Bit Depth & Alpha Channels

[srproductions]

Hello.

I need to get this stright before I begin rendering out my animations before compositing. I know I need to render image sequences.... Check!

Now, I think I have this right but....
If I render a 32 bit TGA image sequence, that means it has a bit depth of 8 and includes an alpha channel... correct?

Just want to make sure! Thanks!

[JohnnyBlaze]

It means that every channel has a depth of 8bits and that indeed includes an alpha-channel. You wanna make sure that your software includes the alpha tho...some tools allow you to choose 32bit TGA and still leave out the alpha.

[srproductions]

Well, I am on Lightwave 8.5. How would I know if it included an alpha channel? And, I was just using TGA as an example. I usually render out either TGA, TIFF, or PNG.

[VFXTalkDotCom]

a 32bit tga would be a 24bit image plus a 8bit alpha channel (4 channels at 8 bits each, R G B A). if there is no alpha - ie its your final rendered animation and everything is in the scene, then you can still render out at 32bit anyway its not a big deal...

[srproductions]

Well, I need to know nt for the final output, but for rendering my 3D for compositing in Combustion. And also, I read my in Combustion 3 User Guide (just now) that a 32 bit image sequence would mean it has a bit depth of 8.

[JohnnyBlaze]

I just wrote that, because i remembered that in Maya you can select to render out color and whether to include alpha and/or zdepth. I don't know how LW deals with that. Just wanted to make sure :)
You can check if it's there, in your compositing-app or in a sequence viewer (like Framecycler) of course.

[srproductions]

I haven't done much 3D comping-so excuse my stupidity-but I don't how to tell if it has an alpha channel. :tongueinc

[o_ren]

tiff supports 12 bit per channel, it's a much higher color qulity. and an alpha channel. there are other even better quality formats like dpx and cineon but they don't usually come built in. about finding out if you got an alpha channel - open one of your frames in photoshop, and look in the channels tab, search for the 4th channel called 'alpha channel'. have fun.

[jmussetter]

I know in Lightwave, that if you render out a 32bit .PNG file, you will get a 24bit (8bits/chan) color image + embedded 8bit alpha channel.

I would assume that Lightwave would output a 32bit .TGA the same way.

If you need the alpha, but don't want it embedded, you can save as a 24bit image, and also select "save alpha" and save that as an 8bit image, and render. It will output 2 sequences, 1 of color only, and 1 just alpha. This would be usefull if you need to re-use the alpha portion in compositing later.