Thursday 17 November 2011
Alexa post - Log-C, LUTs, best practices
I've got three calls since morning from editors in prominent post houses - one with offices in LA, Vancouver, New York... yeah, yeah we know... and another with offices in Bandra, Andheri, Chennai, London…
Complaining that Alexa footage looks 'milky and low contrast'.
I had written earlier about struggles in digital movie-making
And on Arri Alexa Avid workflow
Some details on the Alexa camera itself here…
Here are some simple facts…
The Arri Alexa camera can shoot 'linear' (technically called Rec.709) which looks 'normal'. Or as LogC which looks 'milky and low contrast'.
LogC gives you more latitude. Which, depending on the calibre of the cinematographer, means, he can mess up the exposure and you fix it in post, or he can shoot amazingly and you can change the 'look' and better it in post.
On the set you can shoot LogC (milky) and yet monitor Rec709 (normal). So, many people get fooled into believing what's on the monitor is being recorded.
LogC need to be converted before you can see them normally.
Avid has no method of doing this logC-linear ('milky' to 'normal') conversion.
In FCP you can get Nick Shaw's plug-in for $ 30 (Rs 1500) and apply it to all clips.
But it is 8-bit and not for production.
Alternately you can download a LUT for the Log-C to Rec709 conversion from Arri's web site. Google 'Arri LUT generator' and you'll find it. And also Arri's excellent white paper on how it all works.
You can also use Resolve, or the free Resolve Lite to do this conversion. Download it for free from Blackmagic's web site, struggle with it for a few hours, and then get an expert to do it for you.
Best of all, if you're shooting for TV, and you really don't want to mess with this Log-C business, just shoot linear or Rec709.
About the data coming out of the camera (can't call it 'footage' any more)
Alexa shoots HD 1920x1080 on memory cards - called SxS cards.
or it can shoot '3k' to a Codex digital recorder.
or it can record out to as video to an HDCamSR VTR on to HDCamSR tape.
On memory card it shoots Quicktime movies in the Apple ProRes4444 format.
On the Codex it shoots ArriRAW files that have to be converted before you can edit them.
Copying all this data to WD, or Seagate or LaCie disks is a risk. A drive fails, you need to reshoot. Period.
There are two kinds of people - those who have had to reshoot because of a hard disk failure, and those who have yet to reshoot because of a hard disk failure. Carry a piece of wood to knock on from time to time if you are the latter.
Or, hire someone to do data management for you. Whatever you decide, don't let the post house manage your data. And never leave your data on someone else's hard disk. It is vastly easier to browse, copy and use anyone's data in a post house's shared hard disk - than it used to be in the 'film and video tape' days.
For data storage on movies I'm currently working on - Canon7D, Red, or Alexa, TV or cinema or commercials - I'm currently using RAIDs from Sonnet, G-Tech, and Maxx. All are good. And safe. I also advice backing up to LTO tape for long term storage.
On backup for all this media, I've written about this a while ago, but the basics remain the same…
In terms of disk space…
Shooting HD as ProRes4444 uses up about 140 GB per hour of shoot,
ArriRAW does it at 10 GB per minute, or 600 GB per hour.
ArriRAW has more resolution and latitude than ProRes4444, but at a cost.
There's only one Codex recorder that can shoot ArriRAW, in India, so far.
If all this sounds complicated, it really is just a bit. If you'd like peace of mind, do all that I've recommended and you're safe.