8-bit versus 14-bit DNGs

[sandymc]

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The "8-bit question" seems to come up on a fairly regular basis, and to some extent is fueled by lack of data. Unless Leica lets us get hold of an M8 with modified firmware, we can only speculate as to what the image differences might be.......or maybe not.

 

What we can do is to use a DMR image, which is 16-bit uncompressed, and then process it to look like either a linear uncompressed 14-bit M8 image (the image we would get if Leica modified the firmware), or to look like a compressed 8-bit image, using the M8's compression scheme (the image we do get). Using a modified version of DMR2M8, I've done just that.

 

I've used an image that Pascal Méheut posted on this forum about a year ago - I trust he doesn't mind. Three JPEGs (converted in Aperture, using default settings) below are the 14bit linear file, the 8-bit file, and the differences between them. Note that the difference file is a bit of a cheat - because of gamma effects, looking at file differences translated down to black level isn't really valid. Needless to say, in the JPEGs, you can't see a difference, and even looking at the difference file, you need to look quite closely, or turn up the brightness on your monitor, to see anything.....

 

For those that want to look at the DNGs, I've posted them here:

Any raw devloper (other than C1 V3) will read them.....

 

The 14-bit file (15 MB): YouSendIt - Send large files - transfer delivery - FTP Replacement

 

The 8-bit file (6 MB): YouSendIt - Send large files - transfer delivery - FTP Replacement

 

The difference file (9 MB): YouSendIt - Send large files - transfer delivery - FTP Replacement

 

These files will expire after 7 days.

 

If anybody really wants, and has DMR files, I can also post the hacked version of DMR2M8 used to do this.....

 

Sandy

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[rwfreund]

I wouldn't expect to see any significant difference with that image, as it is all well within a fairly narrow range of luminance.

Where I would explore would be an image with perhaps a sunlit background and a shaded foreground. Make sure that there is some detail "nearly" blown out as well as detail in the shadows.

that would be the test shot to use.

-bob

[sandymc]

I wouldn't expect to see any significant difference with that image, as it is all well within a fairly narrow range of luminance.

Where I would explore would be an image with perhaps a sunlit background and a shaded foreground. Make sure that there is some detail "nearly" blown out as well as detail in the shadows.

that would be the test shot to use.

-bob

 

Agree - unfortunately, I don't have a DMR........

 

Sandy

[Jamie Roberts]

I own both, and if I ever get around to it I'll post some examples.

 

But believe me, after shooting thousands of frames (of the same stuff with similar lenses), there is no printable difference between them except that the M8's sensor, being newer has less noise than the DMR's.

 

Consequently, the M8--not the DMR--has more stuff in the shadows.

 

The expected highlight differences are mostly nowhere to be seen: certainly not in any printable upper midtone detail which is where it counts.

 

They both "blow out" in a very good fasion; if there's any difference at all there might be some at the very extremities of exposure in terms of smoothness, but that would be more affected by the profile used than by sensor response.

[sean_reid]

Leica once offered to let me try an M8 set up to write files that were not compressed to 8-bit. I'll see if that's still possible.

 

Cheers,

 

Sean

[fordfanjpn]

Leica once offered to let me try an M8 set up to write files that were not compressed to 8-bit. I'll see if that's still possible.

 

Which would certainly imply that it's doable. Hopefully with nothing more than a firmware tweak. If you are still able to get your hands on that camera and do a comparison, it would be very interesting to see the results.

 

Bill

[stunsworth]

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Which would certainly imply that it's doable/quote]

 

I'm guessing that among the problems from Leica's perspective would be

 

1. File size - not a problem, cards are cheap, very cheap

2. Write times - maybe more of a problem if the buffer couldn't hold as many shots and the camera stopped while the buffer was cleared

[marknorton]

I think this issue will run and run until someone can do a detailed comparison between the two modes and come to some conclusions, so if Sean was able to persuade Leica to make such a firmware version available to him, and maybe Guy and Jamie as well, I think it would be useful.

 

As for the possible downsides:

 

- Storage costs have decreased markedly since the basic parameters were set for the M8 so I agree with Steve that this would not be a concern.

 

- The contnuous shooting capacity would be reduced because of the increased size of the files and the longer intervals between buffer space being released.

 

- The total battery usage per shot would increase which would reduce the battery capacity but we might see higher capacity batteries in the future.

 

- Writing to the card already interferes with the chimping/menu process, so I'd like to see the card writing done in background so that other than when the raw buffer is full, it doesn't interfere with the operation of the camera.