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Z7II uncompressed files smaller than D850 files

ericbowles ericbowles

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ericbowles Moderator Awarded for his in-depth knowledge and high level skills in various areas, especially Landsc... Writer Ribbon awarded for for his article contributions to the community Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Ribbon awarded as a member who has gone beyond technical knowledge to show mastery of the art a Nikonian since 25th Nov 2005
Tue 02-Feb-21 05:03 PM | edited Tue 02-Feb-21 05:04 PM by ericbowles
While the D850 and Z7II have the same sized sensor - 8256 x 5504 pixels - the uncompressed 14 bit images are 13% smaller than D850 images.

The D850 files - 14 bit Uncompressed Raw files - average around 97 MB. In uncompressed files, ISO and camera settings do not make a difference in file size. Composition of a scene does not make a difference. There are small differences in the embedded JPEG files, but not enough to have a big difference in file size.

The Z7II files - 14 bit Uncompressed RAW files - average around 85.7 MB. Again - there is a little variation of about 0.5% but ISO, scene and other factors make little difference.

So the question is, why are Z7II files so much smaller.

It turns out the answer from Iliah Borg and others at RawDigger are as follows:

"The packing in raw files differs, and that explains the difference in the file sizes. D850 file is packed sparsely, each 14-bit raw value takes 16 bits of raw data; Z 7 II packing is compact, 7-byte chunks contain 14-bit values for 4 pixels: 7bytes*8bits=56bits, 4pixels*14bits=56bits"

So with the D850, files were written as 16 bits but 2 bits did not have image data but did take space. The Z7II files don't have the empty space allowing for a more efficient file.



As far as whether to use Uncompressed files vs. Lossless compressed:

"Uncompressed vs lossless compressed does not mean they are equal. With some software, operations are performed faster with an uncompressed file than with a lossless compressed file. Most notable with LR but the difference is small and with some operations the advantage is reversed. There can also be very very tiny differences in IQ that are generally not noticeable except in extreme shooting situations that almost no one may come across. It usually revolves around tone recorded at the very very extremes of highlights. But again, rare is the scenario where it would be even visually noticeable under close examination and the effect can differ by camera model."

"If an uncompressed file is damaged during a write / copy operation, or because of bit rot, the damage is local and easier to edit - compared to files recorded using compression schemes that depend on the knowledge of values of the "previous pixels"."

So the general practice is still to favor 14 bit lossless compressed files, but the size penalty of using uncompressed files is reduced by 34%. that penalty is even less with high ISO images or very detailed scenes. You might consider uncompressed files with high ISO or high dynamic range scenes.

And now you can add one more fact to interesting data you don't need to know. But if you were concerned, there is no problem with a smaller uncompressed RAW file.

Eric Bowles
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