Think I have found a bug when rendering stills in DV

Nat wrote on 4/28/2003, 10:50 AM

I made a huge animation project involving PNG stills that I animate using effects, track motion, etc. I have a lot of PNG's that include some transparency, for example, a still with some grass and the upper part transparent to let the sky pass through.
Now the probem seems to occur when I render with that grass sequence. If I leave it there and render in DV AVI, my image will be pixelated, like if the still was masking the composition with some nasty stuff. However, you may think the problem is with my PNG. But if I render in any other format, the problem is gone (uncompressed, quicktime, MPg2 etc.) Now If I render and mute that png Still with the grass, the "nast mask" is gone....
Pretty strange.

Comments

Grazie wrote on 4/28/2003, 10:56 AM

This, I'm interested in!

Grazie

Nat wrote on 4/28/2003, 11:28 AM

Would you like me to send you my project (it's small) so you can see for yourself ?

SonyDennis wrote on 4/28/2003, 2:23 PM

I'll email you.
///d@

Nat wrote on 4/28/2003, 6:15 PM

Did you send the mail ? My account is registered to an hotmail account that I rarely monitor.
Thanks,
Nat

Nat wrote on 4/28/2003, 7:00 PM

I posted an archive of my projects with instructions on my server, it's 9 megs.
Click here

You can also check those pictures, one in compressed in DV, the other is not compressed :
Good
Bad

Grazie wrote on 4/29/2003, 12:29 AM

Nat - Thanks for that. Downloaded the files and will get busy looking at etc etc. I'm a PAL user so I'll have to get my head round it soon. It is a shame we don't have Marty Helder back on board as he is a marvel at this stuff. My best bet is that there is something within the various NTSC and PNG ratios that could be skewing the combinations of formats - dunno. If I can, I'll get your veg going and see if I can repeat your issue - yeah? My immeadite thoughts are that it may not be a bug - but hey, I've been wrong before.

Supplemental question - Have had any success in doing this type of process with other versions of Vegas?

Hmmm.... interesting.

BTW - Nice veg!

Grazie

Grazie wrote on 4/29/2003, 12:41 AM

Nat - Haven't rendered yet - Now you say ion your notes to SonicDennis, "Render it using the DV NTSC template at the best setting . . . . " but, now try this :

1 - Render an AVI of offending loop

2 - Place this back on a spare piece of T/L

3 - Now, try rendering this AVI as the NTSC

In essence, try rendering to NTSC what you know to be good. I've read that when "problems" occur in rendering directly to a non-native AVI can create issues. So rendering "from" an AVI - Vegas' natural editing format - MAY give you a way through. Give it a go - it may work. I'll keep looking out for you.

Grazie

Nat wrote on 4/29/2003, 6:49 AM

Thanks Grazie,
I tried to render in a lot of formats and the problem only occurs in AVI DV NTSC. I might try to render it pal to see if it's an NTSC specific problem.

Nat

Nat wrote on 4/29/2003, 7:02 AM

Just tried in PAL, same problem... Even the divx render looks perfect compared to the DV render...

Edit : I only tried with Vegas 4.0.
I have Vegas 3.0 but I guess the file won't open with it ?

Grazie wrote on 4/29/2003, 10:26 AM

This is very annoying - hmmmm...... grazie

SonyDennis wrote on 4/29/2003, 12:56 PM

I posted this in the DMN forum, but I'll post addition responses here, since I can bookmark the thread.
___________________________

Thanks for making the project available, I can now see the problem.

At first I suspected typical DV 4:1:1 chroma downsampling artifacts, but when you mute the grass, it goes away, so now I suspect it's a DV codec bit starvation problem. DV adjusts the DCT quantizing based on how much of the fixed storage space per frame is used. The grass uses so many bits that the sun gets overly quantized, and gets blocky. There may be some tweaks we can make to the codec for a future version to help this, but in the meantime, please apply 0.001 or 0.002 Gaussian Blur to the grass, and the problem is reduced significantly.

///d@

Nat wrote on 4/29/2003, 4:32 PM

Thanks alot, I will try this. I'm just glad to hear it's a sort of limitation of the codec, not my eyes going crazy at 3 am :)

Thanks Dennis.

Nat wrote on 4/29/2003, 6:06 PM

What Dennis is saying is making a lot of sense, I solved my problem by lowering the grass layer so it would take only about 1/8 of the screen space instead of 1/2, so his explanation about the huge amount of information in the picture is right. It's great to have some great skilled programers on the forum to clear things up,

Thanks Dennis.