DNG validation hash

[Kevin Forsmo]

Hi,

[edit: I should probably read up more about what I've bought...I am learning about ImageIngesterPro's included ImageVerifier now.  So to some extent I've found the answer: ImageVerifier might let me play, but I'd still be interested to know if the cataloging apps can, will, or should flag files based on the DNG hash.]

I'm trying to figure out how the DNG RawImageDigest is used.  The software I'm using is Lightroom 2, EM2, ImageIngesterPro, etc.  To start, I'm converting my .NEF files to DNG using DNG converter 5.3 (standalone or via ImageIngester).  Later I may be interested in Lightroom-generated DNGs, and I'm not sure if this calls the DNG converter or has its own algorithm.

Is the validation hash checked by software nowadays?  Ideally I'd like to have someone help me manually corrupt the raw image portion of a dng so I can see how or when the hash is recomputed by various software, and how that information is used.  Basically I'm trying to break things intentionally so I understand how the process works when something breaks unintentionally.

Thanks in advance,

Kevin Forsmo

[peterkrogh]

Kevin
Yes, ACR, Lightroom and the DNG converter all check the hash when opening an image.
Peter

[rogerhoward]

Kevin - to corrupt the data, grab your favorite hex editor, load up the raw file, and have at it - make sure to keep your edits to the raw data... i'd test both modifying data in place (avoiding changing the file size) as well as randomly adding and removing data to change the fsize.

As for the hash, it's used at ingest and when the file is opened for rendering/editing I believe. Curious to hear what you find!

- Roger

[tinamanley]

Do the original DNG files created by Leica cameras have this hash code or do they have to be run through a converter?

Thanks,

Tina
www.tinamanley.com

[peterkrogh]

Tina,
The hash has only been part of the spec since April 2008 or so.  All files created before this won't have it.
Not sure about Leica implementation, but I'd doubt that they have it implemented currently, so, yes, you'd need to reconvert.
Peter

[tho3hite]

I tested some DNG files straight off my M8 (firmware v2.044)and they don't have the hash. I don't know about the M9 but I'll be checking one out at a dealer soon. «« Though I probably won't have enough money to buy one for a very long time. Sob »»

[peterkrogh]

I heard from a reliable source that the Leica does not have the hash (even the M9), but that it's possible it will show up in a firmware update. Leica seems to be more adventurous about what they will do in firmware than other companies.
Peter

[Ale]

Hi,
I would like to know if it is possible to check if a DNG file has the hash.
I should make sure of this with many old files I don't remember with which DNG Coverter version they were generated.
Thanks,
Alessandro

[rogerhoward]

Hi,
I would like to know if it is possible to check if a DNG file has the hash.

Yes, of course - I use Exiftool... the field is called "RawImageDigest" so if that field exists and is populated then the hash is there. I've got a few AppleScripts (which in turn automate Exiftool) for scanning a collection to report on whether each file has this hash - if you're on a Mac and interested I'd be happy to share.

-Roger

[Roelof]

Does someone know a windows script for this perhaps?
Roelof

[JoeThePhotographer]

How do you know whether a dng has a hash or not?

I using Vuescan to scan to DNG, and would like to know whether they are hashed or if I need to re-convert them.

The problem with reconverting Vuescan files is that they are 4-channel (Red Green Blue and Infrared) so I am not sure whether Adobe converter will know what to do with the fourth channel.

[evnglst]

Hi,
I would like to know if it is possible to check if a DNG file has the hash.

Yes, of course - I use Exiftool... the field is called "RawImageDigest" so if that field exists and is populated then the hash is there. I've got a few AppleScripts (which in turn automate Exiftool) for scanning a collection to report on whether each file has this hash - if you're on a Mac and interested I'd be happy to share.

-Roger

Hi Roger. Yes... I would very much like to see your AppleScripts for Exiftool... if you're still reading this thread.

Thanks,
George Jardine