Odd ACR previews with M240 files

[Schrödinger's cat]

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I was doing some quick and dirty depth of field comparisons playing around with my new Tele Elmar 135mm f4 and noticed this in Adobe ACR:

 

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Note that the thumbnail is of something in France and the actual image is of something in Texas

 

I have tried purging the thumbnail cache and it does nothing.  Neither does editing the image and reserving.  The memory card was formatted in SDformatter.  

 

I have had this occur previously where I saw the wrong thumbnail in Bridge, but this is the first time it's come up in ACR.  It ONLY seems to occur with raw files from the M240.

 

Any ideas ?

 

 

 

[tobey bilek]

No but why use sd formatter ?   A simple reformat in camera has always worked for me with Leicas, Nikons or Canon.  

 

Do you have the France pic in the computer and what is the DNG number ?  Is it similar to xxx183 ?   When previously downloaded from France project was the protect image on ?   

 

If SD formatter is working properly,  it should wipe the table of contents and free all storage locations to be overwritten.   It should not do anything to the card firmware that assigns storage locations and rotates them.   

 

The other thing possibly is the cache in bridge.   I would delete it , turn computer off,  and let bridge develop new previews.   It is under preferences.

 

Two other bits of advice,  do not erase anything on a card.   Reformat only .    Secondly,  do not move cards from one camera to another.   Buy new cards with new camera,  format in camera,  and leave it there.

 

My best guess at this time is delete the Bridge cache as above.  Interesting would be if the folder with France in it has a proper preview of xxx183.   If so,  it is doubled up.    

 

Maybe try redownload the bird pics to a trial folder,  then see if the preview is correct.   That should tell you if it a computer or card issue. 

[Guest JonathanP]

I think this is an issue that I bump into every so often with Lightroom, but have always suspected happens in Bridge as well.

 

The wrong preview thumbnail problem is caused by the fact that the M240 doesn't implement the DNG spec correctly. There are 2 EXIF data fields "ImageUniqueId" and "RawDataUniqueId" that are supposed to be always unique. The DNG spec says:

 

 

This tag contains a 16-byte unique identifier for the raw image data in the DNG file. DNG readers can use this tag to recognize a particular raw image, even if the file's name or the metadata contained in the file has been changed.

 

If a DNG writer creates such an identifier, it should do so using an algorithm that will ensure that it is very unlikely two different images will end up having the same identifier. 

 

Lightroom and Bridge use these tags to manage file previews in their cache. Unfortunately the M240 uses a very simple algorithm to generate these numbers which is reset everytime you turn the camera off. This means that every so often a new image has the same IDs as a previous one in your Lightroom/Bridge cache and the wrong thumbnail gets displayed.

 

If you happen to use my "green shadows" Lightroom plugin, running the offending image through that will fix it as the plugin will replace the IDs with genuinely unique IDs. Otherwise clearing the Lightroom/Bridge cache will temporarily appear to fix it until you browse to the other image with the duplicate ID.

 

I do wish Leica would correct this, it wouldn't be hard to fix. Having a quick look at Q and SL raw files they seem to generate much better IDs using a different algorithm, so this may end up remaining just a M240 nuisance if Leica can't be bothered to do anymore bug fixes for the M240.

 

Jonathan

[Echo63]

I think Mr Perkins is correct.

Is happens to me occasionally in Lightroom.

[Schrödinger's cat]

I think this is an issue that I bump into every so often with Lightroom, but have always suspected happens in Bridge as well.

 

The wrong preview thumbnail problem is caused by the fact that the M240 doesn't implement the DNG spec correctly. There are 2 EXIF data fields "ImageUniqueId" and "RawDataUniqueId" that are supposed to be always unique. The DNG spec says:

 

 

Lightroom and Bridge use these tags to manage file previews in their cache. Unfortunately the M240 uses a very simple algorithm to generate these numbers which is reset everytime you turn the camera off. This means that every so often a new image has the same IDs as a previous one in your Lightroom/Bridge cache and the wrong thumbnail gets displayed.

 

If you happen to use my "green shadows" Lightroom plugin, running the offending image through that will fix it as the plugin will replace the IDs with genuinely unique IDs. Otherwise clearing the Lightroom/Bridge cache will temporarily appear to fix it until you browse to the other image with the duplicate ID.

 

I do wish Leica would correct this, it wouldn't be hard to fix. Having a quick look at Q and SL raw files they seem to generate much better IDs using a different algorithm, so this may end up remaining just a M240 nuisance if Leica can't be bothered to do anymore bug fixes for the M240.

 

Jonathan

 

 

Thank you for such a direct and concise response.  This was very helpful.  Thanx again.