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DNG compressed VS uncompressed?


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For my convince .....I'd like to save some space on my card.

Can anyone give me a reason why I shouldn't shoot  DNG compressed?

I did a test and they look very similar if not exactly the same.

 

In a pinch is compressed OK?

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I use compressed DNG with my M9 and compressed DNG is my only option with the M262. Couldn't be happier.

 

I'm sure someone has a reason in their mind for not shooting DNG compressed. I think I read the new MD 262 only records in DNG uncompressed.

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Here's one pretty extensive discussion...

 

http://www.l-camera-forum.com/topic/201563-new-m-dng-compression/

 

Users probably do more to damage the final result in amounts of noise reduction and sharpening in post-processing than you'd ever see attributable to lossless compression.

Edited by Gregm61
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Thanks for that thread......although pages 3and 4 took a turn for the weird

 

To me here's the only reason not to use it.

 

quote form the other thread:

"I believe that some older software tools can't open lossless compressed DNG files." 

 

​True or not it does't matter. My current ACR software opens it fine.

I'm doing a shoot with minimal cards and no external HD. I just want to save a little space.

 

Thanks for the advice its much appreciated.

Edited by ECohen
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Lossless is lossless. Endof.

True.

 

The term "losless" is not the result of a painstaking evaluation of a lab which failed to detect a "meaningful" difference between an uncompressed and a compressed image. It's a technical term which means that mathematical procedures are applied which guarantee that the original data will be restored by a well-defined and usually straightforward procedure.

 

No guessing involved. "Lossless" means that nothing is lost.

 

I would use an uncompressed format if I knew that some of the PP software I was going to use could not deal with the compressed format.

 

Since I do not use such software, I use the losslessly compressed formats.

 

I am not bothered by the space saved on the SD card; however, moving the images from the SD card to disk, from there to the backups, or moving those things over a WiFi or a plain internet connection takes much longer for uncompressed files, and all for no discernible advantage.

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True.

 

The term "losless" is not the result of a painstaking evaluation of a lab which failed to detect a "meaningful" difference between an uncompressed and a compressed image. It's a technical term which means that mathematical procedures are applied which guarantee that the original data will be restored by a well-defined and usually straightforward procedure.

 

No guessing involved. "Lossless" means that nothing is lost.

 

I would use an uncompressed format if I knew that some of the PP software I was going to use could not deal with the compressed format.

 

Since I do not use such software, I use the losslessly compressed formats.

 

I am not bothered by the space saved on the SD card; however, moving the images from the SD card to disk, from there to the backups, or moving those things over a WiFi or a plain internet connection takes much longer for uncompressed files, and all for no discernible advantage.

 

Compressed, and uncompressed file has a specific engineering definition, however I sense among many that they worry that Leica Marketing might be employing the term to Leica's advantage. To those who worry, do not! :) At least in my experience. One of the tests of a compressed vs uncompressed is to compare each after the compressed has been restored (uncompressed), and I know of no such test, but someone smarter than me probably does. We have some very smart people here.

 

A question that comes to this lazy M9 user is whether writing to the SD card is faster with compressed mode. Anyone? (I always use compressed mode.)

.

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Forgive me for not being technical 

I shot a few tests .....processed with them ACR  and compared the Jpg's

To me and for my purposes they looked the same.

I actually don't care about Leica's motives...or even how it works.

I just care that it looks good and works fine......call me naive 

The compressed opened on my copy of ACR........ I don't see an issue.

So for my purpose and for this weeks shoot I'm going  compressed

 

I do appreciate you all ...thanks for keeping me thinking

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I think lossless compression does not have higher data loss probability than simple copying of the original. If you are happy copying files, then lossless compression is fine.

 

No operation is truly lossless. The act of transferring/manipulating a file can incur data loss. That is why there is verification algorithm built in for most copy/move operations. It samples random portions and compares the original with copy. Data loss is a matter of probability. 

 

Information is fully recoverable in lossless compression since the algorithm is a bijective function of the compressed image to an uncompressed one. One-to-one correspondence can only give a shorter file if redundancies of a particular file format are known. There is no universal lossless compression algorithm

 

In the case of DNG compression, compression makes use of predicable behavior in the Bayer array. It re-arranges the data to lump predictable patterns. Compression will differ from image to image.

 

 DNG lossless seems to be a version of lossless jpg compression (not to confuse with the lossy version of jpg). Here is an article on how it is done:

 

http://thndl.com/how-dng-compresses-raw-data-with-lossless-jpeg92.html

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I always wondered why uncompressed option is even there when the compression is lossless.

I can think of two reasons.

 

One: timid users may fear that "lossless" is not really lossless; that's what I seem to observe here.

Two: you may use some peculiar software which does not handle compressed image data or, perhaps, not image data that has been compressed in that particular way.

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Does it matter to anyone other than the user whether they choose one or the other - I'll answer my own question: no.

It does, to me. The compressed files are smaller. They use less room on my server and take less time to copy, handle and open.

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Yes, I chose compressed on M240. I chose compressed on M9 as well even if it was lossy since in my experiments I could not find any difference. Even for complex scenes (with very subtle tonal gradation change where information loss could be visible).

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This is bordering on pedantic and so excuse me for that. There is one additional downside to even lossless compression. If there is any data corruption, then more of the image is affected or it more easily can become unreadable.

 

So say for example a gamma ray from a supernova in Galaxy9 happens to hit your hard disk platter and flips a bit or two in your data (no seriously these things do happen all of the time - In the past I used to write drivers for RAM error detection and correction) or you have a plain old disk sector error due to a subtle manufacturing defect then if the pattern that was corrupted is repeated multiple places in your image, then all of them will be corrupted or if metadata needed to reconstruct the image is corrupted then the image may not be reconstructable. This is one of the reasons people use disk arrays with checksums.

 

Uncompressed data doesn't have as much metadata required to reconstruct a whole image and bit flips caused by high energy photons or subatomic particles only cause localized impacts to an image. It won't be repeated throughout the image.

 

On the other hand, because an uncompressed image physically occupies more space on a disk or in the solid state storage, it makes a bigger target for the aforementioned gamma ray particle from Galaxy9 or there are more sectors on the disk which could potentially become unreadable.

 

All of that being said, having intimate first hand knowledge of all the problems that can possibly occur with digital storage, do I consider that to be justification to not use compressed DNGs. Emphatically NO!!!!!! It is roughly akin to a rancher fearing a terrorist attack by ISIS while watching over a cattle herd grazing the open range in northern Nevada. (OK that may be a bit hyperbolic but what do you expect from a Californian after watching Trump win the nomination?)

 

It does mean that if you are using compressed DNGs (or even uncompressed ones), you should use good digital asset management practices. Drives fail, sectors become corrupted sometimes silently and if they do, that corruption can spread to backups and you might lose something important. Compressed data is more prone to large scale corruption and unrecoverable corruption but uncompressed data has more opportunity to become corrupted in a minor way.

 

I can think of two reasons.

 

One: timid users may fear that "lossless" is not really lossless; that's what I seem to observe here.

Two: you may use some peculiar software which does not handle compressed image data or, perhaps, not image data that has been compressed in that particular way.

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I do not worry as bencoyote does. If something cosmic corrupts images in storage, I consider it time for a vacation, but it has never happened. Further, I come from the age a when we did stupid things like holding radioactive material on our eyes, with eyelids shut, just to experience 'shooting stars' (seriously, they sold such stuff), and had our feet measured at shoe stores using X-Rays. And in-service I was overdosed by radiation. I still have calcified lung tissue for that. Gads, the things we did to keep America Great. :)

 

And that's my excuse for me today. :) Loving to hate Trump. The weenie.

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I do not worry as bencoyote does. 

 

I don't actually worry. :-) I just happen to know what can and does go wrong.

 

I use compressed DNG. My MBP doesn't have ECC RAM nor does the HFS file system or Flash disk have checksums. It isn't until it gets out to the RAID array that it has any data protection. 

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