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Why does the picture on top have 'jpg' capitalized, when they are all JPEG images? Is it because the file size is larger?

enter image description here

Alec
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3 Answers3

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At a guess, one came directly from a camera, the others were saved by an application in the Mac itself.

There is no difference whatsoever in the file type itself, merely that one is a hangover from DOS-compatibility days. Filesystems which expect to write to FAT32 volumes such as SD cards, still maintain that 8.3 upper-case naming convention, for compatibility.

The Mac itself is by default not case-sensitive, so the files ABC123.JPG & abc123.jpg would be considered identical names. You can enforce case-sensitivity, but there are few use-cases for it for most people.

enter image description here

Lower two files came straight from the camera, above that are two conversions made within Nikon's own software, which preserved the filename & added an upper case JPG, top file is from photoshop which prefers lower case for no particular reason I can think of.
Late edit Photoshop's predilection for lower-case is actually a pref in the app itself. Take your pick.

[Neither of these is relevant to the situation itself, but the underscore prefixing the file names is another naming convention which merely signifies the pictures are originally saved with an Adobe RGB 1998 colour profile, as opposed to sRGB, which would use the format DSD_5371.NEF instead. The dash after some of the names is another application convention to prevent duplicate names.]

DSC & IMG are also conventions & in themselves have no real significance at consumer-level. iPhones save IMG, cameras use DSC [DSD is a manual change, done when 10,000 images have been taken, again to prevent name-clashes]

Tetsujin
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    Interesting. All came from a camera, but the first few were in a different airdrop. – Alec Dec 07 '19 at 05:20
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This is just how the files were created.

Someone, or some piece of software, chose to use .JPG in some cases and .jpg in others.

That's it. It doesn't mean anything.

Lightness Races in Orbit
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Mac's filenames are case sensitive.

Some FAT filesystem file names get converted to all uppercase; particularly on older devices.

Unix based systems tend not to rely only on the filename extension to determine their types.

Joe
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    I believe that the default for HFS+ is case-preserving, but not case-sensitive, while APFS is case sensitive. – doneal24 Dec 06 '19 at 17:50
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    "Mac's filenames are case sensitive.", case sensitivity comes from the file system, not from the OS – Ferrybig Dec 06 '19 at 18:23
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    @Ferrybig That's not entirely true. See [this answer](https://superuser.com/a/364062/143055) as well as [this one on Stack Overflow](https://stackoverflow.com/a/34000339/431287) for more detail. – rhino Dec 08 '19 at 00:37
  • @rhino but [The Mac itself is by default not case-sensitive, so the files ABC123.JPG & abc123.jpg would be considered identical names.](https://superuser.com/a/1507884/390541) sounds "more correct" to me than simply "Mac's filenames are case sensitive." – uhoh Dec 08 '19 at 01:39
  • @doneal24 - APFS **can** be case sensitive but is not by default; same as HFS. I just tested - my boot volume is case-insensitive [default converted as part of the upgrade to Mojave]. I cannot rename a file from .jpg to .JPG & put both in the same location. I then formatted an external drive as specifically APFS case-sensitive & it will allow both files simultaneously. [Options at format](https://i.stack.imgur.com/j4BH8.png) and [error message on boot disk](https://i.stack.imgur.com/6QE5I.png) – Tetsujin Dec 08 '19 at 10:35