In general, the bit depth/channel choices for combustion 2 are 8, 10, 12, 16 and 32-bit/floating point per channel - the other responder is incorrect, combustion 2 CAN do floating point processing along with integer bit depths per channel.
What does it mean when the bit depth is set to, for
example, 10 bit?
Do all the subsequent effect actually process the image
in 10 bit?
Yes, they do. All operations are set to the bit depth that is defined at that point in the process tree. If you set footage to 10-bit, or apply a Bit Depth Converter at a particular point in the tree set to 10 bit (or any bit depth for that matter), all subsequent operations and effects work at that exact bit depth, they are not promoted to demoted to 8 or 16-bit unless you specify 8 or 16-bit. This comes in handy for many things, you can actually work in 10-bit or 12-bit native space to get some extra headroom without going up to full 16-bit or float if you don't want to (useful for some video projects, for example). It's more efficient if you don't require the extra headroom and saves memory, too.
What I mean is, are the effects
being written to process 8 or 16 images, or
will new plug in have to handle all these new bit depths?
All the effects and plugins that come with combustion 2 can handle every bit depth that we support, you will not have to worry about that if you use any native plugin. 3rd-party Adobe plugins may not support the other bit depths, however - this will depend on the plugin you use. Since AE 5, some plugins can support a choice of 8-bit or 16-bit, we plan on supporting this in combustion 2.
Are there any effects that specifically process in Log
space?
If not, why would I pick 10 bit instead of 12 or 16 for
cineon files?
There aren't any effects in combustion 2 that specifically work in log space, but there are still advantages to leaving a Cineon file in 10-bit log without converting to linear first, depending on what kind of project you are doing.
As an example, it's very useful when doing rotoscoping and/or cloning work on Cineon files to leave the footage in 10-bit log, just feed the Cineon file directly into a paint operator and start working with it, with a view LUT to adjust the appearance to approximate what it will look like in the final. This way, you don't need to have extra conversions affecting your image data when the type of operation you are doing doesn't need it. There are also many kinds of non-color-correction operations that can be done in log or linear interchangeably, like distortions, or adding elements to footage (text, for example), or channel mapping, or even blurs.
Generally, you will want to convert Cineon files to linear if you plan to mix different kinds of log/linear footage in a composite or if you plan to do extensive color correction. However, the main advantage is that you can pick and choose what works best, whether to leave Cineon footage in 10-bit log, or convert to linear in whatever bit depth.
Does 10/12bit allow for headroom for whiter-than-white
(non-clipped) colors?
You would not be able to do this using 10-bit or 12-bit, these depths have the same clipping restrictions as 8-bit and 16-bit, they're all integer. However, as I mentioned before, combustion 2 does have a float setting and float processing in all places you set the bit depth, so you can have whiter-than-white colors in the process tree and do extreme color correction (and convert back down to any output bit depth later, if you want).
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Greg Niles
combustion Product Specialist
Discreet