An alternative to a clip with an alpha layer.

Laurence wrote on 3/25/2010, 9:24 AM
In the past I have used .mov compression with PNG compression to store video with an alpha layer. This works okay except for two issues: Quicktime gives slow render and timeline preview. There always seems to be a bit of a black halo around the subject edges.

I just tried something new (to me at least). Instead of saving as an alpha layer I just saved with a generated pure green background from the Sony media generator. I used the Sony chroma-key filter which does a really nice job of not having transparent bits within the subject but has an unfortunate black halo around the edges. Now when I want to use this, I just insert the New Blue chroma key filter and shrink out the halo. One setting works on all the clips and it seems to preview and render quickly. Anyone else using this approach? It seems more practical than using a real alpha layer.

Comments

Rory Cooper wrote on 3/25/2010, 9:57 AM
Laurence the halo is an indication that you are not on the correct alpha selection so try premultiplied dirty

I’ve never understood QT PNG render. PNG would imply that the transparency data is contained separate as in RGBA = straight alpha
Premultiplied the transparency is contained within the RGB but you still have to select premultiplied with QT PNG and not straight

You can’t beat a clean alpha channel and it should be perfect without a bur or halo
Your suggestion will cause problems as this will choke yellows, greens and oranges as well

Laurence wrote on 3/25/2010, 10:16 AM
I've tried all the different alpha options and haven't been able to get rid of the halo with any of them. The same key that looks perfect against a background acquires a halo as soon as it is rendered to an alpha layer clip.
Former user wrote on 3/25/2010, 10:30 AM
I would suggest you use the animation codec with alpha. Works very well and I don't notice any extreme difference in rendering times. Playback might be a bit jerky because it is still a mov file

Dave T2
Laurence wrote on 3/25/2010, 11:15 AM
Well I just tried my method and on the render there was a bit of a crawling edge. I'll try the animation codec, but I can't see were it would have much advantage over the PNG method unless you were doing actual animations (which would benefit because they often have solid lines filled in with solid colors).
farss wrote on 3/25/2010, 2:38 PM
I've been complaining about the halo problem for years. I see it in so many composites done by other Vegas users as well.
The wierd thing is even media with alpha generated by Vegas doesn't comp correctly. Take the same media ex Vegas into After Effects, no halo.



Bob.
Laurence wrote on 3/25/2010, 4:47 PM
Thanks Bob. It's reassuring to know it's not just me. So the problem is with Vegas and not with the Quicktime codecs I've tried. Not good news I suppose, but valuable to know.
Rory Cooper wrote on 3/26/2010, 12:17 AM
Bob

That looks strange.

Can you give us some details of the mov and projects settings 8bit, 32bit,
From what app was the mov generated
The Vegas clip looks as if it has a double image sort of interlace artifact

I am not getting a halo at all, but my mov’s are generated from Boris and some 3d apps, progressive, 8bit and 32bit no problem
Composited in Vegas no problem

Here is a scamp I am working on

All mov’s 4 layers the thin black line on flag is on the original flat PNG with a cloth mov displacement and hardlight comp for tones
This is just a scamp = idea for motivation for sponsors

I am working with some guys over there and should film this time next year

Rory
farss wrote on 3/26/2010, 2:09 AM
That was from uncompressed AVIs rendered out of Vegas and then comp'ed back togther again using Vegas. Put the same AVI files into AE and the difference is obvious.
Using Vegas to comp the drop shadows they have a band in them i.e. instead of the white shadow having a linear ramp there's a bump in the graph. When you see what happens to the whole image it's pretty bad. All 8 bit in both Vegas and AE, 32bit made no difference. I've seen the same thing trying to comp clouds, fog and smoke. Do it in Vegas, you get this band just in from the edge, exact same files into AE, no problem. Same thing happens whether they're uncompressed AVI or QT files.

I have a theory about what might be going on and it has to do with what Vegas sees as black compared to what AE sees as black but I've not been able to exactly nail the problem down. In any case I've got AE and now generally prefer to use it for compositing. I probably should put more time into the problem but...

Like your scamp, some unpleasant artifacts on the letters. I'd wind the saturation down a smidge, looks a little overcooked for my tastes. I assume you're planning to shoot a real aerial. Good luck with the budget. I saw some great aerial footage today except all the hero shots as you went over the ridges were stuffed. Took me a while to figure out why.
The gyros held the camera as smooth as silk. But the VCR inside the copter was hit hard by the updrafts off the ridges and the heads lost contact with the tape. Even the pros can blow $60K and not get the shot.

Bob.
Rory Cooper wrote on 3/26/2010, 3:26 AM
Thanks for the input Bob

The text artifacts are actually texture from the cloth so I will use a smooth cloth for the final as it might not come across as texture
After looking at it again dropping the sat will improve the look = more natural, thanks again for that
If you don’t mind when I am closer to what we are going to do if I could run it buy you again for some crit it would be appreciated

Yes we are going to do proper Arial shots, For the Ariel and water shots it’s a barter deal so that easers the budget pressure

I have never rendered Mov’s from Vegas always out from other apps ..so this thread is very interesting , will do some runs and check.

Rory
farss wrote on 3/26/2010, 4:47 AM
Just so there's no confusion, the Mov files I was referring to came from places like Art Beats, I only rendered uncompressed AVI files with alpha out of Vegas. As far as I know there is no real difference between uncompressed AVI and uncompressed QT files.

Re your video. Sure, love to see it as it progresses.
Here is my take on the location. It is simply one of the most beautiful places on the planet. Let the simple beauty sell it, there's no way to make it better, only worse by futzing around. Best cameras you can afford with the best DP and let the simple beauty shine through. In this case less has to be more.

Bob.