In an earlier post, I mentioned that Post Logic Studios did the post and color grading (with a 4K FilmLight Baselight) on Reach for Me, a feature film acquired with the Dalsa Origin camera. In my earlier post, I wondered how long it took Post Logic Studios to de-Bayer the footage.
Here's the answer. First of all, I spoke with Post Logic Studios' executive vp of imaging science Dr. Mitch J. Bogdanowicz, who also spent 32 years at Kodak, mainly in that company's Color Science Engineering Laboratory.
For those of you who wonder what de-Bayering actually is, I'm going to let Dr. Bogdanowicz give a great and succinct description. For those of you who already know, skip down to the bottom where I answer the question posed in the first paragraph (as well as explain the title of this post).
There are a number of cameras out on the market that have a Bayer filter array: Dalsa cameras, the Arri D-21, the Phantom and the Red camera. To cut to the chase, Bayer filter creates an image with twice as many green pixels as red or blue pixels. This is a problem unless you like really green images.
That's why anyone who shoots with one of the above cameras will find themselves faced with the need to de-Bayer the footage. Also cutting to the chase, the de-Bayering process works to fill in the missing red and blue pixels by looking at neighboring pixels to determine what the value would be. "For example, when you have a red pixel, it has red information, but no green or blue," said Bogdanowicz. "It looks for neighboring green pixels and guesses what the green value will be, and does the same for the blue."
"There is an art in the de-Bayering process," he continued. "Not all de-Bayering is created equal." Yes, there are simple algorithms that de-Bayer quickly, but that can create fringing or other artifacts. Good de-Bayering, said Bogdanowicz, takes longer to do a better job.
In particular, he praises Dalsa's de-Bayering algorithm as "sophisticated…that gets the most out of the material." As an operation, de-Bayering is straightforward. The raw images go through a single program. At Post Logic Studios, they de-Bayer to raw linear data and then put their own image processing on top of that to end up with a 10-bit Cineon log file ready to go into the Baselight color correction system.
Reach for Me was an approximately 25 day shoot, producing an average of about 1.5 TB per day. On set, the production used the Codex Digital recording box to produce Quicktimes for editorial. After editors finished the cut, they provided Post Logic Studios an EDL, which only de-Bayered the selects. "On a single CPU that's fairly fast, it'll take 15 seconds to de-Bayer per frame and that adds up," said Bogdanowicz. "We use a render farm with multiple CPUs, and we got our de-Bayering processing time to less than a second. We could probably do two frames per second, but it's still not 24 frames per second."
The amount of time it took to de-Bayer the approximately 90 minutes of footage: 36 hours
How to de-Bayer in one easy step: Call the experts.
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