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loss-less compression ?

thrice

Active member
Nothing wrong with lossless compression!

The Sony compression is lossy, which is not ideal in specific circumstances.

Lossless uncompresses into an indistinguishable image compared to no compression.
hence the term lossless...
 

Knorp

Well-known member
Nothing wrong with lossless compression!

The Sony compression is lossy, which is not ideal in specific circumstances.

Lossless uncompresses into an indistinguishable image compared to no compression.
hence the term lossless...
Thank you - indeed indistinguishable, I have never seen those artifacts with 'compression' selected in my A7R2 images.
If you say 'loss-less compression' is the same as 'uncompressed', all the better, but to me it seems a little weird.
The more so as in the manual in the same table also 'uncompressed' is mentioned ... :lecture:

Sooo - which is what :banghead:
 

thrice

Active member
Ahh yes well...

There are two ways to compress a file, one way throws away data it deems unnecessary (ie. JPEG, simplifies the file by using an algorithm that guesses the data it threw away) this is termed lossy compression.

Then there is lossless compressed. This is what most RAW formats are, another example is FLAC or APE audio formats, they sound exactly like the source but they simply take patterns in the data and call them something simpler which the codec (decompression algorithm) knows how to return to the original state - or one indistinguishable from it.

Sony caused a controversy by creating the 12+1 lossy compressed .arw format which can occasionally cause edge artefacts because the codec is guessing how those transitions should be drawn. Most times it guesses really well.

Uncompressed is top quality
Lossless compression is also top quality but the files can take a little longer to open/process
Lossy compression is a lesser quality as it throws away some information that cannot be truly recovered.
 

k-hawinkler

Well-known member
Thanks Bart, lossless compression is just a different representation of the same information with fewer bits that can be perfectly transformed back into the original form without any loss of information. Basically it's a trade off between requiring fewer storage bits for the data but paying for that with increased processing.

Lossless compression is fundamentally different from lossy compression.
 

Knorp

Well-known member
Thank you, gentlemen !

So there must be some reasoning to it choosing loss-less compressed for the RAW files.
I'd say uncompressed requiring more internal buffer space and more time to write to external media, resulting in perhaps lower FPS versus loss-less requiring higher internal processing and less time to write to external media, but perhaps achieving higher FPS.
Apparently they didn't bother for the High-Res files.
 

k-hawinkler

Well-known member
Thank you, gentlemen !

So there must be some reasoning to it choosing loss-less compressed for the RAW files.
I'd say uncompressed requiring more internal buffer space and more time to write to external media, resulting in perhaps lower FPS versus loss-less requiring higher internal processing and less time to write to external media, but perhaps achieving higher FPS.
Apparently they didn't bother for the High-Res files.
Thanks Bart, good thinking. Having written a lossless compression algorithm myself a long time ago for my own purposes, one always tries to optimize a system. One can do that by trading off computational, communication, memory, and storage requirements against each other to some degree. It's interesting that the E-M1.2 uses lossless compression only when regular raw files are involved and nothing else, provided I read the table you posted correctly. That would indicate to me that overall camera performance can be optimized in that case through lossless compression. However, in the other cases Olympus either hasn't gotten around to it just yet, or computational usage is already stressed by the additional computational requirements. My 2 cents. :grin:
 
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