copy tags from jpg to png: tiff:YCbCrSubSampling property incorrect?

[malenki]

In a bug report at wikimedia it was pointed out that exiftool seems to write the mentioned field incorrect:
https://bugzilla.wikimedia.org/show_bug.cgi?id=31944

The difference should show up between this files:
http://upload.wikimedia.org/wikipedia/commons/archive/5/5d/20111025203210!Museum_in_Frashër%2C_Albania.png
(Metadata copied from a jpg to the png with -tagsFromFile)
and this file:
http://upload.wikimedia.org/wikipedia/commons/5/5d/Museum_in_Frashër%2C_Albania.png
(metadata like the file above but field "Y Cb Cr Sub Sampling            : YCbCr4:2:2 (2 1)" removed)

PS: for coping tags from the jpg to png I used exiftool 8.6 on aptosid.

[Phil Harvey]

Thanks for this bug report.  This is definitely an ExifTool bug.   I'll fix this.

Funny that it went unnoticed for so long.

- Phil

[malenki]

Thank you for the fast reply and confirmation.

Funny that it went unnoticed for so long.

How long did it exist?
To me it looks like a very minor glitch which can get discovered only by accident.

[Phil Harvey]

This glitch has existed since the first version of ExifTool that could write XMP.

Very embarrassing, because ExifTool is one of the most mature XMP writers available.  Bugs like this are common in other applications, but not Exiftool.

- Phil

[Phil Harvey]

To make this thread self-contained, I will include a description of the exact problem as mentioned in the bugzilla report.

The problem is that ExifTool 8.68 and earlier writes XMP-tiff:YCbCrSubSampling as a string:

Code Select Expand

  <tiff:YCbCrSubSampling>2 1</tiff:YCbCrSubSampling>

instead of a list, as it should:

Code Select Expand

  <tiff:YCbCrSubSampling>
   <rdf:Seq>
    <rdf:li>2</rdf:li>
    <rdf:li>1</rdf:li>
   </rdf:Seq>
  </tiff:YCbCrSubSampling>

This bug will be fixed in ExifTool 8.69.

- Phil