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M9 Raw compressed vs uncompressed, any difference?
- Thread starter RayM
- Start date
Godfrey
Well-known member
Interesting that they say the compressed raw format shows only minor deterioration. I wonder why there's any deterioration at all. The M9 raw files are supposed to be DNG format.
The DNG Specification's compression format is 100% lossless, but Adobe doesn't recommend it for use in camera devices because it takes a good bit of processing power to implement it.
The DNG Specification's compression format is 100% lossless, but Adobe doesn't recommend it for use in camera devices because it takes a good bit of processing power to implement it.
The M9 doesn't use in-camera DNG compression, but rather a square root compression algorithm that creates files that are exactly and always 1/2 the size of the original uncompressed file. This is a lossy compression scheme, but is not very processor intensive and in practice doesn't effect image quality that much. For me, I'll shoot compressed for vacation snapshots at Disney, but will switch to uncompressed for serious photo work that I may want to print really large.
The S2, incidentally, does do a lossless DNG compression in camera. It has plenty of processing horsepower and the compressed files actually make the camera shoot faster, not slower. When and if Leica updates the next M camera to use the Maestro processor like that found in the S2, I'm sure lossless compression with be on the menu.
David
Jan Brittenson
Senior Subscriber Member
For anything involving people I shoot compressed - the reason is the camera writes to the card much faster. To me, having the camera ready to shoot is more important than the theoretical trade-off of compression. It's really quite quick writing compressed (with no JPEG) to a Sandisk 16GB Extreme card. For more static uses I shoot uncompressed; there's no reason to make the same trade-offs, theoretical or not. I also use slower cards for this since write speed is no longer of importance.
Bill Caulfeild-Browne
Well-known member
I've done a few direct comparisons and really can't see any difference, at least on screen at 72 dpi. I haven't made comparison prints but I doubt I'd be able to discern any change. Like Jan, I tend to prefer speed to a theoretical quality increase.
Godfrey
Well-known member
Very interesting! Thanks.
Jan Brittenson
Senior Subscriber Member
Like Bill I can't see any difference either... but I haven't done any stress tests. With properly exposed image material I don't think it would ever show.
What's interesting about the M9 compression is that it's not a strict square root function. It's linear up to a certain point, then it uses a root. But it embeds a translation table in the file, with each file potentially having its own slightly different translation. It also makes it easy to fit the entire histogram in the table, so a severely underexposed image that only uses say half the histogram could still use the entire table - it would simply translate to a shortened histogram.
What's interesting about the M9 compression is that it's not a strict square root function. It's linear up to a certain point, then it uses a root. But it embeds a translation table in the file, with each file potentially having its own slightly different translation. It also makes it easy to fit the entire histogram in the table, so a severely underexposed image that only uses say half the histogram could still use the entire table - it would simply translate to a shortened histogram.
Double Negative
Not Available
I have large cards, yet I usually shoot compressed. If I'm going for "artsty" or landscape I might switch to uncompressed, thinking I'll take all the data I can get for post or printing... Doesn't seem to make much difference though, unless you start messing with curves heavily, I would think.