Compressed vs uncompressed NEF

Started 4 months ago | Discussions thread
j_photo Veteran Member • Posts: 3,560
Re: Defining lossless compression

JimKasson wrote:

j_photo wrote:

JimKasson wrote:

fishy wishy wrote:

But isn't it possible he is seeing more noise with uncompressed, because the compression routine is smoothing away some detail? Doesn't mean of course that you couldn't achieve smoothing with post-processing instead, and hey, if you want smooth cooked files with little latitude for post-processing you could go the whole hog to jpeg instead

Lossless compression, in the absence of errors, returns the original bit stream. That is its defining characteristic.

If some detail is being stripped away, the compression is not lossless, by definition.

A question in my mind is how would one go about testing this using the camera? Even it I take two shots of the same scene, with the same lighting, and the same camera settings, there will be differences in the image data at the bit level for all kinds of reasons.

Let's just say you had a suspicion that the in-camera compression was flawed and not truly lossless. How would you go about testing that? Can the camera take one set of raw data and save it as both uncompressed and compressed?

Unfortunately, it cannot.

What I did is make 256 exposures of a 2D gradient target in each mode and then analyzed the statistics of the resultant raw files.

I know, that's not a perfect test of the compression because I didn't have access to the uncompressed version of each compressed file, but it's better than eyeballing it.

Jim

Capture NX 2 (not NX-D) allows Save As NEF with lossless compression. So I suppose I could shoot uncompressed then in NX 2 save as compressed. Those would be two files saved from the same RAW data. Not in camera though.

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