Like the night before Christmas, I find myself too excited to sleep after deciding to go through with my pre-order of the Black Magic Pocket Cinema Camera. I keep scouring the internet looking for any information I can as if they were hints to a present under the tree and keep a tab of my email box open eyeing it like I used to eye the chimney in hopes of catching an early glimpse of Santa Claus.
I've found in these situations it's best to stay productive, so I decided to 'bake the cookies and pour the milk' by figuring out exactly how this new camera will impact my existing workflow.
Process showing how an imaging sensor captures color All the footage I currently work with has already gone through a de-bayer process (or de-mosaic) in camera, this actually creates a file 3x bigger than the RAW image data so the colors are usually 'sub-sampled' down to a lower level of information in order to reduce the file's size which helps storage capacity and bandwidth requirements. Although this processes results in only vaguely lower visual quality it unfortunately throws away pixel data and replaces them with 'interpolation'(pixel clones), causing a 'baked-in' look straight out the camera that makes the image very fragile to edit which causes graphic glitches when pushed too far.
The recipe for required bandwidth and storage capacity is relatively simple for a RAW image compared to 'baking' an interpolated image.
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Take one full cup of resolution, which in the case of the BMPocketCC is 1920x1080, and multiply the horizontal pixels by the vertical pixels. So in this case 1920 x 1080 = 2,073,600 total pixels per frame.
Mix in the recording color depth, the BMPocketCC has a choice of 10 bit or 12 bit, then multiply the total pixels by the color depth. 2,073,600 x 12 = 24,883,200 total bits per frame.
Next add a dash of recording frame-rate, the BMPocketCC has options ranging for 23.976 to 29.97 ATSC standard frames per second, now multiply the total bits by the recording frame-rate. 24,883,200 x 23.976 = 596,599,603.2 bits per second.
Then divide them up into equal portions for 8 bit servings, storage media such as memory cards and hard drives can only take 8 bit 'bites'(aka 1 Byte) at a time, do this by dividing a Byte into the bits per second. 596,599,603.2 / 8 = 74,574,950.4 Bytes per second.
Bake the ingredients together at the specified compression ratio , BMPocketCC plans to use a1.2:1 or 1.5:11.3 compression ratio, divide the total Bytes per second by the compression ratio. 74,574,950.4 / 1.3 = 57,365,346.5 Bytes per second (rounded up to 57 MegaBytes per second).
There you have it, and to figure out how many cards your footage will feed divide the MegaBytes per second into a card's storage capacity, for example a 64GB SD card would be 59.604** / 0.057 = 1039 seconds (rounded down to 17 minutes and 18 seconds) of RAW footage per 64GB card. Yikes! this is going to require a lot of expensive cards! Many people complained about the 12 minute recording limit on DSLRs which have thankfully been fixed in the newest models but with the BMPocketCC recording RAW video we'll be right back there. Hopefully the Secure Digital Card industry will catchup to this technology quickly and start to offer larger capacity high-speed cards and lower prices.
**1,000,000,000 bytes is actually 1,073,741,824 bytes (1024 Bytes in a KB, 1024 KB in a MB, 1024 MB in a GB) so 64,000,000,000 / 1,073,741,824 = 59.604 GBs
Thankfully Black Magic Design had the foresight to include not only a RAW recording option but also a 'lossy compression codec' with medium levels of interpolation that tries to preserve as much information as possible and manages to reduce file sizes down to 220Mbps for situations when a manageable size is more important than higher image quality. Using Apple's 'ProRes HQ' codec the BMPocketCC will preform a '4:2:2 color subsampling', which throws away every other horizontal pixel then clones what's left over to the neighboring column, and opens 10 bits of bandwidth for color capturing, making color reproduction 4x less accurate than 12 bit RAW. This iteration of 'ProRes HQ' preforms a perfectly centered balancing act between 12 bit RAW and the AVC codec found in all current DSLRs and many Professional Camcorders, giving half the image quality of RAW but twice the quality of AVC codec footage found in DSLRs.
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| Examples of color accuracy |
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| Examples of subsampling |
This list has been updated in a new post: http://diffractedmedia.blogspot.com/2013/10/blackmagic-pocket-cinema-camera-sd-cards.html
If anyone knows anymore suitable cards please post them, I'll be updating this list over time.
