Are EXIF InteropIFD tags important?

[aperturemode]

I rebuilt some JPG files using this command:

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exiftool -r -all= -tagsfromfile @ -all:all *.JPG
Since I didn't use the -unsafe argument, these 'unsafe' InteropIFD tags weren't copied over.

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[EXIF:InteropIFD] InteropIndex.                 : R98 - DCF basic file (sRGB)
[EXIF:InteropIFD] InteropVersion                : 0100
[EXIF:InteropIFD] RelatedImageHeight            : 2048
[EXIF:InteropIFD] RelatedImageWidth             : 3072
The images seem fine after the -tagsfromfile was run but I can't figure out what these InteropIFD tags were doing by looking at the documentation. It just seems to be the image size, the color profile and some version number, and the same information is in these maker notes tags in the files:

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[MakerNotes:Canon] ColorSpace                   : sRGB
[MakerNotes:Canon] AFImageHeight                : 2048
[MakerNotes:Canon] AFImageWidth                 : 3072

Are those removed InteropIFD tags unimportant and just give nice to know information or are they important to the image but removing them was ok because the makernotes have the same info? Or, something else?

Thanks for your help.

[Phil Harvey]

The InteropIFD image size tags are unimportant, but the InteropIndex gives information about the colorspace, so it may affect the way the image is displayed.

For JPEG images, the maker notes are really not used by any software other than that of the manufacturer.

- Phil

[aperturemode]

Thanks Phil. If the colorspace also shows up in another EXIF tag, such as:

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[EXIF:ExifIFD]  ColorSpace                      : sRGB
would it be safe to delete the InteropIFD:InteropIndex colorspace tag if I use Lightroom? Or would you suggest keeping both as one or other may be read by certain software (so keeping the image more future proof to using other software). I ask since keeping both groups of tags involves reprocessing a bunch of images from original since the 'InteropIFD' tags were already removed.

I'm also confused what the 'Interop' part of the InteropIFD group name means compared to the ExifIFD group name.

[blue-j]

Please note that the InteropIndex color space is sometimes - actually with remarkable frequency - in conflict with the Maker Notes color space designation (if there is one) which should always preside in my opinion.

If and only if the exif:colorspace is also populated, it is safe to have deleted interopindex:colorspace, but moving forward I would not advise it.  There is just no motivation to do so.

The values are defined in the EXIF 3.0 Spec like this:

"R98" = Indicates a file conforming to R98 file stipulated by ExifR98[1] or to DCF basic file stipulated by Design Rule for Camera File System[2].

"THM" = Indicates a file conforming to DCF thumbnail file stipulated by Design rule for Camera File System[2].

"R03" = Indicates a file conforming to DCF Option File stipulated by Design rule for Camera File System[2].

But have come to indicate color space as well, with R98 indicating sRGB and R03 indicating Adobe RGB.  THM indicates a thumbnail file.

Those are the ONLY values allowed in that tag - no other color space will show.

Interop means Interoperability, and it is a section of the file dedicated to, you guessed it, interoperating with other software.  IFD stands for Image File Directory, and it's used to denote sections of the file (though the Interoperability IFD contains no image data).

- J

[aperturemode]

Thanks for the additional info blue-j. You've convinced me to go back and reprocess the images and make sure those InteropIFD tags aren't delete this time.