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Reader Question: Convert to DNG for Sony’s Space-Wasting 14-bit Uncompressed RAW Files?

See also Understanding Compression of the Sony A7R II Uncompressed ARW Raw Format.

Rich G writes:

Are you comfortable supporting a workflow, if one uses Sony’s new option for 14-bit uncompressed RAW files under firmware release 2.0, that would have one convert the uncompressed RAW file to DNG using Adobe Bridge or Adobe’s DNG converter in order to reduce the file size before post-processing work?

DIGLLOYD: according to Alex Tutubalin of RawDigger, some metadata may be lost. This makes me uncomfortable, though I don't know the details. Plenty of people have long converted NEF / CR2 / ARW to DNG. I never liked that idea for two reasons. First, it takes extra time to do the conversion, second it bloats the files by about 30%, and third, my originals are derivatives, not originals as shot—yuck.

Another concern: I despise the way Photoshop changes the DNG every time it is edited, which changes file modification date and/or size, and requires a backup. This carries a risk of data loss if anything goes wrong (and it has, for example with Nikon Capture a few years ago). Originals should be untouchable, never modified. Sidecar files are a vastly superior approach. With sidecar XMP files (NEF, CR2, ARW, ORF, etc), making changes means backing up a tiny XMP text file instead of a 20-85 MB raw file (dozens or hundreds the way I often work).

Bottom line: I like my originals to be originals, forever and unchanged.

OTOH, the huge bloat of Sony’s wasteful uncompressed raw format* is a practical working headache. So for most users, the conversion probably makes sense simply to get the waste down (but check what DNG conversion actually does, I have not looked into the savings). Another option which may apply for some users: archive project folders of ARW once done, using zip or gzip or similar.

* Sony doesn’t even bit-pack the images, instead using 16 bits to store 14 bits, which is stupidly wasteful. Bit-packing the files would have meant a file size reduction of 85MB to ~76MB or ~9MB per file. But of course the Huffman encoding used by Nikon and Canon is far more effective than that. Sony did not implement it either.

Matt G writes:

It's actually worse than just metadata loss when using Adobe's DNG converter, the conversion process replaces the masked pixels at the edges of the sensor with junk data, and even changes the pixels values themselves:

https://www.dpreview.com/forums/post/56651743
https://www.dpreview.com/forums/post/56611378

There is a solution to the problem of storing uncompressed Sony RAW files: keep the originals, on a compressed drive. Windows users have the option of NTFS drive compression, which is invisible to the user, you can turn it on and carry on working as normal. I'm sure something similar is available for the Apple platform.

Opening files takes longer as the OS has to decompress them, but this is no different to opening a Canon or Nikon RAW which must also be compressed.

The compression algorithm used by Windows (LZNT1) is not image specific, but the methods used by Canon/Nikon (lossless JPEG) etc aren't particularly sophisticated either (predict based on neighboring pixels and Huffman code the error), I haven't benchmarked it but I imagine both methods would be close in efficiency. LZMA (used by 7zip) easily beats lossless JPEG.

DIGLLOYD: I don’t see using a Windows compressed drive as a solution for most (certainly not Mac users, BTW, I wrote DiskDoubler and AutoDoubler years ago and MS was a copycat). Anyway that would mean that other files suffer (incompressible ones). And it does not address the shooting experience and perhaps not backup either (nor do I think a compressed volume is a good idea for backup, given bit rot potential).

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