Photoshop: Corrupt Ancestors tag in XMP causing giant file sizes

 There is an option in Photoshop to turn on writing yet more log data - logging every save of the file, or optionally logging every single action that is done in Photoshop. That can lead to giant blobs of metadata. But by "giant", I mean tens of KB, not megabytes.

 I would think that it would take a malfunctioning machine to generate the kind of bloat we're talking about here.

 UPDATE: The OP (to whom I am married, for the sake of full disclosure) provided me with the files in question and I examined them.

 Two of the images placed in the final PDF had excessive Document Ancestor tags. One was the Tiff Bonnie mentioned in the original post, the other was a JPEG. The Tiff should have been about 25 MB, but was 56.5 MB. The JEPG was 19.8 MB when it should have been 1.7 MB. The stock photo image that was the base image for the bloated Tiff was free of corruption. It had very tidy metadata.

 That suggests that Bonnie's copy of Photoshop, or another in her company may be the offender, making the corrupted files. That's not for certain, though, because the corruption may have been inherited from an ancestor to one of the bad files.

 In the case of the Tiff, ExifTool displayed some 37 KB of Document Ancestor entries - over 1,000 entries. But when that tag was removed from the file's metadata, the files size dropped by 30 MB! Very curious. I suspected that the ancestors data might have been a symptom, rather than the problem, but given that blanking that single tag effected the reduction in file size, that seems doubtful.

 I tried to find a clever GUI-based fix for these files without much success. The fact that the subject file was a Tiff and further that it was in CMYK eliminated most of the software I had at hand from consideration.

 Opening and re-saving the file in various formats in Photoshop didn't work. (And ancestor data survives copy and pasting onto a blank document, that's the idea of it.) Nor did opening the file and exporting it from Lightroom.

 I was able to use Photo Mechanic to strip all XMP metadata from the file. Oddly, there was no immediate impact on file size, but if I then opened the file in Photoshop and did a save-as, the file shrank to a normal size. IIM metadata was preserved, but of course, not XMP.

 If I simply did "Save photo as" in Photo Mechanic, the corruption was removed, but the file was saved in RGB, which wasn't so good. Ditto for the JPEG. A simple "Save photo as" removed the bloat, but the resulting file was RGB. All useful metadata was preserved in this case.

 XnView, ON1 RAW, and Apple Preview all failed to be of assistance.

 The only program I had at hand that was effective was ExifTool. It's free and it doesn't take up much disk space, but it's command line, so it may not appeal to everybody. The advantage of using ExifTool to fix this issue is that you can remove just the offending tag and leave all the rest of the file's metadata intact. The ExifTool command you'll need is simply

 exiftool -XMP-photoshop:DocumentAncestors=  yourFile.tif

 (Note that there are two spaces after the equals sign - one to tell ExifTool to blank the tag and one before the next argument)

 I didn't try Stephen Marsh's Photoshop script."

1. Opened long legacy file from CC 2014 version that's been resaved a lot up to current.
2. Drag-n-drop single layer with some pixel data into cloud library
3. New object is  489x38px and 14mb

1. Made new file
2. made new layer and painted a splotch
3. Drag-n-drop single layer with some pixel data into cloud library
4. New object is  81kb

1. Drag-n-drop layer from new file to old file
2. Drag-n-drop copied layer into cloud library
3. New object is  14mb

1. Scrubbed out ancestor data from old file with a script
2. Drag-n-drop copied layer into cloud library
3. New object is  92kb