I have an Olympus EM-10 III. When I put the SD card in my computer, there is a folder titled ALBM (along with the normal DCIM folder containing photos). Within it, there is a folder called ALB67ZZ8.BIN. When unzipped it with Archive Utility (the default Mac unzipper), it makes a file called ALB67ZZ8.BIN.cpgz. When that is opened, it makes a folder called ALB67ZZ8.BIN 2.cpgz, apparently duplicating itself. What is this file for? How can I open it?

  • My money on some thumbnails collection. – xenoid Mar 12 '19 at 6:34
  • The gz part of the extension seems to indicate gzip, another compressed format. The second file was likely produced after decompression. Try opening it to see if what's inside is recognizable. – xiota Jun 11 '19 at 3:20
  • "bin" is rather generic, just because the extension is associated, it doesn't mean that the software can actually read the file. The behaviour you describe also happens when the file you are trying to extract isn't actually a compressed file (it spits a copy of the file with the cpgz extension). I could not find any info about this on google tho :( – Fábio Dias Jun 11 '19 at 3:53
  • More info on cpgz: wetransfer.zendesk.com/hc/en-us/articles/… – Fábio Dias Jun 11 '19 at 3:55

Firstly, why do you want to open this file? Are you missing some photos/videos/data and suspect they are held within this file? Surely not. The .bin extension would indicate to me that this is a binary file – probably some kind of "catalogue" file, encoded in some proprietary way by Olympus, that the camera uses for organising files or storing quick-view previews or something. I would suggest leave well enough alone.

Secondly, the file is not duplicating itself in some autonomous way. These additional files you are seeing are being created by that program Archive Utility that I've never heard of. Again, there's a clue in the filename – the gz in .cpgz indicates to me that this new file is compressed using gzip. I am guessing that Archive Utility cannot read Olympus' proprietary binary file format either, so it does what it thinks you want it to do – create a new compressed copy of the file.

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  • Archive Utility is the built-in unzipper my Mac tried to open it in. – Stormblessed Mar 12 '19 at 13:17
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    @Stormblessed File extensions are used to indicate to a user and to a computer what the file type is and what application should be able to read that file. (The computer GUI usually displays a particular icon based on the file extension.) But there can be problems when one file extension is used by multiple file formats. Your Archive Utility application seems to be associated with the .bin file extension, but .bin is used for many different actual file types, and there is no guarantee that Archive Utility can read this .bin file from Olympus. Indeed, it seems it can't. – osullic Mar 12 '19 at 14:00
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    Why? Curiosity! More than good enough reason! – Fábio Dias Jun 11 '19 at 3:54

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