If you were to render the space ship, in Lightwave, as a
32 bit Targa file, the render would would be a sequentially
numbered series of pictures of your space ship on a black
background (that uses the first 24 bits), the remaining 8bits
of the image are normally not seen, but they do contain the
alpha channel information. If you used a program that allowed
you to view the alpha channel you would see a black frame
with a white silouette of your space ship. Another program
(including Lightwave, After Effects and many others) can use
that white sillouette to cut out the space ship to allow it to be
pasted onto the beach scene.
If the space ship had a simitransparent dome (cockpit) on
top it, that area, of the alpha channel, wouldn't be completely
white, but rather shades of grey. The grey areas would allow
some of the beach scene to show through the transparent
parts of the dome.
Glows, like flames or lens flares, do not show up in the alpha
channels. These must be composited as a 2 part process.
The first stage is to composite the image by using an additive
or lighten effect using the reverse of the alpha channel. Then
you would composite the image normally using the normal
alpha channel. After Effects has a transfer mode called
"luminecent premultiplied" that can do both steps at once.
I believe, L:ightwave can do that as well.
I heartily recommend the book "The Art and Science of Digital Compositing"
by Ron Brinkmann if you want more info on this topic.
Quote:> i tried to figure out what's the alpha means long time ago...but i still
> cannot get the concept why an alpha must use to implement in some images??
> anyone know?
I would like to know if there is anybody working at projects concerning the
grafic visualisation of concepts.