/mx/flash/video.html)
but I'm confused abuot the final ratio.

I know that DV has non square pixels so it's 720x576.
But my videos don't look squeezed, I think if I'll resize them to square px (768x576? 720x540?)
I'm going to produce incorrect videos (my final output is PC monitor).

Is it possible that I have 720x576 with square px? How can I be sure of that?

:confused:

Any idea?

Thx

[SomeJoe]

Originally posted by gizmo_1
...
I've captured some PAL clips via firewire.
Obviusly they are avi 720x576.
...
But my videos don't look squeezed, I think if I'll resize them to square px (768x576? 720x540?)
I'm going to produce incorrect videos (my final output is PC monitor).

Is it possible that I have 720x576 with square px? How can I be sure of that?


If it was a firewire capture from a DV tape, it's squeezed. It may not look like it, but it is.

Resize to 720x540 to get a square-pixel image.

[gizmo_1]

Even if I did some editing with
Virtualdub (direct streamcopy) they retain
720x576 rectangular px?

You say 720x540 because 768x576 means a
stretch that is not good to image ?

Thx

[mustardman]

The advice you have been given may not be appropriate. Although 720x576 -> 720x540 gives the correct ratio, a critical step is to de-interlace. This would be appropriate if you only ever want to view the image on a PC monitor.

If you want to keep the interlacing, perhaps for output back to TV someday, then resize to 768x576 and don't de-interlace.

DV has an aspect ratio of 1.06777 (or somthing like that). Unless you filmed a perfect circle (with perfect lenses) I think you, or anyone else, would be really hard pressed to tell the difference.

My advice, don't worry about it :)

[bb]

DV video @ 720x576 is indeed squeezed horizontally. You may not notice it, because the distortion is less than 10%. You'll definitely see it, if you shoot at 16:9, though. If you player resizes to a 4:3 or 16:9 aspect ratio during playback, respectively, there's no distortion, of course.

If you want to keep the interlaced structure, and you don't want to upscale, you may still downsize to 720x540 (or even less, like 640x480, depending on your needs). But you have to do an "interlaced resize", which means you separate the fields, then resize on a field basis (half vertical resolution), then weave again. You can do this in AviSynth.

If you prefer to upsize - regular resizing is sufficient as long as you don't touch the vertical resolution of 576 - I recommend to use bicubic or lanczos resize for better quality.

bb

[Kika]

I think it's better to resize to 786x576 instead of 720x540, which isn't in the correct AR.
DV-Video has the same PAR than Broadcast D1 (PAL) has: 1.092:1 ! (720x1.092=786
If you realy want 720x540 with PAR of 1:1 and AR of 4:3, you have to:
Crop to 704x576
Resize to 720x540

But you can simply do the following:
Resize to 786x576
Crop to 768x576

This gives you the PAR of 1:1 and the AR of 4:3 (and a better quality).

A second reason for not changing the vertical Resolution is to prevent some possible problems with the Interlacing.

[SomeJoe]

Kika,

You're actually quite right. I was tending towards recommending a resize down rather than up, because upward resizes can create odd-looking patterns. However, if a good resizer is used (i.e. bicubic or lanczos) this is minimal. Also, you're quite correct that any vertical resize will introduce odd interlacing artifacts.

I had also forgotten that PAL active picture area is 704x576 @ 13.5 MHz sampling. I'm in NTSC land, so I forget these details for PAL. ;)

[gizmo_1]

After reading a lot on the Aspect Ratio Conversions
question :scared:

and your useful posts I think the best thing I could
do with AVIsynth is:

1) Deinterlace with AlignFields (http://www.alignfields.de.tf/) (mode=2)
2) Resize to 786x576
3) Crop to 768x576
4) Encode in flv (btw anybody knows if this last pass could be done in AVIsynth? I'll gain a lot of time...maybe it need a new tread)


Thx for your time guys :)