Compressed VS Uncompressed RAW

[offbeatbryce]

Is it best to shoot Uncompressed Raw or Compressed Raw? I want to eventually get a Black Magic camera and was curious to find out if I would still get good results as far as post production correction if I shot with Compressed Raw? Compressed is a smaller file size as well. Just wondering if I were to save my money for a Black Magic Camera if I really need to spend extra money for a good storage device to record files onto or if compressed would be fine on SD cards.

 

[DLD]

As explained on these forums by people who write their own compression algorithms, a 2:1 compression is pretty much on par with the original uncompressed Raw. Anything beyond that and you begin to lose image quality little by little but it also depends what you do with the compressed footage..

 

[offbeatbryce]

As explained on these forums by people who write their own compression algorithms, a 2:1 compression is pretty much on par with the original uncompressed Raw. Anything beyond that and you begin to lose image quality little by little but it also depends what you do with the compressed footage..

I read something about how compressed Raw can also be unzipped to get the non compresssd version. Is that true of all dng cinema footage?

 

[Samuel H]

The compression in the DNG spec uses Huffman coding, which means it's lossless: it takes less space but contains exactly the same information (similar to a zip file). That's what BM originally implemented (link), I'm not sure if they've changed it afterwards but my guess is that it's still the same (edit: see correction by cpc below: now some cameras offer lossy compressed RAW as well).

 

[DLD]

I read something about how compressed Raw can also be unzipped to get the non compresssd version. Is that true of all dng cinema footage?

It's the same idea but they begin to toss out info ~ at 2:1. But you'll have to do your own grading and so on to see where your camera footage begins to break down. If you expose and WB right, you should be getting no noticeable defects at 6:1.

 

[cpc]

Currently there are no Blackmagic cameras recording uncompressed raw. All their cameras record either losslessly compressed raw (Pocket, Cinema, Production 4k cameras), or both lossless and lossy raw (Ursa, Ursa Mini, Micro cameras). As pointed out by Samuel, losslessly compressed raw loses no information and after decompression the image is exactly the same as the original. It is not that it "can also be unzipped"; there is no choice: the raw processing software must decompress the file to use it, so you always end up with the original image.

Lossy raw (3:1 and 4:1 in Blackmagic cameras), on the other hand, discards some information in order to reduce size further. You still get a raw workflow though. In any case, you don't need external recorders with BM cameras, they all record raw internally.