Hey Rob! Thank you.

You understand that? You ARE a very bright lad indeed. Clear as MUD for me! I'll have another go after my 3rd cup of morning tea.

"Transparent" is NOT the term I'd use. Nice pictorial examples and I can "read" the English.

Once again thanks for the link. I'll get down and dirty with this over the weekend.

G

Does this help?:

Alpha Channel Science

(oops, don't you feel stupid when you post without first updating the threads - I was beaten to it)

It is all about edges, masks and wrapping the results into the final output.

Same thing had me puzzled. If it is a separate channel that drives the pixel mixing - why multiply anything in the file you make? Well, this is about pixel representation - what are the pixels and what is the mask to mean in relationship to it. That lives in your BGRA or YUVA file.

The great thing about alpha channels and effects controlled by other off-the-wall processes ( like convolution matrices for example ) is that you don't need to understand them if you evaluate the differences by experimentation. Did you worry overly when you made the choice between a blur and a gaussian blur?

Who cares where you multiple, premultiply, divide or whatever. It may as well be type-A or type-B etc for how you relate the setting to the result that is brought about.

I'd recommend finding yourself a good set of clips with work on generating a correspondingly harnessed alpha channel from them and then export them in different ways. Then see how they behave when you bring it back together.

You already know how to knock through a single luminance level or colour (chrominance) - how you make the matte or alpha from this is flexible. Also, you know how to vision-mix two video tracks using the opacity control. Alpha keying is about avoiding that opacity control but it's dynamics are instead controlled by what is in the alpha channel and how you influenced it from your source. Vegas is asking you about how to make the alpha channel - or if there is one already - how to rewrite it.

Some edit suites can in fact drive an addition output connection with an alpha channel signal. So you get YCbCr+alpha or RGB+Alpha on a real connection you pass across your studio. This has great benefits in an effects pipeline for live events or TV. However it is almost unheard of outside these circles.

You are cutting through this industry like a knife through butter Grazie. ;)

You understand that?

The first one didn't mean much to me, which is why I searched out and found the video tutorial. That one makes a bit more sense to me. I think the gist of it is that these terms mean the most when you're rendering out the thing that makes use of an alpha channel -- and as far as I can tell, Vegas doesn't gives an option of which to use (premultiplied or straight). I think the idea of the event properties setting is just you telling Vegas what was used when the file was originally created.

Or, in my case, me just guessing until one of them works. ;-)

Rob

Indeed, the Creative Cow tutorial (MP4) is the best reference.
You are right Rob, Vegas' setting is to decipher the source for Vegas' benefit - not to describe what you are about to create or influence other tracks with.

Multiplied is perhaps better described as "functionally-munged" or "colour-assigned-transparency".

RB? "You are cutting through this industry like a knife through butter Grazie. ;)"

You have lauded me with plaudits I certainly do NOT deserve! The only similarity I have to your kind and supportive comments regarding dairy comestibles, is that it's more like hacking through jungle with a BLUNT butter-knife during the equivalent of the Arctic Winter!! - Jungle<>Winter? Hell you get the picture . . Lol!

And yes, RB, I take your very well meant support on board and will ponder on your direction this weekend.

. .and Rob? It's so good to find a fellow "blagger"! We should form some form of "Vegas Blaggers Club" - whatcha fink?

And thank you too.

Functionally Munged? Wasn't that a Pink Floyd tune...?

(Ba-dump-bump.)

Rob

Grazie, I'm searching around for the term "blagger," and I can't tell which way you're using it. So I'm not sure if I'm one or not... ? ;-)

Rob

I will try to answer.

It all works on transperancy information.

Normally you think about storing the color in RGB space and the Alpha in the Alpha channell - RGBA mode.
In this simple case, you are working with the straight mode.

When the system needs to combine to layers - the calculation is
Take the upper layer value, multiplyed by the transparancy and add the lower layer value.
In order to speed the calculation, the upper layer RGB color can be Pre-Multiplied by the alpha value - just to speed processing - this is the premultiplied option, most composition application like Boris Red, AE etc. will create a pre-multiplied file to speed NLE work.

Some 3D application, when creating the pre-multiply data, can leave some pixels not multiplied (value will be too high) in this case you should use the dirty option that tell Vegas that some processing is required.

Udi

Lol on the Pinkies!! Love it!

To Blag: To get something for free by guile. Like a Wedding meal, by making some form of story up about BEING the Bride's long lost 2nd cousin twice removed. It is the "telling" of the story OR making me sound creditable when I ain't that I used the term about myself. Hence "blagging" my way into "understanding" about this weighty issue of Alpha channels.

Other term I could/should have used would be to "wing-it" - like wot musos do when they are "improvising" (wink!) - or NOT knowing the charts or DOTS!

And basically any of the ways in which I've attempted to describe to you "Blag". LOL!

The other derivation, and one I shall do some further research on, is the use of "Blag" to mean a heist, bank robbery. And come to think of it this maybe nearer. T Bolag your way in is to by a means of "forceful" persuasion - "I have 2 Shotguns, you don't have any!", very persuasive I'd say - is more to the point. Seemingly being persuasive by sheer weight of force/argument/selling/propaganda. Hence Blagging.

Udi,

That's the clearest description of Straight, Premultiplied, and Dirty I have ever seen.

It is always a joy to see how simple things can be when somebody really understands!

I always believed that contorted explanations came from unclear thinking...

I'll admit to being unclear until Udi settled it. The fellow from Creative Cow tutorials wasn't far behind.

Sometimes you do have read about these things and then try them to discover what that means to your workflow when layering/compositing/keying/matte'ing/superimposing.

Adobe PSD and Vegas sub-projects are another good mechanism as a layering tool where you can revisit the assets even well down the creative path. The concept of alpha channel seems slightly compromising by comparison.

A lot depends on the piece of work being undertaken I suppose.

Thanks Udi. Well done! And yes I will need to do some further projects to make it sink-in. THANK you!

Yo Grazie -

Well take a little trip with me, for a second.

In 1992 I got my "on-line" AVID - it was good.

Sometimes we'd need to import stuff with alpha.

There were two kinds of alpha - "straight" and "premultiplied".

In the AVID there was a button you'd push. I used to kow which ones were which but I don't remember anymore.

I don't think Vegas has any buttons.

The end.

v

I was under the impression that Grazie was speaking of the asset properties when you place a clip or still on the timeline.

ie
Properties->|MEDIA| - AlphaChannel [V]

Undefined
None (default?)
Straight (unmatted)
Premultiplied
Premultiplied (dirty)

It isn't a button exactly, but it is an import control.
(typically but never say never for other formats coming) - Uncompressed rendering (AVI and probable MOV) has the ability to put transparency info from the aggregation of the assets and the timeline settings into the final render. No preference is mentioned here - but Vegas isn't all things to all people with regard to compositing anyway.........

I wonder how good the render engine is with Vegas..........?