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Lossless compression and the Leica M8

There's a heated debate over on a Leica forum between several posters who are proving just how dangerous a little knowledge can be. Here's the problem: The Leica DMR produced 20 MB raw files from its 10 MP Kodak imager, which is essentially the same silicon that will be used in the M8. But the M8 specs appear to say that its RAW files will be a constant size, 10MB. People poking at the handful of bootleg M8 .DNG files that are around are saying that each pixel is in fact coded as an 8-bit number, although there are plausible reasons to suspect bugs, misinterpretations, etc... And it would seem like a dangerous thing to do, even if the bits are perceptually encoded to represent, say, the logarithm of the linear signal off the CCD, because of the fragile nature of 8-bit images when you start to postprocess them.

I have trouble imagining a loss-less encoding done for the M8 which would not
(a) produce files of varying size
(b) possibly end up with less than one Byte of data per pixel, and certainly not line up by the byte.

But can some of the Canon/Nikon owners let us know how big their RAW files are (expressed as the ratio of Bytes per Pixel). And are they constant size? (I know the answer is NO, and .85 bytes per pixel for .CR2 files from a friend's 20D.)

scott
 

Jan Luursema

New member
From my first 5D shots, the largest is 15,4 MB, the smallest 10,9.

One shoot with the 1D Mk II: 6,7 to 10,8 MB.

The 20D: 6,5 to 9 MB.

Nothing scientific, just some fast numbers.
 

Dierk Haasis

pro member
IIRC, Nikon is the only manufacturer offering the choice between non-compressed and compression. They do not claim lossless but 'visually lossless under most circumstances', which I can attest is correct - I've yet to see an example of visual loss.

Nikon's compress NEFs are not all the same size, they differ by up to several MB, the mean somewhere around 10.5 MB. They are 12-bt with a 16-bit encoding to make it easier for the software programmers. If Leica uses the same compression [i.e. none] for both their digital flagships, one with an 8-bit encoding, the other with 16 bit, the files for the first would be exactly half the size of the latter - every time. And with 'none' as the value for compression, the file size may be the same between files of one camera.

So, technically possible. Would be good if those fighting it out would come up with some real world examples, numbers and tests to give us something to work out the black box mechanisms.
 
M8 bodies with production level firmware are going out to reviewers this weekend, so I expect we will see real sample raw files next week some time.

scott
 
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