Transcoding raw to Prores 4444 vs 422(HQ)

[TKez]

Decided to start another thread as the forum suggested it, but it's really an extension of this thread.

http://www.magiclantern.fm/forum/index.php?topic=8389.0

Appologies If someone's gone here already but I couldn't find it.

Anyhow I couldn't come to a conclusion about what Prores format suits best, and it seems opinions vary.
Do we use 422 and not care about chroma resolution loss as the difference with be negligible?
Or keep all the data and use 4444, possibly wasting space as we don't need alpha?

Well I did a test by bringing in a DNG sequence into AE and using 'Set Matte' to create some alpha.

RGBA -> Prores 4444 = 140.2MB
RGB -> Prores 4444 = 78.4MB     
RGB -> Prores 422(HQ) = 66.1MB 
RGB -> Prores 422 = 49.4MB

RGB-4444 %55 the size of the RGBA, but RGB-4444 is only %18 larger than it's RGB-422HQ counterpart.

So my conclusion is. the lossless compression of the alpha channel is not wasting space.
May as well be safe and use 4444 as the size difference is only marginal over HQ.