Qs for BMD re raw ISO and compression in UMPs

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OwenCrowley

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Qs for BMD re raw ISO and compression in UMPs

PostWed Nov 22, 2017 1:16 am

Two quick questions for Black Magic Design or whoever knows. Please feel free to point to any tech briefings on these.

Q1: During raw shooting on the UMP, what is the effect of ISO settings — Does this merely effect gamut or LUT, or does this cause boosting/attenuation of sensor signal prior to recording it? To put it another way, is ISO entirely resettable in post with no loss of dynamic range due to ISA choices during recording?

Q2: What type of compression is employed for compressed raw? (Lossless, block oriented, wavelet...) The answer might be different regarding different levels of compression.

THanks!
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Denny Smith

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Re: Qs for BMD re raw ISO and compression in UMPs

PostWed Nov 22, 2017 2:05 am

The answer to these questions has been covered in quite a few posts on the BM Cinema cameras, they all work the same where Raw is concerned. ISO is only Meta data, and unlike some cameras, it does not apply analog gain. For a complete discussion on this and the types of compression, do a search here on both subjects and you will find the answers. I am not trying to be difficult, I just do not have the exact details at hand, and a little research on your part will go a long way. You can use Google, to also search this out.
Cheers
Last edited by Denny Smith on Wed Nov 22, 2017 6:05 am, edited 1 time in total.
Denny Smith
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OwenCrowley

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Re: Qs for BMD re raw ISO and compression in UMPs

PostWed Nov 22, 2017 5:01 am

Denny Smith wrote:...ISO is only Meta dats, and in,Ike some cameras, it does not apply analog gain. For a complete discussion on this and the types of compression, do a search here on both subjects and you will find the answers.
Cheers


Ha! Yes, thank you for the suggestion to try a Google search. That found up much more interesting forum discussion than just using the forum search. Looks like people worked really hard to deduce that BMD cameras do not apply gain boost to raw. What they discovered is a good outcome, though so far I can’t find confirmation from BMD itself.
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Denny Smith

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Re: Qs for BMD re raw ISO and compression in UMPs

PostWed Nov 22, 2017 6:07 am

Yes, BM has commented on this here previously. See some of John Brawley’s comments on the Ursa Mini cameras.
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Denny Smith
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Denis Kazlowski

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Re: Qs for BMD re raw ISO and compression in UMPs

PostTue Nov 28, 2017 3:05 am

OwenCrowley wrote:Two quick questions for Black Magic Design or whoever knows. Please feel free to point to any tech briefings on these.

Q1: During raw shooting on the UMP, what is the effect of ISO settings — Does this merely effect gamut or LUT, or does this cause boosting/attenuation of sensor signal prior to recording it? To put it another way, is ISO entirely resettable in post with no loss of dynamic range due to ISA choices during recording?

Q2: What type of compression is employed for compressed raw? (Lossless, block oriented, wavelet...) The answer might be different regarding different levels of compression.

THanks!


Long time listener, first time caller.

Q1: - I don't think BM has ever definitively stated what their internal Camera UI Software tells the Cameras Sensor the fPGA or the Brain to do, in 4K and 4.6K - relative to the ISO software switch changes 200,400,800 and 400,800,1600 with regard to CinemaDNG or ProRes recording - or even shutter angle.

Largely most assumptions about what it does come from ability to white balance CinemaDNG 1:1 in post and the Resolve v12+ user interface when reading the CinemaDNG RAW 1:1 footage in tab where internal camera ISO setting appears to be "metadata", that does not exclude that the camera does or does not do something based on the menu setting however.

Many on this forum and other places have published two mutually exclusive or self contradicting conclusions.

One is - the camera ISO setting is a LUT or a Curve of sorts, which can be dialed off in post -1 stop, and is only recorded as raw file metadata, like EXIF, not impacting the image whatsoever from Sensor to DNG.

While others recommend that you rate the cameras at their 'native' ASAs 400 for 4K CMOSIS and ASA 800 for 4.6K FAIRCHILD/BAE and boost 1 stop or lower 1 stop in post for a less noisier image or to not clip highlights, thereby implying that the ISO menu setting indeed does have impact on the image that is captured in uncompressed CinemaDNG 1:1.

Both conclusions cannot simultaneously be true. Obviously all bets are completely off if any sort of compression or bit depth remapping is applied to the recording such as CinemaDNG 3:1, CinemaDNG 4:1, ProRes of any flavour.

Q2: I don't think BM published any openly available specification nor a easily accessible API toolchain to read their version of Compressed CinemaDNG 3:1/4:1 to many or any third parties thusly keeping the 3:1 and 4:1 compression scheme largely internal to Resolve and this tool - FastCinemaDNG - unsure _how_ that software developer came to the conclusion that 3:1 and 4:1 Cinema DNG files contain some form of Lossless JPG of the LJ92 or Lossless JPEG 1992, DPCM+Huffman. Nor how it's packaged in the CinemaDNG container.

As far as I can google it up BM never mentions the specific sauce used in CDNG which varies by camera and bit-ness, CDNG 3:1 CDNG 4:1, nor can one assume that decoding of BM CinemaDNG 3:1 or CinemaDNG 4:1 from that specific developer is done using the pure LJ92 or Huffman without BM specific tweaks - however - from their page - "CinemaDNG lossless and lossy (BMD RAW 3:1 and 4:1) compression and decompression - done" and their text about "DNG reading, parsing and decoding (lossless JPEG or lossy Blackmagic Design RAW 3:1 and 4:1)"

Best.

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