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Sony NEX-7 — RAW Only 8 Bits?

Sony NEX-7

I shot about 800 images today with the Sony NEX-7 using the Leica 50/1.4, Leica 28/2 and Voigtlander 35/1.2 II.

All of the Sony ARW files come out at 25MB, plus or minus a few tenths of a megabyte. This not possible unless (a) the camera records only 8 bits of data per photosite or (b) the camera is employing lossy compression of arbitrary severity to get down to 25MB. My guess is (a), but see the comments from Daan L further below, which indicate that lossy compression is being used, albeit a sophisticated version using min/max deltas (a technique I believe I think is in one of my patents, but it’s been so long I’m not sure— but I did use delta compression to compress images back in DiskDoubler days in the 90’s).

I know something about compression, having 3 compression patents to my name.

When file sizes never exceed a fixed size (25MB in the case of the NEX-7), something has to give. Well, about 4 bits per photosite to be exact, assuming a 12-bit sensor. That’s a lot.

The Sony NEX-7 has a relatively high level of noise, and thus lossy compression might in effect be throwing away “data” which is as much noise as anything else. So in context, it could be true that a loss would be very hard to detect. It would be at ISO 100 where one would have the only chance of finding a degradation, by ISO 200 the noise has grown enough that I deem it highly unlikely that the compression would be an issue, assuming it is well done, as it seems.


I’m not happy with noise at ISO 400. Sure if one doesn’t sharpen it’s not so obvious, but try sharpening and out pops very strong graininess. ISO 100 is very good, ISO 200 is OK. I shoot real images at dusk a lot— ISO 400 is perfectly usable, but a far cry from a full-frame DSLR.

There is a ton of detail in the NEX-7 images under the right conditions. And this detail is degraded as soon as the ISO goes to 200 and is noticeably degraded at ISO 400— the noise obscures detail as it always does. And makes the 8-bit or 12-bit thing a non-issue.

As far as ergonomics, the flush button to zoom in with manual focus lenses is the worst feature of the camera— hard to find and press. Couple that with the modal nature of zoomed-in focusing and it’s far from a perfect approach. But I got used to it, and had a pretty high success rate.

Manual focus

I was even able to use manual focus (zooming in) to track moving targets fairly well, so long as I centered the subject.

Hungry duck
Sony NEX-7 + Leica 50mm f/1.4

Daan L writes:

First of all, thanks for all your interesting reviews – always interesting to read.

However, I would like to correct you on the NEX7 raw format – it is certainly not 8-bits. The Sony compressed raw file (cRaw) are very smartly compressed – technically, the algorithm is not entirely loss-less but for all practical purposes one can consider it loss-less. If you study the algorithm, one can see that it would be extremely hard to ever produce an image (even artificially) where the difference can be observed; all in all, it is by far the best raw compression I know of. I explain this in more detail here: (under the alias Vivec)

I explain the algorithm with some concrete numbers here:

Richard J writes

Thanks for printing what I have been thinking about the sony 24mp files, everyone has been saying how wonderful they are but I just haven't felt that way from what I have seen. As for the raw being an 8 bit file would this not become evident in the dynamic range and color depth numbers of the sensor witch seem to compare very well with a 5d mkII ?

DIGLLOYD: speaking subjectively based on my impressions, I think the Sony files compare favorably to the Canon 5D Mark II at ISO 100, but as the ISO rises, the noise rises more quickly with the Sony. The Nikon D3x is superior to both, but it’s huge and heavy. I’d love to see a Sony NEX with a full frame sensor that is 24MP; I bet it would perform at a much higher level.
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