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[Solved] PNG conversion metadata: Apple Data Offsets field disappears

Posted: Mon Feb 27, 2023 6:43 pm
by es
I've noticed when converting a screenshot that exiftool shows has the following field

Code: Select all

Apple Data Offsets : (Binary data 28 bytes, use -b option to extract)
after conversion disappears and there is this Comment instead

Code: Select all

Comment : iDOT chunklen 28 ignored:.ASCII: ...........©...(...©...©...#.HEX: 0000000200000000000000A900000028000000A9000000A900001523
Don't know what this field is, google surprisingly gives only 1 result for it, so I'd say it's something useless, but I'm just worried a bit that there might be a more general issue in metadata conversion during image editing which might lead to a loss of something more useful
Is there a way to maybe just preserve those chunks/tags instead of ignoring them?

Re: PNG conversion metadata: Apple Data Offsets field disappears

Posted: Mon Feb 27, 2023 8:41 pm
by forum_adm
Here is a helpful detail:
https://stackoverflow.com/questions/338 ... idot-chunk

It is not a standard chunk. GraphicConverter does not write it upon resaving the file.

Re: PNG conversion metadata: Apple Data Offsets field disappears

Posted: Tue Feb 28, 2023 2:42 am
by es
Oh, I see, the "Apple data offset" is exiftool naming, that's why couldn't find anything about it
Thanks for the clarification!

However, given the fact that the PNG spec requires removing such chunks on conversion (due to capitalized T), maybe this fact should just be mentioned in the Comment without carrying the now useless value?
(Or maybe it shouldn't be mentioned at all? Not sure)

Re: PNG conversion metadata: Apple Data Offsets field disappears

Posted: Tue Feb 28, 2023 6:36 am
by forum_adm
I added now a preference to build 6015:
Screenshot 2023-02-28 at 06.35.jpg
Screenshot 2023-02-28 at 06.35.jpg (94.85 KiB) Viewed 3617 times

Re: [Solved] PNG conversion metadata: Apple Data Offsets field disappears

Posted: Tue Feb 28, 2023 10:35 am
by es
Thank you!