John, welcome to my world!!!!!!!!!! Bizarre.
BTW: I now have TWO other people who are running Windows 10 Pro on PCs with very different configurations, and both are seeing exactly what I do when the .dng files are displayed in loupe view. One of the two ALSO does focus stacking with a completely different tool for creating the stacks and a different version of Helicon Focus for rendering. He downloaded my 3 images and found them to identical in both loupe and Develop, then ran one of HIS stacks through HF, generated multiple different outputs, ran multiple HF sessions, and even did some other fiddling with output images. Every time, his outputs looked IDENTICAL... I'm not sure what's different between the 4 systems we're using and what y'all are doing, but he contacted Helicon Support and THEY have now reproduced the problem in Lightroom.
Needless to say, their first response, and the one that continues to today, is - it's not their fault.. It's Lightroom.
Yesterday morning I opened two .dng files in Word. You can read the “header” xmp stuff. I took a 19 image stack and a 7 image subset and did a file compare on the xmp part. They were done in TWO different sessions so I’d expect SOME differences. The ONLY three fields that differed were the date at the top, the xmp:ModifyDate and the xmp:MetadataDate. One is 19:44:09, the other is 19:45:30.
As near as I (and the compare) can tell, EVERYTHING ELSE in there is identical. In Lightroom they look the same.
I took a .NEF file, in Lightroom, changed the exposure to about -3 and exported as a .dng. Changed the exposure to about +4 and exported a .dng. Different names. Opened THOSE and compared:
The three dates are different (expected)… BUT, there are OTHER differences:
xmpMM
ocumentID
xmpMM:InstanceID
crs:Exposure2012
stEvt:InstanceID
stEvt:when
And when imported into Lightroom, they look VERY different.
The Exposure is -3.xx vs +4.xx so crs:Exposure2012 isn’t important. I suspect stEvt:when isn’t either.
xmpMM
ocumentID, xmpMM:InstanceID and stEvt:InstanceID ALL CONTAIN THE SAME VALUE.
Back to Helicon…
I ran a NEW stack. Ran 16 images in method B, then ran the first 4 images in method B. Saved each as it was created. Exited from Helicon then exported the first 8 images from Lightroom and ran them method B, and saved. So, it’s a different time, a different number of images, and all the filenames are different.
In Lightroom loupe, ALL THREE images look identical. Comparing the .dng files, the 16 image run and the 4 image subset are identical – as near as I can tell there are NO fields in the xmp text that differ. There’s nothing I know of to tell Lightroom these are anything but two identical files with different names. PRESUMING Lightroom is using something in this xmp data to decide what constitutes a "different" image.
Then I compared the 16 image and the SEPARATE 8 image subset renders. This time the three dates differed, and the xmpMM
ocumentID, xmpMM:InstanceID, stEvt:InstanceID, stEvt:when differed as they did in the two .dng files I created from the .NEF. Further down in the xmpMM:History section there are repeated occurrences of the stEvt:instanceID that repeat earlier values, but there are TWO different values of stEvt:instanceID in various places in the text… All differ from the values in the stack of the 8 image subset.
So, there is data in the .dng that SEEMS to be unique when I run a SEPARATE session, yet in Lightroom, ALL 3 .dng files, 16 images, 4 image subset, 8 image subset, all look the same.
What DOES appear to be the same in all of the .dng images from these runs is the xmpMM:OriginalDocumentID, and in the “xmpMMDerivedFrom” section, the stRef:documentID, and the stRef
riginalDocumentID, which match the xmpMM:OriginalDocumentID earlier in the text.
What is LIGHTROOM using to decide there are two different files? If it’s InstanceID, that only appears to change if a different Helicon Focus session is run. But, if it’s stRef:documentID or stRef
riginalDocumentID, those are the same in all 3 .dng files.
I took a subset of images from the middle of the stack, and ran those. All the above differ, PLUS the crs:RawFileName, aux:ImageNumber and the stRef:documentID, and stRef
riginalDocumentID that were the same previously. This render output, that started with an image in the middle of the stack rather than the first image in the stack, IS DIFFERENT in Lightroom...
From all this fiddling around, I have more data, but have no idea what is and isn’t meaningful. The question “How does Lightroom determine two .dng files are the same (or different)?” hasn’t been answered. As far as I can tell, Helicon doesn’t do it’s own .dng conversion. It uses the Adobe .dng converter – when you install HF, it appears to install an Adobe .dng converter. So, is it Lightroom, Adobe dng converter, or Helicon that’s not doing what’s needed to make Lightroom treat the .dng files as unique?