M9 - Compressed vs Uncompressed DNGs
Old 02-23-2014   #1
Jubb Jubb
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M9 - Compressed vs Uncompressed DNGs

I've just noticed that I have been shooting compressed DNGs on my M9.
Is there any difference between compressed and uncompressed files?

I notice the size is significantly bigger, at 34mb per file.
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Old 02-23-2014   #2
Richard G
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Apparently there is, but not much. I have been shooting compressed and have been quite happy. I can't shoot compressed on the Monochrom and 34MB per file sure eats drive space. It is certain there will be advice almost immediately that it is mad to use an M9 and then use compressed DNG. Also mad to use the M9 black and white jpegs. Also mad to spend the extra on an M9-P when you can just buy a screen protector. Also mad to buy an M9 when you can buy a lot of film for the same money....etc etc
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Old 02-23-2014   #3
jippiejee
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I understood that compressed dng's on the M9 reduce the output to 8-bit files (like jpegs) vs the normal 14-bit raw files of uncompressed dng's. The latter files will give you much more leeway when adjusting shadows or highlights in post.
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Old 02-23-2014   #4
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I've done some testing between compressed and un-compressed raw files out of the M9. The difference is there, but it is quite small.

It might be significant if you are doing work that requires very high resolution capture for very large output prints ... think detailed landscape views made with the M9 tripod-mounted with your best lenses that you want to print to 20x30 inch, etc.

For more normal shooting purposes, compressed DNGs do just fine and are nothing to worry about IMO. Most of my M9 work was done with compressed DNGs and I haven't had any quality problems with prints up to 13x19 inch in size.

It's nice that they provide the choice.

G
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Old 02-23-2014   #5
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Quote:
Originally Posted by Godfrey View Post
I've done some testing between compressed and un-compressed raw files out of the M9. The difference is there, but it is quite small.

It might be significant if you are doing very work that requires very high resolution capture for very large output prints ... think detailed landscape views made with the M9 tripod-mounted with your best lenses that you want to print to 20x30 inch, etc.

For more normal shooting purposes, compressed DNGs do just fine and are nothing to worry about IMO. Most of my M9 work was done with compressed DNGs and I haven't had any quality problems with prints up to 13x19 inch in size.

It's nice that they provide the choice.

G
Seconded.

Cheers,

R.
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Old 02-23-2014   #6
Godfrey
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Quote:
Originally Posted by jippiejee View Post
I understood that compressed dng's on the M9 reduce the output to 8-bit files (like jpegs) vs the normal 14-bit raw files of uncompressed dng's. The latter files will give you much more leeway when adjusting shadows or highlights in post.
I don't think so. I haven't seen any reduction in dynamic range or editing overhead which would be the case if that were true: I can still use the M9 sensors "ISO-less" characteristic to expose at 5 stops under nominal and pull up the image in post processing to a very usable state.

What I see is a small reduction in absolute resolving power.

G
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Old 02-23-2014   #7
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I've never tried compressed files, but isn't having more raw data depth to work with better in post? Isn't that the whole point of shooting raw vs jpegs too?
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Old 02-23-2014   #8
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It was my understanding that the type of compression used was equivalent to taking the square root of the amplitude at each pixel.
The idea is to retain almost all bit level detail at low levels and to discard fine tonality in highlights.

<edit > : Here is a link to the details behind the scheme

"out of 16 bits.....the finest gradations are contaminated by noise....simply crossed out....The processor of the M8 now multiplies the 14 bit number of every pixel with 4 and extracts the integral square root from that sum.The resulting values are somewhere between 0 and 255 and can be written with 8 bits. By squaring them and dividing them by 4 we again achieve the values of the 14 bit tonal spectrum"

http://www.l-camera-forum.com/leica-...ompressed.html
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Old 02-23-2014   #9
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Quote:
Originally Posted by FrozenInTime View Post
It was my understanding that the type of compression used was equivalent to taking the square root of the amplitude at each pixel.
The idea is to retain almost all bit level detail at low levels and to discard fine tonality in highlights.

<edit > : Here is a link to the details behind the scheme

"out of 16 bits.....the finest gradations are contaminated by noise....simply crossed out....The processor of the M8 now multiplies the 14 bit number of every pixel with 4 and extracts the integral square root from that sum.The resulting values are somewhere between 0 and 255 and can be written with 8 bits. By squaring them and dividing them by 4 we again achieve the values of the 14 bit tonal spectrum"

http://www.l-camera-forum.com/leica-...ompressed.html
Whether this is true or not, I don't have the time (or interest, really) to figure out.

What I can say for sure is that the in-camera compressed DNGs are only very slightly degraded from the uncompressed DNGs, and I have observed no reduction in editing overhead in tonality and such.

G
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Old 02-23-2014   #10
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Is the compression linear or exponential?

If the higher photon count region of the signal is compressed preferentially, the shot noise is filtered. This is not a bad thing as the statistic for shot noise is rigorously defined and shot noise can be added (to the the brighter regions) during post processing if needed.
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