Metadata question

[Carlo Didier]

When listing all the metadata from my DNGs, I see these values which I am interested in (I want to find all DNGs which don't have a full size preview embedded):

Code Select Expand

[SubIFD]        Subfile Type                    : Full-resolution Image
[SubIFD]        Image Width                     : 6034
[SubIFD]        Image Height                    : 4028
[SubIFD]        Bits Per Sample                 : 16
[SubIFD]        Compression                     : JPEG


I'm specifically looking for the attributes under [SubIFD], but I can't find those anywhere in iMatch as variables (for example to display in the Metadata panel or to filter or for use in a datadriven category).

[Mario]

Check the Tag Manager and make sure that you have set IMatch to import this data. IMatch by default does not import most maker notes and other data which is of no or limited use to humans. IMatch by default does not import tags like image width or height because it gets that info from the image processor / WIC codec.

[Carlo Didier]

Mario, these are DNG files with embedded previews generated by ACR, though the original files were NEFs (or ARWs, or MRWs).
Under the Nikon tags, there is only the NikonPreviewIFD group which does not contain the information that exiftool shows.
I can't find this information anywhere in the Tag Manager.

[Mario]

Use the -G1 parameter in ECP to find out the group name, then search for that group in the Tag Manager. I don't know without a sample file and looking at the ET output under which group and tag name ExifTool imports this data.

[Carlo Didier]

The relevant ECP output is shown in my first post.
Attached is a complete listing of exiftool -G1 -all -a {Files} (in ECP)
I thought the data I'm looking for started at line 29, but I'm not sure anymore as a DNG where I deliberately updated the preview with medium resolution showed the same entries in those lines, but exiftool was unable to extract a preview ...

[attachment deleted by admin]

[Mario]

Can't you just make a small 600 pixel DNG and attach it? Or send me a sample? This is not leading us to anything. It may very well that IMatch drops sub ifs when importing metadata because they are not needed anywhere in IMatch.

[Carlo Didier]

How could I make a 600px DNG file? I don't have a camera that produces 600px images ...

Meanwhile, I'm not sure whether I have correctly identified the metadata. I'll do some more controlled tests and tell you what I find. I can then make a full size real DNG available for download for you if I still can't access the metadata I want.

[Carlo Didier]

Ok, I did a systematic extraction. Attached are three text files with the exported metadata from ECP and a sample screenshot of a compare (with Notepad++) of those with a full and a medium preview.
The full preview has a size of 6016x4016 pixels and a different compression. Problem is, there are several subIFDs in each DNG and I would have the one which seems to always be under subIFD2.

So, to resume, I need the tags "Image width" and "Image height" under [subIFD2]. I can't see any other indication to check if a full size preview is embedded.

You can download the 3 DNG files here.

[attachment deleted by admin]

[Mario]

I will look at the files soon. I'm downloading right now.

But I think I remember that IMatch deliberately skips some redundant sub ifds during import. IMatch is only interested in the original image, the embedded preview is only used when creating the cache image and thumbnail, but not to process, edit or display metadata. IMatch is only interested in the EXIF data of the main image. And it would double/triple the EXIF data in the database, without having any use. A RAW may contain a preview and a thumbnail (all with separate EXIF data) or maybe even multiple embedded previews, for different resolutions...

If the "embedded image in image EXIF data" tags you#re looking for fall into this category, you are out of luck - at least with IMatch. IMatch does not need or process that info and strips it very early.

[Mario]

I checked the files.
My memory of how this is implemented is correct.
IMatch only imports the EXIF data for the SubIFD for the SubFileType "Full-resolution Image". It does not import EXIF metadata from the embedded thumbnail or preview IFD, if there are some.

If you really need to access the information recored in the EXIF metadata associated with the preview JPEG, you will need to use the ECP or ExifTool command line. You can use ExifTool to transfer this info into one of the freely usable EXIF tags (user comment or so) or into XMP data. Then you will have the info also available in IMatch.

[Carlo Didier]

Thanks for the info, Mario.
I can read this information, through exiftool, in a script. Maybe I'll assign a category to that or an attribute. Probably a category.