![]() FWIW, DNG 3:1 will consistently have an SSIM score in excess of 0.99, which is excellent structural fidelity (not that SSIM should be trusted blindly, either). You can google an excellent article by Wang and Bovik on the applicability of MSE based measures (like PSNR). Now, whether PSNR is a good measure in this case is another story. Of course, it is possible that ProRes is better than DNx. Actually, the numbers I usually get with 4:2:2 versions are similar, except the difference is in the opposite direction. Obviously, I've done hundreds of tests similar to yours (mostly using DNxHR, cause I am on Windows), and you'd need to step up to a 4:4:4 DNx codec version to get to PSNR similar to 3:1 DNG. But fundamentally, these all work similarly. Now, there are many tricks you can do, and choices to make even within a single codec, which would account, for example, for the differences between DNG 3:1 in-camera and slimRAW DNG 3:1. Regarding lossy, there aren't any fundamental differences between DNG or ProRes or DNx, or anything else based on DCT. Actually, putting aside the forementioned impediments, BM lossless in-camera is quite efficient - slimRAW will typically gain 10 to 20% doing lossless recompression with losslessly compressed raw from other cameras, but will typically only gain up to ~5% on a BM lossless source. Raw from most cameras will compress to around 2:1 using lossless (including most linear raw cameras, as well as Arri log raw), but not BM cameras (around 1.6:1 is typical for these a bit less in-camera). BM cameras do suffer a bit from the lack of OLPFs, but also the tonal curve is not friendly to (lossless) compression down the pipe. Regarding lossless DNG, the compression achieved depends not only on image complexity, but also on the choice of a tonal compression curve. In another thread ( ) which I found a BM staffer says "The Pocket, BM4K, and URSA all use lossless compressed raw at roughly 1.5:1" - but rates for this 1.5:1 are not mentioned in the Ursa specs. In the Ursa specs there's no mention of uncompressed and its data rates. In the 4k they say that each frame is about 8mb for uncompressed. They're not given for Ursa like they're given for let's say the 4k Production. Makes sense but then what are the storage rates for (math) lossless? So to reiterate what you're saying: There are 3 compression modes: 4:1 I assume would lose more of the original information than 3:1 but still be visually lossless to the eye when comparing it the original.įor mathematically lossless, meaning you get back the exact original DNGs so that nothing is lost, you'd need compression ratios of the order of 1.5:1, hence lower than visually lossless compression rations. That's why the compression ratios can be high and also different. So if you could decompress back, it wouldn't be the original uncompressed DNGs. Johnny Harris wrote:Sorry if I'm a bit thick but all the info I could find on this issue is not very clear at all. It's probably something I'm missing but if anyone here can explain this it would be much appreciated. why work with 180 mb/s when you can work with 130 mb/s and get same result. If it is so, then what's the storage rates for uncompressed raw? You can clearly see the rates for 3:1 and 4:1, but no uncompressed.Ģ) If the compression is lossless, then why have a 3:1 AND a 4:1 ratio? Wouldn't it make sense to keep it at the 4:1 to get better data rates. Not trying to be picky, but grammatically that statement with the comma as in "Lossless CinemaDNG RAW, RAW 3:1 and RAW 4:1" denotes 3 separate things. OR does that mean that it's Raw in either 3:1 and 4:1. But I don't understand the above even taking that into account:ġ) The recording formats cites "Lossless CinemaDNG RAW, RAW 3:1 and RAW 4:1" - Does that mean that it's Raw uncompressed, and then the compressed versions 3:1 and 4:1? I understand that Raw compression can be akin to zipping a file, so it is lossless. Lossless CinemaDNG RAW, RAW 3:1 and RAW 4:1 How exactly is the compression of Raw working taking into account the following (from the BM Ursa specs): Sorry if I'm a bit thick but all the info I could find on this issue is not very clear at all.
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