Thanks John, didn't know that. But it doesn't affect my question about an alpha object does it? Am I right about alpha adding transparency to objects in tracks above it (i.e. higher track numbers)? That still seems the only way I can square what happens in practice with the model of looking down through tracks from higher to lower numbers.

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Terry, East Grinstead, UK

Hi Terry

It does, however I think of it as

'what does it let show through from a lower track number',

So in your example, depending on where the black is, whatever is on a lower track number will show through.

If the Alpha mask is on track 1 then wherever it is black will black ie the virtual track 0 is always black so you see black.

Hope this help with the mental gymnastics of inverse logic depending on which track the alpha mask is on.

John

Hi John,

I'm going to have to read that again in the morning a few times, after a large coffee! But right now I still don't grasp how I can see anything if the highest track number (the 'top' layer) contains a simple image or video. It's opaque. So how can anything else underneath be seen? Unless, as I conjectured, giving one of those lower track objects the 'magical' alpha atttibute somehow copies its transparent sections to the higher tracks?

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Terry, East Grinstead, UK

Hi Terry

Invert your thinking ie think of it as  Top layer - Down and not Bottom layer - Up

John

Thanks John, but the penny still hasn't dropped for me. How does that help me to visualise what's happening in the example I specified? And are you saying that you think of it 'bottom up' only when alpha is involved?

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Terry, East Grinstead, UK

I'll jump in with an image which I hope shows clearly the Magix track viewing convention -- Looking UP through tracks from higher to lower numbers as if they were planes of a model stage set.

Of course you would only see the front wall track in the project shown above until we introduce some alpha masks. I think of masks as mirrors with some areas of silver removed -- you see what's in front (higher number track) where it is silver and what's in back (lower number track) where it is plain glass. The silver/glass relate to white/black of the mask (OR black/white if you click on the up down arrow of an alpha track to reverse the effect.)

So now lets add a rectangular mask between the 'back wall' and the 'figures' ('mid wall' has been removed to keep it simple preserve a bit of my sanity.)

With track 4 and 5 muted you get to see the back wall only where the alpha mask is black. Sorry about the bits of black at the top and bottom -- that's seeing John's virtual black track 0 as I didn't proportion my back wall image properly.

With all five tracks visible we now see the front wall (pixilated for emphasis) only where the big circle mask is white. Where it is black we see everything that's behind (higher on screen - lower number tracks) -- which in this case happens to be a composite of two images and an interleaved alpha mask.

Simple!  

Regards,

Carl

ADDED: Not to forget that alpha masks can be grey scale as well to give partial transparency. A colored mask is interpreted on brightness levels. And if you want to explore further apply the alpha mask effect to a video clip! 

Hi Carl,

Many thanks! Much appreciate your help. I'm going to set aside enough time today to study that carefully. Or maybe tonight with a glass of Shiraz...

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Terry, East Grinstead, UK